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COMPARATIVE EVALUATION OF MARGINAL DISCREPANCY AND
SURFACE ROUGHNESS OF CAST COPINGS MADE BY CONVENTIONAL AND
ACCELERATED CASTING TECHNIQUES USING TWO DIFFERENT PATTERN
MATERIALS - AN INVITRO STUDY.
DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT
FOR THE DEGREE OF MASTER OF DENTAL SURGERY (M.D.S)
TO
Dr. N.T.R UNIVERSITY OF HEALTH SCIENCES
NOVEMBER 2009 Dr.A.PREMALATHA
DEPARTMENT OF PROSTHODONTICS INCLUDING CROWN
AND BRIDGE AND IMPLANTOLOGY
NARAYANA DENTAL COLLEGE & HOSPITAL
BATCH: 2007-2010
CERTIFICATE
This is to certify that the dissertation entitled “COMPARATIVE EVALUATION
OF MARGINAL DISCREPANCY AND SURFACE ROUGHNESS OF CAST COPINGS MADE BY
CONVENTIONAL AND ACCELERATED CASTING TECHNIQUES USING TWO DIFFERENT
PATTERN MATERIALS - AN INVITRO STUDY” submitted for the degree of Master of Dental
Surgery (M.D.S) is a bonafide work carried out by DR. A.PREMALATHA, during the period
from 2007-2010 under our guidance and that this work has not formed the award of any other
degree, diploma, associateship, fellowship or other similar titles.
DR.P.MAHESH. MDS
Guide
Professor & HOD, Dept of Prosthodontics
Principal, Narayana Dental College
DR.P.SRINIVAS RAO. MDS
Co-Guide
Professor, Dept of Prosthodontics
Narayana Dental College.
Place – Nellore
Date – November 2009
ENDORSEMENT BY
THE PRINCIPAL OF THE INSTITUTION
This is to certify that the dissertation entitled “COMPARATIVE EVALUATION OF
MARGINAL DISCREPANCY AND SURFACE ROUGHNESS OF CAST COPINGS MADE
BY CONVENTIONAL AND ACCELERATED CASTING TECHNIQUES USING TWO
DIFFERENT PATTERN MATERIALS - AN INVITRO STUDY” is a bonafide research work
done by Dr. A. Premalatha under the guidance of Dr. P. Mahesh, Professor & HOD, Department
of Prosthodontics including Crown and Bridge and Implantology.
Date: November 2009
Place: Nellore
Dr. P. MAHESH Principal
Narayana Dental College & Hospital, Nellore.
ACKNOWLEDGEMENTS
“A journey is easier when you travel together”. This dissertation work is the result of many accompanied, supported and guided people. So it is a pleasant aspect that I have the opportunity to express my gratitude for all of them.
I express my sincere indebtedness and heartfelt thanks to my guide, role model teacher and excellent academician Dr.P.Mahesh MDS, Professor and Head, Department of Prosthodontics, Narayana Dental College and Hospital, for his constant support, encouragement and valuable guidance that enabled me comprehend this dissertation and research and its successful culmination.
I sincerely express my deepest gratitude and humble thanks to my esteemed teacher, Dr.P.Srinivas Rao MDS, Professor, Department of Prosthodontics, Narayana Dental College and Hospital, for his immeasurable encouragement, unwavering guidance and constructive suggestions.
I would like to express my deepest gratitude to Dr.Dwarakananda Naik MDS, Reader, Department of Prosthodontics, Narayana Dental College and Hospital, for his constant support and extreme help.
I would like to specially express my appreciations and sincere gratitude to Dr.T.Pavan Kumar MDS, Sr. lecturer for his extreme support, help and valuable suggestions. Iam also highly indebted to him for his help during the study in the fabrication of die and preparing the samples.
I would like to express my heartfelt thanks to Dr.V.H.C.Kumar MDS, Sr. lecturer for his constructive suggestions and precious ideas.
I express my heartfelt thanks to Dr. A. Sudheer MDS, Sr.Lecturer for his appreciation, guidance and precious ideas.
Iam also thankful to Dr. Vijay Shankar Yadav & Dr.D.V.V. Vamsikrishna MDS, senior lecturers for their valuble support and guidance during my study period.
I sincerely express my gratitude to Dr.V.Vamsi Krishna Reddy MDS, Sr.Lecturer for his extreme help, support and timely suggestions.
I sincerely express my thanks to Mr. Ravi Chandra, Department of Nuclear Physics, Madras University, Chennai, for doing the vertical marginal discrepancy measurements in the study.
I express my deepest gratitude to Dr.Omkumar and Mr.Balan, Manufacturing Engineering Department, Anna University, Chennai, for doing the surface roughness measurements in the study.
I thank Mr.R. Ravanan, Bio-statistician for help to carryout the analysis of the study.
I extend my gratitude to my batch mates, Dr. K. Shalini, Dr. K. Kiran Kumar Reddy, my seniors Dr.V. Vamsi Krishna Reddy, Dr. M. Reddi Narasimha Rao, Dr. P. Gautham and my loving juniors, Dr.Y.ManojKumar, Dr.M.Dhanalakshmi, Dr.K.Surya Narayana Murthy, Dr. B. Swapna, Dr. C. Sameer Kumar Reddy, Dr. M.Mahesh Babu and without whom I would not have completed this work.
My sincere special thanks to Dr.V.Vamsikrishna Reddy, my senior for his cooperation during the study, guidance and precious ideas.
I thank all non-teaching staff of Department Of Prosthodontics for their assistance through the study.
Last but not least, I express my heartfelt gratitude to all my family members especially my husband Mr. M.Bharadwaja, who supported through out my life, my loving daughter M.Kusuma Chowdary, my dearest son M.Venkata Ramarao Chowdary, my parents, mother in-law, father in-law, sister, brother, sister in laws, who deserve the credit for what I am, and for all what I have achieved.
Dr. A.Prema latha.
CONTENTS
S .NO: CONTENTS PAGE
1 INTRODUCTION 1-4
2 REVIEW OF LITERATURE 5-25
3 MATERIALS & METHODS 26-47
4 RESULTS 48-59
5 DISCUSSION 60-69
6 SUMMARY & CONCLUSION 70-72
7 BIBLIOGRAPHY 73-78
LIST OF TABLES
TABLE TITLE PAGE
Table 1
The results obtained in this study for the vertical marginal discrepancy along with the mean estimated for each sample in the G-I technique calculated in microns (µ)
48
Table 2
The results obtained in this study for the vertical marginal discrepancy along with the mean estimated for each sample in the G-II technique calculated in microns (µ)
48
Table 3
The results obtained in this study for the vertical marginal discrepancy along with the mean estimated for each sample in the G-III technique calculated in microns (µ)
49
Table 4
The results obtained in this study for the vertical marginal discrepancy along with the mean estimated for each sample in the G-IV technique calculated in microns (µ)
49
Table 5The mean vertical marginal discrepancy obtained from basic mean values of four techniques (G-I, G-II,G-III & G-IV)
52
Table 6Test of significance for the mean vertical marginal discrepancy obtained from four techniques (G-I, G-II,G-III &G-IV)
53
Table 7
The results obtained in this study for the surface roughness along with the mean estimated for each sample in the G-I technique calculated in microns (µ).
54
Table 8
The results obtained in this study for the surface roughness along with the mean estimated for each sample in the G-II technique calculated in microns (µ).
54
Table 9
The results obtained in this study for the surface roughness along with the mean estimated for each sample in the G-III technique calculated in microns (µ).
55
Table 10
The results obtained in this study for the surface roughness along with the mean estimated for each sample in the G-IV technique calculated in microns (µ).
55
Table 11The mean surface roughness obtained from basic mean values of four techniques (G-I,G-II,G-III & G-IV)
58
LIST OF GRAPHS
GRAPH TITLE PAGE
GRAPH 1The basic data of vertical marginal discrepancy results obtained by G-I technique.
50
GRAPH 2The basic data of vertical marginal discrepancy results obtained by G-II technique.
50
GRAPH 3The basic data of vertical marginal discrepancy results obtained by G-III technique.
51
GRAPH 4The basic data of vertical marginal discrepancy results obtained by G-IV technique.
51
GRAPH 5
Comparison of the mean vertical marginal discrepancy obtained from basic mean values of four techniques (G-I,G-II,G-III &G-IV)
52
GRAPH 6The basic data of surface roughness results obtained by G-I technique.
56
GRAPH 7The basic data of surface roughness results obtained by G-II technique.
56
GRAPH 8The basic data of surface roughness results obtained by G-III technique.
57
GRAPH 9The basic data of surface roughness results obtained by G-IV technique.
57
GRAPH 10
Comparison of the mean surface roughness obtained from basic mean values of four techniques (G-I,G-II,G-III &G-IV)
58
LIST OF FIGURES
FIGURE TITLE PAGE
FIG.1 Axial view of custom made stainless steel former assembly (A) and stainless steel master die (B)
36
FIG.2 Occlusal View of Custom made stainless steel former assembly (A) and stainless steel master die (B)
36
FIG.3 Line Diagram of custom- made stainless steel master die and custom-made stainless steel former
37
FIG.4 Line diagram of custom-made stainless steel master die & stainless steel former in place. a. Custom – made stainless steel die. b. Custom- made stainless steel former.
37
FIG.5 A. Pattern Resin and B. Inlay wax 38
FIG.6 Investment powder & special Liquid 38
FIG.7 Nickel – Chromium alloy 38
FIG.8 Photo Microscope 39
FIG.9 Surface Roughness analyzer 39
FIG.10 Preparation of Inlay Wax Pattern 40
FIG.11 Preparation of Pattern Resin 40
FIG.12 Wax coping showing 0.5mm thickness 40
FIG.13 Pattern Resin coping showing 0.5mm thickness 40
FIG.14 Wax Pattern Attached to crucible former 41
FIG.15 Ring Liner Placed 3mm short of Ring Margin 41
FIG.16 Wax pattern in position in the casting ring 41
FIG.17 Divested casting 41
FIG.18 Cast coping seated on the die 42
FIG.19 Metal Coping showing 0.5mm thickness 42
FIG.20 Marginal gap of 34.02 at 80x magnification by using photo microscope of a cast coping obtained by conventional casting technique employing three stage wax elimination
43
FIG.21 Marginal gap of 44.39 at 80x magnification by using photo microscope of a cast coping obtained by Accelerated casting technique employing single stage wax elimination
43
FIG.22 Marginal gap of 37.06 at 80x magnification by using photo microscope of a cast coping obtained by conventional casting technique employing three stage Resin elimination
44
FIG.23 Marginal gap of 46.86 at 80x magnification by using photo microscope of a cast coping obtained by Accelerated casting technique employing single stage Resin elimination
44
FIG.24 line diagram of custom made stainless steel coping holder 45
FIG.25 custom made stainless steel coping holder with coping 45
FIG.26 custom made stainless steel coping holder with coping on surface roughness Analyzer
45
FIG.27 surface roughness graph obtained by conventional casting technique with three stage wax elimination
46
FIG.28 surface roughness graph obtained by Accelerated casting technique with single stage wax elimination
46
FIG.29 surface roughness graph obtained by conventional casting technique with three stage Resin elimination
47
FIG.30 surface roughness graph obtained by Accelerated casting technique with single stage Resin elimination
47
Dedicated to my husbandMr. BHARADWAJA
Introduction The success of any cast restoration depends upon its fit on to the underlying tooth
structure.1 The accuracy of the restoration is essential for its longevity, as it allows less plaque
accumulation at the marginal area provides better mechanical properties, less cement space and
improves the esthetic result.2,3 A deficient margin leads to plaque retention resulting in gingival
inflammation, marginal leakage which can lead to secondary caries, sensitivity, gingival
recession, cement dissolution and debonding of the restoration.1,4,5
The marginal discrepancies of cast restorations are inevitable, inspite of careful
attention to waxing, investing and casting procedures. Even though published data on clinically
acceptable gaps varies from 30µm to 200µm, standard reference6 on cast restorations mention a
marginal gap of up to 74µm is clinically acceptable. It is one of the tasks of luting cements to
close these discrepancies. However, cement will dissolve rapidly under the margins if the
discrepancy is too large.4The rate of luting cement dissolution has been related empirically to the
degree of marginal opening. Thus, the larger the marginal discrepancy and subsequent exposure
of the dental luting cement to oral fluids the more rapid is the rate of cement dissolution. Saliva
increasingly influences the dissolution of the cement if the marginal discrepancies are wider than
150µm.4, 7
The objective of the casting process is to accurately reproduce a wax pattern. A
defective casting results in a considerable loss of time and effort.8 Types of defects in castings
have been classified into 4 broad categories:
1. Distortion
2. Surface roughness and irregularities
3. Porosities
4. Incomplete or missing castings.6, 8
Surface roughness refers to finely spaced imperfections, of which the height,
width and direction establish the predominant surface pattern. The average surface roughness of
castings made from noble alloy according to Pomes et al was in the order of 0.76µm.8 Various
studies demonstrate that the surface roughness of as-cast gold alloy specimens ranged from
approximately 2 to 30µm on average.9 The surface roughness of dental castings is often greater
than that of the wax patterns from which they are cast. Surface roughness can be lessened by
abrading and polishing procedures, ensuring in this way a good tissue response to the alloy.8 A
smooth surface not only prevents plaque and calculus accumulation, but it also improves the
corrosion resistance of the alloy. The surface roughness on the intaglio surface of the cast
restoration affects the fit of the restoration. Therefore, the smaller these flaws, the better the fit of
a restoration to the surface of the prepared tooth.8
Several implications are related to surface roughness of metal copings in PFM’s
especially in relation to adhesion. If the ceramic penetrates well and locks with the metal, it
provides more room for chemical bonds to form there by increasing the ceramic –metal interface
bond. If the ceramic does not penetrate into the surface and voids present on the interface it may
lead to bond failure and also compromise esthetics.10
There are a variety of factors that have an important role in controlling surface
roughness and irregularities. These factors include the liquid-powder ratio of the investment, air-
bubbles in the investment, water films, rapid heating rates, under heating, prolonged heating, the
temperature of the melting alloy, casting pressure, composition of the investment ,investment
technique, foreign bodies, impact of molten alloy, carbon inclusions, and mixing and melting
different alloys together.8
Keeping this in mind, many materials and methods have been suggested by various
authors to improve the fit, marginal accuracy and surface roughness of the casting. The marginal
fit and surface roughness is affected by the quality of the preparation, the impression, the
working cast, the type and quality of the wax used for the lost wax technique, and by the
accuracy of the casting.2The accuracy of the casting is subjected to volumetric changes occurring
due to shrinkage of wax, resin and alloys. This shrinkage can be compensated by setting
expansion, hygroscopic and thermal expansion of the investment.3
There have been numerous reports, on attempts to perfect the casting procedures
by improving investment materials and techniques.2,3,9,11,12 The majority of these efforts deal with
so-called “conventional” investing and casting techniques, which usually require at least 1 hour
bench set for the investment, followed by a one, two or three stage Inlay Wax and Pattern Resin
elimination cycle as recommended by the manufacturer before the casting procedure.6,9,12,13 The
whole process is time consuming and requires approximately 2 to 4 hours for completion.9,12
The accelerated casting techniques have been reported in an effort to achieve
similar quality results in significantly less time.9, 12 The pattern is invested, cast and delivered in a
cost effective, time saving manner. This combination offers many advantages to the patient,
dentist, and dental laboratory technician, and has received increased attention as a method of
improving productivity.12 Though studies9,12 have reported that marginal discrepancies and
surface roughness by accelerated casting technique are with in the clinically acceptable limits,
some studies9,11,12 have reported that this procedure is technique sensitive. Most of these studies
have reported the effect of accelerated casting procedures on the fit of noble alloy castings.
However, the effect of accelerated procedures on the marginal discrepancy and surface
roughness of base metal alloy restorations has not been adequately studied.
Hence this invitro study was conducted to measure and compare the vertical
marginal discrepancy and surface roughness of base metal alloy cast copings made by
conventional and accelerated casting techniques using Inlay Wax and Pattern Resin.
The objectives of this study included the following:-
1. To evaluate the vertical marginal discrepancy of cast copings obtained by conventional casting
technique using Inlay Wax and Pattern Resin.
2. To evaluate the vertical marginal discrepancy of cast copings obtained by accelerated casting
technique using Inlay Wax and Pattern Resin.
3. To compare the vertical marginal discrepancy of cast copings obtained by conventional and
accelerated casting technique using Inlay Wax and Pattern Resin.
4. To evaluate the surface roughness of cast copings obtained by conventional casting technique
using Inlay Wax and Pattern Resin.
5. To evaluate the surface roughness of cast copings obtained by accelerated casting technique
using Inlay Wax and Pattern Resin.
6. To compare the surface roughness of cast copings obtained by conventional and accelerated
casting technique using Inlay Wax and Pattern Resin.
Review of literature
Cooney JP et al (1979)14 evaluated two phosphate-bonded investments and one
calcium sulfate investment for the surface smoothness and marginal fit they impart to gold
castings. A modified technique was also evaluated for each phosphate-bonded investment, where
the silica sol was not diluted and the spatulation time was reduced. The results of this study lead
to the following conclusions: (1) The marginal fits obtained with all four phosphate-bonded
methods were comparable to each other and superior to that obtained with the calcium sulfate
investment. (2) The presence of nodules on the surface of the castings was more prevalent with
the phosphate-bonded investments. However, this effect was not statistically significant. (3)
Clinical assessment of the roughness of the castings revealed that all the methods tested
produced clinically acceptable castings. (4) Visual observation by five dentists revealed that both
the recommended and modified techniques for one of the phosphate-bonded investments
(Ceramigold) produced a smoother surface than any other investment tested. Rating of scanning
electron microscope photographs (X 600) revealed no difference in the surface roughness
between any of the castings .Consequently, no definitive relation between investment type or
technique and surface roughness was established. (5) No correlation was demonstrated between
surface roughness, as evaluated by either clinical observation or scanning electron microscope
photography, and marginal fit of the castings.
Neiman R, Sarma AC (1980) 15 studied the setting reactions and thermal degradation of
the phosphate binders are interpreted from the DTA and X-ray diffraction data. The simple
chemical reaction has generally been shown to be: MgO + NH4H2PO4 = NH4MgPO4.6H2O.
However, the setting reaction is in reality a more complex system of multi-molecular structure as
described herein. On heating, the set product (NH4MgPO4.6H2O)n dehydrates to
(NH4MgPO4.H2O)n and subsequently degrades into polymeric (Mg2 P2 07 )n', crystalline Mg2 P2
07 ; then the latter reacts with excess MgO present to form the final product, Mg3(PO4)2.
Duncan JD (1980)16 studied nickel-chromium alloys as substitutes for gold alloys in
casting crown and bridge prostheses and found out more definitive research is needed on the
casting accuracy, finishing characteristics, porcelain-to-alloy bonding, and corrosion sensitivities
of these materials.
Gavelis J.R. et al (1981)17 conducted his study to correlate margin design with the
seating and sealing of cemented full cast crowns under standardized, simulated clinical
conditions. The crowns were waxed on the steel dies, invested, and cast. The crowns were
cemented onto the Duralay dies and tested in an Instron testing machine. Measurements were
made of the cement thickness at the margin, shoulder, axial wall, and occlusal surface. The
cement thickness at the margin and occlusal surface were analyzed to find the amount of seal and
seat afforded by the various preparations. The 90-degree shoulder had a cement space of 67 µ at
the margins. The 45-degree shoulder, shoulder with 30-degree bevel, and shoulder with 45-
degree bevel followed, with spaces of 95, 99, and 105 µ, respectively. With regard to seating of
the restoration, the 90-degree full shoulder demonstrated the best seat, followed in order by the
45-degree shoulder, 90- degree shoulder with 45-degree bevel, featheredge, 90-degree shoulder
with 30-degree bevel, chamfer with parallel bevel, and finally go-degree shoulder with parallel
bevel.
Ogura H et al (1981)18 investigated six variables that could affect the surface roughness
of a casting. The variables were (1) type of alloy, (2) mold temperature, (3) metal casting
temperature, (4) casting machine, (5) sandblasting, and (6) location of each section. It was
determined that the trailing portion of a complete cast crown had rougher surfaces than the
leading portion. Higher mold and casting temperatures produced rougher castings, and this effect
was more pronounced in the case of the base metal alloy. Sandblasting reduced the roughness,
but produced scratched surfaces. Sandblasting had a more pronounced affect on the surface
roughness of the base metal alloy cast either at a higher mold temperature or metal casting
temperature.
Duncan JD (1982)19 investigated the casting accuracy of four nickel-chromium alloys
(Ultratek, Omega, Microbond N/P2, and Nobil-Ceram) was compared to that of a precious alloy,
Jelenko “0”. The experiment indicated that Jelenko “0” had the greatest casting accuracy,
followed successively by Ultratek, Nobil-Ceram, Microbond N/P2, and Omega. The following
conclusions may be drawn from this experiment: (1) The nickel-chromium alloys tested did not
cast as consistently or as accurately as precious alloy Jelenko“0”. (2) The casting accuracy may
be related to the amount of casting shrinkage that occurs in each alloy type, and further research
is necessary to determine if expansion compensation of the selected phosphate-bonded
investment recommended by the alloy manufacturers is adequate for the casting shrinkage of the
test alloys. (3) Alloy composition and technique parameters may also influence the accuracy of
the casting, but further research is necessary to determine their singular effects.
Lacy AM et al (1983)20 investigated the related effects of (1) mixing rate, (2) ring liner
position, and (3) storage conditions on the setting expansion of both gypsum-bonded and
phosphate-bonded investment molds; and subsequently to correlate casting size with measured
expansion data. The results of these studies indicate the need for careful standardization of
investing and casting techniques if consistent results are to be expected. Results also reveal that
the position and extent of ring liners, rates of mixing, and conditions of storage may be even
more significant in determining ultimate casting size than classically accepted factors such as
liquid/powder ratios or numbers of ring liners. The dynamic nature of setting expansion within
the first 60 minutes after mixing suggests that consistent results demand waiting at least that long
prior to burnout. If molds are to be stored overnight, maximum dimensional stability is probably
ensured by keeping them in 100% relative humidity, particularly if CaSO4. 2H2O-containing
gypsum-bonded investments are used.
Vermilyea SG et al (1983)21 assessed the influence of three such investment
materials, Ceramigold 2 and Hi-Temp Casting Investment (Whip-Mix Corp., Louisville, Ky.)
and Neoloy Hi-Heat Crown and Bridge Investment (Neoloy Products, Inc., Posen, III.), on the fit
of copings cast from five base metal alloys (Biobond, Dentsply International, York, Pa.;
Ceramalloy II, Ceramco, Inc., East Windsor, N. J.; Unibond, Unitek, Inc., Monrovia, Calif.;
Biocast, Jeneric Gold Co., Wallingford, Conn.; and Neobond II, Neoloy Products, Inc.). Overall,
the fit of the test castings was poor. Individual alloy-investment interaction appears to be
significant. Although marketed for use with base metal alloys, it appears that investment
manufacturers’ recommended techniques require alteration to enhance the fit of base metal
restorations.
Marsaw FA et al (1984) 22 developed a technique to evaluate setting expansion in
the pattern region of an investment mold. The volumetric system provides a method to acquire
information on setting expansion at the location of the wax pattern. Internally determined setting
expansion values do not agree with values derived from external measurements (ADA trough
method). Measurements obtained by the volumetric method show less variability than those
obtained by the trough method. No significant difference in volume was seen between a
restricted metal ring and an unrestricted split rubber ring, which suggests a semisolid behavior of
the investment during the period of setting. The findings indicate a need to reevaluate the
methods by which setting expansion is measured, as well as the mechanism by which the
expansion takes place. The need for further study by means of multiple VRSs or strain gauges
embedded in the investment is indicated, and investigation is currently in progress. The influence
of variously shaped casting rings and pattern position on resulting accuracy of the casting could
be determined by this method of investigation.
Dedmon HW (1985)23 studied the marginal fit of full cast crowns made by
commercial dental laboratories with the design of the margin. When cast restorations were made
by commercial dental laboratories, margins prepared with unbeveled heavy chamfers and
shoulders were most likely to have openings that exceeded 39 µm on the dies. Unbeveled heavy
chamfers and shoulders were also most likely to have metal flash left on the margins. Knife-
edged and beveled margins were least likely to have metal flash or openings that exceeded 39
µm on the dies.
Smith CD et al (1985)24 in this study developed a method for measuring the changes in
size and in marginal length of a complete crown wax pattern that occur during the casting
process. These values, combined with initial wax margin discrepancy, are used to calculate
marginal discrepancy values that are as accurate as the direct measurement of the same
discrepancy. This method is capable of measuring the effect of individual variables on casting
size, marginal reproduction, and marginal discrepancy. The method is capable of determining
these values for oversized as well as undersized castings.
Schwartz IS (1986)25 reviewed the methods and techniques to improve the fit of cast
restoration because the marginal fit of castings is one factor that leads directly or indirectly to
secondary caries, adverse pulpal reactions and periodontal disease. He found several factors that
were necessary for good fit of the castings and some of them were perceptive tooth preparation,
accurate impressions, precision castings and careful finishing procedures, but in addition to these
factors he reported that internal relief was basic for accurate marginal fit of the cemented
restorations.
Asgar K (1988)26 reviewed casting metals in dentistry. In the literature, credit is given to
Dr. Swasey (1890), who introduced a technique where a solid gold inlay could be prepared. Wax
was used for making gold inlays for the first time by Martin (1891). A few years later, Dr.
Philbrook (1896) introduced a pressure-casting method of producing gold inlays. About 10 years
later, Dr.Taggart (1907) presented a paper before the New York Odontological Group, in which
he discussed his casting technique and machine. Castings made using Taggart's casting machine
and his investment were generally too small and did not fit the cavities properly. Van Horn
(1910) suggested and promoted the idea of thermally expanding wax patterns prior to investing.
The development of cristobalite investment by Coleman and Weinstein in 1929, who obtained a
U.S. patent a few years later (1933), as well as the introduction of the hygroscopic technique
(Scheu, 1932), were responsible for the greatest improvement in the fit of dental castings. From
the time that Dr. Scheu introduced his hygroscopic technique, various aspects of hygroscopic
investments were studied by many individuals, and some theories were postulated. Finally,
Mahler and Ady (1960), in their classic paper, showed that the hygroscopic expansion of dental
investments is a continuation of setting expansion and proposed the theory which is accepted
today. The quality of dental castings would not be where it is today if a better understanding of
the basic nature of dental castings and improvement in investments and alloys had not been
accomplished. Much work in the various aspects of dental casting techniques — such as the
effect of mold and metal temperature on the fit of castings, castability of the various alloys,
choice of sprue as well as its size and location, and the effects of various types of dental wax on
the resultant casting — has been reported.
Holmes JR et al (1989)5 inferred that the measurements of misfit at different
locations are geometrically related to each other and defined as internal gap, marginal gap,
vertical marginal discrepancy, horizontal marginal discrepancy, overextended margin, under
extended margin, absolute marginal discrepancy, and seating discrepancy. The significance and
difference in magnitude of different locations are presented. The best alternative is perhaps the
absolute marginal discrepancy, which would always be the largest measurement of error at the
margin and would reflect the total misfit at that point.
Hunter AJ, Hunter AR (1990)27 in this review stated that there is variation regarding
the maximum acceptable marginal discrepancy, there is little argument that poorly fitting
margins are a frequent finding. Large discrepancies are clinically significant, since they facilitate
plaque retention. Margins incorporating slip joint geometry have usually been favored as a
method of minimizing seating and sealing discrepancies. However, many of these discussions
largely ignored the effects of the cementing medium and the clinical applicability of slip joint
geometry is based on questionable assumptions with regard to casting accuracy and seating.
Greater understanding of the role of restorative margins and gingival health indicates the need
for shallow margin placement within the crevice, which requires a reassessment of the use of
long bevels. Horizontal margins can be made accurately and, when combined with procedures to
maximize crown seating, may provide the best method of minimizing seating discrepancies and
maximizing gingival health.
Felton DA et al (1991) 28 evaluated the relationship between marginal adaptation
of dental castings and periodontal tissue health quantitatively. Forty-two crown restorations in 29
randomly selected patients were selected for this study using three criteria. (1) The crowns were
placed at the University Of North Carolina School Of Dentistry; (2) the crowns were in service
for a minimum of 4 years; and (3) the crown margins were within the intracrevicular crevice
(subgingival). Replica impressions of the facial margins of specific crowns were made with a
vinyl polysiloxane impression material, and poured casts were prepared for scanning electron
micrograph evaluation. Marginal discrepancy measurements were identified on each micrograph
at 10 equally spaced locations along the margin and averaged for each specimen. Periodontal
indices of pocket depths, crevicular fluid volume, and gingival index were accumulated for
clinical measurements. Pearson correlation and Bonferroni adjusted probability tests were
performed, but no significant correlation was found between marginal discrepancy (0.16 ± 0.13
mm) and pocket depth (2.4 ± 0.9 mm). However, a strong correlation (p < 0.001) existed
between marginal discrepancy and gingival index (2 ± 0.8) and between marginal discrepancies
and crevicular fluid volume (49.9 ± 31.1). These results established that a significant quantitative
relationship existed between the marginal discrepancy and periodontal tissue inflammation for
subgingivally located crown margins.
Jacobs MS et al (1991) 29 investigated the rate of type I zinc phosphate cement
solubility as it relates to the degree of marginal opening. Standardized test samples were
constructed that would simulate clinically relevant marginal gaps of 25, 50, 75, and 150 microns
and their subsequent cement lines. The study was divided into two phases. Phase 1 evaluated the
effects of simple diffusion on cement solubility in a static environment, whereas phase 2
investigated the effects of convective forces on cement dissolution in a dynamic environment.
Both the phase 1 and phase 2 studies demonstrated no significant difference in the rate of cement
dissolution for the 25-, 50-, and 75-micron test groups. The 150-micron test groups for both and
phase 2 studies should not be compared because different methodologies were used.
Campagni WV et al (1993)30 study compares an accelerated technique for the casting
of post-and-core restorations with four traditional techniques. The accelerated technique uses two
phosphate-bonded investments and the traditional techniques use gypsum- and a phosphate-
bonded investment. The study measures and compares the differences between the seating of the
casting and the seating of the acrylic resin pattern. The seating of the patterns after 3 months of
storage was consistently worse than the 2-week measurements of fit. The ferrule and nonferrule
patterns were not statistically different in seating. Measurement of the castings showed that the
ferruled castings seated significantly worse than the nonferrule castings. The difference in the
seating of the castings as compared with the patterns was considered clinically unacceptable,
showing a range of 0.301 mm t o 0.528 mm. The nonferrule castings showed a significant
difference in seating among groups. The difference ranged from -0.099 mm to 0.322 mm. The
effects of the techniques on the fit of castings with and without a ferrule are also compared. The
castings of the ferrule subgroups were considered clinically unacceptable and were not analyzed
for significance. Among the nonferrule castings, the group using a gypsum investment and
conventional technique for investing and burnout but no ring liner showed the best seating. The
accelerated technique was intermediate in seating with a difference of 0.148 mm from the seating
of the patterns. This group was significantly different from the two best groups but not from the
remaining three groups.
Hutton JE Marshall GW (1993) 31 in this study determined whether three
different phosphate bonded investments could provide adequate expansion to compensate for the
casting shrinkage of AgPd. The investments were mixed with distilled water or their unique
special liquids provided by the manufacturers and allowed setting times of 1 hour or 24 hours.
Setting expansions were measured with a vertical dilatometer. When mixed with special liquid,
material I had a mean setting (1 hour) expansion of 0.19% ± 0.01%; material II, 0.14% ± 0.03%;
and material III, 1.17% ± 0.08%. Twenty-four hours of setting did not significantly increase the
setting expansion (p > 0.05). Mixing the three investments with distilled water drastically
reduced setting expansions. A three-way analysis of variance was computed to evaluate the data
and investigate significant interactive and main effects. The two-way interaction (material x
liquid) was significant. The results were consistent with the concept of a higher silica-containing
special liquid for material III compared with the other materials.
Bailey JH, Sherrard DJ (1994) 32 study determined the mean time interval from
start of mixing to the maximum exothermic setting reaction temperature for each investment. A
chromel/alumel thermocouple was placed at the heat center of a methylcellulose lined casting
ring, using wet or dry ring liner. Investments were vacuum mixed at the recommended ratio for
the accelerated technique. Colloidal silica solution and ddH2O were combined at a 50:50 ratio to
meet the manufacturer's recommended liquid volume. Part two determined the dimensional
reproduction of a standardized pattern and its casting using both casting techniques. Mixing
ratios were the same as in part one for the accelerated technique and 75% colloidal silica to 25%
double-distilled water (ddH20) for the conventional technique. The accelerated technique used
the mean setting time established in part one followed by a 15-minute furnace holding time at
725°C (1350°F). The conventional technique used a I-hour bench setting time, followed by
placing the mold into a cold furnace. A controlled rate of climb to a maximum temperature of
725°C (1350°F) was used with a I-hour soak time. Each pattern and its casting were measured at
four sites: (1) Length of the post-and-core assembly, (2) maximum core diameter, (3) post
diameter at the core base, and (4) post diameter at its apex. A significant difference was found
between the time interval to maximum exothermic setting reaction temperature for all the
investments (P < .01). The accelerated technique produced castings with a relative dimensional
increase of 0.11% to 4.80%. The conventional technique ranged from a 0.04% decrease in size to
an increase of 3.65%. Castings made with the accelerated technique were significantly different
than those made with the conventional technique (P < .01) Differences in the time interval to
maximum exothermic setting reaction temperature indicate that each phosphate investment
should have a recommended setting time before introduction into the furnace. The carbon-
containing investment showed the least relative change of the three investments evaluated for
both casting techniques.
Schneider RL (1994) 33 investigated an accelerated method of using a light-cured
acrylic resin and rapid burnout for casting a direct-pattern post and core restoration. Light-cured
acrylic resins are an alternative to chemically cured acrylic resins or indirect patterns formed
from an elastomeric impression. The procedure can eliminate an appointment for the patient in
the fabrication of the post and core restoration and can be completed in most dental offices with
minimal laboratory facilities. Chair-side time is saved because of the elimination of one
provisional restoration when two are usually required. Laboratory time is also saved because of
the decrease in investment setting and burnout time.
Iglesias A et al (1996) 34 compared the marginal fit of MOD inlay and full-crown
patterns fabricated from wax, autopolymerized acrylic resin, and two light-polymerized,
diacrylate resin pattern materials on standardized dies. For the MOD inlay patterns, marginal
gaps ranged from 7 to 23 µm, and the light-polymerized, diacrylate resins and autopolymerized
acrylic resin material had statistically smaller gaps than the inlay wax. For the full-crown
patterns, marginal gaps ranged from 10 to 23 µm, with the exception of the autopolymerized
acrylic resin prepared by the bulk technique (40 to 46 µm). With the incremental technique, the
light-polymerized, diacrylate resins and inlay wax had statistically smaller gaps than the
autopolymerized acrylic resin material. Overall, the incremental technique produced equal or
smaller marginal gaps than the bulk technique for full-crown patterns. Generally, the patterns
measured at 1 hour had smaller marginal gaps than at 24 hours. When measured on intra- and
extracoronal master dies, the light-polymerized, diacrylate resins had equal or better marginal fit,
compared with wax or autopolymerized acrylic resin, and were less affected by placement
technique and storage. The marginal gaps of all four pattern materials ranged from 7 to 46 µm
and are within the range of clinical acceptability.
Ito M et al (1996)35 evaluated the relationship between flow characteristics,
bending strength, and softening temperature of paraffin and dental inlay waxes to casting
shrinkage when patterns were invested with a phosphate-bonded investment. This study found
that the casting shrinkage decreased as the flow of the wax pattern increased. The flow of the
wax pattern increased as the exothermic reaction increased. A larger casting ring is suggested for
castings when a relatively thick wax pattern or an inlay wax that has a high strength, softening
temperature, and low flow percentage is used. When wax patterns are formed for cast
restorations, it is important to select the type of wax with the most desirable properties for the
margin and the occlusal portions. Moreover, to accurately fabricate castings, it is necessary to
understand the physical properties of the chosen waxes.
Earnshaw R et al (1997) 36 In an earlier investigation, it was shown that when
full crowns are cast in gypsum-bonded investments, their relative inaccuracy is affected by both
the investment's potential expansion and its hot strength. This study repeated the earlier one, but
used a high-melting gold alloy and two phosphate-bonded investments. The investments were
used under conditions which gave a range of potential expansions and hot strengths. Casting
inaccuracies were determined both diametrally and axially. All castings showed distortion, which
varied under the different conditions. All were oversized axially, by amounts varying from
+0.8% to +2.3%. Diametral inaccuracies ranged from -0.2% to + 0.7%. Investment expansion
had a strong effect on axial inaccuracy, but a negligible effect on diametral inaccuracy.
Conversely, hot strength had a strong effect on diametral inaccuracy, but only a very weak effect
on axial inaccuracy. With phosphate-bonded investments, both potential expansion and hot
strength are important parameters of relative casting inaccuracy. In combination, these properties
showed very strong correlations with both diametral and axial inaccuracies. The observed
distortions were the result of anisotropic mould expansion and anisotropic alloy shrinkage. The
best fit, and least distortion, occurred with an investment setting under dry conditions.
Konstantoulakis E et al (1998) 9 evaluated the marginal fit and surface roughness of
complete crowns made with a conventional and an accelerated casting technique, and found out
no statistical difference in the marginal discrepancy of cast crowns made by using accelerated
technique as compared with conventional technique. There was no difference in the average
surface roughness of cast crowns between the accelerated and the conventional techniques.
Clinically acceptable complete castings can be obtained with the accelerated technique if
optimum heating conditions are selected for each investment. Therefore they concluded that the
accelerated casting technique described in this study could be a vital alternative to the time-
consuming conventional technique.
Schilling ER et al (1999)12 measured the marginal gap and determined the clinical
acceptability of single castings invested in a phosphate-bonded investment with the use of
conventional and accelerated methods. The following conclusions were drawn from this study:
(1) Marginal gaps for castings made with an accelerated technique showed no statistical
difference when compared with a conventional casting group. (2) The accelerated casting
technique offers a cost effective and time-saving method by which single-unit castings for
metal/ceramic crowns can be fabricated. (3) The methods used for accelerating the casting
process are technique sensitive. Minor variations in the procedures can cause casting defects
such as nodules, fins, and porosity. Repeated use of the accelerated technique can provide the
dental laboratory technician with predictable, clinically acceptable castings for metal/ceramic
crowns.
Blackman RB (2000)11 This pilot study investigated the effect of 2 rapid mold
preparation schedules on full crown castings by comparing size, margin sharpness, and surface
roughness. Three groups of 10 crowns were cast with a type III gold alloy. All crowns were
nominally identical, only their mold preparation schedules differed. Two groups used accelerated
schedules; the third group was cast using a conventional schedule. Group comparisons were
based on direct microscopic measurements of crown diameters (×50 magnification), and surface
roughness was measured. Margin sharpness was judged by amount of marginal length lost in the
axial direction as a result of the casting process. Crowns were successfully cast using accelerated
mold preparation techniques and considerable time was saved, but a small loss of margin length
or fineness was observed.
Castillo RD et al (2000)37 evaluated the influence of: (1) a cellulose ring liner,
and (2) a lower casting temperature of the metal ring, on the dimensions of a cast post.
Experimental posts were measured before and after casting to determine the effect of ring liner
and casting ring temperature on the dimensional behavior of a phosphate-bonded investment
material. Within the limits of this study, it was found that decreasing the casting ring temperature
from 815°C to 600°C, along with the absence of a ring liner, produced undersized cast posts. A
slightly undersized cast post may be easier to fit and cement in the prepared root canal, and thus
decrease chairside time.
Groten M et al (2000) 38 in this study estimated the minimum number of gap
measurements on margins of single crowns to produce relevant results for gap analysis. Ten all-
ceramic crowns were fabricated on a master steel die. Gaps along crown margins were
investigated in a scanning electron microscope on the master steel die without cementation and
on replica dies after conventional cementation. Measurements were made in 100 µm steps
according to 3 gap definitions. The initial number of measurements per crown (n = 230) was
reduced to smaller subsets using both systematic and random approaches to determine the impact
on the quality of results. On the data of gap definition 1, reduction from 230 to about 50
measurements caused less than ±5 µm variability for arithmetic means. Analysis of standard
errors showed slowly increasing values smaller than 3 µm, both indicating no relevant impact on
the quality of results. Smaller data sizes yielded accelerated increase of standard errors and
divergent variabilities of mean. The minimum of 50 measurements did not depend on gap
definition or on cementation condition. Fifty measurements are required for clinically relevant
information about gap size regardless of whether the measurement sites are selected in a
systematic or random manner, which is far more than what current in vitro studies use.
Lombardas P et al (2000) 2 compared the vertical margin accuracy of lost wax
castings produced with the conventional casting technique using a metal ring and a technique
that uses a ringless system. The following conclusions were drawn: (1) The vertical margin
discrepancy of the ringless group for the buccal, the lingual, and the distal sites were
significantly less than that of the 2 ring groups (P<.001). (2) There was no significant difference
of the vertical margin discrepancy between the 2 metal ring groups. (3) There was no significant
difference in the vertical margin discrepancy at the buccal, lingual, mesial, and distal surfaces
within the same group. (4) The ringless technique was clinically acceptable and can be used for
the fabrication of fixed prosthodontic restorations.
Ushiwata O et al (2000)39 evaluated the technique of internal adjustment of
castings with use of duplicated stone dies and a disclosing agent to improve marginal fit
discrepancy. Marginal fit discrepancies of copings were significantly reduced with an internal
adjustment technique (mean > 52%) for all experimental groups. Tooth preparations with greater
convergence and internally relieved castings recorded a better marginal fit. The casting internal
adjustment technique with use of duplicated stone dies and a disclosing agent substantially
reduced marginal fit discrepancy.
Ayad MF (2002) 40 characterized the elemental compositional stability of as-
received and recast type III gold alloy. The effect of combining these alloys on the marginal
accuracy of complete cast crowns also was evaluated. Elemental composition was significantly
different among the casting groups (P<.001). The mean weight percentage values were 72.4% to
75.7% Au, 4.5% to 7.0% Pd, 10.7% to 11.1% Ag, 7.8% to 8.4% Cu, and 1.0% to 1.4% Zn.
Statistically but not clinically significant differences also were found for marginal accuracy. The
marginal discrepancy was less than 25 µm for all casting conditions, with the lowest value
recorded for Group A (7 µm), the highest for Group C (12 µm), and an intermediate value for
Group B (9 µm) specimens. Recasting type III gold alloys may adversely affect the marginal
accuracy of complete cast crowns.
Ito M et al (2002)41 investigated the relationship between wax characteristics and the
casting accuracy of a three-quarter crown. Dental casting accuracy is influenced by the setting
expansion of investment materials. Although setting expansion can help compensate for casting
shrinkage, it cannot be fully realized under a confined wax pattern. Exactly how soft a wax
pattern should be to ensure optimum setting expansion has not been determined. Within the
limitations of this study, casting shrinkage was affected by the type of wax used and was
sensitive to the site at which dimensional measurements were performed. The higher the
softening temperature, the larger the casting shrinkage. At gingival measurement sites, less
casting shrinkage was found when 100% special liquid investment was used with all waxes
except P38. At facial measurement sites, only S42 exhibited a significant difference between
100% and 75% special liquid investments.
Bezzon OL et al (2004)42 evaluated the surface roughness of 2 base metal alloys,
submitted to different casting techniques, to determine the influence of surface roughness on loss
of mass after polishing compared to commercially pure titanium castings. Within the limitations
of this study, the following conclusions were drawn: (1) Vacuum casting provided significantly
smoother alloy specimens compared to flame casting. (2) Vacuum casting of base metal alloys
provided specimens with a surface smoothness that was not significantly different from those of
commercially pure titanium. (3) There were no significant differences in loss of mass after
polishing for all tested specimens.
Gassino G et al (2004) 43 evaluated the marginal fit of experimental and custom-made
fixed prosthetic restorations through a new 360-degree external examination. The minimum
number of gap measurements required to produce relevant results for gap analysis was also
investigated. The marginal fit of six experimental and eight custom-made crowns was observed
microscopically by means of a mechanical device, and software was employed to measure the
gap. Two crowns, chosen from among the 14 previously evaluated, were reanalyzed to determine
the minimum number of gap measurements required to produce significant results for gap
analysis. Differences in fit between experimental specimens and custom-made ones showed that
experimental results might not always be obtained in clinical practice. Within the limitations of
the protocol of this study, the minimum number of measurements required to ensure relevant
results for gap analysis was 18 for experimental and 90 for custom-made crowns.
Milan FM et al (2004)44 evaluated the relationship between the application of die-
spacer prior to wax pattern fabrication and metal removal from the inner surface of the casting on
marginal and internal discrepancies of complete cast crowns. One hundred and twenty complete
crowns were cast with palladium-silver alloy melted by gas-oxygen torch or electrical resistance
and cast with a centrifuge casting machine. After casting, the crowns were seated on each type of
different marginal configuration dies (90-degree shoulder, 20-degree beveled shoulder, and 45-
degree chamfered shoulder) with a static load of 90 N during 1 min. Evaluation of the marginal
fit of the specimens was made using a digital micrometer. The crowns were embedded in acrylic
resin and longitudinally sectioned to verify the internal discrepancy that occurred in lateral and
occlusal interfaces with a digital micrometer. The data were submitted to ANOVA and Tukey’s
test with a significance level of 5%. The best marginal and inner fits were obtained with the gas-
oxygen torch source. The 45-degree chamfered shoulder showed the best marginal and inner fit,
and better internal relief was obtained in the crowns abraded with 50 µm Al2O3 particles.
Abhyankar V, Nagda S et al (2005)45 investigated the effect of ring liner and casting
ring temperature on the dimensional changes in morphologic cast posts. Prosthodontic treatment
of an endodontically treated tooth poses a challenge to the practitioner. Endodontic therapy has
provided a solution to retain mutilated teeth. Coronoradicular reconstruction in the form of cast
post and core is used as a method to provide retention and resistance form to the restoration. To
prevent fracture and support crown and bridge, reinforcement in the form of intraradicular
devices is being used. A cast post is one such method. A cast post and core should fit passively
in the canal. Even a minimally oversized post can lead to transfer of stresses to the canal walls
and increase the risk of root fracture. Therefore it is necessary to ensure that there is passive fit
of the post and core. Shrinkage of the mould cavity is desired during the casting process to allow
a passive fit. The effect of lined and unlined rings in the dimensional behavior of the investment
during setting and subsequent heating has been investigated and it is shown that casting made of
unlined rings are undersized.
Boeckler AF et al (2005)4 study describes the correlation between objective
marginal fit and its subjective evaluation by dentists and dental technicians. All crowns showed
marginal gaps as well as marginal overextensions. All marginal gaps and overextensions were in
a clinically acceptable range. Objective measurement of marginal gaps and overextended
margins correlated significantly with their subjective evaluation by dentists and technicians. The
findings regarding the marginal gap and the overextended margin correlated significantly with
the subjective evaluation of the clinical acceptability of dentists and technicians. Evaluations of
dentists and technicians showed a significant correlation. The marginal gap had no significant
influence on the decision among dentists and technicians regarding the marginal fit and the
perceived clinical acceptability of the tested crowns. Overextended margins had significant
effects on the decision of dentists and technicians regarding marginal fit and clinical
acceptability of the crowns.
Brosnon MR et al (2005) 1 studied to examine margin acceptability using an
explorer versus the actual marginal gap widths at four locations on uncemented crowns on three
extracted teeth using both predoctoral students and prosthodontists as evaluators. Upon casting,
marginal gaps ranged from 40µm to 615µm. The data provided evidence that those surfaces
associated with greater marginal gaps tended to have a greater proportion of ratings of “clinically
unacceptable.’’ The proportion of prosthodontists and predoctoral students rating a margin
“clinically unacceptable’’ were highly correlated.
Singh GP, Datta K (2005) 3 evaluated the marginal gap of complete crowns made
by using wet and dry ceramic ring liners using a scanning electron microscope. Two groups of
thirty castings each were prepared with dry and wet ceramic ring liners respectively and assessed
for marginal fit. Results showed that crowns made by using dry ceramic ring liners had
significantly less marginal gap as compared to the crowns made by using wet ceramic ring liners.
Yang CC et al (2007) 46 evaluated the characteristics of commercial quick-heating
phosphate-bonded investments. Two different heating methods – the Quick Heating Method
(QHM) and Conventional Heating Method (CHM) – were used with the investments. The
dimensional accuracy and surface roughness of the nickel-chromium alloy castings obtained
from the investments were also examined. The setting expansion (1.1% to 2.2%) was obtained
after a 30-minute setting time; the fired strength of both investments was greater with QHM
(21.2 to 27.7 MPa) than with CHM (13.8 to 17.9 MPa); the thermal expansion of the investments
was higher with QHM (1.4% TO 1.7%) than with CHM (1.2% to 1.4%). In addition, the surface
roughness of the Ni-Cr castings obtained from the investment was not significantly dependent on
the heating method and the dimensional accuracy of the castings using the investments, are
acceptable.
Bedi A et al (2008)8 evaluated the surface roughness and irregularities of gold
palladium alloy castings obtained using different investment techniques. Within the limitations
of this study, the following conclusions were drawn: (1) The surface roughness values of
castings obtained by 4 investment techniques tested using carbon-free phosphate-bonded
investment material were not significantly different. (2) Specimens allowed to set under
atmospheric pressure are more likely to present surface irregularities than specimens set under
positive pressure. As a result, adjustment and finishing of the crown can be easier for both the
technician and the clinician, while the fit of the restorations can be improved as well.
Materials & Methods This study was conducted to measure the vertical marginal discrepancy and
surface roughness of base metal alloy cast copings made by Inlay Wax and Pattern Resin with
two different methods of casting techniques (conventional casting technique with three stage wax
elimination and accelerated casting technique).
The following materials were used for the study:
1. Inlay wax (GC Corporation, TOKYO, JAPAN) (Fig-5B).
2. Pattern Resin (Acrylic resin for patterns, GC corporation,TOKYO, JAPAN) (Fig-5A).
3. Die lubricant (DIE LUBE WAX SEP, Dentecon, LosAngeles, USA).
4. Sprue wax, 2.5mm diameter (YETI DENTAL, DURON, GERMANY).
5. Ring liner (Flexvest liner, Ivoclar Vivadent,GERMANY).
6. Surfactant spray (Aurofilm, Bego, GERMANY).
7. Phosphate bonded investment powder (PCT Flexvest ivoclar vivadent technical, Italy)
(Fig-6).
8. PBI liquid (PCT Flexvest liquid, Ivoclar vivadent technical,Italy) (Fig-6).
9. Distilled water.
10. Base metal Nikel Chromium Alloy (CB80, DENTSPLY SANKIN, JAPAN) (Fig-7).
11. Aluminium oxide powder for sand blasting (110 micron) (Delta, INDIA).
12. Separating discs (0.25 to 0.7 mm thickness) (Dentorium, New York, USA).
The following equipments were used for the study:
1. Stainless steel master die and stainless steel former assembly (custom-made)
(Fig-1 & 2).
2. Crucible former (Whip mix, USA).
3. Alloy casing rings of 4 cm diameter and 5 cm length (Whip mix, USA).
4. Vacuum power mixer (Tornado product).
5. Muffle furnace (Technico, Technico laboratory products PVT.LTD, Chennai, INDIA).
6. Induction casting machine (LC-cast60, Belgium).
7. Sand blaster (Ideal blaster, Delta, Delta labs, INDIA).
8. High speed alloy grinder (RAY FOSTER DENTAL Equipment, CA).
9. Reichert Polyvar 2 met photo microscope (Reichert AUSTRIA) (Fig-8).
10. Stainless steel coping holder for making the cast coping parallel to the ground for
measuring surface roughness (custom-made) (Fig – 25).
11. Taly Surf computer controlled surface roughness analyzer (Kosaka lab.) (Fig-9).
Description of custom made stainless steel master die and stainless steel former assembly:-
The stainless steel master die and stainless steel former (Fig-1 & 2)employed in this
study was custom made, based on the model employed by Konstantoulakis et al, Schilling et
al for their studies. This assembly essentially is of 2 parts namely, the stainless steel master
die and the stainless steel former which fits over the die. The base has a height of 30mm and
a diameter of 20mm.The base is sectioned along its circumference which divides it into an
upper one third part and a lower two third part. The upper one third can be moved up and
down from the lower two third of the base. This aids in easy removal of wax pattern. The
stainless steel master die simulated a crown preparation with a 10-degree total axial wall
taper. The height of the die and its occlusal diameter is 6mm. The occlusal surface had
occlusal cross hairs (or grooves) to aid in repositioning of the pattern and casting. Four
markings present on the base of the die, separated by 90-degree, each serve as standard
reference points for measurement of the vertical marginal discrepancy of all the cast copings.
A custom-made stainless steel former was fabricated, such that it can be accurately
positioned over the stainless steel master die. The internal surface of the stainless steel former
assembly was larger than the die in all dimensions by 0.5mm uniformly. This was done to
maintain a space of 0.5mm throughout between the master die and former. This space helped to
obtain the wax patterns with a uniform thickness of 0.5mm and a 90-degree shoulder margin.
METHODOLOGY
The following methodology was adopted for the study:
a) Inlay Wax and Pattern Resin fabrication with attachment of sprue and removal of
pattern from master die.
b) Investing the Inlay Wax and Pattern Resin separately.
c) Inlay Wax and Pattern Resin burn out procedure with two different techniques.
d) Casting procedure.
e) Devesting, sprue cutting and finishing the cast coping.
f) Evaluation of vertical marginal discrepancy.
g) Evaluation of surface roughness.
This study was conducted to evaluate the vertical marginal discrepancy and surface
roughness of 40 cast copings obtained by 4 techniques (G-I, G-II, G-III and G-IV) as given
below:
G-I: Conventional casting technique of Inlay Wax copings with 3 stage burnout
procedure (10 samples).
G-II: Accelerated casting technique of Inlay Wax copings with single stage burnout procedure
(10 samples).
G-III: Conventional casting technique of Pattern Resin copings with 3 stage burnout procedure
(10 samples).
G-IV: Accelerated casting technique of Pattern Resin copings with single stage burnout
procedure (10 samples).
a) INLAY WAX & RESIN PATTERN FABRICATION WITH ATTACHMENT OF SPRUE
AND REMOVAL OF PATTERN FROM MASTER DIE:
The custom made stainless steel master die and former assembly as described previously was
used to fabricate standardized wax and resin pattern. A fine coating of die lubricant (Die Lube
Wax sep, Dentecon, Los Angeles, USA) was applied on to the die and the fitting surface of the
stainless steel former using small paint brush for easy removal of Inlay Wax and Pattern Resin
from the die and prevents the pattern from adhering to the stainless steel former. The stainless
steel former was filled with molten Inlay Wax (GC Corporation, TOKYO, JAPAN) and pressed
on the stainless steel die. The die former assembly was held together for 1 minute with finger
pressure. The die separated from the former and the Wax pattern obtained. The excess Inlay Wax
was trimmed using a PKT no.4 carver/BP blade. For easy removal of the Wax pattern and to
minimize distortion, the Inlay Wax pattern was sprued with preformed wax sprue (YETI
DENTAL, DURON, GERMANY) of 2.5 mm diameter and 2.5cm length and was attached to the
Inlay Wax and Pattern Resin with a reservoir 3mm from the end of the pattern. One end of the
sprue was attached to the pattern at an angle of 450. The Inlay Wax and Pattern Resin was
removed from the die with a gentle pressure and the other end of the sprue was attached to the
crucible former. The Inlay Wax and Pattern Resin was cleaned to obtain clean pattern with
surfactant spray (Aurofilm, Bego, GERMANY) to reduce surface tension of all Inlay Wax and
Pattern Resin there by improving wettability with the investment. Then pattern was checked with
wax caliper to verify the even distribution of 0.5mm thickness. A total of 20 Inlay Wax patterns
were fabricated. Similarly 20 Pattern Resin copings were made. They were divided into 4
groups, namely G-I, G-II, G-III and G-IV and ten specimens were prepared for each group of the
study.
b) INVESTING THE INLAY WAX & PATTERN RESIN SEPARATELY:
After spruing each pattern, they were invested immediately to minimize distortion. Casting
rings were lined with one non overlapping layer of wet ceramic ring liner (Flexvest liner, Ivoclar
vivadent, GERMANY) by leaving 3mm of space below and top. Inlay Wax and Pattern Resin
were invested individually with carbon free, phosphate bonded investment material (PCT
Flexvest, Ivoclar vivadent technical, Italy). The liquid is prepared by mixing the PCT Flexvest
liquid with distilled water at a ratio of 80:20 respectively to achieve optimum expansion;
therefore 800 ml of Flexvest PCT liquid (Ivoclar, vivadent technical, ITALY) was mixed
with200 ml of distilled water to obtain the above mentioned ratio. Weight of 60 gm of phosphate
bonded investment (PCT Flexvest, Ivoclar vivadent technical, Italy) was mixed with 13ml of
premixed liquid. Initially the powder and liquid mixed normally with spatula to wet the powder
particles thoroughly and then mechanical mixing was done under vacuum using vacuum mixer
(Tornado products) for 90 seconds. Once the investment was mixed the pattern was painted with
a thin layer of investment using small paint brush to avoid air bubble entrapment. The casting
ring (whip mix, USA) was positioned on the crucible former, and the remainder of the
investment was poured slowly in to the ring under vibrations. Excessive vibration is avoided to
prevent formation of the bubbles and separation of the pattern from the sprue. The investment
pattern was allowed to bench set for 30 minutes. All the 40 patterns in four groups are invested
in the same procedure.
c) INLAY WAX & PATTERN RESIN BURN OUT PROCEDURE WITH TWO DIFFERENT
TECHNIQUES:
The Inlay Wax and Pattern Resin burnout procedure is different for each of the four test
groups (G-I, G-II, G-III and G-IV) as described below:
1) G-I: Conventional casting technique of Inlay Wax copings with 3 stage burnout procedure
(10 samples)
After a 30 minute bench set time, the set investment mold ring was placed in burnout
furnace (Technico, Technico laboratory products PVT LTD, Chennai, INDIA). The wax burnout
was done using a programmed preheating schedule, i.e. the ring was kept in the furnace at room
temperature and was heated till 2700 c rise of temp at a rate of 80 c / min and was held at this
temperature for 30 min. Then ring was heated from 2700 c to 5600 c rise of temp at a rate of 80 c /
min and was held at this temperature for 30 min. Terminal burnout was carried out from 5600 c
to 8500 c rise of temp at a rate of 80 c / min and was held at this temperature for 30 min. The
investment mold was placed initially into the furnace such that it allows for the escape of molten
wax and vapours. The investment mold was later averted near the end of the burnout cycle with
the sprue hole facing upward to enable escape of the entrapped gases and allow oxygen to
contact to ensure complete burnout of the wax pattern and mold expansion.
2) G-II: Accelerated casting technique of Inlay Wax copings with single stage burnout
procedure (10 samples)
After a 30 minute bench set time, the set investment mold ring was placed directly in a
preheated burnout furnace (Technico, Technico laboratory products PVT LTD, Chennai, INDIA)
at 8500 c, and held for 30 min to ensure complete burnout of the wax pattern. The investment
mold was placed into the furnace such that it allows for the escape of molten wax and vapours.
The investment mold was later averted near the end of the burnout cycle with the sprue hole
facing upward to enable escape of the entrapped gases & allow oxygen to contact to ensure
complete burnout of the wax pattern & mold expansion.
3) G-III: Conventional casting technique of Pattern Resin copings with 3 stage burnout
procedure (10 samples)
After a 30 minute bench set time, the set investment mold ring was placed in burnout
furnace (Technico, Technico laboratory products PVT LTD, Chennai, INDIA). The resin
burnout was done using a programmed preheating schedule, i.e. the ring was kept in the furnace
at room temperature and was heated till 2700 c rise of temp at a rate of 80 c / min and was held at
this temperature for 40 min. Then ring was heated from 2700 c to 5600 c rise of temp at a rate of
80 c / min and was held at this temperature for 40 min. Terminal burnout was conducted from
5600 c to 8500 c rise of temp at a rate of 80 c / min and was held at this temperature for 40 min.
The investment mold was placed initially into the furnace such that it allows for the escape of
molten Pattern Resin and vapours. The investment mold was later averted near the end of the
burnout cycle with the sprue hole facing upward to enable escape of the entrapped gases and
allow oxygen to contact to ensure complete burnout of the Pattern Resin and mold expansion.
4) G-IV: Accelerated casting technique of Pattern Resin copings with single stage burnout
procedure (10 samples)
After a 30 minute bench set time, the set investment mold ring was placed directly in a
preheated burnout furnace (Technico, Technico laboratory products PVT LTD, Chennai, INDIA)
at 8500 c, and held for 40 min to ensure complete burnout of the Pattern Resin. The investment
mold was placed into the furnace such that it allows for the escape of molten Pattern Resin and
vapours. The investment mold was later averted near the end of the burnout cycle with the sprue
hole facing upward to enable escape of the entrapped gases & allow oxygen to contact to ensure
complete burnout of the Pattern Resin & mold expansion.
d) CASTING PROCEDURE:
The casting procedure was performed quickly to prevent heat loss from the ring resulting in
the thermal contraction of the mold. The preheated casting crucible and the investment mold
were taken out of the furnace and were placed in the casting machine. The casting was done in
an induction casting machine (LC-Cast 60). The Nickel-Chromium alloy (CB 80, non precious
alloy, DENTSPLY) was heated sufficiently till the alloy ingot turned to molten state and the
lever was released and centrifugal force ensures the completion of the casting procedure.
Investment was allowed to cool down to room temperature. The casting procedure followed was
same for all the test samples. A total of 40 castings were made to obtain cast copings for the
evaluation in this study. Among the 40 castings 10 were obtained for G-I technique, 10 for G-II
technique, 10 for G-III technique and 10 for G-IV technique.
e) DEVESTING, SPRUE CUTTING AND FINISHING THE CASTING:
Following casting, the hot casting ring was bench cooled to room temperature, and
devesting was carried out carefully by tapping the button of the casting with mallet. Adherent
investment was removed from the casting initially with hand instrument and then by sandblasting
with 110 micron alumina at 80 psi pressure. The sprue was removed at the junction of the coping
with an ultra thin abrasive disc (Dentorium, New York, USA) and the copings were subjected to
ultrasonic cleaning & checked visually. The internal surface was inspected & relieved of all
nodules with a round carbide bur. This procedure was followed for each of the ten samples of the
four test groups.
f) EVALUATION OF VERTICAL MARGINAL DISCREPANCY:
Each casting was seated on the stainless steel die with finger pressure until
resistance was met. Microscopic measurements were recorded at 80 X magnification
perpendicular to the axial wall with a photomicroscope (Reichert Polyvar 2 met
photomicroscope, Reichert, AUSTRIA) at the department of Nuclear Physics, Madras
University, Chennai, INDIA. Measurements were recorded from coping margin to the stainless
steel die margin for vertical marginal discrepancy. Marginal discrepancies were measured to the
nearest micron on each casting at the 4 predetermined sites on the base of the stainless steel die
separated by 900 each. The same procedure was followed to record the vertical marginal
discrepancy for each of the ten test samples belonging to the four test groups. The measurements
thus obtained were tabulated and statistically analyzed.
g) EVALUATION OF SURFACE ROUGHNESS:
Description of custom- made stainless steel coping holder for measuring surface roughness:
For measuring surface roughness the cast metal coping should be exactly perpendicular
to the diamond indentor. The stainless steel coping holder employed for measuring surface
roughness was custom-made, with dimensions of 5cm in length, 5cm in breadth and 1.5cm in
height. The coping holder has a depression horizontally in the center to accommodate the coping
precisely in to it. The dimensions of the depression were 6.5mm in length, 3.5mm in depth at the
base of the coping, 3.25mm in depth at occlusal surface of the coping with a taper of 100 from
base to top of the coping. Only half of the coping will be inside the depression, when it is placed
horizontally in the custom-made stainless steel coping holder.
Each metal coping was placed horizontally on the coping holder for making the coping
perpendicular to the diamond indentor. The surface roughness was measured by passing the
diamond indentor over the coping surface for a distance of 1.6mm.The readings were obtained
graphically as crest and troughs with surface roughness analyzer (Taly Surf Computer Guided
Surface Roughness Analyzer, Kosaka Lab) at the Manufacturing Engineering Department, Anna
University, Chennai, INDIA. Surface roughness was measured to the nearest micron at 3
surfaces on the coping. The same procedure was followed to record the surface roughness for
each of the ten test samples belonging to the four test groups. The measurements thus obtained
were tabulated and statistically analyzed.
Fig-1 Axial view of custom made stainless steel former assembly (A) and stainless steel master die (B)
BA
Fig-2 Occlusal View of Custom made stainless steel former assembly (A) and stainless steel master die (B)
BA
20 MM
22 MM
2 MM
6 MM
50
6.5 MM
6 MM
3a
8 MM
6.5 MM
Fig -3a. Line Diagram of custom- made stainless steel master die.
3b. Line diagram of custom-made stainless former
20 MM
20 MM
6.5 MM
7 MM
3b
Fig – 4 Line diagram of custom-made stainless steel master die & stainless steel former in place. Colored space indicates the space for wax pattern.
a . Custom – made stainless steel die. b. Custom- made stainless steel former.
b
a
Fig – 5A Pattern Resin, 5B Inlay wax
A B
Fig – 6 Investment powder & special Liquid
Fig – 7 Nickel – Chromium alloy
Fig – 8 Photo Microscope
Fig – 9 Surface Roughness analyzer
Fig – 10 Preparation of Inlay Wax Pattern
Fig – 11 Preparation of Pattern Resin
Fig – 12 Wax coping showing 0.5mm thickness
Fig – 13 Pattern Resin coping showing 0.5mm thickness
Fig – 14 Wax Pattern attached to crucible former
Fig – 15 Ring Liner Placed 3mm short of Ring Margin
Fig – 17 Divested casting Fig – 16 Wax pattern in position in the casting ring
Fig – 18 Cast coping seated on the die
Fig – 19 Metal Coping showing 0.5mm thickness
Fig – 20 Marginal gap of 34.02 at 80x magnification by using photo microscope of a cast coping obtained by conventional casting technique
employing three stage wax elimination. a- Margin of custom made stainless steel die, b-Marginal gap, c- Margin of cast coping
Fig – 21 Marginal gap of 44.39 at 80x magnification by using photo microscope of a cast coping obtained by Accelerated casting technique employing single stage wax elimination
a cb
a c
b
Fig – 22 Marginal gap of 37.06 at 80x magnification by using photo microscope of a cast coping obtained by conventional casting
technique employing three stage Resin elimination
Fig – 23 Marginal gap of 46.86 at 80x magnification by using photo microscope of a cast coping obtained by Accelerated casting
technique employing single stage Resin elimination
a cb
a cb
6.5mm mm
5 cm
1.5 cm
Fig – 25 Custom made stainless steel coping holder with coping
Fig – 24 line diagram of custom made stainless steel coping holder
Fig – 26 Custom made stainless steel coping holder with coping on
surface roughness Analyzer
Cutoff 0.8mm E.length 2.371mm S.length 1.185mm
Ra 4.9µm Ry 29.6µm Rz 21.3µm
Cutoff 0.8mmE.length 1.014mmS.length 1.014mm
Ra 4.4µm Ry 25.5µm Rz 21.2µm
Fig – 27 surface roughness graph obtained by conventional casting technique with three stage wax elimination
Ra - Roughness AverageRy – Maximum height of the profile
Rz – Average Maximum height of the Profile
Fig – 28 surface roughness graph obtained by Accelerated casting technique with single stage wax elimination
S.Length – Sampling Length E. Length – Evaluation Length
Cutoff 0.8mmE.length 1.134mmS.length 1.134mm
Ra 10.7µm Ry 69.3µm Rz 36.6µm*
Cutoff 0.8mm
E.length 1.600mm
S.length 0.800mm
Ra 7.1µm
Ry 48.5µm
Rz 32.4µm*
Fig – 29 surface roughness graph obtained by conventional casting technique with three stage Resin elimination
Fig – 30 surface roughness graph obtained by Accelerated casting technique with single stage Resin elimination
Results
Table 1 shows the basic data of the results and mean obtained in G-I (Conventional casting
technique of Inlay Wax copings with 3 stage burnout procedure) to evaluate the vertical marginal
discrepancy in microns (μ).
Table 1
S.No. Point 1(µ) Point 2(µ) Point 3(µ) Point 4(µ) Mean(µ)1 28.14 37.45 28.66 29.02 30.822 35.16 29.96 32.41 40.51 34.513 36.26 37.54 31.05 30.29 33.784 39.06 41.52 31.31 33.46 36.345 29.10 32.87 36.72 29.64 32.086 46.15 32.67 31.01 28.16 34.507 34.26 38.14 31.35 45.18 37.238 35.59 42.33 29.14 30.23 34.329 30.09 31.11 29.81 38.75 32.4410 36.60 33.54 30.64 36.05 34.21
Table 2 shows the basic data of the results and mean obtained in G-II (Accelerated casting
technique of Inlay Wax copings with single stage burnout procedure) to evaluate the vertical
marginal discrepancy in microns (μ).
Table 2
S.No. Point 1(µ) Point 2(µ) Point 3(µ) Point 4(µ) Mean(µ)1 45.77 45.67 39.37 45.08 43.972 43.45 38.06 40.88 44.17 41.643 40.59 35.86 43.22 42.45 40.534 42.57 46.71 45.62 45.81 45.185 46.77 41.08 49.28 46.87 46.006 46.08 46.11 45.25 46.14 45.907 44.58 43.29 45.01 47.87 45.198 45.74 42.05 41.52 45.97 43.829 46.22 48.46 43.09 47.25 46.2610 47.32 42.79 44.91 46.76 45.44
Table 3 shows the basic data of the results and mean obtained in G-III (Conventional casting
technique of Pattern Resin copings with 3 stage burnout procedure) to evaluate the vertical
marginal discrepancy in microns (μ).
Table 3
S.No. Point 1(µ) Point 2(µ) Point 3(µ) Point 4(µ) Mean(µ)1 32.76 37.43 35.68 40.52 36.602 41.52 35.78 31.86 37.49 36.663 38.24 36.72 42.05 39.61 39.164 43.72 34.65 32.43 32.45 35.815 36.29 30.24 39.67 41.15 36.846 42.24 40.15 38.09 35.78 39.077 41.22 37.62 30.15 34.62 35.908 39.82 44.59 32.18 35.36 37.999 33.42 36.78 29.21 34.62 33.5110 35.69 38.57 39.86 42.09 39.05
Table 4 shows the basic data of the results and mean obtained in G-IV (Accelerated casting
technique of Pattern Resin copings with single stage burnout procedure) to evaluate the vertical
marginal discrepancy in microns (μ).
Table 4
S.No. Point 1(µ) Point 2(µ) Point 3(µ) Point 4(µ) Mean(µ)1 51.25 49.62 45.87 46.75 48.372 49.62 40.71 39.85 43.62 43.453 42.67 38.75 42.23 39.12 40.694 44.13 50.22 46.15 49.72 47.565 46.86 43.12 49.37 51.16 47.636 47.12 46.85 51.32 50.17 48.867 45.52 43.71 46.02 47.69 45.748 46.64 39.22 51.29 49.56 46.689 55.62 50.35 47.92 47.92 50.6510 45.11 47.93 53.19 49.76 49.00
Graph 1 shows the basic data of the results and mean obtained in G-I (Conventional casting
technique of Inlay Wax copings with 3 stage burnout procedure) to evaluate the vertical marginal
discrepancy in microns (μ).
Graph 1
Graph 2 shows the basic data of the results and mean obtained in G-II (Accelerated casting
technique of Inlay Wax copings with single stage burnout procedure) to evaluate the vertical
marginal discrepancy in microns (μ).
Graph 2
Graph 3 shows the basic data of the results and mean obtained in G-III (Conventional casting
technique of Pattern Resin copings with 3 stage burnout procedure) to evaluate the vertical
marginal discrepancy in microns (μ).
Graph 3
Graph 4 shows the basic data of the results and mean obtained in G-IV (Accelerated casting
technique of Pattern Resin copings with single stage burnout procedure) to evaluate the vertical
marginal discrepancy in microns (μ).
Graph 4
Table 5 shows the mean vertical marginal discrepancy obtained from basic mean values of four
techniques (G-I, G-II, G-III and G-IV) calculated in microns (μ).
Table 5
G-I(µ) G-II(µ) G-III(µ) G-IV(µ)
Mean (μ) 34.02 44.39 37.06 46.86
Graph 5 shows the comparison of the mean vertical marginal discrepancy obtained from basic
mean values of four techniques.
Graph 5
The obtained results were statistically analysed, mean and standard deviations were
estimated for each study group. The data were analyzed by use of t-test. In the present study,
p<0.001 was considered as the level of significance.
Table 6 shows the test of significance for the mean obtained from four techniques (G-I, G-II, G-
III and G-IV). t-test was used to calculate the P value.
Table 6
Technique Mean(μ) S.D. p-value G-I 34.02 1.91
<0.001 ** G-II 44.39 1.93 G-III 37.06 1.80 G-IV 46.86 2.93
Note: - ** denotes significant at 1% level.
* denotes significant at 5% level.
Inference:
The table 6 shows the comparison of the mean value of the vertical marginal discrepancy
obtained for each of the four techniques. Since the p-value is less than 0.001, there is highly
significant difference between the four techniques with regard to vertical marginal discrepancy.
The mean vertical marginal discrepancy values obtained from the two conventional casting
techniques G-I (34.02µ) and G-III (37.06µ) has minimal statistical difference. The mean vertical
discrepancy values obtained from the two accelerated casting techniques G-II (44.39µ) and G-IV
(46.86µ) has minimal statistical difference. However higher values of vertical marginal
discrepancy were found with accelerated casting techniques G-II (44.39µ) and G-IV (46.86µ)
when compared to the conventional casting techniques G-I (34.02µ) and G-III (37.06µ) and this
difference was statistically significant.
Table 7 shows the basic data of the results and mean obtained in G-I (Conventional casting
technique of Inlay Wax copings with 3 stage burnout procedure) to evaluate the surface
roughness in microns (μ).
Table 7
S.No. Area 1(µ) Area 2(µ) Area 3(µ) Mean(µ)1 4.90 5.40 5.90 5.402 4.60 5.50 6.20 5.433 3.70 4.10 4.30 4.034 4.20 3.90 4.10 4.075 3.80 4.30 4.20 4.106 4.40 3.70 4.10 4.077 4.20 3.80 4.00 4.008 4.80 4.10 4.40 4.439 5.00 4.20 4.30 4.5010 3.70 4.10 3.60 3.80
Table 8 shows the basic data of the results and mean obtained in G-II (Accelerated casting
technique of Inlay Wax copings with single stage burnout procedure) to evaluate the surface
roughness in microns (μ).
Table 8
S.No. Area 1(µ) Area 2(µ) Area 3(µ) Mean(µ)1 4.90 4.40 5.60 4.972 4.20 7.30 4.50 5.333 4.60 6.90 4.50 5.334 6.30 5.80 6.10 6.075 6.20 6.00 5.90 6.036 4.80 5.50 5.70 5.337 5.20 4.90 4.70 4.938 4.70 5.30 5.10 5.039 6.10 5.70 5.40 5.7310 5.80 5.50 4.80 5.37
Table 9 shows the basic data of the results and mean obtained in G-III (Conventional casting
technique of Pattern Resin copings with 3 stage burnout procedure) to evaluate the surface
roughness in microns (μ).
Table 9
S.No. Area 1(µ) Area 2(µ) Area 3(µ) Mean(µ)1 6.40 10.70 6.30 7.802 10.20 7.00 6.40 7.873 3.40 4.00 5.80 4.404 8.70 9.20 7.10 8.335 9.30 7.60 8.10 8.336 10.10 8.70 6.30 8.377 9.70 6.50 8.20 7.138 4.90 8.30 10.70 7.979 7.30 10.60 9.40 9.1010 6.70 7.50 8.80 7.67
Table 10 shows the basic data of the results and mean obtained in G-IV (Accelerated casting
technique of Pattern Resin copings with single stage burnout procedure) to evaluate the surface
roughness in microns (μ).
Table 10
S.No. Area 1(µ) Area 2(µ) Area 3(µ) Mean(µ)1 3.20 12.10 12.20 9.172 5.12 10.50 7.10 7.573 5.70 6.20 8.30 6.734 11.60 5.70 8.90 8.735 8.50 12.60 9.40 10.176 9.70 10.90 11.70 10.777 10.80 11.60 8.70 10.378 6.90 10.50 8.60 8.679 8.70 11.80 9.60 10.0310 12.50 9.70 8.40 10.20
Graph 6 shows the basic data of the results and mean obtained in G-I (Conventional casting
technique of Inlay Wax copings with 3 stage burnout procedure) to evaluate the surface
roughness in microns (μ).
Graph 6
Graph 7 shows the basic data of the results and mean obtained in G-II (Accelerated casting
technique of Inlay Wax copings with single stage burnout procedure) to evaluate the surface
roughness in microns (μ).
Graph 7
Graph 8 shows the basic data of the results and mean obtained in G-III (Conventional casting
technique of Pattern Resin copings with 3 stage burnout procedure) to evaluate the surface
roughness in microns (μ).
Graph 8
Graph 9 shows the basic data of the results and mean obtained in G-IV (Accelerated casting
technique of Pattern Resin copings with single stage burnout procedure) to evaluate the surface
roughness in microns (μ).
Graph 9
Table 11 shows the mean surface roughness obtained from basic mean values of four techniques
(G-I, G-II, G-III and G-IV) calculated in microns (μ).
Table 11
G-I(µ) G-II(µ) G-III(µ) G-IV(µ)
Mean (μ) 4.38 5.41 7.8 9.24
Graph 10 shows the comparison of mean surface roughness obtained from basic mean values of
4 techniques.
Graph 10
The obtained results were statistically analysed, mean and standard deviations
were estimated for each study group. The data were analyzed by use of t-test. In the present
study, p<0.001 was considered as the level of significance.
Table 12 shows the test of significance for the mean obtained from four techniques (G-I, G-II, G-
III and G-IV). t-test was used to calculate the p-value.
Table 12
Technique Mean(μ) S.D. p-value G-I 4.38 0.58
<0.001 ** G-II 5.41 0.41 G-III 7.8 1.26 G-IV 9.24 1.32
Inference:
The table 12 shows the comparison of the mean value of the surface roughness obtained
for each of the four techniques. Since the p-value is less than 0.001, there is highly significant
difference between the four techniques with regard to surface roughness. The mean surface
roughness values obtained from castings done with Inlay Wax in G-I (4.38µ) and G-II (5.41µ)
techniques has minimal statistical difference. However higher values of surface roughness were
found from castings done with Pattern Resin in both G-III (7.8µ) and G-IV (9.24µ) techniques
and this difference was statistically significant.
Discussion Casting metals by lost-wax process has been recognized in industry and in arts for many
years. No record exists when and where this type of casting procedure was first developed.26In
dentistry lost wax process of casting metals became common practice after it was introduced by
Taggart in 1907.9 Castings made by Taggart were generally too small and did not fit the cavities
properly.2, 26
The fit of a casting can be defined best in terms of “misfit” measured at various points
between the casting surface and the tooth. Measurements between the casting and the tooth can
be made from points along the internal surface of the margin or on the external surface of the
casting.4,5Clinically important measurements are the marginal gap, which is the distance from the
internal surface of the casting to the axial wall of the preparation at the margin.4
The accuracy of fit of casting is essential for longevity and clinical success of the cast
restoration in the oral cavity.3 Lack of adequate fit is potentially detrimental to both the tooth and
the periodontal tissues. Clinically, defective margins act as a niche for plaque. Insufficient
marginal fit can cause secondary caries below the margins of the crown.4, 5, 11, 38 Precise marginal
sealing is important in dental restorations to fulfill biologic, physical and cosmetic requirements
lest the restoration will fail.
Marginal discrepancies are inevitable, despite careful attention to waxing, investing and
casting. It is one of the tasks of the luting cement to close these discrepancies. However, cement
can be washed out under the margins if gap is too large.4 Because of their solubility, luting
cements in general, have been described as weak link in restoring teeth with cast restorations.29
The rate of cement dissolution has been related empirically to the degree of marginal opening,
thus larger the marginal gap and subsequent exposure of the dental luting cement to oral fluids,
the more rapid is the rate of cement dissolution.29 Thus for the success of cast restoration,
marginal gap must be as minimal as possible.
From the time that dental castings were first introduced, at about the turn of the century,
efforts have been made to produce more accurate and better fitting casting with minimal
marginal discrepancy.24 The accuracy of fit is affected by the quality of tooth preparation, the
impression, the working cast, the quality of the wax that is used, and the accuracy of the casting
procedures. The accuracy of casting is subjected to the volumetric changes occurring due to
shrinkage of wax and alloys. This shrinkage can be compensated by normal setting expansion,
hygroscopic expansion and/or thermal expansion of the investment.2, 3
The casting process used in dentistry based on the lost wax technique has been receiving
continuous investigations. The majority of the efforts deal with the conventional casting
technique. The conventional investing and casting techniques require atleast 1 hour bench set for
the investment. The usual burnout temperatures for phosphate-bonded investments range from
7500 to 10300C. The highest temperatures are required for base metal alloys, especially those that
are used for ceramometal restorations. Initially one stage wax burnout procedure was followed
traditionally to achieve complete burnout as well as thermal expansion. Later on manufacturers
added a two or three stage burnout procedures to conventional techniques to achieve maximum
thermal expansion by maximum conversion of the refractory used in the investment. The entire
process involving phosphate-bonded investments takes a long time; the demand for time saving
is more. Investment manufacturers have attempted to answer this demand and accelerated casting
techniques have been reported in an effort to achieve similar quality results in significantly less
time. These techniques have the ability to shorten the investing and casting process, there by
improving productivity. This accelerated technique uses a typical method of setting and burnout
of the phosphate-bonded investment.
Usually, a bench setting time of 12 to 15 minutes and a mold burnout time of 12 to 15
minutes are employed before the casting process. The first published attempt to accelerate the
lost wax technique with the use of phosphate-bonded investment for complete crown was made
in 1988 by Marzouk and Kerby who recognized the importance of investment temperature. Their
study revealed no statistical circumferential difference between investment groups introduced in
a 13500C preheated oven after 15 minute bench set and the conventional technique.12 Campagni
et al30 tested the fit of dowel and cores made of noble alloy by an accelerated casting technique,
and similar studies were subsequently conducted by Bailey and Sherrard and Schneider.32,33 All
these investigations concluded that the use of a predetermined bench set time reduced investment
weakness and that standardized accelerated procedures for all types of investments were
inadvisable.12
Blackman11 measured marginal sharpness and diameter changes for crowns cast with type III
gold alloy by using phosphate-bonded investment and rapid burnout techniques, and concluded
that rapid mold preparation resulted in loss of marginal fineness. Konstantoulakis9 evaluated the
marginal fit and surface roughness of complete cast crowns made with a conventional and
accelerated casting technique and reported that crowns fabricated with the accelerated casting
technique were not significantly different from those fabricated with conventional technique.
Schilling et al12 evaluated marginal gap of crowns made with a phosphate-bonded investment and
accelerated technique and reported that the marginal gaps for castings made with an accelerated
technique showed no statistical difference when compared with conventional casting technique.
The accuracy of base metal alloy castings obtained by different investing and burnout procedures
with phosphate-bonded investments were not adequately studied. Though studies9,12 have
reported that marginal discrepancies by accelerated casting technique are within the clinically
acceptable limits, some studies9,11,12 have reported that this procedure is technique sensitive.
Surface roughness of dental castings is an important aspect of their quality and can potentially
affect their marginal fit and the time required for finishing and polishing. It is preferable that the
surface of as-cast crowns be smoother to obtain better marginal fit and curtail finishing or
polishing time. Surface roughness of castings is believed to be affected by several factors such as
type of alloy, mold material, mold temperature, wax pattern, and casting machine.9 Bedi et al
reported that specimens set under atmospheric pressure are much more likely to present surface
irregularities than specimens set under positive pressure. The use of pressure can help produce
castings with fewer surface irregularities.8
Thus, the fit of the casting is a critical issue in determining the longevity of the restoration
and investing and burnout procedures are an important parameter in determining the quality of
the fit of the casting. The surface roughness of the casting affects the ceramic-metal interface
bond. Hence, this study was conducted to investigate the differences in the marginal discrepancy
and surface roughness of base metal alloy cast copings employing two different techniques with
two different materials to achieve thermal expansion of the investment. The introduction of
ceramometal technology required the use of higher melting range alloys to with stand the firing
cycle of porcelain with out noticeable distortion. Base metal alloys are one of the alloys that are
routinely used for obtaining ceramometal restorations. The alloy used in this study was a nickel-
chromium alloy used for ceramometal restorations. An investment that can resist higher
temperatures and higher stress during casting2 is required. A phosphate-bonded investment
fulfills these requirements and hence used in this study.
A custom made stainless steel master die was used to fabricate the standardized Inlay Wax and
Pattern Resin. The master die was based on the models employed in similar previous studies.9,12
This standardized stainless steel dies facilitated in standardizing the dimensions of the test Inlay
Wax and Pattern Resin. Four markings present on the base of the die, separated by 90-degree,
each serve as standard reference points for measurement of the vertical marginal discrepancy of
all the cast copings. Another custom made stainless steel coping holder was used for
measurement of the surface roughness. This coping holder was fabricated for making the coping
perpendicular to the surface roughness analyzer. Each pattern was immediately invested to
minimize distortion.2,3,12 Different ratios of special liquid to distilled water have been
recommended to obtain the required mold expansion. In this study, the ratio of special liquid to
distilled water of approximately 80:20 in volume was employed. This special liquid to distilled
water ratio has been shown to offer adequate expansion for complete crown castings, as
recommended by the manufacturer and hence employed in this study. The liquid to powder ratio
was as recommended by the manufacturer i.e., 60g powder-13ml liquid.
Vacuum mixing was done and investing of all the samples was done as recommended by the
manufacturer. Two different techniques with two different materials were used for achieving
complete burnout: conventional casting technique with three stage Inlay Wax and Pattern Resin
elimination, accelerated casting technique with single stage Inlay Wax and Pattern Resin
elimination.
The conventional burnout procedures usually recommend burn out temperatures for
phosphate-bonded investments in a range of 7500c to 10300c. The highest temperatures are
required for base metal alloys, especially those that are used for ceramometal restorations.6 Some
manufacturers recommend additional holding stages (either 2-stage/3-stage) during burn out for
their investments. This could be attributed to maximum conversion of the refractories used in the
investment there by achieving maximum expansion of the investment. A three stage burn out
procedure was employed for obtaining the cast copings for the conventional technique as it was
recommended by the manufacturer (PCT Flexvest, Ivoclar) of the investment employed in this
study.
Accelerated techniques are time saving and hence offer advantage to commercial laboratories.
The pattern is invested, casted, and delivered in a cost-effective, time-saving manner.
Accelerated casting technique was employed for obtaining the cast copings for the second and
fourth test groups in this study. The manufacturer of the phosphate-bonded investment material
(PCT Flexvest) employed in this study recommends that the investment can be used for an
accelerated as well as for the conventional casting technique with three stage wax/resin
elimination. Hence, this material was chosen for investing the wax/resin for all the test groups in
this study. Also using a single investment material for all the test groups helps to eliminate any
variability in the test results.
The casting procedure was performed by using an induction casting machine. All castings,
one at a time were seated on the stainless steel die with finger pressure till the resistance is
obtained and the vertical marginal discrepancy was measured on four predetermined areas that
were marked on the metal die using a photomicroscope (Reichert Polyvar 2 met photo
microscope, Reichert, AUSTRIA) at a magnification of 80X. The results of this study have been
tabulated as a basic data and interpretation of this data was done by statistical analysis.
All castings, one at a time were seated on the stainless steel die and the surface roughness
was measured on three surfaces using a Taly Surf computer controlled surface roughness
analyzer (Kosaka lab.)
The basic data for vertical marginal discrepancy shows a mean value of 34.02 µm
for conventional casting technique of Inlay Wax copings with three stage burn out procedure (G-
I), 44.39 µm for accelerated casting technique of Inlay Wax copings with single stage burn out
procedure (G-II), 37.06 µm for conventional casting technique of Pattern Resin copings with 3
stage burn out procedure (G-III) and 46.86 µm for accelerated casting technique of Pattern Resin
copings with single stage burn out procedure (G-IV).
The basic data for surface roughness shows a mean value of 4.38 µm for conventional
casting technique of Inlay Wax copings with three stage burn out procedure (G-I), 5.41 µm for
accelerated casting technique of Inlay Wax copings with single stage burn out procedure (G-II),
7.80 µm for conventional casting technique of Pattern Resin copings with 3 stage burn out
procedure (G-III) and 9.24 µm for accelerated casting technique of Pattern Resin copings with
single stage burn out procedure (G-IV).
The statistical analysis by t-test indicated that the difference in the vertical marginal
discrepancy and surface roughness measurements for the four techniques showed the p-value of
< 0.001. This denotes significance at 1% level. The mean vertical marginal discrepancy values
obtained with the two conventional casting techniques has minimal statistical difference between
copings made with Inlay Wax and Pattern Resin. However higher values of vertical marginal
discrepancy were found with accelerated casting technique copings made with Inlay Wax and
Pattern Resin when compared with the conventional casting technique.
The mean surface roughness values obtained with the copings made with
Inlay Wax has minimal statistical difference in both G-I and G-II techniques. However higher
values of surface roughness were found with copings made with Pattern Resin in both G-III and
G-IV techniques.
The results indicate that, with in the limitations of the study, the castings produced by
conventional casting technique showed a lesser vertical marginal discrepancy and surface
roughness values than the castings produced using accelerated casting technique. The castings
made with Inlay Wax have lesser marginal discrepancy and lower surface roughness values
when compared with the Pattern Resin.
Papadopoulos and Axelsson reported a superior fit of crowns on dies if phosphate-bonded
investment moulds were prepared with longer burn out schedules; marginal gaps were 5 times
greater with shorter burn out schedules.11 Longer burn out cycles as recommended by
manufacturer were used in this study and was probably the reason for lesser vertical marginal
discrepancy and surface roughness values of castings made by conventional casting technique as
compared to the castings produced using accelerated casting technique. Though the marginal
discrepancy and surface roughness due to accelerated casting technique is significantly larger
than the conventional casting technique in the study, the mean marginal discrepancy of 44.39 µm
& 46.86 µm obtained by accelerated casting technique with Inlay Wax and Pattern Resin in this
study is with in the clinically acceptable limits. Accelerated techniques may take advantage of
characteristic exothermal setting reaction of phosphate-bonded investments. Heat-enhanced
setting expansion continues uninterrupted as the mold is transferred into a preheated furnace for
thermal expansion.12 This may probably be the reason for the marginal discrepancy and surface
roughness of cast copings by accelerated technique to be with in the clinically acceptable limit.
In this study two types of pattern materials, Inlay Wax and Pattern Resin were used. Most
of the studies by Schneider,33 Bailey and Sherrard32 deal pattern resin with intra coronal
restorations (post & core). Alan Iglesias MS34 compared the marginal discrepancy of both intra
coronal and extra coronal restorations using inlay wax, auto polymerized acrylic resin and two
types of light polymerized resin pattern materials. The results showed that light polymerized
resin pattern was superior with less marginal discrepancy than other two materials. The author
compares the incremental and bulk addition techniques, in which incremental technique
produced smaller marginal discrepancy than the bulk techniques.
The result of this study is correlated with Alan Iglesias study. 34 The results showed that
marginal discrepancy was minimal for Inlay Wax when compared with the auto polymerized
resin pattern with the bulk technique for extra coronal restorations. The auto polymerized resin
pattern due to high polymerization shrinkage has greater marginal discrepancy when compared
with the wax.
Accelerated casting technique has greater marginal discrepancy when compared with
the conventional casting technique. This may be due to bulk addition of the material. Most of the
literature on accelerated casting technique shows better marginal fit with intra-coronal
restorations. How ever further research to be done on the extra-coronal restorations.
In this study the surface roughness of resin pattern is greater than the Inlay Wax. This
may be due to the greater size of the polymer beads (approximately 150µm)47 and also due to
evaporation of the monomer which could not be controlled.
The specimens are fabricated with a bulk technique and smoothening of the surfaces was
not possible as it would increase the desired standardized thickness of 0.5mm. The surfactant
which is used to decrease the surface tension and contact angle probably has the little effect in
improving the contact of the investment with the pattern.
Due to rapid heating in the accelerated casting technique there is sudden production of
steam with in the investment that carries some of the salts and modifiers on to the inner wall of
the mold space. After evaporation of the steam, these modifiers settle on the inner surface of the
mold and are responsible for increase in surface roughness in accelerated casting technique.
Due to greater surface roughness on Pattern Resin it can be mostly used for
ceramometal restorations. The greater the surface roughness; better will be the mechanical
bonding.
Accelerated casting techniques using phosphate-bonded investments are considered to
have some desirable advantages. Unquestionably time is saved. Past investigations make it
apparent that, within commercially available phosphate-bonded investments, dissimilar
performance characters are expected. This knowledge suggests that casting techniques should be
studied with broad sample of alloys and phosphate-bonded investments, considering the
possibility that there may be an optimum combination in each situation.
The results of this study encourage further research with accelerated technique and
reinforce the need to identify the factors that facilitate better marginal fit and surface roughness
of cast restorations. Only one single wax pattern is investigated per casting in this study. The
performance of the described accelerated casting technique when more than one wax pattern or
fixed partial dentures invested in the same ring requires further investigation. Four
predetermined points were used to record the marginal gaps in this study. More number of
reference points for marginal gap measurements for each coping may yield a better confirmative
result. An 80% special liquid was used in this study. A further evaluation of different special
liquid to distilled water ratios on the marginal gaps and surface roughness of cast restorations
help to improve the outcome of this study. A further investigation on the influence of surface
roughness of dental casting affecting the marginal fit and the time required to finish and polish
the base metal cast restoration will enhance the outcome of these procedures. Further studies
which incorporate the above considerations are required to enhance the results obtained with this
study.
Summary & Conclusion
This study has been done to evaluate and compare the vertical marginal
discrepancy and surface roughness of cast copings made by two different casting
techniques with two different materials. The four techniques used in the study were,
conventional casting technique of Inlay Wax copings with 3 stage burnout procedure (G-
I), accelerated casting technique of Inlay Wax copings with single stage burnout
procedure (G-II), conventional casting technique of Pattern Resin copings with 3 stage
burnout procedure (G-III) and accelerated casting technique of Pattern Resin copings
with single stage burnout procedure (G-IV).
A total of 20 Inlay Wax copings, 20 Pattern Resin copings were fabricated with
stainless steel master die and former assembly, and divided into 4 groups with 10
specimens for each technique. A phosphate bonded investment was used to invest all
Inlay Wax and Pattern Resin copings with 80% special liquid in a metal ring with
ceramic ring liner. Specific burn out cycles were followed according to each technique
and all the samples were cast in nickel chromium alloy in induction casting machine. The
cast copings obtained were sand blasted. The internal surface was inspected and finishing
procedures done. The copings were seated on the stainless steel die with finger pressure
till the resistance obtained and vertical marginal discrepancy measurements were
recorded using a photo microscope. The results obtained were statistically analyzed.
A custom made stainless steel coping holder was used for measurement of
surface roughness to make the coping perpendicular to the surface roughness analyzer.
The surface roughness measurements were recorded using computer controlled surface
roughness analyzer. The results obtained were statistically analyzed.
The vertical marginal discrepancy of cast copings obtained by accelerated casting
technique showed a significantly higher value as compared to those obtained by
conventional casting technique; cast copings obtained by Pattern Resin showed a
significantly higher value as compared to those obtained by Inlay Wax. The mean vertical
marginal discrepancies of all the copings obtained by the four techniques were within
clinically acceptable limit.6
The surface roughness of cast copings obtained by accelerated casting technique
showed a significantly higher value as compared to those obtained by conventional
casting technique; cast copings obtained by Pattern Resin showed a significantly higher
value as compared to those obtained by Inlay Wax. The mean surface roughness of all the
copings obtained by the four techniques was within clinically acceptable limit.9
The following conclusions were drawn from the data obtained in this study of
comparative evaluation of the vertical marginal discrepancy and surface roughness of
cast copings obtained by conventional and accelerated casting techniques using two
different pattern materials – an invitro study.
1. The order of discrepancy values of vertical marginal discrepancy of the cast copings in
this study is as follows:
a. Least marginal discrepancy - conventional casting technique of Inlay Wax copings
with 3 stage burn out procedure (G-I) - 34.02 µm.
b. Moderate marginal discrepancy - conventional casting technique of Pattern Resin
copings with 3 stage burn out procedure (G-III) - 37.06 µm.
c. Maximum marginal discrepancy - accelerated casting technique of Inlay Wax
copings with single stage burn out procedure (G-II) - 44.39 µm and accelerated casting
technique of Pattern Resin copings with single stage burn out procedure (G-IV) - 46.86
µm.
2. The order of roughness values of surface roughness of the cast copings in this study is as
follows:
a. Least surface roughness - conventional casting technique of Inlay Wax copings with 3 stage
burn out procedure (G-I) - 4.38µm
b. Moderate surface roughness - accelerated casting technique of Inlay Wax copings with
single stage burn out procedure (G-II) - 5.41 µm
c. Maximum surface roughness - conventional casting technique of Pattern Resin copings
with 3 stage burn out procedure (G-III) -7.80 µm and accelerated casting technique of Pattern
Resin copings with single stage burn out procedure (G-IV) - 9.24 µm.
3. The mean vertical marginal discrepancy and surface roughness of all the cast copings obtained
by the four techniques (G-I, G-II, G-III and G-IV) were within the clinically acceptable limits.
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