ARTICULATORS

INTRODUCTION

It is well adjudged that the mouth comprising bi-maxilla and the two

tempero-mandibular joints as the best articulator. But due to the innumerable

procedures carried out to fabricate a prosthesis, a mechanical device

stimulating the two jaws and the tempero-mandibular joints is needed for ease

of work and comfort of the patient. This device is called and

“ARTICULATOR”.

DEFINATION:

Articulator is a mechanical device that represents the tempero-

mandibular joints and the jaw members to which maxillary and mandibular

casts may be attached to simulate some or all the mandibular movements.

Many devices that are called articulators do not satisfy this definition.

Some of these devices make no attempt to represent the tempero-mandibular

joints (face bow transfer) or their paths of motion (eccentric registration).

Some instruments allow eccentric motion determined by inadequate

registrations (positional registration). Some utilize average or equivalent

pathways. Some attempt to reproduce the eccentric pathways of the patient

from three dimensional registration. Some other articulators record even the

fourth dimension, i.e., the timing of the Benett movement.

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HISTORY:

The history of articulators parallels that of the varying concepts of

occlusion. Attempts were made to record anatomic relationships of reproduce

functional movements of the mandible and transfer this to the mechanical

devices to stimulate the conception of natural movements.

More sophisticated instruments evolved as more learned about the

anatomy, mandibular movements and mechanical principles. The objective

was always the same: to produce or reproduce occlusal relationships

extraorally.

The plaster articulator devised by Philip Pfaff in 1756 consisted of

plaster extension on the distal portion of maxilarry and mandibular casts

grooved to each other. This was commonly known as slab articulator.

The first mechanical articulator was described in 1805 by J.B. Gariot.

He designed the hinge joint articulator which consisted of two metal frames to

which the casts were attached, a hinge to join them and set crew to hold the

frames in a fixed vertical position.

In 1840, Cameron and Evans made attempts to device the plane line

articulator.

Bon will, a mathematician, in 1858 developed an a articulator based on

his theory of occlusion on the theory of equilateral triangle, with which he

demonstrated the anatomic and balanced occlusion.

W.E. Walter in 1896 said that dentures which balanced on Bonwill’s

articulator did not balanced in the mouth and pointed the absence of condylar

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inclination as the dictating factor. He devised the Clinometer which had

provision for gothic arch tracings.

Later every investigator tried to reproduce the individual movements of

the patients mandible. They said that the condyle path varied from person to

person and even in the same person, it differs.

George B. Snow in 1899 first devised the face-bow. Later in 1906,

articulator knows as New Century Instrument was developed. He improved the

Gritmann articulator of 1899 by adding the adjustable condylar paths and a

tension spring for a greater range of movement. This articulator was developed

in accordance with Bonwill’s theory. In the modified version of the New

Century Articulator, incisal pin was incorporated.

This articulator was developed in accordance with Bonwill’s theory. In

the modified version of the New Century Articulator, incisal pin was

incorporated.

The ‘Acme’ articulator was an elaboration of Snow’s New Century

Instrument which had straight condylar path, adjustable condylar inclination

and provision for Benett movement.

Alfred Gysi in 1910 introduced the Gysi Adaptable Articulator. In

1914, the Gysi Simplek’ was introduced as a mean value articulator which had

fixed condylar guidance at 33 degrees.

Hall (1915) and Monson (1918) developed the Anatomic articulator and

Maxillo-mandibular instrument based on Conical theory and the theory of

Spherical articulator respectively.

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According to Monson-Hall school, the articulation of teeth during

mastication guides the mandibular movements. Failure of these articulators

based on theories is because provision was not made for variations from the

theoretical relationship that occurred in different persons.

Rudolph L. Hansu, an engineer, during the time of First World War in

1921 developed a research model called the Mansu Model C Articulator which

had provision for controlled movement with more accurate and accessible

controls, and its adjustments and operation much simplified. Later in 1923, he

devised the

‘Kinoscope’ which provided exact measurement of mandibular

movements. In the later years, Mansu introduced more measurements such as

model 110 which had individual condylar guidance adjustments in both sagittal

and horizontal planes and the lateral icondylar angle calculated by the formula

L= H/B + 12, H = Horizontal condylar angle. In 1927, he modified the model

110 with the introduction of ‘Incisal guide table’.

Wadsworth believed in Monson’s Spherical theory but did not accept

the bilateral condylar symmetry. In 1924, he developed the articulator for

which facebow was used to mount the cast. It had an adjustable intercondylar

distance and the condylar paths were slightly curved.

Staneberry in 1929, designed the ‘Tripod Articulator’. He did not

accept all positional records. This instrument does not have a hinge nor

mechanical equivalent or representation of condyles. The articulator

reproduces positions but not movements.

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Charles Stuart in 1989 designed the Fully Adjustable Articulator.

Later, in 1964, he introduced the Whip-Mix Semi adjustable Arcon Articulator

with three intercondylar adjustments – small, medium and large.

Later, Granger, Stuart. Ney and Guichet introduced the ‘Pantographic

Tradings’.

Recent advances in electronic and computer technology facilitated the

development of electronic techniques to record the motion of the mandible.

The main advantage of these technique is that, they could accurately record the

dynamic motion of the mandible. Because of their reduced size, these devices

provide negligible interferences with the natural motion of the mandible.

The three dimensional kinematic characteristics of the tempero-

mandibular joints during any mandibular activity can be measured, analyzed

and described using these devices. These devices do not require head fixation,

does not alter or interface with natural occlusion and is light in weight.

An electronic, computerized pantograph was compared with mechanical

pantograph and was found 93% of immediate size shift measurement with

0.3mm., 92.5% of progressive side shift measurement with 4 degree, 87% of

protrussive inclination measurement within 6 degrees.

Using electronic and computerized pantograph, errors occurring in the

transfer of measurement can be minimized.

RELATING ARTICULATOR TO PATIENTS DENTAL MECHANISM

The articulator is a rigid device with movement patterns determined by

solid pathways, whereas the mandible is guided by muscles, ligaments and

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non-rigid joint surfaces, by the teeth and by complex neuro-muscular system.

The mandible suspended by the ligaments and muscles is resilient and flexes

under normal biologic stresses and the teeth are suspended in the membranes

that respond to stresses in an elastic manner.

The more adjustable the articulator, the factors of mandibular

movements can be reproduced with a greater degree of accuracy. At the same

time, more complicated the device, more the human errors involved.

ESSENTIAL REQUIREMENTS:

In view of the importance of the co-ordinated functions of anatomy,

physiology and geometrics and their relation to prosthetic technique, it is a

must that an articulator have certain characteristics which enable it to accept

and maintain various functions.

The condyle spheres should be situated on the lower member and the

fossa on the upper member, to ensure that all rotations (axial, centers of

rotation) become the sole functions – Benett protrusive, Lateral Protrusive with

curvilinear paths of condylar guidance should be attributed to the upper

member.

Since protrusive and lateral excursions are registered while the jaw is in

an open position, an articulator is set for these excursions in the same open

position, an articulator must be capable of accepting a hinge axle mounting.

It should have provision to adjust intercondylar distance since this

dimension in correlation with the Bennett adjustment, determines horizontal

radi and is a necessary factor in the duplication of a given path of cusp tip.

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When the intercondylar distance is adjusted, the axis should not distort

in any way, so that the magnitude and direction of the axis remains constant.

Provision should be made for benett adjustment.

For the normal functional movements of the patient to be stimulated, the

construction of an articulator should permit the change of the condyle path to

that of a specific curvature dictated by the patient.

An articulator should have an incisal table that is capable of rotation

about the frontal axis and being locked in a determined position. This is

necessary to accommodate the amount of overbite dictated by the anterior

guidance in relation with the straight protrusive movement dictated by the

condyle path.

An incisal table should have lateral incisal guide planes, capable of

limited rotation about the sagittal axis and being locked in a determined

position to accommodate the amount of overbite dictated by the canine in

relation with the lateral excursive movement dictated by the condyle path.

It should also contain a point on which the incisal guide pin rests in

centric position and has the capability of being raised or lowered and locked in

a determined position.

The incisal guide table can be a plastic table which is customized with

auto polymerizing resin.

The construction of an articular should be accurate, rigid and of a non-

corrosive material. The moving parts should resist wear. Adjustments should

be able to move freely and be definitely secured.

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It should have provision for easy removable and to reattach the casts

without loosing their correct horizontal and vertical relationship.

Functionally, an articulator should be sturdy and exact in construction,

simple but efficient in mechanics of operation, and capable of maintaining

constants and duplicating desired movements. It should accept pantographic

registrations and accurate mandibular movements which controls the accuracy

of the fabricated prosthesis.

USES: Articulators are used to mount diagnostic casts, to study the oclusion of

a patient and as an aid in planning treatment procedures.

It is used to hold the opposing casts in a predetermined fixed

relationship.

As an aid in the fabrication of dental restorations and lost gental parts.

In the arrangement of artificial teeth for complete dentures, removable

partial dentures and waxing in field partial dentures.

ADVANTAGES:

Better visualization of the casts in occlusion from the lingual view.

The resiliency and like effect of the supporting tissues or denture bases

hinders the operation in refining the complete denture occlusion in the oral

cavity.

Chair side and patient appointment time is reduced along with saliva,

tongue and cheek being absent.

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LIMITATIONS:

An articulator is a mechanical instrument. It is subject to eror in tooling

and errors resulting from fatigue and wear.

An articulator can stimulate but not duplicate jaw movements.

Since the articulator may not reproduce exactly intraborder and

functional movements, the mouth would be the best place to complete the

occlusion, but using the jaws as an articulator also has limitations:

- Inability of humans to detect visually the finer changes in the motion.

- Making accurate marks in the presence of saliva.

- Exact location of the condyles

- The resiliency of the supporting structures.

- The dentures are movable.

Effectiveness of an articulator depends on the person who understands

its constructions and purpose, the anatomy of the joints, their movements and

the neuromuscular system, precision and accuracy in registering law relations

and the sensitivity of the instrument to record these.

CLASIFICATION OF ARTICULATORS:

1. Articulators based on theories of occlusion.

2. BONWILL’S THEORY OF OCCLUSION

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Teeth move in relation to each other as guided by the condylar control

and the incisal point.

It is also known as the theory of equilateral triangle which has a 4 inch

(10cms) distance between the condyles and between each condyle and to the

lower central incisor point.

Eg: Bonwill’s articulator, Gysi simplex articulator

Since condylar guidances were not adjustable, only movement in

horizontal plane is permitted.

b) CONICAL THEORY OF OCCLUSION:

Lower teeth move over the surfaces of the upper teeth as over the

surface of a cone, with a generating angle of 45 degrees and the central axis of

the cone tipped at 45 degrees to the occlusal plane. Eg. Hall Automatic

articulator-teeth with 45 degrees cusps were necessary for constructing

dentures on this type of articulator.

c) SPHERICAL THEORY OF OCCLUSION:

Proposed by G.S. Monson in 1918. The lower teeth move over the

surface of the upper teeth as over the surface of a sphere with a diameter of 8

inches (20cms). The centre of the sphere is located in the region of the glabella

and the surface of the sphere passes through the glenoid fossa along the

articulating eminences or concentric with them.

This theory was based on observations of natural teeth and skulls by

Van Spee, a German anatomist.

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Eg: Monson’s Maxillo-Mandibular Instrument.

The failure of these articulators based on theories is because of one

common fault – provision was not made for variations from the theoretical

relationship that occur in different persons.

II. Articulators based on the types of records used for their adjustment:

a) INTROCCLUSAL RECORD ADJUSTMENT:

In this type only one potential relationship is possible in centric,

protrusivae and centric or lateral relation.

Teeth casts on the articulator are accurate only at that position where the

interocclusal records are made.

The mechanical features that determine whether or not an articulator can

be adjusted to accommodate interocclusal records includes

- Include adjustable horizontal condylar guidances.

- Variable control for the Bennett movement.

- Variable intercondylar distance.

- Split axis condylar guidance controls and adjustable incisal guidance control.

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B) GRAPHIC RECORD ADJUSTMENT:

Since the border movements of the mandible is curved and are recorded

graphically, the articulators also should be capable of producing or simulating

these curved movements.

These recordings are difficult and unreliable in edentulous patients.

C) HINGE AXIS LOCATION FOR ADJUSTING ARTICULATORS:

The correct location of the opening axis of the mandible should be

made, if not, the correct adjustment of these instruments are impossible.

III) Many investigators have classified articulators in various methods:

1. Gills (1926), Boucher (1934), Kingery (1934) divided articulator into adjustable and nonadjustable.

2. Back (1962) classified into suspension instrument, axis instrument and the tripod movement.

3. Weinberg (1963) – arbitrary, positional, semi-adjustable and fully adjustable.

4. Possult (1968) – plane line, mean value and adjustable.

5. Thomas (1973) – arbitrary, positional and functional.

6. Sharry (1974) – simple, hinge type, fixed guide type and adjustable.

7. Ralini (1980) – fully adjustable, semi adjustable and non adjustable.

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IV. Articulators based on instrument functions:

According to the International Prosthodontic Workshop on Complete

Denture Occlusion at University of Michigan in 1972.

CLASS I:

Simple holding instruments capable of accepting a single static

registration.

The first articulators were coined as “SLAB ARTICULATORS”.

Plaster indices extended from the posterior portion of the casts and were keyed

to each other by means of these indices.

Eg: J.B. Gariot’s hinge articulator (1805).

CLASS II

Instruments that permit horizontal as well as vertical motion but do not

orient the motion to the tempero-mandibular joint with facebow transfer.

CLASS – II – A:

Permit eccentric motion based on average or arbitrary values.

In this type, the condyles are on the lower member and their paths are

inclined at 15 degrees. Casts are amounted to this articulator according to

Bonwill’s theory.

Eg: Gritmann articulator (1899)

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Alfred Gysi’ Simplex articulator (1914). This has the condylar path

inclined at 30 degrees and the incisal fixed at 60 degrees.

CLASS II- B

Permit eccentric motion based on arbitrary theories of motion.

Eg. Maxillo-mandibular instrument designed by Monson in 1918 based

on his spherical theory of occlusion.

CLASS II-C:

Permit eccentric motion based on engraved records obtained from the

patient.

CLASS III:

Instruments that simulate condylar pathways by using average or

mechanical equivalents for all or part of the motion and allow for joint

orientation of the casts with a facebow transfer.

CLASS – III – A:

Accept facebow transfer and a protrusive interocclusal record.

Eg. Hanau Model H designed by Rudolph Hana in 1923 Dentatus

articulator (1944)

Bergstroms Arcon articulator designed in 1950 similar to Hanau H,

except that the condyles are on the lower member and the condylar guides are

curved and are on the upper member.

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Bergstrom’s instrument was not the first arcon instrument, but he was

the first person to coin the “ARCON”. It is believed from Articulator the xxxx

instruments has its condyles on the lower member and the condylar guides on

the upper member.

Back and Morrison said that by fixing the condylar guides to the upper

member of the articulator, theoretically the reproduction of mandibular

movement was more accurate because a constant relationship always exists

between the maxillary occlusal plane and the condylar guides at any position of

the upper member.

Instruments that have the condyles on the upper member and condylar

guides on the lower member are referred as condylar instruments or non-arcon

instrument.

Advantages of Arcon :

Condyles move in a relationship to their condylar housing that is similar

to the way the condyles move in relationship to the glenoid fossae in the skull.

This makes visualization and understanding of condylar movements easier.

According to Weinberg, arcon and condylar instruments produced the

same motion. The motion resulted from the action of a condylar ball on an

inclined plane and reversing their relationship did not change the motion.

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CLASS- III – B

Accept face-bow transfer, protrusive interoclusal records and some

lateral inter-occlusal records.

Eg: Gysi in 1926 introduced the Trubite articulator. It is a non-arcon

instrument with a fixed intercondylar distance. The horizontal condylar

inclinations are individually adjustable, and the individual Bennett adjustments

are located near the center of the intercondylar axis. The incisal guide table is

adjustable.

In 1927, Hanau designed the Kinoscope which has a double condylar

posts on each side. The inner-condylar posts have the horizontal condylar

guides and are adjustable mediolaterally to produce mechanical equivalents of

intercondylar distance.

Stanberry in 1928 designed a tripod type articulator, De Pietro in 1960

designed a true arcon instrument –Ney articulator. It is the first articulator to

have condylar housing that contained adjustable, rear, medial and top walls in

one assembly. The intercondylar distance is adjustable.

The Hanau 130-21 is designed by Richard Ben and James Jaink in 1964.

It had a split horizontal axis that can be adjusted vertically and horizontally,

adjustable intercondylar distance, adjustable Bennett guides and adjustable

condylar path guides.

Taledyne articulator designed by Richard Ben in 1975 is an arcon

instrument with adjustable medial and rear walls and adjustable horizontal

condylar guidances. It has a fixed inter condylar path guides.

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Teledyne articulator designed by Richard Ben in 1975 is an arcon

instrument with adjustable medial and rear walls and adjustable horizontal

condylar guidances. It has a fixed inter-condylar distance.

CLASS – IV –1:

Instrument accept three dimensional dynamic registration and utilize a

face-bow transfer.

CLASS-IV-A:

The condylar pathways are formed by registrations engraved by the

patient.

Eg: TMJ instruments designed by Kenneth Swanson in 1965.

CLASS –IV – B:

Condylar pathways are selectively angled and customized.

Eg. Gnathoscope designed by Charles Stuart in 1955, Niles Guichet in

1968 designed the Denar (D4A) fully adjustable articulator. The latest

instrument in Denar series is D5A which has the plastic condylar inserts. This

has provision for a both immediate and progressive side shift Bennett

adjustment.

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HANAU ARTICULATOR – H2:

Hanau articulator is a condylar or non-arcon type. It has a fixed

intercondylar distance of 110mm. The maxillary cast is mounted to the

articulator using a face-bow transfer. Both arbitrary and kinematic face-bows

can be used.

The articulator must have extendible condylar shaft to receive

kinematic face-bow during fixed prosthodontic procedures.

The horizontal condylar inclination is determined by means of

protrusive interocclusal records with height tracers. The amount of lateral

movement is calculated by Benett angel L = H/B + 12. The vertical condylar

posts are then rotated to the calculated Benett angulation.

The araticulator has a mechanical incisal guide table with a single

sagittal adjustment along with right and left frontal adjustments. These

adjustments are made to compensate for the amount of horizontal and vertical

overlap incorporated in the anterior arrangement of teeth.

The incisal guide pin is straight. Any change in vertical dimension will

alter the position of the incisal guidetable. This phenomenon is utilized to

adjust the horizontal and vertical overlap during protrusive record.

WHIPMIX ARTICULATOR:

It is an arcon articulator designed by Charles Stuart in 1955. The inter

condylar distance is adjustable in three positions.: Small (s) – 94mm, Medium

(M) –110mm and large (L) –124mm. By means of removable condylar

guidance spacers along the horizontal axis for the face –bow record, the

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earpiece and kinematic face bows are used. For accurate transfer of the true

hinge axis with kinematic face –bow the articulator has the hinge axis transfer

fixtures which have extendible condylar axis pins. The ear piece face-bow

utilizes the external auditory canal as posterior preference point. During the

face-bow transfer, the condylar part must be utilized depending upon whether

the patient condylar distance is S.M. OR L. The bridge of the nose is use as

the anterior reference point. The horizontal condylar inclination is determined

by means of either protrusive inter-occlusal record or lateral interocclusal

record. The Bennett angle is set with lateral interocclusal records. Optional

immediate side shift or immediate Bennett movement condylar guides are

available from 0.25mm to 1.00 mm.

The whip-max articulator is equipped either with a mechanical or a

plastic incisal guide table. Plastic guide table can be customized individually

with auto polymerizing resin. The mechanical guide table has a single sagittal

adjustment and right and left frontal adjustment.

The incisal guide pin is straight, of which one end is flat and is used

with mechanical incisal guide table and the other rounded end used to

customize the plastic table.

REVIEW OF LITERATURE:

According to Hisatoshi Tanaka 1,2, the primary purpose of an articulator

is to simulate mandibular movement and is also used as diagnostic and

treatment planning aid. The choice of articulator depends upon how well the

instrument is handled. The mechanism of an articulator must be precise, easy

to adjust and simple to understand.

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Wilson and Lang said that the evolution of an articulator closely

associates with the knowledge and understanding of the functional activity of

the chewing mechanism.

Closer the articulator simulates mandibular movements, more complex

they become in designing fully adjustable articulators simulate most accurately

but their usefulness is limited because of the complexity of recording and

adjusting.

Semi adjustable articulator can be used for individual static record. The

arcon type produces more constant condylar paths. This type of arrangement is

used during articulator construction. Semi-adjustable articulatoar guides only

the medial component of the balancing side, whereas, the fully adjustable can

guide bot balancing and working side.

Semi-adjustable articulators have either a fully or semi-adjustable

intercondylar distance mechanism. The latter type do not allow the change of

the patients vertical rotational centers, whereas , the former type allows the

change.

According to Neal D. Bellant 4, the semi-adjustable articulator guides

only the lateral component of the rotating condylar movement, whereas, all

component of mandibular movement are set to simulate in fully adjustable

articulator.

Accuracy of the simulation of the jaw movement controls the accuracy

of the fabricated prosthesis. Lack of accuracy results in parafunctional habits.

The intercondylar width in small and medium range is reproduced in

semi adjustable articulator. It is incapable of reproducing any variation in the

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timing of mediotrusion, but is capable of simple laterotrusion. When centric

and lateral positions are accurately transferred to the articulator, the paths

between these position is interpolated as a straight line.

In patients with a backward and upward component in laterotrusion, the

rotating condyle contracts posterior or superior wall of the condylar fossa

before it reaches its final position, but in patients with a forward or downward

component, the rotating condyle is anterior or inferior from the condylar fossa.

At some point, all articulators fall to represent the chewing mechanism.

Articulators have no inherent ability to do something for the operator. An

expert who knows the limitation of a simple instrument in producing

mandibular movements can achieve better results with it than some one using a

more complex instrument that he did not fully understand.

DISCUSSION:

Evolution of articulators through the years ha given an insight of the

researchers trying to develop a mechanical device that simulates the jaw

members and its movements.

The purpose of using an atriculator is to develop a prosthesis that will be

harmonious in the oral cavity. Various articulators have been developed and

are being improved upon as and when the functions of the jaws are understood

better.

Accordingly, in the present day, the availability of articulators range

from simple hinge type to fully adjustable articulators.

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Selection of articulators depends upon the clinical situation. In complete

denture prosthesis, semi-adjustable articulators suffice the requirements to

develop a good denture. Fully adjustable articulators is used for fixed

prosthesis.

It is difficult to manour fully the adjustable articulators in complete

denture patients because the clutches used to obtain the hinge axis and

condylar movements are more cumbersome to be used in edentulous patients

which in turn does not provide accurate records.

REFERENCES:

1. HISATOSHI TANAKA, et.al., A new semi-adjustable articulator part-1.

Concept behind the new articulation J.P.D., 1975. 33. 10.

2. HISATOSHI TANAKA , et.al., part-2, Adjustment of a new concept

articulator J.P.D., 1975, 33, 158.

3. WILSON AND LANGE, Practical crown and bridge prosthodontics.

4. NEAL D. DELLANTI, J.P.D., 1974, 29, 269.

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