Sample Chapter Conservative Dentistry Exam Preparatory Manual for Undergraduates, 1e by Gupta To...

1. Define cavity and cavity preparation. Enumerate the need for restorations and fundamental concepts of tooth preparation.

Cavity is defined as ‘a defect in enamel, dentine or cementum resulting from the pathological processes, mostly the dental caries’.

Cavity preparation/tooth preparation is defined as ‘mechanical alteration of defective, injured or diseased tooth to receive a restorative material that re-establishes a healthy state for the tooth, including aesthetic corrections where indicated and with normal form and function’.

–Sturdevant

Types of tooth preparation

1. Conventional preparation. It requires specifi c wall forms, depth and marginal forms owing to the properties of restorative material. It relates to amalgam, cast and direct fi lling gold.

2. Modifi ed preparation. Because of improved resistance and retention achieved by bonding and micromechanical retention, composites, GIC and other direct aesthetic materials require less specifi c preparation.

Need for restorations

Teeth require restorations so as to:Repair a tooth after destruction from a ● carious lesion.Replace or repair of restorations ● with critical defects, such as improper proximal contact, overhanging or defective open margins, or compromised aesthetics.To restore proper form and function. ●

For aesthetic reasons. ●

Fundamental concepts of tooth preparation

No weakened tooth structure should be left. ●

Th e fault, defect or caries should be removed. ●

Th e remaining tooth structure should be left as strong as possible. ●

Underlying tooth structure should be protected. ●

Th e restorative material should be retained in strong, aesthetic and functional form. ●

Q.

Fundamentals of Tooth Preparation

8

Chapter-08.indd 133Chapter-08.indd 133 12/11/2012 5:38:11 PM12/11/2012 5:38:11 PM

EXAM PREP MANUAL FOR UNDERGRADUATES: CONSERVATIVE DENTISTRY134

2. Write in brief the historical development of concepts of cavity preparation.

Cavity Preparation: Historical Development

GV Black concept

GV Black (1891) gave the concept of extension for prevention. His concept included: ●

Removal of all the infected and aff ected dentine. ❍

For better access and visibility, even healthy tooth structure can be removed. ❍

Extension of preparation ❍ in adjacent pits and fi ssures for prevention.Should have defi nite mechanical retention in the restoration. ❍

Th e advantage was self-cleansing area which prevents the reoccurrence of decay in the tooth ●

surface adjoining restoration.

Prime concept

Prime’s concept was based on the philosophy: Adapt the fi lling material to the tooth. ●

Achieve a proximal triangular form. ●

Achieve ‘independent surface retention’. ●

Extension for prevention is not necessary. ●

Current perspective:‘Extension for prevention’ is no longer a valid concept. ●

‘Prevention of extension’, or as Sigurjons states, ‘constriction with conviction’ are the opera- ●

tive phrases in modern cavity preparation.Increased knowledge of caries progression, prevention and remineralization of tooth struc- ●

ture, improved amalgam alloys and other restorative materials, systemic and topical fl uo-ridation, precision instrumentation, advanced diagnostic aids, better oral hygiene, have infl uenced changes in the design of cavity preparations.

Summitt and Osborne concept

Do not extend for prevention in class 1 preparations – only prepare in areas of diagnosed ●

caries.Keep preparations as narrow as caries allows. ●

Do not extend class 2 preparations into occlusal grooves, if occlusal surface is not involved ●

by caries at all.If occlusal extension is less than 1.2 mm wide, augment retention of proximal box with ●

retention locks on facial/lingual walls.

3. Enumerate the objectives of tooth preparation. Describe briefly factors affecting tooth preparation.

Objectives of Tooth Preparation

Removes all defects and provides necessary protection to the pulp. ●

Extension of the margins of restoration as conservatively as possible. ●

Cavity is formed such that under forces of mastication, the tooth or restoration, or both will ●

not fracture and restoration will not be displaced.Allows for aesthetic and functional placement of a restorative material. ●

Q.

Q.


FUNDAMENTALS OF TOOTH PREPARATION 135

Factors affecting Tooth Preparation

1. General factors 2. Tooth factors 3. Restorative material factors.

General factors

Diagnosis: A complete and thorough diagnosis is essential before any restorative procedure. ●

Need for the restoration may include caries, fractured teeth, aesthetic, or improved form ●

or function.Assessment of pulpal and periodontal status of the tooth. ●

Assessment of the occlusal relationships. ●

Patient’s concern for aesthetics. ●

Knowledge of the anatomy of each tooth and its related parts. ●

A gross picture, both internal and external of the individual tooth being operated on, must ●

be visualized.Th e direction of the enamel rods, the thickness of the enamel and dentine, the size and posi- ●

tion of the pulp and the relationship of the tooth to supporting tissue must all be known.Assessing whether it is deciduous or permanent tooth. ●

Type and location of tooth. ●

Type of anomaly, e.g. enamel hypoplasia. ●

Patient factors: Patient’s economic status ● .Age of the patient. ●

Elderly patients who have physical or medical complications may require special position- ●

ing for restorative treatment, as well as shorter, less stressful appointments.Patient’s concern for a ● esthetics. Aesthetic consideration infl uences the tooth preparation, selection of restorative material and extension of the preparation.Xerostomia. ●

Diet. ●

Assessment of the caries index of the patient. ●

General health. ●

Parafunctional habits. ●

Supplementary intake of fl uorides. ●

Tooth factors

To conserve the tooth structure. ●

To repair the damage from dental caries and preserve the vitality of the tooth. ●

Restorations should be as small as possible. ●

Lesser the tooth structure removed, lesser the chances for pulpal damage. ●

Some of the conservative tooth preparation features are: ●

1. Minimal extensions of the tooth preparations, especially faciolingually and pulpally.2. Supragingival margins.3. Rounded internal line angles.



Restorative material factors

Choice of restorative material affects the tooth preparation and is based upon the following:

Th e patient’s decision, economic status and aesthetic concern. ●

Extensiveness of the problem. ●

Type of restoration. ●

Moisture control. ●

Physical properties of restoration. ●

Operator variability. ●

4. Write in brief the terminologies used in tooth preparation.

Tooth Preparation Terminology

a. Depending on the number of walls involved: 1. Simple – if only one tooth surface is involved. 2. Compound – if two surfaces are involved. 3. Complex – if three or more surfaces are involved.

b. Abbreviated description of tooth preparation:

For example:Occlusal tooth preparation is an ‘O’ ●

Mesial and occlusion surfaces is an ‘MO’ ●

Mesial, occlusal, distal surface is an ‘MOD’. ●

c. Tooth preparation walls: ● Internal wall – a prepared surface that does not extent to the external tooth surface. ● Axial wall – an internal wall parallel with the long axis of the tooth.

Pulpal wall ● – an internal wall that is both perpendicular to the long axis of the tooth and the occlusal of the pulp.

● External wall – prepared surface that extends to the external tooth surfaces, e.g. facial, mesial, distal, lingual and gingival.

● Floor or seat – prepared wall that is relatively fl at and perpendicular to the occlusal forces which are directed along the long axis of the tooth, e.g. pulpal and gingival walls. Enamel wall ● – that portion of the prepared external wall which is composed of enamel.Dentinal wall ● – that portion of the prepared external wall which is composed of dentine.

d. Tooth preparation angles: Th e junction of 2 or more prepared surfaces is called an angle. ●

● Line angle – junction of two planal surfaces of diff erent orientation along a line. It can be: 1. Internal line angle – line angle whose apex points into the tooth.2. External line angle – whose apex points away from the tooth.

● Point angle – the junction of three planal surfaces of diff erent orientation, e.g. class I cavity has 8 line angles and 4 point angles; class II cavity has 11 line angles and 6 point angles.

● Cavosurface angle – refers to the angle of the tooth structure formed by the junction of a prepared wall and the external tooth surface.

Q.



● Cavosurface margin – actual junction of the prepared wall and the external tooth surface. Combination of terms – ● two or more surfaces can be combined to form a term, e.g. mesio-occlusal or MO preparation.

e. Junctions: ● Dentinoenamel junction (DEJ) – it is the junction of the enamel and dentine. ● Cementoenamel junction (CEJ) – junction of the cementum and enamel. It is also called

‘ cervical line’.

f. Intracoronal tooth preparation: It is usually ‘box-like’ having both internal and external preparation walls. It refers to a cavity that is prepared in the interior of the tooth.

Extracoronal tooth preparation – it is usually ‘stump-like’ and involves the external surface of the tooth.

g. Anatomic tooth crown: Portion of the tooth covered by the enamel. Clinical tooth crown – portion of the tooth exposed to the oral cavity.

5. Write a short note on enamel margin strength.

Enamel Margin Strength

1. Strongest enamel margin. This margin is formed by full-length of enamel rods whose inner ends should rest on sound dentine. These enamel rods should be buttressed on the preparation side by progressively shorter rods where outer ends are cut off but their inner ends are on sound dentine. Since enamel rods are usually perpendicular to the enamel surface, the strongest enamel margin results in a cavosurface angle greater than 90º.

2. An enamel margin which is composed of full-length rods that rest on sound dentine but are not buttressed tooth-side by shorter rods on sound dentine are termed as strong (but not the strongest). Generally, this margin results in a 90º cavosurface angle.

3. An enamel margin composed of rods that do not run uninterrupted from the surface to sound dentine are called unsupported, and this marginal enamel has a tendency to split or fracture off, resulting in a V-shaped ditch along the margin of a restoration. This weakened enamel margin either has a cavosurface angle less than 90º or has no dentinal support.

Features

In order to prevent fracture of the tooth structure at the margin, all enamel wall should have ●

full length rods supported by sound dentine. Th e cavity should be prepared parallel to the direction of the enamel walls. To remove unsup- ●

ported tooth structure, a gingival bevel of 15º–20º is given in class II amalgam restorations. In cast restorations, a short bevel is given while in gold foil, an ultrashort bevel is given.Th e preparation outline and wall should have smooth curves and the junction of the enamel ●

walls and the respective margins should be slightly rounded. Design of the cavosurface angle varies according to the type of restorative material employed. ●

For amalgam, a 90º cavosurface angle or butt joint is recommended to compensate for the low edge strength of the material. For composite and cast metal restorations, bevels are indicated to allow better marginal sealing and improved bonding. For cast restorations, smooth walls are required; while for amalgam, direct fi lling gold and ●

composite slight roughness is desirable.

Q.



6. Write a short note on classification of the tooth preparation.

Classifi cation of Tooth Preparation

GV Black (1947) classified tooth preparation based on anatomic areas involved and the associated type of treatment. He classified tooth preparation into five original classes. Later class VI was added to the original classification by Simon.

Class I (Figs 8.1–8.3). All pit and fi ssure restorations are included in this class. Class I restora-tions can be divided into three groups: 1. Restoration on occlusal surface of premolars and molars. 2. Restoration on occlusal two-thirds of the facial and lingual surfaces of molars. 3. Restoration on lingual surface of maxillary incisors.

* Class I cavity preparation has eight (8) line angles and four (4) point angles.

Class II (Figs 8.4–8.6). All restorations on proximal surface of posterior teeth. a. MO – Mesio-occlusal preparation b. DO – Disto-occlusal preparation c. MOD – Mesio-occlusal distal preparation.

* Class II cavity preparation has eleven (11) line angles and six (6) point angles.

Q.

f

m

lP

d

f � Faciald � Distall � Lingualm � Mesialp � Pulpal

Fig. 8.1. Typical class I cavity preparation on maxillary premolar.

Fig. 8.2. Schematic representation of class I cavity preparation walls.

dfpfp

mfp

mfmp

mlplpdlp

dldp

df

ml

Line angles (8):fp � Faciopulpaldf � Distofacialdp � Distopulpaldl � Distolinguallp � Linguopulpalml � Mesiolingualmp � Mesiopulpalmf � Mesiofacial

Point angles (4):dfp � Distofaciopulpaldlp � Distolinguopulpalmlp � Mesiolinguopulpalmfp � Mesiofaciopulpal

Fig. 8.3. Schematic representation of class I cavity preparation line angles and point angles.



Class III (Figs 8.7–8.9). Restoration on the proximal surfaces of anterior teeth that do not involve the incisal edge.

* Class III cavity preparation has six (6) line angles and three (3) point angles.

Fig. 8.4. Typical class II mesio-occlusal cavity preparation on maxillary premolar.

f

p

f

g

d

l

l

a

f � Facial wall of proximal and occlusal portionsg � Gingivall � Lingual wall of proximal and occlusal portionsd � Distalp � Pulpala � Axial

Fig. 8.5. Schematic representation of class II cavity preparation walls.

df

dfp

fp

afp

af

afg

fg

dl

dlp

lpapalp

al

alg

lgag

dp Line angles: (11)df � Distofacialfp � Faciopulpalaf � Axiofacialfg � Faciogingivalag � Axiogingivallg � Linguogingivalal � Axiolingualap � Axiopulpallp � Linguopulpaldl � Distolingualdp � Distopulpal

Point angles: (6)dfp � Distofaciopulpalafp � Axiofaciopulpalafg � Axiofaciogingivalalg � Axiolingualgingivalalp � Axiolinguopulpaldlp � Distolinguopulpal

Fig. 8.6. Schematic representation of class II cavity preparation line angles and point angles.



l

g

fa f � Facial

a � Axialg � Gingivall � Lingual

Fig. 8.7. Class III cavity preparation on maxillary central incisor.

Fig. 8.8. Schematic representation of class III cavity preparation walls.

ial

alg

lg

ai

affg

afg

ag

Line angles: (6)al � Axiolinguallg � Linguogingivalag � Axiogingivalfg � Faciogingivalaf � Axiofaciali � Incisal

Point angles: (3)alg � Axiolinguogingivalafg � Axiofaciogingivalai � Axioincisal

Fig. 8.9. Schematic representation of class III cavity preparation line angles and point angles.

l

m

p

lg

ffa

f � Facial of proximal and incisal portionsg � Gingivall � Lingual of proximal and incisal portionsa � Axialm � Mesial

Fig. 8.10. Class IV cavity prepa-ration for inlay on maxillary

canine.

Fig. 8.11. Schematic representation of class IV cavity preparation walls.

Class IV (Figs 8.10–8.12). Restoration on the proximal surfaces of anterior teeth that do involve the incisal edge.

* Class IV cavity preparation has eleven (11) line angles and six (6) point angles.



mfmfp

fp

afp

afg

fg

mp

mlmlplpapalpalalglgag

Line angles: (11)mf � Mesiofacialfp � Faciopulpalaf � Axiofacialfg � Faciogingivalag � Axiogingivallg � Linguogingivalal � Axiolingualap � Axiopulpallp � Linguopulpalml � Mesiolingualmp � Mesiopulpal

Point angles: (6)mfp � Mesiofaciopulpalafp � Axiofaciopulpalafg � Axiofaciogingivalalg � Axiolinguogingivalalp � Axiolinguopulpalmlp � Mesiolinguopulpal

Fig. 8.12. Schematic representation of class IV cavity preparation line angles and point angles.

i

m

a

d

g

m � Mesialg � Gingivald � Distali � Incisala � Axial

Fig. 8.13. Class V cavity preparation. Fig. 8.14. Schematic representation of class V cavity walls.

Line angles: (8)mi � Mesioincisalam � Axiomesialmg � Mesiogingivalag � Axiogingivaldg � Distogingivalad � Axiodistaldi � Distoincisalai � Axioincisal

Point angles: (4)ami � Axiomesioincisalamg � Axiomesiogingivaladg � Axiodistogingivaladi � Axiodistoincisal

ami

miammg

amg

aiadidiaddgadg

ag

Fig. 8.15. Schematic representation of class V cavity preparation line angles and point angles.



Class V (Figs 8.13–8.15). Restoration on the gingival third of the facial or lingual surfaces of all teeth (except pit and fi ssure lesion).

* Class V cavity preparation has eight (8) line angles and four (4) point angles.

Class VI. Restoration on the incisal edge of anterior teeth or the occlusal cusp height of posterior teeth.

* Class VI cavity preparation has eight (8) line angles and four (4) part angles.

7. Enumerate the stages and steps of tooth preparation.

Stages in Tooth Preparation

Stage 1 – initial tooth preparation stageStep 1 ● – outline form and initial depthStep 2 ● – primary resistance formStep 3 ● – primary retention formStep 4 ● – convenience form.

Stage 2 – fi nal tooth preparation stageStep 5 ● – removal of any remaining infected dentine or old restorative material, if indicatedStep 6 ● – pulp protection, if indicatedStep 7 ● – secondary resistance and retention formStep 8 ● – procedures for fi nishing external wallsStep 9 ● – fi nal procedure – cleaning, inspecting and sealing.

8. Define initial tooth preparation and outline form. Discuss the factors governing the outline form of any cavity.

Defi nitions

Initial tooth preparation. ‘Initial tooth preparation is the extension and initial design of the external walls of the preparation at a specified, limited depth so as to provide access to the caries or defect, reach sound, tooth structure (except for later removal of infected dentine on the pulpal or axial walls), resist fracture of the tooth or restorative material from masticatory forces principally directed with the long axis of the tooth and retain the restorative material in the tooth’.

–Sturdevant

Outline form. It is defined as, ‘placing the preparation margins in the position they will occupy in final restoration except for finishing enamel walls and margins and preparing an initial depth of 0.2–0.8 mm pulpally of DEJ or normal root surface position’.

–Sturdevant

Principles of Establishing Outline Form

All weakened enamel should be removed. ●

All faults should be incorporated. ●

All margins should be placed in a location that aff ords good fi nishing of the margins of the ●

restoration.

Q.

Q.



Features for establishing proper outline form and initial depth

1. Preserving cuspal strength. 2. Preserving marginal ridge strength. 3. Minimizing faciolingual extension. 4. Enameloplasty. 5. Connecting two close faults (less than 0.5 mm apart). 6. Restricting the depth of preparation to a maximum of 0.2 mm into dentine for pit and

fissure caries and 0.2–0.8 mm for axial wall of smooth surface caries.

Factors determining the outline form

Extent of the carious lesion, defect or faulty old restoration. ●

Aesthetic and occlusal requirements. ●

Occlusal relationship which may require alteration in the outline form. ●

Cavosurface marginal confi guration which varies with type of restorative material used. ●

Caries index of the patient. ●

Type of restorative material. ●

Adjacent tooth contours. ●

Relationship to soft tissues. ●

The outline form includes the external outline form and internal outline form. ● External outline form is the area of the tooth surface or the enamel margin to be included

in the fi nished cavity. ● Internal outline form includes the inner dimensions and details of the prepared cavity.

Th e internal outline form should be prepared carefully in young people to avoid the pulp exposure as the pulp chambers are high.

Outline form and initial depth for pit and fi ssure lesion

It is controlled by three factors: 1. Extent of enamel involved by the carious process. 2. The extensions made along the fissures to achieve sound and smooth margins. 3. The limited bur depth related to the tooth’s original surface during extension of the

preparation to sound external walls that have a pulpal depth of approximately 1.5–2 mm of which maximum depth of 0.2 mm is in the dentine.

Rules for establishing outline form for pit and fi ssure tooth preparation: 1. Preparation margins should extent until sound tooth structure is obtained and no

unsupported or weakened enamel exists. 2. Termination of margins on extreme eminences such as cusp heights or ridge crest should

be avoided. 3. If extension from the primary groove includes more than one-half of the cuspal incline,

then cusp capping should be considered. 4. Extend the preparation to include all the fissures that cannot be eliminated by

enameloplasty. 5. Restrict the pulpal depth of the preparation to maximum 0.2 mm into the dentine. 6. If two pit and fissure preparations are 0.5 mm apart, then they should be joined to

eliminate a weak enamel wall between them. 7. Outline form should be extended to provide sufficient access for proper tooth preparation,

placement of restorations and finishing procedures.



Outline form and initial depth of smooth surface lesions

Smooth surface lesion occurs in two different locations: a. Proximal surfaces b. Gingival portions of the facial and lingual surfaces.

It is controlled by 8 factors: 1. Position and crest of healthy gingival. 2. Extent of caries on the proximal lesion. 3. Dimension of the contact area. 4. Oral hygiene of the patient. 5. Masticatory forces falling on restoration. 6. Aesthetic concerns of patient. 7. Margins in self-cleansing area. 8. Age and caries index of the patient.

Certain conditions requiring reduced extensions are: Root proximity. ●

Aesthetic requirement. ●

Proximal cavities and contours. ●

Use of modifi ed cavity designs. ●

Certain conditions requiring increased extensions are:Increased age of patient. ●

Tooth contour adjustments. ●

Mentally and physically handicapped patient. ●

For additional resistance and retention form. ●

Restoration of tooth as partial denture abutment. ●

Rules for establishing outline form for smooth surface lesions (proximal surface) – class II, III, and IV: 1. Preparation margins should be extended until sound tooth structure is obtained. 2. The margins should not terminate on extreme eminences such as cusp heights, ridge

crests. 3. Extend the margins to permit sufficient access to the manipulative procedures. 4. Axial wall pulpal depth to a maximum of 0.2–0.8 mm into the dentine. 5. Provide minimum clearance of 0.5 mm between the gingival margin and adjacent tooth. 6. Place the facial and lingual margins in proximal preparations into respective embrasures

to provide specified clearance between margins and adjacent tooth. 7. Axial wall should follow the contour of the external tooth surface or the curvature of the

dentinoenamel junction buccolingually and occlusogingivally. 8. In class III preparations, it is acceptable to position the incisal margin in the area of

contact, especially if aesthetic material is used or the incisal embrasure is not large enough to allow extension incisal of contact.

Outline form for class V lesion

It is controlled by these factors: 1. Health and position of the gingiva. 2. Extent of carious lesion. 3. Buccal and lingual surface contours.



4. Oral hygiene of the patient. 5. Forces of mastication falling on restoration. 6. Age of the patient.

Rules for establishing outline form for class V lesion: 1. Extend the preparation mesially, distally, gingivally and occlusally till the sound tooth

structure is reached. 2. The axial wall pulpal depth at the gingival wall without an enamel portion should be

0.8 mm. 3. The axial wall pulpal depth at the occlusal wall should be more, i.e. 0.5 mm extension

into dentine (rest being enamel).

9. Write a short note on enameloplasty.

Enameloplasty refers to eliminating the developmental fault by removing it with the side of a flame-shaped diamond stone, leaving a saucer- or round-shaped smooth surface, thereby conserving tooth structure.

It is done on an area of imperfect coalescence of enamel. ●

Th e surface left by enameloplasty should meet the tooth preparation wall, preferably with ●

a cavosurface angle no greater than approximately 100º. Th is would produce a distinct margin for amalgam of no less than 80º. No more than one-third of the enamel thickness should be removed. ●

Th e enameloplasty does not extend the outline form. ●

It confi nes the preparation at one surface. ●

Th e recontoured area is self-cleansing, fi nishable and allows conservative placement of the ●

margins. Th e restoration is not done in the recontoured area. ●

Enameloplasty is indicated in supplemental grooves and shallow fi ssures that approach or ●

cross the facial or lingual ridge.

10. Write a short note on primary resistance form.

Primary Resistance Form

Defi nition

‘Primary resistance form may be defined as that shape and placement of the preparation walls that best enable both the restoration and the tooth to withstand, without fracture, masticatory forces delivered principally in the long axis of the tooth’.

–Sturdevant

Fundamental principles of primary resistance form

1. Box shape cavity should have flat floor (Fig. 8.16). 2. Restricted extension of the external walls. 3. Inclusion of weakened tooth structure. 4. Preservation of cusps and marginal ridges. 5. Rounding of internal line angles to reduce stress concentration and fracture of tooth. 6. Rounding of external line angle, e.g. axiopulpal to resist the fracture of the restoration. 7. To provide enough thickness of restorative material to prevent its fracture under the load.

Q.

Q.



8. At least three, i.e. tripodal seats on sound dentine peripheral to excavations of the infected dentine.

9. To cap the weakened cusp to resist from obliquely directed forces. 10. To bond the material to the tooth structure, when appropriate.

Flat pulpal floor preventsrestoration movement

Rounded pulpal floorproduces wedging force

(a) (b)

Fig. 8.16. Resistance form.

Factors affecting the resistance form

1. Assessment of the occlusal contact on the restoration and remaining tooth structure. 2. Amount of remaining tooth structure: In class IV restorations, the cavity is kept narrow

faciolingually to obtain resistance form. 3. All weakened, friable tooth structure should be removed. 4. Occlusal stresses on the tooth: Greater the occlusal force, more the potential of fracture. 5. Enhancement of resistance form by bonding of the restoration to the remaining tooth. 6. Type of restoration: The minimum thickness of restorative material required for restoration

with amalgam is 1.5 mm, for cast restoration is 1 mm, for porcelain is 2 mm to resist fracture. The glass ionomer restorations and composite restorations are more dependent on the occlusal wear of the restoration. Restorative material Minimal thickness required

Amalgam 1.5 mm

Cast gold 1–2.0 mm

Porcelain 2.0 mm

Composite 1–2.0 mm

11. Write a short note on primary retention form.

Primary Retention Form

Defi nition

‘Primary retention form is that shape or form of the conventional preparation that resists displacement or removal of the restoration by tipping or lifting forces’.

–Sturdevant

Q.



Principles of retention form – dependent on the type of restorative material used

For amalgam:In some class I and all class II, the amalgam is retained by developing the external tooth ●

walls that converge occlusally.Occlusal convergence of the preparation walls. ●

Occlusal dovetail prevents tipping of the restoration by occlusal forces. ●

Th e cavosurface angle where the proximal facial and the lingual walls meet the marginal ●

ridge is desirable of 90º because of the occlusal convergence of the preparation.Slight undercuts given in the dentine. ●

Occlusal convergence of the proximal portion helps in conserving the marginal ridges. ●

Bonded amalgam restoration retains by micromechanical retention by use of adhesive ●

system.

For composite:Acid etching and bonding provide micromechanical retention. ●

Enamel bevel also enhances retention. ●

For cast metals:Close parallelism of the opposing walls with small angle of divergence (2 ● –5°) from the line of draw to enhance retention form.

● Occlusal dovetail. ● Reverse bevel at the gingival wall.

For direct filling gold:Elastic compression of dentine during condensation. ●

12. Write a short note on convenience form. Add a note on pulp protection.

Convenience Form

Defi nition

‘Convenience form is that shape or form of the preparation that provides for adequate observation, accessibility, and ease of operation in preparing and restoring the tooth’.

–Sturdevant

Features

Suffi cient extension of the cavity for adequate vision and accessibility. ●

In class II cavity, occlusal access is made to reach proximal caries. ●

Occlusal divergence of vertical walls in class II cast gold restorations. ●

In class III cavities, lingual access is made to preserve the facial tooth structure. ●

Widening of the cavity for direct fi lling gold to facilitate the movement of condenser at the ●

starting point.Proximal clearance of contact area. ●

Pulp protection: Refer Chapter 19.

13. Write a short note on secondary resistance and retention forms.

Secondary resistance and retention forms are of two types:

Q.

Q.



1. Mechanical preparation feature. 2. Cavity wall conditioning features, i.e. treatment of the preparation wall with etching,

priming and adhesive materials.

Mechanical preparation features

These are mechanical alteration in the tooth preparation to improve retention form by additional removal of the tooth structure. These include the following: a. Retention locks, grooves and coves b. Grooves extension c. Skirts d. Bevelled enamel margins e. Pins, slots, steps and amalgapins.

a. Retention locks, grooves and coves: Vertically oriented retention locks and grooves are used to provide additional retention for ●

the proximal portion of some tooth preparation. Locks ● are used for amalgam restorations and grooves are for the cast metal restorations. Horizontal-oriented retention grooves are prepared in most class III and V preparation for ●

amalgam and root surface preparation for the composite restoration. ● Retention coves are placed in undercuts for incisal retention of class III amalgams and some

class V amalgam restorations.

b. Grooves extension: Added retention is provided by the extension of preparation on to the facial or lingual ●

surface to include a facial or lingual groove. Th is results in almost parallel walls for retention. ●

Th is is usually done for cast metal restorations. ●

c. Skirts: Th ese are provided for cast gold restorations, when the preparation extends around some, if ●

not all of the line angles of the tooth. Skirts provide additional opposed vertical walls for retention. ●

Placement of skirts also improves resistance form. ●

d. Bevelled enamel margins:Cast gold/metal and some composite restorations include bevelled enamel margins. ●

In case of the composite restoration, bevel increases the surface area for etching and thus ●

greatly improves the bonding between the restoration and the tooth. Bevel for cast restoration may improve retention form, when there are opposing bevels but ●

primarily they aff ord a good marginal junction.

e. Pins, slots, steps, amalgapins: Pins are primarily used with amalgam restoration, when there is a need for improving reten- ●

tion and resistance.Pins and slots greatly increase retention and resistance form. ●

Amalgapins and properly positioned steps also improve retention form but less than pins ●

and slots.

Conditioning procedures

These include the following:



1. Enamel wall conditioning: Enamel walls are etched for bonded restorations that use porcelain, composite and ●

amalgam.Th is procedure consists of microscopically roughening the enamel surface to which the ●

restoration is mechanically bonded.Th is improves the retention and the resistance form. ●

2. Dentine conditioning:Th e dentine surface may require etching and priming before bonding porcelain, composite ●

or amalgam.For most composite restorations, dentine bonding agent is used. ●

Retention of the indirect restoration is improved by the type of luting agent used. ●

14. Write short notes on the finishing, cleaning and conditioning procedures.

Finishing the External Walls of the Preparation

Defi nition

‘Finishing the cavity walls is the further development, when indicated, of a specific cavosurface design and degree of smoothness or roughness that produces the maximum effectiveness of the restorative material being used.’

–Sturdevant

Objectives

To create the best ● marginal seal possible between the restorative material and the tooth structure.To aff ord a smooth marginal junction. ●

To provide maximum strength of both the tooth and the restorative material at and near ●

the margin.

Factors to be considered during finishing of the enamel walls and margins: 1. Direction of enamel rods. 2. Support of enamel rods both at the DEJ and at the preparation side. 3. Choice of the restorative material. 4. Location of the margin. 5. Degree of the smoothness desired.

Features of fi nishing external walls

a. Design of the cavosurface angle. b. Degree of smoothness or roughness of the wall.

a. Design of the cavosurface angle:Depends on the type of restorative material used. ●

Tooth preparation cavosurface angle of 90° produces maximum strength for the amalgam. ●

No bevels are placed at the cavosurface for the amalgam restoration ● except on the gingival fl oor of the class II preparation in enamel.Bevelling of the external walls are used for intracoronal cast gold/metal and composite ●

restoration.Bevelling of the cavosurface is contraindicated in the porcelain restorations. ●

Q.



Functions of bevel:Produces stronger enamel margins. ●

Allows marginal seal in slightly undersized castings. ●

Provides marginal metal that is easily burnished and adapted. ●

Assists in adaptation of the gingival margins of the castings. ●

Advantages of bevelling the composite restorations:Adjacent minor defects are included. ●

Aesthetic quality is improved. ●

Marginal seal is increased. ●

b. Degree of smoothness or roughness of the wall:When high-speed cutting procedure is used for fi nishing ● plain cut, fi ssure burs should be used.Hand instruments such as enamel hatchet, margin trimmers are useful in planing enamel ●

walls, cleaving enamel and establishing enamel bevels.

Cleaning, Inspecting and Sealing Preparation

Includes checking for and removing all chips and loose debris that have been accumulated, ●

drying the cavity and making a fi nal complete inspection of preparation for any remaining infected dentine and unsound enamel margins.Removal of the debris is done by warm water. ●

Th e debris can be loosened by explorer or a small cotton pellet. ●

Preparation is dried free of visible moisture. ●

Th e tooth should not be dehydrated during the process of drying by overuse of air or appli- ●

cation of alcohol. Very mild disinfectant can be used after the tooth preparation. ●

Th e conditioning of the cavity is done in glass ionomer restorations by using mild acids or ●

etchants for 8–10 seconds.Th us making the surface more conducive for bonding with glass ionomer by reorientation ●

of surface calcium. For composite restorations, the surface is etched and smear layer is modifi ed for good bonding.


Sample Chapter Conservative Dentistry Exam Preparatory Manual for Undergraduates, 1e by Gupta To...

Documents

Transcript of Sample Chapter Conservative Dentistry Exam Preparatory Manual for Undergraduates, 1e by Gupta To...