Principles of cavity preparation by Dr .rupali

PRINCIPLES OF CAVITY PREPARATION

Presented By,Rupali Balpande

Guided By,Dr.Sarvesha BhondaveDr.Vishal Mahajan

CONTENTINTRODUCTION CAVITY PREPARATION DEFINITIONHISTORYOBJECTIVES OF CAVITY PREPARATIONFACTORS AFFECTING CAVITY

PREPARATIONCLASSIFICATION STAGES OF CAVITY PREPARATION

Introduction• Dr. G.V. Black

Chicago, Illinois1836-1915

• "The Grand Old Man of Dentistry" • The basic principles governing the design

of cavity and steps in their preparation was first suggested by American Dentist and teacher Dr.G.V.Black in the first decade of last century.

Definition of Cavity preparation

The mechanical alteration of a defective, injured, or diseased tooth in order to best receive a restorative material which will re-establish a healthy state for the tooth including esthetic corrections where indicated, along with normal form and function.

HISTORY

Archaeological evidence of dental treatment

from 5000 BC1800 early drills by hand1955-Page Chyles handpiece-1st driven angle handpiece9 th century –cavity prepared for inlay19 th century Hamelton Jameson -1st emphasized the

organized cavity preparation.Extension For Prevention- Marshall Ebb & G.V. Black1930-G.V.Black-systemic approach to cavity preparationSimon –sixth classification1998 G.J.Mount classification

OBECTIVES OF TOOTH PREPARATION

• Remove all defects and provide

necessary protection to the pulp.

• Extend the restoration as conservatively as possible .

• Tooth prep such that under mastication both the tooth and restoration will not fracture or displace.

• Allow the functional and esthetic placement of a restorative material.

Factors affecting tooth Preparation

GENERAL

FACTORSDiagnosis Prevention InterceptionPreservationRestoration

PATIENTS

FACTOREconomic statusAgeChoice of Material

Classification G.V. Black Classification

Modification of G.V.Black

Classification

Graham J Mount

V.K. Sikri

G.V.Black ClassificationFirst ClassificationUniversally AcceptedBased on type of treatment and area

involvedControlled by no. of factorsI.To gain access & visibility

II.Removal of affected dentin from floor

III.Room for restorative material

IV.Extension for prevention

V.Retentive designs

VI.Cavosurface margins self cleaning areas

G.J.Mount classification-design to simplify identification of lesions

According to site lesion1.Pits &fissure

2.Contact area

3.Cervical

According to size of lesion1.Minimum

2.Moderate

3.Enlarged

4.Extensive

Sikri classification-classify same as G.V. Black

and then gave division in each class

TOOTH PREPARATION TERMINOLOGY :

• Simple tooth preparation -Only one tooth surface is involved.

• Compound tooth preparation – Only two tooth surface is involved.

• Complex tooth preparation – Involves three or more surfaces.

Terminology in Cavity Preparation

Definition – Cavity-Cavity is defined as a defect in enamel or dentin resulting from pathologic process of dental caries(breach in the continuity of the surface integrity of tooth). The term cavity was used to describe a carious lesion in a tooth that has progressed to the point that part of tooth structure had been destroyed.

Tooth preparation wallsINTERNAL WALL-An internal is prepared surface that does not extend to external tooth surface.

AXIAL WALL – An axial wall is an internal wall parallel with the long axis of the tooth.

PULPAL WALL- A pulpal wall is an internal wall that is perpendicular to the long axis tooth and occlusal of pulp.

External wall – An external wall is prepared surface that extend to the external tooth surface

Floor / seat-A floor is a prepared wall that is reasonably flat and perpendicular to the occlusal forces that are directed occlusogingivally.

Enamel wall –Enamel wall is that portion of a prepared external wall consisting of enamel.

Dentinal wall- The dentinal wall is that portion of a prepared external wall consisting of dentin ,in which mechanical features can be located.

CAVITY PREPARATION ANGLES : Line angle : It is the junction of two planar surfaces of

different orientation along a line. internal line

angle and an external line angle. Internal line angle : Is a line angle whose apex points into

the tooth

e.g. FP. External line angle : Is a line angle whose apex points away

from the tooth e.g. ap. Point angles : A point angle is junction of three planal

surfaces of different orientation.

Cavo surface angle :

The cavo surface angle is the angle of the tooth structure formed by the junction of a prepared cavity wall and the external surface of the tooth.

Line angles & point angles Cavo-surface angle

Classification of cavityClassification of cavity

Class I Class II Class III Class IV Class V Class VI

— G. V. Black

CLASS I CAVITY

1) Pits & fissures2) Occlusal surface of premolars & molars3) Occlusal 2/3 rd of buccal & lingual surface4) Lingual surface of maxillary incisors

CLASS II CAVITY1) Restoration on Proximal surface of posterior teeth

CLASS III CAVITY1)Restoration on the proximal surface of the anterior teeth that do not involve incisal edge.

CLASS IV CAVITY1)Restoration on the proximal surface of anterior teeth that do involve the incisal edge .

CLASS V CAVITY1) Restoration on the gingival third of the facial / lingual surfaces of all teeth.

CLASS VI CAVITY

1) Restoration on incisal edge of anterior teeth and occlusal cusp height of posterior teeth.

2) It is given by Simon.

Stages of Cavity Preparation INITIAL STEPS OF CAVITY PREPARATION

FINAL STEPS OF PREPARATION

1. Outline Form and Initial Depth

Definition: placing the cavity margins in the positions they will occupy in the final preparation except for the finishing enamel walls and margins;

preparing an initial depth of 0.2~0.8 mm pulpally of the dentinoenamel junction.

Principles :1.All friable and weakened enamel should be removed.2.All fault should be included3.All margin should be placed in a position to afford good finishing of margins of restoration.

PROCEDURE

Features:1.Preserving cuspal strength.2.Preserving marginal ridge.3.Minimizing facio-lingual extension.4.Using enameloplasty5.Connectiong two close faults of the tooth which are < 0.5 mm apart

6.Restricting depth of penetration into dentin

for pits and fissure-0.2 for smooth surface-0.2 to 0.8

1.Preserving cuspal strength-avoiding termination of the margin on extreme eminence, such as cusp height-if extension of primary groove includes half / > of cusp incline, then CUSP

CAPPING consider.

2. Preserving marginal ridge strength

• Remaining Marginal ridge should be greater than 1.6 mm for premolar & 2mm for molar

• If Remaining Marginal ridge

will be less than 1.6 mm there there may be the chances of

fracture due to undermining

the ridge.

Direction of mesial & distal walls• When >1.6 mm

thickness width is remained at mesial /distal marginal ridge , then mesial / distal wall should be parallel.

• When less than/= 1.6 mm thickness width is remained at mesial /distal marginal ridge , then mesial / distal wall should be divergent.

3. Minimizing facio –lingual Extension

- Minimizing facio –lingual Extension ,which

prevents the weakening of cusp.

- For conservative class I CAVITY

facio-lingual width should be 1 to 1.5 mm

4. Depth of preparation Restricting depth of penetration into dentin

for pits and fissure-0.2

for smooth surface-0.2 to 0.8Because,

1.To avoid the seating

of the restoration on

the very sensitive DEJ.

2.To give the bulk of

restoration.

3.To take advantages of

dentin elasticity during

insertion and function.

5. Enameloplasty• This is the procedure of reshaping the enamel surface by

making it rounded / Saucered ,the area becomes cleansable and finishable.

• It is indicated when remaining fissure is not greater than 1/3 rd of enamel thickness.

Outline form for class I • The outline form varies from one tooth to another .• Premolars-• Upper premolars have “ Dumb- bell “ shape with

their ends triangular.• In lower premolar –are confined to pit only

but if they involve entire occlusal surface ,then they resemble like upper premolar.

• In tricuspid lower premolar it will assume Y-shape

Class I upper premolar

Class I lower premolar

Class I & II Outline form for MOLARS

• Preparation in lower molars have an elongated shape mesio-distally with three lateral extensions.

• In upper molars if cavity involves all the occlusal surfaces ,the preparation elongated mesio-distally .

• If the oblique ridge is not involved the mesial preparation will assume kidney shape & distal will appear as heart shape .

• In class II the shape of proximal box is Inverted Truncated Cone.

Mandibular Maxillary

Class outline formⅠOcclusal view Proximalview

Class II outline form

Position of Gingival floor

• In class II cavity preparation ,gingival margin should be extended apically of proximal contact to provide a minimum of 0.5 mm clearence between the gingival margin and djacent tooth.

Position of Embrassure wallIsthmus –By G.V.Black- Advocate that class II cavity

preparation with isthmus width

equal to 1/3rd of intercuspal distance.

By Vale & Brooner- It should be 1/4th of intercuspal distance.

The axio-pulpal line angle should be beveled to reduce the concentration of stresses and provide grater bulk of material in the isthmus area, which is liable to fracture.

Final location for the facial and lingual Walls of proximal box relative to the contact area

REVERSE CURVE –When viewed from occlusal outline form of class II cavity particularly in max . teeth the proximal contact lies towards the buccal surface whereas the groove line occurs in the central portion of th occlusal table. This disparity necessitates

occlusal outline with a REVERSE CURVE.Advantages1.It preserve the triangular ridge of cusp2.Facilitates formation of 90°angle between proximal wall & the tangent of proximal surface.

Initial cavity preparation stage

Step 1 Outline form and initial depth

Step 2 Primary resistance form

Step 3 Primary retention form

Step 4 Convenience form

2. 2. Primary Resistance Form Primary Resistance Form

Definition: It is defined as that shape and placement of

the cavity walls that best enable both the restoration and the tooth to withstand, without fracture, when masticatory forces delivered principally in the long axis of the tooth.

Primary Resistance Form Primary Resistance Form

Principles: To utilize the box shape with a relatively flat floor to resist occlusal loading by virtue of being at right angles to mastication force;

To restrict the extension of the external walls (keep as small as possible) to allow strong cusp and ridge areas to remain with sufficient dentin support;


Principles:To have a slight rounding of internal line angles to reduce stress concentration in tooth structure;

To provide enough thickness of restorative material to prevent its fracture under load.


Feature: Box shape

Relatively flat floors

Inclusion of weakened tooth structure

Preservation of cusps and marginal ridges

Rounded internal line angles

Adequate thickness of restorative materials

Reduction of cusps for capping if indicated

Flat pulpal floor prevents rocking of the restoration which produce wedging forces

Pulpal wall is flat in all cases except in lower 1st premolar ,where the lingual cusp is very small & buccal cusp is pronounced with very large pulp horn. So in this case we have to make flat pulpal floor which is parallel to imaginary line joining the tips of the and lingual cusp.

Exception

Rounding of line angles prevents stress concentration & provide resistance form

&Shows strongrst enamel margin by full length of enamel rods

Facio-lingual width should be not more than ¼ th the intercuspal distance . As minimum tooth structure is removed, it increases the resistance of tooth.

¼ th intercuspal distance

The type of restorative material also dictates resistance form need

Silver amalgam needs thickness -1.5 mm

Cast metal needs thickness -1to2mm

Porcelain needs thickness - 2 mm

3. Primary Retention Form Primary Retention Form

Definition: primary retention form is the shape

or form of conventional preparation that resists displacement or removal of the restoration from tipping or lifting forces.

In many respects retention and resistance form are accomplished in the same cutting procedure.

Principal means of retentionFrictional retention -1.Greater surface area (length, width, depth)produces greater frictional component.

2.Parallel walls / convergent wall provide greater frictional retention

3.Proximity –bringing the restorative material closer to tooth structure during insertion provide greater frictional retention component.

4.Elastic deformation of dentin –during condensation within dentin proportional limit can add more gripping action.

4.Inverted truncated cones

-In class II cavity preparation , proximal surface have inverted truncated cones shape

-It prevents the occlusal displacement of restoration in class II Cavity.

6. DovetailIn Class II Cavity

-Dovetail provide retention in class II

cavity .

-It prevents lateral displacement of

restoration in class II cavity.

In Class I Cavity

-In class I ,it is given for the purposeful modification in outline usually for

‘EXTENSION FOR PREVENTION’

Primary Retention Form Primary Retention Form

Principles: For Amalgam restoration: -developing external cavity walls that converge occlusally. -Adhesive system provide retention by micromechanically bonding amalgam to tooth structure.

Primary Retention Form Primary Retention Form

Principles: Composite restoration:

a mechanical bond between the material

and conditioned, prepared tooth structure.

4 . 4 . Convenience Form Convenience Form

Conception: The shape or form of the cavity that

provides for adequate observation, accessibility, and ease of operation in preparing and restoring the cavity.

Convenience Form Convenience Form

Principles:

Allow access for caries removalAllow access for restoration placementAllow access to margins for finishing,

evaluation and cleaning

Convenience Form

-In class II cast restoration divergence of vertical wall -extending proximal preparation beyond proximal contact -In class III cavity convenience form mainly through lingual side.- In class I & V , divergence of wall of cavity

in INLAY

Final cavity preparation stage

Step 5 Removal of any remaining infected

dentin or old restoration, if indicated

Step 6 Pulp protection

Step 7 Secondary resistance & retention form

Step 8 Procedure for finishing external walls

Step 9 Final procedures

6. 6. Removal of any remaining Removal of any remaining infected dentin or old infected dentin or old restoration, if indicatedrestoration, if indicated

Definition: The elimination of any infected carious

tooth structure or faulty restorative material left in the tooth after initial cavity preparation.

Removal of dentinal caries using round burs and spoon excavators

Removal of dentin depends on the two condition

whether it is affected or infected?• Affected dentin

-Does not contain micro-organisms

-can be remineralise by restorative mean.

-it is accepted to allow affected dentin to remain in prepared tooth.

• Infected dentin

-It contain micro-organisms

-can not be remineralise by restorative mean.

-it should be removed during cavity preparation.

-Soft decay can be best removed using spoon excavator by flaking up the caries -Hard decay, heavily discolored should removed using very low speed bur.-care should have to take during removal as pulp may infected by forcing micro- organisms into dentinal tubules through excessive pressure.



dentin if indicated





6. 6. Pulp protectionPulp protection - Using liners or bases

- to protect the pulp or

- to aid pulpal recovery or both.LINERS-liners are volitile /aquous

suspension /dispersion of zinc oxide or calcium hydroxide that can be applied to tooth surface in relatively thin film & are used to effect a particular pulpal response.

BASES-Are those cements used in thicker dimensions beneath permanent restoration to provide for mechanical, chemical ,thermal protection of the pulp

-Liners are primarily used to provide a barrier to protect dentin from residual reactants.

-Bases are used to provide thermal protection for the pulp and to supplement mechanical support for the restoration by distributing local stresses from restoration across the underlying dentin surface.

If remaining dentin overlying the pulp is 2mm then no need of liners

But if it is less than 2mm ,pulp protection is mandatory .

Schematic view of needs for pulpal protection below metallic restoration

Schematic examples of liners & bases for amalgam restoration

For shallow tooth preparation

For moderate tooth

preparation

For very deep tooth

preparation



dentin if indicated





7. 7. Secondary resistance and Secondary resistance and retention forms retention forms

Most compound and complex cavity preparations require additional resistance and retention form.

The exception being those preparations that are very conservative.

Secondary resistance and Secondary resistance and retention forms retention forms

Mechanical forms

Cavity wall conditioning form

Mechanical form:

Retention locks, grooves, and coves Groove extensionsSkirtsBeveled Enamel MarginsPins, Slots, Steps, Amalgampins

Proximal Grooves for cast restoration

Retention locks for amalgam

Incisal retention coves

Incisal & Gingival retention groove

Groove extensions & skirts

When lingual wall absent or inadequate in proximal preparation, then retention form can be improved by facial skirt extension.

Pins slots steps & amalgampins

Beveled Enamel margins-The bevels for cast metal may improve retention form -Primarily to afford a better junctional relationship-Beveled margins increases the surface area of etchable enamel

Dentin slots Amalgampins

Cavity wall conditioning form

Placement of etchant , Primer , Adhesive on prepared wall

-in addition to mechanical alteration to tooth structure certain bonding agents also provide some extent of retention & resistance form

-such treatment require in bonded restoration like porcelain , composite , or amalgam materials

Micromechanical retention of bonding system to dental enamel



dentin if indicated



Step 8 Finishing external walls


8. 8. Finishing the external walls Finishing the external walls

Definition: is the further development of a

specific cavosurface design and degree of smoothness that produces the maximum effectiveness of the restorative material being used.

Finishing the external walls Finishing the external walls

Objectives: To create the best marginal seal possible

between the restorative material and tooth structure;

To afford a smooth marginal junction; To provide maximum strength of both the

tooth and the restorative material at and near the margin.

The strongest enamel margin is that marginwhich is composed of full-length enamel rodsthat are supported on the cavity side by shorterenamel rods, all of which extend to sound dentin.

Finishing the external walls Finishing the external walls

The design of the cavosurface angle

The degree of smoothness of the wall

The design of the cavosurface angle: depending on the material

amalgam: 90°(Cavosurface margin 90°-Butt joint)

Help to minimize the marginal deterioration of restoration by locating the margins away from the enamel eminence where occlusal forces may be concentrated.composite: beveling 30°~ 40° Is indicated primarily in larger restoration because the potential for retention increased by increasing the surface area of enamel available

for etch.

Occlusal cavosurface

margin

Proximal cavosurface

margin

Vertical section of Class II Tooth preparation-a slight bevel is given to remove unsupported

enamel rods

Gingival Bevel placed with an instrument

Gingival marginal trimmer



dentin if indicated





Final proceduresFinal procedures

cleaning

inspecting

Sealing

A .Water, air, or combinations of bothB . Dry cotton pellets are very efficient and safer way to dry preparation .C. Using cavity cleaner (vey low conc. Of citric acid ,ascorbic or acetic acid),dilute sol. Of hydrogen peroxide.D. Scraping preparation walls with sharp hand instrument.E. Irrigate the cavity with saline before drying.F. Inspecting the cavity for any remaining debris G. Sealing the cavityH. Composite requires etching ,priming & bonding before insertion of restoration.

Cavity preparation seen after final procedure

References

1.Sturdevants- Art and Science Of Operative Dentistry

2.Marzouk – Modern Theory and Practice

3.G.V. Black –Work on operative dentistry

3.Vimal Sikri- Textbook of Operative Dentistry

4.Journal of Australia- Conservative Dentistry

5.American Dental Association Document

6.Vale –Cavity preparation

7.www.googleimages.com

8.www.dentalacademy/images/cavity preparation.com

Principles of cavity preparation by Dr .rupali

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