Principles of Cavity Preparation

from Dr. Anne

Grand old man of dentistry

G.V. Black

Who suggested the basic principles governing the design of cavity and steps in their preparation?

G. V. Black

Cavity Preparation (Definition)

mechanical alteration of a defective, injured, or diseased tooth in order to best receive a restorative material

5000 BC

Archeological evidence of dental treatment

1800

Early drills by hand

1955

Page Chyles handpiece

What is the 1st driven angle handpiece?

Page chyles handpiece

19th century

cavity prepared for inlay

Hamelton Jameson(19 cent)

First emphasized the organized cavity preparation

Who suggested "Extension For Prevention"?

Marshall Ebb & GV Black

1930

G.V.Black-systemic approach to cavity preparation

Who refined GV Black's Class VI classification?

Simon

1998

G.J.Mount classification

Objectives of Tooth Prep

• Remove all defects and provide protection to pulp
• Extend the restoration as conservatively as possible
• Tooth prep that under mastication both tooth and resto will not fracture/displace
• Allow the functional and esthetic placement of a restorative material

Factors affecting tooth prep

General and Patients Factors

Geenral factors

Diagnosis, Prevention, Interception, Preservation, Restoration

Patients Factors

Economic status, Age, choice of material

Simple tooth preparation

One tooth surface involved

Compound tooth preparation

Two tooth surface involved

Complex tooth preparation

3 or more surfaces

Cavity(definition)

-defect in enamel or dentin resulting from pathologic process of dental caries
-carious lesion in a tooth that has progressed to the point that part of tooth structure had been destroyed.

Tooth Preparation walls

Internal: axial, pulpal wall
External: floor/seat, enamel, dentinal wall

Internal wall

prepared surface that does not extend to external tooth surface

Axial wall

internal wall parallel with the long axis of the tooth

Pulpal wall

internal wall that is perpendicular to the long axis tooth and occlusal of pulp

External wall

prepared surface that extends to external tooth surface

Floor/Seat

prepared wall that is reasonably flat and perpendicular to the occlusal forces that are directed occlusogingivally

Enamel wall

Portion of a prepared external wall that consists of enamel.

Dentinal wall

Portion of a prepared external wall that consists of dentin
-mechanical feature located here

Cavity Preparation angles

Line angle, internal line angle, external line angle, point angle

Line angle

-junction of two planar surfaces of different orientation along a line
-combi of two walls
Ex. Mesio-buccal line angle

External line angle

line angle whose apex points away from the tooth
Ex. Axio-pulpal line angle

Internal line angle

line angle whose apex points into the tooth
Ex. Facio-pulpal line angle

point angles

junction of three planar surfaces of different orientation
Ex. Gingivo-axio-pulpal point angle

Cavo-surface angle

angle of the tooth structure formed by the junction of a prepared cavity wall and the external surface of the tooth.
-angle of prepped wall and unprepped wall

Cavo surface margin

formed by the junction of the wall of the preparation and the untouched surface of the tooth
(Walang angle na na-mention)

Classification of cavity

class I,II,III,IV,V,VI

Class I cavity

pit and fissure
Occlusal surface of PM and M
Occlusal 2/3rd of buccal & lingual surface
Lingual surface in max. Incisors

Class II cavity

proximal surfaces of premolars and molars

Class III Cavity

Anterior interproximal cavities, do not involve incisal angles

Class IV cavity

Anterior interproximal cavities including the incisal edge

Class V cavity

Gingival third of the facial or lingual surface of any tooth

Class VI cavity

Incisal edge(without proximal) on anterior teeth
Occlusal cusp height of posteriors

Stages of cavity prep

Initial and final steps of cavity prep

Initial steps of cavity prep

1. Outline form and initial depth
2. Primary resistance form
3. Primary retention form
4. Convenience for

Final steps of cavity prep

1. Removal or remaining infected dentin/old resto
2. Pulp protection
3. Secondary retention and resistance form
4. Finishing external walls
5. Cleaning, inspecting sealing

Outline form and initial depth

placing the cavity margins in the positions they will occupy
-preparing inital depth

Initial depth

0.2 to 0.8 mm pulpally to DEJ

Outline form and initial depth principlea

1. All friable and weakened dentin is removed
2. Fault included
3. Margin placed in a position to afford good finishing of margins of resto

Features of outline form and initial delth

1. Preserve cuspal strength
2. Preserve marginal ridge
3. Minimize facio-lingual extension
4. Using enameloplasty
5. Connecting 2 close faults
6. Restricting depth of penetration

What should be the distance between two close faults for u to connect the two?

Less than 0.5 mm

Depth of penetration (pits and fissure)

0.2 mm

Depth of penetration(smooth surface)

0.2-0.8 mm

Preserving cuspal strength

Avoid termination of margin on extreme eminence(cusp height)

If the extension of primary groove includes half or greater than that of \_____ then what can be considered?

Half/greater than CUSP INCLINE, cup capping

Remaining marginal ridge in Premolar

greater than 1.6 mm

Remaining marginal ridge for molar

2 mm

If Remaining Marginal ridge will be less than 1.6 mm there there may be the chances of?

Fracture bcs of undermining the ridge

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

Minimizing facio-lingual extension helps prevent ?

Weakening of cusp

conservative class I CAVITY facio-lingual width

1 to 1.5 mm

Depth of penetration should be restricted bcs?

1. To avoid seating resto on very sensitive DEJ
2. give bulk of resto
3. Take advantage of dentin elasticity during insertion and function

Enameloplasty

procedure of reshaping the enamel surface by making it rounded / Saucered , therefor cleansable and finishable

Enameloplasty is indicated when?

remaining fissure is not greater than 1/3 rd of enamel thickness

Upper premolars outline form

Dumb-bell shape with triangular ends

Lower premolar out line form

Confined to pit only(snake eye)
But, if entire occlusal plane is involved, it looks like upper premolar

Tricuspid lower premolar outline form

Y-shape

Lower molars outline form(Class 1 and 2)

Elongated shape mesio-distally, with 3 lateral extensions

Upper molars outline form

(If cavity involves all the occlusal), prep elongated mesio-distally

If oblique ridge is not involved, mesial prep shape

Kidney shape

If oblique ridge is not involved,distal prep shape

Heart shape

Class II, shape of proximal box

Inverted truncated cone

In class II cavity prep, gingival margin should be extended \___ of proximal contact.

Apically

A gingival margin extended apically of proximal contact in a class 2 prep, will provide the minimum clearance between gingival margin and adjacent tooth. What is the minimum clearance?

0.5 mm

Isthmus width in class 2 cavity prep acc to GV black

equal to 1/3rd of intercuspal distance

Isthmus width in class 2 cavity prep acc to Vale &Brooner

1/4th of intercuspal distance.

axio-pulpal line angle should be beveled, why?

reduce the concentration of stresses and provide grater bulk of material in the isthmus area

Final location for the facial and lingual Walls of proximal box should be?

Relative to contact area

Reverse curve

Used when class 2 cavity(esp. in max teeth), proximal contact lies in buccal surface, with groove lies in central portion

Reverse curve advantages

1. Preserved triangular ridge of cusp
2. Makes 90°angle between proximal wall & the tangent of proximal surface

primary resistance form

shape and placement of the cavity walls that enable both the restoration and the tooth to withstand masticatory forces without fracture

Primary resistance form principles

1. Utilize box shape with flat floor to resist occlusal loading
2. restrict the extension of the external walls for strong cusp and ridge areas
3. have a slight rounding of internal line angles to reduce stress
4. provide enough thickness of restorative material to prevent its fracture

Primary resistance form festures

1. Box shape
2. Relatively flat floor
3. Rounded internal line angles
4. Adequate thickness of resto mat
5. Reduction of cusps for capping(if indicated)
6. Inclusion of weakened tooth structure
7. Preservation of cusp and marginal ridge

Pulpal wall is flat in all cases except in?

lower 1st premolar
Bcs the lingual cusp is very small & buccal cusp is pronounced with very large pulp horn, so pulpal floor is parallel to the tips of lingual and buccal cusp

Silver amalgam needs what thickness for its resistance form

1.5 mm

Cast metal needs what thickness for its resistance form

1-2mm

Porcelain needs what thickness for its resistance form

2 mm

Primary Retention Form

shape or form of conventional preparation that resists displacement or removal of the restoration

Principal means of retention

By frictional retention:
1. Greater surface area
2. Parallel wall/convergent wall
3. Proximity
4. Elastic deformation of dentin

benefit of inverted truncated cones shape in class 2

prevents the occlusal displacement of restoration in class II Cavity.

Dovetall(Class 2)

Provide retention
-prevents lateral displacement of restoration

Dovetail(class 1)

Purposeful modification of outline for EXTENSION FOR PREVENTION

Primary retention form principle for amalgam resto

External walls\=converge occlusally
Retention is from adhesive system that micromechanically bonds amalgam to tooth

Primary retention form principle for composite resto

Mechanical bonds between material and conditioned(after etchant), prepared tooth

Convenience form

shape or form of the cavity that provides for adequate observation, accessibility, and ease of operation in preparing and restoring the cavity

Convenience form principles

- Allow access for caries removal
- Allow access for restoration placement
- Allow access to margins for finishing, evaluation and cleaning

Final cavity prep stages(step 5)

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

Final cavity prep stages(step 6)

Pulp protection

Final cavity prep stages(step 7)

Secondary resistance & retention form