Conservative cavity preparation

of
both amalgam and composite

Tooth preparation is defined as the mechanical alteration of a

defective, injured, or diseased tooth to best receive a restorative
material that will reestablish a healthy state for the tooth, including
esthetic corrections where indicated, along with normal form and
function
OBJECTIVES OF
TOOTH PREPARATION
1. remove all defects and provide necessary protection to the
pulp.
2. extend the restoration as conservatively
as possible.
3. form the tooth preparation so that under the force of
mastication the tooth or the restorationor both will not fracture and
the restoration will not be displaced
4. allow for the esthetic and functional placement of a
restorative material .
Factors Affecting Tooth Preparation
Diagnosis:

 The reason for placing the restoration in the tooth

 Periodontal & pulpal status

  Esthetic factor

 Relationship with other treatment plans

 The risk potential of the patient for other dental caries

2. Knowledge of Dental Anatomy:

 Gross picture of the tooth both internally and externally must

be visualized.

 The thickness of enamel, dentin and position of the pulp.

 Relation to other supporting tissues.

3. Patient Factors:

 The patient knowledge & appreciation for good dental health.

 Patient’s economic status.

 The patient age

3. Conservation of Tooth Structure:

• Preservation of the vitality of the tooth by avoiding the

application of poor or careless operative procedures on the
tooth.

• Restorations should be made as small as possible.

• Small tooth preparations result in restorations that has little

effect on both inter-arch & intra-arch relationships as well as
esthetics.
4. Restorative Material Factors:

• Amalgam Vs resin composite.

• The ability to isolate the operating field.

• The extension of the problem (i.e. caries).

G.V. Black’s classification of cavity design:

Class I Restorations:

 A class I lesion affects the pit and fissures of the teeth.

 Surfaces involved are:

– Occlusal surfaces of premolars and molars.
– Occlusal two thirds of the facial surfaces of mandibular
molars.
– Occlusal third of the lingual surfaces of the maxillary
molars.
– Lingual surfaces of maxillary incisors, most frequently
in the pit near the cingulum.
Class II restoration:

 A class II lesion is an extension of the class I lesion into the

proximal surfaces of premolars and molars.

 Areas for class II decay involve:

– Two-surface restoration of a posterior tooth.
 – Three-surface restoration of a posterior tooth.
– Four- or more surface restoration of a posterior tooth.
Class III and IV Restorations:
 A class III lesion affects the interproximal surface of incisors
and canines.
 A class IV lesion involves a larger surface area, which
includes the incisal edge and the interproximal surface of
incisors and canines.
Class V Restorations:
 A class V restoration is classified as a smooth surface
restoration. These decayed lesions occur at:
– The gingival third of the facial or lingual surfaces of
any tooth.
– The root of a tooth, near the cementoenamel junction.

ACCORDING TO SITE INVOLVED:

 Site 1 . Pits, fissures and enamel defects on occlusal surfaces

of posterior teeth or other smooth surfaces.

 Site 2 . Approximal enamel in relation to areas in contact

with adjacent teeth.

 Site 3 . The cervical one third of the crown or, following

gingival recession, the exposed root surface.
 ACCORDING TO THE SIZE OF THE LESION:

 Size 0 . The earliest lesion that can be identified as the initial

stages of demineralisation. This needs to be recorded but will
be treated by eliminating the cause and should therefore not
require further treatment,

 Size 1 . Minimal surface cavitation with involvement of

dentine just beyond treatment by remineralisation alone.
Some form of restoration is required to restore the smooth
surface and prevent further plaque accumulation,

 Size 2 . Moderate involvement of dentine following cavity

preparation. Remaining enamel is sound, well supported by
dentine and not likely to fail under normal occlusal load. The
remaining tooth is sufficiently strong to support the
restoration,

 Size 3 . The lesion is enlarged beyond moderate. Remaining

tooth structure is weakened to the extent that cusps or incisal
edges are split, or are likely to fail if left exposed to occlusal
load. The cavity needs to be further enlarged so that the
restoration can be designed to provide support to the
remaining tooth structure,

 Size 4 . Extensive caries or bulk loss of tooth structure e.g.

loss of a complete cusp or incisal edge has already occurred.
 Classification of caries according to Site & Size of the
lesion:

Stages and Steps of Tooth Preparation:

Initial Stage
1. Outline form & initial depth
2. Primary resistance form
3. Primary retention form
4. Convenience form
Final Stage

 5. Removal of any remaining infected dentin

 6. Pulp protection if indicated

  7. Secondary resistance & retention forms

 8. Procedures for finishing external walls

 9. Final procedures: cleaning, inspecting & sealing

Initial Tooth Preparation Stage
1. Outline form & initial depth

 Placing the preparation margins in the positions they will

occupy in the final preparation.

 Preparing an initial depth of 0.2 to 0.8 mm pulpaly of the

DEJ position.
Including 3 principles:
1. All weakened enamel should be removed.
2. All faults should be included.
3. All margins should be placed in position to afford good
finishing of the margins of the restoration.
2. Primary resistance form:
The shape & 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 access of the
tooth”
Principles of resistance form:
1. Box shape with relatively flat floor.
- Masticatory forces are directed along the long
access of the tooth
2. Keep the cavity as small as possible.
- Pulpal & axial walls should be maintained just in dentin if at all
possible.
- If caries invaded the interjacent dentin, only the carious dentin
should be removed.
3. Rounded well-defined internal line angles.
Well-defined line angles aid in establishing uniform depth and
prevent rotation of the restoration.
4. Cap cusps or include weakened tooth structure within the
restoration.
5. Provide enough thickness of restorative material to
prevent its fracture.
- The restorative material may fracture if the cavity
preparation is too shallow.
6.To bond the material to tooth structure when possible.
Factors Affecting Resistance Form:
 Remaining tooth structure: Affect need and type of
resistance form.

 Type of restorative material: amalgam Vs composite

3. Primary Retention Form:
“The shape or form of the conventional preparation that resist
displacement or removal of the restoration from tipping or
lifting forces”

PRINCIPAL MEANS OF GAINING RETENTION:

• Inverted truncated cones or undercuts.
• Dovetail.
• Elastic deformation of dentin e.g. gold foil.
• Friction – which depends on surface area,
• opposing walls or surfaces involved,
• parallelism or non-parallelism,
• proximity of material to walls.
Retention mean for Amalgam

 Parallel walls and flat pulpal floor or gingival floors

 Occlusal convergence of walls (axial retention) in class of

class II.

 Occlusal convergence and dovetail

 Proximal retention in the from of axiofacial and axiolingual

locks

 Slots in gingival floor.

 Retention for composite

 Acid conditioning.

 Retentive cavity preparation.

 Physico-chemical retention.

 Posts
4-Convenience form
Convenience form is defined as that form of cavity
preparation that allows adequate observation, accessibility
and case of operation in preparing and restoring the cavity.

 Allows adequate observation, accessibility, and ease of

operation during the preparation and restoration of the tooth.

 Only the minimal amount of reduction that will provide the

necessary convenience should be done.
Modification in tooth preparation for convenience form:

 Occlusal step in classII.

 Labial/lingual access for classIII/classIV.

 Occlusal divergence of cavity walls in cast restorations.

5. Removal of any remaining infected dentin:

 Amelodentinal junction caries

 Pulpal caries

 Indirect pulp capping

6. Pulp protection if indicated

 Direct pulp capping if indicated.

Although the placement of liners and bases is not a step in tooth
preparation in the strict sense of the word, it is a step in adapting
the preparation for receiving the final restorative material.
Therefore a basic discussion of this subject follows.

7. Secondary resistance & retention forms

After removal of any remaining enamel pit or fissure, infected
dentin, and/or old restorative material if (indicated) and pulpal
protection has been provided by appropriate liners and bases,
additional resistance and retention features may be deemed
necessary for the preparation.
Extra retention mean:
1. Pin
2. Holes
3. Groove
4. Slots
5. Box preparation
8. Procedures for finishing external walls

 No undermined enamel rods

 Smooth enamel surface

  Cavosurface angle 90

 No beveling for amalgam

 Composite needs a bevel to provide greater enamel surface

area for etching and micromechanical retention.
9. Final procedures: cleaning, inspecting & sealing

 The prepared cavity should be free from all debris

 No disinfectant should be used to clean the cavity.

 Don’t desiccate it.

Cavity Preparation
1.Conventional
2.Beveled conventional
3.Modified

Beveled conventional cavity

Preparations are similar to conventional preparation,
in that the outline form has external, “box-like” walls, but with
beveled enamel margin.
Modified cavity preparation (scooped)

 Have neither specified cavity wall structure nor specified

pulpal depth, and have enamel margins

 Conserve more tooth structure

Modified class II cavity preparations
 Approximal slot preparation: lesion is accessed via the
buccal or lingual surfaces.
 Tunnel restoration: tunneling through from the occlusal
surface leaving the marginal ridge intact.
 Conservative class II resin restoration: if lesion is small but
has weakened marginal ridge, small cavity is cut and restored
with composite.
Tunnel design
Indication:
 When the approximal carious lesion is small and the occlusal
pits and fissures are either carious or very deep and
vulnerable to caries attack.
Advances in methods of cavity preparation:
1. Laser
2. Air-abrasive system
3. Cavisol+hand piece
4. Heal ozone
5. Enzymes
6. Sonic and ultrasonic
7. Air-polishing