Principles of cavity preparation

Tooth preparation1. Definition.2. Objectives.3. Principles:

i. biological.ii. Mechanical.

Definition

• Tooth preparation is the mechanical alteration of a defective, injured, or diseased tooth to receive a restorative material that reestablishes a healthy state for the tooth, including esthetic corrections where indicated and normal form and function.

Mechanical alteration

Defective

Injured

Diseased

Restorative material

tooth

Healthy state

Esthetic Form Function

• For tooth:1. Remove the defect conservatively.2. Provide necessary protection to the pulp.3. Prevent further fracture of tooth.

.

Objectives of cavity preparation

• For the restoration:1. Prevent further fracture of restoration under

masticatory forces2. Prevent displacement of restoration3. Allow for esthetic and functional placement

of restoration

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Objectives of cavity preparation

Principles of cavity preparation:

• Biological principles.

i. Protection of the pulp(thermal, mech, chem, bact.).

ii. Prevention of caries recurrence.

iii. Aseptic conditions.

• Mechanical principles.

I. Biological principles

Biological principles

• Health and integrity of remaining tooth tissues

1 .Protection of the pulp 2 .Prevention of caries recurrence

3 .Aseptic procedures

1. Protection of the pulp.i. Mechanical .ii. Thermal.iii. Chemical.iv. Bacterial.

I. Mechanical irritation.

Protection of the pulp

AVOID!!!1. Overcutting of enamel (width).2. Overcutting of dentin (depth) Cutting of the OP

close to the cell body may result in irreversible injury3. Excessive pressure application during excavation

or use of rotary tools4. Injudicious use of small pointed instrument.5. Avoid use of eccentric rotary tools “Shock-

wave” phenomena.6. Cutting across recessional lines of pulp

II. Thermal irritation.

Thermal irritation:

TTZ (thermal tolerance zone) of dentin which

ranges between 85-132 F

1. Minimizing the frictional heat resulting in

cavity preparation via, decreasing friction:

speed, pressure, area of cutting, mode and time

of cutting. Using tools with high cutting

efficiency (sharp, suitable, and proper sized).

2. the intentional use of coolants

• copious in amount

• Multi directed

Air-water spray jet is considered to be the most appropriate (Why?)

air drying stream desiccate the dentin water stream disturbs visibility during work.

The temperature of coolant should be that of the mouth i.e.37 C (Why?)• Lower temperatures fogging, disturbs vision

and may irritate the pulp. • Higher temperatures not effective in cooling.

Thermal Injury:“Blushing” of teeth during or after cavity prep is

attributed to frictional heat• Pink or purple color due to vascular stasis of sub-odontoblastic capillary plexus blood flow which rupture and release RBC’s.

III. Chemical irritation.

Chemical irritation:

• Cavity cleansers, cavity sterilizers like

phenolic and alcoholic agents proved to

have an insignificant role in preventing or

decreasing secondary caries and thus their

use must be omitted.

• Chemical irritation to dentine-pulp organ

without pulpal bacterial contamination did

not produce harmful effects on the pulp in

spite the existence of a very thin protective

dentin bridge or even in cases of micro- or

macroscopic pulp exposures.

IV. Bacterial irritation.

Bacterial irritation:

• Sterilization of instruments is essential

since bacterial ingress to the pulp can pass

through minute undetected exposures in

case of thin dentine bridge barrier

• Use of rubber dam to isolate the field of

operation

:

2. Prevention of caries recurrence

Prevention of caries recurrence

1. Remove all carious enamel and dentin2. Inclusion of all liable areas (pits &fissures)

Recurrent caries due to improper extension

3. Removal of all undermind enamel

4-Correct CSA compatible with restorative material

3. Aseptic procedures.

Aseptic procedures

1. Use of sterile instruments

2. Isolation of operative field

3. Use of personal protective barriers

II. Mechanical principles

Mechanical principles

• Structural integrity of both tooth and restoration demanding:

Provision of correct resistance Provision of adequate retention

Correct cavity design decrease the magnitude of the destructive stresses by:

• Inclination of walls

• Locating the margins

• Flat, smooth walls and floors

• Line and point angles

• The cavity design should decrease the deleterious and damaging effect of tensile stresses created within the tooth as a result of defect by:

1. Conservation2. Removal of weakened tooth structure and undermined

enamel3. Provision of bulk in the brittle restorations for stress

distribution so that the destructive forces could not damage the brittle restoration.

4. Provision of adequate means of retention to prevent displacement of restoration under functional forces.