Principles of cavity preparation

Tooth preparation Definition. Objectives. Principles: biological. 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 Mechanical alteration Restorative material tooth Healthy state Esthetic Form Function

Objectives of cavity preparation For tooth: Remove the defect conservatively. Provide necessary protection to the pulp. Prevent further fracture of tooth. .

Objectives of cavity preparation For the restoration: Prevent further fracture of restoration under masticatory forces Prevent displacement of restoration Allow for esthetic and functional placement of restoration .

Principles of cavity preparation: Biological principles. Protection of the pulp(thermal, mech, chem, bact.). Prevention of caries recurrence. 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 1. Protection of the pulp. i. Mechanical . ii. Thermal. iii. Chemical. iv. Bacterial.

I. Mechanical irritation.

Protection of the pulp AVOID!!! Overcutting of enamel (width). Overcutting of dentin (depth) Cutting of the OP close to the cell body may result in irreversible injury Excessive pressure application during excavation or use of rotary tools Injudicious use of small pointed instrument. Avoid use of eccentric rotary tools “Shock-wave” phenomena. Cutting across recessional lines of pulp

II. Thermal irritation.

Thermal irritation: TTZ (thermal tolerance zone) of dentin which ranges between 85-132 F 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).

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 : 2. Prevention of caries recurrence

Prevention of caries recurrence Remove all carious enamel and dentin Inclusion of all liable areas (pits &fissures)

Recurrent caries due to improper extension

Removal of all undermind enamel

4-Correct CSA compatible with restorative material

3. Aseptic procedures.

Aseptic procedures Use of sterile instruments Isolation of operative field 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: Conservation Removal of weakened tooth structure and undermined enamel Provision of bulk in the brittle restorations for stress distribution so that the destructive forces could not damage the brittle restoration. Provision of adequate means of retention to prevent displacement of restoration under functional forces.