1. Principles of cavity preparation

2. Tooth preparation
Definition.
Objectives.
Principles:
biological.
Mechanical.

3. 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.

4. Mechanical alteration
Defective
Injured
Diseased
Mechanical alteration
Restorative material
tooth
Healthy state
Esthetic
Form
Function

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

6. 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 .

7. Principles of cavity preparation:
Biological principles.
Protection of the pulp(thermal, mech, chem, bact.).
Prevention of caries recurrence.
Aseptic conditions.
Mechanical principles.

8. I. Biological principles

9. Biological principles
Health and integrity of remaining tooth tissues
1. Protection of the pulp
2. Prevention of caries recurrence
3. Aseptic procedures

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

11. I. Mechanical irritation.

12. 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

14. II. Thermal irritation.

15. Thermal irritation:
TTZ (thermal tolerance zone) of dentin which ranges between 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).

16. the intentional use of coolants
copious in amount
Multi directed

17. 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.

18. 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.

19. III. Chemical irritation.

20. 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.

21. 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.

22. IV. Bacterial irritation.

23. 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

25. 2. Prevention of caries recurrence:
2. Prevention of caries recurrence

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

27. Recurrent caries due to improper extension

28. Removal of all undermind enamel

29. 4-Correct CSA compatible with restorative material

31. 3. Aseptic procedures.

32. Aseptic procedures Use of sterile instruments
Isolation of operative field
Use of personal protective barriers

33. II. Mechanical principles

34. Mechanical principles
Structural integrity of both tooth and restoration demanding:
Provision of correct resistance
Provision of adequate retention

35. 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

37. 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.