1. Fundamentals in Tooth Preparation
Dr. Ramesh Bharti
Assistant Professor
Conservative Dentistry &Endodontics
King George’s Medical University
Lucknow

2. Definition of Operative Dentistry
Operative dentistry is the ART and SCIENCE of the diagnosis, treatment, prognosis of defects of teeth which do not require full coverage restorations for correction, such treatments should results in the restoration of proper tooth form, function, and esthetics while maintaining the physiologic integrity of the teeth in harmonious relationship with adjacent hard and soft tissue, all of which enhance the general health and welfare of the patient.

3. Objectives of Cavity Preparation
Remove all defects and give the necessary protection to pulp.
Locate the margins as conservatively as possible.
Form the cavity so that both the restoration and tooth can withstand the load of mastication.
Allow for the esthetic and functional placement of a restorative material.

4. Need of Restoration Caries Malformed, discolored or fractured teeth
Restoration replacement

5. Factors affecting tooth preparation
1. General Factors
Pulpal & periodontal status
Occlusal relationship
2.Dental anatomy
Direction of enamel rods
Thichness of enamel /dentin
Size and positionof pulp
Relationship of tooth to its supporting tissues

6. 3.Patient factors 4.Affected & infected Dentine
Age
Esthetic consideration
Economic status
Patients with high risk caries
4.Affected & infected Dentine
5. Restorative material factors

7. Approach of Operative. cont…..
Cavity preparation
Matrix application
Preparation of materials
Insertion and carving of materials
Finishing and Polishing

8. Cavity Preparation
The mechanical alteration of a defective, injured, or diseased tooth in order to best receive a restorative material which will re- establish a healthy state for the tooth including esthetic corrections where indicated, along with normal form and function.

9. Cavity Structure
walls
angles
Floor

10. Classification of cavity
Class II
Class III
Class IV
Class V
Class VI
—G.V.Black in 1908

11. Cavity Simple cavity: only one tooth surface is involved.
Compound cavity: two surfaces are involved.
Complex cavity: three or more surfaces are involved.

12. Class 1
Class 6
Class 1
Class 4
Class 3
Class 2
Class 2
Class 5

13. Stages and Steps in Cavity preparation
Initial cavity preparation stage
Final cavity preparation stage

14. Initial cavity preparation stage
Step 1 Outline form and initial depth
Step 2 Primary resistance form
Step 3 Primary retention form
Step 4 Convenience form

15. Final cavity preparation stage
Step 5 Removal of any remaining infected
dentin if indicated
Step 6 Pulp protection
Step 7 Secondary resistance & retention form
Step 8 Procedure for finishing external walls
Step 9 Final procedures

16. Outline Form and Initial Depth
Definition:
placing the cavity margins in the positions they will occupy in the final preparation.
preparing an initial depth of 0.2~0.8 mm pulpally of the dentinoenamel junction position or normal root surface position.

17. Maxillary Class Ⅰ outline form

18. Mandibular Class Ⅰ outline form

19. Maxillary Class Ⅱ outline form

20. Mandibular Class Ⅱ outline form

21. Common Error

23. Outline Form and Initial Depth
Principles:
all friable and/or weakened enamel should be removed
all faults should be included
all margins should be placed in a position to afford good finishing of
the margins of the restoration.
Margins of the preparation will be located on finishable, self –cleansing area.

24. Outline Form and Initial Depth
Features:
preserving cuspal strength
preserving marginal ridge strength
minimizing facio-lingual extension
using enameloplasty
connecting two close faults or cavities
restricting the depth of the preparation into dentin.

25. Auxillary Factors Conservation
Adjacent enamel cracks or decalcification could be involved in the preparation.
Type of restorative material.
Extension for access.
anatomy and alignment.
If possible, no margins will be in occlusion with opposing teeth.
Esthetics

29. Outline Form and Initial Depth for pit and fissure cavities
Controlled by three factors
1- Extension to which enamel has been involved by caries.
2- Extension to achieve sound and smooth margins.
3- Limited bur depth while extending the preparaton

30. Rules
Capping of cusp should be done when cavity extension is two-third from central fissure to cuspal eminence.
Include all fissures that cannot be eliminated by enameloplasty.
Restrict the depth.
Join two lesions if they are less than 0.5 mm apart.

31. Outline Form and Initial Depth for smooth surface cavities
Extension of cavity.
Sufficient access.
Depth.
Sufficient clearance with adjacent tooth.

32. Initial cavity preparation stage
Step 1 Outline form and initial depth
Step 2 Primary resistance form
Step 3 Primary retention form
Step 4 Convenience form

33. Primary Resistance Form
Definition:
The shape and placement of the cavity walls that best enable both the restoration and the tooth to withstand, without fracture, masticatory forces delivered principally in the long axis of the the tooth.

34. Primary Resistance Form
Principles:
To utilize the box shape with a relatively flat floor to resist occlusal loading by virtue of being at right angles to mastication force.
To restrict the extension of the external walls (keep as small as possible) to allow strong cusp and ridge areas to remain with sufficient dentin support.

35. Primary Resistance Form
Principles:
To have a slight rounding of internal line angles to reduce stress concentration in tooth structure;
The presence of sharp internal line angles in GOLD FOIL resist the movement of the restoration
Sharp internal line and point angles in dentin serve as convenient “starting” points for compacting of direct gold.
To provide enough thickness of restorative material to prevent its fracture under load.

36. Primary Resistance Form
Feature:
Box shape
Relatively flat floors
Inclusion of weakened tooth structure
Preservation of cusps and marginal ridges
Rounded internal line angles
Adequate thickness of restorative materials
Reduction of cusps for capping if indicated

37. Primary Resistance cont….
Designing the outline form so that minimal of restoration is exposed to occlusal stress.
Seat on sound dentin.

38. Vale Experiments 1 MR at 1/4th ICD -10% Loss of FR
1 MR at 1/2 of ICD -40% Loss of FR
2 MR at ½ of ICD -45% Loss of FR

40. Initial cavity preparation stage
Step 1 Outline form and initial depth
Step 2 Primary resistance form
Step 3 Primary retention form
Step 4 Convenience form

41. Primary Retention Form
Definition:
The shape or form of the prepared cavity that resists displacement or removal of the restoration from tipping or lifting forces.

42. Primary Retention Form
Principles: depending on the materials
Amalgam restoration:
developing external cavity walls that converge occlusally and dovetail design

43. The devotail design provide retention form
to the occlusal portion of the cavity.
The occlusal convergence of the walls offers
retention in the proximal portion of the cavity
against displacement occlusally.

45. Primary Retention Form
Principles: depending on the materials
Composite restoration:
a mechanical bond between the material
and conditioned, prepared tooth structure.

46. Dentin etched with 32% phosphoric acid Collagen exposed by the acid.

47. Bonding of resin to dentin, using a "total-etch" technique
FIG
Bonding of resin to dentin, using a "total-etch" technique

48. 16 Bonding to dentin using a self-etching primer.

49. Scanning electron micrograph of the transition between
composite resin (C) adhesive (A), adhesive-hybrid layer
(H), and hybrid layer-dentin.

50. Initial cavity preparation stage
Step 1 Outline form and initial depth
Step 2 Primary resistance form
Step 3 Primary retention form
Step 4 Convenience form

51. Convenience Form Conception:
The shape or form of the cavity that provides for adequate observation, accessibility, and ease of operation in preparing and restoring the cavity.

52. Convenience Form Principles: Allow access for caries removal
Allow access for restoration placement
Allow access to margins for finishing,
evaluation and cleaning

53. Convenience Form

54. Final cavity preparation stage
Step 5 Removal of any remaining infected
dentin if indicated
Step 6 Pulp protection
Step 7 Secondary resistance & retention form
Step 8 Procedure for finishing external walls
Step 9 Final procedures

55. Removal of any remaining infected dentin if indicated
Definition:
The elimination of any infected carious tooth structure or faulty restorative material left in the tooth after initial cavity preparation.

56. Removal of dentinal caries using round burs and spoon excavators
A: use of a round carbide bur, with air coolant and slow speed.
B: use of spoon excavators.
Removal of dentinal caries using round burs and spoon excavators

57. Pulp protection
Using liners or bases to protect the pulp or to aid pulpal recovery or both.
If the infected dentin more than 2 mm deeper from the initial pulpal or axial wall then a Liner is indicated.

62. Final cavity preparation stage…..
Step 5 Removal of any remaining infected
dentin if indicated
Step 6 Pulp protection
Step 7 Secondary resistance & retention form
Step 8 Procedure for finishing external walls
Step 9 Final procedures

63. Secondary resistance and retention forms
Most compound and complex cavity preparations require additional resistance and retention form.
The exception being those preparations that are very conservative.

64. Secondary resistance and retention forms
Mechanical forms
Cavity wall conditioning form

65. Mechnical form:
Proximal locks
Proximal slots

66. Proximal locks

69. Slot on gingival wall

70. Final cavity preparation stage….
Step 5 Removal of any remaining infected
dentin if indicated
Step 6 Pulp protection
Step 7 Secondary resistance & retention form
Step 8 Finishing external walls
Step 9 Final procedures

71. Finishing the external walls
Definition:
Finishing the preparation walls is the further development of a specific cavosurface design and degree of smoothness that produces the maximum effectiveness of the restorative material being used.

72. Finishing the external walls
Objectives:
To create the best marginal seal possible between the restorative material and tooth structure;
To afford a smooth marginal junction;
To provide maximum strength of both the tooth and the restorative material at and near the margin.

73. The strongest enamel margin is that margin which is composed of full-length enamel rods that are supported on the cavity side by shorter enamel rods, all of which extend to sound dentin.

74. Finishing the external walls
The design of the cavosurface angle
The degree of smoothness of the wall

75. The design of the cavosurface angle depending on the material:
Amalgam: 90°
Composite: beveling 30°~ 40°

79. Final cavity preparation stage……..
Step 5 Removal of any remaining infected
dentin if indicated
Step 6 Pulp protection
Step 7 Secondary resistance & retention form
Step 8 Procedure for finishing external walls
Step 9 Final procedures

80. Final procedures
cleaning
inspecting
varnishing
conditioning

83. Multiple Choice Questions
Q.1. In cavity prepartion cavo-surface margin will be a junction between : a) Cavity wall/floor and adjacent tooth surface. b) Cavity wall and floor. c) Floor of the occlusal box and aproximal box d) Axial wall and occlusal floor.

84. Q.2 Toilet of the cavity is:
a) Removal of debris by washing with water
b) Removal of debris by cold air
c) Removal of debris by hot air
d) Washing the cavity with water.

85. Q.3 Most common fracture seen in amalgam restoration at:
a) Cavosurface margin.
b) Contact area
c) Isthmus area
d) Proximal box

86. Q 4 G. V Black concluded that following area of tooth surface are relatively non-selfcleansing:
A) Pit and fissures
B) Tips and cusps
C) Fossa
D) Marginal ridge

87. Q.5 Class III amalgam restorations areusualy prepared on:
a) Distal surface of anterior teeth
b) Mesial surface of canine
c) Distal surface of canine
c) Mesial and distal surface of all teeth.