The document discusses principles of tooth preparation for dental restorations. It covers biological considerations like preserving tooth structure, margin placement, and preventing pulp injury. Mechanical considerations include providing retention and resistance form to prevent restoration deformation or displacement. Ideal preparation taper is 2.5-6.5 degrees. Surface area and roughness increase retention while resistance depends on forces and preparation geometry. Margin types include featheredge, chamfer, bevel and shoulder. Occlusal and axial reduction are needed with functional cusp bevels. Esthetic results factor preparation for all-ceramic, metal-ceramic or partial coverage restorations.

1. Principles of Tooth Preparation

3. Biological Considerations

4. I. Preservation of Tooth Structure
1- Use of partial coverage rather than full coverage restorations

5. 2- Preparation of tooth with minimal practical convergence angle
(Taper) between axial walls

6. 3. Preparation of occlusal surface following the anatomical
contour to give uniform reduction

7. 4. Reduction of axial walls with maximal thickness of remaining
dentin surrounded the pulp

8. 5. Selection of marginal geometry which is conservative and
compatible with other principles

9. 6. Avoidance of unnecessary apical extension of the preparation

10. Reduce
Retention
Reduce
Resistance
Over reduction
Increase
Hypersensitivity
Pulp
inflammation and
necrosis
Tooth fracture

11. On of the most common violation of
this principle is seen in discriminate use
of full porcelain coverage in a situation
when partial veneer coverage can be
used

12. Also you should be careful about;
1- Adjacent tooth
- by using matrix band of the adjacent tooth
- cutting in the enamel of prepared tooth with
fine tapered stone
2- Soft tissues
- by using mirror or the flange of saliva ejector

13. 3- Pulp

14. Causes of Pulp Injury;
1- Thermal
2- Chemicals
3- Bacterial

15. Avoidance of over contour
• Gingival inflammation is commonly associated with crowns and
FPD abutments having excessive axial contours, probably because it
is more difficult for the patient to maintain plaque control around
the gingival margin. A tooth preparation must provide sufficient
space for the development of good axial contours.
• Under most circumstances a crown should duplicate the contours
and profile of the original tooth (unless the restoration is needed to
correct a malformed or malpositioned tooth). If an error is made, a
slightly under contoured flat restoration is better because it is
easier to keep free of plaque; however, increasing proximal contour
on anterior crowns to maintain the interproximal papilla may be
beneficial.
• Sufficient tooth structure must be removed to allow the
development of correctly formed axial contours, particularly in the
interproximal and furcation areas of posterior teeth, where
periodontal disease often begins

17. Margin placement
Whenever possible, the margin of preparation
should be supragingivally, where the supragingival
margin is prepared on sound enamel, while the
subgingival margin is often prepared on cementum
advantages:
1- Easier to prepare accurately without trauma to
soft tissue.
2- Prepared on hard enamel.
3- Easy to finished.
4- More easily to kept clean.
5- Impression are more easily made.
6- Restoration can be easily to evaluated at recall
appointment.

18. Indications of subgingival finish line
1- Dental caries, cervical erosion, restoration extend
subgingivally.
2- Proximal contact area extend near gingival crest.
3- Short tooth and additional retention is required.
4- The margin of metal-ceramic restoration is to be
hidden subgingivally.
5- Root sensitivity cannot be controlled by
conservative procedures.

21. Marginal Geometry
Ideal requirements of finish lines:
1.
They must fit closely to the finish line of the
preparation.
2.
They must have sufficient strength to
withstand the force of mastication.
3. Whenever possible, finish line should be
located in areas where the dentist can finish
and inspect them, and the patient can clean
them

22. Types of finish line

23. Featheredge
Chisel
Chamfer
Bevel
Shoulder
Sloped
Shoulder
Beveled
Shoulder

24. √
X

25. Occlusal Considerations

26. Preventing of tooth fracture

27. Mechanical Considerations

28. Principles
1- Providing Retention form
2- Providing Resistance form
3- Preventing deformation of
restoration (structure durability)

29. Retention & Resistance
What is the Retention?
The ability of the preparation to prevent
removal of the restoration along the path of
insertion.
What is the Resistance?
The ability of the preparation to prevent
dislodgment of restoration by force directed
in an along apical oblique and horizontal.

30. Tensile stress
Shearcompression
Shear stress
compression

31. I. Retention Form
Factors affecting retention:
1- Taper.
2- Total surface area
3- Roughness of tooth structure.
4- Film thickness
5- Type of luting agent

32. Taper
The more nearly parallel the opposing walls of preparation
the greatest will be the retention.
The optimum degree of taper is 2.5 to 6.5
degrees
The recommended degrees of taper are: 3 : 5,
6, 10 : 14
the degree of taper
stress in the
cement interface between the preparation
and restoration
the degree of taper
retention

35. Average degree of tooth preparation taper

36. Surface area
The greatest the surface area of preparation,
the greatest the retention of restoration.
Grooves
surface area
Boxes

39. The longer the occluso-gingival
height, the more surface area.
The more diameter of prepared
teeth, the more surface area.

40. Surface roughness
The prepared teeth should not be highly
polished.
Microscopic roughness, increase the retention

41. Film Thickness
there is a doubt (no certain data)
Type of luting agent
1- Resin cement
2- Glass ionomer cement
3- Polycarboxylate cement
4- Zinc phosphate cement
5- Zinc oxide eugenol cement

42. II. Resistance form
Mastication and parafunctional activity may
subject a prosthesis to substantial horizontal ,
oblique or apical forces. These forces are normally
much greater than the ones overcome by retention
Factors affecting resistance to displacement:
1. Magnitude and direction of the dislodging forces
2. Geometry of the tooth preparation
3. Physical properties of the luting agent

43. Magnitude and direction of the dislodging forces
In a normal occlusion, biting force is distributed
over all the teeth; most of it is axially directed. If a
fixed prosthesis is carefully made with a properly
designed occlusion, the load should be well
distributed and favorably directed . However, if a
patient has a biting habit such as pipe smoking or
bruxing, it may be difficult to prevent fairly large
oblique forces from being applied to a restoration

44. Geometry of the tooth preparation
What is the definition of Tipping Path?
It is the path along which the
restoration, could be displaced
under the displacing occlusal
force

45. The more convergence
more displacement

47. Short occlusogingival height
more displacement

48. The presence of the grooves
less displacement

49. Path of insertion
Definition
That direction through which the restoration
could be precisely seated on the corresponding
tooth or teeth
Parallel to the long axis of the tooth
Parallel to the incisal 2/3 of the tooth

50. Exception;
Tipped tooth
Should parallel to occlusal plane

53. III. Preventing deformation
(Structural Durability)
1. Occlusal reduction
2. Axial reduction

55. Functional Cusp Bevel
Palatal
Buccal

57. Axial Reduction
Proper axial reduction
Thin restoration
Insufficient axial
reduction
Over contour

58. Esthetic Considerations

59. 1.All Ceramic Restorations
2.Metal Ceramic Restorations
3.Partial Coverage Restorations