principles of tooth preperation 1.ppt Tooth

principles of tooth preperation 1.ppt Tooth

2. INDIVIDUAL TOOTH PREPARATION
FOR
FULL VENEER, ALL-CERAMIC,
METAL-CERAMIC, PRATIAL VENEER,
INLAY AND ONLAY RESTORATIONS
- Dr. Sumit. Deshpande
TOPIC

3. Contents
•Introduction
•Instrumentation
•Full veneer crowns
•All ceramic crowns
•Metal ceramic crowns
•Partial veneer crowns
•Inlays and Onlays

4. Introduction

5. Definition:
Tooth preparation is defined as the mechanical
treatment of dental disease or injury to hard tissues that
restores a tooth to its original form.
Tooth preparation is governed by the principles of tooth
preparation.

6. Principle’s of tooth preparation
•Preservation of tooth structure.
•Retention and Resistance form.
•Structural durability of the restoration.
•Marginal integrity.
•Preservation of periodontium.

7. Preservation Of Tooth Structure
•Means, avoid unnecessary reduction of the natural tooth
structure.
•Causes weakening of tooth structure, pulpal irritation,
hypersensitivity of the tooth, over taper/over shortening.
•Guidance for this is best understood by knowing the
average thickness of the enamel and dentin for the
individual tooth.

8. •The first choice for any restoration should be a partial
veneer restoration, although the full coverage
restorations have superior retention and resistance.
•Full coverage restoration is advised in conditions with,
Inadequate retention or esthetics being the primary
demand.

9. •Geometry of the preparation determines the orientation
of the direction of the forces and the type of forces
generated.
i.e. shear, tensile or compressive
•Forces perpendicular to the cement film are best
resisted.
•Cements hold the restoration and the tooth together by
the mechanical interlock at the two surfaces.

10. •Retention:
Resistance to removal of restoration in the path of
insertion.
•Resistance:
Prevention of dislodgement of a restoration from apical,
oblique and horizontal forces.

Retention and Resistance

11. Retention depends on
•Degree of taper
•Surface area of the cement film
•Area of cement under shear
•Roughness of surface

12. Resistance
•More the perpendicular forces acting on the restoration,
more is the resistance.
Factors for resistance,
•Leverage action from the oblique forces.
•Length of the preparation.
•Width of the preparation.
•Taper produced.
•Rotation around the vertical axis.

13. Additional grooves for retention and resistance can be
added.
Grooves and wings are added to prevent rotation.

14. Durability and toughness of the restoration
Occlusal reduction
Functional cusp bevel
Adequate axial reduction
Reinforcement struts

15. FINISH LINE AND PERIODONTIUM
•Should be close fitting- minimum cement exposure
•Adequate strength
•Locatable to the dentist and cleansable to patient
Types:
Knife edge
Shoulder
Bevel shoulder
Chamfer

16. •Sub-gingival finish line
•Supra-gingival finish line

17. •BIOLOGICAL WIDTH

18. INSTRUMENTATION
History:
Morisson developed the first dental foot engine inspired
from Singer and Howe’s sewing machine.
Till 1940’s, adapting of electric works were only the
developments in equipments for tooth preparation.
After the world war II -
Diamond cutting instruments-1930
Carbide burs-1947
Speed of hand piece-1950
Belt driven
Air driven

19. Speeds of 12,000 rmp were used, and it was laborious to
dentist and uncomfortable to the patient. For effective cutting,
large diameter diamond stones, wheels and discs were used
for bulk reduction of enamel and dentin.
Speeds in excess of 1,00,000 rmp, with smaller instruments
made it possible to achieve better and sophisticated designs in
practice. Removal of enamel became much easier than ever
before.

20. Water-air cooling
Cutting dry produces 3 times more dentinal burning than
cutting with water spray.
Temperature at 0.5mm from the cutting surface of bur in
dry can be 245
0
F(180
0
C) -Brown et al
20
0
F rise in temperature can lead to pulpal death- Zanch
In non-vital teeth, dry heat may cause micro-fracture of
enamel, hence causing marginal failure.
Use of only dry air as coolant causes dehydration and
odontoblastic displacement due to pulpal damage.

21. Low quality water spray causes dentinal scorching, hence
the orifice that produces a higher water velocity is
preferred. It also washes the debris and prevents clogging
when diamonds are used under pressure.
Disadvantages:
• The spray may interfere the vision of dentist
• Discomfort to the patient
• Water spray on the mirror surface
Remedies:
• Use of proper suction
• Mirrors coated with detergents can be used

22. Rotary instruments are
classified as:
•Stones-abrasives
•Burs-miniature milling cutters
•Drills-boring
(least used)
The three types of rotary instruments
used in tooth preparation are, left to
right the diamond stone, the tungsten
carbide bur, and the twist drill.

23. Stones
Small, irregular shaped, sharp edged diamond chips are
electroplated with nickel or chromium bonding medium to a
steel instrument head of desired head shape.
• Most effective in cutting enamel and porcelain
• Cutting efficiency is 2-3times more than burs (Eames et al)
These can vary with grain size and shape of the blank used.
The choice for the instrument depends on the application and
the operator.

24. The basic set of stones include:
Round ended tapered, flat ended
tapered, long needle, short needle,
small round edge, wheel diamond,
torpedo, flame shaped.
Diamonds with small diameter and tips
are to be used cautiously to prevent loss
of diamond particles. Heavy pressure
causes failure of bonding medium and
loss of abrasiveness of the instrument.

25. Burs
Tungsten burs:
Best for precise preparations
and smoothening of
enamel/dentin surfaces
Tungsten carbide and cobalt
powder are sintered and
pressure molded under heat and
vacuum into small cylinders.

This is then attached to steel
rods by soldering or welding to
form blanks

26. The carbide is then machined
to specific heads with diamond
disc’s. The shank is then
adjusted to fit the latch or
friction fit hand piece.

27. Burs with 6-8 blades are used for cutting
and burs with 12, 20, 40 blades are used
for polishing.
Cutting edge in a bur is formed by two
surfaces, FACE and LAND
Clearance angle:
Angle formed between the back of the
blade and the surface being cut.
Larger the diameter, smaller the
clearance angle
Optimum clearance angle is required
If reduced, the blade back may rub the
surface to be cut, heat is produced and
the cutting efficiency is decreased.

28. Rake angle:
Angle at which the face of the blade
meets a line extending from the cutting
edge to the bur axis.
Rake angle can be,
Positive- most efficient in cutting,
but have a weak edge
Neutral- less efficient in cutting
Negative- least cutting efficiency, long life
of bur
Hence, burs with negative and neutral
rake angle are preferred for its long life
(less likely to wear off or chip off)

29. Spirals and flutes
Flutes are the grooves between the spirals or helical angle
of the blade
More the number of spirals, smoother the finish, reduced
chatter/vibration of the bur, reduces clogging and reduced
wear of tungsten carbide.
Dentate burs (cross cut burs)
Burs with blades interrupted by cuts across the edge
More efficient than the non- dentate burs, but leaves deep,
severe striations at right angles to the path of the
preparation

30. Twist drills
• Made of steel.
• Cuts at the tip and has a Self limiting
collar.
• It has a twin helical flute that winds
around the shaft in a tight spiral helping to
remove the chips from the hole.
• Used to produce small, uniform diameter,
parallel sided holes in dentin to receive
the retentive pins for restorations.
• Used at low speed to avoid the breakage
of drill.

31. Diameter of the drill used is slightly larger than the pin to be
used when to be cemented.
Diameter of the drill used is slightly smaller than the
diameter of pin to be used when threaded pins are to be
used.
Twist drills tend to crawl along the sloping surfaces hence,
Pilot hole is made to insure the hole is made at the intended
position.
The drill should not be stopped while it is in the hole.

32. Diamond/Bur dual instrumentation
•Diamonds remove more of the tooth
structure, but leave a rough surface.
•Tungsten carbide burs cut slow, but
produce a smooth surface.
•Hence the combination of both is
used to make the preparation fast
and also get a smooth finish.

33. •Both the diamond and the bur are used alternatively and
are used of the same size.

•Rough surface aids in retention of the cement used for
the cementation of the restoration, but excessive
roughness prevents the marginal fit of the restoration.
•12 blade bur is usually used for the finish.

34. GRADES OF INSTRUMENTS
COLOUR CODING
WHITE
YELLOW
RED
BLUE
GREEN
BLACK

35. FULL VENEER CROWNS
(Full Crowns, Full Cast Crowns, Complete Crowns)
Work horse of cast restorations.
Used as the final attempt to preserve the tooth-in case of
severe tooth breakdown.
Have better retentive value, so used when maximum
retention is needed.

36. INDICATIONS
•Extensive destruction of tooth (caries/trauma)
•Endodontically treated tooth
•Existing restorations
•Need of maximum retention and strength
•To provide contours to receive a removable appliance
•Minor corrections in mal-inclinations
•Correction of occlusal plane

37. Contra-indications
•Esthetics
•Retention required is less than maximum

38. Steps In Cutting A Classic Full Veneer Crown
Preparation
•Planar occlusal reduction
•Functional cusp bevel
•Facial and lingual axial reduction
•Complete axial reduction
•Finishing of chamfer
•Placement of seating groove

39. Planar Occlusal Reduction
Done using a round ended tapered
diamond and no 171 bur.
Round ended tapered- to make the depth
orientation grooves on the triangular rides
and the primary developmental grooves.
The depth orientation grooves are 1.0 mm
on non-functional cusps and 1.5mm on
the functional cusps.
Occlusal reduction is done in an inclined
plane pattern/cuspal contour, preserving
the occlusal morphology.

40. Functional Cusp Bevel
Done using round end tapered
diamond and no 171 bur
Depth orientation grooves are placed
across the facial occlusal line angle of
mandibular molars/premolars and
Lingual occlusal of the maxillary tooth
It should be parallel to the inward
facing inclines of cusps of opposing
tooth, forming an angle of 45
0
to the
axial wall

41. Strip of red utility wax is used to
check the occlusal clearance
Imprint of the surface is
examined for adequate clearance
Thickness can be measured, but
becomes difficult because of the
softness of the wax
Depth of functional bevel-1.5mm

42. Facial And Lingual Axial Reduction
Done using torpedo diamond.
Chamfer is the preferred gingival
finish line.
Supra-gingival/sub-gingival margin.
Facial axial reduction- 2.5
0
to 6.5
0
taper to the uncut facial surface is
preferred.
Lingual axial reduction.

43. Complete Axial Reduction
Done using a short, thin tapered
diamond and torpedo diamond
Mesial axial reduction
Distal axial reduction
Finish line preferred is chamfer
Critical areas – line angles of the
preparation – inadequate
reduction causes over contoured
restoration and a scallop

44. Finishing Of Chamfer
Done using a chamfer finishing
torpedo bur
The bur is taken around the
finish line and the axial walls,
specially around the line angles
to produce a distinct, clear finish
line

45. Placement Of Seating Groove
Placed using a No. 171 bur
Placed 0.5mm above the chamfer at
the facial surface
Helps to guide the crown during
cementation
A second groove can be added
elsewhere, which will be an excellent
escape vent for cement and permit
complete seating of the restoration if
not reproduced in the restoration

46. Completed Preparation

47. ADVANTAGES
•Strength imparted to the tooth structure
•High retention
•Resistance form is easy to obtain
•Option to modify form and occlusion
•Contact areas and embrasures can be developed

48. DISADVANTAGES
•Removal of intact tooth structure
•Adverse effects on the tissues
•Vitality test not readily feasible
•Display (restricted to posterior teeth only)
•Over contoured if under reduced
•Uniform gingival finish line is challenging to attain
•Time consuming
•Post-cemental gingival caries is difficult to detect

49. All ceramic / Porcelain jacket crown
•Feldspathic porcelain
•Aluminous reinforced porcelain-McLean & Hughes (1965)
•Bonded platinum foil coping
•Glass ceramics
•Leucite reinforced porcelain-optec HPS
•Injection molded glass ceramic(IPS EMPRESS)
•Glass infiltrared alumina core ceramic(In ceram)
•CAD-CAM ceramics
•Zirconium oxide (ZrO
2
) ceramics

50. •Bulk of the material needed when used as
connectors/retainers in F.P.D causes impingement of
interdental papilla
•Wear of the natural opposing tooth.

51. INDICATIONS
•High esthetic requirements
•Intact tooth structure
•Centric contacts on the porcelain can be supported by
the tooth structure.

52. CONTRA-INDICATIONS
•When conservative restorations are favorable.
•Increased occlusal load and reduced esthetic demand.
•Unfavorable occlusal loads.

53. Steps In Tooth Preparation
•Index made using a putty
addition silicone covering
atleast one tooth on either
side of the tooth to be
prepared
•Sectioning of the index

54. Placement of Depth Orientation Grooves.
•Flat end tapered diamond
is used.
•Position of the flat
tapered diamond is
parallel to the gingival
portion of the facial
surface.

55. Two plane reduction is preferred
The diamond is inserted to full
diameter or more deeper, the tip
is slightly supra-gingival at the
point
The grooves are placed at the
• Mesio-distal centre of the
facial surface,
• Halfway between the mid-
sagittal groove and
• Each of the proximal line
angles.

56. •Two or more vertical cuts are
made in the incisal portion of the
facial surface.
•These sunk into the enamel and
disappear near the middle of the
facial surface where the curvature
of the surface is highest.

57. Orientation depth grooves for incisal reduction
•Placed facio-lingually,
•Incisal reduction of 2mm
is best recommended for
esthetics

58. The reduced incisal surface is
parallel to the former edge
(perpendicular to the masticatory
forces)
45
0
inciso-lingual bevel is created at
the incisal edge

59. Two plane reduction completed as,
•Incisal half
•Gingival half

60. •The facial reduction is extended
to the proximal surfaces with
the flat ended tapered diamond,
producing a shoulder.
•This can also be extended
lingually, but delayed until the
cingulum is reduced.

61. Lingual reduction
•Depth orientation marks are
made using 1.4mm ball diamond
•Reduction is done using a small
wheel diamond, to produce
concave cingulum reduction.
•Two concavities are produced in
a canine with ridge in between.
•0.5-1.0mm is the recommended
lingual reduction.

62. Lingual axial reduction is
done using a flat ended
tapered diamond.

63. •Vertical lingual wall is
prepared using a flat
ended tapered diamond
and extends 1mm into the
tooth.
•Taper in relation to the
gingival portion of the
facial surface is avoided,
as it can cause wedge
like forces and fracture of
the crown.

64. Each axial surface is blended to
the adjacent axial surface.

65. Axial finishing is done using a
No.171 bur

66. •Shoulder finishing is done using
No.957 bur.
•Shoulder of 1mm is preferred.
•Should be placed perpendicular to
the long axis of the tooth.
•Smoothened with a end cutting bur
or a 1mm wide enamel hatchet.
•Shoulder-less restorations are
usually over contoured.

67. HORIZONTAL SECTION

68. MID-SAGITTAL SECTION

69. •d
Completed tooth preparation

70. All ceramic tooth preparation for posterior teeth
Index is made with addition
silicone putty and sectioned.

71. •Using a round ended
tapered diamond
•Depth grooves are placed
and the remaining reduction
is done

Occlusal reduction

72. Large round end- tapered
diamond is used
Functional cusp bevel

73. Occlusal reduction is
checked using 1.5mm leaf

74. Facial and lingual axial reduction
Large round ended tapered
diamond

75. Complete axial reduction
Short tapered needle and
large round end tapered diamond
Shoulder finish

76. Finishing the preparation
Round end tapered carbide bur

77. Sharp angles are rounded-off

78. Horizontal section
Mid-sagittal section

79. COMPLETED TOOTH PREPARATION
•x

80. ADVANTAGES
•Superior esthetics.
•Good tissue response.
•Conservative reduction approach on the facial surface.
•Appearance can be influenced by the color of the
cement used for the cementation.

81. Dis-advantages
•Reduced strength
•Increased tooth reduction on the proximal and the lingual
surfaces
•Proper design is critical(90
0
cavo-surface angle is
needed.
•Proper supported incisal edge is needed(not favorable in
severely damaged tooth).