4. INTRODUCTION
The process of removal of diseased and/or healthy enamel, dentin and cementum to shape
a tooth to receive a restoration.
GPT-8
Tooth preparation may be defined as the mechanical treatment of dental disease or injury
to hard tissue that restores a tooth to the original form. (Tylman)
The mechanical preparation or the chemical treatment of the remaining tooth structure,
which enables it to accommodate a restorative material without incurring mechanical or
biological failure. (Marzouk)
5. Principles
Preservation of tooth structure
Retention and resistance
Structural durability
Marginal integrity
Preservation of periodontium
By Shillingburg
7. Biologic principles
Methods of prevention
A metal matrix band placed around the adjacent tooth.
Damage to adjacent teeth is prevented by positioning the diamond so
a thin lip of enamel is retained between the bur and the adjacent
tooth.
Note that the orientation of the diamond parallels the long axis.
The enamel should be maintained mesial to the path of the diamond
as the reduction progresses.
8. Soft tissues
Damage to the soft tissues of the tongue and cheeks can be prevented
by careful retraction with an aspirator tip, mouth mirror , or flanged
saliva ejector.
Great care is needed to protect the tongue when the lingual
surfaces of mandibular molars are being prepared.
10. Preservation of tooth structure
Can be done by:
• Using partial coverage than complete coverage restoration
when possible
• Preparation of teeth with minimum practical taper.
• Preparation of occlusal surface following the anatomic
planes.
• Axial surfaces: if necessary, teeth should be
orthodontically repositioned.
11. Margin Integrity
Margin – The outer edge of a crown , inlay, onlay or other restoration.
GPT-8
The restoration can survive in the biological environment of the oral
cavity only if the margins are closely adapted to the cavosurface
finish line of the preparation.
The configuration of the preparation finish line dictates the shape
and bulk of restorative material in the margin of the restoration It
also can affect both marginal adaptation and the degree of seating of
the restoration
12. Supragingival Margin
At or above the gingival crest.
Margin should be placed supragingivally whenever
possible.
13. ADVANTAGES
- Place on enamel
- Easy to prepare without trauma to soft tissues.
- Can be easily finished
- Impression making is also less traumatic to soft issues & easy to
reproduce.
- Fit of the restorations can be easily evaluated.
- Can be easily maintained by patient
14. Subgingival Margins
Major aetiologic factor in peridontitis.
Deeper the restorative margin is in the sulcus ,greater is the
inflammatory response.
Place at least 2mm above the alveolar crest so that the biologic
width is not encroached.
15. Indications
Caries ,erosion or restorations extending subgingivally.
Aesthetics – when metal ceramic restorations are used.
Additional retention – in case of short crowns
Root sensitivity.
Modification of axial contour.
Proximal contact extending to gingival crest.
16. Finish Line
Definition:
The point at which a preparation terminates on the tooth
is called the finish line. It is also defined as the peripheral
extension of a tooth preparation (GPT-8).
17. The finishline serves the following functions:
During visual evaluation of the tooth preparation,it is a measure of the
amount of tooth structure already removed.It also delineates the extent of
the cut in an apical direction.The more distinctitis,the better it serves these
purposes.
The finish line is one of the features that can be used to evaluate the
accuracy of the impression made for indirect procedures.
In the die,a distinct finish line helps to evaluate the quality of the die and
helps in accurate die trimming.
18. Finish line configuration
Chamfer Finish Line
Shoulder
Shoulder With Bevel
Radial Shoulder
Slope Shoulder
Knife Edge
19. Chamfer Finish Line
It is an obtuse angled finish line.
It is distinct.
Exhibits less stress.
Most conservative.
Adequate seal
Minimal tooth reduction
Can be done with round ended diamond or torpedo diamond burs.
20. Indications-
Cast metal crowns
Metal-only portion of PFM crowns.
Contraindications
Should not be indicated for porcelain restorations as the obtuse angle
produces shearing forces which is not tolerated by porcelain
21. Shoulder
• Finish line is perpendicular to axial surfaces of teeth
• All-ceramic crowns
• Facial margin of PFM crowns where esthetics is more important.
Wide ledge-
• resistance to occlusal forces
• minimizes stresses which leads to fracture of porcelain
Flat-end tapered bur is used
Less conservative
Healthy contours
Maximum esthetics
22. Radial shoulder
Modified shoulder
Cavosurface 90°
Shoulder width lessened with rounded internal angles
Lesser stress concentration
Good support for porcelain
Done with flat end tapered diamond and end cutting parallel sided carbide
finishing bur
Finishing is done with modified special bin-angle chisel.
23. Sloped shoulder
120° sloped shoulder margin
Facial margin of a metal-ceramic crown
No unsupported enamel, yet sufficient bulk to allow thinning of the metal
framework to a knife-edge for acceptable esthetics
24. Shoulder with a bevel
Similar to shoulder but external bevel is created on the
gingival margin of facial line.
Indications:
Proximal box of inlays, onlays
Occlusal shoulder of onlays and mandibular ¾ crowns
Facial finish line of metal-ceramic restorations (gingival
esthetics not critical)
Situations where a shoulder is already present
(destruction by caries, previous restorations)
25. Knife edge
Permit acute margin of metal
Axial reduction may fade out
Thin margin - difficult to wax and cast
Susceptible to distortion
Indications:
• Mandibular posterior teeth with very convex axial
surfaces
• Lingually tilted lower molars
• Full metal crown in young patient.
26. Marginal adaptation
The junction/space between a cemented restoration & tooth is always a
potential site for recurrent caries or periodontal disease because of
dissolution of luting agent & inherent roughness.
Hence ,preparing a smooth & even margin is the beginning of various steps
tissue displacement,impression making ,die formation ,waxing
finishing,casting ,involved in making a restoration fit better with least space.
27. Clinically acceptable marginal gap is 10 microns for cast metal & up to 50
microns for ceramic restorations. The discrepency in adaptation can have a
horizontal & vertical component.
28. Retention form
Retention prevents removal of the restoration along the
path of insertion or long axis of the tooth preparation.
Primary
Sleeve
Wedge
Secondary
Pin, box and grooves
29. Resistance form
Resistance prevents dislodgement of the restoration by
forces directed in an apical or oblique direction and
prevents any movement of the restoration under occlusal
forces.
31. Structural durability
Restoration must contain bulk of material that is adequate
to withstand the forces of occlusion.
This bulk must be confined to the space created by the
tooth preparation.
32. 1) Occlusal reduction
Provides adequate bulk of metal
Should reproduce the Basic Inclined Plane pattern of occlusal
surface – planar reduction
functional cusp Non functional cusp
Gold alloys 1.5 mm 1 mm
Metal
ceramic
1.5 to 2 mm 1 to 1.5 mm
All ceramic 2 mm 2 mm
33. Inadequate reduction makes restoration weaker, provides no space
for functional morphology and the perforation may occur while
finishing procedure.
A flat occlusal surface may over shorten the preparation.
34. 2) Functional cusp bevel
Provides space for an adequate bulk of metal in an area of
heavy occlusal contact.
35. Lack of functional cusp bevel may produce several
problems :
A. Thin area or perforation.
B. Over inclination of the buccal surface will destroy
excessive tooth structure reducing retention.
C. Over contouring and poor occlusion.
36. 3) Axial reduction
securing space for an adequate thickness of the
restorative material.
Inadequate reduction : Distortion, over contouring the
axial surface and consequently periodontal problems.
