Tooth Prep Flashcards
Preservation of Tooth Structure golden rule
Be conservative without compromising the mechanical and
aesthetic rules of tooth preparation.
Conservative prep includes
The conservative preparation:
1. Reduce harmful pulpal effects
Preparation extending deeply
toward the pulp increases the chance
of irreversible pulpal response
2. Reduce the amount of materials
used.
Avoid unnecessary apical
extension of the preparation
Retention
Retention prevents removal of the restoration along the path
of insertion or long axis of the tooth preparation.
Resistance
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.
Retention classification
Primary retention
1- Sleeve Retention: provided by the
opposing vertical surfaces of the
tooth preparation. Vertical retention
ie: extracoronal /crown.
2- Wedge Type: Retention: seen in
intracoronal restorations.
B- Secondary Retention: pins boxes grooves
Factors affecting the retention of
fixed prosthesis
- Degree of Taper.-
- Freedom of Displacement.
- Length.
- Substitution of internal features.
- Path of insertion.
Taper
The axial walls of the preparation must be taper slightly to permit the restoration to seat on the prepared toot. The degree of taper is inversely
proportional to retention form.
The more nearly parallel the opposing
walls of a preparation, the greater
should be the retention.
Too small taper
Undercut
Too large taper
Less retention
Torquing and twisting forces reduced by
Freedom of displacement:
Torquing and twisting forces reduced by:
A- Single path of insertion.
B- Proximal box preparation.
Length increases retention how
Length :
o Increase the length, increase the surface area and thus
increase the retention.
o Increase the height increase the cementation area
The height of the prepared tooth should be greater than the
tipping arc of displacement.
When you do substitution
Substitution of internal features;
Like boxes- grooves and retention pin holes.
Grooves decrease the arc of displacement.
Indications:
1- Over tapered preparation.
2- Partial veneer crowns.
3- Absence of two opposing walls (caries).
Grooves decrease the arc of displacement.
Path of insertion
It is imaginary line along which the restoration will be placed onto or
removed from preparation.
Considered in 2 directions: mesiodistal and faciolingual.
The mesiodistal inclination parallel to the contact areas of the adjacent
teeth.
Better the prosthesis have only one path of insertion to improve
prosthesis’s retention.
Detection of path of insertion
Detection of the
path of the
insertion:
Can be examine
through:
a. Visual survey.
b. Using dental
mirror.
Visual survey.
Performed to detect if the
preparation is undercut or over-
tapered. View the center of the
occlusal surface with one eye from
a distance of 30 cm (12’’).
Binocular vision should be
avoided as undercut
preparation can appear to
have an acceptable taper.
5.Path of insertion
a) Retention :
B. Mirror detection.
Luting cement
The luting cement:
oThe material of the luting
cement affect the prosthesis’s
retention.
oAdhesive cement improve the
prosthesis’s retention.
The factors that determine the resistance of the fixed prosthesis:
The factors that determine the resistance of the fixed prosthesis:
1. Dislodging forces.
oMastication and parafunctional activity result in both horizontal and oblique forces.
o Theses forces tend to displace the restoration by causing
rotation around the gingival margin.
2. Luting agent being used.-oResistance to deformation affected by the compressive
strength as well as the modulus of elasticity of the
luting agent.
3. Geometry of the tooth preparation.
Structural Durability:
The ability of the restoration to withstand destruction due to
external forces.
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
reduction without departing from the normal contours of the tooth
Structural Durability: obtained by
Can be obtained by:
A- Occlusal reduction.
B- Functional cusp bevel.- provide a space for an adequate bulk of
metal in an area of heavy occlusal contact.
C- Axial reduction.- securing space for an
adequate thickness of restorative material.
Inadequate axial reduction can result in a crown with thin, weak walls.
For gold alloys:
1.5 mm clearance on the functional cusp. (lingual of maxillary molars and
premolars and buccal of mandibular molars and premolars ).
1mm clearance on the nonfunctional cusp.
For Metal-ceramic : 1.5-2.0mm on the functional cusps and 1.0-1.5mm
on nonfunctional cusps.
For all-ceramic crowns : 2.0 mm clearance is needed
A flat occlusal surface may over shorten the preparation.
Marginal Integrity:
The restoration margin should closely adapt to
the cavosurface finish line of the preparation..
Preservation Of The Periodontium
• Biologic width is the distance from the epithelial attachment to the
crest of the alveolar bone
• It is normally about 2.0 mm wide, including the epithelial and
connective tissue attachments .
When the margin of a restoration intrudes into the biologic width,
inflammation and osteoclastic activity are stimulated
• Bone resorption will continue until the alveolar crest is at least 2.0
mm from the restoration margin.
The best biological result can be expected from margins that having
the following characteristics:
As smooth as possible and are fully exposed to cleansing action of the patient
• Supragimgival margin is preferable as the restoration can be finished by the
dentist and kept clean by the patient.
• The Subgingival restorations can be the etiologic factor in periodontitis.
The placement of the finish lines can be altered from ideal locations
by caries, the extension of previous restoration, trauma, esthetics, or to
increase the retention in short teeth.
It must be duplicated by the impression, without tearing or deformation.
• It should be placed in enamel when it is possible to do so.
finish line should be away from the alveolar crest than 2.0mm, which is
the combined dimension of the epithelial and connective tissue attachments.
