Basics of Tooth Preparation Flashcards
When preparing a tooth, you must balance what three qualities?
- Biologic
- Mechanical
- Esthetic
Why is the amount of reduction an esthetic consideration for metal-ceramic crowns?
If there is an insufficient reduction, there will be a reduced porcelain thickness that leads to gray, unappealing color change
What are “biologic considerations” during tooth preparation?
- Prevention of damage (adjacent tooth, pulp, soft tissue)
- Conservation of tooth structure (follow anatomy)
- Marginal Integrity
To protect the pulp, use _____ or ______ as a _______.
Air or Water
Coolant
Conservation of tooth structure can be achieved by following the anatomy of the tooth, by maintaining the biological width, and by selecting the appropriate ________.
Margin Design
Whenever possible, the margin of the preparation should be ______.
Supragingival
What are two methods that may be used to check for proper margin adaptation?
- Pig-Tail Explorer (intra oral)
2. Radiograph Evaluation (extra oral)
Of the three designs for axial walls, which two are inappropriate for crown preparation?
Parallel and Divergent
want CONvergent
Why are parallel wells inappropriate for crown preparation?
Parallel walls create friction that makes seating the crown nearly impossible
The total convergence angle of a crown prep should be ____ degrees.
6 (each side with a 3 degree taper)
Which bur should be used during the occlusal reduction?
242.6M
Which bur should be used when creating axial walls for an MCC prep?
The shoulder (facially) should be created with a 702.8 bur The chamfer (lingually) should be created by a 242.6 bur
Molars and premolars have different POWs. When choosing a POW with which to relate the bridge, the molar is preferred over the premolar. Why?
The premolar POW will cause the bridge too look very buccally oriented.
The molar POW will cause the premolar to be slightly over-reduced at the HOC….this is the lesser of two evils
True or False: The first planes of the abutment teeth should be parallel to each other and to the long axis of the molar.
True
For good esthetics, what should the occlusal reduction measure on the facial cusp of an MCC prep?
1.5 mm
For an MCC prep, how wide is the shoulder?
1.2 mm (use 702 bur)
During placement of axial guide grooves for an MCC prep, the finish line is originally placed 0.75mm supragingival. What is the final location of the shoulder and what is its angulation? What tool is used during this step?
120 degrees
0.5mm
Hatchet
What is the problem with a flat occlusal surface?
Under-reduction or Over-reduction
Under-reduction: insufficient space for materials
Over-reduction: Pulp exposure or poor resistance form
For an MCC prep, the finish line design is a _______ with a width of _______ and at a ______ degree angle.
Shoulder
1.2-1.5mm
120
True or False: As long as the abutments have common/parallel paths of withdrawal, the bridge will seat properly.
FALSE: The surrounding teeth need to also be considered. The common angulation may not coincide with teeth surrounding the abutments.
The quality of a preparation that prevents the restoration from being dislodged by forces parallel to the POW is known as _______ form.
Retention
Which mechanical quality is influenced by degree of taper?
Retention form (best retention if 3-5 degrees)
What is resistance form?
Quality of the preparation that will resist lateral forces which tend to displace the restoration in an oblique direction
Which mechanical quality protects a restoration from dis-lodgement during occlusal movements/forces?
Resistance Form
