Tooth Preperation Flashcards
What’s the Restorative considerations that dictate placement of margins below the gingiva ?
1) creating adequate resistance and retention form
2) allowing the margin to be placed on sound tooth structure below any decay or existing restoration
3) masking the tooth/ restoration interface in order to mask a color change between the restoration and the tooth
Margins placed deeper than 1 mm disadvantages ?
- greater difficulty in preparing a smooth margin
- Difficult obtaining an accurate impression,
- Difficult in evaluating the marginal fit of the final restoration
These difficulties will hinder future plaque removal and may impinge on the biologic width
Tooth preparation margins that are within the attachment create a biologic width violation (BWV)
What’s the feather edge mean complication? And why ?
Do not provide adequate bulk at the margins the most conversative finish line
Overcontoured restorations because reduction was insufficient to make restorations of adequate thickness within the confines of correct anatomic form
Complication of each of them ?
Tilting instrument away from the tooth
Angling it toward the tooth leads to
Should never be prepared wider than half the tip of the diamond
produces an undercut
excessive convergence and reduction and loss of retention
Unsupported lip of enamel
How much alloy thickness in functional cusps ?
about 1.5 mm over functional cusps
(buccal in the mandible, lingual in the maxilla)
How much alloy thickness in non-functional cusps ?
The less stressed non-functional cusps can be protected with less metal (1 mm)
Too prevent undercuts or excessive convergence during axial reduction how should we deal with handpeace ?
must be maintained at the same angulation
Support by second finger
What’s preperation steps ?
Occlusal depth grooves
Occlusal reduction and functional cusp bevel
Axial alignment grooves
Axial reduction
Finishing and evaluation
Why depth grooves are useful ?
ensure that occlusal reduction generally follows anatomic configuration and thus minimizes the loss of tooth structure while ensuring adequate clearance, as dictated by the mechanical properties of the alloy
Where to Place depth grooves in occlusion ?
in the buccal and lingual developmental grooves and in each triangular ridge
they should extend approximately from the cusp tip to the center of its base
Place depth holes approximately 1 mm deep in the central, mesial, and distal fossae, and connect them so that a channel runs the length of the central groove and extends into the mesial and distal marginal ridge.
The functional cusp bevel is prepared by slanting the rotary instrument at a flatter angle (dashed line) than the cuspal angulation why ?
This ensures the necessary clearance over the functional cusp
What’s the grooves direction on functional and non-functional cusps ?
On the nonfunctional cusp, depth grooves parallel the intended cuspal inclination
on the functional cusp, they should be angled slightly flatter to ensure additional clearance that must be achieved on the functional cusp
Where to place the alignment grooves ?
placed in each buccal and lingual wall
On molars, one alignment groove placed in the center of the wall, and one in each mesial and distal transitional line angle
How much aligment grooves depth gingival ?
Gingivally, the depth of the alignment grooves should therefore be no more than half the width of the tip of the diamond
alignment grooves determine the path of placement of the restoration
Why Unsupported enamel cannot be tolerated on the chamfer margin ?
because it is likely to fracture when the restoration is evaluated or cemented,
which, if undetected, will result in an open margin and premature restoration failure
