tooth prep Flashcards
principles of tooth prep
3 broad categories
1) biologic considerations
- health of oral tissues
2) mechanical considerations
- affects integrity and durability of restoration
3) aesthetic considerations
points to cover under biologic considerations of tooth prep
1) prevention of damage during tooth prep
- dont damage adjacent teeth
- retract soft tissues carefully
- pulp can be affected by extreme temperatures, certain dental materials (chemical), bacterial action
2) conservation of tooth structure
- remaining dentine thickness
- minimum TOC
- choose margin design that is conservative
- avoid unnecessary apical extension of prep
3) if there is improper tooth prep, it can affect future dental health
- insufficient axial reduction results in overcontoured restos that hinder plaque control, result in perio
- for posterior teeth with furcation involvement, can do fluting to follow the contours of furcations to aid in cleaning
- subg margins
points under mechanical consideratins of tooth prep
1) support & stability
- see amount of remaining tooth structure available to support an extra coronal restoration
- might need foundation restorations to re establish missing tooth structure and provide support and structural foundation for crowns
- need for CL?
2) resistance & retention form
5 factors affecting retention & resistance form:
- magnitude & direction of dislodging forces
- geometry of tooth prep
- roughness of internal surface of restoration (air abrading with 50 microns alumina)
- material being cemented (base metal more retentive than noble alloy)
- film thickness & properties of luting agent
3) prevent deformation
- alloy selection: restoration must have sufficient strength to prevent permanent deformation during function (type I & II gold alloys are ok for intracoronal restos but too soft for crowns)
- need to have adequate tooth reduction to have sufficient bulk to withstand occlusal forces
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what should the occlusal-cervical: facio-lingual ratio be
2:5 (0.4)
to give sufficient resistance if the TOC is <24 degrees
where can cohesive failure occur when the crown is loaded
can occur through the cement layer when induced stresses are greater than the strength of the luting agent
- such stresses are not uniform but concentrated at the junction of the axial & occlusal surfaces
what is circumferential form
the pyramidal form with corners, to increase resistance
- opposite of circular preps bc circularpreps lack anti rotation features and should be avoided
