1/25: Class I and Class V Prep. Fundamentals Flashcards
Having a means for isolation of the site does what three things?
- Visibility
- Access
- Moisture control (especially when restoring composite resin)
What are 4 principles of isolation?
- Rubber dam (gold standard)
- Retraction cord
- Cotton rolls
- Isovac
All undermined enamel must be ________ from all margins
Removed
What is undermined enamel?
Enamel that is not supported by dentin under it
*Dentin MUST be supported by all surface enamel
Margins should be ______ degrees at the cavosurface on all axial surfaces
90*
On the occlusal surface, margins may be slightly _______ in some areas, but must NEVER be ________ anywhere on the tooth
obtuse; acute
*enamel would break
Ideal preparations are ______ to _______ into the dentin
0.2mm to 0.5mm
*must prepare through the ENTIRE enamel layer
*in a live patient, this is determined by caries
A prep of 0.2mm to 0.5mm into the dentin means that?
Different depths in different places on the tooth
*it will depend on the thickness of the enamel in the area
What does retention form mean?
Holds a restoration in a tooth (RETAINS the restoration)
Amalgam doesn’t bond to _______
Tooth structure
Smaller amalgams are held in by _____________ if no walls can converge
Converging walls and/or by retention grooves
What are elements in the design of a tooth preparation that will help both restoration and tooth resist fracturing?
Resistance form
What makes the tooth less likely to fracture?
- Maintaining as much tooth structure as possible
- Rounding internal line angle on a preparation (a little bit)
Preparing to PROPER DEPTH prevents ___________ in the restoration
Weakness (resists fractures)
- NEVER leave enamel on the floor of an amalgam preparation
- NEVER leave a partial-depth ledge on the enamel wall of an occlusal preparation like a class I amalgam
Avoid leaving _________ under an amalgam that is subject to occlusal stress
Sharp external line angles
- This could result in fracture of the RESTORATION
ex: axial wall of class II prep
What makes a restoration less likely to fracture?
- Having some areas on the floor of a multi-surface preparation that are perpendicular to occlusal forces
- Smoothly rounding outline forms
What classification is a buccal pit amalgam?
Class I
*NOT a class V desite being on axial surface
Where does a class I buccal pit amalgam occur?
2/3 of molar tooth
What does a class I buccal pit restoration restore?
Developmental pit
The walls at the terminal ends of the buccal and lingual grooves ______ _______ degrees
Diverge 3 degrees
Walls in the isthmus areas ___________ on each side of the preparation
Converge 3 degrees
Isthmus width is _______ minimum
1mm
Walls adjacent to marginal ridges ____________
Diverge 3 degrees
_________ the mesial or distal wall adjacent to the marginal ridge leaves _________ for the ridge in this area
Diverging; dentin support
What is the occlusal amalgam depth?
.2mm inside dentino-enamel junction
*plastic molars: 2mm total
*plastic premolars: 1.5mm total
________ the wall adjacent to the marginal ridge risks ______________ for the marginal ridge
Converging; destruction of the dentin support
What happens when wall converges where it should diverge?
Marginal ridge is weak
What happens when wall diverges too much?
Amalgam at margin would be weak
How do you avoid an off-axis preparation?
Enter teeth parallel to the long axis of the tooth crown not the patient
Bur inclines more mesially in the ________ and more distally in the __________ the further posteriorly we go, due to the ____________
Mandible; maxilla; curve of spee
Bur inclines more lingually in the ________ and more buccally in the __________ the further posteriorly we go, due to the ____________
Mandible; maxilla; curve of wilson
What do angular outline form cause?
Areas of stress concentration, fracturing amlgam
At ______mm of depth on an ordinary molar, the bur has/has not penetrated into dentin
1.5mm; has not
What kind of prep do 245 burs cut?
Undercut prep with ROUNDED internal line angles
What are the measurements of a 245 bur?
3mm top to bottom, half of the head is 1 1/2 mm and 2/3 the head is 2 mm
Where are retention grooves located?
Always in dentin, just inside the D.E.J even when axial wall is deeper than ideal due to caries
