Retention, Resistance, & Convenience Flashcards
What is the retention form:
Design features which lock or retain the restoration and prevent the restoration from coming out
What are the shape of retention form of the internal walls?
What burs create this?
Facial & Lingual Walls may be slightly convergent or straight
- 245 or 330
A smaller isthmus allows for what?
Greater convergence
The larger the isthmus, how does that affect the convergence of your prep
The less your preparation will converge due to the orientation of the enamel rods
What part of the tooth are the retention grooves in?
Are in the Dentin
What bur is used for retention grooves?
1/4 round bur or the tip of a thin tapered diamond bur
Does the retention grooves cut into the axial wall?
No, only facial & lingual walls
How do amalgam bonding resins affect retention
Decreases marginal fracture and increases retention of amalgam
What is resistance form:
Design features which help the restoration and tooth resist fracturing as a result of occlusal forces
Need a minimum of what depth in amalgam restoration
Minimum of 1.5 mm depth starting from the central groove
Require a minimum of what axial depth when removing caries axially
Minimum of 1 to 1.2 mm (bi’s vs molars)
Extend 1/2 mm past the DEJ
What is the number one reason for fracture in amalgam
Isthmus width
Minimal width is 1mm
T or F, Effects of strain and fracture propagation are not cumulative
False, Are cumulative
What is the problem with over-converging the enamel
Will create unsupported enamel and this will fracture away under occlusal strain and create open areas
The 90 degree Cavo-Surface helps do what?
Reduce creep and expansion
