Textbook Ch. 09: Principles of Tooth Preps Flashcards
What are the 5 Principles of Sound Preparation Design?
Preservation of Tooth Structure Retention and Resistance Structural durability Marginal integrity Preservation of the periodontium
How much tooth must be removed for an MOD onlay
1.5 mm
Why is retention and resistance so important?
Because there are no biologically compatible adhesives strong enough to withstand the forces of mastication by chemical adhesion alone
What does Retention prevent
Displacement of the crown via the path of insertion
What does Resistance prevent
Dislodgement of the crown by apical or oblique forces
And any movement under occlusal forces
What is the essential element of retention?
Two opposing vertical surfaces
Do the vertical surfaces have to be internal walls?
No, they can be external
What happens to retention as the taper angle increases?
It decreases
Why can’t the taper be perfectly perpendicular and parallel?
It is an unrealistic expectation
In the occlusal direction, interior vertical walls must __________ and exterior walls must __________ . (Diverge/Converge)
Interior = Diverge Exterior = Converge
What is considered the optimal range for taper angles
2.5-6.5 degrees
When taper angles raise above this threshold, stress concentration increases sharply
20 degrees
What is the minimum taper angle estimated to be required in order to prevent any undercuts?
12 degrees
How can you improve retention in regards to the number of paths by which a crown can be removed?
Retention improves by limiting the number of paths, ideally there should only be one way on and off
How does occlusogingival length relate to retention?
Longer preps have more surface area by which to provide retention
