Principles of Tooth Preparations Flashcards
What are the principles of tooth design and restoration design?
- Preservation of tooth structure
- Retention form
- Resistance form
- Added preparation features
- Marginal integrity
- Structural durability of the restoration
- Preservation of the periodontium
A crown preparation is an __________ surgical procedure
irreversible
What are the biological factors to consider for a crown prep?
-Dental Pulp
-Gingival Tissues
-Adjacent teeth
What kind of injuries can occur from a crown prep?
-Mechanical damage
-Temperature damage
-Chemical damage
-Bacterial damage
What is important to know about the pulp during a crown prep?
-Any time a bur touches a tooth, the pulp is
stimulated to respond.
-A crown preparation “traumatizes” the pulp
What are the responses of the pulp to a crown prep?
-Most pulps respond with a healthy healing response
-Some pulps respond by dying (pulpal necrosis)
-Some remain hypersensitive with lingering pulpal inflammation
Why can the pulp be damaged during a crown prep?
-Decreased thickness of dentin remaining between prepared walls and pulp
-Heat transferred to tooth during preparation
Leave at minimum ____mm of dentin surrounding pulp/vital core
1mm
If there are risks like killing the pulp, why do we prepare teeth for crowns?
-Esthetics
-Prevention of catastrophic fracturing
-Protection of Root Canal Teeth
-Make tooth stronger
What must we balance for a crown prep?
-Unnecessary destruction of sound tooth structure
-Preservation of the structural integrity of the remaining tooth structure
VERSUS
-Mechanical requirements the patient needs
-Esthetic requirements the patient desires
When preparing a tooth for a crown in a conservative manner, the operator allows for a ___________ Reduction.
Morphological
What is morphological reduction?
Preservation of the basic primary tooth anatomy within the preparation (axial wall and occlusal anatomy)
What does morphological reduction of a crown prep allow for?
-Leaves the maximum thickness of residual tooth structure surrounding the pulp
-Also, leaves anti-rotational features, retentive and resistive features in the tooth preparations
As we create our crown preparation, we need to form the tooth utilizing geometric form criteria we call:
Retention
Resistance
What is retention?
Prevention of removal along the path of insertion
When does retention of a crown usually fail?
patient eating sticky foods
How is retention created?
-two opposing vertical surfaces with converging surfaces held to within certain parameters
- cements which offer frictional resistance to dislodgement (shear stress aiding in retention)
- mechanical factors such as Dental cements hold through mechanical interlocking of projections of cement into irregularities
What is resistance?
-Prevention of restoration being dislodged by apical or oblique forces
What is the reason for issues with resistance?
occlusal forces
_________ is the greatest determining factor in a crown’s dislodgment
Resistance
-Resistance is also aimed to oppose lateral forces which are not along the…
path of insertion
How is resistance build into a prep?
forming walls to block anticipated movement due to:
-Leverage
-Rotation (either vertically or horizontally)
What factors can affect the Resistance form of a tooth preparation?
-Total Occlusal Convergence (TOC)
-Preparation wall length
-Tooth Width after preparation
-Geometric forms (Grooves, Boxes, Vertical Planes, Pins, Morphological reduction)
-Surface area of the tooth preparation
What is total occlusal convergence?
the angle of convergence of taper between two opposing walls of a tooth preparation
What is inclination?
the angle of convergence of taper of one wall of a preparation in relationship to the long axis of the preparation
What is the ideal total occlusal convergence (TOC)?
6 degrees
A tapered diamond bur will place a ______ degree converging angle to a tooth wall if the shank of the bur is held parallel to the intended path of insertion
2 or 3
Two opposing surfaces, each with 3 degree taper, addtogether for an overall TOC of ___ degrees
6