Principles of Tooth Prep Flashcards
What are the 5 principles of tooth prep and restoration design?
1) Preservation of tooth structure
2) Retention and resistance form
3) Structural durability of the restoration
4) Marginal integrity
5) Preservation of the periodontium
•Trauma from tooth preparation•Decreased thickness of dentin protection•Remaining dentin thickness (between prepared walls and pulp) key to its protective nature→Hypersensitivity→Pulpal inflammation and necrosis
•Pulpal Insult
•A guide as to how much tooth structure can be removed w/o harming the pulp•Pulp + 1mm minimum surrounding dentin•Retentive features cut no deeper than 1.5mm (axial) -2mm (central fossa)
•Vital core
: reinforcement and protection of remaining tooth structure
•Cuspal Coverage
•Preserves the basic primary axial and occlusal tooth anatomy within the preparation.•Maximal thickness of residual tooth structure surrounding the pulp is retained.
•Morphologic reduction:
•Preparations must be designed to resist dislodging forces.
Resistance and retention form
•The ______ form of the preparation is the most important of the factors under operator control which will determine if a restoration will remain cemented in place.
geometric
Prevents removal along path of insertion•Occurs with sticky foods •(least common problem)•Provided for by: •Two opposing vertical surfaces with minimal convergence
Retention form
_______ hold through the mechanical interlocking of projections of cement into irregularities of the surfaces being joined.Weakest -tension Strongest –compression
Dental Cements
•Prevents restoration dislodgement by apical or oblique forces.•Occlusal forces•Resistance to lateral forces, and not retention along the path of placement, is the greatest determining factor in a crown’s resistance to dislodgement.
Resistance form
- Resistance form is built into a preparation by forming walls to block anticipated movement due to:
- Leverage
- Rotation around a vertical or horizontal axis
Resistance form
What are the 5 factors affecting resistance form?
- Total Occlusal Convergence ( Taper)
- Preparation Wall Length(OC or IC Dimension)
- Tooth Width (FL Dimension) -(Ratio of wall length : tooth width)
- Geometric Form (Limited Path of Insertion)i. Grooves, boxes, vertical planes, pinsa. (Supplemental / internal prep features)ii. Morphologic reduction / pyramidal shape of prep
- Surface Area
:relationship of one wall of a preparation to the long axis of the preparation
Inclination
:the relationship of taper between two opposing walls of a preparation.
Angle of convergence or total occlusal convergence
What is the ideal TOC?
6 degrees
At what TOC is there maximum retention?
5 degrees
•For every 5 degree increase in the total convergence angle, the retention and resistance form may decrease up to _____%.
50%
•Molar tooth preps have ______ TOC than premolars and anterior preps.
greater
Mandibular tooth preps have ______ TOC than max tooth preps
greater
posterior preparations generally require _____ TOC than anterior preparations.
less
What is the clinically acceptable TOC?
10-20 degrees
The greater the height of a prep the _____ the retention of the prep
Greater
Wall length (height of the preparation) should be _____ than the tipping arc of displacement, to prevent displacement of the restoration.
greater
T/F: The preparation with longer walls (a) interferes with the tipping displacement of the restoration better than the short preparation (b).”
True
For every 1 mm increase in preparation length, the retention and resistance form increases up to____.
10%
The shorter the preparation the ____ the taper must be.
less
The longer the preparation, the ______ the taper maybe.
greater
A narrow (smaller diameter) tooth can have _____ resistance than a wider (larger diameter) tooth with same wall length
greater
For adequate R&R form, the height:baseratio should be greater than ______ for all teeth
0.4
What is the minimum height for incisors and premolars?
3 mm
What is the minimum height for molars?
4 mm
What are 3 examples of 2o Auxiliary Retentive Features limits the paths of withdrawal to ONE
Boxes, grooves, and pin holes
________ preparations have increased resistance form (morphologic reduction).•Preserve facio-proximal and linguo-proximal corners (line angles)
Pyramidal
The ______ the surface area, the greater the retention
greater
T/F; Reducing the TOC from 20°to 8°in the cervical 2 mm of the axial walls significantly increased the resistance form.
True
- Casting must be rigid enough not to flex.
- Sufficient tooth structure must be removed to create space for an adequate bulk of restorative material without over-contouring the restoration.
Structural durability of the restoration
What are the 3 prep features that contribute to structurability?
- Occlusal / Incisal Reduction
- Functional Cusp Bevel
- Axial Reduction
_________ provides:
•Adequate occlusal/incisal clearance without excessive removal of tooth structure.
•Uniform restoration thickness
•Parallels the major planes of the tooth (not flat)
•Morphologic Occlusal Reduction
__________ Reduction:
•Allows for adequate thickness of restorative material
•without undue sacrifice of tooth structure
•without over-convergence
•Morphologic Functional Cusp Bevel
_______: creates space for an adequate bulk of metal within the normal axial contours of the tooth.
Axial Reduction
Requirements for successful restoration margins:
- Fit as closely as possible to minimize cement film width (25μ)
- Sufficient strength to withstand forces of mastication (geometry of prep)
- Located where dentist can finish and inspect, and patient can clean
Marginal integrity
•The margin should fit as closely as possible to minimize cement film width_____ μ
(25 μ)
