Principles of Tooth Preparation (Pt. I) Flashcards by J L

Anatomy of Preparation

Planar occlusal reduction: ____

Functional and non-functional cusp bevel: ____

Seating
groove: ____

Axial reduction: ____

Finish line: ____

structural durability
structural durability
retention and resistance
retention and resistance
junction between restoration and preparation

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Principles of Tooth Preparation

Biologic
Affects ____

Mechanical
Affects ____ of restoration

Esthetic
Affects ____ of patient

health of oral tissues
integrity and durability
appearance

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I. Biologic Considerations

Prevent ____

damage

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I. Biologic Considerations
Conservation of Tooth Structure

• Use ____ restorations, where possible
• Minimize ____ to maximize remaining tooth structure surrounding pulp
– Sufficient ____ necessary for restorative material
• Amount depends on ____ being used
– Thickness of remaining dentin
• inversely proportional to ____
• Avoid unnecessary apical extension of preparation

partial coverage
reduction
reduction
restorative material
pulpal response

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I. Biologic Considerations
Conservation of Tooth Structure

With periodontally involved tooth, ____ margins preferred

____ extension of preparation results in additional tooth reduction due to decrease in ____ diameter

supragingival
apical
coronal

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I. Biologic Considerations
Avoidance of Overcontouring

• Axial reduction
– Need ____ for development of
good axial contours
– Generally, crown should duplicate ____ of original tooth
• Unless correction of malformed or malposed tooth

insufficient axial reduction > ____ restoration > gingival ____

sufficient space
profile and contours
overcontoured
inflammation

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I. Biologic Considerations
Avoidance of Overcontouring

For ceramo-metal restorations, adequate porcelain thickness is essential for ____ and ____

strength

esthetics

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Once restorations are recontoured, gingival health ____

returns

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I. Biologic Considerations
Margins
• (1)Margin \_\_\_\_ 
• (2)Margin \_\_\_\_ 
• (3)Margin \_\_\_\_

placement
adaptation
geometry

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(1)Margin Placement
Supragingival vs. Subgingival
• Supragingival margins when possible
– Easier to prepare with ____ tissue trauma
– Usually in ____, not cementum or dentin
– Easier to keep ____-free
– Impressions or optical capture more easily made
• less soft tissue damage
– Restorations can be easily evaluated at time of ____ and recall appointments

minimal
enamel
plaque
placement

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(1)Margin Placement
Supragingival vs. Subgingival
• Subgingival margins
– Major etiologic factor in \_\_\_\_ disease 
– Indications
• \_\_\_\_, cervical erosion, or subgingival restorations present
• \_\_\_\_ extends to the gingival crest
• \_\_\_\_ and/or resistance needed
• \_\_\_\_ to hide margin
• Inability to control \_\_\_\_

periodontal
dental caries
proximal contact area
additional retention
esthetics
sensitivity

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(2)Margin Adaptation

Junction between restoration and tooth is always a potential site for ____ caries
More accurately restoration is adapted to tooth, lesser chance of recurrent decay or periodontal disease
Well designed preparation has smooth and even margin
Rough, irregular or 􏰄____􏰅 junctions reduce adaptation accuracy of the restoration

recurrent

stepped

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(2)Margin Adaptation
Time spent obtaining a smooth margin makes the subsequent steps of tissue displacement, impression making, die fabrication, waxing, and finishing much easier and results in a ____-lasting restoration

Smooth margins particularly important when fabricating restorations with ____ (computer-aided design/computer-aided manufacture)

longer

CAD/CAM

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(3)Margin Geometry

• Margin configuration VERY controversial
• Guidelines for acceptable margin design
– Ease of preparation without ____ enamel
– Ease of ____ in impression and on die
– Distinct ____ to which wax pattern can be finished or design terminated
– Sufficient ____ of material
– Conservation of ____

overextension or unsupported
identification
boundary
bulk
tooth structure

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(3)Margin Designs
• (a)\_\_\_\_
• (b)Chamfer with \_\_\_\_ • (c)\_\_\_\_
• (d)Shoulder with\_\_\_\_ • (e)\_\_\_\_ shoulder
• (f)\_\_\_\_ edge

chamfer
bevel
shoulder
bevel
sloped
feather

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(3)Margin Designs (a)Chamfer

• Chamfer finish line
– A design in which the ____ meets the external axial surface at an ____ angle

gingival aspect

obtuse

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(3)Margin Designs (a)Chamfer

• Chamfer margin
– Tapered diamond
with rounded tip
– Hold along ____

path of placement

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(3)Margin Designs (a)Chamfer

Tilting away will create ____ and ____ walls

Tilting toward tooth will ____ and result in excessive ____

undercut
divergent
over-reduce
contour

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(3)Margin Designs (a)Chamfer

• The chamfer should never be prepared wider than ____ the tip of the diamond; otherwise an ____ lip of enamel may result

half

unsupported

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(3)Margin Designs (a)Chamfer

Advantages
Distinct ____, adequate bulk easier to control

Disadvantages
Care to avoid ____ lip of enamel

Indications
____ restorations, lingual margin of metal- ceramic crowns

margin
unsupported
cast metal

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(3)Margin Designs
• Bevel
– A slanting
edge
• May be more suitable for \_\_\_\_

• Objective
– Allow the cast metal margin to be ____ against the prepared tooth structure
• If do not have access to burnish, may be little advantage to ____
– Minimize ____ (??)
– Protect unprepared tooth structure from
____
• Removing ____ enamel

cast restorations
bent or burnished
marginal discrepancy
chipping
unsupported

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(3)Margin Designs
Bevel

Effect of Bevel on Marginal fit at Gingival Margin

If internal cross section of crown is same or < prepared tooth&raquo_space;> ____o bevel decreases marginal discrepancy by ____%

If internal diameter is slightly larger** than prepared tooth&raquo_space;> Beveling increases ____

45
70
marginal discrepancy

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Chamfer with bevel

Advantages:
____ of material, advantages of ____

Disadvantages:
Extends preparation ____

Indications:
____ restorations, lingual margin of ____ crowns

bulk
bevel
apically
cast metal
metal-ceramic

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(3)Margin Designs (c)Shoulder
• Shoulder finish line
– design where the gingival floor meets external axial surfaces at approximately a ____ angle

right

(3)Margin Designs (c)Shoulder • Forms 90-degree angle with unprepared tooth surface – ____ angle may chip • Allows room for ____ • Usually ____ which leads to poor contours or ____

acute porcelain underprepared esthetics

Shoulder Advantages ____ of restorative materia Disadvantages Less ____ of tooth structure Indication ____ margin of metal- ceramic crowns, complete ____ crowns

bulk conservation facial ceramic

Chamfer (1) is more ____ than shoulder (2)

conservative

(3)Margin Designs (d)Shoulder with Bevel • Sometimes recommended for ____ surface of metal ceramic restoration with metal collar • ____ preferred for biologic and esthetic reasons

facial | shoulder or sloped

Shoulder with bevel Advantages ____ of material, advantages of bevel Disadvantages Less ____ of tooth structure, extends preparation ____ Indications Facial margin of ____ crowns

bulk conservation apically metal-ceramic crown

(3) Margin Designs (e) Sloped shoulder • ____ degree sloped shoulder margin • Sometimes used as alternative to ____ degree shoulder • Reduces possibility of leaving ____ enamel but leaves sufficient bulk to allow ____k to knife edge

120 90 unsupported metal framework

Sloped shoulder Advantages ____ of material, advantages of ____ Disadvantages Less ____ of tooth structure Indications ____ margin of metal- ceramic crowns

bulk bevel conservation facial

(3)Margin Designs (f)Feather edge * 􏰄____􏰅prep * Should be ____ because does not provide adequate ____ at the margins * Configuration is difficult to accurately produce and may be hard to read, wax, and locate on die and cast

shoulderless avoided bulk

Feather edge Advantages ____ of tooth structure Disadvantages Does not provide sufficient ____of material Indications ____ involved teeth where diminishing diameter of ____ surface is encountere

conservation bulk periodontally root surface

``` (3)Margin Designs • Research has NOT validated the expectation of enhanced fit being associated with a specific margin design • Selection based on: – ____ of crown – ____requirements – ____ of formation – ____ experience ```

type esthetic ease operator

(3)Margin Designs University of Pennsylvania Preparation ____ Cast metal preparation Circumferential internally ____ with ____ Porcelain fused to metal preparation Circumferential internally ____ All ceramic preparations Circumferential internally ____

finish rounded shoulder bevel rounded shoulder rounded shoulder

I. Biologic Considerations Harmonious Occlusion • Need enough tooth reduction to create sufficient space for functional occlusal scheme • Supraerupted teeth require more ____ to even occlusal plane – May shorten tooth preparation excessively, which may affect ____ – May need ____ treatment – ____ and tooth preparation necessary to develop optimum occlusion

reduction resistance and retention endodontic diagnostic waxing

II. Mechanical Considerations Path of Insertion • Before any tooth structure is cut, need to evaluate path of insertion – Direction in which a prosthesis is placed on the abutment teeth • Especially important with fixed dental prosthesis – multiple paths of insertion must be ____ • A path must be selected to allow margins of retainers to fit against preparation finish lines – with removal of ____tooth structure • Path should not encroach upon ____ or adjacent teeth

parallel minimum pulp

II. Mechanical Considerations Path of Insertion • Generally, path of insertion for crown on posterior tooth in normal alignment parallels ____ of tooth For a tipped tooth, the path of insertion is ____ to the occlusal plane

long axis | perpendicular

(1)Retention Form • The quality o fthe preparation that prevents ____ parallel to the path of placement – Ex. Opening jaw after eating ____ food • Main ____ of failure for crowns and FDP – After ____

dislodgement sticky cause dental caries and porcelain fracture

(1)Retention Form | • External retention is provided by approximation of the restoration to the ____ walls of the preparation

opposting external axial

``` (1)Retention Form • Considerations – (a)Magnitude of ____ forces – (b)____ of tooth preparation – (c)____ of fitting surface of restoration – (d)____ agent ```

dislodging geometry roughness luting

(a)Magnitude of Dislodging Forces • Dislodgement forces along path of insertion ____ compared to seating or tilting forces – ____ beneath connectors – Very ____ foods (greatest removal forces) • Magnitude depends on – ____ of food – ____ and surface texture of restoration

``` small floss sticky stickiness surface area ```

(b)Geometry of Tooth Preparation ``` • Most fixed prostheses depend on ____ form of preparation rather than ____ for retention • Considerations – (1)____ – (2)____ – (3)____ ```

``` geometric adhesion taper surface area stress concentration ```

(b)Geometry of Tooth Preparation (1)Taper • Taper – ____ of two opposing walls of a tooth preparation as viewed in a given plane • The ____ of those planes form the angle of convergence

convergence | extension

(b)Geometry of Tooth Preparation (1)Taper • Theoretically, maximum retention is obtained if tooth has ____ walls – HOWEVER, to avoid undercuts and allow complete seating of the restoration during cementation, the walls must have some ____ • ____ taper is clinically desirable – As taper increases, so does free movement of the restoration » retention will be ____

parallel taper slight reduced

(b)Geometry of Tooth Preparation (1)Taper • Howmuchtaper? – Recommend ____o on each surface which would result in ____o taper (convergence angle) – Use rotary instrument of desired taper held at constant angulation • Do not ____ handpiece to create taper! Evaluate taper ____ AND ____

3 6 tilt mesiodistally buccolingually

(b)Geometry of Tooth Preparation (1)Taper • Undercuts (negative taper) must be eliminated, or it will prevent the restoration from ____ • Viewwith____eye (____cm away) to see all axial walls of preparation with adequate taper

seating one 30

(b)Geometry of Tooth Preparation (1)Taper | • With ____ vision, a preparation that is undercut can appear to have an acceptable degree of ____

binocular | taper

(b)Geometry of Tooth Preparation (1)Taper • Where direct vision not possible, ____ is used • Entire preparation should be visible to one eye from one ____ position • Make an alginate

mirror | fixed

(b)Geometry of Tooth Preparation Fixed Dental Prosthesis • To verify parallel paths of insertion, the image of one preparation is centered in the mirror and then, moved ____ without changing ____ until second preparation is centered

bodily | angulation

(b)Geometry of Tooth Preparation (1)Taper • Grooves may enhance retention by restricting the ____ or insertion Excessively tapered cone has infinite number of ____ along which a crown could be withdrawn.

path of withdrawal | paths

(b)Geometry of Tooth Preparation (2)Surface Area • If a restoration has a limited path of placement, its retention depends on the ____ of its path (____ in sliding contact) – Crowns with tall axial walls are more ____ than short axial walls – Crowns with ____ diameter are more retentive than narrower diameter

length surface area retentive wider

(b)Geometry of Tooth Preparation (2)Surface Area • With all other factors remaining constant, the greater ____ of cement film, greater retention

surface area

(b)Geometry of Tooth Preparation (2)Surface Area • With crowns of equal height, ____ diameter will have greater retention than narrow

wider

(b)Geometry of Tooth Preparation (3)Stress Concentration | • Sharp occlusoaxial line angles should be ____ to minimize stresses which could precipitate retentive failure

rounded

(c)Roughness of Surfaces Being Cemented • Adhesion of dental cements depends on projections of cement into microscopic ____ and ____ on surfaces being joined – prepared tooth surface should not be ____ – Casting should be ____ • However, failure rarely occurs at ____ interface – Do NOT deliberately ____ preparation • roughness can make impression making and waxing more difficult

``` irregularities recesses highly polished air-abraded cement-tooth roughen ```

(d)Type of Luting Agent • Type of luting agent affects ____ • Base luting agent decision on other factors • Data suggests ____ are most retentive – Long term clinical evidence about durability of bond not ____ – Long term studies show deterioration of resin dentin bond in association with ____

retention adhesive resin cements available nanoleakage

Factors influencing retention slide!

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Principles of Tooth Preparation (Pt. I) Flashcards

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