pedagogy finish lines in fpd

8/11/2019 Pedagogy Finish Lines in FPd

1/25


2/25

Contents

IntroductionDefinitionsGuidelines for margin preparationTypes of finish lines for full veneercrownsSummary of types of margins

Criteria for selectionConclusionReferences


3/25

IntroductionCharles Henry Land- Porcelain Jacketcrowns, as early as 1880s.Biologic,

Mechanical,Esthetic, andPsychological advantages

of preserving coronal tooth structure werefirst presented.

Specific details later presented by Spaldingand Land in 1904. The shoulder finish line.


4/25

Definitions: GPT -5Margin:

The outer edge of a crown,inlay, onlay, or otherrestoration.The boundary surface of atooth preparation and/orrestoration is termed the finishline or finish curve .

The terminal portion of theprepared tooth.Peripheral extension of a toothpreparation.


5/25

BIOLOGICAL

Considerations

MECHANICALConsiderations

AESTHETICConsiderations

1

Conservation of tooth structure

2 Prevention against damage

3 Harmonious Occlusion

4

Protection against Tooth fracture

5 Considerations affecting future dental

health

i. Axial Reduction

ii. Margin Placement

iii. Margin Adaptation

iv. Margin Geometry

v. Margin Designs

Principles of tooth preparation


6/25

Shillingberg

Marginal Integrity: To prepare a finishline to accommodate a robust marginwith close adaptation to minimize microleakagePreservation of periodontium: To shapethe preparation such that the crown is

not over contoured and its margin isaccessible for optimal oral hygiene.


7/25

Marginal discrepancies disrupt

smooth surface thus vulnerable toplaque accumulation leading to

secondary caries & micro leakageat the margins.


8/25

Guidelines for margindesign

Ease of preparation withoutoverextension or unsupported enamelEase of identification in the impressionand on the die

A distinct boundary to which the waxpattern can be finished

Sufficient bulk of materialConservation of tooth structure


9/25


10/25


11/25

FEATHER-EDGE/ SHOULDERLESS/KNIFE EDGE

ADVANTAGES DISADVANTAGES

Conservation of tooth structure. Fail to provide adequate bulk at

margins (to enable the wax pattern tobe handled without distortion and togive the restoration strength and,when porcelain is used, esthetics).

This margin is used for full veneermetal crowns , small crowns andalready designed margins byprevious dentist.

Over contoured restorations.


12/25


13/25

BEVELADVANTAGES DISADVANTAGES

A beveled margin, under certaincircumstances, is more suitable forcast restoration particularly if aledge or shoulder already exists.

When access forburnishing is limited,there is littleadvantage inbeveling.

The objective in beveling is threefold: To allow the cast metal margin tobe bent or burnished against theprepared tooth structure. To minimize the marginal

discrepancy caused by a completecrown that fails to seat completely. To protect the unprepared toothstructure from chipping (e.g. byremoving unsupported toothenamel).

In cases of gingivalmargins bevelingwould lead to sub-gingival extension ofthe preparation orplacement of the

margin on dentinrather than onenamel.


14/25

CHAMFER

n.


Particularly suitable for castmetal crowns and the metal-only portion of metal-ceramiccrowns.

Tilting it away from the tooth willcreate an undercut; angling ittowards the tooth will lead toover-reduction and loss ofretention.

Distinct and easily identified,provides room for adequate

bulk of material.

Marginal accuracy dependsupon having high quality

diamond and a true runninghand-piece.

Can be placed with precision,although care is needed toavoid leaving a ledge of

unsupported enamel.

Chamfer should never beprepared wider than half the tipof the diamond an

unsupported lip of enamel canresult.


15/25


16/25


17/25


18/25

SHOULDER WITH BEVEL


Recommended for facial surface of ametal-ceramic restoration where ametal collar (as opposed to aporcelain labial margin) is used.

Less preferred toshoulder or sloped-shoulder for biologicand esthetic reasons.

Removes unsupported enamel andallows some finishing of the metal.

Allows improved esthetics because

metal margin can be trimmed down aknife-edge and hidden in the sulcuswithout the need for positioning themargin closer to the epithelialattachment.


19/25

SLOPED SHOULDER


20/25

Placement of margins withrespect to gingival crevice


21/25

Various marginsunder SEM


22/25

Summary of margins


23/25

CRITERIA FOR MARGINSELECTION

ShoulderShoulder bevelSlope shoulder

ShoulderShoulder bevel

Shoulderdesign with aporcelain labialmargin.


24/25

Summary

Various finish lines in FPD arediscussedRight selection of margin type dependsupon the choice of the restoration.Margins are the primary factor indetermining the success of the final

restoration.Right geometry and design places themat the apex of principles of preparation.


25/25

pedagogy finish lines in fpd

Documents