GINGIVAL FINISH LINES OF CROWNS & BRIDGES

Sana Mateen Munshi

OUTLINE (Focusing on TYPES)

Introduction

Importance

Precautions

Types of margin placement and design

Criteria for selection of margin design

FINISHING LINE (RESTORATIVE MARGIN DESIGN)

“The peripheral extension of a tooth preparation.”

“The terminal portion of a prepared tooth.”

GPT

IMPORTANCE ???

Disrupt smooth surface thus vulnerable to plaque accumalation

leading to secondary caries & microleakage at the margins.

MARGINAL DISCREPENCIES!!!

AESTHETIC FAILURE!!!

INADEQUATE MARGINS….

MAPPING ……

BIOLOGICAL

Considerations

MECHANICAL

Considerations

AESTHETIC

Considerations

P R I N C I P L E S O F TO OT H P R E PA R AT I O N1

• 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

PRECAUTIONS

USE ROTARY INSTRUMENTS WITH CAUSTION!

Conservation of tooth structure!

Check Position of bur!

Unsupported enamel should be removed!!

PROPERLY SEATED- MINIMAL MARGINAL GAP WIDTHS!!

MARGIN PLACEMENT

SUPRAGINGIVAL MARGINS

SUBGINGIVALMARGINS

Biological width violation depends more on margin placement than on margin design

SUPRAGINGIVAL MARGIN (IDEAL) Easier to prepare accurately

without trauma to the soft tissues.

Usually situated on hard enamel.

They can be easily finished.

They are more easily kept clean.

Impressions are more easily made, with less potential for soft tissue damage.

Restorations can be easily evaluated at recall appointments.

SUBG

INGI

VAL M

ARGI

N

Dental caries, cervical erosion, or restorations extend sub-gingivally, and a crown lengthening procedure is not indicated.

The proximal contact area extends to the gingival crest.

Additional retention is needed.

The margin of metal ceramic crown is to be hidden behind the labiogingival crest

It is also used to produce a cervical crown ferrule on endodontically treated tooth.

Root sensitivity cannot be controlled by more conservative procedures, such as the application of dentin bonding agents.

Modification of the axial contour is indicated.

BASICS

FEATHER-EDGE/ SHOULDERLESS/ KNIFE EDGE:

ADVANTAGES DISADVANTAGES

Conservation of tooth structure.

Fail to provide adequate bulk at margins (to enable the wax pattern to be handled without distortion and to give the restoration strength and, when porcelain is used, esthetics).

This margin is used for full veneer metal crowns , small crowns and already designed margins by previous dentist.

Over contoured restorations.

SHOULDER MARGIN / BUTT JOINT:

ADVANTAGES DISADVANTAGES

Allows room for porcelain recommended for facial part of the metal ceramic crowns.

An acute angle is likely to chip. Placement of margin deep into the gingival sulcus.

It is less conservative of tooth structure.

It should form a 90-degree angle with the unprepared tooth surface.

CHAMPER MARGIN:CHAMPER: A finishing design line for crown preparation which makes an obtuse angle between the axial wall of the tooth surface and the prepared margin.

ADVANTAGES DISADVANTAGES

Particularly suitable for cast metal crowns and the metal-only portion of metal-ceramic crowns.

Tilting it away from the tooth will create an undercut; angling it towards the tooth will lead to over-reduction and loss of retention.

Distinct and easily identified, provides room for adequate bulk of material.

Marginal accuracy depends upon having high quality diamond and a true running hand-piece.

Can be placed with precision, although care is needed to avoid leaving a ledge of unsupported enamel.

Chamfer should never be prepared wider than half the tip of the diamond an unsupported lip of enamel can result.

SHOULDER MARGIN Cont’d

A 120-degree sloped shoulder margin is used as an alternative to the 90-degree shoulderfor the facial margin of a metal-ceramic crown. The sloped shoulder reduces the possibility of leaving unsupported enamel and yet leaves sufficient bulk to allow thinning of the metal framework to a knife-edge for acceptable esthetics

SHOULDER BEVEL MARGIN:

ADVANTAGES DISADVANTAGES

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

Less preferred to shoulder or sloped- shoulder for biologic and esthetic reasons.

Removes unsupported enamel and allows some finishing of the metal.

Allows improved esthetics because metal margin can be trimmed down a knife-edge and hidden in the sulcus without the need for positioning the margin closer to the epithelial attachment.

BEVEL MARGIN:ADVANTAGES DISADVANTAGES

A beveled margin, under certain circumstances, is more suitable for cast restoration particularly if a ledge or shoulder already exists.

When access for burnishing is limited, there is little advantage in beveling.

The objective in beveling is three fold:•To allow the cast metal margin to be bent or burnished against the prepared tooth structure.•To minimize the marginal discrepancy caused by a complete crown that fails to seat completely.•To protect the unprepared tooth structure from chipping (e.g. by removing unsupported tooth enamel).

In cases of gingival margins beveling would lead to subgingival extension of the preparation or placement of the margin on dentin rather than on enamel.

MARGIN DESIGNS SUMMARY

STEPS OF CROWN PREPARATIONI. Guiding grooves or depth orientation grooves (on

both facial and incisal surfaces).

II. Labial reduction (first gingival third and then incisal third).

III. Incisal or occlusal reduction (if required).

IV. Proximal reduction (not beyond contacts).

V. Lingual reduction (enhances mechanical retention and increases surface area for bonding).

VI. Finishing of all prepared surfaces.

The selected margin should provide a predictable level of marginal integrity.

To minimize plaque accumulation, the selected margin should present smooth materials to the gingival sulcus.

Margin should also must provide acceptable esthetics.

CRITERIA FOR MARGIN SELECTION

ShoulderShoulder bevelSlope shoulder

ShoulderShoulder bevel

Shoulder design with a porcelain labial margin.