“The peripheral extension

of a tooth preparation.”

“The terminal

portion of a

prepared tooth.”

BIOLOGICAL Considerations

MECHANICAL Considerations

AESTHETIC Considerations

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

MARGIN PLACEMENT

SUPRAGINGIVAL

MARGINS

SUBGINGIVAL

MARGINS

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.

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.

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.

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.

n.

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.

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.

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 subgingivalextension of the preparation or placement of the margin on dentin rather than on enamel.

I. 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.

ShoulderShoulder bevelSlope shoulder

ShoulderShoulder bevel

Shoulder design with a porcelain labial margin.