Margin (Finish line) placement

Finish line of the preparation is the end of tooth preparation.

Finish Line

Studies have supported the use of supra-gingival or equi-gingival finish lines rather than sub-gingival finish line whenever possible to ensure periodontal health

Supra-gingival finish line

v Sub-gingival finish lineHanaa I. Sallam

Hanaa I. Sallam

Advantages of supra-gingival margins:Easily preparedNo soft tissue traumaEasy impressionEasy finishing, easy cleaningEasy evaluation of the preparation margins at the time of placement and at the call appointments

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Rasha Nabil Sami

1-Cervical caries , erosion, abrasion or restoration.

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Hanaa I. Sallam

Proximal contacts extending to the gingival crest.

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Hanaa I. Sallam

To increase the occluso-gingival dimension for better retention and resistance .

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For esthetics in anterior region

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Hanaa I. Sallam

Root sensitivity which cannot be controlled by more conservative procedures (such as application of dentin bonding agents).

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Hanaa I. Sallam

When a subgingival finish line is required, it has been suggested that extension to the epithelial attachment be avoided.

The distance from the epithelial attachment to the crest of the alveolar bone has been described as the Biologic Width. It is normally about 2mm wide, including the epithelial attachment and the connective tissue attachment.

If the margin of a restoration intrudes into this biologic width inflammation will result and osteoclastic activity is stimulated.

*Hanaa I. Sallam

Hanaa I. Sallam

3- Margin AdaptationThe presence of marginal discrepancies in the restoration exposes the luting agent to the oral environmentThe longevity of tooth could be compromised not only by caries but also by periodontal disease.

Clinically acceptable marginal gap values of cast restorations have been reported in the literature to be up to 50-70m A well-designed preparation has a smooth and even margin. Rough, irregular, or "stepped" junctions greatly increase the length of the margin and substantially reduce the adaptation of the restoration

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Hanaa I. Sallam

A : Poor preparation design leading to increased margin length. C: rough, irregular margin will make the fabrication of an accurately fitted restoration almost impossible.

4- Margin Geometry:

.The configuration of the preparation finish line dictates the shape and bulk of restorative material in the margin of the restoration. It also affects both: marginal adaptation and degree of seating of the restoration.

Guidelines for establishing a good finish line1. It should be easily prepared

2- It should be easily identified in both impression and die

3-It should not be overextended cervically

4- It should provide a definite edge to which the wax pattern could be easily adapted and finished

5- Should allow sufficient bulk of material to :

Enable wax pattern handling without distortionProvide sufficient strength at the restoration marginsProvide enough bulk for porcelain (in PFM) to enhance good esthetic.

6- Allow conservation of tooth structure as possible.

7- Ideally whenever possible the margins should be placed in areas where the dentist can finish and inspect them and the patient can clean them.

Types of Gingival finish lines

1-Feather- edge Finish lineIt is mainly indicated for cast metal crowns .Advantages:Less destruction of tooth structure than is necessary for a shoulder or a chamferDose not leave a fragile lip of unsupported enameltooth

Disadvantages:

It is difficult to follow on both tooth and die (location of the margin is difficult to control )Thin margins are difficult to wax and cast , thus being thickened by technicians lead to over-contoured restoration .The margin is weaktooth

2- Chisel edge marginIt is mainly indicated for cast metal crowns .It is a variation of the feather edge finish line and its is formed when there is a large angle between the axial surfaces and the unprepared tooth structure.tooth

Unfortunately, this margin is frequently associated with an excessively tapered preparation

or one in which the axial reduction is not correctly aligned with the long axis of the tooth(tilted teeth)

3-Bevel Finish Line This type is frequently indicated for cast metal restorations, specially if a ledge or shoulder already exists due to caries, cervical erosion or a previous restoration.Its shape forms an obtuse angle with the unprepared axial tooth surfacetooth

Objectives of beveling :1-Allows cast metal margin to be burnished against prepared tooth structure.

2-Protect the unprepared tooth structure from chipping by removing the unsupported enamel.

N.B. If no accessibility for burnishing, there is minimal advantage of this type of finish line

4-Chamfer Finish Line `It is mainly indicated for cast metal crowns .

The instruments which made this FL. Is tapered stone with roundtip .The chamfer should never be prepared wider than half the tip of the diamond; otherwise, an unsupported lip of enamel could result.

tooth

5- Shoulder Finish LineThis type of finish line is usually recommended for the all-ceramic crowns and the facial part of metal-ceramic crowns particularly when the porcelain margin technique is used. It is not used as a finish line for cast metal restorations.

tooth

Advantages :Provides space for proper porcelain bulk thus enhancing resistance to occlusal forces and minimizes stresses which might lead to porcelain fracture.

Facilitates constructing healthy restorations of good contours and maximum esthetics tooth

Disadvantages:The preparation requires destruction of more tooth structure than any other finish line.Some claimed that its sharp 90degree internal line angle would concentrate stress in the tooth and increases its liability to coronal fracture. tooth

6-Rounded ( modified) Shoulder Finish Line It is a modified formof shoulder finish line characterized by a rounded internal angle (gingivo-axial). It is indicated for All- ceramic crown preparationtooth

Advantages:Less stress concentrationSome claimed that its preparation is less destructive

7-Sloped Shoulder Finish Line It is a modification of the classic shoulder finish line being characterized by a 120 as an alternative to the 90.

Its advantage reduce the possibility of leaving unsupported enamel and still leaving sufficient metal thickness to allow for its thinning to a knife edge for good adaptationtooth

8-Shoulder with Bevel Finish Line This type is recommended for the facial surface of a metal-ceramic restoration in those situations where gingival esthetics are not critical and a shoulder is already present either because of destruction by caries or the presence of previous restorations The beveling removes unsupported enamel and may allow finishing of the metal.tooth

4- Margin geometry

**Rasha Nabil Sami

Rasha Nabil Sami