Finish Lines of a Crown Preparation

The margins of crowns preparations in fixed Prosthodontics are place in three positions

  1. Supragingival
  2. Equigingival
  3. Subgingival

Advantages supra-gingival finish line:

  1. It is conducive for better periodontal health
  2. It facilitates accurate impression making
  3. It allows accurate assessment of the fit

Advantages of Equigingival finish line:

  1. It provides better better retention
  2. It is conducive for better periodontal health

Advantages of sub gingival finish line:

  1. It is used when additional retention is needed
  2. It is indicated in anterior zone where aesthetics is a prime consideration
  3. it is used in cervical erosion and root hypersensitivity cases

Finish line in Crown & Bridge Preparation

Shoulder Finish Line

Indications

  1. All ceramic crowns
  2. Porcelain fused to metal crown
  3. Injectable porcelain

Advantages

  1. Good contour of crowns
  2. Improved Aesthetics
  3. Less distortion of crown
  4. Provides adequate bulk to the crown

Disadvantages

  1. Minimal conservative to tooth
  2. Poor marginal adaptation of crown

 

Shoulder with Bevel

Indications

  1. Proximal boxes of onlays and inlays
  2. Labial finish line of metal ceramics
  3. Occlusal shoulder of onlays

Advantages

  1. Provides superior marginal adaptation
  2. It resists distortion
  3. It facilitates removal of unsupported enamel rods

Disadvantages

  1. It requires subgingival extension
  2. Detection of post Cementation Carriers is difficult

 

Chamfer Finish Line

Indications

  1. Cast metal restorations
  2. Labial aspect of metal ceramics

Advantages

  1. Conservative to tooth
  2. Good marginal adaptation of crowns
  3. It provides bulk to crown

Disadvantages

  1. Improper fabrication may result in an unsupported tip of the margin

 

Knife Edge Finish Line

Indications

  1. Young patients
  2. In MOD onlays
  3. Inaccessible areas
  4. Finish line in cementum

Advantages

  1. Conservative to tooth structure
  2. Ideal for marginal adaptation

Disadvantages

  1. It does not provide a distinct finish line
  2. Waxing, polishing, and casting become critical
  3. Gets over-contoured in attempt to obtain bulk in crown

Burs Used to Prepare Different Types of Finish Line of A Crown

 

Different types of burs are used to prepare different type of margins of a crown preparations. They are as follows:

Chamfer Finish Line:

The round and tapered cylinder and torpedo diamonds are used to prepare a chamfer finish line.

 

Shoulder Finish line:

The end cutting burs are used to prepare the shoulder finish line.

 

Radial shoulder:

The radial fissure bar or flat end tapered diamond burs are used for radial shoulder finish line.

 

Groove:

Tapered fissure burs are used to prepare the groove.

 

All ceramic Crowns Finish Line:

Shoulder finish line is the choice of finish line for all ceramic crowns. The wide ledge provides resistance to occlusal forces and minimizes stresses that might lead to fracture of the porcelain.

 

Shoulder with a bevel:

It can be used for the facial finish line of metal ceramic restorations where aesthetics are not critical, for example, in posterior teeth.