Achieving Perfect Marginal Integrity in Dental Restorations

Biological Marginal Integrity

For a restoration to survive in the oral cavity, its margins must be perfectly adapted to the finishing line of the preparation. The configuration of the finishing line determines the shape and thickness of the restoration's margin. The termination must be precise and located in the cervical area of the clinical crown's greatest diameter.

Finishing Lines

Bevel or Knife Edge

This is performed with a tapered bur, creating surface wear that covers only the enamel polish.

Advantages

• Good protection of enamel rods.
• Minimal tooth wear.
• Low risk of pulpal aggression.

Disadvantages

• The margin is very thin, which can lead to the deformation of castings.
• The limit is not well-defined.
• Poor visualization in the mouth.
• Risk of over-contoured restorations.

Indications

• Cast crowns.
• Young patients.
• Teeth with minimal wear.
• Teeth with very convex axial surfaces.

Right-Angle Shoulder (Non-Rounded Axiogingival Angle)

The external line angles of the preparation are perpendicular to the long axis of the tooth. It is created using a flat-tipped cylindrical diamond stone with no rounded corners, removing enamel and deepening into the dentin.

Benefits

• Provides increased thickness for the restoration.
• Reduces the risk of casting deformation.
• Creates a well-defined and precise cervical termination limit.

Disadvantages

• Does not allow for a tight, close fit, generating a horizontal plane.
• The right angle can lead to poor adaptation of the restoration.
• Can cause faults during impression-taking and cementation.
• Requires more tooth structure removal.

Indications

• Cast crowns or inlays.
• Metal-ceramic crowns.
• Resin and all-ceramic crowns.

Right-Angle Shoulder (Rounded Axiogingival Angle)

This is similar to the above, but the axiogingival angle is rounded. This feature enhances the sliding of the restoration along the path of placement. It is created using a flat-tipped cylindrical stone with rounded corners.

Chamfer

A concave, extracoronal finishing line created with a flame-shaped diamond bur. It provides an acceptable gingival area, good stress distribution, and a good seal.

Advantages

• Good protection of the enamel rods.
• Provides a good sliding zone.
• Creates a well-defined limit with little tooth wear.

Disadvantages

• The margin has little thickness.
• Deformation of the casting pattern may occur.

Indications

• Cast crowns and inlays.

Deep Chamfer

This is the most commonly used type of chamfer. It is deepened with a smooth, rounded, conical, or cylindrical stone, which generates a larger diameter hollow.

Benefits

• Provides very good thickness for the restorative material.
• Creates a well-defined limit.
• Features a good axiogingival glide angle.

Indications

• All-ceramic crowns.
• Cast metal crowns.