What is a Bevel ?
Bevels are the angulation which is made by 2 surfaces of a prepared tooth which is other than 90 degrees. Bevels are given at various angles depending on the type of material used for restoration and the purpose the material serves.
Definition of Bevel: “Any abrupt incline between the 2 surfaces of a prepared tooth or between the cavity wall and the Cavo surface margins in the prepared cavity”
Bevels are the variations which are created during tooth preparation or cavity preparation to help in increased retention and to prevent marginal leakage. It is seen that in Bevels Occlusal cavosurface margin needs to be 40 degrees which seals and protects enamel margins from leakage and the Gingival Cavo surface margin should be 30 degrees to remove the unsupported enamel rods and produce a sliding fit or lap joint useful in burnishing gold.
Types or Classification of Bevels based on the shape and tissue surface involved :
Partial or Ultra Short Bevel:
- Beveling which involves less than 2/3rd of the Enamel thickness. This is not used in Cast restorations except to trim unsupported enamel rods from the cavity borders.
- Entire enamel wall is included in this type of Bevel without involving the Dentin. This bevel is used mostly with Class I alloys specially for type 1 and 2. It is used in Cast Gold restoration
- Entire Enamel and 1/2 Dentin is included in the Bevel preparation. Long Bevel is most frequently used bevel for the first 3 classes of Cast metals. Internal boxed- up resistance and retention features of the preparation are preserved with Long Bevel.
- Complete Enamel and Dentinal walls of the cavity wall or floor are included in this Bevel. It is well reproduced by all four classes of cast alloys, internal resistance and retention features are lost in full bevel. Its use is avoided except in cases where it is impossible to use any other form of bevel .
- It is used only when capping cusps to protect and support them, opposite to an axial cavity wall , on the facial or lingual surface of the tooth, which will have a gingival inclination facially or lingually.
There is another type of Bevel called the Minnesota Bevel or the Reverse Bevel, this bevel as the name suggest is opposite to what the normal bevel is and it is mainly used to improve retention in any cavity preparation
If we do not use functional Cusp Bevel –
- It Can cause a thin area or perforation of the restoration borders
- May result in over contouring and poor occlusion
- Over inclination of the buccal surface will destroy excessive tooth structure reducing retention
Types or Classification of Bevels based on the Surface they are placed on:
Classification of Bevels based on the two factors – Based on the shape and tissue surface involved and Based on the surface they are placed on –
Based on the shape and tissue surface involved:
- Partial or Ultra short bevel
- Short Bevel
- Long Bevel
- Full Bevel
- Counter Bevel
- Reverse / Minnesota Bevel
Based on the surface they are placed on:
- Gingival bevel
- Hollow ground bevel
- Occlusal bevel or Functional cusp bevel
Functions of Gingival bevel:
- Removal of Unsupported Enamel Rods.
- Bevel results in 30° angle at the gingival margin that is burnishable because of its angular design.
- A lap sliding fit is produced at the gingival margin which help in improving the fit of casting in this region.
- Inlay preparations include of two types of bevel Occlusal bevel Gingival bevel
Hollow Ground (concave) Bevel: Hollow ground bevel allows more space for bulk of cast metal, a design feature needed in special preparations to improve material’s castability retention and better resistance to stresses. These bevels are ideal for class IV and V cast materials. This is actually an exaggerated chamfer or a concave beveled shoulder which involves teeth greater than chamfer and less than a beveled shoulder. The buccal slopes of the lingual cusps and the lingual slope of the buccal cusps should be hollow ground to a depth of at least 1 mm.
Functions of Occlusal Bevel:
- Bevels satisfy the requirements for ideal cavity walls.
- They are the flexible extensions of a cavity preparation , allowing the inclusion of surface defects , supplementary grooves , or other areas on the tooth surface.
- Bevels require minimum tooth involvement and do not sacrifice the resistance and retention for the restoration
- Bevels create obtuse-angled marginal tooth structure, which is bulkiest and the strongest configuration of any marginal tooth anatomy, and produce an acute angled marginal cast alloy substance which allows smooth burnishing for alloy.
Functional cusp Bevel:
An integral part of occlusal reduction is the functional cusp bevel. A wide bevel placed on the functional cusp provides space for an adequate bulk of metal in an area of heavy occlusal contact.