WHAT IS THE BEST TYPE OF BEVEL TO ACHIEVE DURABILITY IN OUR RESTORATIONS?
In any restoration, the weakest link can be found on the margin between the restorative material and the tooth. That is why there is a need to prepare and design the cavosurface properly, so, that the tooth and the restoration may create a favorable relationship as one structure. This can be accomplished through the creation of beveling.
Beveling, if you remember, is defined as any abrupt incline between 2 surfaces of a prepared tooth or between the cavity wall and the cavosurface margins on the prepared tooth. Bevels have different variations in regards to the intended cavity preparation designs. They do provide several functions that when done correctly can give benefits to the success of our restorations, such as the following:
➢ Bevels improve the retention of the restorative material and
➢ Prevents marginal leakages in the restoration.
➢ Considered as flexible extensions in tooth preparation which involves grooves, surface defects and other areas of tooth surfaces which only requires minimal reduction that doesn't sacrifice the resistance and retention of the restoration.
➢ Used in cosmetic procedures to create seamless repairs and restorations.
Considering their actual importance, we often forget the type of bevel we should be preparing in order to really benefit from its usefulness when we do our cavity preparation, so, on this post, let's have a review on the different types of bevels, how it's properly prepared and its indications.
PARTIAL OR ULTRA SHORT BEVEL
➢This type of preparation involves only 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.
➢ This preparation requires the entire enamel wall without involving the Dentin.
➢ This bevel is used mostly with Class I alloys specially for type 1 and 2.
➢ This preparation includes the entire enamel and 1/2 Dentin in the 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.
➢ This type of bevel complete Enamel and Dentinal walls of the cavity wall or floor.
➢ It is well reproduced by all four classes of cast alloys, however, the internal resistance and retention features are lost on this type of 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.
HOLLOW GROUND OR CONCAVE BEVEL
➢ This bevel allows more space for bulk of cast metal during crown preparation. A design feature needed in special preparations to improve material's castability retention and better resistance to stresses.
➢ This bevel is ideal for class IV and V casting materials.
➢ This is actually an exaggerated chamfer or a concave bevelled shoulder which involves teeth greater than chamfer and less than a bevelled shoulder. The buccal slopes of the lingual cusps and the lingual slope of the buccal cusps should be hellew ground to a d
➢ It is placed at the dentinal portion of the cervical wall towards the axiogingival line angle.
➢ This type of beveling at gingival wall will prevent tipping movements.
➢ The hydrostatic pressure during cementing a cast restoration can produce a rotational displacement of the castings with flat gingival walls. This effect is resisted by the reverse bevel resulting in even seating of the cast restoration.•
➢ It is given on the labial shoulder of metal ceramic crowns to effectively improve the esthetics at the margin.
➢ This type of preparation removes most of all unsupported enamel rods.
➢ It is mostly used in Inlay or onlay preparations,
➢ The bevel results a 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 on this region.
➢ Occlusal Bevels creates an obtuse angled marginal tooth structure, which is the bulkiest and the strongest configuration of marginal tooth anatomy to be subjected to resist stress. Thus, making the produced substance amenable to burnishing.
➢ In wider cavities, and in deeper ones, they are extended to improve the taper. This design employs the principle of the cone to provide a snug fit of the casting against the surrounding walls of the preparation.
We often focus ourselves on big considerations when we are doing tooth preparations and forget about these little nuances that are actually critical in ensuring that our restorations don't really break or fracture such as our curing time and techniques and these beveling that supposedly second in our nature to do when we are doing the work. As conservation of tooth structure while maximizing the retention is the main objective of beveling, it is important that we do take note on these things as we implement our restorative treatment plan. It is in improving the relationship of the margin of the restoration and the tooth that our restorations can last longer , improves its quality and can prevent further damaging the tooth. These factors are actually the big considerations that our patients expect us to deliver at the end of the day...that is the longevity of their restoration they dearly paid for.
Dr. Bryan Anduiza - Writer
Dr. Mary Jean Villanueva - Editor