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STATE OF THE ART
At the moment there are no generally accepted standard preparations for posterior composite resin, as strange as that may seem. That is why discussion of form begins with axioms for enamel margins, and a similar set for dentin axioms. It would seem that if all the axioms were sound, and scientifically indisputable, then a consensus of design would emerge.
The reality is that for the next 20 years the majority of restorations will not be on virgin teeth but on teeth already cut to a GV Black form that are being re-restored. So that is one starting point- how do we modify these preps to improve their service with bonded composite?
The second question – what is the ideal form for a virgin teeth- can be explored as a fresh start.
But things are not well in the performance of Class II composites. Clinicians Report in November 2012
researched the safety of conventional Class II box preparations from a review of 800 practitioners and found that 80% of adjacent teeth suffered damage of the proximal surface.
However, a variety of external and internal forms meet these criteria, and each dental school seems to have not only its own preferred form, but also its own preferred instrumentation. Preps are created by round diamonds, fissurotomy diamonds, pear- shaped burs, fissure burs, all over the world.
Our classic training in amalgam, cast gold inlay/onlay method, bonded porcelain inlay /onlay method, suggests forms and instrumentation.
But the goals are different: composite doesn’t need a prep that draws, like indirect forms. It doesn’t need strictly parallel or retentive box forms like amalgam. There is no need to create internal slots and grooves, all the surfaces are adhesive. But one does have to follow strict rules to achieve maximum adhesion to both enamel and dentin substrates.
And one has to use the best products and processes, applied in a diligent and consistent manner, to achieve high level consistent adhesion. That is the meat of this website.
Radically different preps have been proposed by Dr David Clark, an energetic promoter of a completely different approach to cutting and restoring teeth. A critique of these methods is planned on this site, as being a poor balance between conservative removal of tooth structure and lacking an organized scientific basis for margin design, which I begin with.