In a recent article, I went over the ideals for restoring teeth in the posterior with direct composite. However, there will be times when direct composite is not the best choice, especially when you start seeing evidence of weakened cusps from a very wide isthmus or from visible cracks in the cusp seen when the old restoration is removed.

Over the years, there has been a lot of controversy about the concept of using bonding of direct composite or inlays to support weakened cusps from within.

The literature does suggest it increases the strength of the tooth, if the study simply looks at the amount of force required to fracture the restored tooth. However, if you search the literature looking for fatigue studies on the restored tooth, what you will find is evidence that ultimately the bond to the cusps will fail, and the tooth returns to the weakened state it started in.

My bias is that when you start seeing cracks undermining cusps, it's not a good indication to use a conventional prep direct composite or inlay, and instead that the cusp should be reduced and covered. For myself, whenever I see cusps that are not well supported by dentin, or if I see cracks within cusps, I will treat those teeth with indirect onlays to achieve the most successful result.

What we are really talking about here is the concept of reinforcement via bonding the pieces together, versus the containment of holding the pieces together by cuspal coverage. Once we onlay the tooth, the strength is now determined by the strength and the durability of the restorative material, not just the bond.


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Commenter's Profile Image Gerald Benjamin
August 13th, 2013
I would like to respectfully disagree with Frank on this subject. It has never made sense to me when I have heard a dentist state that in order to strengthen a tooth, a crown needs to be placed. The worst possible treatment for any tooth (excluding endodontically treated posterior teeth) is the placement of a full crown which removes the only strong material (enamel) from the tooth. The direct resin is the only restorative material used in dentistry that does not require the removal of significant amounts of healthy tooth structure. In the early 2000s Frank questioned the longevity of bond strengths and at that point in time, no one could dispute Frank's skepticism because clinical long term results were unknown. However, in the year 2013, we see few to no clinical degradation of the bond leading to clinical failures. I have veneers, resin and porcelain onlays and direct resins which exceed 20 years of clinical use and most look nearly the same as the day the restorations were bonded to place... The reality is that great isolation and ideal adhesive protocols have allowed indirect restorations to survive despite their predicted failure to long term failure of bonds. My favorite restoration is the direct posterior restoration and for the last 20 years, I have paid little attention to existing fractures within the dentin or enamel or the size of the restoration. Without talent, education, meticulous attention to adhesive principles, isolation, resin placement and precise curing protocols the use of resin is doomed to failure compared to placing crowns. There are many reasons to place indirect restorations and few of them are based on the NEED of the tooth/teeth. The financial rewards for indirect restorations are four times as great as for those dentists that place resins in the average, insurance dependent dental office. If dentists could earn the same hourly production for direct resins as indirect restorations, the number of indirect restorations would decline dramatically and teeth would service a patient for their entire lifetime