To paraphrase one of my favorite people in dentistry, the late Dr. Bob Barkley, "the best dentists help patients fail at the slowest possible speed." Drilling on a tooth never makes it stronger, wouldn't you agree? Would removing dentin ever be beneficial to a tooth or its long-term prognosis?
In treating caries, we remove diseased tooth structure and we replace it in various ways to protect the tooth from further destruction and return it to function. When we recommend a crown for our patients' tooth, we are hoping to extend its useful life and protect it from further breakdown, but we hardly make it stronger! I think we could all agree that clinicians like Dr. Frank Spear and Dr. Gregg Kinzer are examples of experts in the field of restorative dentistry and have lectured extensively on conservative crown preparations simply because of the huge value they place on natural tooth structure. I would propose that neither clinician picks up a handpiece without considering the negative ramifications of what dentin removal does to a tooth.
With that in mind, I'd like to discuss tooth reduction in endodontics. As an endodontist, my practice selects for failing endodontic treatments – I see A LOT more than the average general dentist. After careful examination of this stream of cases, it has become abundantly clear that the vast majority of failing endodontic cases that were previously successful for a long period of time, are failing for structural reasons. They break! They either snap off or suffer vertical root fractures, and the root cause is a serious lack of dentin.
The 54-year-old male patient attached to these images presented for retreatment of #14 and #15, with pain and swelling. Examination revealed that his symptoms were coming from tooth #14. Radiographically, there are findings with both teeth; the CBCT images suggested missed MB2 canals in both and an untreated DB canal in tooth #15. (Fig. 1-4) Here's how I evaluate these teeth and their long-term prognosis:
First, tooth #15. Its endodontic access is bigger than I would make and the furcal floor is somewhat damaged – but all in all, there appears to be sufficient tooth structure to recommend retention. However, the previous canal preparations, particularly in the MB root, are HUGE. (Fig. 5) If this tooth was retreated and any additional tooth structure removed from the root, the chances of a subsequent vertical root fracture are significant. My recommendation is to retreat with an expectation of a five to 10 year outcome. He has deferred treatment for this tooth.
Tooth #14 has the opposite problem. The endodontic access has greatly weakened the tooth since too much of the most valuable dentin has been unnecessarily removed. The canal preparations, however, are reasonable. My recommendation is to retreat with an expectation of a five to 15 year outcome. The largest file in the MB2 canal was a 17/04. (Fig. 6) All symptoms resolved. He will be closely followed over the years to come, and we’ll see what happens with #15! For more information on this topic, stay tuned for my upcoming lecture on canal preparation where I will discuss this more extensively. Glen E. Doyon, DMD, Spear Contributing Author [ www.CMSEndo.com ]