New Calcified Dental Tissue May Produce Increase in Root Wall Thickness, Root Length Histologic Characterization of Regenerated Tissues in Canal Space After the Revitalization/Revascularization Procedure of Immature Dog Teeth With Apical Periodontitis

Background: Management of the necrotic immature permanent incisor has long been a difficult clinical problem. The Frank technique of multiple applications of calcium hydroxide, although often successful, required multiple appointments and could take years to complete. More recently, the single-appointment mineral trioxide aggregate (MTA) apical plug technique reduced the multiple appointments to 1 but did nothing to encourage additional root maturation. Multiple case reports and a pilot investigation have described an alternative to these techniques that seeks to encourage tissue growth into the canal space after pulp necrosis with the goal of continued root maturation. The technique has met with some clinical success, but the nature of the resultant calcified or canal space soft tissue has not been documented. Objective: To characterize tissues that are produced in a revitalization/revascularization technique. Methods: In this animal study, dog pulp spaces were opened and infected with calculus and sealed until signs of apical periodontitis were present. The teeth were treated with an intracanal medication consisting of 3 antibiotics. The canals were then re-accessed, and a stainless steel file was inserted into the apical tissues to induce bleeding with the intent of filling the canal space with blood. Collagen solution was introduced into the canal, and the tooth was sealed with white MTA and silver amalgam. The teeth were followed up for 3 months. The animals were then sacrificed, and the teeth were harvested for histological analysis. Results/Conclusions: Root growth was noted in the experimental teeth, but the newly calcified tissue was predominantly cementum. Some bone was seen in scattered deposits within the canal space in some samples. This new calcified dental tissue produced an apparent increase in root wall thickness and root length. Reviewer's Comments: It appears from this investigation that calcified tissue produced by revitalization/revascularization is not dentin but rather is predominantly cementum. The tissues appear to arise from apical ingrowth of vital tissues that produce new cementum, some bone, and periodontal ligament within the canal space. In a perfect world, the new laid-down calcific material would be normal dentin that would provide increased root strength and lead to apical maturation as occurs in normally developing vital teeth. As a consequence of finding that cementum is the tissue being deposited, the investigators pose 2 clinically relevant questions. (1) Does the thickened cementum provide the required structural root strength that would occur when roots mature normally? (2) How can a tooth treated by revitalization/revascularization technique be managed should it become infected a second time? This well-executed investigation can't answer these questions, but it provides the foundation for these questions to be investigated. (Reviewer-Michael J. Casas, DDS).