Decision-Making and Management of Immature Permanent Teeth with Crown Fractures in Small Animals-A Review

Clinical, radiographic and histological findings of seven teeth from two California sea lions (Zalophus californianus) housed under professional care

Seven teeth extracted from two adult California sea lions (Zalophus californianus) due to pulp exposure and/or to gain access to the mandibular canine teeth were histologically evaluated, and the findings were compared with clinical and radiographic findings. Three teeth were diagnosed with pulp exposure, and two of these showed no radiographic signs of endodontic disease and were histologically vital with prominent coronal pulpitis and a pulp polyp. Another tooth with pulp exposure was showing clinical and radiographic signs of endodontic disease and was histologically confirmed with pulp necrosis. A discoloured incisor tooth was showing radiographic signs of endodontic disease and was also histologically non-vital. Two clinically and radiographically healthy mandibular first premolar teeth and one second incisor tooth had no evidence of pulpitis or pulp necrosis but had pulp canal obliteration. Regular clinical and radiographic follow-up for 5 months to 3 years after the procedures confirmed uneventful healing of the extraction sites, despite initial flap's dehiscence. Although extractions of affected teeth in California sea lions are considered the most practical and beneficial therapy, these are associated with the risks of extensive trauma and anaesthesia and the need to perform these surgical procedures on-site under variable conditions. As California sea lions can be trained to allow conscious dental radiographic re-checks, monitoring teeth with clinical signs of pulp polyp formation and without radiographic signs of endodontic disease warrant further evaluation/reconsideration from previous recommendations. Endodontic treatment of abscessed teeth in California sea lions is reportedly unsuccessful and is discouraged. However, vital pulpectomy could be an alternative treatment to extraction in teeth with pulp polyps as it was found to be highly successful in humans, but the possibility of endodontic failure and need for further treatments should be weighted in the treatment choice.

Periodontal Ligament Cells Are Involved in the Formation of Intracanal Cementum-Like Tissue After Regenerative Endodontic Procedures: A Mouse in situ Model

Regenerative endodontic cell-homing procedures are frequently performed on injured immature teeth diagnosed with pulp necrosis and/or apical periodontitis. The representative histological finding after those procedures is cementum-like tissues filling in the root canal but details of the healing process remain unknown. We investigated that healing process histologically using a mouse in situ model. Regenerative endodontic procedures were experimentally performed on noninfected maxillary first molars of 6-week-old male C57BL/6 mice, after which the healing process was investigated using histology and immunohistochemistry. Immediately after the regenerative endodontic cell-homing procedures, blood clots were seen in the root canals that disappeared over time. On day 7, the blot clot in the root canal was replaced by granulation tissue. From day 14 onward, cementum-like tissues were filled in the root canals, while the amount of fibrous tissue was reduced. Immunohistochemically, positive reactions for periostin were seen in the fibrous tissue in the root canal, the apex, and periodontal ligament cells. On the other hand, positive reactions for nestin were not detected in the root canal. CD31-positive cells with a luminal structure were also observed in the fibrous tissue around the apex and around the newly formed cementum-like tissues in the root canal. Thus, in this study, we have established an in situ mouse model of regenerative endodontic procedures. The results of this study suggest that periodontal ligament cells and vascular endothelial cells grow into the root canals from the apex, replace the blood clots, and participate in the formation of cementum-like tissues with angiogenesis during the healing process of regenerative endodontic procedures.