In a recent retrospective study assessing the clinical outcomes of 24 cases, it was reported that targeted endodontic microsurgery had a 91.7% success rate in a short-term assessment of 1 year.30 However, long-term investigations that reveal the prognosis of targeted endodontic microsurgery are still needed. To ensure long-term prognosis, it is crucial to consider not only the biological aspects but also the biomechanical aspects of endodontic microsurgery. Therefore, maximum von-Mises stress and tooth displacement values of targeted endodontic microsurgery were analyzed through a finite element study before the findings of long-term follow-up studies.
This study simulated two surgical conditions: endodontic microsurgery, which produces a horizontal resection pattern, and targeted endodontic microsurgery, which generates a round resection pattern. As a result, these different surgical situations had a minor impact on the biomechanical responses of the resected tooth.
Concerning the maximum von-Mises stress on the bone, the horizontal resection pattern following endodontic microsurgery exhibited a lower stress value compared with the round resection pattern that resulted from targeted endodontic microsurgery. The reason could be that exactly 90º of horizontal cutting perpendicular to the root axis was simulated in endodontic microsurgery. However, in clinical situations, it is sometimes impossible to obtain an accurate 90º angulation of the horizontal cut using a bur. On the other hand, targeted endodontic microsurgery provides precise perpendicular cutting with the aid of a digitally planned surgical guide.16,31,32 Moreover, in a study comparing a surgical simulation between endodontic microsurgery and targeted endodontic surgery conducted by Hawkins et al.10, it was reported that targeted endodontic microsurgery provides a bevel angle more closely approaching zero degrees. In this study, it was observed that the maximum stress value of targeted endodontic microsurgery was lower than the control model, indicating an acceptable stress distribution on the bone. Moreover, bone grafting demonstrated greater favorable stress distribution on the alveolar bone.
The pattern of the remaining root apex following root-end resection influences the biomechanical response of the resected tooth.20 Therefore, in this study, we compared the stress distribution behaviors at the root apex between the horizontal and round resection patterns following two different surgical techniques. The results of the study showed that both patterns of resection induced lower stress distribution at the root apex compared to the control model. Although using a trephine bur to perform an apical resection resulted in a round resection pattern in the apical region of the resected tooth, the maximum stress value did not significantly differ from that obtained with a horizontal resection. The reason for this finding could be that both types of resections were conducted in a perpendicular plane. This behavior was also observed in previous studies where cutting in a perpendicular plane to the long axis of the tooth was related to positive biomechanical outcomes.18–20
Interestingly, using bone grafting, the maximum von-Mises stresses at the root apex were significantly increased in both patterns of resection, where round resection presented with a slightly more favorable outcome compared with horizontal resection. However, no bone resorption was suggested with both studied conditions as the micro-strain values were within the physiologic limit.33
Another important factor associated with the long-term prognosis of the endodontic surgery is the occurrence of clinical tooth mobility following apical root resection. Perlitsh34 reported the capacity of the remaining attachment apparatus to reverse existing clinical tooth mobility, determined by the amount of remaining alveolar bone support. Therefore, in this study, maximum tooth displacement values were also analyzed to reproduce clinical tooth mobility. As a result, both horizontal and round resection patterns following respective surgical protocols exhibited similar displacement values in comparison with the control model. The explanation for this finding could be the remaining sufficient amount of residual supporting alveolar bone in both surgical settings.
von Arx et al.35 stated the association between the diameter of bony defects in the periapical region and the clinical outcomes of endodontic surgery. Furthermore, in one prospective study regarding the clinical outcomes of endodontic microsurgery, it was reported that a positive clinical outcome can be expected with a residual of more than 3 mm of buccal bone height following the osteotomy.36 The findings of this FEA study indicated the ability of the remaining supporting tissue in preventing future clinical tooth mobility, supporting those previous findings.
In this FEA study, all the structures involved in the analysis were considered to be homogenous, isotropic, and linear. Moreover, the simulation of different structures, including tooth morphology, periodontal conditions, and endodontic procedures, could not exactly reflect real clinical situations. In this study, although the analysis was performed only with oblique occlusal loading, further studies with horizontal or vertical loadings are necessary to predict the biomechanical response of the resected tooth after targeted endodontic microsurgery.