2021 年 12 巻 1 号 p. 40-44
Aims: The mandibular first molar is an important tooth that is the key to occlusion. However, since it is among the earlier permanent teeth to erupt, it often requires dental treatment such as root canal treatment. The success rate of root canal treatment is by no means high, so there is a need to consider and address the underlying causes. The mandibular first molar is known to sometimes have an additional distolingual root (DLR) called the radix entomolaris, and we have previously clarified the prevalence of this root in Japanese people and the prevalence in treated teeth. The purpose of the present study was to clarify the causes of apical lesions in DLRs.
Material and Methods: The subjects were 228 patients who had cone-beam computed tomography (CBCT) scans during the period from February 2019 to July 2020. Data on 70 three-rooted mandibular first molars with a separate DLR in which the whole tooth was visible on CBCT were sequentially extracted. The number of three-rooted mandibular first molars with a separate DLR, the root canal treatment status, and the presence or otherwise of root apical region radiolucency were recorded, and the prevalence of DLR and the causes of apical lesions were analyzed.
Result: The prevalence of DLR in the present study was 30.7%. The proportion of three-rooted mandibular first molars with a separate DLR that had undergone root canal treatment was 42.9%, and the CBCT findings showed radiolucency in the root apical region in 31.4% of these. The success rate in teeth that had undergone root canal treatment was 26.7%, and the rate of failure, in which root apical region radiolucency was found, was 73.3%. The breakdown of failures showed that the root canal was overlooked in 36.4% of cases, with zipping/ledging/perforation in 63.6% of cases, and broken instruments in 0% of cases. The results of the analysis showed that there was a significantly greater proportion of overlooked root canals with root apical region radiolucency than with no root apical radiolucency (p<0.01). With teeth that had undergone root canal treatment, root apical radiolucency was significantly more common in teeth with zipping/ledging/perforation (p<0.01).
Conclusions: The results showed that the success rate of root canal treatment of three-rooted mandibular first molars with a separate DLR in Japanese people was 26.7%. Overlooking the DLR and zipping/ledging/perforation were shown to be causes of apical lesions.