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This retrospective study evaluated the frequency of development of root resorption in dental trauma cases involving supporting tissue. For 249 traumatized teeth of 125 patients aged between 7 and 51 years, we collected data on the gender and age of the patient, the teeth involved, the type of trauma, and the period between dental injury and initial examination. Radiographic parameters examined in relation to root resorption included the presence of inflammatory external root resorption, internal root resorption, replacement resorption, and canal calcification. Data were analyzed by chi-squared test, Fisher's exact test, and mult iple logistic regression (P < 0.05). The results indicated that there was a significant relationship between the period from the date of injury until initial examination and the occurrence of inflammatory external resorption (P = 0.0199), as well as the type of injury (P = 0.0406). Furthermore, external resorption was most frequently associated with intrusive luxation (92.8%), followed by avulsion (89.0%), lateral luxation (80.2%), and extrusive luxation (77.4%). Among the types of dental injury, replacement resorption was observed more frequently in cases of avulsion (87.2%). The only factor that was significantly associated with this type of resorption was the type of injury (P < 0.0001). Root resorption is observed more frequently and its risk of development is higher in cases of severe trauma, especially avulsion and intrusive luxation. (J Oral Sci 57, 73-78, 2015)

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Background: The aim of this study was to investigate the prevalence of the middle mesial canal (MMC) and radix entomolaris (RE) in mandibular rst permanent molars in a western Chinese population using cone-beam computed tomography (CBCT). Methods: A total of 1174 CBCT images of the mandibular rst molars were collected from West China Hospital of Stomatology, Sichuan University. The following information was recorded and evaluated: the detection rate and location of the MMC and RE, the curvature of the RE, the canal con guration and bilateral symmetry. Results: The detection rates of the MMC and RE were 3.41% and 25.04%, respectively, as calculated by individuals, and 1.79% and 22.15%, respectively, as calculated by total teeth. The average curvature in the buccolingual (BL) orientation (40.63±14.3 9°) was signi cantly larger than that in the mesiodistal (MD)orientation (17.64±7.8 2°) (p<0.05). Of 587 patients, 71.72% (421/587) had bilateral symmetry according to the root canal morphology. The incidence of three-rooted mandibular rst molars was higher in males than in females, while the incidence of two-rooted mandibular rst molars was higher in females than in males. Conclusions: Our results showed that the RE could be detected in almost 1/4 of the western Chinese population; thus, RE detection requires special attention and careful assessment in endodontic treatment.

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