Objectives This study investigated the prevalence and characteristics of external cervical resorption (ECR) regarding sex, age, tooth, stages of progression, and portal of entry, using cone-beam computed tomography (CBCT) scans. Materials and Methods CBCT scans of 1,313 patients from a Brazilian subpopulation comprising 883 female and 430 male patients (mean age, 55.2 years), acquired using a PreXion 3D CBCT unit, were evaluated. All permanent teeth included in the scans were evaluated for the presence of ECR according to the 3-dimensional classification and the portal of entry. The association between the presence of ECR and the factors studied was assessed using the χ 2 test. Intra-observer agreement was analyzed with the kappa test ( α = 0.05). Results In total, 6,240 teeth were analyzed, of which 84 (1.35%) were affected by ECR. A significant association was found between the presence of ECR and sex, with a higher prevalence in male patients ( p = 0.002). The most frequently affected teeth were the mandibular and maxillary central incisors. The most common height was the mid-third of the root. For the portal of entry, 44% of cases were on the proximal surfaces, 40.5% on the lingual/palatal surface and 15.5% on the buccal surface. Intra-observer agreement was excellent. Conclusions The prevalence of ECR was 1.35%, with a higher prevalence in male patients and a wide age distribution. The mandibular and maxillary central incisors were the most commonly affected teeth, and cases of ECR most frequently showed a height into the mid-third of the root and proximal entry.

Objectives: To determine the prevalence of Middle Mesial Root Canal (MMC) in a Brazilian subpopulation, verify whether its presence is related to anatomical characteristics of the tooth, and propose a classification using cone-beam computed tomography (CBCT). Methods: CBCT scans of 284 patients were evaluated by two radiologists to determine the presence of the MMC in mandibular first and second molars. Subsequently, the mesio-distal and buccal-lingual measurements of the mesial roots were obtained; the measurements between the root canals, and from MMC to the mesiobuccal canal and to the mesiolingual canal were also obtained. The MMC was classified according to its relationship with mesiobuccal and mesiolingual canals. The data were analyzed using chi-square and Fisher’s exact test, Multiple Logistic Regression analysis, Student’s t-test, κ and Intraclass correlation coefficient (p < 0.05). Results: The intra examiner agreements for the presence of the MMC and the measurements were considered almost perfect (0.953 and 0.999, respectively). Of 216 mandibular first molars, 11.1% had the MMC, and of 228 mandibular second molars, only 1.75% had the MMC. The presence was significant higher in the mandibular first molar (p < 0.0001). The buccal-lingual measurement and the measurement between mesiobuccal and mesiolingual canals were higher in teeth with MMC (p = 0.024 and p = 0.005, respectively). It was possible to classify the configuration of MCC into four types: Independent (60.7%) Confluent (14.3%), Mesiolingual confluent (14.3%), and Mesiobuccal confluent (10.7%). Conclusions: The prevalence of MMC is more pronounced in mandibular first molars and anatomical measurements, such as greater measurement between mesiobuccal and mesiolingual canals, may alert clinicians to its presence. It was found 4 types of configurations of MMC.

Objective: To determine the prevalence of Middle Mesial Canal (MMC) in a Brazilian subpopulation, verify whether its presence is related to anatomical characteristics of the tooth, and propose a classification using cone-beam computed tomography (CBCT).Material and methods: CBCT scans of 284 patients were evaluated by two radiologists to determine the presence of the MMC in mandibular first and second molars. Subsequently, the mesio-distal and buccal-lingual measurements of the mesial roots were obtained; the measurements between the root canals, and from MMC to the mesiobuccal canal and to the mesiolingual canal were also obtained. The MMC was classified according to its relationship with mesiobuccal and mesiolingual canals. The data were analyzed using chi-square and Fisher's exact test, Multiple Logistic Regression analysis, Student's t-test, Kappa and Intraclass correlation coefficient (p<0.05).Results: The intra-examiner agreements for the presence of the MMC and the measurements were considered almost perfect (0.953 and 0.999, respectively). Of 216 mandibular first molars, 11.1% had the MMC, and of 228 mandibular second molars, only 1.75% had the MMC. The presence was significant higher in the mandibular first molar (p<0.0001). The buccal-lingual measurement and the measurement between mesiobuccal and mesiolingual canals were higher in teeth with MMC (p=0.024 and p=0.005, respectively). It was possible to classify the configuration of MCC into four types: Independent (60.7%) Confluent (14.3%), Mesiolingual confluent (14.3%), and Mesiobuccal confluent (10.7%).Conclusions: The prevalence of MMC is more pronounced in mandibular first molars and anatomical measurements, such as greater measurement between mesiobuccal and mesiolingual canals, may alert clinicians to its presence. It was found 4 types of configurations of MMC.Clinical relevance: The knowledge of the prevalence of anatomical variations is important to alert clinicians about the possibility of finding them in the clinical routine.