PurposeTo investigate the prevalence of bifid and trifid mandibular canals using cone-beam computed tomography (CBCT) images, and to measure their length, diameter, and angle.Materials and MethodsCBCT images of 500 patients, involving 755 hemi-mandibles, were used for this study. The presence and type of bifid mandibular canal was evaluated according to a modified classification of Naitoh et al. Prevalence rates were determined according to age group, gender, and type. Further, their diameter, length, and angles were measured using PACSPLUS Viewer and ImageJ 1.46r. Statistical analysis with chi-squared and analysis of variance (ANOVA) tests was performed.ResultsBifid and trifid mandibular canals were found in 22.6% of the 500 patients and 16.2% of the 755 sides. There was no significant difference between genders and among age groups. The retromolar canal type accounted for 71.3% of the identified canals; the dental canal type, 18.8%; the forward canal type, 4.1%; and the trifid canal type, 5.8%. Interestingly, seven cases of the trifid canal type, which has been rarely reported, were observed. The mean diameter of the bifid and trifid mandibular canals was 2.2 mm and that of the main mandibular canal was 4.3 mm. Their mean length was 16.9 mm; the mean superior angle was 149.2°, and the mean inferior angle was 37.7°.ConclusionBifid and trifid mandibular canals in the Korean population were observed at a relatively high rate through a CBCT evaluation, and the most common type was the retromolar canal. CBCT is suggested for a detailed evaluation of bifid and trifid mandibular canals before mandibular surgery.

PurposeTo determine the conversion coefficients (CCs) from the dose-area product (DAP) value to effective dose in cone-beam CT.Materials and MethodsA CBCT scanner with four fields of view (FOV) was used. Using two exposure settings of the adult standard and low dose exposure, DAP values were measured with a DAP meter in C mode (200mm×179 mm), P mode (154 mm×154 mm), I mode (102 mm×102 mm), and D mode (51 mm×51 mm). The effective doses were also investigated at each mode using an adult male head and neck phantom and thermoluminescent chips. Linear regressive analysis of the DAP and effective dose values was used to calculate the CCs for each CBCT examination.ResultsFor the C mode, the P mode at the maxilla, and the P mode at the mandible, the CCs were 0.049 µSv/mGycm2, 0.067 µSv/mGycm2, and 0.064 µSv/mGycm2, respectively. For the I mode, the CCs at the maxilla and mandible were 0.076 µSv/mGycm2 and 0.095 µSv/mGycm2, respectively. For the D mode at the maxillary incisors, molars, and mandibular molars, the CCs were 0.038 µSv/mGycm2, 0.041 µSv/mGycm2, and 0.146 µSv/mGycm2, respectively.ConclusionThe CCs in one CBCT device with fixed 80 kV ranged from 0.038 µSv/mGycm2 to 0.146 µSv/mGycm2 according to the imaging modes and irradiated region and were highest for the D mode at the mandibular molar.

Abstract, Results: They should be replaced with "For the C mode, the P mode at the maxilla, and the P mode at the mandible, the CCs were 0.058 μSv/mGycm Tables 8, 9, and 10 contain some errors. The corrected versions of them are given below:Page 25, Results, The patient effective dose: Sentences from second to fourth should be replaced with "The effective doses in the adult exposure setting were 216.44 μSv in the C mode and 365.70 μSv and 344.61 μSv in the P mode for the maxilla and mandible, respectively. Additionally, the effective doses for the I mode in the maxilla and mandible were 187.17 μSv and 236.10 μSv, respectively. In the D mode, the effective doses were 28.51 μSv, 31.81 μSv, and 127.77 μSv for the maxillary incisors, maxillary molars, and mandibular molars, respectively."Page 25, Results, The conversion coefficients: Sentences from second to fourth should be replaced with "For the C mode, the P mode at the maxilla, and the P mode at the mandible, the conversion coefficients were 0.058 μSv/mGycm 2 , 0.081 μSv/mGycm 2 , and 0.076 μSv/mGycm 2 , respectively. For the I mode, the conversion coefficients at the maxilla and mandible were 0.097 μSv/mGycm 2 and 0.122 μSv/mGycm 2 , respectively. For the D mode at the maxillary incisors, molars, and mandibular molars, the conversion coefficients were 0.050 μSv/ mGycm 2 , 0.052 μSv/mGycm 2 , and 0.197 μSv/mGycm 2 , respectively."─ 255 ─

Objectives: This study aimed to assess mandibular and maxillary cortical bone thickness using a cone beam computer tomogram (CBCT) image to determine the safe zone to insert mini-screws. Methods: In this three factorial design study, we included 100 subjects divided into age group 1 (age 16-44 yrs.) and age group 2 (age 26-42 yrs.