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ABSTRACT Objective: To determine the discrepancy of crown-root morphology of anterior teeth, using cone-beam computed tomography (CBCT), and to provide a guidance for proper torque expression. Methods: A total of eligible 200 CBCT were imported into Invivo v. 5.4 software, to obtain the middle labio-lingual sections of anterior teeth. AutoCAD 2007 software was applied to measure the crown-root angulation (Collum angle) and the angle formed by a tangent to the center of the labial surface and the long axis of the crown (labial surface angle). SPSS 18.0 was used for statistical comparisons of the two measurements, at the level of p< 0.05, and the Pearson correlation analysis was applied to investigate the association between the two measurements. Results: The value of Collum angle in maxillary central incisor was close to 0°. Significantly negative Collum angle in lateral incisors and maxillary canine, and positive value in mandibular canine were detected (p < 0.001). The labial surface angle in canine was significantly greater than the intra-arch incisors (p< 0.001), and no significant difference was detected between the central and lateral incisors (p > 0.05). Notably, there was also a significant positive correlation between the two measurements. Conclusions: The crown-root angulations were greatly different among anterior teeth. Accompanying the obvious crown-root angulations, the canines both in maxillary and mandibular arches presented considerable labial surface curvatures. Hence, equivalent deviation during bracket bonding might cause greater torque expression error and increase the risk of alveolar fenestration and dehiscence.

Introduction: Individual diversity is the cornerstone of human biology, so is the crown and root morphology of teeth. The maxillary and mandibular anterior teeth can be differentiated on the basis of their crown root morphology, by measuring collum angle, labial surface angle and torque angle. Aim: To evaluate and correlate the collum angle, labial surface angle and torque angle in maxillary and mandibular anterior teeth in different skeletal patterns in Bengali population. Materials and Methods: The study was conducted on 90 CBCT scans of young adult patients aged 18-24 years. They were divided into 3 groups based on ANB angle as skeletal Class I (2o < ANB < 4), Class II (4o < ANB) and Class III (2o > ANB) with 30 subjects in each group. All the CBCT scans were selected from the pool of patients reported to the department. Results: Positive correlation was found between collum angle and labial surface angle in all types of malocclusions. Smallest collum angle is found in lower left central incisor. Maxillary lateral incisor has larger crown root angulation than central incisor. Maxillary canine and mandibular central incisor has smallest of all collum angle in maxillary arch and mandibular arch respectively. On moving from 3.5 mm to 5 mm in calculation of labial surface angle, difference of 3.9o is seen for maxillary incisors and 3.5o for mandibular incisor. Conclusion: Statistically significant difference has been seen among maxillary and mandibular anterior teeth crown root morphology. By knowing the variations and correlations among collum angle, torque angle and labial surface angle in different sagittal skeletal malocclusions the clinicians can enhance orthodontic treatment. [ABSTRACT FROM AUTHOR]

Abstract Background To determine the discrepancy of crown-root morphology of central incisors among different types of skeletal malocclusion using cone-beam computed tomography (CBCT) and to provide guidance for proper torque expression of anterior teeth and prevention of alveolar fenestration and dehiscence. Methods In this retrospective study, a total of 108 CBCT images were obtained (ranging from 18.0 to 30.0 years, mean age 25.8 years). Patients were grouped according to routine sagittal and vertical skeletal malocclusion classification criteria. The patients in sagittal groups were all average vertical patterns, with Class I comprised 24 patients—14 females and 10 males; Class II comprised 20 patients—13 females and 7 males; and Class III comprised 22 subjects—13 females and 9 males. The patients in vertical groups were all skeletal Class I malocclusions, with low angle comprised 21 patients—12 females and 9 males; average angle comprised 24 patients; and high angle comprised 21 patients—11 females and 10 males. All the CBCT data were imported into Invivo 5.4 software to obtain a middle labio-lingual section of right central incisors. Auto CAD 2007 software was applied to measure the crown-root angulation (Collum angle), and the angle formed by a tangent to the central of the labial surface of the crown and the long axis of the crown (labial surface angle). One-way analysis of variance (ANOVA) and Scheffe’s test were used for statistical comparisons at the P

Objective: To investigate the discrepancy of crown-root morphology of upper and lower central incisors in adult patients with different skeletal malocclusions using cone-beam CT (CBCT). Methods: Patients visiting the Department of Orthodontics, College of Stomatology, Xi'an Jiaotong University from January 2015 to December 2017 were selected, including 108 cases (52 males, 56 females, aged from 18 to 30 years, mean age 25.8 years). According to CBCT data and cephalometric analysis, 66 patients with average angle were selected as the sagittal skeletal group, including 24 Class Ⅰ patients, 20 Class Ⅱ and 22 Class Ⅲ patients. In the other selected 66 skeletal Class Ⅰ patients including 21 low angle patients, 24 average angle patients (from the sagittal skeletal Class Ⅰ subgroup) and 21 high angle patients. Invivo 5 software was used to locate the CBCT image three dimensionally and then obtain the middle labio-lingual section of right central incisor. Auto CAD 2007 software was applied to measure the angle formed by the long axis of root and the extension line of the long axis of crown (Collum angle), and the angle between the long axis of crown and the lip tangent line passing through the center of the labial surface of crown (labial surface angle). One-way ANOVA and Scheff were used to analyze the discrepancies among classifications and Pearson correlation analysis was used to determine the correlation between the Collum angles and labial surface angles. Results: Significant differences were found in Collum angles and labial surface angles among different sagittal skeletal patterns ( P< 0.05). The Collum angle of maxillary central incisors in Class Ⅱ patients was 5.18°±4.97° and the average labial surface angle was 17.78°±3.74°, which were both significantly higher than that of maxillary central incisors in Class Ⅰ and Ⅲ subgroups ( P< 0.05). Similarly, the above two angles of mandibular central incisors in Class Ⅲ were 5.59°±5.64° and 15.32°±3.05°, which were significantly higher than that of mandibular central incisors in Class Ⅰ and Ⅱ subgroups ( P< 0.05). There was no significant difference among different vertical skeletal patterns ( P> 0.05). Notably, the Collum angles of maxillary or mandibular central incisors presented significantly positive correlation with labial surface angles (maxillary: r= 0.723, P <0.001; mandibular: r= 0.752, P <0.001). Conclusions: The long axis of the crown of the maxillary central incisor in skeletal Class Ⅱ patients and the mandibular central incisor in skeletal Class Ⅲ patients are obviously deviated toward the lingual side relative to the long axis of the root, and correspondingly there is a greater labial surface angle of the crown, which indicates that equivalent positioning deviation during bracket bonding can cause greater torque expression error.