| The tooth-alveolar bone complex, whose main function is to transfer the occlusal force from the tooth to the surrounding bone, is a complicated mechanical structure consisting of mineralized and periodontal soft tissue. The morphology of the tooth-alveolar bone complex is an important factor in orthodontic treatment planning, assessment of treatment progress, and the determination of treatment outcomes. The structure of the tooth-alveolar bone complex changes following alterations in loading by forces developed through the dentition and joint as the muscles contract during function Various growth patterns have different biting forces and biological adaptations, and therefore, result in different mandibular tooth-alveolar structures.Numerous investigations have been conducted to assess the relationship between the growth pattern and the tooth-alveolar bone complex. These studies demonstrated that the evaluation of tooth-alveolar bone can differ according to the observers or their era and social environment, particularly when they are considering subjects’ racial characteristics. However, there have been no previous studies on the tooth-alveolar bone complex among the Chinese population.Radiographic cephalometry is arguably one of the most significant diagnostic advancements in orthodontics. However, the information it provides is limited by its two-dimensional (2D) nature, resulting in a lack of perspective, errors in projection and superimposition, imaging artifacts, variations in magnification, information voids, and head position errors Furthermore, the2D images fail to represent the complex curving structures of the tooth-alveolar complex. To circumvent these limitations, cone beam computed tomography (CBCT) technology, which gives a realistic representation of a patient’s head, has emerged as a comprehensive imaging modality for orthodontics. CBCT offers an undistorted view of the dentition that shows the details of individual dental morphology, as well as the three-dimensional (3D) spatial orientation of the teeth and roots. A cross-sectional view of the tooth-alveolar bone complex generated from CBCT can reveal the dimensions of alveolar bone and the space limitations for intrusion or expansion. The multidimensional nature of imaging and reconstruction of CBCT allows for a comprehensive visualization of the tooth-alveolar bone complex and ensures reliable and anatomically accurate measurements.Using CBCT, the present study was undertaken to determine whether a correlation exists between the morphology of the mandibular tooth-alveolar complex and growth patterns in a Chinese population with normal occlusion.The whole dissertation consists of five parts:Part1:Measurement of inclination of molars and alveolar boneForty subjects (20males,20females), aged23to39years, were included in the study. There is no sex difference between groups. They were subdivided into different growth pattern types according to their Frankfort-mandibular plane angle (FMA) and facial height index (FHI). The measurements for FMA and FHI were obtained from conventional cephalograms. Images were obtained using the Galileos CBCT scanner (Sirona, Bensheim, Germany) in Shandong University, China. The data were reconstructed into3D volumes using CBWorks2.1software. Three doctors performed these measurements independently.Inclination of tooth:the angle between the basal line (right and left inferior border of the mandibular section) and the tooth long axis. The long axis of the tooth was defined as the line passing through the mid-point at one-half of the crown width and the mid-point at one-third of the distance from the root apex.Inclination of alveolar bone:the angle between the basal line and the line passing through the alveolar ridge crest and the inferior border of the mandible.Differences in tooth-alveolar complex morphology between patients with vertical or horizontal growth patterns were analyzed using the Student’st-test. There were significant differences in the inclination of the first and second molars (P<0.05) between the two groups, but no significant difference in the inclination of the second premolar. Compared with molars of patients with the vertical growth pattern, molars of those with the horizontal growth pattern had a significantly greater buccal inclination in the posterior region. However there was no statistical difference in the inclination of mandibular bone in the region of the first or second molar or the second premolar.Part2:Measurement of least and average cortical bone thicknessForty subjects (20males,20females), aged23to39years, were included in the study. There is no sex difference between groups. They were subdivided into different growth pattern types according to their Frankfort-mandibular plane angle (FMA) and facial height index (FHI). The measurements for FMA and FHI were obtained from conventional cephalograms. Images were obtained using the Galileos CBCT scanner (Sirona, Bensheim, Germany) in Shandong University, China. The data were reconstructed into3D volumes using CBWorks2.1software. Three doctors performed these measurements independently.Least thickness of cortical bone:the shortest length of the alveolar bone in the horizontal direction.Average thickness of cortical bone:the mean thickness of10points in one fifth of the middle region of the alveolar.Average thickness of basal bone:the mean thickness of5sections in the basal region.Differences in tooth-alveolar complex morphology between patients with vertical or horizontal growth patterns were analyzed using the Student’s t-test.No significant differences were observed in the least thickness of buccal and lingual cortical bone among patients in the horizontal and vertical growth pattern groups. In the region of the first and second molars, and the buccal side of the second premolar, the average thickness of the cortical bone in patients with the horizontal growth pattern was greater than that in those with the vertical growth pattern (P<0.05). There were no statistical differences in the average thickness of the basal bone.Part3:Measurement of mandibular bone heightForty subjects (20males,20females), aged23to39years, were included in the study. There is no sex difference between groups. They were subdivided into different growth pattern types according to their Frankfort-mandibular plane angle (FMA) and facial height index (FHI). The measurements for FMA and FHI were obtained from conventional cephalograms. Images were obtained using the Galileos CBCT scanner (Sirona, Bensheim, Germany) in Shandong University, China. The data were reconstructed into3D volumes using CBWorks2.1software. Three doctors performed these measurements independently.Height of mandibular bone:the vertical length from the alveolar ridge crest to the inferior border of the mandible.Differences in tooth-alveolar complex morphology between patients with vertical or horizontal growth patterns were analyzed using the Student’s t-test.The mandibular posterior alveolar height of patients with the horizontal growth pattern was greater than that of those with the vertical growth pattern. The difference was greatest (P<0.001) in the region of the second molar, followed by the region of first molar (P<0.01), and the region of second premolar (P<0.05).Part4:Measurement of mandibular bone widthForty subjects (20males,20females), aged23to39years, were included in the study. There is no sex difference between groups. They were subdivided into different growth pattern types according to their Frankfort-mandibular plane angle (FMA) and facial height index (FHI). The measurements for FMA and FHI were obtained from conventional cephalograms. Images were obtained using the Galileos CBCT scanner (Sirona, Bensheim, Germany) in Shandong University, China. The data were reconstructed into3D volumes using CBWorks2.1software. Three doctors performed these measurements independently.Width of mandibular bone:the longest length from the buccal side to the lingual side and parallel to the standard plane.Differences in tooth-alveolar complex morphology between patients with vertical or horizontal growth patterns were analyzed using the Student’s t-test.No significant differences were observed in the width of the mandibular bone of patients from the horizontal and vertical growth pattern groups.Part5:Linear regression analysis and correlation analysisForty-five subjects (23males,22females), aged21to41years, were included in the linear regression and correlation analysis. The measurements for FHI were obtained from conventional cephalograms. Images were obtained using the Galileos CBCT scanner (Sirona, Bensheim, Germany) in Shandong University, China. The data were reconstructed into3D volumes using CBWorks2.1software. Three doctors performed these measurements independently.The relationships analyzed were those between:the FHI and the inclination of molars; the FHI and the average thickness of cortical bone; and the FHI and mandibular height. Analyses were performed using Excel and SAS9.0.Significant positive correlations were found between the FHI and the inclination of molars (P<0.05), between the FHI and the average thickness of buccal cortical bone (P<0.01), between the FHI and the average thickness of lingual cortical bone (P0.01), and between the FHI and mandibular height (P<0.01).Conclusions1. The first and second molars of patients with the horizontal growth pattern have a greater buccal inclination compared to those of patients with the vertical growth pattern. 2. The average thickness of the buccal and lingual cortical bone at the first and second molars in patients with the horizontal growth pattern was thicker compared to that of patients with the vertical growth pattern.3. The bone height at the first and second molars and the second premolar of patients with the horizontal growth pattern was greater than that of those with the vertical growth pattern.4. There were significant positive correlations between:the FHI and the inclination of the molars; the FHI and the average thickness of cortical bone; and the FHI and mandibular height. |
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