Association between mandibular posterior alveolar morphology and growth pattern in a Chinese population with normal occlusion

Association between mandibular posterior alveolar morphology and growth pattern in a Chinese population with normal occlusion 1 first-author 1 1 1 1 1 1 1 2 1 corresp ‡Corresponding Authors ‡Corresponding Authors †E-mail:liudongxu@sdu.edu.cnwangchl@sdu.edu.cn †E-mail:liudongxu@sdu.edu.cnwangchl@sdu.edu.cn liudongxu@sdu.edu.cn 1 corresp ‡Corresponding Authors ‡Corresponding Authors †E-mail:liudongxu@sdu.edu.cnwangchl@sdu.edu.cn †E-mail:liudongxu@sdu.edu.cnwangchl@sdu.edu.cn liudongxu@sdu.edu.cn Department of Orthodontics, Shandong Provincial Key Laboratory of Oral Biomedicine, Shandong University, Jinan 250012, China Department of Orthodontics, Shandong Provincial Key Laboratory of Oral Biomedicine, Shandong University, Jinan 250012, China Department of Radiology, Shandong Provincial Key Laboratory of Oral Biomedicine, Shandong University, Jinan 250012, China Department of Radiology, Shandong Provincial Key Laboratory of Oral Biomedicine, Shandong University, Jinan 250012, China Objective: 2 To investigate the relationship between growth patterns and mandibular posterior tooth-alveolar bone complex morphology in a Chinese population with normal occlusion. Methods: 2 Forty-five patients with normal occlusion (23 males, 22 females) were included in this study. Among these patients, 20 displayed the vertical growth pattern, and 20 had the horizontal growth pattern, while the remaining patients displayed the average growth pattern. All of the patients underwent dental cone beam computed tomography (CBCT), which included the region of the mandibular posterior teeth and the alveolar. A linear regression analysis and a correlation analysis between the facial height index (FHI) and the alveolar bone morphology were performed. Results: 2 The inclination of the molars, the thickness of the cortical bone, and the height of the mandibular bone differed significantly between patients with the horizontal growth pattern and those with the vertical growth pattern ( P < 0.05). Significant positive correlations were found between: the FHI and the inclination of the molars; the FHI and the thickness of the cortical bone; and the FHI and the height of the mandibular bone. Conclusions: 2 The mandibular posterior tooth-alveolar bone complex morphology may be affected by growth patterns. Cone beam computed tomography (CBCT) Growth pattern Alveolar morphology Normal occlusion Introduction 1 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 (Aasen and Espeland, 2005 2005 ). 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 (Ingervall and Thilander, 1974 1974 ; Dechow and Hylander, 2000 2000 ). Various growth patterns have different biting forces and biological adaptations, and therefore, result in different mandibular tooth-alveolar structures (Dechow and Hylander, 2000 2000 ). Numerous investigations have been conducted to assess the relationship between the growth pattern and the tooth-alveolar bone complex (Kasai et al., 1999 1999 ; Kawamura, 1999 1999 ; Masumoto et al., 2001 2001 ; Brown, 2006 2006 ; Utsuno et al., 2010 2010 ; Swasty et al., 2011 2011 ). 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. Anthropometric analysis is important for research into disease and the development of new technologies and therapies. 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 (Liang et al., 2006 2006 ; Pohlenz et al., 2008 2008 ). Furthermore, the 2D 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. Materials and methods 1 Subjects and CBCT scanning 2 This research was reviewed and approved by the Research Ethic Committee of Shandong University Dental School. All the subjects were informed and consented to participate in the study. The selection criteria for the subjects included: (1) complete dentition with or without the third molars; (2) Class I molar relationship and normal incisor relationship (over jet: 1.5–3.0 mm; overbite: 1.0–3.5 mm), and crowding was limited within 3.5 mm; (3) no remaining deciduous teeth or obvious periodontal disease (community periodontal index (CPI) <3); (4) all subjects had symmetric mandibles and none were currently receiving orthodontic treatment; (5) subjects were excluded if they had missing teeth, any mandibular surgery, pathology, syndromes, or disease conditions that might affect musculoskeletal function or development (e.g., temporomandibular joint disorder or rheumatoid arthritis). Forty-five subjects (23 males, 22 females), aged 21 to 41 years, were included in the linear regression and correlation analysis, and 40 of them (20 males, 20 females), aged 23 to 39 years, were subdivided into different growth pattern types according to their Frankfort-mandibular plane angle (FMA) and facial height index (FHI) (Fig. 1a 1a ). The measurements for FMA and FHI were obtained from conventional cephalograms. This produced 20 horizontal growth pattern patients (FMA < 27°, FHI > 65°) and 20 vertical growth pattern patients (FMA > 37°, FHI < 62°). Five subjects were not included, because they did not belong to a single type according to their FMA and FHI. (a) Cephalogram. S: sella; N: nasion; Go: gonion; Me: menton; FMA: the angle from the Frankfort plane to Me-Go. Facial height index (FHI) is defined as the sum of distances from S and Go to the Frankfort plane divided by the sum of distances from N and Me to the Frankfort plane. (b) Axial image demonstrating the locations of the sites where the cross-sections were taken. (c) Sagittal image demonstrating the locations where the cross-sections were taken Images were obtained using the Galileos CBCT scanner (Sirona, Bensheim, Germany) in Shandong University, China. The scanning parameters were 85 kVp, 21 mA, 14 s per revolution, and 12 in field of view (FOV) (F mode). These settings produced a voxel of 0.38 mm×0.38 mm×0.38 mm. The data were reconstructed into 3D volumes using CBWorks 2.1 software, exported as digital imaging and communications in medicine (DICOM) files, and saved into the AVIA program (Hitachi, Tokyo, Japan). In order to keep the mandibular plane parallel to the floor, all images were reoriented using the “Z” subroutine. The “Z” subroutine was defined as the plane containing the gonion and menton points. Measuring parameters 2 A total of four mandibular cross-sections (P2, V12, M1, and M2) were taken for each subject (Figs. 1b and 1c 1b and 1c ). The cross-sections were perpendicular to the alveolar arch and defined as follows: P2, the cross-section passing through the center of the second premolar; V12, the cross-section passing through the coronal line of the middle of the inter-alveolar septum between the second premolar and the first molar; M1, the cross-section passing through the center of the mesial root of the first molar; M2, the cross-section passing through the center of the mesial root of the second molar. The images of these sections contained the teeth roots, and displayed the relationship between the roots and bone most clearly, and were therefore clinically beneficial and were chosen by the majority of the researchers. For each section, several parameters defining the morphology of the tooth-alveolar complex were calculated. The parameters were defined as follows: 1: tooth inclination; 2: bone inclination; B: buccal; L: lingual; Ba: basal Intra-operator and inter-operator reliabilities 2 Three doctors performed these measurements independently. The intra-operator error for each operator was obtained by repeating measurements on 16 randomly selected subjects three months after the initial measurements. The average scores of the 16 subjects measured by the three doctors were 0.993, 0.994, and 0.996, which indicated reproducibility using the AVIA software with a single examiner. Inter-operator errors were evaluated by having operators take measurements on the same subjects. These results were recorded in a spreadsheet and compared with Lin ( 1989 1989 )’s concordance correlation. Fifteen patients were randomly chosen for inter-operator error measurements. They were divided into three random groups, with five subjects per group. A total of five subjects were measured by Operators 1 and 2, five subjects were measured by Operators 1 and 3, and five subjects were measured by Operators 2 and 3. The mean concordance between Operators 1 and 2 was 0.973. For Operators 2 and 3, the average was 0.981, and for Operators 1 and 3, the average was 0.983. The results demonstrated reproducibility among the operators. Statistical analysis 2 Differences in tooth-alveolar complex morphology between patients with vertical or horizontal growth patterns were analyzed using the Student’s t -test. Pearson correlation coefficients were calculated to illustrate relationships between the FHI and variables, and linear regression was used to determine forecasting. 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 SAS 9.0. Results 1 Molars of the horizontal growth pattern had a greater buccal inclination in the posterior region 2 Table 1 1 shows the differences in the inclination of teeth and bone between patients with the horizontal or the vertical growth patterns. 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. Data are expressed as mean±SD ( n =20) P < 0.05 2 2 Measurement 2 Inclination (°) 2 P Horizontal Vertical 3 Teeth M2 82.85±4.30 77.86±3.48 0.0232 * * M1 82.69±1.92 80.23±2.10 0.0283 * * P2 85.75±4.56 87.73±4.07 0.0873 3 Bone M2 74.20±5.29 72.00±5.33 0.4212 M1 81.51±2.88 81.31±5.15 0.9250 P2 84.44±4.89 85.90±5.12 0.5682 Average thickness of the buccal cortical bone was greater in patients with the horizontal growth pattern 2 Table 2 2 shows the least thickness of buccal and lingual cortical bone among patients in the horizontal and vertical growth pattern groups. No significant differences were observed. Table 3 3 shows the average thickness of the cortical bone of the two 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. Data are expressed as mean±SD ( n =20) 2 2 Measurement 2 Least thickness (mm) 2 P Horizontal Vertical 4 Buccal M2 1.98±0.40 1.94±0.32 0.8066 M1 2.06±0.24 1.93±0.28 0.3745 V12 1.11±0.29 1.06±0.18 0.6769 P2 2.12±0.30 2.07±0.27 0.7721 4 Lingual M2 1.30±0.16 1.14±0.17 0.0707 M1 1.41±0.10 1.48±0.14 0.3432 V12 1.04±0.37 1.14±0.33 0.5792 P2 1.75±0.18 1.68±0.40 0.7281 Data are expressed as mean±SD ( n =20) P < 0.05 2 2 Measurement 2 Average thickness (mm) 2 P Horizontal Vertical 4 Buccal M2 3.60±0.25 3.08±0.52 0.0221 * * M1 3.03±0.54 2.75±0.55 0.0440 * * V12 2.64±0.52 2.53±0.19 0.3531 P2 2.73±0.46 2.36±0.39 0.0485 * * 4 Lingual M2 2.25±0.19 1.93±0.33 0.0480 * * M1 2.31±0.31 2.07±0.45 0.0345 * * V12 2.18±0.30 2.13±0.14 0.6763 P2 2.53±0.55 2.28±0.39 0.3243 4 Basal M2 3.51±0.79 3.36±0.28 0.6420 M1 3.86±0.53 3.56±0.70 0.7385 V12 4.32±0.34 3.94±0.35 0.4637 P2 4.43±0.46 4.05±0.89 0.5377 Mandibular posterior alveolar height of patients with the horizontal growth pattern was greater 2 Fig. 3a 3a shows the mandibular posterior alveolar height of the second premolar, and the first and second molars. 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 the first molar ( P < 0.01), and the region of the second premolar ( P < 0.05). Data are expressed as mean±SD ( n =20). *** P < 0.001, ** P < 0.01, * P < 0.05 Widths of mandibles of the two groups were equal 2 Fig. 3b 3b shows the width of the mandibular bone of patients from the horizontal and vertical growth pattern groups. No significant differences were observed. Linear regression analysis and correlation analysis 2 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 ( P < 0.01), and between the FHI and mandibular height ( P < 0.01). Discussion 1 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, similar to the results of Janson et al. ( 2004 2004 ). Functional hyperactivity of the masticatory system imposes increased stress on the bony structures of the craniofacial complex with possible influences on its structure (Kiliaridis et al., 1995 1995 ). There are three main factors which affect the inclination of the teeth: lingual force (the muscles of the tongue), buccal force (buccinator and masseter), and occlusal force (loading during mastication). The 3D position of the teeth and jaw bone is dependent on the combination of these three forces. Initially, the mandibular molars erupt lingually, and then move buccally due to tongue pressure and masseter function (Janson et al., 2004 2004 ). Finally, the molars reach a balanced position (Masumoto et al., 2001 2001 ). The lower molars are close to the attachment area of the masseter (Ingervall and Thilander, 1974 1974 ; Tabe, 1976 1976 ), and therefore are more influenced by the force of the masseter. Subjects with horizontal growth pattern have a stronger masseter (Ingervall and Helkimo, 1978 1978 ), and it is not surprised that the molars of patients with the horizontal growth pattern have a greater buccal inclination compared to the molars of those with the vertical growth pattern. In clinical orthodontic treatment, it is important to acquire space for patients with crowded teeth. An expansion arch is an efficient method to acquire space if all of the teeth are kept (Motoyoshi et al., 2002 2002 ). Since the molars of patients with the horizontal growth pattern have a greater buccal inclination, the mandibular arch expansion of this group should be limited within a suitable range to guarantee the stability of orthodontic treatment. In contrast, mandibular arch expansion of patients with the vertical growth pattern could be performed within a larger range to acquire space. In the posterior region, the average thickness of the cortical bone of patients with the horizontal growth pattern was greater than that of those with the vertical growth pattern. Our results were similar to those of Swasty et al. ( 2011 2011 ), who reported that a long-face group had slightly more narrow cortical bone than others. Subjects with the horizontal growth pattern had a stronger masseter (Ingervall and Helkimo, 1978 1978 ). These studies suggest that a horizontal growth pattern is seen mostly in individuals with a strong masseter. There were no significant differences in the masseter between males and females (Kiliaridis et al., 1995 1995 ), and we could not predict that a horizontal growth pattern is seen mostly in men. We could expect a thicker bone in individuals with a stronger masseter and a horizontal growth pattern. Recently, the microimplant anchor has become more popular in clinical treatment. Park et al. ( 2006 2006 ) suggested that the stability of a microimplant is influenced by a number of factors, including cortical bone thickness, oral hygiene, implant site, and inflammation. Miyawaki et al. ( 2003 2003 ) demonstrated that the cortical bone was thinner in high angle cases compared with low angle cases in the buccal posterior teeth area, which affected the stability of the microimplant anchor. Since the cortical bone thickness influences the stability of the microimplant (Park et al., 2006 2006 ), measurement of the cortical bone thickness helps orthodontists to predict problems and to plan steps in clinical treatments. When the microimplant is used in patients with a horizontal growth pattern, more attention should be given to the direction of the implant, compared with its stability. Alternatively, when it is used in patients with a vertical growth pattern, more attention should be given to the stability of the microimplant. The mandibular height of patients with the horizontal growth pattern is greater than that of those with the vertical growth pattern. Our results for mandibular height measurements were similar to those of other studies (Brown, 2006 2006 ; Swasty et al., 2011 2011 ). The difference was greatest in the second molar region, followed by the regions of the first molar and the second premolar. This supports the hypothesis that the height of the mandibular bone is associated with the growth pattern. There is more space for doctors to fix mandible implants in people with the horizontal growth pattern. The range of traction angles generated by implants is larger for those with the horizontal growth pattern. We found no significant difference in the width of the mandibular bone between the two groups. In contrast, Swasty et al. ( 2011 2011 ) reported that a long-face group showed a statistically narrower cross-section of the mandible in the upper third region compared with average-face and short-face groups, and that the mandible was wider and taller in males compared with females. Our research defined the bone width as the longest length from the buccal side to the lingual side and parallel to the standard plane, but not the length from the buccal cortical bone to lingual cortical bone, in order to avoid the disturbance caused by the linea mylohyoidea and linea oblique. In the regions of the first and second molars in patients with the horizontal growth pattern, the inclination of teeth was more buccal, while the inclination of the bone and the width of the bone were equivalent when compared to patients with the vertical growth pattern. These results suggest that the distance between the molar root tip and the mandibular edge in patients with the horizontal growth pattern might be smaller than that of those with the vertical growth pattern. Future research should further assess this measurement, as it may guide mandibular arch expansion and torque control. Significant correlations were found between the FHI and the inclination of molars, between the FHI and the average thickness of cortical bone, and between the FHI and the mandibular height. These results could be used in forecasting the morphology of the mandibular posterior tooth-alveolar bone complex in clinical treatment. The inclination of molars, average thickness of the cortical bone, and the height of the mandibular bone can be obtained only by CBCT (Wang et al., 2012 2012 ) or spiral CT (Guo et al., 2011 2011 ), while the FHI can be obtained using cephalometric film, which is cheaper and easier to acquire in the clinic. The tooth-alveolar complex morphology of patients may be approximated by doctors by assessing the FHI in cephalometric film. Future studies should address additional possible correlations by linear regression and correlation analysis. In regards to the impact of mesial-distal angulations of the molars on the results obtained, the buccal-lingual sections used for the measurements were parallel to the long axis of the teeth. If the vertical and horizontal growth pattern patients have different mesial-distal angulations of the molars, the accuracy of the bone height measurements would be affected. However, further work needs to be done to establish whether differences exist and if any differences are significant enough to influence the bone height measurements. The disadvantage of CBCT is its high radiation dose. 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J Zhejiang Univ-Sci B (Biomed & Biotechnol) , 2012 . 13 ( 11 ): 942 - 947 . 23125087 DOI: 10.1631/jzus.B1200052 http://doi.org/10.1631/jzus.B1200052 . Establishment of reference mandibular plane for anterior alveolar morphology evaluation using cone beam computed tomography 10.1631/jzus.B1200122 Project supported by the Shandong Science and Technology Planning Project (Nos. 2010G0020232, 2010HM053, and 2010GSF10269), the Shandong Provincial Natural Science Foundation (No. ZR2012 HM087), the Jinan Science and Technology Planning Project (No. JN201202042), and the Shandong University Project (Nos. 2011JC009 and 2012JC031), China 2012-04-23 2012-12-17 2012-09-27 2022-01-05 Copyright © Zhejiang University and Springer-Verlag Berlin Heidelberg 2013 2013 Journal of Zhejiang University-SCIENCE B (Biomedicine and Biotechnology) 01 14