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BACKGROUND: This study investigated the characteristics of Monson's sphere in Chinese young adult females with individual normal occlusion to provide a reference for oral rehabilitation in prosthodontic and orthodontic treatments. METHODS: Points at the dental cusps and incisal edges were selected from 51 digital mandibular dental models of Chinese young adult females (aged 18-22 years) with individual normal occlusion. Monson's spheres were fitted to the selected points based on the least-squares principle and the radii were calculated. The deviation of each selected point from its relative spherical surface was also calculated. The radii and deviations of these points were examined using conventional descriptive statistics and distributions of the most deviated points inside and outside the spheres were analyzed. RESULTS: The mean radius of Monson's sphere in Chinese young adult females was 79.60 ± 14.13 mm. The deviation of each selected point from its relative sphere surface was 0.38 ± 0.30 mm. The maximum deviations inside and outside the sphere were 0.93 ± 0.25 mm and 0.95 ± 0.30 mm, respectively. The most deviated points outside the spheres were mainly distributed at the distolingual cusps of the mandibular second permanent molars (31.37%), while those inside the spheres were mainly distributed at the mesiolingual cusps of the mandibular first permanent molars (45.10%). CONCLUSIONS: The radius of Monson's sphere in Chinese young adult females was smaller than the classic four-inch value suggested by Monson. Deviation was observed from all selected points to their Monson's sphere surface, with the most deviated points distributed primarily in the molar region.

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Background: Various clinical studies performed in adults have shown the relationship between craniofacial morphology and masticatory muscle function. However, the growth of the masticatory muscle has not received such attention, when compared with the volume of studies on the skeletal growth of face. With this background and considering the widespread use of ultrasonography (USG), the following study was undertaken to provide some insights into the relationship between muscle and bone and facial morphology. Methods: This was a prospective, observational study conducted over a period of three years from 2012 to 2015 to assess the correlation between the thickness of the masseter muscle in Angle's normal occlusion and the various malocclusions of the dental arch as well as the facial form. Patients with a full complement set of teeth, normal tooth morphology, Angle's normal occlusion, Angle's class I-III malocclusion, those with a history of third molar extraction, and impaction were included in the study. Those with a history of any prior orthodontic treatment, restorations, or any missing teeth (except the third molar) were exempted from the study. The greater thickness of masseter muscle in relaxed and clenched state was recorded on USG. Facial morphology was determined with the aid of facial photographs. Results: The study was conducted on 140 patients. The class I normal occlusion group had the thickest masseter muscle, while the class III malocclusion group had the thinnest masseter muscle. Facial parameters showed highly significant gender-wise differences in class I normal occlusion, class I malocclusion, and class II division II malocclusion. There was a significant negative co-relation between the thickness of masseter muscle and facial forms in all the categories of Angle's classification as indicated by a negative regression coefficient B (P < 0.05). Conclusion: The masseter muscle thickness correlated directly with male gender and normal occlusion, and inversely with the degree of malocclusion and facial form.

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Objective: The purpose of this research was to investigate the measurements of maxillary and mandibular basal arch width in male and female with normal occlusion, and to compare dental arch width difference between normal occlusion and ClassⅡ malocclusion groups could be helpful in orthodontic diagnosis and treatment planning. Methods: Cone-beam computed tomography (CBCT) images from 133 individuals (76 males and 57 females) with normal occlusion and 64 (25 males and 39 females) with skeletal Class II malocclusions were evaluated. The distances between canines, first molars (basal arch widths: BAW) and second molars were measured from CRs (center of resistance) of the teeth and the projection of first molars on buccal bones (WALA distance) were measured. Results: There were significant differences in male and female maxillary and mandibular dental transverse widths. The normal range of the maxilla and mandible basal bone widths differences were -2 mm-2 mm (-0.05 ± 2.17 mm). The normal occlusion and Class Ⅱ groups exhibited significant differences in the width of the intercanine and first molars. Sella-nasion-A point angle (SNA) and Sella-nasion-B point angle (SNB) in the Class Ⅱ male group were positively correlated with the width between the maxillary canines. For individuals with normal occlusions, the width of the mandible at the second molar was greater than that of the maxilla, so more attention should be paid to the width of the second molar when considering clinical treatment. Conclusion: Measuring the width of the maxilla and mandible basal bones from the resistance center of the first molar was a feasible and repeatable method can be used in clinical practice. The data could serve as a reference for orthodontic treatment planning. More consideration should be paid to the horizontal dental problems of the treatment plan for Class Ⅱ patients. And the width of the mandible at the second molar was greater than that of the maxilla, so more attention should be paid during treatment.

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OBJECTIVE: The aging of the occlusion and tooth wears influence the smile design This study aimed at evaluating the aging changes of maxillary anterior teeth in nontreated subjects. METHODS: The sample comprised dental models of 23 subjects (13 male, 10 female) with normal occlusions, taken at 13 (T1), 17 (T2) and 61 (T3) years of age. The following variables were measured in the maxillary anterior teeth using digital dental models: crown width/height proportion, anterior view width, crown angulation, gingival and incisal steps between central/lateral incisors and central incisors/canines. Interphase comparisons were evaluated using repeated measures analysis of variance followed by Tukey tests or Friedman tests. Sexual differences were evaluated using t tests (P < 0.05). RESULTS: From 13 to 61 years of age, a decrease of crown width/height proportion (P = 0.008 and P = < 0.001, for the lateral incisor and canines, respectively) and mesiodistal angulation (P = < 0.001, P = 0.001 and P = 0.025 for the central incisor, lateral incisor and canines, respectively) of the maxillary anterior teeth were observed. The steps of the gingival margin and the incisal steps decreased with aging. CONCLUSIONS: From adolescence to late adulthood, untreated individuals with normal occlusions demonstrated changes in the maxillary anterior teeth that may impair the smile esthetics and attractiveness.

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Objective@#To establish a three⁃dimensional cephalometric standardized value database for Anhui province , to study the craniofacial characteristics of normal adult population in Anhui , China and to provide effective information for making orthodontic and orthognathic surgery treatment plans of the craniofacial deformity.@*Methods@#160 normal occlusal volunteers were selected according to the inclusive and exclusive criteria and were photographed by Cone Beam CT (CBCT) . The coordinate system was established for the 3D model reconstructed with Dolphin based on CBCT data , and 38 hard tissue landmarks were located. 40 lines and 20 angles were defined and measured , and measurements were analyzed with SPSS 17. 0 , to evaluate craniofacial features of the overall , midface , maxilla , mandible , alveolar bone , and dentition of the standard population.@*Results@#The 3D cephalometric measurements of craniofacial hard tissues of normal adults in Anhui were obtained. The symmetry of craniofacial hard tissues was good both in males and females with the maximum asymmetry ratio of 2. 2% and the minimum of 0. 01% . The gender comparisons showed that most of lines measured of males were larger than those of females (P< 0. 01) , while there was no significant difference in the measurements of the midline deviation of upper and lower mandible , the relative deviation of the maxillary and mandible and the protrusion of upper and lower incisor. Additionally , there was no statistical significance in angles measured between genders , except for the occlusal plane angle. The results also showed that Chinese had unique facial features based on the measured data , compared with other ethnic populations.@*Conclusion@#The normal occlusal and maxillofacial hard tissue of Anhui Han has good symmetry. The gender obviously influences line measurements , with generally the measurements of males larger than females , but it has no effect on most angle measurements.

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Objectives: To study the transverse widths of maxilla and mandible and their relationship with the inclination of first molars. Materials and Methods: Fifty-six untreated adults (12 males, 44 females) with normal occlusion were included. On each Cone Beam Computed Tomography (CBCT) image of the subject, inter-buccal and inter-lingual bone widths were measured at the levels of hard palate, alveolar crest and furcation of the first molars, and maxillomandibular width differentials were calculated. In addition, the buccolingual inclination of each first molar was measured and its correlation with the maxillomandibular width differential was tested. Results: At the furcation level of the first molar, the maxillary inter-buccal bone width was more than the mandibular inter-buccal bone width by 1.1 ± 4.5 mm for males and 1.6 ± 2.9 mm for females; the mandibular inter-lingual bone width was more than the maxillary inter-lingual bone width by 1.3 ± 3.6 mm for males and 0.3 ± 3.2 mm for females. For females, there was a negative correlation between the maxillomandibular inter-lingual bone differential and maxillary first molar buccal inclination (p < 0.05), and a positive correlation between the maxillomandibular inter-lingual bone differential and mandibular first molar lingual inclination (p < 0.05). Conclusions: This is a randomized clinical study on transverse analysis of maxilla and mandible in adults with normal occlusion using CBCTs. On average: (1) At the furcation level of the first molars, the maxillary inter-buccal bone width was slightly wider than mandibular inter-buccal bone width; whereas the mandibular inter-lingual bone width was slightly wider than maxillary inter-lingual bone width; (2) A statistically significant correlation existed between the maxillomandibular transverse skeletal differentials and molar inclinations.

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OBJECTIVES: The purpose of this study was to investigate the prevalence of alveolar bone dehiscence and fenestration of Class I individuals with normality patterns in the anterior region using cone-beam computed tomography (CBCT). MATERIALS AND METHODS: A total of 4715 retrospective cases from January 2018 to December 2020 in the Orthodontic Department of xxx Hospital were screened. Sixty-one cases were Class I individuals with normality patterns in the anterior region. Their incidence of dehiscence and fenestration in the anterior teeth region was studied and statistically analyzed. RESULTS: Dehiscence was found in 27.46% of the evaluated anterior teeth and fenestration was found in 26.91% of anterior teeth. Severe dehiscences and fenestrations mainly occurred in mandibular canines and maxillary canines, respectively. Alveolar bone defects were present in 100% of patients, while one patient had alveolar bone defects in 91.67% of the anterior teeth. CONCLUSIONS: Dehiscence was found in 27.46% of the anterior teeth of Class I individuals with normality patterns, while fenestration was found in 26.91% of them. Alveolar bone defects were present in 100% of patients. CLINICAL RELEVANCE: Alveolar bone dehiscence and fenestration were normal and common in our sample, indicating that they are more likely to be physiological rather than pathological defects. Orthodontists should be aware of the presence and severity of these defects before treatment in order to avoid both possible complications and overtreatment.

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BACKGROUND: Any irregularity of the teeth or a mal-relationship of the dental arches is known as malocclusion. Among all the oro-facial problems, tooth decay is considered the most prevalent one followed by periodontal disease and dental malocclusion. Dental malocclusion is not a life-threatening condition. However, it is closely related to an individual's self-esteem and psychosocial wellbeing. The prevalence of malocclusion varies among different ethnic groups, age-groups, and gender. OBJECTIVES: This study was conducted with the objective to find out the prevalence of normal occlusal traits and to identify the proportion of different types of malocclusions among dental and nursing students of Seven North-Eastern states studying at a tertiary care Medical Institute. METHODS AND MATERIALS: This cross-sectional study included 432 students with a mean age of 21.42 years, who satisfied the inclusion criteria. Inclusion criteria consisted of the presence of all permanent teeth with or without third molars. The oral cavity was examined using a sterile mouth mirror and flashlight followed by evaluation of all the occlusal relationships in centric occlusion position (COP). COP was achieved by asking the participant to swallow, and then to bite on his or her teeth together. The occlusion traits were assessed as normal occlusion or malocclusion using the first permanent molars as described by E.H. Angle and deviation from line of occlusion. Descriptive statistics like mean and proportions were calculated. RESULTS: The prevalence of normal occlusal traits was 48.4%, and that of malocclusion was 51.6%. Class I malocclusion was most prevalent occlusal trait followed by Class II malocclusion and Class III malocclusion showed the least prevalence. CONCLUSIONS: Class I malocclusion was most prevalent followed by Class II malocclusion and Class III malocclusion showed the least prevalence.

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INTRODUCTION: The purpose of the present study was to evaluate the long-term variations in maxillary second molar position in untreated subjects with normal occlusion. SETTING AND SAMPLE POPULATION: A sample of 39 subjects (18 females and 21 males) selected from the University of Michigan Growth Study (UMGS) was followed longitudinally with digital dental casts at 3 observation times: T1, when the maxillary permanent second molars were fully erupted, T2, last observation available in the longitudinal series (38 subjects), and T3, at least 20 years after T2 (12 subjects). MATERIALS AND METHODS: Digital measurements were recorded with an open-source software. Outcome variables were sagittal and transverse inclinations of the upper second molars. Two mixed-effect models were performed. RESULTS: The maxillary second molars had a distolingual inclination at T1, T2 and T3. Sagittal and transverse inclination showed progressive significant uprighting from T1 through T3 (P < .001). From T1 to T2, the adjusted difference in sagittal crown inclination was 8.0° (95% CI from 6.5° to 9.6°; P < .001). From T2 to T3, the adjusted difference was 5.5° (95% CI from 3.0° to 8.1°; P < .001). From T1 to T2, the adjusted difference in transverse crown inclination was 1.9° (95% CI from 0.4° to 3.5°; P = .011). From T2 to T3, the adjusted difference was 6.0° (95% CI from 3.4° to 8.5°; P < .001). CONCLUSIONS: Along with age, maxillary second molars showed a progressive significant uprighting with a decrease in the distal and lingual inclinations.

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BACKGROUND AND OBJECTIVE: Dental study casts play a vital role in the diagnosis and treatment planning of various orthodontic cases. This study was carried out to compare the tooth widths, arch widths, and arch lengths in Class-I normal dentition to those in Class-I and Class-II crowded dentition in an effort to improve treatment planning and to eventually reduce treatment duration. METHODS: Total 170 patients, 12 to 40 years of age with a complete set of permanent teeth till 1st molars; who presented to the Orthodontics Department at Armed Forces Institute of Dentistry (A.F.I.D), Rawalpindi from Sep 2019 to Feb 2020, were included in the study. Non-probability purposive method of sampling was used. The dental casts obtained were used to measure tooth widths, arch widths, and arch lengths. Subjects were classified into Class-I normal and Class-I and Class-II crowded occlusion and comparison of the sum of tooth widths, arch widths, and arch length discrepancies were determined among the three occlusion groups. Data was analyzed in SPSS version 21 and independent samples t-test was used to differentiate the variables of interest. RESULTS: Out of 170 subjects, 73 (42.9%) subjects had Class-I normal occlusion while 97 (57%) had Class-I and Class-II crowded occlusions. No statistical difference was found between the occlusal groups with regard to the sum of tooth widths, inter-canine widths, inter-first premolar widths, inter-second premolar widths and inter-molar widths. However, a remarkable difference was observed between the occlusal groups with respect to arch perimeters and arch length discrepancies (p = 0.000 and 0.000 respectively). CONCLUSIONS: Results of the current study indicate that crowding of teeth occurs as a consequence of decreased arch perimeters which may lead to increased arch length discrepancies. However, no prominent difference was noticed in the sum of tooth widths and arch widths among different occlusal groups.

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BACKGROUND: Because racial discrepancies in dental characteristics are known to exist, designing preadjusted appliances according to racial normal occlusion data would be expected to improve treatment results. However, whether modifications based on racial characteristics can improve treatment outcomes in the clinic remains to be investigated. METHODS: To study the influence of prescription type on treatment outcomes, 91 patients treated with Chinese or Roth prescription appliances were selected as an initial sample. Two groups of patients were selected by propensity score matching (1:1) to limit the effects of confounding factors, including age, sex, case complexity, and extraction plan. Discrepancy Index and cervical vertebral maturation values were used to quantify case complexity and patient age, respectively. After matching, the final sample of 60 patients consisted of two groups of 30 patients each: group 1 had been treated with a Chinese prescription appliance and group 2 had been treated with a Roth prescription appliance. ABO casts and radiograph evaluation (CR-Eval) and lateral cephalograms were utilized to compare the treatment outcomes of the two groups. RESULTS: The total ABO scores of groups 1 and 2 were 22.03 and 23.87, respectively. There were no significant differences between the two groups in total ABO score or in seven other sub-scores; however, there was a significant difference between the two groups in mandibular canine alignment score. CONCLUSIONS: There are no significant differences in overall treatment outcomes between the Chinese and Roth prescription appliances. The Chinese prescription yielded better alignment results in the mandibular canine for Chinese patients.

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BACKGROUND: The objectives of this study were to describe and classify lingual arch form in dental students with normal occlusion and explore the possibility to provide a lingual arch form template for Nepalese population. METHODS: The occlusion and arch form of 220 undergraduate dental students were analyzed and thirty-three subjects (14 males, 19 females) fulfilling the inclusion criteria were selected for the study. Reference points were drawn on the lingual surfaces of the teeth of study model using an indelible marker. A transparent ruled grid was used to obtain x and y coordinate values of the reference point. Following distances were measured with a digital caliper: inter-canine width, inter-molar width, inter-second molar width, canine depth, first molar depth, and second molar depth. Two-step cluster analysis was used to further classify the arch. The mean reference point values of each cluster were entered into the software (CurveExpert 1.4, Hymas developers). The curve finder tool of the software was used to obtain the curve which best described the arch forms. RESULTS: Two-step cluster analysis identified two distinguished clusters of lingual arch forms. Tenth degree polynomial was chosen as the best possible fit for lingual arch forms by using Curvefinder tool of the software CurveExpert 1.4. CONCLUSION: Two types of anatomical lingual arch forms derived from Nepalese dental students with normal occlusion have been described and templates for the same have been generated.

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OBJECTIVES: : The aim of this study was to evaluate the relationship between masticatory muscle thickness and mandibular morphology in young Korean adults with normal occlusion and mandibular prognathism. PATIENTS AND METHODS: Multidetector computed tomography (MDCT) was used to measure the masticatory muscle thickness on the right side in 100 Korean young adults (50 normal occlusion group, 50 mandibular prognathism group). Cephalometric analysis was done to measure mandibular morphology. Pearson correlation analysis was done to investigate the relationship between the masticatory muscle thickness and mandibular morphometry. RESULTS: The four masticatory muscles showed positive correlation with intergonial width in all subjects. All muscles, except temporalis, positively correlated with height of the ramus and mandibular length. Positive correlation was also observed in all muscles, except medial pterygoid, with thickness of the ramus. In the normal occlusion group, all four masticatory muscles showed positive correlation with intergonial width and ramus thickness. Positive correlation was also observed in all muscles (except lateral pterygoid) with mandibular length. Masseter and lateral pterygoid positively correlated with height of the ramus. In the mandibular prognathism group, all masticatory muscles, except lateral pterygoid, showed positive correlation with intergonial width. The masseter muscle showed negative correlation with ANB. CONCLUSION: The results suggest a positive correlation of the thickness of masticatory muscles with both horizontal and vertical dimensions of the mandible. However, thickness of the masseter was found to decrease in patients with increasing severity of mandibular prognathism.

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OBJECTIVE: This study aimed to analyze the detailed three-dimensional measurements of temporomandibular joint (TMJ) in Chinese adults with normal occlusion and harmonious skeleton. METHODOLOGY: In 51 subjects 102 joints were analyzed using Anatomage Invivo dental 5.4. The measurements include: joints' parameters, position, angulation, and inclination of the condyle and articular fossa as well as 3D volumetric of the joint-spaces. All measurements were statistically analyzed by paired Student's t test to find out the differences between the left- and right sides. Pearson correlation coefficient test was done to figure out the relationship of the TMJ parts in the normal situation. RESULTS: The inter-condyle distances medially, geometrically, and laterally were 90.2 ± 5.2,107 ± 6.1, and 125 ± 5.5 mm, respectively. However, the 102 condyles were angulated on three planes 54.9º ± 11.2, 71.8º ± 7.3, and 12.5º ± 6.3 at vertical-, horizontal-, and midsagittal planes, respectively. The joint spaces measurements were 2.6 ± 0.7 mm, 2.5 ± 0.8 mm, 2.4 ± 0.7 mm, and 3.3 ± 0.7 mm for anterior-, medial-, posterior-, and superior joints, respectively. The total volume of the whole joint-space was 404.3 ± 71mm3. The left condyle position was on the centric position whereas the right condyle was eccentric (slightly anterior). CONCLUSION: Chinese subjects are characterized by wide inter-fossa distance and inter-condyle distance; however, no significant correlations with joint spaces in normal occlusion were found. The asymmetries between right- and left mandibular condyle were distinguished in angular and linear-vertical measurements. Finally, this study could be considered as reference data for upcoming research in the Chinese population.

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OBJECTIVES: To identify the mesiodistal angulation and faciolingual inclination of whole tooth and clinical crown in Chinese young adults with normal occlusion, by examining CBCT digitalized images. SETTING AND SAMPLE POPULATION: Forty-two volunteers, who presented with normal occlusion and without previous orthodontic treatment, were selected for this study. MATERIALS AND METHODS: The subjects were advised to take dental CBCT and the digital images of the dentition were obtained. The widely recognized University of Southern California (USC) root vector analysis was adopted to detect the angulation and inclination of the whole tooth, as well as of the clinical crown. RESULTS: No statistically significant difference was detected between male and female subjects. The fluctuations of the angulation and the inclination of the whole tooth from anterior to posterior in both arches manifested distinctive trends. The changes in maxillary dentition seem relatively marked, whereas those in mandibular dentition show less obvious, demonstrating moderate fluctuation both in angulation or inclination. The angulation and inclination of clinical crown are obtained and are shown positively correlated with that of each whole tooth. CONCLUSIONS: The normal range of the mesiodistal angulation and faciolingual inclination of whole tooth and clinical crown in Chinese adults with normal occlusion are identified. This study could establish clinical standards for designing 3D dental data-based orthodontic appliances for Chinese, and for providing the guidance for orthodontic treatment.

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OBJECTIVE: We aim to examine teenagers with varying vertical facial skeletal types with near-normal occlusion. We further aim to identify and study mandibular morphology and dentition characteristics to establish normal ranges and variations for future clinical reference. METHODS: According to the results of the case studies, 42 adolescents with near-normal occlusion were divided into three groups, namely, low- (7 cases), average- (23 cases) and high-angle (12 cases) groups. We used Invivo 5 software for Digital Imaging and Communications in Medicine (DICOM) data to calculate the cant of occlusal plane, axis corner of L6, ∠L1/MP, ∠L6/MP, Balkwill angle and Bonwill triangle of each group. RESULTS: Markedly, the finding shows that the cant of occlusal plane and axis corner of L6 in the low-angle group were smaller than those of the other two groups. In the average-angle group, ∠L1/MP was larger than that of the high-angle group. Lastly, in the high-angle group, ∠L6/MP was smaller than those of the two other groups. On the one hand, these differences were considered statistically significant (P<0.05). On the other hand, other measurements show that these differences were considered statistically non-significant (P>0.05). CONCLUSIONS: In the low-angle group, the parallelisation of the occlusal plane tends to be more obvious compared with the two other groups. In the coronal section of the low-angle group, the axis of the mandibular first molar is up-right, whereas it is distally tilted in the sagittal section of the high-angle group. Furthermore, a number of differences are noted in the adult groups. Factors, such as aging and development in the craniofacial region, lead to changes in functional occlusion.

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BACKGROUND: Tongue plays an important part in oral and maxillofacial system. Measurement of tongue pressure helps to evaluate the performance of tongue movement. OBJECTIVES: To establish a system for measuring tongue pressure against hard palate and to preliminarily explore pressure distribution of individual normal occlusions and the relationship with dental arch form. METHODS: A total of 19 volunteers of individual normal occlusions out of 189 dental students met inclusion criteria (nine males, ten females, aged 25.53 ± 0.96 years). A force-sensing resistor device was used to measure tongue pressure at rest and functional state (swallowing). We observed tongue pressure of four channel (anterior, posterior and lateral sides of hard palate) in sitting, supine position and swallowing. We analysed pressure differences according to gender and explored correlation relationship between tongue pressure and dental arch width and length using 3D digital maxillary image. RESULTS: In rest, tongue pressure against hard palate increased from front to back in both sitting and supine position, without gender differences. When swallowing saliva, the pressure at lateral sides of females was found significantly higher than that of males. Bivariate correlation analysis revealed duration of swallowing was positively correlated with BMI and weight at posterior region and positively correlated with palatal length at anterior palate. The greater the dental arch width, the smaller the pressure of swallowing in the anterior and lateral region. CONCLUSION: In rest, there was consistent pressure of tongue against hard palate. The pressure increased significantly during swallowing, especially in females. Tongue pressure was related to dental arch length, width, BMI and weight.

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OBJECTIVE@#We aim to examine teenagers with varying vertical facial skeletal types with near-normal occlusion. We further aim to identify and study mandibular morphology and dentition characteristics to establish normal ranges and variations for future clinical reference.@*METHODS@#According to the results of the case studies, 42 adolescents with near-normal occlusion were divided into three groups, namely, low- (7 cases), average- (23 cases) and high-angle (12 cases) groups. We used Invivo 5 software for Digital Imaging and Communications in Medicine (DICOM) data to calculate the cant of occlusal plane, axis corner of L6, ∠L1/MP, ∠L6/MP, Balkwill angle and Bonwill triangle of each group.@*RESULTS@#Markedly, the finding shows that the cant of occlusal plane and axis corner of L6 in the low-angle group were smaller than those of the other two groups. In the average-angle group, ∠L1/MP was larger than that of the high-angle group. Lastly, in the high-angle group, ∠L6/MP was smaller than those of the two other groups. On the one hand, these differences were considered statistically significant (P0.05).@*CONCLUSIONS@#In the low-angle group, the parallelisation of the occlusal plane tends to be more obvious compared with the two other groups. In the coronal section of the low-angle group, the axis of the mandibular first molar is up-right, whereas it is distally tilted in the sagittal section of the high-angle group. Furthermore, a number of differences are noted in the adult groups. Factors, such as aging and development in the craniofacial region, lead to changes in functional occlusion.

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Objective:To analyze the differents in the upper airway morphology and hyoid position between skeletal class III malocclusion of high-angle and normal occlusion by cone beam CT(CBCT), and to study the influence of skeletal class III malocclusion of high-angle in the upper airway and hyoid position of the adults preliminarily.Methods:A total of 42 adults in Department of Orthodontics, Dalian Stomatology Hospital were chosen, including 21 adults with skeletal class III malocclusion of high-angle and 21 adults with normal occlusion. MIMICS 20.0 software was used to measure the line spacing, cross-sectional area and volume of each upper airway segment and line distance of hyoid of the patients on CBCT; SPSS 20.0 software was used for statistical analysis.Results:Compared with normal occlusion group, the maximum lateral distance (LAT1) of the nasopharynx, the maximum anterior-posterior distance (AP2) of the velopharyngeal, and the volume of the velopharyngeal (VOL2) of the patients in skeletal class III malocclusion of high-angle group were increased (P0.05)Conclusion:Cross-sectional area and volume of velopharyngeal have the tendency of increase, but cross-sectional area and volume of laryngopharynx have the tendency of decrease in the patients with skeletal class ? malocclusion of high-angle. The hyoid bone has a tendency to shift forward and upward in the patients with skeletal class ? malocclusion of high-angle.

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OBJECTIVES: The aims of this investigation in a group of Emiratis were (1) To study overall and anterior tooth size ratios in Class I normal occlusion, (2) To estimate overall and anterior tooth size ratios in different malocclusion groups, (3) To compare overall and anterior tooth size ratios in Class I normal occlusion with the Bolton standards, and (4) To determine the distribution of overall and anterior tooth size ratios ± 2 SD from Bolton mean values in all occlusion groups. MATERIALS AND METHODS: In this cross-sectional investigation, consecutive patients' files, including dental casts, were selected from the archives of orthodontic clinics of the Dubai Health Authority. The final sample was formed following the application of specific inclusion criteria. The sample consisted of 521 pairs of dental casts representing both sexes (males: 188; females: 333) and different malocclusion groups (Class I: 288; Class II: 110; Class III: 30) and Class I normal occlusion (93). The mean age of patients was 16.18y for Class I, 15.73y for Class II, 15.83y for Class III, and 16.55y for Class I normal occlusion. The dental casts were scanned and digitized by the first author using the Ortho Insight 3D laser scanner. Measurements were made regarding maxillary and mandibular sums of mesiodistal tooth dimension of the overall (6-6) and anterior (3-3) groups of teeth. Statistical analysis included descriptive statistics, paired t-test and Analysis of Variance (ANOVA). The level of significance was set at p<0.05. RESULTS: There were statistically significant differences among malocclusion groups with regard to overall and anterior tooth size ratios. However, the comparison between the Class I normal occlusion group and the Bolton standards showed no statistically significant differences. Only five cases in Class II malocclusion presented an anterior tooth size discrepancy outside plus 2 SD from Bolton mean values and one case in Class I malocclusion presented with an overall tooth size discrepancy outside plus 2 SD from Bolton mean values. CONCLUSION: This study of the different occlusion groups of the Emirati sample concluded that (a) Class I normal occlusion cases presented similar overall and anterior tooth size ratios to Bolton standards; (b) Overall and anterior tooth size ratios among different malocclusion groups exhibited statistically significant differences; (c) Five cases in Class II malocclusion presented an anterior tooth size discrepancy outside plus 2 SD from Bolton mean values, and (d) One case in Class I malocclusion presented an overall tooth size discrepancy outside plus 2 SD from Bolton mean values.