Relationships among facial type, buccolingual molar inclination, and cortical bone thickness of the mandible

The purpose of this study was to evaluate the relationships between different facial types, and both the buccolingual molar inclination and cortical bone thickness of the mandible. The material consisted of 31 dry skulls of modern Japanese males from the Museum of the University of Tokyo. They all demonstrated normal occlusion with minimal dental discrepancy, and without crossbite or facial asymmetry. The buccolingual inclination of the second molar (M2) in the long-faced subjects was significantly smaller than the same dimension in the average- and short-faced subjects. It was found that the teeth of long-faced subjects were more lingually inclined than those of the short-faced subjects. The cortical bone thickness of the first molar (M1) and M2 sections was thicker in short-faced subjects than in average- and long-faced subjects. The results of this study provide evidence that a significant, but complex relationship exists between structures of the mandibular body and facial types. The morphological features that relate to masticatory function and facial types are associated with the cortical bone thickness of the mandibular body, and the buccolingual inclination of the first and second molars.     

偏颌畸形患者的牙弓特征

目的　分析偏颌畸形患者的牙弓特征,为临床矫治提供参考。方法　采用三维坐标测量仪在20例偏颌 畸形患者(试验组)和20例正常人(对照组)的牙模型上测量上下颌尖牙、前磨牙和磨牙牙尖的三维坐标值,分 析牙弓矢向和横向的对称性、上下牙弓的协调性和牙齿倾斜度,采用SAS 6·03进行统计学检验。结果　试验组上 颌尖牙和第一前磨牙距腭中缝的距离偏向侧大于偏离侧(P<0·05),下颌从尖牙到第二磨牙偏向侧距中线的距离 小于偏离侧(P<0·05);上颌尖牙和第一前磨牙的牙弓宽度比率较对照组小(P<0·05),而上颌第二前磨牙和第一 磨牙的牙弓宽度比率与正常无统计学差异(P>0·05);上颌后牙偏向侧颊向倾斜度大于偏离侧,下颌后牙偏向侧 舌向倾斜度大于偏离侧(P<0·05);上颌偏向侧和偏离侧牙齿的矢向位置无统计学差异(P>0·05)。结论　偏颌畸 形患者上牙弓前部窄于下牙弓,上颌牙齿矢向位置无差别,而上下颌两侧后牙颊舌向倾斜度存在明显差异。     

Tooth axis and skeletal structures in mandibular molar vertical sections in jaw deformity with facial asymmetry using MPR images

The objective of the present study was to investigate frontal morphological asymmetry in the mandibular molar region in terms of tooth axis and skeletal structures using vertical MPR sections in jaw deformity accompanied by facial asymmetry. Subjects consisted of 15 patients with jaw deformity accompanied by facial asymmetry aged 17.4 years to 37.8 years. There were four men and eleven women. Based on X-ray computed tomography (CT) scans, DICOM viewer software was used to prepare multiplanar reconstruction (MPR) sections. The mandible was then positioned on a reference plane based on the menton and left and right gonions, and a vertical MPR section passing through the mesial root of the first mandibular molar was prepared. The following measurements were made on both the shifted and non-shifted sides: maximum buccolingual width of the mandibular body; height of the mandibular body; inclination angle of the mandibular body; degree of buccal protrusion of the mandibular body; and inclination angle of the buccolingual tooth axis of the first molar. Furthermore, degree of median deviation in the menton was measured using frontal cephalograms. Differences in morphological parameters between the shifted and non-shifted sides were assessed. Furthermore, the relationship between median deviation and asymmetry were statistically analyzed. There was no significant asymmetry in the maximum buccolingual width of the mandibular body, the height of the mandibular body or the degree of buccal protrusion of the mandibular body. However, when compared to the shifted side, the inclination angle of the buccolingual tooth axis of the first molar for the non-shifted side was significantly greater. There was a relatively strong correlation between median deviation and inclination angle of the mandibular body. The above findings clarified that, in orthognathic surgery for jaw deformity accompanied by facial asymmetry, actively improving asymmetry in the buccolingual inclination of the tooth axis of the molar region during presurgical orthodontic treatment is important in achieving favorable post-treatment occlusal stability and facial symmetry.     

Relationship between transverse dental anomalies and skeletal asymmetry.

The recognition and elimination of dental compensation is essential in presurgical orthodontic treatment to achieve successful stabilization of the occlusion after surgery. However, the relationship between a transverse dental anomaly and skeletal asymmetry is not fully understood. To evaluate this relationship, frontal cephalometric and 3-dimensional dental model analyses were carried out on 44 adult Japanese Class III patients (mean age 21 years 11 months) who required surgical orthodontic treatment. The patients were divided into 2 groups: a facial asymmetry group in which the mandibular transverse deviation exceeded +/- 1 SD from the norm, and a control group in which the mandibular transverse deviation was within +/- 1 SD of the norm. Statistical comparison with a control group showed characteristic dental anomalies in the facial asymmetry group, including asymmetry of the curve of Spee, molar inclination, dental arch form, lateral overjet, and slanting of the occlusal plane. Stepwise linear regression analysis showed that transverse and vertical skeletal asymmetry variables including the mandible and the maxilla were effective parameters for characteristic dental anomaly variables, and a significant high correlation between dental anomalies and skeletal asymmetry was found.     

Morphologic evidence of muscle influence on dental arch width.

Tests on hypotheses to explain changes in arch width during correction of distoclusion with the activator appliance used in this study showed that statistically significant increases occurred in both maxillary and mandibular arch widths during treatment. The increase was substantially larger in the maxilla than in the mandible. The arch width showed no statistically significant decrease after completion of treatment. The activator designed for this study affected orofacial muscle balance. The findings suggest that there were changes in the influence of tongue and cheek muscles on the maxilla. Available experimental as well as clinical data support the assumption that the tongue had taken a higher and more anterior position in the palatal area and that the tension of the cheek muscles was reduced relative to the posterior part of the maxillary dental arch.     

Ⅲ类错(牙合)下颌偏斜正畸疗效的初步分析

目的 探讨Ⅲ类错(牙合)牙性、功能性和轻度骨性下颌偏斜的正畸矫治效果,为临床治疗提供参考.方法 选择Ⅲ类错(牙合)牙性、功能性和轻度骨性下颌偏斜患者共35例,男性14例,女性21例,年龄7～22岁(平均16.5岁).牙性偏斜主要通过扩大上颌牙弓,促使下颌自动复位;功能性下颌偏斜应用双颌式功能矫正器或不对称性前方牵引和Ⅲ类颌间牵引进行治疗;轻度骨性下颌偏斜行拔牙正畸掩饰性治疗.结果 通过正畸临床矫治,22例Ⅲ类错(牙合)牙性和功能性下颌偏斜患者的颜面外形和咬合均达到满意的疗效.13例Ⅲ类错(牙合)骨性下颌偏斜患者,拔牙掩饰性正畸矫治仅可改善颜面美观.结论 Ⅲ类错(牙合)牙性和功能性下颌偏斜是正畸治疗的适应证;而对于Ⅲ类错(牙合)轻度骨性下颌偏斜的患者,单纯正畸治疗仅可减轻牙(牙合)畸形的程度.     

偏[牙合]伴反殆患者治疗前后牙弓形态变化的研究

目的：分析与比较偏颌伴反[牙合]畸形矫治前后的牙弓形态变化。方法：选择偏颌伴反[牙合]畸形病例9例,制取矫治前后石膏模型。将模型平行于基准平面扫描到计算机。应用计算机测量软件测量上下颌尖牙、前磨牙和磨牙牙尖的纵横坐标值,分析牙弓矢向和横向的对称性、上下牙弓的协调性。采用SPSS11．0进行统计学分析。结果：矫治前上颌尖牙和第一前磨牙距腭中缝的距离偏向侧大于偏离侧（p〈0．05）,下颌从尖牙到第二磨牙偏向侧距中线的距离小于偏离侧（p〈0．05）;上颌尖牙和第一前磨牙的牙弓宽度比率较矫治后小（p〈0．05）,上颌第二前磨牙和第一磨牙的牙弓宽度比率矫治前后无统计学差异（P〉0．05）;上颌偏向侧和偏离侧牙齿的矢向位置变化无统计学差异（p〉0．05）,下颌牙齿在矢状方向第一磨牙偏向侧大于偏离侧（p〈0．05）。结论：偏颌畸形患者上牙弓前部较下牙弓前部窄,矫治易先扩大上颌牙弓,使得矫治后上下牙弓宽度比例协调。     

Three-dimensional analysis of molar compensation in patients with facial asymmetry and mandibular prognathism

Objective:To evaluate the characteristic transverse dental compensations in patients with facial asymmetry and mandibular prognathism and to compare features of dental compensations between two types of mandibular asymmetry using 3-dimensional (3D) cone-beam computed tomography (CBCT).Materials and Methods:Seventy-eight adult patients with skeletal Class I (control group; n  =  33; 19 men and 14 women) or skeletal Class III with facial asymmetry (experimental group; n  =  45; 23 men and 22 women) were included. The experimental group was subdivided into two groups according to the type of mandibular asymmetry: translation type (T-type; n  =  20) and roll type (R-type; n  =  19). CBCT images were acquired before orthodontic treatment and 3D analyses were performed.Results:The transverse dental distance was significantly different between the two groups only at the palatal root apex of the maxillary first molar (P < .05). In the experimental group, the first molar axes were compensated significantly on both arches except the maxillary nondeviated side. The vertical molar heights were different between the two groups only on the maxillary arch (P < .001). The R-type showed greater mandibular ramal length difference and menton deviation than the T-type (P < .001). In the R-type, transverse compensation of the maxillary first molars was more obvious than with the T-type, which resulted in canting in the maxillary occlusal plane.Conclusions:Mandibular asymmetry with prognathism showed a characteristic transverse dental compensation pattern. The mandibular asymmetry type influenced the amount and direction of molar compensation on the maxillary arch.     

Components of adult class III malocclusion

To identify the skeletal and dental relationships of adults who have class III malocclusion, lateral cephalograms of 302 adult patients who had a class III molar and cuspid relationship were traced. Ninety-four of the patients had had presurgical orthodontic treatment and 208 had not. The tracings were digitized, and the following sets of measures were analyzed: maxillary skeletal position; maxillary dentoalveolar position; mandibular dentoalveolar position; and mandibular skeletal position. In addition, the mandibular plane angle and lower anterior facial height were measured as an indicator of vertical facial dimensions. None of these values demonstrated significant gender differences except lower anterior facial height; therefore, the subjects were treated as a group. Although there was considerable variation among patients, the most common combination of variables was a retrusive maxilla, protrusive maxillary incisors, retrusive mandibular incisors, a protrusive mandible, and a long lower facial height.     

Dental characteristics of patients with Duchenne muscular dystrophy

A comprehensive assessment of the dental characteristics of 23 patients with Duchenne muscular dystrophy (DMD) was carried out, based on dental records, oral examinations and dental models. Decreasing muscle function was associated with increased plaque and calculus accumulation, leading to gingival inflammation, but caries experience was low. Disturbances in tooth form, number and eruption of the second premolars were observed in 39% of patients. Anterior and posterior open bites were common, associated with lip incompetence, mouth breathing, macroglossia and tongue thrusting. Maxillary and mandibular arch breadths were significantly larger, on average, in the DMD group than in controls. Rather than a normal parabolic arch form, the dental arches in DMD patients tended to be hyperbolic, with the posterior teeth being displaced buccally, consistent with an imbalance between the lingual and facial musculature.     

偏颌与颜面不对称畸形的诊断、分类及临床意义

依据临床特征、病理机制及颌骨结构,偏颌与颜面不对称畸形可分为单纯颌位性、关节源性与颌骨发育性3大类.单纯颌位性偏颌包括咬合阻碍、咬合代偿及咬合习惯亚型,关节源性偏颌包括髁突不对称吸收与不对称增生亚型,颌骨发育性偏颌包括上颌源与下颌源亚型.正畸治疗偏颌与颜面不对称畸形的重要原则是最大限度地纠正形成下颌偏斜的功能性颌位因素...     

Further studies of the pressure from the tongue on the teeth in young adults.

The pressures from the tongue on the teeth were recorded simultaneously in four locations lingual to the upper and lower central incisors, and left first molars in 20 young adults with largely normal occlusion. Measurements in the rest position, and during chewing and swallowing were made with an extra-oral pressure transducer incorporated in a fluid-filled system with intra-oral mouthpieces. The size of the dental arches was determined from dental casts. The median pressures in the rest position were low and negative at the upper incisors. Negative pressures at rest were recorded in a few subjects at all four points of measurement, most frequently at the upper incisors and least frequently at the lower molar. The pressures during swallowing were 2-4 times greater than those during chewing. There were no significant correlations between the pressures found and those recorded in the same individuals at an examination 2 years earlier. Positive correlations were found between the pressures recorded in the four locations during the various functions. This was interpreted as being an effect of the size of the tongue. The relatively few correlations between the pressures and the parameters describing the dental arch size indicated an adaptive role of the tongue within the confines of the dental arches.     

儿童骨性下颌偏斜患者的牙弓形态及颌骨对称性分析

目的：研究骨性下颌偏斜儿童的牙弓形态,并对颌骨对称性进行分析。方法：选择13例骨性下颌偏斜患者作为研究对象,在模型上以腭中缝为参考标准,测量两侧的牙弓宽度,分析其对称性;在X线片上测量两侧下颌升支高度、下颌体长度及下颌骨综合长度,并进行统计分析。结果：骨性下颌偏斜患者的牙弓形态存在明显的不对称,偏斜侧的牙弓宽度明显大于对侧（P〈0.05）;偏斜侧下颌升支高度和下颌体综合长度明显小于对侧（P〈0.05）,而两侧下颌体长度无明显差异（P〉0.05）。结论：骨性下颌偏斜患者的下颌骨存在明显不对称,牙齿也出现了不同程度的代偿,在临床正畸治疗中,应进行综合分析。     

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目的研究应用舌刺纠正不良舌习惯并联合头帽颏兜限制下颌骨过度生长矫治前牙反的疗效。方法选择2010年10月至2012年3月在中国医科大学附属口腔医院正畸科就诊的安氏Ⅲ类前牙反患儿24例,全部病例均设计应用舌刺破除不良习惯并消除舌对下牙弓的异常推力,配合头帽颏兜限制下颌骨的过度生长。结果 24例患儿均达到良好的矫治效果,舌不良习惯及不良位置得到了纠正,前牙反解除,后牙咬合关系良好,达到了治疗反和改善面部美观的目的。结论舌刺能有效纠正舌不良习惯及不良位置,去除了舌对下牙弓的异常推力,配合头帽颏兜限制下颌骨过度生长,是矫治安氏Ⅲ类前牙反的可行的矫治方案。     

平面与下颌矢状向位置关系的 X线头影测量研究

目的明确下颌处于不同矢状向位置时的牙形态,以及下颌矢状向位置与平面倾斜度的关系,为下颌矢状向位置异常患者的非手术正畸治疗提供策略依据。方法选取114例女性正畸患者治疗前的114张头影侧位片,根据ANB角的大小分为3组,每组各测量25项指标。对3组之间及两两组之间的差异进行方差分析和多重比较分析,对骨性指标与牙性指标的相关性进行直线相关分析。结果后牙平面（OP-P）倾斜度和上颌第二磨牙的垂直高度与下颌矢状向位置相关（P<0.05）。下颌后缩时,上颌第二磨牙垂直向萌出相对不足,OP-P倾斜度增加;下颌前伸时,上颌第二磨牙垂直向萌出相对过度,OP-P更平坦。当下颌处于不同位置时,牙轴近远中倾斜度有不同的代偿。下颌后缩患者上颌牙列牙轴远中倾斜,下颌牙列牙轴近中倾斜;下颌前突患者上颌牙列牙轴近中倾斜,下颌牙列牙轴远中倾斜。结论不同骨性环境下形态各有不同,正畸治疗下颌位置异常的患者时应重视后牙垂直高度的控制和对OP-P倾斜度的改变。     

Effects of head position on intraoral pressures in Class I and Class II adults

Variations in resting lip and tongue pressures and their relationship to alterations in head posture were investigated in subjects with Class I and Class II dental and skeletal morphology. Intraoral pressures were measured by means of transducers mounted in plastic carriers, customized for each subject from dental casts. Transducers were placed in the carriers to measure posterior lingual, anterior lingual, and labial pressures along the mandibular dentition. Ten Class I subjects and eleven Class II subjects participated. Pressures were recorded in natural head position, with 20 degrees of head extension and 20 degrees of head flexion. The Friedman two-way analysis of variance using ranked data was used to compare transducer location and head posture within skeletal classes. Anterior pressures were found to differ from posterior pressures in both classes. In Class I subjects, posterior lingual pressures were consistently different from labial pressures in all head positions. In Class II subjects, posterior lingual pressures differed from labial pressures in flexion and natural head positions, and from anterior lingual pressures in flexion and natural head positions. No increase in labial pressures with head extension was found in either Class I or Class II samples. Since every subject showed pressure changes with changes in head position, the influence of posture should be considered in studies on facial morphology and dental equilibrium.     

Orthognathic treatment for a patient with facial asymmetry associated with unilateral scissors-bite and a collapsed mandibular arch

Subapical mandibular surgeries have been used to correct vertical malocclusion and interdental problems associated with mandibular deformity. Subapical surgery to the anterior part of the mandible is applicable in many patients with anterior open bite and deepbite. Surgery of the posterior part of the mandible is needed less frequently than surgery of the anterior part. This case report describes the surgical-orthodontic treatment of a 21-year-old woman who underwent posterior subapical mandibular surgery. Her chief complaint was facial asymmetry, and she had a collapsed mandibular arch with a scissors-bite of the right premolars and molars. After subapical osteotomy, surgically assisted correction of the collapsed right mandibular arch was performed with a lingual arch appliance. Comprehensive orthodontic treatment was initiated in both arches after this correction. Le Fort I osteotomy and sagittal split ramus osteotomy were used to correct the facial asymmetry. Her facial appearance and temporomandibular problems were markedly improved, and she achieved a functional and stable occlusion after these treatments. This case report demonstrates the efficiency of posterior subapical mandibular surgery for a patient with a collapsed mandibular arch and a scissors-bite.     

The incidence of mandibular third molar impactions in different skeletal face types

Background: The cause of mandibular third molar impaction is said to be due to inadequate space between the distal of the second mandibular molar and the anterior border of the ascending ramus of the mandible. The amount of space is determined primarily by facial growth. This study aimed to assess whether different patterns of facial growth lead to a different incidence of mandibular third molar impaction. It was hypothesized that those with predominantly horizontal (brachyfacial) would have lower incidence of mandibular third molar impaction compared with those with a predominantly vertical growth pattern (dolichofacial). Methods: Ninety‐eight dental records were sourced from the records of orthodontic patients in the Royal Dental Hospital of Melbourne and all lateral cephalometric radiographs and orthopantomograms were assessed. The degree of impaction was determined by the Pell and Gregory system, and the facial type categorized by the facial axis angle. Results: The overall rate of mandibular third molar impaction was 58.76 per cent. Those with a facial axis angle >93 (brachyfacials) demonstrated an almost two times lower incidence of mandibular third molar impaction as compared to subjects with a facial axis angle <87 (dolichofacials). Conclusions: Within the limitations of the study, it was concluded that the greater horizontal facial growth pattern of brachyfacial subjects over dolichofacial subjects provides increased space for full eruption of the mandibular third molars.     

Fluctuating asymmetry of the permanent mandibular molars in a Japanese population

The purpose of the present study is to investigate the pattern of fluctuating odontometric asymmetry of permanent mandibular first and second molars in a Japanese population. Dental plaster casts of 112 (57 males and 55 females) Japanese undergraduate dental students were used. The mesiodistal and buccolingual diameters of the whole crown and trigonid and talonid crown components were taken on the left and right sides of the mandibular permanent first and second molars. Crown areas were also calculated. The fluctuating asymmetry (FA) value was obtained by dividing the absolute side difference by the absolute mean size of the left and right teeth: FA = abs (R?L)/((R + L)/2). Fluctuating asymmetry between mandibular first and second molars was significantly different with the mandibular second molar showing higher asymmetry in both males and females. Meanwhile, fluctuating asymmetry between males and females in the first and second molars was not significantly different in all measured dimensions. With regard to trigonid and talonid components, fluctuating asymmetry of the distal talonid area was significantly larger than the mesial trigonid area in the mandibular permanent first molar of males (P < 0.01), and asymmetry of buccolingual diameter of the talonid was also larger than that of the trigonid in the mandibular permanent second molar of males (P < 0.05). In conclusion, these findings suggest that the crown dimensions of later developing teeth in the mandibular molar tooth class and crown component in the same molar tooth show more asymmetry and, therefore, are more affected by external factors.     

Lower premolar extraction/removable plastic Herbst treatment for mandibular retrognathia

The patient was a 12-year-old girl with a Class I malocclusion characterized by maxillary arch width constriction, dental crowding, and mandibular retrognathia. Treatment goals related to the chief compliant were anterior mandibular repositioning, maxillary arch expansion, and dental alignment. Because the preexisting overjet was minimal and prevented adequate anterior repositioning of the mandible, lower first premolar extraction was recommended to increase the overjet and allow greater anterior repositioning. Treatment was divided into four stages: (1) extraction of mandibular first premolar teeth, alignment, space closure, and an increase in the overjet, (2) anterior mandibular repositioning with a removable plastic Herbst appliance, (3) arch alignment and detailing of the occlusion with full fixed appliances and a tooth positioner, and (4) retainers. At the end of treatment, the patient had an acceptable dental alignment with a Class III molar relationship and an improvement in facial appearance.