Associations between incisor and mandibular condylar movements during maximum mouth opening in humans

This study evaluated the common clinical assumption that condylar translation and mouth opening at the incisor are closely related. The sample studied comprised 27 adult females (23-35 years), selected for normal temporomandibular function, occlusion, and skeletal patterns. Condylar and mandibular central incisor movements (straight-line distances and curvilinear pathways) were recorded in three dimensions (3D) for 20 s with an optoelectric (Optotrak(R)) jaw-tracking system while each participant performed multiple maximum opening cycles. Masticatory analysis and multilevel statistical programs computed the 3D movements of the incisors and condylar hinge axis during opening and closing. The incisor point moved an average straight-line distance of 46.6 mm during opening and 45.9 mm during closing; the lengths of the opening and closing curvilinear pathways were 48.6 and 47.7 mm, respectively. The condyles moved average straight-line distances of 11.9 and 12.2 mm during opening and closing, respectively. The condyles' curvilinear pathways during opening and closing were 14 and 14.6 mm, respectively. Ranges of condylar movement varied widely between individuals. The straight-line distances and curvilinear pathways were highly correlated for the incisors (R=0.98) and the condyles (R=0.98). Neither the straight-line distances nor curvilinear pathways of the incisors were correlated with those of the condyles. Incisor straight-line distances and curvilinear pathways were moderately correlated with mandibular rotation (R(between subjects)=0.82 and R(between repeats)=0.88). During repeated openings, both condylar and incisor excursions increased, but during repeated closings only incisor excursions increased. It is concluded that (1) maximum incisor opening does not provide reliable information about condylar translation and its use as a diagnostic indicator of condylar movement should be limited, (2) healthy individuals may perform normal opening with highly variable amounts of condylar translation, (3) the straight-line distances of the incisor and condyles provide adequate information about the length of the curvilinear pathway, and (4) variation in maximum incisor opening is largely explained by variation in the amount of mandibular rotation.     

Temporal coordination between mandibular and head-neck movements during jaw opening-closing tasks in man

Previous finding of concomitant mandibular and head movements during jaw function suggest a functional relation between the human jaw and neck regions. This study examined the temporal coordination between mandibular and head-neck movements during maximal jaw opening-closing tasks, at fast and slow speed. Twenty-four healthy individuals, median age 25 years, participated in the study. They were seated with firm back support but without head-neck support. Mandibular and head movements were simultaneously monitored by a wireless optoelectronic system for three-dimensional movement recording. The timing of head movement in relation to mandibular movement was estimated at defined time-points (start, peak, end and maximum velocity of movement), and during the entire course of the jaw-opening and jaw-closing phases. The results showed that the head in general started to move simultaneously with or before the mandible, reached the peak position simultaneously with, before or after the mandible, and reached the end position after the mandible. A higher degree of temporal coordination was found for fast speed at the start and the peak positions. The head most often attained maximum velocity after the mandible, and mostly lagged behind the mandible during the entire jaw-opening and -closing phases. These findings support the notion of a functional linkage between the human temporomandibular and craniocervical regions. They suggest that "functional jaw movements" comprise concomitant mandibular and head-neck movements which involve the temporomandibular, the atlanto-occipital and the cervical spine joints, and are caused by jointly activated jaw and neck muscles. It is proposed that these jaw and neck muscle actions, particularly at fast speed, are elicited and synchronized by preprogrammed neural command(s) common to both the jaw and the neck motor systems. From the present results and previous observations of concurrent jaw and head movement during fetal yawning, we suggest that these motor programmes are innate.     

错(牙合)与正常(牙合)之间的髁突运动轨迹的比较研究

目的讨论正常(牙合)者与错(牙合)者在下颌极限运动时、咀嚼运动及磨牙时,髁突在矢状向与水平向移动的运动轨迹.方法正常(牙合)22人,Angle分类的AngleⅡ1错(牙合)22人、AngleⅡ2错(牙合)19人,An-gleⅢ错(牙合)21人,应用计算机化的髁突运动轨迹仪(CAD1AX)记录开闭口运动、前伸运动、左右侧方运动、咀嚼以及磨牙时髁突的运动轨迹,测量髁突矢状方向最大移动量,侧方(水平)最大移动量,最大旋转量.结果1)AngleⅡ1组,前伸后退运动时矢状向最大移动量明显大于正常(牙合)组.2)AngleⅡ2组前伸运动时的侧方移动量显著增大.3)AngleⅡ1组左侧方运动时,平衡侧髁突的侧方移动量显著增加.4)AngleⅡ2组,左侧方移动平衡侧髁突的侧方移动量明显增加.5)AngleⅡ2组咀嚼时,磨牙时髁突侧方移动量增加.6)AngleⅢ组前伸运动时矢状向最大,移动量显著减小.结论AngleⅡ2病人组在极限运动与功能运动时,侧方运动量显著增加.揭示AngleⅡ2组的颞颌关节韧带松弛比例高.     

Correlation between direction and severity of temporomandibular joint disc displacement and reduction ability during mouth opening

The most common temporomandibular joint (TMJ) internal derangement is an abnormal relationship of the disc with respect to the mandibular condyle, articular eminence and glenoid fossa‐disc displacement. The aim of our study was to analyse the correlation between partial/complete disc displacement in the intercuspal position (IP) and its reduction in the open‐mouth position (OMP) in both oblique sagittal and coronal planes on magnetic resonance imaging (MRI) in patients with temporomandibular disorders. Multisection MRI analysis of 382 TMJs was conducted in 191 patients with disc displacement according to the RDC/TMD criteria (148 women, 43 men; aged 14‐60 years). The disc position was evaluated on all oblique sagittal and coronal images in the IP and the OMP. Univariate logistic regression analysis showed that the severity of disc displacement in the sagittal plane is a statistically significant predictor of reduction ability during mouth opening (B = 3.118; P < .001). Moreover, the severity of disc displacement in both planes is also a significant predictor of disc reduction in OMP (B = 2.200; P < .05). In conclusion, reduction ability during mouth opening is associated with the severity of disc displacement in IP, in both sagittal and coronal planes. Multisection analysis of all MR images allows distinguishing the correct disc position from disc displacement and can improve the ability to distinguish between various stages of TMJ internal derangement.     

Integrated jaw and neck function in man. Studies of mandibular and head-neck movements during jaw opening-closing tasks

This investigation was undertaken to test the hypothesis of a functional relationship between the human temporomandibular and craniocervical regions. Mandibular and head-neck movements were simultaneously recorded in healthy young adults using a wireless optoelectronic system for three dimensional movement recording. The subjects were seated in an upright position without head support and were instructed to perform maximal jaw opening-closing movements at fast and slow speed. As a basis, a study was undertaken to develop a method for recording and analysis of mandibular and head-neck movements during natural jaw function. A consistent finding was parallel and coordinated head-neck movements during both fast and slow jaw opening-closing movements. The head in general started to move simultaneously with or before the mandible at the initiation of jaw opening. Most often, the head attained maximum velocity after the mandible. A high degree of spatiotemporal consistency of mandibular and head-neck movement trajectories was found in successive recording sessions. The head movement amplitude and the temporal coordination between mandibular and head-neck movements were speed related but not the movement trajectory patterns. Examination of individuals suffering from temporomandibular disorders and whiplash associated disorders (WAD) showed, compared with healthy subjects, smaller amplitudes, a diverse pattern of temporal coordination but a similar high degree of spatiotemporal consistency for mandibular and head-neck movements. In conclusion, the results suggest the following: A functional linkage exists between the human temporomandibular and craniocervical regions. Head movements are an integral part of natural jaw opening-closing. "Functional jaw movements" comprise concomitant mandibular and head-neck movements which involve the temporomandibular, the atlanto-occipital and the cervical spine joints, caused by jointly activated jaw and neck muscles. Jaw and neck muscle actions are elicited and synchronised by neural commands in common for both the jaw and the neck motor systems. These commands are preprogrammed, particularly at fast speed. In the light of previous observations of concurrent jaw and head movements during foetal yawning, it is suggested that these motor programs are innate. Neural processes underlying integrated jaw and neck function are invariant both in short- and long-term perspectives. Integrated jaw and neck function seems to be crucial for maintaining optimal orientation of the gape in natural jaw function. Injury to the head-neck, leading to WAD may derange integrated jaw-neck motor control and compromise natural jaw function.     

Incisal and condylar paths during habitual mouth opening movement of children with anterior reverse bite in the primary dentition

The purpose of this study was to evaluate whether the path of habitual mouth opening was influenced by anterior reverse bite malocclusion in children. Two groups of children with the primary dentition were chosen: (i) 10 children with anterior reverse bite (reverse bite group) and (ii) 10 with normal occlusion (normal occlusion group). Their habitual mouth opening movements were measured by an opto-electronic movement-analysing system with 6 d.f. at a sampling rate of 100 Hz. These movements were projected on the sagittal plane at the incisal and condylar points. To characterize the path, we used the angles between the path and the horizontal plane. In the initial stage of opening, the incisal path of the reverse bite group was displaced more posteriorly from the intercuspal position than that of the normal occlusion group. However, as opening continued, the direction of the path of the reverse bite group was more anterior than those of the normal occlusion group. During the entire opening movement, the condylar path of the reverse bite group was flatter than those of the normal occlusion group. In conclusion, it was demonstrated that anterior reverse bite in the primary dentition clearly affects the paths of habitual opening movements.     

不同垂直骨面型正常(牙合)人切牙区颌骨形态结构正常值的建立

目的 :建立不同垂直骨面型正常牙合人切牙区颌骨形态结构的正常值。方法 :通过X线头影测量技术对 169名恒牙初期正常牙合人进行研究 ,选择测量项目包括URa PC、URa ULC、URa PP、MxAD、LRa TC、LRa LLC、LRa GoGn、MdAD。结果 :建立了不同垂直骨面型正常牙合人切牙区颌骨形态结构的正常参考值。结论 :建立的不同垂直骨面型正常牙合人切牙区颌骨形态结构正常值可供临床参考。     

Relationships between jaw muscle cross-sections and craniofacial morphology in normal adults, studied with magnetic resonance imaging.

In 32 Caucasian adult males serial MRI scans of the jaw muscles were taken approximately perpendicular to the mean fibre direction of the jaw muscles to determine their cross-sectional areas. These areas are proportional to the maximal isometric strength of a muscle. To describe facial skeletal variation, nine angular and 21 linear cephalometric measurements were recorded, and statistically reduced by means of multiple regression and principal component analysis. Six components were extracted, rotated, and subsequently correlated with the maximal cross-sectional areas of the jaw elevators and anterior digastric muscle. Positive significant correlations were found between a linear combination of several transversal skull dimensions on the one hand, and the maximal temporalis and masseter cross-sections on the other. A negative significant correlation was found between the flexure of the cranial base and the temporalis cross-section. Surprisingly, no significant correlations were found between either anterior facial height or posterior facial height and any of the jaw muscles cross-sections. It was concluded that, in adult males with normal skull shape, relationships exist to a limited extent between craniofacial morphology and the cross-sectional areas of the jaw muscles.     

Association between mouth opening and upper body movement with intake of different-size food pieces during eating

Head rotation is coordinated with mandibular movement during mouth opening, and the range of head rotation and mouth opening change with food size. However, past research did not include upper body movement, and no reports have related head and mandibular movement during realistic eating. The purpose of this study was to analyse head and mandibular movements with intake of different-sized food pieces during realistic eating. The test food consisted of apple cut into two different cube sizes (10mm and 20mm). Head and mandibular movements of 20 healthy young adults eating the apple pieces were simultaneously recorded in three dimensions by a wireless opto-electronic system. Reflective markers were attached to the upper lip and chin to measure the mouth opening range. Five markers were attached to eyeglasses frames to measure linear motion and rotation of the head. One marker was attached to the jugular notch of the sternum to measure linear motion of the upper body. Linear motion, and the inclination angle of the head and upper body, and mouth opening range were compared during intake of different-sized apple pieces. Mouth opening, head-neck rotation angle and the amount of upper body forward translation and inclination increased with larger apple pieces. However, isolated relative head motion was stabilized. We conclude that upper body forward motion and head-neck rotation assist mouth opening whilst stabilizing head orientation, and that the range of head-neck rotation angle, upper body translation and range of mouth opening change with food size during realistic eating.     

Relationship between jaw movement and masticatory performance in adults with natural dentition

Objective. This study determines the relationship between several characteristics of jaw movement and masticatory performance determined by multiple regression analysis and adjusted for occlusal contact area and bite force. Materials and methods. Forty-two young adults with natural dentition participated in this cross-sectional study. Occlusal contact area was determined at the maximum intercuspal position by scanning interocclusal records. Maximum unilateral force was measured by means of a gnathodynamometer. The height and amplitude of mastication, occlusal glide length, lateral guidance angle, anterior–posterior distance and cycle duration were recorded using the ARCUSdigma II system. Masticatory performance was determined by sieving the Optosil particles resulting from 20 chewing cycles. Results. Median particle size was negatively associated with height of mastication, maximum bite force, occlusal contact area and amplitude of mastication. Stepwise multiple linear regression analysis revealed that the height of mastication and dental guidance angle are the characteristics of jaw movement most closely related to masticatory performance. Conclusions. In adults with natural dentition, a large vertical height of mastication and a small dental guidance angle are the characteristics of jaw movement most closely associated with good masticatory performance, determined by multiple regression analysis and adjusted for occlusal contact area and bite force.     

汉族正常(牙合)成年男女面部软组织三维测量与对比研究

目的:建立汉族正常成年男女面部软组织三维参考数据并探寻男女面部特征.方法:选取汉族18~35 岁个别正常男30 人,女32 人,拍摄面部3dMD图像导入mimics软件,对27 个标志点的19 个线距、8 个角度和10 个比例项目进行测算,利用SPSS 19.0统计分析并对比男女面部差异.结果:体现面部及各器官轮廓宽度、高度的线距值男性大于女性(P<0.05),但面部高宽比例男性小于女性(P<0.05);男性鼻额角和鼻凸角小于女性(P<0.05),鼻面角大于女性(P<0.05).结论:汉族正常男性面部整体及各器官轮廓比女性更大,男性面部外形更偏扁圆,女性更显窄长,男性鼻部更前突.     

中国汉族成人正常（牙合）牙体舌侧形态的测量研究

对中国汉族年轻成人正常（牙合）牙齿的舌侧形态进行三维测量,为研发基于中国人牙体舌侧形态的舌侧直丝弓托槽提供数据参考。方法：采用上海正雅齿科科技有限公司开发的数字化正畸设计系统软件,对普查获得的64副中国汉族正常（牙合）个体的牙齿模型进行三维扫描,并对三维数字模型舌侧面进行计算机定点及测量分析。结果：获得正常（牙合）人群牙齿舌侧的轴倾度、转矩角、冠凸距和尖牙与磨牙补偿角指标的参考值,与国内相关研究结果相近。结论：本研究的测量结果可用于研发中国人舌侧直丝弓托槽标准型。     

The relationship between dental occlusion, muscle activity and associated jaw movement in man.

Experiments were carried out on adult subjects before and after occlusal adjustment, and during atypical mastication, to study the relationship between occlusion of the teeth, muscle activity and associated jaw movements. A computer-based system was used to record and analyze the electromyographic activity in the right and left anterior temporal, posterior temporal and masseter muscles, as well as the displacement, in 3 planes, of an incisor point on the mandible. Clinical examination of the occlusion was performed by means of a standard procedure, which permitted numerical values to be assigned to variables commonly observed in clinical practice. Unilateral gum-chewing tasks were carried out by each subject. Five subjects were tested both before and two weeks after occlusal adjustment. Two subjects acted as controls. The series also included one subject with a history of bruxism and another who undertook specific chewing tasks. The results indicated a tendency for occlusal adjustment to be associated with an increase in the lateral excursions of the mandible during jaw closure and, in some cases, with a closer approximation of peak muscle activity to the intercuspal position of the teeth. Specific occlusal features showed no clear association with either muscle activity or jaw displacement, although all subjects developed maximum muscle effort very close to, or at, the intercuspal position. Jaw-closing speed during natural chewing appeared to decrease abruptly before maximum bolus resistance was met by the teeth, suggesting the existence of a neuromuscular control mechanism which operates before closing forces become very large.     

A multiparametric analysis of occlusal and periodontal jaw reflex characteristics in young adults with normal occlusion

summary Periodontal jaw reflex, duration of percussion sounds, tooth mobility, and time-moment analysis of occlusal contacts by the T-scan system was recorded in nine periodontally healthy volunteers. The results showed that (i) reflex responses to the pressure applied to the uppercentageral incisors in the lingolabial direction varied, depending on the background jaw-clenching force (BCF) of the same-sided first molars. The BCF levels to elicit excitatory reflexes were 6–8Kgf, and inhibitory reflexes were clearly elicited with a BCF of l0Kgf and beyond. (ii) Duration of percussion sounds via an occlusal sound analyser (4.73–4.84mS: upper first molars. 4.89–5.00mS: uppercentageral incisors) and tooth mobility using a 'Periotest' (3.3–3.5: upper first molars, 5.5–5.6: uppercentageral incisors) showed a normal value. (iii) The time moments of occlusal contacts were symmetrical toward the midsagittal axis of the occlusal plane. The centre of the anterioposteriol occlusal contacts was located in the first molar regions.     

成人正常(牙合)与双颌前突错(牙合)侧貌特点的临床研究

目的 :从常用的软组织侧貌测量项目中确定影响双颌前突侧貌美观的主要因素 ,为临床诊治提供参考。方法 :对 5 6例侧貌美的正常牙合及 38例侧貌不协调的安氏 I类双颌前突错牙合进行软硬组织 X线头影测量。结果 :通过判别分析筛选出 3项软组织侧貌美学指标及与其相关联的硬组织指标。结论 :影响双颌前突侧貌美观主要为唇颏关系不协调 ,特别是软组织颏部形态     

Correlation between maxillary central incisor crown morphology and mandibular dental arch form in normal occlusion subjects

The aim of this study was to evaluate the correlation between the morphology of the mandibular dental arch and the maxillary central incisor crown. Cast models from 51 Caucasian individuals, older than 15 years, with optimal occlusion, no previous orthodontic treatment, featuring 4 of the 6 keys to normal occlusion by Andrews (the first being mandatory) were observed. The models were digitalized using a 3D scanner, and images of the maxillary central incisor and mandibular dental arch were obtained. These were printed and placed in an album below pre-set models of arches and dental crowns, and distributed to 12 dental surgeons, who were asked to choose which shape was most in accordance with the models and crown presented. The Kappa test was performed to evaluate the concordance among evaluators while the chi-square test was used to verify the association between the dental arch and central incisor morphology, at a 5% significance level. The Kappa test showed moderate agreement among evaluators for both variables of this study, and the chi-square test showed no significant association between tooth shape and mandibular dental arch morphology. It may be concluded that the use of arch morphology as a diagnostic method to determine the shape of the maxillary central incisor is not appropriate. Further research is necessary to assess tooth shape using a stricter scientific basis.     

Correlations between EMG jaw muscle activity and facial morphology in complete denture wearers

In a sample of fifteen partially edentulous subjects assigned for immediate complete denture treatment, a correlation analysis was performed between pre-extraction facial morphology determined from lateral cephalograms, and EMG activity of the anterior temporal and masseter muscles in maximal clench and tapping of teeth. Marked correlations observed between vertical and sagittal jaw relations and mean voltages of the jaw-closing muscles indicated strong biting activity in subjects with a square facial type. No significant associations were observed between biting strength and the age of the subjects. Correlations between facial morphological changes and changes in EMG biting activity after denture insertion and during 1 year of denture wear indicated that the anterior temporal muscles were extremely sensitive to sagittal changes in anterior occlusion. The masseter muscles were less sensitive, but responded in some instances to changes in vertical jaw relationship.