Is the postretention relapse of maxillary and mandibular incisor alignment related?

Previous studies suggest a poor association between initial and postretention pattern of incisor irregularity. One explanation may be that the incisor movements are limited by the boundaries provided by the incisors in the opposite arch. If so, postretention malalignment of the maxillary and mandibular incisors may be related. To test this hypothesis, long-term postretention study models of 96 patients with acceptable occlusion at the time of appliance removal were examined. The occlusal surfaces of the postretention study models were photocopied, and tooth anatomical contact points were digitized. An algorithm was used to fit the dental arch to the digitized points. The amount of incisor rotation and anatomical contact point displacement of maxillary and mandibular anterior teeth, relative to their respective dental arches, were computer generated. Overbite, the number of occlusal contact points in the anterior segment, and concavity of the lingual surfaces of the maxillary incisors were recorded manually. Statistical analyses demonstrated a significant association (P <.05) between the overall irregularity of the maxillary and mandibular incisors. The association did not differ among subgroups that were stratified according to overbite or number of occlusal contacts. No associations were found for the overall amount of incisor rotation in the 2 arches (P >.05). The amount and direction of displacement of antagonistic pairs of maxillary and mandibular central incisors were also associated (P <.05), but not the amount and direction of rotation (P >.05). The lingual configuration of the maxillary incisors did not affect the pattern of mandibular incisor malalignment.     

The treatment of some disorders of the maxillo-mandibular apparatus. II. Osteo-arthritis

This paper describes the diagnosis and treatment of three cases of osteo-arthritis and one case of potential osteo-arthritis of the temporomandibular joint complex. Diagnosis was based on tomography of the joint, radiology of the nasal fossae, and in certain cases electrodiagnosis. All cases showed asymmetrically positioned or displaced condyles. Electrodiagnosis showed inordinately long open-close-clench (OCC) cycles, suppressed or incomplete jaw opening reflexes, and an inordinately prolonged duration of elevator muscle contraction prior to initial tooth contact (DMC). Signs of the maxillo-septal syndrome were present in three, and it is emphasized that this syndrome usually formed the basis for TMJ pathosis. Treatment consisted of occlusal splints to reposition the mandibular condyles, and in one case rapid maxillary expansion (RME) to unlock the bite.     

Chewing performance and occlusal contact area with the shortened dental arch

The aim of this study was to investigate the effect of the loss of posterior teeth on the effectiveness of mastication. To evaluate this, chewing performance and occlusal contact area were investigated in 10 edentate subjects having implants stabilising a mandibular overdenture. A copy of the original lower denture was made for each subject, with removable teeth, which could be separated to convert a complete dental arch to a shortened dental arch, an extremely shortened dental arch, or a broken dental arch. Both post canine occlusal contact area and chewing performance demonstrated significant differences between the different arches. It was concluded that chewing performance is reduced by removing posterior teeth from implant stabilised mandibular complete dentures.     

The effects of Fr?nkel II treatment on arch width and arch perimeter

Changes in dental arch width and total arch perimeter in 24 Class II, Division 1 patients treated with the Fr?nkel II appliance were compared with changes in an untreated control group. Measurements were made on pretreatment and posttreatment plaster casts at three points on each of four maxillary and four mandibular teeth. Increases in width were computed at the occlusal point and compared for the two samples. A significant increase in occlusal arch width for all measures was suggestive of both a minor tipping movement of the maxillary teeth and a bodily movement of the mandibular teeth. Width development in the maxilla was greater than in the mandible. Occlusal arch width increased more in the molar and premolar regions in the maxilla and in the premolar region in the mandible. Wide arches were found to have as much increase as narrow arches. The total arch perimeter decreased significantly less in the treatment sample than in the control sample. The documented gains in arch width and arch perimeter would not be sufficient to relieve severe crowding, but could be useful in avoiding removal of teeth in borderline extraction cases.     

A comparison of the signs of temporomandibular joint dysfunction and occlusal discrepancies in a symptom-free population of men and women

To date, there has been no conclusive explanation for the predominance of female patients with temporomandibular joint (TMJ) dysfunction. The purpose of this study was to survey a normal population without symptoms for the presence of certain putative signs of TMJ dysfunction in association with certain signs of occlusal discrepancy and to determine the presence of any gender variation. The subjects (217 men and 217 women) were examined for the presence of three putative signs of TMJ dysfunction: limited mandibular opening (under 37 mm), deviation on opening, and joint sounds. The subjects were also examined for the presence of four signs of occlusal discrepancy: an anterior slide from centric relation (CR) to centric occlusion (CO), lateral slide from CR to CO, nonworking occlusal contacts, and working disclusive contacts distal to the canines. CR is the mandibular position at which the condyles are in their most superior position on the posterior aspect of the articular tubercles. CO is the mandibular position at which the mandibular and maxillary teeth are in maximum intercuspation. There were no significant differences in the prevalence of the putative signs of TMJ dysfunction and occlusal discrepancy between men and women. It was concluded that factors other than the presence of these signs of TMJ dysfunction and occlusal discrepancy are responsible for the high predominance of female patients with TMJ dysfunction.     

Effect of biomechanical disturbance of the temporomandibular joint on the prevalence of internal derangement in mandibular asymmetry

The aim of the present study was to elucidate the relationship between biomechanical changes of the temporomandibular joint (TMJ) and internal derangement (ID) symptoms in mandibular asymmetry. Posteroanterior cephalograms (PA) of 140 patients with TMJ ID associated with mandibular asymmetry were used to investigate the inclination of the frontal occlusal plane (FOP), and were analysed in conjunction with the results of a report providing information on ID symptoms. A three-dimensional (3D) finite element model (FEM) of the entire mandible was created to investigate the distribution of TMJ forces during clenching. The inclination of the FOP was modified to simulate various degrees of vertical asymmetry. The stresses on the TMJ on the ipsilateral and contralateral sides were analysed and their values were compared with those of the standard model. The results showed that the symptomatic sides were significantly related to the degree of inclination of the FOP. Increasing its angulation resulted in a decrease of the symptoms on the ipsilateral side and an increase of those on the contralateral side. The analysis showed that stress-distribution patterns and overall stresses of the articular disc were influenced by the angulation of inclination of the FOP. These mechanical changes exhibited a distinct relationship with the prevalence of ID in the patients. These results suggest that disturbances in the stresses either in amount or direction due to occlusal inclination can be responsible for ID. Therefore, an attempt to establish a flat occlusal plane is an important orthodontic treatment objective in maintaining the normal health and structure of the TMJ.     

Computer-assisted morphological analysis of dental casts with maxillary prognathism and reversed occlusion

The morphologic characteristics of the dentition with maxillary prognathism and reversed occlusion were examined by a computer-assisted dental cast analysing system. Dental casts with normal occlusion, maxillary prognathism and reversed occlusion were selected and measured by a 3D shape measuring system. The dental arches and anteroposterior occlusal curves were approximated numerically by the polynomial expression with a fourth order and second order coefficients, respectively. The coefficients were analysed statistically. Maxillary dental arches with mandibular prognathism showed a more acuminate shape (V-shape) with a significant larger second order coefficient, while arches with reversed occlusion showed more angulate shapes (U-shape) with significantly smaller second order coefficients compared with arches with normal occlusions. However, a notable difference in the shape of the mandibular dental arches was not observed. The mandibular dental arches with maxillary prognathism were positioned backward relative to maxillary dental arches, while the arches with reversed occlusion were positioned forward. The anteroposterior occlusal curves with maxillary prognathism showed larger curvatures in maxilla and mandible, while the curves with reversed occlusion showed smaller curvatures in mandible comparing with the curves with normal occlusion. These results suggest that the present method could offer a useful and objective examination technique for the diagnosis of malocclusion.     

下颌第二磨牙咬合接触变化对颞下颌关节应力分布的影响

目的 用力学研究方法结合有限元技术分析下颌第二磨牙咬合接触部位改变时，相同压强咬合载荷条件下颞下颌关节应力的变化。方法 在包括左侧下颌第二磨牙在内的颞下颌关节三维有限元模型上，设计下颌第二磨牙牙尖交错He(ICO)、远中和颊侧3种加载部位的工况，通过有限元运算探讨双侧髁突应力分布的变化规律。结果 由于咬合加载部位的牙面承载形态不同，在双侧髁突上产生了不同的应力效应，其变化包括应力性质和应力分布特点等方面，远中加载和颊侧加载时对侧髁突的Von Mises应力最大值由ICO加载时的51．51MPa分别增加到72．15MPa和69．57MPa。结论 与单侧下颌第二磨牙承载部位变化相关的咬合力方向变化，可使同一力值的咬合力产生不同的双侧髁突应力效应。     

A study on occlusal stability in shortened dental arches

PURPOSE: The aim of this study was to verify the hypothesis that shortened dental arches constitute a risk to occlusal stability. MATERIALS AND METHODS: Using cluster samples, 725 subjects with shortened dental arches comprising intact anterior regions and zero to eight occluding pairs of posterior teeth and 125 subjects with complete dental arches were selected. Subjects with shortened dental arches were classified into eight categories according to arch length and symmetry. Parameters for occlusal stability were interdental spacing, occlusal tooth wear, occlusal contact of incisors in intercuspal position, and vertical and horizontal overlap. Additionally, tooth mobility and overeruption of unopposed teeth were assessed. Influence of independent variables (dental arch category, age, gender, and residence) on the parameters for occlusal stability was assessed by one-way ANOVA and Tukey's multiple range tests. RESULTS: Extreme shortened dental arches (zero to two pairs of occluding premolars) had significantly more interdental spacing, occlusal contact of incisors, and vertical overlap compared to complete dental arches. Occlusal wear and prevalence of mobile teeth were highest in these categories. The category with three to four occluding premolars had significantly more interdental spacing and, for the older age group, more anterior teeth in occlusal contact compared to complete dental arches. Age was consistently associated with increased changes in occlusal integrity. CONCLUSION: Signs of increased risk to occlusal stability seemed to occur in extreme shortened dental arches, whereas no such evidence was found for intermediate categories of shortened dental arches.     

Clinical symptoms of open lock position of the condyle. Relation to anterior dislocation of the temporomandibular joint.

Nine cases of open lock position of the condyle of the temporomandibular joint (TMJ) are reported. In two patients recurrent dislocation of the TMJ was diagnosed clinically, and four had previous episodes of anterior dislocation. An arthrotomographic examination revealed that the condyles of the affected TMJs were located anterior to the anterior bands of the disks at an open-mouth position. An arthrographic fluoroscopic examination showed that the anterior bands mechanically obstructed the anteriorly displaced condyles from posterior movement into the articular fossae to various degrees at open-mouth position. One cause of anterior dislocation of the TMJ is thought to be fixation of the condyle in the open lock position resulting from a disturbance of a neuromuscular mechanism. In the two patients with dislocation, occlusal treatment eliminated muscular symptoms and the dislocations completely disappeared.     

β函数拟合正常(牙合)牙弓形态的研究

目的　本研究应用β函数,通过比较正常的三种牙弓形态,评价其对不同牙弓形态的拟合程度。方法　选择22副个别正常模型(男4人,女18人),平均年龄为13.6岁。分为三组:方圆形8副、卵圆形10副、尖圆形4副。将模型平行于平面扫描到计算机。由中切牙接触点、双侧尖牙牙尖点和双侧第二恒磨牙远中颊尖点五个点确定个体弓形。计算模型上其他各点与曲线的拟合度-相关系数(r)以及各点到拟合曲线的垂直距离之和、平均距离。比较β函数对三组弓形的拟合程度。结果　1β函数模拟22副模型的拟合度-相关系数(r)均大于0.96。三组曲线拟合度-相关系数(r)没有差别。2 方圆组上、下颌牙弓各点到拟合曲线的垂直距离之和、平均距离均比尖圆组大,P<0.05。3 三组弓形的 e值具有显著性差异,P<0.01。4 上颌磨牙宽度、深度分别比下颌大 4.9mm、4.4mm, P<0.001。而上、下颌牙弓 e值没有显著差异。结论　β函数可以较好地拟合正常弓形,对尖圆形牙弓比方圆形牙弓拟合更准确。β函数参数e值大小可以区分方圆、卵圆和尖圆三种牙弓形态。正常个体上、下颌牙弓形态相似。     

少牙畸形患者牙弓长度和宽度的临床研究

目的研究少牙畸形患者牙弓的长度和宽度,为临床诊治提供参考。方法选取少牙畸形与正常的牙模型各50副,用游标卡尺测量并计算牙弓长度和宽度的各项参数,采用ANOVA法进行统计分析。结果少牙畸形患者较正常的上、下牙弓长度分别少4.40mm和2.80mm,上、下颌尖牙宽度分别少2.82mm和2.70mm,上、下颌磨牙宽度分别少3.40mm和1.80mm。两组测量项目的差异均有统计学意义(P<0.01)。结论正畸治疗时,应当考虑到少牙畸形患者的牙弓长度和宽度均较正常小。     

Short-term treatment effects of quad-helix on maxillomandibular expansion in patients with maxillary incisor crowding

The purpose of this study was to evaluate the effects of the maxillary arch expansion on maxillomandibular arch widths in patients treated with the quad-helix versus untreated controls. The treatment group consisted of 50 consecutive patients treated for maxillary incisor crowding with a quad-helix appliance in the early mixed dentition. Lateral cephalograms and dental casts taken at the start (T0) and end (T1) of the quad-helix treatment were obtained. The control group consisted of 50 untreated patients with the same type of malocclusion. Two consecutive lateral cephalograms and dental casts of each untreated patient were taken at about the same time as T0 and T1. All these study materials were analyzed for comparison between the two groups. The mean ages at T0 and T1 in the two groups were about the same. The maxillary first molars moved and tipped distally in the treatment group and mesially in the control group. The quad-helix treatment actually expanded the mandibular and maxillary arches concurrently. The more the maxillary arch widths were expanded and the less the maxillary first molars were inclined distally, the more the mandibular arch widths were expanded. The quad-helix activation caused lingual tipping and mesiobuccal rotation of the maxillary first molars. The mesiobuccal rotation of the maxillary first molars could turn molar occlusal relationships for the better from Class II to Class I. The quad-helix treatment gives rise to spontaneous expansion of the mandibular arch concurrent with maxillary expansion in the early mixed dentition patients with maxillary incisor crowding.     

Dental crowding in primary dentition and its relationship to arch and crown dimensions among preschool children of Davangere

The purpose of the present study was to evaluate dental crowding in the deciduous dentition and its relationship to the crown and the arch dimensions among preschool children of Davangere. Stratified randomized selection of one hundred, 3-4 year old healthy children with all primary teeth erupted was done and divided into two groups. One group had children with anterior crowding in both the arches while the other had spacing. Alginate impressions of the upper and lower arches were made and the study casts were obtained. The tooth and arch dimensions were determined. Mesiodistal dimensions of all the teeth were significantly larger in the crowded arch group. However, the buccolingual dimensions of the maxillary right central incisor, mandibular lateral incisors and the maxillary molars and the crown shape ratio of maxillary lateral incisors, mandibular canines and mandibular right second molar was statistically different. No significant correlation was found between the arch width and the presence of crowding of deciduous dentition. The arch depth of the spaced dentition was greater when compared to the crowded ones. The arch perimeter of the crowded arches was significantly less than the spaced arches.     

下颌前伸时颞下颌关节应力分布的三维有限元研究

目的探讨下颌前伸运动时颞下颌关节内的应力分布情况。方法利用可视化人体图像建立包括上下牙列、下颌骨、颞下颌关节在内的三维有限元模型,在Patran中采用位移加载的方法模拟下颌前伸运动至对刃位,在Marc中计算并分析接触情况和应力分布特性。结果关节盘随髁突向前、下运动,髁突的前斜面首先与关节盘中间带中央部发生接触,随后髁突的外斜面与关节盘的中间带外侧部、关节窝的顶部与关节盘的后带发生接触。关节盘的中间带外侧部(3.10 Mpa)和髁突的前斜面(5.05 Mpa)等部位的应力值较大。结论在前伸运动时,应力集中区位于关节盘的中间带外侧部和髁突的前斜面。     

Retrospective evaluation of treatment outcome in Japanese children with complete unilateral cleft lip and palate. Part 1: Five-year-olds' index for dental arch relationships.

OBJECTIVE: To evaluate the dental arch relationships of Japanese children with complete unilateral cleft lip and palate (UCLP) and to examine the 5-year-olds' index for its validity. DESIGN: Retrospective study and comparison with previous reports. SUBJECTS: One hundred thirty-six children with complete UCLP who received primary cheiloplasty and palatoplasty in the Kyushu University Hospital from 1966 to 1999. MATERIALS: Dental models taken from children 53 to 67 months of age and their cephalograms. Methods: Study models were assessed using five scores; 1=excellent, 2=good, 3=fair, 4=poor, and 5=very poor, in accordance with the 5-year-olds' index and also evaluated using Huddart and Bodenham's numerical classification. Dental arch widths, three-dimensional maxillary dental arch form, and lateral cephalograms were traced and measured. The outcome by 5-year-olds' index was compared with Huddart and Bodenham's numerical classification, dental arch dimensions, and cephalometric measurements. RESULTS: Occlusal outcome evaluated by the 5-year-olds' index was rated 2.95, which was classified as fair. This index rating showed a significant relationship with numerical classification and dental arch length, but not with dental arch width. The index showed a relationship with mandibular form and position, but not with maxillary position. CONCLUSION: The occlusal outcome of the cases with UCLP was fair as evaluated using the 5-year-olds' index. The index evaluates the anteroposterior relationship of maxillary/mandibular dental arches but does not evaluate the collapse of maxillary segments.     

Fully digital fabrication of an occlusal device using an intraoral scanner and 3D printing: A dental technique

This dental technique describes a fully digital method for fabricating occlusal devices using a complete-arch intraoral scan and 3D printing. The maxillary and mandibular arches of a healthy, fully dentate volunteer were digitized using an intraoral scanner. A second scan and modified recording of the centric relation enabled a virtual arrangement of the maxillary and mandibular arches, both in centric relation and in the desired vertical dimension of occlusion. An occlusal device was subsequently designed virtually and fabricated from a light-polymerizing acrylic resin using a 3D printer. The occlusal device was tested for fit, occlusion, and patient-friendly handling. As only minor occlusal corrections were required, the fully digital procedure described is suitable for the fabrication of occlusal devices.     

An evaluation of asymmetry in TMJ radiographs.

The asymmetry of the mandibular fossae and condyles were measured to determine if there was a significant difference when comparing one side with the other. After all measurements were taken the test groups were separated into 70 acute TMJ patients and 70 control patients from general practice. It was found that the average differences between the right and left fossae of the TMJ and control groups were 0.17 mm and 0.16 mm respectively. Similarly the average difference between the right and left mandibular condyles of the two groups was approximately 0.2 mm. The differences in symmetry, obtained by comparing one side with the other, were clinically insignificant.There does not seem to be any reasonable possibility that the high incidence of TMJ dysfunctionpain syndrome reported in association with condylar displacement^{8–11, 14–16} is a result of fossae asymmetry or condylar asymmetry between the right and left sides. The controversy may be partially resolved in that only the superior portion of the fossa and a proportionally smaller part of the condyle are used to determine condylar position in the fossa. Marked asymmetry in the extreme anterior and posterior portions of the two mandibular condyles would not necessarily produce a significant difference in shape in that small part of the superior portion used to determine condylar position in the fossae.Based on this and previous research, the conclusion can be drawn that condylar displacement in the fossacannot be attributed to distortion in the radiographs, changes in head position, a lack of accuracy, or asymmetry of the mandibular condyles and fossa relative to the cranium or from one side to the other.     

Adaptive functional changes in the swallowing pattern of the tongue following expansion of the maxillary dental arch in subjects with and without cleft palate

In seven subjects with unilateral cleft lip and palate (UCLP), two subjects without cleft but with complete lingual crossbite, and two subjects with normal occlusion, tongue contact patterns against the hard palate, lingual surfaces of maxillary and mandibular teeth, and mandibular lingual mucosa during swallowing were analyzed three-dimensionally using electropalatography (EPG), before and after lateral expansion of the maxillary dental arch and after 3 months of retention. Before maxillary lateral expansion, all of the subjects with cleft palate showed no palate-tongue contact at rest, and limited movement of the tongue anteriorly and upward through the entire swallow cycle. Furthermore, the tongue contacted the hard palate for a relatively brief time during swallowing compared with the subjects without cleft with normal occlusion. After expansion, the tongue was seen to contact all areas of the hard palate and the lingual surface of the maxillary dentition for a longer period of time. After 3 months of retention, the tongue maintained contact with all lingual areas of the mandibular and maxillary arches and the hard palate.     

前方牵引矫治器不同力值反作用力的三维有限元分析

目的：通过建立包含颞下颌关节的颅颌面三维有限元模型,模拟前方牵引矫治器反作用力的加力方式,分析其在颞下颌关节区、颌骨的应力分布情况以及对各部位节点位移的影响。方法：选择1名健康男性受试者,通过CT扫描得到颅颌面的二维图像数据,借助Mimics、Magics、MSC等专用软件,采用连续、均质、线性、各向同性的线弹性材料,建立包括颞下颌关节和上、下颌骨的颅颌面三维有限元模型。然后在此基础上,根据前方牵引装置的反作用力原理建立加力模型,即采用与平面成后上方37°的施力方向,于下颌最底部加载3~6 N的力值,采用ANSYS10.0有限元分析软件,测定颞下颌关节区、颌骨的应力分布情况以及各部分位移的变化,并对结果进行分析、归纳和整理。结果：在同一角度下,关节窝和髁突头、颈部应力随加载力的增大而增大,下颌最大应力出现在节点力加载部位颏部,上颌最大应力出现在刚性固定面。同时该模型出现微小的位移变化,颅颌面各部分位移随节点力的增大而增大,颅上颌位移由颅底部和平面向颅顶部逐渐减小,下颌骨的位移由前部到后部逐渐减小,并出现顺时针方向旋转。结论：前方牵引矫治器对颞下颌关节区及颌骨产生反作用力的影响,且随着加载力的增大,其产生的反作用力和形变随之增大。颏部可能出现变形,下颌顺时针方向旋转。