Kinesiographic study of the mandible in young patients with unilateral posterior crossbite.

It is generally assumed that children with posterior crossbites have abnormal mandibular movements; however, this assumption has not been clearly evaluated. The purpose of this investigation was to study the movements and the resting position of the mandible in 2 samples of 30 subjects, one aged 10 to 14 years with right posterior crossbite, the other aged 10 to 15 years with normal occlusion. Subjects in both groups exhibited a Class I skeletal relationship and mesofacial growth pattern. A mandibular kinesiograph was used to record both the mandibular resting position and dynamic movements. Mandibular movements were recorded during (1) maximum excursions (opening-closing, protrusion, right and left excursions), (2) swallowing, and (3) mastication. The results showed no differences between groups in the extension of the movements during closing and protrusion. However, crossbite patients exhibited a significant lateral shift during these movements. Right and left excursions were also similar between groups. The dimension of the freeway space was similar between groups, but the lateral shift found in centric occlusion was also present in the crossbite group when the mandible was at rest. The crossbite group more frequently showed a pattern of abnormal swallowing. No differences were found in any of the parameters studied during the masticatory cycle. There was no relationship between the side of the crossbite and the masticatory preference side. In conclusion, posterior crossbite patients showed a lateral shift in some movements that persisted when the mandible was at rest.     

Functional unilateral posterior crossbite. Orthodontic and functional aspects

summary The purpose of the study was to evaluate the effect of early orthodontic treatment of functional unilateral posterior crossbite (FUPC) and to evaluate temporomandibular function in the short and long term. Orthodontic treatment consisted of slow expansion of the maxillary dental arch by means of a removable expansion plate, with flat coverage of the occlusal surfaces of the left and right posterior teeth. Evaluation of the occlusion showed a strong correlation between the crossbite side and the direction of the RCP-ICP slide and with the side of first occlusal contact in RCP. In 26 of 27 children that were treated (one withdrew), the average time required for correction of the crossbite was 7 months, followed by a retention period, on average, for 6 months after completion of treatment. Early orthodontic treatment resulted in an elimination of occlusal disturbances, and the crossbite remained stable on follow-up during an average of 8 years after the retention period, except in two children with a class III tendency. In nine other children an orthodontic anomaly had developed requiring further treatment (two children showed crowding and seven children showed a class II malocclusion). This study showed that FUPC can be treated adequately by early orthodontic intervention; however, its correction does not guarantee the absence of functional disturbances at a later age. Therefore, FUPC should be treated early in order to achieve normal growth and development rather than to prevent temporomandibular disorders.     

The unilateral posterior functional crossbite: an opportunity to restore form and function

The unilateral posterior crossbite (UPXB) with functional shift of the mandible is commonly encountered in young children and adolescents. Differential diagnosis and the impact this type of malocclusion might have upon the growth and development of dental and facial components are discussed. Impaired function and compromised facial esthetics may be consequences of untreated UPXBs with functional shifts. Appropriate treatment protocols and specific orthodontic appliances intended to correct these problems are presented.     

早期上颌扩弓纠正单侧后牙反改善功能性下颌偏斜

目的:通过头颅定位后前位片(P-A)测量,探讨上颌扩弓纠正单侧后牙反牙合,改善早期功能性下颌偏斜的临床效果。方法:混合牙列或早期恒牙列,上颌单侧后牙反牙合伴有/或不伴有前牙反牙合,下颌功能性偏斜病例16例,采用上颌Quad-Helix扩弓方法,矫治前后头颅定位后前位片(P-A)测量分析,用统计软件处理数据。结果:单侧后牙反牙合矫正后,面部不对称有明显改善。结论:混合牙列或早期恒牙列,由于单侧后牙反牙合导致的功能性下颌偏斜,采用扩大上颌牙弓方法,可使下颌骨的不对称得到明显改善,是早期纠正下颌功能性偏斜的有效方法。     

早期上颌扩弓纠正单侧后牙反(牙合)改善功能性下颌偏斜

目的:通过头颅定位后前位片(P-A)测量,探讨上颌扩弓纠正单侧后牙反(牙合),改善早期功能性下颌偏斜的临床效果.方法:混合牙列或早期恒牙列,上颌单侧后牙反(牙合)伴有/或不伴有前牙反(牙合),下颌功能性偏斜病例16例,采用上颌Quad-Helix扩弓方法,矫治前后头颅定位后前位片(P-A)测量分析,用统计软件处理数据.结果:单侧后牙反(牙合)矫正后,面部不对称有明显改善.结论:混合牙列或早期恒牙列,由于单侧后牙反(牙合)导致的功能性下颌偏斜,采用扩大上颌牙弓方法,可使下颌骨的不对称得到明显改善,是早期纠正下颌功能性偏斜的有效方法.     

Morphological and positional asymmetries of young children with functional unilateral posterior crossbite.

This prospective clinical study evaluated the morphological and positional mandibular asymmetry of young patients with functional unilateral posterior crossbite. The sample included 9 girls and 6 boys (8.8 +/- 1.0 years of age), evaluated at the initiation of treatment and approximately 6 months after the retention phase (1.1 +/- 0.2 years after initiation of treatment). Each patient had a complete unilateral posterior crossbite involving 3 or more posterior teeth, a functional shift from centric relation-intercuspal position, and no signs or symptoms of temporomandibular disorder. A bonded palatal expansion appliance was used to rapidly expand the maxilla (1 month) and retain the treatment changes (6 months). Zonograms were used to assess articular joint spaces, and submental vertex radiographs were used to assess morphological and positional asymmetry. The results showed that the mandible was significantly longer on the noncrossbite side than it was on the crossbite side. The asymmetry was most evident for the ramus and involved both the condylar and the coronoid processes. The posterior and superior joint spaces were larger on the noncrossbite side than they were on the crossbite side. After treatment and retention, the mandible showed no significant morphological asymmetries. Mandibular growth was greater on the crossbite side than it was on the noncrossbite side, and the mandible had been repositioned; the crossbite side had rotated forward and medially toward the noncrossbite side. We concluded that unilateral posterior crossbites produce morphological and positional asymmetries of the mandible in young children, and that these asymmetries can be largely eliminated with early expansion therapy.     

单侧后牙扩弓的有效方法

目的:探讨附颊屏的(牙合)垫矫治器进行单侧后牙扩弓,治疗单侧后牙反(牙合)的可行性.方法:选择混合牙列期或恒牙列早期的单侧后牙反(牙合)病例4例,男2例,女2例,年龄12～15岁,平均13.5岁,应用附颊屏的(牙合)垫矫治器配合改良横腭杆进行治疗,对矫治前后模型进行测量分析.结果:4例患者经过3～5个月的治疗,单侧后牙反(牙合)均纠正,效果满意.模型分析显示,反(牙合)侧治疗前后第一、第二前磨牙腭尖及第一磨牙近中腭尖到腭中缝的距离变化均较正常侧明显.结论:附颊屏的(牙合)垫矫治器配合改良横腭杆治疗单侧后牙反(牙合),既可保持正常侧良好的咬合关系,又可快速矫治后牙反(牙合).     

Unilateral posterior crossbite with mandibular shift: a review

Based on this literature review, early orthodontic treatment of unilateral posterior crossbites with mandibular shifts is recommended. Treatment success is high if it is started early. Evidence that crossbites are not self-correcting, have some association with temporomandibular disorders and cause skeletal, dental and muscle adaptation provides further rationale for early treatment. It can be difficult to treat unilateral crossbites in adults without a combination of orthodontics and surgery. The most appropriate timing of treatment occurs when the patient is in the late deciduous or early mixed dentition stage as expansion modalities are very successful in this age group and permanent incisors are given more space as a result of the expansion. Treatment of unilateral posterior crossbites generally involves symmetric expansion of the maxillary arch, removal of selective occlusal interferences and elimination of the mandibular functional shift. The general practitioner and pediatric dentist must be able to diagnose unilateral posterior crossbites successfully and provide treatment or referral to take advantage of the benefits of early treatment.     

Class III malocclusion with severe facial asymmetry, unilateral posterior crossbite, and temporomandibular disorders.

A 22-year-old woman had a Class III malocclusion with severe facial asymmetry, unilateral posterior crossbite, and temporomandibular disorders. A clicking sound was noted in the temporomandibular joint on the posterior crossbite side during jaw opening, and she complained of pain in the masticatory muscles on both sides. The articular disc on the crossbite side was displaced anteriorly without reduction. The patient was treated orthodontically with edgewise appliances and surgically with LeFort I and intraoral vertical ramus osteotomies. The result of the combined surgical-orthodontic treatment was facial symmetry and optimal occlusion. The displaced articular disc moved into a normal position, and most of the temporomandibular disorder symptoms improved. At the 2.5-year follow-up, the temporomandibular joint conditions had been maintained.     

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后牙反是一种临床常见的错畸形,可引起关节、肌肉、咬合等方面的功能和结构改变,从而诱发颞下颌关节紊乱病(temporomandibular disorders,TMD)。本文针对后牙反的病因和机制及其导致颞颌关节的功能和结构性改变,后牙反与TMD的症状和体征的关系及早期矫治后颞下颌关节的变化,回顾相关文献,做一综述。     

Alterations of the rat temporomandibular joint in functional posterior displacement of the mandible

Functional malocclusion that induces posterior condylar displacement may affect the remodeling processes of the temporomandibular joint structures. We tested the hypothesis that intermittent posterior condylar displacement due to functional malocclusion traumatizes condylar cartilage and joint innervated nerve fibers. Thirty-nine eight-week-old Wistar rats were used. To induce functional posterior condylar displacement, guiding appliances were attached to maxillary incisors of 24 rats for four, seven, and 14 days. Fifteen normal rats served as controls. Sections were stained with hematoxylin and eosin or processed for immunohistochemistry of protein gene product 9.5 and growth-associated protein-43 (GAP-43). Functional posterior condylar displacement led to a diminution in proliferative cells, reduction in cartilage width, and re-expression of GAP-43-immunoreactive nerve fibers. These results indicate that intermittent posterior condylar displacement due to functional malocclusion causes dysfunctional remodeling of condylar cartilage and nerve injury.     

Effect of functional shift of the mandible on lubrication of the temporomandibular joint

Lubrication of synovial joints reduces the coefficient of friction of the articular cartilage surface. To investigate the effect of malocclusion on the lubrication of the temporomandibular joint (TMJ), we evaluated lubricin expression in the rat TMJ immunohistochemically, under conditions of functional lateral shift of the mandible, during period of growth. Thirty 5-week-old male Wistar rats were divided into experimental, recovery, and control groups. Each rt in the experimental and recovery groups was fitted with an acrylic-plate guiding appliance. The rats in the experimental and control groups were killed at 14 and 28 days after the appliance was attached. Each rat in the recovery group was detached from the appliance at 14 days, and was killed 14 days after the appliance was removed. In the experimental group, the expression of lubricin staining in TMJ cartilage was significantly decreased during the experimental period. In the recovery group, the expression of lubricin staining in TMJ cartilage was significantly greater than in the experimental group, and there was no significant difference at 28 days between the control and recovery groups. Analysis of these data suggests that a functional lateral shift of the mandible during the growth period influences lubrication of the TMJ.     

单侧后牙反(牙合)者髁突侧向运动轨迹的研究

目的 通过记录单侧后牙反（牙合）者与正常（牙合）者下颌侧向运动时髁交在三雏方向上的运动轨迹，探讨单饲后牙反（牙合）者髁突饲向运动轨迹的特征，揭示其与正常（牙合）之间的差异。方法 正常（牙合）15例，单饲后牙反（牙合）7例。应用计算机化的髁突运动轨迹描记仪（computer-Aided Axiography，CADIAX）Ⅰ型以及分析软件（Gamma Dental Software for Windows 2．3．2．22，GDSW）记录下颌做左右饲向运动时髁突在水平面及矢状面上的 运动轨迹。结果实验组侧向运动中非工作侧矢状向最大位移量显著小于正常对照组，工作侧髁突向后运动的幅度大于正常对照组。结论 单侧后牙反（牙合）者髁突侧向运动轨迹形态与正常（牙合）有明显差异，其两侧关节囊、韧带松驰。     

Mandibular asymmetry and condylar position in children with unilateral posterior crossbite.

The purpose of this retrospective study was to determine if condylar position in children with functional unilateral crossbites was different from that found in children with Class I noncrossbite malocclusions and if there was a change in condylar position after correction of the crossbite by palatal expansion. Mandibular asymmetry in children with functional unilateral posterior crossbite was also compared to that of a Class I noncrossbite group. Thirty-one children aged 6 to 14 years (mean, 9.3 years; standard deviation, 2.2) with functional unilateral crossbites were compared to 31 children aged 9.5 to 14.1 years (mean, 11.9 years; standard deviation, 1.3) exhibiting Angle Class I noncrossbite malocclusions. Pretreatment submentovertex radiographs were used to study mandibular skeletal, dental, and positional asymmetries with reference to cranial floor and mandibular coordinate systems. In addition, the anterior, superior, and posterior joint spaces were measured to determine differences between the groups with the use of pretreatment and posttreatment horizontally corrected tomograms of the temporomandibular joints. Finally, the distances of the mesiobuccal cusp of the upper first molar relative to the buccal groove of the lower first molar were measured in both groups before treatment. Univariate analyses revealed that the mandibles of children in the functional unilateral posterior crossbite group exhibited asymmetry in both anteroposterior and transverse dimensions when compared with the Class I noncrossbite group (P <. 05). These asymmetries were the result of a functional deviation of the mandible that was present in all subjects in the crossbite group. This deviation was manifested occlusally by a Class II subdivision on the crossbite side as indicated from the study model analysis (P <.05). Examination of condylar position as evidenced by horizontally corrected tomograms demonstrated a large standard deviation, resulting in an inability to detect any significant differences within or between groups at both T1 and T2 (P >.05). This study raised the question of the appropriateness of measuring joint spaces for routine diagnostic purposes.     

Improvement of masticatory kinematic parameters after correction of unilateral posterior crossbite: Reasons for functional retention

Objective:To evaluate reverse-sequencing chewing cycles (RSCC) and their kinematic parameters on both sides before and after correction with the Function Generating Bite (FGB) appliance.Materials and Methods:Forty-seven patients, 8.3 ± 1.1 (mean ± SD) years of age, with unilateral posterior crossbite (35 on the right side, 12 on the left side) and 18 age-matched controls (9.1 ± 0.8 years) were selected for the study from the orthodontic division of the University of Turin, Italy. The crossbite was corrected in all patients using FGB, and mandibular motion was recorded with a kinesiograph K-7 (Myotronics, Tukwila, Wash), during chewing on both sides of a soft and a hard bolus before and after correction.Results:After correction, the percentage of RSCC significantly decreased for soft and hard (P < .001) boluses and fell within the normal range for 75% of the patients. The indices of the chewing pattern (closure angle, axis, maximum lateral excursion) significantly improved (P < .001), becoming symmetric between sides.Conclusions:The results of this study showed that the functional appliance, FGB, was able to lower the percentage of RSCC significantly, bringing them back to the normal range in 75% of cases, and to improve the kinematic parameters that become symmetric between sides.     

儿童功能性单侧后牙反患者的髁突对称性及矫治后髁突位置变化的研究

目的探讨儿童功能性单侧后牙反患者的髁突对称性及上颌扩弓治疗后髁突位置的变化。方法选择22例通过上颌扩弓成功矫治的功能性单侧后牙反儿童患者,男10例,女12例,年龄6.0-8.5岁,平均7.5岁作为实验组。另选择22例正常患者,男11例,女11例,年龄6.5-9.0岁,平均7.5岁作为对照组。反组矫治前后与对照组患者均拍摄曲面断层片和双侧闭口位矫正薛氏位片,测量髁突形态的不对称指数和髁突在关节窝中的相对位置。用SPSS 12.0软件进行统计分析。结果反组患者两侧髁突形态无明显不对称,与对照组相比,髁突高度(CH)、升支高度(RH)以及两者之和(CH+RH)的不对称指数均无统计学差异。反组矫治前(T1)两侧髁突在关节窝中的位置有明显差异,非反侧关节前间隙减小(P<0.05),上后间隙增大(P<0.05)。非反侧髁突在关节窝中的位置(R)相对反侧更加靠前(P<0.01)。矫治后(T2)双侧髁突位置变得相对对称。结论儿童功能性单侧后牙反患者的髁突形态相对对称,而髁突位置存在不对称性,说明下颌向反侧发生功能性偏斜,而这种偏斜并未导致髁突发生骨性不对称;正畸治疗可使两侧髁突位置更加协调。     

Long-term follow-up of early treatment of unilateral forced posterior crossbite with regard to temporomandibular disorders and associated symptoms

Forty-four subjects, who at the age of 4 years had been treated for unilateral forced cross-bite by grinding or by maxillary arch expansion, were 16-19 years later followed-up by means of a questionnaire about their present condition with regard to temporomandibular disorders (TMD). Twenty-two of them had received only early treatment (early questionnaire group) and 22 had received late treatment (late questionnaire group). Fourteen of the subjects who received late treatment also received early treatment. Twenty-nine of the subjects were also examined clinically. Eighteen of these had only received early treatment at 4 years of age (early clinical group), whereas 11 of them also received later treatment in the mixed or permanent dentition because of relapse (late clinical group). No significant differences were found between the early and late groups with regard to signs and symptoms of TMD. Most of the young adults who had undergone orthodontic treatment had well-functioning masticatory systems, and severe TMD signs and symptoms were rare. The results of this study suggest that relapse of early orthodontic treatment and further need of treatment does not influence the later status of subjective symptoms or clinical signs of TMD in young adults.     

Tooth abrasion in unilateral posterior crossbite in the deciduous dentition

The aim of this study was to evaluate the degree of abrasion in posterior teeth of subjects with unilateral posterior crossbite in the deciduous dentition. A group of 54 untreated subjects in deciduous dentition (test group, TG) was selected from a parent sample of 1500 patients from the files of the Department of Orthodontics of the University of Florence. A sample of 20 subjects with normal occlusion in the deciduous dentition was selected as the control group (CG). As experimental units in TG, 54 crossbite sides (CB, consisting of 33 right and 21 left crossbite sides) and 54 noncrossbite sides (NCB) were used. In CG, one randomly chosen single side for each subject (NCBC) was used for comparisons. The findings of the present study indicated that subjects with unilateral crossbite in the deciduous dentition showed a significantly smaller degree of dental abrasion in the crossbite side when compared with both the opposite side and control group sides. The lack of abrasion in crossbite sides was primarily due to a significantly lesser degree of abrasion of the upper deciduous canines.