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.     

单侧后牙正锁(牙合)患者下颌侧方运动时的髁突轨迹特征

目的:探讨单侧后牙正锁(牙合)患者在下颌侧方运动过程中髁突的运动轨迹特征及其与正常(牙合)者之间的差异.方法:选取单侧后牙正锁(牙合)患者26例为实验组,个别正常(牙合)26例为对照组,应用髁突运动轴图描记仪(computer aided diagnosis axiograph,CADIAX)记录下颌侧方运动时髁突的运动轨迹.实验数据采用SPSS10.0软件包分析,选用成组t检验、配对t检验或秩和检验比较组间差异有无统计学意义.结果:实验组下颌侧方运动过程中髁突轨迹不流畅变异大,两侧运动轨迹不对称.非锁(牙合)侧髁突的矢状位移、垂直位移以及空间最大位移大于锁(牙合)侧和对照组,水平位移小于后者,差异有统计学意义(P<0.05);非锁(牙合)侧髁突的矢状倾斜度大于锁(牙合)侧和对照组,水平倾斜度小于后者,差异有统计学意义(P<0.05).结论:单侧后牙正锁(牙合)患者下颌侧方运动过程中两侧髁突运动轨迹不对称.     

单侧后牙反(牙合)髁突前伸运动轨迹的研究

目的:探讨单侧后牙反牙合髁突前伸运动轨迹的特征并比较与正常牙合之间的差异。方法:正常牙合5人,单侧后牙反牙合7人,采用计算机化的髁突运动轨迹Ⅰ型描记仪及分析软件,记录下颌最大前伸运动时髁突在水平面及矢状面上的运动轨迹。结果:单侧后牙反牙合者前伸后退运动轨迹多不重合,反牙合侧前伸髁道斜度明显大于对侧。结论:单侧后牙反牙合者存在前伸牙合干扰,其两侧颞下颌关节不对称。     

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。     

单侧后牙反(牙合)患者的咀嚼肌肌电图分析

目的: 通过对单侧后牙反(牙合)患者咀嚼肌肌电检查,分析单侧后牙反(牙合)对咀嚼功能的影响.方法:用肌电图仪记录20 例(男11 例,女 9 例)单侧后牙反(牙合)患者和20 例(男10 例,女10 例)正常对照组在下颌姿势位、紧咬和双侧咀嚼时咬肌和颞肌前束的肌电数据.计算咬肌的活动不对称指数(ASMM)和颞肌前束的活动不对称指数(ASTA),然后进行统计学分析.结果:在紧咬和双侧咀嚼时,单侧后牙反(牙合)组咬肌和颞肌前束肌电值明显低于对照组(P＜0.05),反(牙合)侧明显低于非反(牙合)侧;单侧后牙反(牙合)组与对照组ASMM和ASTA在紧咬和双侧咀嚼时有显著性差异(P＜0.05);单个后牙反(牙合)组与多个后牙反(牙合)组ASMM和ASTA在紧咬和双侧咀嚼时有显著性差异(P＜0.05).结论:单侧后牙反(牙合)对咀嚼肌功能有明显的影响,应对其进行积极治疗.     

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.     

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.     

Muscular activation during reverse and non-reverse chewing cycles in unilateral posterior crossbite

The aim of this study was to characterize the kinematics and masseter muscle activation in unilateral posterior crossbite. Eighty-two children (8.6 ± 1.3 yr of age) with unilateral posterior crossbite and 12 children (8.9 ± 0.6 yr of age) with normal occlusion were selected for the study. Electromyography (EMG) and kinematics were concurrently recorded during mastication of a soft bolus and a hard bolus. The percentage of reverse cycles in the group of patients was 59.0 ± 33.1% (soft bolus) and 69.7 ± 29.7% (hard bolus) when chewing on the crossbite side. When chewing on the non-affected side, the number of reverse cycles was 16.7 ± 24.5% (soft bolus) and 16.7 ± 22.3% (hard bolus). The reverse cycles on the crossbite side were narrower with respect to the cycles on the non-affected side. Although both types of cycles in patients resulted in lower EMG activity of the masseter of the crossbite side than of the contralateral masseter, the activity of the non-affected side was larger for reverse than for non-reverse cycles. It was concluded that when chewing on the crossbite side, the masseter activity is reduced on the mastication side (crossbite) and is unaltered (non-reverse cycles) or increased (reverse) on the non-affected side.     

Transverse skeletal and dental asymmetry in adults with unilateral lingual posterior crossbite.

BACKGROUND: Posterior unilateral lingual crossbite (PUXB) is a common malocclusion in children. However, the extent to which PUXB affects the dentition and craniofacial structures in adults has not been fully defined. We investigated dental and skeletal asymmetry in adults with PUXB. METHODS: We randomly selected 15 crossbite subjects (mean age, 26.2 years) and 15 matched controls (mean age, 30.6 years) from 3000 records. Mounted pretreatment dental casts were measured to assess dentoalveolar asymmetry, and posteroanterior radiographs were used to evaluate left-right skeletal asymmetry and positional deviations of the mandible. RESULTS: A statistically significant difference in mandibular transverse dental asymmetry was observed between adults with PUXB and the control group. However, no significant differences were found in the right-left skeletal asymmetry, although the PUXB group showed more positional deviation of the mandible. Moreover, condylar position analysis indicated that the crossbite group did not show any greater functional shifts than the control group. CONCLUSIONS: We concluded that PUXB in adults is primarily due to dentoalveolar asymmetry and positional deviation of the mandible and not simply to right-left skeletal asymmetry of the mandible. These data suggest that untreated PUXB in children might lead to progressive asymmetric compensation of the condyle-fossa relationship and result in a positional deviation of the mandible, which, along with a distinct dentoalveolar asymmetry, maintains the crossbite occlusion in adults.     

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).     

Reverse-sequencing chewing patterns evaluation in anterior versus posterior unilateral crossbite patients

It is well established that patients with a unilateral posterior crossbite exhibit reverse-sequencing chewing patterns when chewing on the affected side. The aim of the study was to compare the prevalence of reverse-sequencing chewing cycles in patients with anterior versus posterior unilateral crossbite during chewing soft and hard boluses. Eighty-six children (39 boys, 47 girls) were included in the study: 26 (10.4 ± 2.7 years) with unilateral anterior crossbite, 43 (10.2 ± 4.2 years) with unilateral posterior crossbite, and 17 (10.6 ± 2 years) with normal occlusion were selected for the study. Mandibular movements were measured with a kinesiograph (K7, Myotronics Inc. Tukwila). The kinematic signals were analyzed using custom-made software. The results showed a low prevalence of reverse-sequencing chewing cycles in patients with anterior crossbite, without any significant difference between sides and with the control group, with both soft (P = 0.33) and hard (P = 0.29) bolus. The patients with posterior unilateral crossbite showed a significant higher prevalence of reverse-sequencing chewing cycles during chewing on the crossbite side with respect to the non-crossbite side (P < 0.001) and to the control group (P < 0.001). Comparing the patients with anterior versus posterior unilateral crossbite, a significant difference (P < 0.001) in the prevalence of reverse chewing cycles was demonstrated during chewing on the posterior crossbite side only with both soft and hard bolus. In conclusion, patients with anterior versus posterior unilateral crossbite show different functional characteristics depending on which dental region is involved.     

Effects of therapy on masseter activity and chewing kinematics in patients with unilateral posterior crossbite

ObjectiveTo describe the effects of therapy on masseter activity and chewing kinematic in patients with unilateral posterior crossbite (UPC).DesignFifty children (age: mean ± SD: 9.1 ± 2.3 years) with UPC (34 on the right side, 16 on the left side) and twenty children (age: 9.5 ± 2.6 years) with normal occlusion were selected for the study. The mandibular motion and the muscular activity during chewing soft and hard boli were simultaneously recorded, before and after correction with function generating bite, after a mean treatment time of 7.3 ± 2.4 months plus the retention time of 5–6 months. The percentage of reverse cycles and the percent difference between ipsilateral and contralateral peaks of the masseter electromyography envelopes were computed.ResultsBefore therapy, the percentage of reverse cycles during chewing on the crossbite side was greater in patients than in controls (P < 0.001) and significantly reduced after therapy (P < 0.001) towards the reference normal value (soft bolus; pre: 57 ± 30%, post:12 ± 17%; hard bolus; pre: 65 ± 34%, post: 12 ± 13%; reference value: soft bolus 4 ± 2%, hard bolus 5 ± 3%). Before therapy the percent difference between electromyography envelope peaks in patients was lower than in controls (P < 0.01) and significantly increased after therapy (P < 0.05) becoming similar to the reference normal value.ConclusionsThe correction induced a normal-like coordination of masseter muscles activity together with a significant reduction of the reverse chewing patterns. The previous altered muscular activation corresponded to the altered kinematics of reverse chewing cycles that might be considered a useful indicator of the severity of the masticatory function involvement.     

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.     

Motion of the human mandibular condyle during mastication

It has been reported that loading to the mandible during closing movement makes the condylar path move more in the superior direction than that during the free closing movement. In this study, the hypothesis was tested that the displacement of the condyle on the chewing side is greater in the direction of the mandibular fossa than that on the non-chewing side. Using a six-degrees-of-freedom jaw movement recording system, we recorded condylar motion in 12 healthy adults without TMD, during the chewing of a large hard gummy jelly. The maximum displacements at the condyle on the chewing side from the maximum intercuspation (CO) position were significantly larger in the superior and medial directions at the initial stage and in the posterior direction at all stages (0.5 mm, 0.5 mm, and 0.6 mm, respectively) than those on the non-chewing side (0.0 mm, 0.1 mm, and 0.1 mm, respectively). This suggests that, in healthy adults, the condyles at CO are located in a position such that excessive load is not applied to the temporomandibular joint when there are the aforementioned displacements.     

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.