Mandibular Displacement Research Articles

The influence of altered occlusal guidance on condylar displacement

This study investigated mandibular displacement and masticatory muscle activity during clenching in lateral occlusal position in relation to the lateral occlusal pattern. Twenty healthy human subjects (mean = 26.5 years) volunteered for this study. Metallic occlusal overlays were fabricated for the lower working side canine to second molar and non-working side second molar in order to simulate a canine protected occlusion, group function occlusion and bilateral balanced occlusion (balancing contact). Three-dimensional displacements of the bilateral condyle and electromyography (EMG) activities in the bilateral masseter, anterior and posterior temporalis were recorded during maximal clenching. The experimental occlusal pattern was revealed to have statistically significant effects on both condylar displacement and EMG activity (P < 0.001 and P < 0.001, respectively). When compared to the simulated group function occlusion, the simulated canine protected occlusion and balancing contact caused statistically significant smaller superior displacements of the non-working side condyle, which suggests that they may result in reduced temporomandibular joint (TMJ) loading. Furthermore, the simulated canine protected occlusion was associated with the lowest EMG activity, which suggests that this occlusal pattern has the capacity to reduce the level of parafunctional activity.

A histomorphometric study of adaptive responses of cancellous bone in different regions in the sheep mandibular condyle following experimental forward mandibular displacement

Forward mandibular displacement in animal models is associated with faster and/or redirected condylar growth. Here the effect of forward displacement induced with an intraoral appliance on modelling/remodelling of the mandibular condyle was investigated in eight, 4-month-old, castrated male Merino sheep, randomly allocated to experimental and control groups ( n=4 in each group). The study period was 15 weeks, during that time, (1) calcein, (2) tetracycline, and (3) alizarin red S fluorochromes were given to all animals from day 1. Midsagittal sections of the temporomandibular joints were selected for analysis. Dynamic variables of bone formation, static indices of bone-forming and -resorbing activity, and structural indices of trabecular bone were estimated histomorphometrically. The sampling site was divided into two regions for analysis: (a) a ‘subchondral region’ (2 and 3 labels only), believed to be the bone newly formed during the experimental period; (b) a ‘central region’ (labelled by all three fluorochromes), believed to be the bone that existed before the experiment. Regional differences in adaptive response were found. In the experimental group, the bone-volume fraction (BV/TV) of the subchondral regions had decreased, although the specific bone-surface and bone-formation rates had increased. This low BV/TV was associated with decreased trabecular thickness and increased trabecular separation. In the central condylar region of the experimental group, BV/TV was unchanged, but an increased osteoid surface was apparent when the eroded surface was taken into consideration. These adaptive condylar responses to forward mandibular displacement appeared to be the result of increased osteoblastic activity. Further studies are recommended to examine why the subchondral and central regions responded differently.

Mandibular skeletal growth and modelling between 10 and 15 years of age.

This study pertains to a random sample of untreated French-Canadian adolescents (79 females and 107 males) evaluated at 10 and again at 15 years of age. Superimpositions on natural reference structures were performed to describe condylar growth and modelling of 11 mandibular landmarks. Superimpositions on natural cranial/cranial base reference structures were performed to describe mandibular displacement and true rotation. The results showed significant superior and posterior growth/modelling of the condyle and ramus. Males underwent significantly (P < 0.01) greater condylar growth and ramus modelling than females. With the exception of point B, which showed significant superior drift, modelling changes for the corpus landmarks were small and variable. The mandible rotated forward 2-3.3 degrees and was displaced 9.6-12.7 mm inferiorly and 1.9-2.7 mm anteriorly. Individual differences in ramus growth and modelling, both amount and direction, can be explained by mandibular rotation and displacements. Multivariate assessments revealed that superior condylar growth and ramus modelling were most closely associated with forward rotation and inferior mandibular displacement. Posterior growth and modelling were most closely correlated with anterior mandibular displacement and forward rotation. Modelling of the lower anterior border was independent of rotation and displacement.

Displacement of the Mandible in a Child With Congenital Unilateral Temporomandibular Joint Ankylosis Treated With Two-Stage Condylar Replacement: A Long-Term Study With the Aid of Roentgen Stereometric Analysis

Abstract Objective: To monitor mandibular displacement in three dimensions with a high degree of accuracy before, during, and after treatment. Design: Prospective roentgen stereometric analysis from age 3 years 7 months to age 13 years 8 months. Setting: Center for Craniofacial Anomalies and Department of Maxillofacial Surgery, Malmo University Hospital, Malmo, Sweden. Patient: Girl with unilateral congenital temporomandibular joint (TMJ) ankylosis and marked facial asymmetry. Interventions: Epipharyngeal inspection at age 2 years 6 months and insertion of implants under general anesthesia. Resection of the affected right condyle at age 5 years 4 months, replacement of the ramus-condyle complex with a custom made titanium prosthesis at age 5 years 5 months, and replacement of the artificial condyle by a costochondral graft at age 9 years 7 months. Roentgen examinations were performed at intervals from age 3 years 7 months to age 13 years 8 months. Body length was measured annually. Main Outcome Measures: ...

Impact of balancing-side tooth contact on clenching induced mandibular displacements in humans.

This study investigated mandibular displacements during clenching in the lateral mandibular position in relation to lateral occlusal relationships. Twelve healthy human subjects (mean=26.7 years) volunteered for this study. Acrylic occlusal devices were fabricated for the lower working-side canine, working-side second molar and balancing-side second molar in order to simulate a dominant canine guidance, working-side interference (WI), balancing-side interference (BI) and bilateral balanced occlusion (BO). Vertical displacements of the mandible were recorded by linear variable differential transformers during submaximal clenching in the right lateral position. The four experimental occlusal conditions were revealed to have a significant effect on mandibular displacement patterns (ANOVA, P < 0.001). A dominant canine raiser caused a mandibular elevation with the smallest displacement at the working-side premolar and the largest displacement at the balancing-side second molar. Clenching on a WI or BI caused a mandibular elevation with the smallest displacement at the working- or balancing-side second molar, respectively. A BO resulted in the smallest upward displacement among the four experimental conditions. These results suggest that the nature of reaction forces at the temporomandibular (TM) joints caused by the elevation of the mandible varies in a predictable manner depending upon lateral occlusal relationships.

Changes in mandibular position and upper airway dimension by wearing cervical headgear during sleep.

We previously reported that the wearing of cervical headgear induced forward displacement of the mandible in awake subjects. However, it was unclear whether such mandibular displacement also occurred during sleep. The purpose of this study was to examine changes in mandibular position and oropharyngeal structures that were induced by the wearing of cervical headgear during sleep. Ten healthy adults (7 male and 3 female) who gave their informed consent were included in this study. A pair of lateral cephalograms was taken with the patient in the supine position with and without cervical headgear at end-expiration during stage 1 to 2 non-rapid-eye-movement sleep. The Wilcoxon signed-rank test was used for a statistical analysis. The amount of jaw opening was significantly decreased by the wearing of the cervical headgear (P <.05), although no significant anteroposterior mandibular displacement was induced. The sagittal dimension of the upper airway was significantly reduced (P <.05); however, no significant changes were observed in the vertical length of the upper airway. Although the hyoid bone and the third cervical vertebra moved significantly forward by the wearing of the cervical headgear (P <.05), the relationship among the mandibular symphysis, the hyoid bone, and the third cervical vertebra did not change. These results suggest that cervical headgear significantly reduced the sagittal dimension of the upper airway during sleep, although there was no significant anteroposterior displacement of the mandible.

Dental evaluation of scuba diving mouthpieces using a subject assessment index and radiological analysis of jaw position

Objective—To compare two experimental scuba mouthpieces with a commercially available design. Methods—A laboratory study using six men to assess effort, muscle pain, muscle fatigue, facial discomfort, tooth discomfort, and loss...

Influence of periodontal receptors on the jaw-jerk reflex amplitude in man.

To study the role of periodontal mechanoreceptors in the modulation of the human jaw-jerk reflex, 60 reflexes were elicited in each of six healthy individuals under three different conditions: (a) with unilateral tooth support on the ipsilateral side; (b) with support on the contralateral side; and (c) with support and local anesthesia of the periodontal tissues on the ipsilateral side. During all conditions, background muscle activity and mandibular displacement were kept as constant as possible. Using on-surface EMG and the amplitude of the first peak of the biphasic jaw-jerk potential as the outcome variable, a condition-dependent reflex amplitude was found for the visually controlled right anterior temporalis muscle. Specifically, the 'ipsilateral support plus anesthesia' condition yielded higher amplitudes than the 'ipsilateral support' condition. Highest amplitudes were found for the 'contralateral support' condition. It was concluded that periodontal mechanoreceptors on the ipsilateral side have an inhibitory effect on the jaw-jerk reflex amplitude in the anterior temporalis muscle.

下顎骨前方移動術を行った７症例の顎態変化

The purpose of this study was to examine dentofacial changes treated by orthognathic surgery, and to clarify morphological factors affecting the stability of postoperative occlusion.Seven adult patients treated by surgical orthodontics using symmetrical mandibular advancement with the Obwegeser sagittal osteotomy, were selected for this study. Lateral cephalograms taken at five stages: pre-treatment, immediately before and after surgery, at the beginning of retention, and under retention (more than one year after retention began), were used for quantitative evaluation of dentofacial changes.Changes in dental and skeletal components, and anterior occlusion at each period, were analyzed in the anteroposterior and vertical dimensions, respectively.The following results were obtained:1. During the preoperative orthodontic treatment period, a remarkable correction of the malpositioned maxillary and mandibular incisors, associated with a little mandibular displacement, contributed to the change in the anterior occlusion.2. Before and after surgery, marked improvement in anterior occlusion was completed by the surgical mandibular advancement. In some cases, positional changes in the maxillary and mandibular incisors were found in both the anteroposterior and vertical dimensions, leading to a skeletal relapse of the mandible.3. During the postoperative orthodontic treatment period, a tendency of skeletal relapse was found. However, the anterior occlusion was generally stable because of compensatory changes in the dental components by the postoperative orthodontic treatment.4. During the retention period, a notable deterioration in the anterior occlusion was found in a case presenting condylar resorption. Except for this case, the overjet was stable due to the compensatory changes in the dental components for the skeletal relapse, while the overbite was unstable because of the dental relapse.The postsurgical stability of the anterior occlusion could be affected by the dentoskeletal relapse due to the amount of advancement, inadequate postoperative position of the condyle, fixation technique, and condylar resorption.

Dental changes and space gained as a result of early treatment of pseudo-Class III malocclusion

Abstract This study was designed to investigate the dental changes and the space gained following early treatment of pseudo-Class III malocclusion, using a simple fixed appliance. Twenty-one consecutively treated patients who had a pseudo-Class III malocclusion comprised the treated group. Fifteen untreated control subjects were used as matched controls for the three-year follow-up after completion of treatment. Lateral cephalograms and study models were analysed for the treated, the control and the follow-up group. The arithmetic mean and standard deviation were calculated for each variable, and paired t-tests were performed to assess the effects of treatment on the treated group. The Mann-Whitney test was performed to evaluate the difference between the follow-up group and the control group. Anterior crossbites and mandibular displacements were eliminated after the treatment. On average, the space gained as a result of the treatment was 4.7mm in the upper arch (p&lt;0.001°). Comparison of the space available as a result of early treatment with the space required for alignment of posterior segments in the upper arch of the untreated control group indicated that there was enough space for the eruption of the canines and premolars as a result of early treatment; whereas, lock of space was evident in the untreated controls. In conclusion, a pseudo-Class III malocclusion, proclination of the upper incisors and/ or retroclination of the lower incisors contributed to the correction of anterior crossbite and the elimination of mandibular displacement. Proclination of the upper incisors, utilisation of leeway space, and arch-width increase provided the space required for eruption of the premolars and canines.

Improved clinical use of Twin-block and Herbst as a result of radiating viscoelastic tissue forces on the condyle and fossa in treatment and long-term retention: Growth relativity

Understanding mechanisms of action for orthopedic appliances is critical for orthodontists who hope to treat and retain the achieved corrections in patients with initial Class II mandibular retrognathism. That knowledge can help orthodontists produce clinically significant bone formation and avoid compression at the condyle-glenoid fossa region. It also assists us to understand the differences between short-term and long-term treatment results. It was previously thought that increased activity in the postural masticatory muscles was the key to promoting condyle-glenoid fossa growth. By analyzing results from several studies, we postulate that growth modification is associated with decreased activity, which leads to our nonmuscular hypothesis. This premise has its foundation on 3 key specific findings: significant glenoid fossa bone formation occurs during treatment that includes mandibular displacement; glenoid fossa modification is a result of the stretch forces of the retrodiskal tissues, capsule, and altered flow of viscous synovium; observations that glenoid fossa bone formation takes place a distance from the soft tissue attachment. The latter observation is explained by transduction or referral of forces. Evidence is presented, therefore, that the 3 trigger switches for glenoid fossa growth can similarly initiate short-term condylar growth modifications because the 2 structures are contiguous. These are displacement, several direct viscoelastic connections, and transduction of forces. Histologic evidence further shows that stretched retrodiskal tissues also insert directly into the condylar head’s fibrocartilaginous layer. The impact of the viscoelastic tissues may be highly significant and should be considered along with the standard skeletal, dental, neuromuscular, and age factors that influence condyle-glenoid fossa growth with orthopedic advancement. These biodynamic factors are also capable of reversing effects of treatment on mandibular growth direction, size, and morphology. Relapse occurs as a result of release of the condyle and ensuing compression against the newly proliferated retrodiskal tissues together with the reactivation of muscle activity. To describe condyle-glenoid fossa growth modification, an analogy is made to a light bulb on a dimmer switch. The condyle illuminates in treatment, dims down in the retention period, to near base levels over the long-term. (Am J Orthod Dentofacial Orthop 2000;117:247-66)

Diagnostic criteria for pseudo–Class III malocclusion

The aim of this study is to identify the diagnostic criteria for pseudo–Class III malocclusion and compare it with Class I malocclusion in the southern Chinese population. Sixty-seven patients (mean age, 10.9 ± 1.8 years) were included in this study; 36 patients represented pseudo–Class III malocclusion. Selection criteria included the following: (1) anterior crossbite (at least 2 incisors with negative overjet and overbite); (2) mandibular displacement; (3) all patients were southern Chinese who had been followed after the growth spurt, none had developed a skeletal Class III malocclusion; (4) the patients were treated for an average of 7 months to procline upper incisors and retrocline lower incisors. None of the cases received any treatment that might affect skeletal growth. Thirty-one patients with Class I malocclusion were included in the Class I malocclusion group for the comparison of dentoskeletal characteristics with the pseudo–Class III malocclusion group. Selection criteria included the following: (1) skeletal Class I malocclusion with normal overjet and overbite, (2) mild to moderate crowding with Class I molar relationship, (3) straight facial profile. The following were included in the assessment of pseudo–Class III malocclusion cases: (1) family history, (2) molar and canine relationships at habitual occlusion and centric relation, and (3) dentoskeletal morphology. The results were that 72% of the examined cases in the pseudo–Class III malocclusion group showed no family history and 75% showed Class I molar relationship at habitual occlusion. Compared with the Class I malocclusion group, subjects in the pseudo–Class III malocclusion group showed a significantly decreased midface length, increased maxillary-mandibular difference, more retroclined upper incisors, and a retrusive upper lip. In conclusion, a pseudo–Class III malocclusion is characterized by retroclined upper incisors, retrusive upper lip, decreased midface length, and increased maxillary-mandibular difference. Findings of this study showed that patients with a pseudo–Class III malocclusion exhibit certain morphologic, dental, and skeletal characteristics that should be of aid in the diagnosis of pseudo–Class III malocclusion. (Am J Orthod Dentofacial Orthop 2000;117:1-9)

Changes in masticatory mandibular movements in growing individuals: a six-year follow-up

The pattern of mandibular movement during chewing is influenced by several central and peripheral factors. The aim of the present study was to determine whether changes in masticatory function, characterized by mandibular velocity and displacement, occurred during individuals' normal growth. Forty-seven children, 9-15 years of age, were followed over a 6-year period. All had an Angle Class I occlusion with no obvious orthodontic problems. Oral motor function with respect to mandibular displacement, duration, and velocity was monitored 3-dimensionally with an opto-electronic method. The chewing cycle was divided into an opening, closing, and occlusal phase. Total body height was measured. During the follow-up period, all masticatory variables except the 3-dimensional opening distance showed significant changes. The total chewing cycle duration, the opening and occlusal time of the chewing cycle, and the 3-dimensional closing distance increased during the growth period, while the closing time of the chewing cycle, the 2-dimensional lateral and vertical distances and both the opening and closing velocity decreased. The children who grew proportionally most in height during the 6-year period, i.e. the youngest children in the group studied, showed a significantly larger decrease in the opening velocity. From this study it becomes evident that the variables of the chewing cycle undergo a continuous process of change during growth. This is possibly a reflection of anatomical changes, maturation of the central nervous system, and altered functional demands.

Influence on myoelectric discharges of anteroposterior displacement of the mandibular position near the tapping point.

The purpose of this study was to examine the influence that the anteroposterior mandibular displacement near the tapping point exerts on the myoelectric activity of masseter and temporal muscles at a specific occluding force and to clarify the possibility of judging the mandibular position by measuring the amount of myoelectric discharge. Eight dentulous subjects were selected for the study. Surface electrodes were placed over the anterior, middle and posterior regions of the masseter muscle and over the anterior, middle and posterior bundles of the temporal muscle. Independently of the measurement region, the changes in the masseter and temporal muscle myoelectric activity which accompanied the anteroposterior mandibular displacement, were low. Moreover, when the mandible was displaced anteroposteriorly, the total amount of the myoelectrical discharge from all the recorded places, as well as the amounts of myoelectrical discharge over the middle part of the masseter muscle and the anterior bundle of the temporal muscle reached their lowest values in those mandibular positions which included the tapping point in less than half of the subjects. Therefore, this study indicates that the possibility of judging anteroposterior mandibular displacement by masseter and temporal muscle electromyography is quite low.

Mandibular motion after closed and open treatment of unilateral mandibular condylar process fractures

Purpose: This study compared mandibular and condylar mobility after open or closed treatment for fractures of the mandibular condylar process. Patients and Methods: One hundred thirty-six patients (111 male, 25 female), 74 treated by closed and 62 by open methods, were included in this study. They underwent testing of mandibular and condyle mobility at 6 weeks, 6 months, and 1, 2, and 3 years postsurgery. A jaw-tracking device was used to assess mandibular motion. Radiographs that were traced and digitized were used to assess condylar displacement and condylar mobility. Standard statistical methods were used to assess differences between groups. Results: Patients treated by open reduction had significantly greater initial displacement of their condylar processes than did the group treated closed. Immediately after treatment and uprighting of the condyles in the open treatment group, patients treated closed had significantly more displacement. At 6 weeks, patients treated closed had some measures of mandibular mobility that were significantly greater than those in patients treated by open reduction. However, after the 6-week period there were minimal differences in mandibular mobility between groups. At 6 weeks, patients treated by open reduction had significantly greater vertical mobility of the condyle than patients treated closed despite less mouth opening. After the 6-week period, patients treated by open reduction continued to have greater condylar mobility on the fractured side than did patients treated by closed methods. No measures of postsurgical displacement correlated with mobility measures in patients treated by open reduction. However, several measures of mandibular displacement correlated with measures of mobility in patients treated closed, indicating that the more displaced the condylar process, the more limited the mobility of the mandible. Conclusions: Based on this study, patients treated for fractures of the mandibular condylar process by open reduction had somewhat greater condylar mobility than patients treated closed, even though the former group had more severely displaced fractures before surgery. Therefore, open reduction may produce functional benefits to patients with severely displaced condylar process fractures.

A case of involuntary mandibular displacement with the complaint of inconvenience during mastication and conversation

A case of involuntary mandibular displacement with the complaint of inconvenience during mastication and conversation

Early Treatment of pseudo Class III malocclusion in mixed dentition

Aim To illustrate a simple effective method for early treatment of pseudo Class III in the mixed dentition and to highlight the advantages of early treatment by showing a 4-year follow-up of the treatment effects. Subjects Twenty-one consecutive southern Chinese patients with a mean age of 9.6 years were included in the early treated group with pseudo Class III malocclusion. Methods Lateral cephalometric films taken at the beginning and at the end of treatment were analysed. The arithmetic mean and standard deviation (SD) were calculated for each cephalometric variable and paired t-tests were performed to assess the statistical significance of the treatment effects. Results Anterior crossbites and mandibular displacements were eliminated after the treatment. The angulation of the upper incisors to the maxillary plane showed an increase by a mean of 9.5° (P < 0.001), while the angulation of the lower incisors to the mandibular plane showed a decrease by a mean of 4.9° (P < 0.001). Conclusion In pseudo Class III malocclusion, proclination of upper incisors and/or retroclination of lower incisors with simple fixed appliances contribute to the correction of anterior crossbite and the elimination of mandibular displacement. Proclination of upper incisors, use of Leeway space and arch width increase provide space required for the eruption of the premolars and canines.

Management of pseudo Class III malocclusion in southern Chinese children.

To illustrate a simple effective method for early treatment of pseudo Class III in the mixed dentition and to highlight the advantages of early treatment by showing a 4-year follow-up of the treatment effects. Twenty-one consecutive southern Chinese patients with a mean age of 9.6 years were included in the early treated group with pseudo Class III malocclusion. Lateral cephalometric films taken at the beginning and at the end of treatment were analysed. The arithmetic mean and standard deviation (SD) were calculated for each cephalometric variable and paired t-tests were performed to assess the statistical significance of the treatment effects. Anterior crossbites and mandibular displacements were eliminated after the treatment. The angulation of the upper incisors to the maxillary plane showed an increase by a mean of 9.5 degrees (P < 0.001), while the angulation of the lower incisors to the mandibular plane showed a decrease by a mean of 4.9 degrees (P < 0.001). In pseudo Class III malocclusion, proclination of upper incisors and/or retroclination of lower incisors with simple fixed appliances contribute to the correction of anterior crossbite and the elimination of mandibular displacement. Proclination of upper incisors, use of Leeway space and arch width increase provide space required for the eruption of the premolars and canines.

こう合接触部位の違いが側方クレンチング時の下顎の変位に及ぼす影響

To investigate the relationship between occlusal scheme and joint loading, mandibular displacement was measured during lateral clenching under experimentally altered occlusal conditions. Acrylic occlusal devices were fabricated for the lower working-side canine, working-side second molar, and balancingside second molar. With the aid of these devices, various occlusal states were simulated. Eight healthy subjects volunteered for this study and performed clenching tasks. Vertical displacements of the mandible were recorded by linear variable differential transformers, and the results were as follows:1. Clenching efforts in the lateral mandibular position caused elevation of the mandible.2. When a single occlusal device was placed unilaterally, the amount of the upward displacement near the supporting tooth tended to be smallest.3. Insertion of three occlusaldevices (bilateral tooth contacts) reduced the amplitude of mandibular displacement.These results suggested that the nature of reaction forces at the temporomandibular joints caused by the elevation of the mandible would be influenced by the occlusal status.

Long-term comparison of extraction and nonextraction alternatives in matched samples of African American patients

African American orthodontic patients often present with morphologic characteristics that prompt the extraction of premolars. Referring dentists, however, commonly see extraction as a cause of “dished in” profiles, collapsed arches, and temporomandibular dysfunction. If true, these claims imply that African American patients are disproportionately at risk of clinical misadventure. Unfortunately, a meaningful long-term comparison of alternative treatments—be it retrospective or prospective—requires samples of patients who were equally susceptible to the two alternatives. Thus, if a retrospective study is to be free of susceptibility bias, the samples must be matched with respect to the anatomic differences that prompted the clinicians’ choice of treatments. The goals of this investigation, therefore, were the following: to gather a large sample of African American expatients and to identify by means of discriminant analysis the characteristics that seem to have been important to the extraction decision, to use this knowledge to assemble subsamples of extraction and nonextraction expatients (both Class I and II) who were similar before treatment, and, finally, to recall them so that the long-term impact of the two strategies could be compared. In the end, 60 expatients—30 extraction and 30 nonextraction—were recalled, on average, nearly 8 years after the completion of treatment. In general, both treatments reduced irregularity and neither seemed to produce posterior mandibular displacement. Premolar extraction led to a modest reduction in dental and soft tissue protrusion (half the incisor retraction minus one); nonextraction, by way of contrast, produced an increase. Long term, the difference between the two treatments was about 2 mm at the upper lip and 4 mm at the lower. Excessive profile flattening was not a common finding. Our findings thus imply that the various “functional orthodontic” arguments against premolar extraction do not apply to African Americans any more than they do to whites. (Am J Orthod Dentofacial Orthop 1998;114:393-403)