Maximum Mandibular Opening Research Articles

Mandibular Flexure and Its Significance: An In Vivo Cone Beam-Computed Tomography Proof-of-Concept Study.

The aim of this study was to assess intra-arch mandibular dimensional changes that may occur during mouth opening using cone beam-computed tomography (CBCT). Fifteen patients in need of any type of treatment whose execution considered a pre- and post-CBCT assessment consented and were enrolled. CBCTs were taken with the following settings: 90 kV, 8 mA, field of view (FOV) 140 by 100 mm (height and diameter), Voxel size 0.25 mm (high resolution). The pre-CBCT was executed in the maximum mandibular opening (MO), while the post-CBCT was in the maximum intercuspation (MI). A thermoplastic stent with radiopaque fiducial markers (steel ball bearings) was fabricated for each patient. Measurements were made using radiographic markers between contralateral canines and contralateral first molars and between ipsilateral canines and first molars on both sides. Paired t-tests were performed to evaluate the difference between open and closed positions on these four measurements. In the MO position were registered a significative tightening of the mandible at the canine (-0.49 mm, SD 0.54 mm; p < 0.001) and molar points (-0.81 mm, SD 0.63 mm; p < 0.001) and a significative shortening of the mandible on the right (-0.84 mm, SD 0.80 mm; p < 0.001) and left sides (-0.87 mm, SD 0.49 mm; p < 0.001). Within the study limitations, mandibular flexure determined a significant shortening and tightening between maximum intercuspation to maximum opening positions. Mandibular dimensional changes should be considered in light of other patient factors in the treatment planning of implant positioning and long-span complete arch implant-supported fixed prostheses in order to avoid technical complications.

Massage, Relaxation And Exercise In Bruxism: Is There Difference? A Randomized Clinical Trial

Objective: To compare massage and stretching exercises; relaxation and imagination therapy; and a combination of these two interventions in bruxism. Methods: Seventy-two participants were randomly assigned to Group 1 (massage with stretching exercises, n=24), Group 2 (relaxation with imagination therapy, n=24) or Group 3 (two interventions combinate, n=24). The treatment lasted 6-week. Assessments were made before, after 6-week and two months. Muscle pain, pain threshold, maximum mandibular opening, anxiety, stress, depression, oral health, and sleep were established as outcome variables. Results: After six weeks and two-month, significant improvements were observed in muscle pain, state anxiety, stress, depression, and sleep for three groups (p&lt;0.05). In the comparison among the three groups, there were significant differences for the most outcomes with the higher improvement of Group 3 after 6-week and two months (p&lt;0.05). Therefore, there is the superior effect of the combination of two physical therapy interventions in bruxism.

Cryptococcal osteomyelitis of the Zygomatic bone: a case report

BackgroundDisseminated cryptococcosis is a well-characterized complication in immunocompromised patients with cryptococcal pneumonia or meningitis; however, isolated cryptococcal osteomyelitis is a rare entity that occurs in approximately 5% of patients with cryptococcosis. Cryptococcal osteomyelitis in the head and neck region is extremely rare. To the best of our knowledge, no cases of cryptococcal osteomyelitis affecting only the zygomatic bone have been reported to date.Case presentationA 78-year-old man without other comorbidities presented with progressive swelling of the right cheek along with pain and trismus. Clinical examination revealed a tender swelling in the right zygomatic region; the maximal mandibular opening was about 2 cm. Laboratory data showed mildly elevated inflammatory indices (C-reactive protein: 0.45 mg/dL; erythrocyte sedimentation rate: 35 mm/h). Computed tomography showed a 30-mm-diameter lesion at the right zygomatic arch. A part of the lesion has extended to the subcutaneous area of the cheeks with signs of bone destruction and surrounding contrast effects. Histopathological examination of fine-needle aspirate and needle biopsy showed cryptococcus. Furthermore, culture of the aspirate showed growth of Cryptococcus neoformans. No evidence of any other site involvement was observed. Therefore, the patient was diagnosed with isolated cryptococcal osteomyelitis and was initiated on fluconazole therapy. The treatment was effective, and all symptoms were resolved in 4 weeks. Fluconazole therapy was stopped after 6 months. There are no signs of recurrence as of 15-month follow-up. The patient has no cosmetic abnormalities or sequelae.ConclusionsFine-needle aspiration cytology, needle biopsy, and fungal culture were useful for definitive diagnosis. Immunocompetent patients with isolated osteomyelitis may be cured with oral fluconazole alone.

Drug Resistance, Genotype and Site-Specificity: Do they Affect Biofilm Formation in Mycobacterium tuberculosis?

The purpose of the study was to compare the mandibular movement during speech in patients with temporomandibular disorder (muscular TMD) and in asymptomatic volunteers using computerized electrognathography. Twelve asymptomatic volunteers (Group I control group) and 12 patients with muscular TMD (Group II) were selected. Both groups were subjected to a phonetic test and evaluated according to: maximum mandibular opening amplitude (mm), mandibular velocity during opening and closing (mm/sec) and maximum lateral deviation to both right and left sides (mm). Regarding to the mandible movements both frontal and horizontal planes, as well as the mandible deviations, there was no difference between Group I and Group II for all parameters analyzed. Regarding to the mandible movements in frontal and horizontal planes as well as the mandible deviations, there was no difference between group I and group II (muscular TMD and Asymptomatic). There was a statistical difference for the maximum mandibular velocity during opening and closing during speech in symptomatic patients.

Electrognathographic Analysis of Jaw Movements during Speech: An Exploratory Study

The purpose of the study was to compare the mandibular movement during speech in patients with temporomandibular disorder (muscular TMD) and in asymptomatic volunteers using computerized electrognathography. Twelve asymptomatic volunteers (Group I control group) and 12 patients with muscular TMD (Group II) were selected. Both groups were subjected to a phonetic test and evaluated according to: maximum mandibular opening amplitude (mm), mandibular velocity during opening and closing (mm/sec) and maximum lateral deviation to both right and left sides (mm). Regarding to the mandible movements both frontal and horizontal planes, as well as the mandible deviations, there was no difference between Group I and Group II for all parameters analyzed. Regarding to the mandible movements in frontal and horizontal planes as well as the mandible deviations, there was no difference between group I and group II (muscular TMD and Asymptomatic). There was a statistical difference for the maximum mandibular velocity during opening and closing during speech in symptomatic patients.

The Prevalence of Symptoms and Signs of Temporomandibular Disorders among a Group of Young Adult Jordanian Population

Objective: The aim of this study is to determine the prevalence of signs and symptoms of temporomandibular joint in 18 years old Jordanian population and to establish a baseline data for comparison with other studies. Methods: A group of young adult Jordanians presented to Officer Election Committee for Mu’tah Military University in 2004 were included in this study. A questionnaire was designed to assess the anamnestic and clinical dysfunction indices according to Helkimo. The anamnestic examination was based on the reported symptoms. While the clinical examination was based on maximum mandibular opening, protrusive and lateral movements, auscultation of temporomandibular joint and palpation of joint and muscles of mastication. Data were collected, tabulated, and analysed using Chi-square test and Correlation coefficients tests. Results: A total of 5,312 Jordanians (3,871 males, 1,441 females) were examined. There were no significant differences between males and females either in reported symptoms or clinical signs. Whilst about 63% reported no symptoms (Ai 0), 21.5% reported mild, and severe symptoms (Ai I) and (Ai II). Similarly, 31.2% showed no signs of dysfunction (Di 0); 47.9% had mild signs (Di I); 17.1% showed moderate signs (Di II); and 3.8% showed severe signs of dysfunction (Di III). There were low but significant correlations between Anamnestic index score (Ai) and the recorded signs (Di) as well as the clinical dysfunction score. Conclusion: The data obtained from the physical examination and questionnaire identified a high prevalence of signs and symptoms of temporomandibular disorders in 18-year-old Jordanians. Further studies are required to evaluate the prevalence of signs and symptoms of temporomandibular disorders in older age groups among Jordanian population.

The relationship between the changes in three-dimensional facial morphology and mandibular movement after orthognathic surgery

PurposeThe purpose of this study was to investigate the relationship between changes in three-dimensional (3D) facial morphology and mandibular movement after orthognathic surgery. We hypothesized that facial morphology changes after orthognathic surgery exert effects on 3D mandibular movement. Materials and methodsWe conducted a prospective follow-up study of patients who had undergone orthognathic surgical procedures. Three-dimensional facial morphological values were measured from facial CT images before and three months after orthognathic surgery. Three-dimensional maximum mandibular opening (MMO) values of four points (bilateral condylions, infradentale, and pogonion) were also measured using a mandibular movement tracking and simulation system. The predictor variables were changes in morphological parameters divided into two groups (deviated side (DS) or contralateral side (CS) groups), and the outcome variables were changes in the MMO at four points. ResultsWe evaluated 21 subjects who had undergone orthognathic surgical procedures. Alterations in the TFH (total facial height), LFH (lower facial height), CS MBL (mandibular body length), and DS RL (ramus length) were negatively correlated with changes in bilateral condylar movement. The UFH, DS MBL and CS ML (mandibular length) showed correlations with infradentale movement. The CS ML, DS ML, MBL, UFH, and SNB were correlated with pogonion movement. ConclusionThe height of the face is most likely to affect post-operative mandibular movement, and is negatively correlated with movement changes in the condyles, infradentale and pogonion. The changes in CS morphological parameters are more correlated with mandibular movement changes than the DS. The changes in CS MBL and bilateral RL were negatively correlated with condylar movement changes, while the bilateral MBL and CS ML were positively correlated with changes in infradentale and pogonion.

Orthodontic-surgical treatment: neuromuscular evaluation in skeletal Class II and Class III patients

ObjectivesThe aim of this study was the evaluation of the neuromuscular response to treatment according to diagnostic phases, as a follow-up of patients under surgical orthodontic treatment. The patient sample was subdivided into sub-samples, according to clinical characteristics. Materials and methodsAll of the patients who underwent orthognathic surgery in the Department of Orthodontics (University of Milan) were subjected to periodic electromyographic evaluation of the masticatory muscles (masseter and anterior temporal muscles), and to electrokinesiographic evaluation of the mandibular movements. The patient sample comprised 80 patients (37 males; and 43 females) at the end of growth. The electromyographic instruments used in the study included a Freely and a K6-I electromyography. Statistical evaluation was carried out with the Student's t-tests for independent samples. ResultsThere are many differences between the skeletal Class II and skeletal Class III patients that are shown through the analysis of these data obtained. In the beginning phases of the treatment the muscular activities were higher in the Class II patients than in the Class III patients. Nevertheless this difference was reversed at the end of the treatment. A similar difference could be found in the mandibular kinesiology, in fact the maximum mandibular opening movement was greater in the skeletal Class II patients than in the skeletal Class III patients at the beginning of the treatment. At the end of the treatment this difference was lost. At the beginning of the treatment the Class II patients showed a greater protrusive movement of the mandibular than the Class III patients. At the end the treatment however this gap was reduced without being reversed. ConclusionsFunctional evaluation in patients in surgical orthodontic therapy is an important element in the diagnostic–therapeutic recordings, so as to reduce as much as possible any incorrect neuromuscular activity that can result in relapse.

Valutazione elettromiografica ed elettrognatografica del trattamento ortodontico-chirurgico

Objectives Electromyography and electrognatography are very useful to assess neuromuscular function in the diagnosis and treatment of patients during orthodontic surgical treatment. The aim of this work is to evaluate both neuromuscular function and mandibular movements in 70 patients undergoing orthodontic surgical treatment. Material and methods During the orthodontic surgical treatment all patients were submitted to usual clinical and radiographic exams and to periodical electromyographic and electrokinesiographic evaluations. The test group consisted of 70 patients (27 men and 43 women) at the end of growth. Electromiography and kinesiography were performed at the time of diagnosis, at the beginning of orthodontic therapy, periodically during orthodontic treatment before surgery, the day before surgery, during the intermaxillary block, at the removal of the fixation, during orthodontic treatment after surgery, at the removal of orthodontic appliance and the during follow up. The instruments used in this research were a Freely electromiograph and a K6-I EMG electromiograph and electrognatograph. The anterior temporal and the masseter muscles were tested. The control group consisted of adult patients with skeletal class I, with no temporomandibular disorders and no previous orthodontic or surgical-orthodontic treatments. Mandibular movements were assessed by a Myotronics K6-1 kinesiograph. The results were statistically analyzed by t test and ANOVA test. Results At the beginning of treatment the patients of the test group showed a malocclusion-compensating balance. During orthodontic treatment before surgery electromyographic and electrognathographic values started to worsen and continued to worsen until surgery. They improved during orthodontic treatment after surgery. After removing orthodontic appliances, electromyographic values improved and reached optimal values. Recover of mandibular movements was also satisfying even if it took a longer time than muscular rehabilitation. At the end of the treatment maximum mandibular opening was still smaller than before treatment. Conclusions This study confirms that functional rehabilitation of patients during orthodontic-surgical treatment is timely and good. Functional evaluation is important to reduce as much as possible a faulty neuromuscular activity that may cause a relapse; it also helps clinicians to control treatment and results.

Limites de movimentos mandibulares em crianças

identification of the mandibular movement range is an important procedure in the evaluation of the stomatognathic system. However, there are few studies in children that focus on normal parameters or abnormalities. to determine the average range of mandibular movements in Brazilian children aged 6 to 12 years; to verify the difference between genders, in each age group, and between the different age groups: 6-8 years; 8.1-10 years; and 10.1-12 years. participants of the study were 240 healthy children selected among regular students from local schools of São Paulo State. The maximum mandibular opening, lateral excursion and protrusive movements, and deviation of the medium line, if present, were measured using a digital caliper. Student T test, Analysis of variance and Tukey test were considered significant for p < 0.05. the mean values observed in the studied sample were: 44.51mm for maximum mandibular opening; 7.71mm for lateral excursion to the right; 7.92mm for lateral excursion to the left; 7.45mm for protrusive movements. No statistical difference was observed between genders. There was a gradual increase in the range of mandibular movements, with significant differences mainly between the ages of 6-8 years and 10.1-12 years. during childhood the range of mandibular movements increases. Age should be considered in this analysis for a greater precision in the diagnosis.

Translation and rotation movements of the mandible during mouth opening and closing

To assess the relative contribution of rotation and translation of the temporomandibular condyle-disc assembly during opening and closing movements, free movements of maximum mouth opening and closing were recorded in healthy subjects (12 men, 14 women) using an optoelectronic three-dimensional motion analyzer. For each subject, the displacement of the lower interincisal point, the path of the condylar reference point, the degree of rotation around the three orthogonal rotational axes, and the relative contribution of translation and rotation were calculated during all movement of mouth opening and closing. The distance covered by the interincisor point and the rotational angle about the transverse axis at maximum mouth opening were larger in men than in women, but the difference cancelled after correcting for mandibular radius in the sagittal plane; mandibular rotation was always larger than translation, but never approaching 100%; opening and closing translations were similar within sex, but their paths were longer in men than in women (P < 0.05); rotational angles around vertical and sagittal axes were negligible; the linear correlation between maximum mandibular opening and condylar translation was minor and not significant. In normal subjects, mouth opening and closing as modeled at the interincisor point was determined more by mandibular rotation than by translation, but in no occasion a pure rotation was found. The percentage rotation was not identical during mouth opening and closing; female and male paths were not totally coincident; no correlation between maximum mandibular opening and condylar translation was found.

Assessment of the Relationship Between the Recovery of Maximum Mandibular Opening and the Maxillomandibular Fixation Period After Orthognathic Surgery

The purpose of this study was to evaluate the differences in the recovery of maximum mandibular opening (MMO), and the relationship between MMO and the maxillomandibular fixation (MMF) period after sagittal split ramus osteotomy (SSRO) and intraoral vertical ramus osteotomy (IVRO), with and without Le Fort I osteotomy. Sixty-eight patients with diagnosed mandibular prognathism with or without asymmetry were divided into 4 groups (SSRO, IVRO, SSRO with Le Fort I osteotomy, and IVRO with Le Fort I osteotomy). MMO and the MMF period were measured preoperatively and at 1, 3, 6, 12, and 18 months after surgery. The differences among surgical procedures and the relationship between MMO and the MMF period were examined statistically. In relation to time-dependent changes in MMO, there were no significant differences among the groups. There were significant positive correlations between MMO and the MMF period from 1 month to 6 months after surgery. However, there were no significant correlations at 12 and 18 months after surgery. This study suggests that there were no significant differences between single-jaw surgery and double-jaw surgery in terms of postoperative time-dependent changes in the recovery of MMO. However, the MMF period was associated with the recovery of MMO.

顎運動解析パラメータの標準化に関する検討―切歯点における限界運動路解析―

To establish standardized evaluating methods for jaw movements analysis independently of the reference coordinate system. In this paper, we focused on the analysis of incisor point paths of border movements. Then we investigated parameters that are independent of the reference coordinate system and can be utilized among different systems. Recorded data of jaw border movements from 20 healthy male adults were employed as basic samples. First, the effects of changes of the reference coordinate systems on the analysis were investigated. Second, the line between incisor points at the intercuspal position and the maximal mandibular opening position was used as the reference line. Then the area index of incisor paths was calculated with the length of the perpendicular line dropped from the incisor point to the reference line and the displacement of the foot of the perpendicular. Changes of the spatial relation between a reference plane of the coordinate system and border movements pathways had an effect on a measured area of projected pathways, about 2% - 5% differences of projected area on the frontal plane with 10 degrees rotation around a horizontal axis. The area index of incisor paths showed close correlation with the actual area of a 3-dimensional plane bounded by the incisor path [sagittal border movement: r = 0.53 (p = 0.016), left border opening pathway: r = 0.97 (p < 0.001), right border opening pathway: r = 0.98 (p < 0.001), Spearman rank correlation]. The results suggest that new parameters could measure jaw border movements quantitatively independent of the reference coordinate system.

Movimentos mandibulares na fala: interferência das disfunções temporomandibulares segundo índices de dor

temporomandibular disorders can cause general alterations of the mandibular movements due to modification in the condition of muscles and articulations. Electrognathography, a computerized exam used to complement the diagnosis of these disorders, allows the objective delineation and record of the mandibular movements, determining their amplitude and speed. to verify the characteristics of mandibular movements of individuals with temporomandibular dysfunction and in asymptomatic individuals during speech, through computerized electrognathography, analyzing possible interferences of this dysfunction and severity implications regarding pain indexes. 135 adults were divided in four groups based on their pain indexes, using a numeric scale: zero for pain absence, one for mild pain, two for moderate pain and three for severe pain. Mandibular movements were observed during the sequential naming of balanced pictures taking in consideration the occurrence of phonemes in the Brazilian Portuguese language. Records were obtained using computerized electrognathography (BioEGN - BioPak system). the analysis of the results point that differences indicated as significant for mandibular opening amplitude and mandibular closing speed occurred between index zero and all of the other pain indexes. Regarding mandibular opening speed during speech, statistically significant differences were obtained between index zero and index three. It was observed that mandibular movements in speech are discreet, with an anteroposterior component and deviations in laterality. the presence of temporomandibular dysfunctions causes reduction in the values of maximum mandibular opening and a reduction in both mandibular opening speed and mandibular closing speed during speech The different pain indexes: mild, moderate and severe do not seem to determine larger reduction of these values.

Temporomandibular joint problems and self-registration of mandibular opening capacity among adults with Ehlers-Danlos syndrome. A questionnaire study.

To study maximal mandibular opening capacity and the prevalence of temporomandibular joint (TMJ) problems reported among a larger group of adults with Ehlers-Danlos syndrome (EDS). Furthermore, to compare proportions of disorders with those in a cohort of randomized population- based controls. A questionnaire study with self-registration of maximal mandibular opening capacity. One hundred and fourteen persons with EDS and 114 controls in a randomized population-based cohort. Experimental variables - Self-registered maximal mandibular opening capacity values that were calculated from the markings of maximal interincisal distance on spatulas and the assessments of overbite with the aid of photos. Questions concerning EDS, TMJ problems and other related questions. Mean values of maximal mandibular opening capacity compared between groups. Proportions of affirmative answers about TMJ problems compared between persons with EDS and controls who did not have the syndrome. The EDS persons who reported problems with poor mouth opening capacity when biting into thick pieces of food had a lower mean maximal mandibular opening value compared with the other EDS persons (p < 0.05). The proportions of affirmative answers concerning mobile joints during mouth opening, present TMJ problems, poor mouth opening capacity when biting into thick food, clicking, crepitations and permanent locking were greater compared with the controls (p < 0.05). These data corroborate the reports in literature that persons with EDS are naturally predisposed to TMJ problems. The self-registration of maximal mandibular opening capacity was a useful diagnostic tool to provide an objective clinical measure of movement capacity of the TMJ. The clinical measure was in line with the affirmative answers on having problems with poor mouth opening capacity among the EDS persons.

The post-orthodontic prevalence of temporomandibular disorder and functional occlusion contacts in surgical and non-surgical cases

This study aimed to assess mandibular mobility and the prevalence of functional occlusal contacts in subjects treated to a Class 1 incisor relationship by fixed orthodontic appliance therapy. Two hundred and thirty subjects participated (mean age=18 years) of whom 42 underwent orthognathic surgery. All subjects were in retention with a mean time of 7 months between debond and examination. Maximal mandibular opening, lateral and protrusive excursions were all significantly reduced in the surgical cases compared to the non-surgical group. Centric and eccentric non-ideal occlusal contacts were not different between surgical and non-surgical groups. Non-working side contacts occurred in 30% of subjects, posterior contacts on protrusion in 20% and RCP-ICP prematurities in 18% of subjects. Non-working side contacts were significantly more frequent in post-graduate cases compared to staff cases (P<0.05). An overbite less than the mean of 2.4 mm resulted in a reduced likelihood of canine guidance on the working side (P<0.001) and an increased frequency of non-working side contacts and posterior contacts on protrusion (P<0.001).

Relationship between craniofacial morphology and maximum mandibular opening

Relationship between craniofacial morphology and maximum mandibular opening

Análise funcional da oclusão na dentadura decídua: avaliação dos movimentos mandibulares

Analisou-se funcionalmente a oclusão decídua de 20crianças leucodermas de 3,5 a 5,5anos de idade, determinando-se a capacidade de abertura bucal máxima e a extensão dos movimentos de lateralidade e protrusão em relação a sexo, tipos de arco e de registros dos movimentos, utilizando-se régua milimetrada, traçado do arco gótico e microscópio comparador. Concluiu-se que a média da capacidade de abertura máxima foi de 45,72mm, sem diferença estatística entre as variáveis. As médias da capacidade de protrusão máxima foram de 8,34mm, com régua milimetrada, e de 7,25mm no arco gótico, com diferença estatisticamente significante em nível de 5% entre os dois tipos de avaliação e na interação dos fatores avaliação/tipo de arco e avaliação/sexo. As médias do movimento de lateralidade máxima com régua milimetrada foram de 8,11mm para o lado direito e 8,15mm para o lado esquerdo e, pelo arco gótico, de 7,96mm para o lado direito e 7,79mm para o lado esquerdo, com diferença estatisticamente significante em nível de 5% para o fator tipo de arco. Portanto, os determinantes funcionais da oclusão na fase da dentadura decídua podem ser estabelecidos, servindo de embasamento para a manutenção, a interceptação e a recuperação morfológica e funcional do sistema estomatognático da criança quando este apresentar-se alterado, assegurando o seu desenvolvimento adequado e o da oclusão permanente

Elongated styloid process in a temporomandibular disorder sample: Prevalence and treatment outcome

An elongated styloid process is an anatomic anomaly present in 2% to 30% of adults; it is occasionally associated with pain. Its prevalence among patients with classic temporomandibular disorder pain symptoms is unknown. The effect of conservative treatment on patients who have symptoms of temporomandibular disorders and an elongated styloid process is also unknown. The objectives of this study were to determine the prevalence of the elongated styloid process in a sample of patients with temporomandibular disorders and to compare patients with and without the elongated styloid process on initial presenting signs and symptoms and treatment outcome. A total of 100 panoramic radiographs of patients with symptomatic temporomandibular disorders were examined to ascertain the presence or absence of an elongated styloid process. All patients participated in a conservative treatment program of biofeedback and stress management and a flat-plane intraoral appliance. Initial symptoms and treatment outcome of patients with and without an elongated styloid process were compared by use of multivariate analysis of variance on several oral-paraoral and psychosocial-behavioral methods. The prevalence of an elongated styloid process in this clinic sample of temporomandibular disorders was 27%. The patients with or without an elongated styloid process were not significantly different in pretreatment symptoms, and both groups exhibited substantial treatment gains. However, patients with an elongated styloid process showed significantly less improvement on unassisted mandibular opening without pain than did patients who did not have an elongated styloid process. This suggests that an elongated styloid process may place structural limitations on pain-free maximum mandibular opening. The results support conservative management of patients with symptoms of temporomandibular disorders when an elongated styloid process is present.

Functional movements of putative jaw muscle insertions

The craniomandibular muscles control jaw position and forces at the teeth and temporomandibular joints, but little is known regarding their biomechanical behaviour during dynamic function. The objective of this study was to determine how jaw muscle insertions alter position during different jaw movements in living subjects. Computer 3D reconstruction of MR images and jaw-tracking were combined to permit the examination of movement with six degrees of freedom. Maximum mandibular opening, protrusive and laterotrusive positions were recorded in four subjects, and the translation and rotation of the putative insertions of masseter, temporal, medial, and lateral pterygoid muscles were measured. The sizes and shapes of regional attachments varied markedly among subjects, and their displacement patterns were different in specific muscles. For instance, when the jaw closed to the dental intercuspal position from maximum gape, the region near the superior insertion site of the masseter moved backward and upward, whereas the region near the inferior insertion site displaced mainly forward. In three subjects, the jaw's rotational center during this act was approximately 26-34 mm below the mandibular condyles. Since the movements of each muscle part differ according to variations in the size and shape of insertion areas, individual musculoskeletal form, and patterns of jaw motion during function, the prediction of motion-related muscle mechanics in any one subject is unlikely to be possible without direct measurement of the motion of visualized muscle parts. The present study shows that this information can be obtained.