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Mandibular Position (mandibular + position)
Selected AbstractsVariation in masticatory muscle activity during subsequent, submaximal clenching effortsJOURNAL OF ORAL REHABILITATION, Issue 6 2002F. Lobbezoo In previous studies to the relative contribution of the jaw closing muscles to the maintenance of submaximal clenching levels, a considerable variation in the electromyography (EMG) activities of these muscles during subsequent efforts was found. In this study, it was examined to what extent this variation could be explained by coincidental variations in mandibular positioning. From seven healthy individuals, a total of 90 EMG sweeps was recorded: three conditions (intercuspal position and two types of stabilization appliances) × three clenching levels (10, 30 and 50% of maximum voluntary contraction level) × 10 repetitions. Mandibular position was monitored with a six degrees of freedom opto-electronic jaw movement recording system. Variations in mandibular positioning during subsequent, submaximal clenching efforts explained up to 25% of the variance in the indices that quantify the relative contribution of the jaw closing muscles to the total clenching effort (P=0·000; ANOVA). Only a weak dependency of positioning upon clenching condition was found whereas during higher clenching levels, the positioning effect tended to be smaller than during lower levels. In conclusion small, coincidental variations in mandibular positioning during subsequent clenching efforts partly explain the variance in EMG activity of jaw closing muscles, especially at lower clenching levels. [source] The relationship between non-working-side occlusal contacts and mandibular positionJOURNAL OF ORAL REHABILITATION, Issue 10 2001T. Ogawa No clear description can be found regarding the lateral position when examining non-working-side occlusal contacts. The objective of this study was to test the hypothesis that the non-working-side contact pattern varies with the mandibular position. The characteristics of the non-working-side contact pattern were also determined relative to the working-side contact pattern. Occlusal contacts of 86 young adults were examined using shim stock in standardized lateral positions: 0·5, 1, 2 and 3 mm from the maximum intercuspation (MI), where the 0·5, 1 and 2 mm positions were defined as lateral positions close to the MI and the 3 mm position as an edge-to-edge position. The frequency of non-working-side occlusal contacts decreased gradually from 0·5 to 3 mm position. The frequency of non-working-side contacts was significantly greater in the 0·5 and 1 mm positions than in the 3 mm position. Non-working-side occlusal contacts occurred in nearly half of the 0·5 mm positions. Non-working-side contacts were significantly less frequent with canine protection than with group function for the 0·5 and 1 mm positions. There were no significant differences between the two occlusal schemes for the 2 and 3 mm positions. In conclusions, the non-working-side contact pattern varied with the mandibular position. These results suggest that clinical examination should include contact patterns both in a position close to the MI and in an edge-to-edge position, i.e. in functional and parafunctional ranges. Likewise, data from occlusal contact research should include a standardized definition of mandibular position. [source] Craniomandibular joint in South American burrowing rodents (Ctenomyidae): adaptations and constraints related to a specialized mandibular position in diggingJOURNAL OF ZOOLOGY, Issue 3 2006D. H. Verzi Abstract A quali-quantitative morphofunctional analysis of the craniomandibular joint in subterranean rodents of the family Ctenomyidae showed that specializations of this joint are coupled with adaptations to digging. The presence of a postglenoid articular region in the skull of Eucelophorus and Ctenomys implies a new position of the mandible in digging, different from those involved in gnawing and chewing. In this third position of the mandible, the mandibular joint is stabilized when the deeply inserted incisors attack the soil or an obstacle, preventing dislocation. The proposed new mandibular function imposes a mechanical constraint on size and shape of the auditory bullae in tooth-digger ctenomyids, because inflated bullae preclude a satisfactory opening of the mandible when it articulates in the postglenoid region. The configuration of the craniomandibular joint and other specializations for digging of Eucelophorus are unique among all South American rodents. The presence of non-homologous, and even more specialized, postglenoid cavities in burrowing rodents of other continents suggests a common requirement for stabilizing the mandibular joint when strong forces with incisors are developed. The less specialized postglenoid region of Eucelophorus and Ctenomys, with respect to that of other rodent clades, may be related to the more recent differentiation of ctenomyids. [source] Cephalometric evaluation of condylar and mandibular growth modification: a reviewORTHODONTICS & CRANIOFACIAL RESEARCH, Issue 1 2006G Shen Structured Abstract Authors ,, Shen G, Darendeliler MA Objective ,, Based on a wealth of orthodontic archives, this work aims to review the cephalometric analysis systems that can identify the changes in condylar and mandibular position as well as growth direction in response to bite jumping therapy. Design ,, Numerous cephalometric approaches were screened to testify their feasibility and reliability in accurately depicting the growth modification of the condyle and the mandible. The critical assessment of the working mechanisms of these cephalometric methods was elaborated to help build up the rationale and justification for their clinical use. Results ,, 1) The changes in condylar and mandibular size, position and growth direction can be identified by using lateral cephalograms with closed-mouth or open-mouth posture. 2) With superimposition methods where the anatomical structures for superimposition registration must be stable and reproducible, the growth modification of the condyle and the mandible between two time-points is qualitatively demonstrated in a diagram if reference lines are not constructed. The growth modification can be quantitatively identified if the reference lines are created. 3) With non-superimposition methods, the size and position of the condyle and the mandible are separately identified for each time-pint by relating them to the stable reference structures. The growth modification between two time-pints is evaluated by comparing the two separate measurements. Conclusion ,, The application of a standardized and well designed cephalometric evaluation system may reduce the bias that attribute to the arbitrariness of the clinical effects of bite jumping functional appliances. [source] Postural Cephalometric Analysis and Nasal Resistance in Sleep-Disordered Breathing,THE LARYNGOSCOPE, Issue 7 2003Paula Virkkula MD Abstract Objectives The study was designed to compare upright and supine cephalometric measurements in snorers and to evaluate the effects of mandibular position and nasal resistance on pharyngeal dimensions. Anthropometric, rhinomanometric, and cephalometric measurements were used to investigate predictors of apnea-hypopnea index. Study Design Prospective, cross-sectional. Methods Forty consecutive habitually snoring men waiting for nasal surgery (mean age, 44 y; mean body mass index, 28 kg/m2) underwent an overnight polysomnographic, anterior rhinomanometric, and cephalometric analysis in upright and supine positions. Results Nasal resistance correlated positively with minimal pharyngeal airspace at the level of tongue. The opening of jaws after voluntary relaxation of the mandibular position on lying down correlated with decrease in pharyngeal airway measurements at both velopharyngeal and tongue-base levels. In stepwise multiple regression analysis the overall patient model explained 68% of the variation in apnea-hypopnea index with body mass index as the largest predictor. In the nonobese patients, the model explained 86% of variation in apnea-hypopnea index with change in anteroposterior position of the lower jaw in upright and supine measurements and combined nasal resistance after mucosal decongestion as independent determinants. In selected skeletal subtypes the models predicted 83%, 79%, 61%, and 90% of the variation in apnea-hypopnea index. Conclusions In the nonobese patients nasal resistance and change in mandibular position on lying down were found to be independent contributing factors to the apnea-hypopnea index. Further research on supine cephalometry and relaxed mandibular position may improve prediction of sleep-disordered breathing in snorers. [source] The influence of age and dental status on elevator and depressor muscle activityJOURNAL OF ORAL REHABILITATION, Issue 2 2006I. Z. ALAJBEG summary, The objective of this study was to determine whether the muscle activity at various mandibular positions is affected by age and dental status. Thirty edentulous subjects (E), 20 young dentate individuals (G1) and 20 older dentate individuals (G2) participated in this study. Surface electromyographic (EMG) recordings were obtained from the anterior temporal (T), masseter (M) and depressor muscles (D). Muscle activity was recorded during maximal voluntary contraction (MVC), maximal opening (Omax) and in six different mandibular positions. One way anova and the Bonferroni tests were used to determine the differences between groups. Significant differences between the three tested groups were found at MVC and Omax for all examined muscles (P < 0·001). The differences in muscle activity in dentate subjects of different age were found in protrusion for depressor muscles (P < 0·05) and in lateral excursive positions for the working side temporal (P < 0·05) and non-working side masseter and depressor muscle (P < 0·05). There was a significant effect regarding the presence of natural teeth or complete dentures in protrusion and maximal protrusion for all muscles (P < 0·05) and in lateral excursive positions for non-working side temporal (P < 0·05) and working side masseter muscle (P < 0·05). Muscle activity at various mandibular positions depends greatly on the presence of the prosthetic appliance, as edentulous subjects had to use higher muscle activity levels (percentages of maximal EMG value) than age matched dentate subjects in order to perform same mandibular movement. Different elevator muscles were preferentially activated in the edentulous subjects when compared with dentate group in lateral excursive positions of the mandible. The pattern of relative muscle activity was not changed because of ageing. [source] Differential activity patterns in the masseter muscle under simulated clenching and grinding forcesJOURNAL OF ORAL REHABILITATION, Issue 8 2005H. J. SCHINDLER summary, The aim of this study was to investigate (i) whether the masseter muscle shows differential activation under experimental conditions which simulate force generation during clenching and grinding activities; and (ii) whether there are (a) preferentially active muscle regions or (b) force directions which show enhanced muscle activation. To answer these questions, the electromyographic (EMG) activity of the right masseter muscle was recorded with five intramuscular electrodes placed in two deep muscle areas and in three surface regions. Intraoral force transfer and force measurement were achieved by a central bearing pin device equipped with three strain gauges (SG). The activity distribution in the muscle was recorded in four different mandibular positions (central, left, right, anterior). In each position, maximum voluntary contraction (MVC) was exerted in vertical, posterior, anterior, medial and lateral directions. The investigated muscle regions showed different amount of EMG activity. The relative intensity of the activation, with respect to other regions, changed depending on the task. In other words, the muscle regions demonstrated heterogeneous changes of the EMG pattern for the various motor tasks. The resultant force vectors demonstrated similar amounts in all horizontal bite directions. Protrusive force directions revealed the highest relative activation of the masseter muscle. The posterior deep muscle region seemed to be the most active compartment during the different motor tasks. The results indicate a heterogeneous activation of the masseter muscle under test conditions simulating force generation during clenching and grinding. Protrusively directed bite forces were accompanied by the highest activation in the muscle, with the posterior deep region as the most active area. [source] Short-term effects of a mandibular advancement device on obstructive sleep apnoea: an open-label pilot trialJOURNAL OF ORAL REHABILITATION, Issue 8 2005G. AARAB summary, Obstructive sleep apnoea (OSA) is a common sleep disorder, which is, among others, associated with snoring. OSA has a considerable impact on a patient's general health and daily life. Nasal continuous positive airway pressure (nCPAP) is frequently used as a ,gold standard' treatment for OSA. As an alternative, especially for mild/moderate cases, mandibular advancement devices (MADs) are prescribed increasingly. Their efficacy and effectiveness seem to be acceptable. Although some randomized clinical trials (RCTs) have been published recently, most studies so far are case studies. Therefore, our department is planning a controlled RCT, in which MADs are compared with both nCPAP and a control condition in a parallel design. As a first step, an adjustable MAD was developed with a small, more or less constant vertical dimension at different mandibular positions. To test the device and the experimental procedures, a pilot trial was performed with 10 OSA patients (six mild, four moderate; one women, nine men; mean age = 47·9 ± 9·7 years). They all underwent a polysomnographic recording before as well as 2,14 weeks after insertion of the MAD (adjusted at 50% of the maximal protrusion). The apnoea,hypopnoea index (AHI) was significantly reduced with the MAD in situ (P = 0·017). When analysed as separate groups, the moderate cases showed a significantly larger decrease in AHI than the mild cases (P = 0·012). It was therefore concluded from this pilot study that this MAD might be an effective tool in the treatment of, especially, moderate OSA. [source] | ||||||||||