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Twelve healthy subjects with an intact permanent dentition and normal occlusion were selected for sampling of myoelectrical activity of their left and right anterior temporal and masseter muscles during habitual clenching level in varied positions. The proportionality of normalized myoelectrical potentials of anterior temporal muscle to masseter muscle at ICP and RCP was greater than one, while the proportionality at PP was less than one. In the lateral position, the proportionality on the working side was approximately equal to that at RCP, while the proportionality on the non-working side was similar to that at PP. These results suggest that temporal muscle contraction can bring the mandible upward and backward whilst the masseter muscle can elevate the mandible upward and forward.
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PMID:Observation of proportionality of myoelectrical activity of anterior temporalis to masseter muscle during clenching at varied jaw positions. 145 66

This review highlights the consensus existing in past research on the role of functional occlusal factors in the pathophysiology of temporomandibular disorders (TMD). The functional occlusal relationships considered are balancing and working occlusal contacts, length and symmetry of retruded contact position-intercuspal position (RCP-ICP) slides, occlusal guidance patterns, parafunction, and dental attrition. Controlled studies fail to demonstrate any association between occlusal interferences and TMD signs or symptoms. Temporomandibular joint condylar autorepositioning secondary to intracapsular arthrosis is associated with larger and asymmetric RCP-ICP slides. Other TMD conditions are not associated with any slide length or asymmetries. Occlusal guidance patterns are not associated with TMD symptom provocation or, conversely, health. Parafunction appears to be universal and is not associated with TMD development or symptomatology in healthy individuals. Furthermore, parafunction is not provoked by longstanding, naturally occurring occlusal variations. Dental attrition is not associated with TMD, and any observed increased attrition in osteoarthrosis patients is likely the result of age effects and occlusal alterations secondary to condylar positional changes.
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PMID:The role of functional occlusal relationships in temporomandibular disorders: a review. 181 69

A group of ten adolescents was treated with fixed appliances at the Department of Stomatology and Oral and Maxillofacial Surgery, Graz. Subsequently the patients were fitted with a gnathological positioner. On the day of band removal ten sets of models were made and subsequently two, four and twelve weeks later. They were mounted on an articulator and cephalometric measurements were taken three times by each of the examiners. These records served to provide evidence of discrepancies of the condylar position between ICP and RCP in all three planes. In the second part of the examination, the patients were instructed to wear the appliance at night for another year. Casting of models, mounting in articulators and condymetric measurements were repeated as above. After wearing the positioner for three months, we observed a definite improvement of the occlusion and a wide conformity of the RCP and ICP measurements. After one year of night-time retention there was a slight increase of the mean values. In addition, we could establish statistically that condymetric model measurements are independent of the examiner and the method employed.
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PMID:[The positioner--a possibility for the fine adjustment of the occlusion objectively assessed by condylar measurements of the discrepancy between the ICP and RCP]. 261 45

One hundred ninety-six TMJ patients differentiated into five diagnostic groups (disk displacement with reduction [n = 40], disk displacement without reduction [n = 14], TMJ osteoarthrosis with a history of past locking [n = 32], TMJ osteoarthrosis without a history of past locking [n = 30], myalgia only [n = 80]) were compared with 222 nonpatient controls for specific occlusal variables. The patient groups could not be differentiated according to the absence of RCP-ICP slide per se, crossbite, or symmetry of RCP contacts. Among males with reducing disk displacement, Class I was less common and Class II division 1 was more common than in controls. Asymmetric RCP-ICP slides and a combination of unilateral RCP contact and no clinically visible RCP-ICP slide were more prevalent in women with reducing disk displacement. Large RCP-ICP slides, asymmetric slides, and anterior open bite were associated with osteoarthrosis, but this study could not state if these associations were etiologic or secondary. Totally asymptomatic controls were characterized by a lack of anterior open bite, small symmetric RCP-ICP slides (greater than 0 less than 1 mm), and bilateral occlusal contact in RCP. By comparing a control group to well-defined patient diagnostic groups rather than according to symptoms, selective occlusal variables appear more closely associated with some TMJ disorders than indicated in past studies with less specific populations.
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PMID:Association of occlusal variables among refined TM patient diagnostic groups. 263 60

To investigate whether orthodontic cases can fulfil gnathologic requirement, models of 10 adolescent patients (of the Department of Orthodontics at the University Dental Clinic, Graz) were mounted in an articulator at band removal and 2, 4 and 12 weeks and one year later. During this year the patients wore a gnathologic positioner. Using a condymeter, discrepancies between RCP and ICP in three spatial planes were measured and the spatial diagonal computed. Statistical analysis showed a clear reduction of the means of slide in centric during continuous wearing of the positioner, after 3 months, RCP and ICP being almost identical. After a further 7 months, during which the positioner was worn only at night, the amount of slide increased again slightly. The increase of the spatial diagonal was due to an increase of the sagittal and vertical slides whereas the lateral slide remained constant.
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PMID:Changes in occlusion and condylar positioning during retention with a gnathologic positioner. 267 70

The variability in the assessment of occlusal variables was investigated in eight subjects by the repeated registrations of four observers. The following variables were investigated in three different ways: sliding between the RCP (retruded contact position) and the ICP (inter-cuspal contact position) in the sagittal, vertical and lateral plane. Interferences during lateral movements on the working and balancing sides as well as interferences causing deviation of the mandible during protrusive movements were recorded. The intra- and inter-observer error for the measurement of sagittal and vertical distance RCP-ICP was within acceptable limits. There was no significant difference between the three methods used. The intra- and inter-observer agreement between duplicate recordings of the lateral distance RCP-ICP was high and there were no differences between the different measurement modalities. The inter-observer agreement was lower than the intra-observer agreement concerning presence/absence of balancing side interferences, and positive inter-observer agreement was only found on lateral movement more than 3 mm from the RCP or the ICP. The observer error for the variable working side interferences should be acceptable for future research, while the observer error for measurement of lateral deviation of the mandible upon protrusion was somewhat larger.
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PMID:Assessment of occlusal interferences. 274 16

Two complete classes of freshman dental and dental hygiene students, 120 men and 102 women (mean age 23.9 years) were assessed for the presence of masticatory pain or dysfunction by questionnaire, clinical examination, and evaluation of dental casts according to strict criteria. The purpose was to identify the degree of association between observable signs of TMJ disorders and selected combinations of occlusal variables. TMJ tenderness was more frequent in class II, division 2 than in class I (p less than .05), but overall was not associated with occlusal factors such as deep overbites, length of a symmetric RCP-ICP slide, and unilateral contact in RCP. Overall, clicking was not associated with Angle class, deep overbite, length of symmetric RCP-ICP slide, or unilateral RCP contact. Among subjects with unilateral RCP contact, those with no clinically obvious RCP-ICP slide (p less than .005) and those with asymmetric slides (p less than .05) had more TMJ clicking than subjects with symmetric slides. Luxation clicking of the condyle over the articular eminence on wide opening was absent in class II, division 2 subjects, but was most frequent in subjects with some teeth in unilateral posterior crossbite, particularly when this was a unilateral condition (p less than .001). Certain occlusomorphologic conditions may require less adaptation in the TMJs. This article indicates that an ICP anterior to the RCP in association with bilateral occlusal stability may be protective.
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PMID:Temporomandibular disorders. Part II: Occlusal factors associated with temporomandibular joint tenderness and dysfunction. 316 77

A three-dimensional condylar analysis of the ICP relative to the RCP was completed for 75 patients by using a system of styli adapted to an arcon articulator. The recorded sagittal condylar positions were seen in three of the four quadrants, the posterior-superior quadrant was devoid of registrations. The percent of registration was approximately equal for the right and left sides; anterior-inferior quadrant, 60%; posterior-inferior quadrant, 30%; and anterior-superior quadrant, 10%. Midcondylar value of the ICP presented the smallest standard deviation but the data concerning condylar position were unreliable because symmetrical and asymmetrical movement may produce similar midcondylar values. Seventy-two percent of the anterior-posterior and 45% of the superior-inferior condylar ICP recordings of patients fell within the range of a dentally healthy sample of young men. Only 2% of recordings the patients were outside this range in a superior direction. These data were nearly equal numerically for the right and left sides and conformed to the anatomic freedom of TMJ. Slightly more than 57% of the sample had an MLD greater than 0.3 mm compared with a dentally healthy sample. There was a 42% greater incidence of skew greater than 0.7 mm and a 22% greater occurrence of tilt greater than 0.7 mm in the dental patient sample, compared with the findings of Hoffman et al. An index ICP asymmetry was proposed that indicates the relative value of skew and tilt in a single quantitative factor. Three mandibular movements were identified, skew and tilt with angular components and MLD, translation. These three movements have 3 degrees of freedom, right or left movement or no movement, resulting in 27 permutations. The combination of these elements make it difficult to determine condylar position from occlusal midline observation.
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PMID:Condylar retruded contact position and intercuspal position correlation in dentulous patients. Part I: Three-dimensional analysis of condylar registrations. 346 49

This article investigates the influence of occlusion on condylar position as seen on TMJ tomograms in a group of 44 young adults with no histories of orthodontic or occlusal therapy and no objective signs of masticatory dysfunction; the sample was screened from a population of 253 students. Nonconcentric condylar position at ICP was a feature of Class II malocclusion with significantly more anterior positions in Class II, Division 1 than in Class I. Condylar position was unrelated to the amount of sagittal RCP-ICP slide, although most slides were less than 0.5 mm. The frequency of lateral slides was low, but was mildly related to bilaterally asymmetric condylar positions. Position was unrelated to the degree of overbite, which ranged from 0 to 10 mm. Bilateral condylar position asymmetry was not related to the direction of dental midline discrepancy, which ranged from 0 to 2 mm. No open bites or mandibular overjets were seen in this asymptomatic normal sample.
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PMID:Relationship of mandibular condylar position to dental occlusion factors in an asymptomatic population. 346 6

Electromyographic and clinical characteristics of 42 myogenous craniomandibular disorder (CMD) patients were related to 40 healthy control subjects. Surface EMG recordings were obtained from the masseter and the temporal muscles. The clinical examination included active maximum mouth opening, endfeel distance, active laterotrusion and lateral endfeel distance, dental abrasion, the presence of a lateral slide (RCP-ICP) and the amount of static pain. Orthopantomographic X-rays were available from 32 CMD patients for measuring the condylar and ramus asymmetry. Compared to the control group lower masseter and temporal EMG amplitudes were found for myogenous CMD patients (P < 0.001). When the activity of the temporal muscle was compared with the activity of the masseter muscle, the CMD patients showed proportionally higher temporal muscle activities than the controls (P < 0.05, 50% clenching level). CMD patients also showed smaller mandibular excursions, larger endfeel distances and more dental abrasion than controls. The temporal muscle asymmetries showed significant negative correlations with the ramus asymmetries. The lower and upper quartile of the distribution of the mean masseter EMG amplitudes were used to distinguish weak and strong muscles in patients and controls. Weak patients showed proportionally high temporal muscle activities, larger masseter and temporal muscle asymmetries, and larger endfeel distances compared to strong CMD patients. These differences were not found between weak and strong controls. In conclusion, it can be said that the electromyographic and clinical findings of the myogenous CMD patients suggest a functional difference between weak and strong patients and indicate the need for more individually designed treatment modalities for functional muscle and joint CMD problems.
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PMID:EMG differences between weak and strong myogenous CMD patients and healthy controls. 763 12


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