Effect of masticatory muscle fatigue on cranio-vertical head posture and rest position of the mandible

Occlusal Vertical Dimension: Best Evidence Consensus Statement

PURPOSE

Patients in need of extensive prosthodontic treatment may need restoration of their occlusal vertical dimension (OVD) due to tooth wear, tooth loss, or changes that have occurred to existing prostheses over time. Prosthodontic treatment is based on the clinical application of the available evidence regarding interocclusal distance (IOD), the positional stability of rest vertical dimension (RVD), and the effect of altering the OVD. Hence, the purpose of this consensus document is to examine available data related to IOD, RVD, and alteration of the OVD.

MATERIALS AND METHODS

The search was limited to Clinical trials, Randomized Controlled Trials, Systematic Reviews and Meta-analyses. Key words were healthy patient, mean, range, interocclusal rest distance; healthy patient, mean, range, freeway space; and dentistry, interocclusal gap, and no citations appeared. Dentistry, interocclusal distance, revealed 5 not relevant citations. Dentistry, inter occlusal rest space, and dentistry, interocclusal rest distance, both had the same single not relevant citation. Dentistry, freeway space revealed over 7,000 citations. Dentistry, occlusal vertical dimension, revealed 253 citations, 7 of which were related to the search question but only 1 which was different from the previous search. Mandible, rest vertical dimension, age changes, found 7 citations, none relative to the question. Expanding the search to include journal article found 260 citations with only one relevant to the question. Mandible, rest vertical dimension, alteration, harm revealed no citations; mandible, occlusal vertical dimension, alteration, revealed 15 citations, 1 of which was relevant; mandible, occlusal vertical dimension, changes, revealed 75 citations, none of which were relevant; mandible, occlusal vertical dimension, rehabilitation revealed 10 citations, none of which were relevant. Expanding the search strategy to include Journal article, mandible, occlusal vertical dimension, alteration, received 159 citations, 4 of which were relevant; mandible, occlusal vertical dimension, restoration revealed 208 citations, 1 of which was relevant. Numerous other articles were culled by going through the reference lists of the aforementioned articles.

RESULTS

For IOD, 27 articles were found relevant to the search question, which confirmed a mean of 3.0 mm with ranges from 1 to 9 mm. Five articles revealed little evidence as to whether the RVD changes during life. For OVD, 20 articles, including 4 systematic reviews, revealed some evidence that skeletal growth continues from mid adolescence into mid adulthood; strong anecdotal evidence that some unopposed teeth will continue to erupt; no clinical evidence to support the concept that abraded teeth in occlusion in a patient with bruxism will undergo continuous eruption; and some evidence from clinical case reports that restoring OVD in patients with severe abrasion is a successful treatment.

CONCLUSIONS

There is a range of dimensions for the interocclusal distance (IOD) with many normal dental patients functioning with a higher or lower IOD than the commonly used 3.0 mm average dimension. The resting vertical dimension (RVD) is a 3-dimensional range with little evidence related to changes in the RVD during life. However, aging can cause a decrease in muscle tone which could affect the RVD. The restoration of the OVD can be successfully accomplished if proper diagnosis and treatment planning are performed.

Effects of masticatory muscle training on maximum bite force and muscular endurance

OBJECTIVE

This study evaluates the effects of chewing training on strength and endurance of the masticatory muscles.

MATERIALS AND METHODS

Of the 49 healthy young adults included in the study, nine served as controls for a baseline measurement of bite force. The 40 participants who actively trained their masticatory muscles were randomly divided into a 'continuous training group' (CTG) and an 'intermittent training group' (ITG). The participants performed oral motor training by clenching silicon tubes (Chewy Tubes(™)) according to a designed protocol. The muscular strength was studied in terms of maximum bite force. Muscular endurance was evaluated by measuring the duration for which the participants held 50% of their maximum bite force value.

RESULTS

Both the maximum bite force and the muscular endurance capacity increased after intensive training for both groups. After 2 months, the ITG stopped training for 1 month. At this point, a significant difference was identified both in the mean bite force values and the mean muscular endurance duration: the ITG exhibited lower values. For both groups, the highest values were attained after 3 months of training. The maximum bite force values and the muscular endurance duration were observed to follow similar patterns. The effects attained decreased rapidly in both groups when the training stopped.

CONCLUSIONS

For both the continuous and intermittent training groups, 4 months of chewing exercises strengthened masticatory muscles, but such effects diminished gradually for both groups when the exercises stopped.

Clinical considerations for increasing occlusal vertical dimension: a review

The purpose of this article is to discuss the clinical considerations related to increasing the occlusal vertical dimension (OVD) when restoring a patient's dentition. Thorough extraoral and intraoral evaluations are mandatory to assess the suitability of increasing OVD. In the literature, multiple techniques have been proposed to quantify OVD loss. However, the techniques lack consistency and reliability, which in turn affects the decision of whether to increase the OVD. Therefore, increasing OVD should be determined on the basis of the dental restorative needs and aesthetic demands. In general, a minimal increase in OVD should be applied, though a 5 mm maximum increase in OVD can be justified to provide adequate occlusal space for the restorative material and to improve anterior teeth aesthetics. The literature reflects the safety of increasing the OVD permanently, and although signs and symptoms may develop, these are usually of an interim nature. Whenever indicated, the increase in OVD should be achieved with fixed restorations rather than a removable appliance, due to the predictable patient adaptation. The exception to this is for patients with TMD, where increasing the OVD should still be achieved using removable appliances to control TMD-associated symptoms before considering any form of irreversible procedure.

Effects of anterior cruciate ligament (ACL) injury on muscle activity of head, neck and trunk muscles: a cross-sectional evaluation

This study evaluated the that effects a pathology of the knee, due to an anterior cruciate ligament (ACL) injury, has on muscular activity of neck, head, and trunk muscles. Twenty-five (25) subjects (mean age 28+/-9 years) with ACL injury of the left knee were compared with a control no-pathology group. Surface electromyography (sEMG) at mandibular rest position and maximal voluntary clenching (MVC) wasused to evaluate muscular activity of the areas: masseter, anterior temporalis, posterior cervicals, sternocleidomastoid (SCM), and upper and lower trapezius. The sEMG activity of each muscle, as well as the asymmetry index between the right and the left sides, were compared between the two groups. Subjects in the study group showed a significant increase in the asymmetry index of the sEMG activity of the anterior temporalis at mandibular rest position (p<0.05). At rest, the areas of anterior temporalis and masseter in the control group showed a significantly lower sEMG activity compared with subjects in the study group, both in the right and the left sides (p<0.05). The same was found for the sEMG activity of the areas of SCM and lower trapezius. At MVC, the right areas of anterior temporalis and masseter in the study subjects showed a significantly lower sEMG activity compared with the control group. The same was observed for the lower trapezius area, both in the right and the left sides. In general, ACL injury appears to provide a change in the sEMG activity of head, neck and trunk muscles.

Cervical lordosis in patients who underwent anterior cruciate ligament injury: a cross-sectional study

It has been proposed that intraoral devices can influence cervical posture. Cervical posture might also be influenced by stimuli from the lower limbs, such as injury of the knee. The hypothesis to be tested is that intraoral devices are useful during the rehabilitation of orthopedic patients to accelerate the restoration of postural control. This study evaluates cervical posture on lateral skull radiographs in subjects who suffered anterior cruciate ligament (ACL) injury of the left knee. Twenty adult Caucasian males (mean age 30.6+/-9.2 yrs.) with ACL injury of the left knee were compared with 40 control subjects (mean age 27.9+/-7.2) who did not show any ACL injury. Lateral skull radiographs, made in natural head position (mirror position), were obtained for all subiects. Various postural and morphological variables were individualized on each radiograph. To assess errors due to landmark identification, duplicate measurements were made of 15 radiographs and compared using the Dahlberg formula. The method error from both sources was less than 0.5 degrees for all angular measurements and less than 0.5 mm for all linear measurements. No difference was observed between the two groups in any of the morphological variables of face or in the cervical lordosis angle (CVT/EVT). However, subjects in the study group showed significantly higher craniocervical angulations (SN/OPT, SN/CVT, SN/EVT, pns-ans/OPT, pns-ans/CVT, pns-ans/EVT, GoGn/OPT, GoGn/CVT, GoGn/EVT) compared with the control subjects (p<0.001). The subjects with ACL injury had significant head extension compared with the control subjects.

Effects of anterior cruciate ligament (ACL) injury on postural control and muscle activity of head, neck and trunk muscles

The aim of the study was to evaluate the effects that an anterior cruciate ligament injury of the knee has on postural control and activity of neck, head and trunk muscles to investigate the existence of connections between the masticatory system and body posture. Surface electromyographic activity of the muscles at mandibular rest position, and during maximal voluntary clenching and posturometric and stabilometric measurements of 25 adult patients having pathology on the left knee were compared with a control non-pathological group. At rest, the patients showed a higher muscular activity of anterior temporalis, masseter, sternocleidomastoid and lower trapezius, compared with the control subjects (P < 0.05). At maximal voluntary clenching, the patients showed a lower muscular activity of the right anterior temporalis and masseter and a higher muscular activity of the lower trapezius, compared with the control subjects. For the stabilometric measurements, all the subjects showed a significant reduction in the postural centre of pressure path length during the test with eyes open and cotton rolls, compared with the test with eyes closed and mandibular rest position (P < 0.05). In addition, the patients showed a significant displacement of the postural centre of pressure in a forward direction (P < 0.05) and into the right side (P < 0.05), compared with the control subjects. Anterior cruciate ligament injury appears to be associated to a change in the activity of head, neck and trunk muscles and to a change in the position of the postural centre of pressure. Cotton rolls seem to improve the stability of the subject.

Orientation of craniofacial planes and temporomandibular disorder in young adults with normal occlusion

The aim of this study was to investigate the relationship between orientation of craniofacial planes relative to the true horizontal and temporomandibular disorder (TMD), in normal occlusion. Fourteen university dental students, with full natural dentition and bilateral Angle Class I occlusion, who exhibited signs and symptoms of TMD, were compared with 14 age- and sex-matched healthy controls. Frontal and lateral photographs were taken in natural head position with the subject standing up, clenching a Fox plane and having a facial arch positioned. Photographs were examined by a standardized image analysis. Inter-pupillary axis, Frankfurt, occlusal and Camper planes were evaluated. In frontal view, the Frankfurt plane was right rotated relative to the true horizontal both in TMD subjects (P < 0.01) and controls (P < 0.05), but rotation was larger in TMD subjects (mean difference between groups, 1.1 degrees, 95% confidence interval, 95% CI, 0.2-2.0 degrees ). No significant deviation from the horizontal or difference between groups was observed for the interpupillary axis and occlusal plane. In lateral view, the Frankfurt plane was upward-orientated relative to the true horizontal in TMD group (mean angular deviation 2.8 degrees, 95% CI, 1.0-4.6 degrees ). The occlusal and Camper planes were downward-orientated in both groups (P < 0.0001), but inclination of occlusal plane tended to be smaller in TMD subjects (mean difference between groups, -3.8 degrees, 95% CI, -7.6-0.1 degrees ). Angles between any craniofacial planes did not significantly differ between groups. The findings show that in young adults with normal occlusion, a weak association exists between the orientation of craniofacial planes in natural head position and signs and symptoms of TMD. Furthermore, they suggest that, within this population, TMD might be mainly associated with head posture rather than with craniofacial morphology.

Effects of the antigravitary modification of the myotension of asset (MAGMA) therapy on myogenic cranio-cervical-mandibular dysfunction: a longitudinal surface electromyography analysis

This study was aimed at evaluating the effects of a novel physiotherapy machine called MAGMA (AntiGravitary Modification of the Myotensions of Asset) on postural and masticatory muscles of subjects with myogenic cranio-cervical-mandibular dysfunction (CMD), by using surface electromyography (sEMG). Fifteen subjects, nine males and six females (mean age 27.6 years), with CMD were included in the study. The bilaterally monitored muscles were: masseter, anterior and posterior temporalis, digastric, posterior cervical, sternocleidomastoid, and upper and lower trapezius. All muscles were monitored at rest, with a second record of maximal voluntary clenching (MVC) for both the masseter and anterior temporalis. Patients were subjected to MAGMA therapy for one session/week of 30 min over ten weeks. The surface EMG activity was recorded twice, at the baseline and at the end of the therapy. After MAGMA therapy, the sEMG activity at rest of the monitored muscles was significantly better when compared to the baseline; the only exception was the anterior and posterior temporalis muscles which did not improve. On the contrary, with the MVC, all the monitored muscles (masseter and anterior temporalis) significantly improved their sEMG activity. Although more investigations are needed, these results indicate that the use of such antigravitary therapy can provide a tool for resolving myogenic CMD.

Relationship between dental occlusion and posture

The purpose of this study is to show the effects of dental occlusion on postural position. Thirty subjects were divided into two groups: an experimental group who wore mandibular orthopedic repositioning appliances (MORA) and a control group who wore no oral device. All of the subjects underwent the same Fukuda-Unterberger experimental stepping test to check their postural attitude. Any deviation of the subject during the test from his initial position was analyzed. The results seemed to confirm that altering dental occlusion by wearing an oral appliance could induce some fluctuations in dynamic postural attitude. The phenomenon occurs after prolonged wearing of a MORA. Feedback effects are gradual after removing the mandibular splint.

Relationship between dental occlusion and visual focusing

The purpose of this study is to show the effects of dental occlusion on visual focusing. Thirty subjects were divided into two groups: an experimental group who had worn mandibular orthopedic repositioning appliances and a control group who had not worn any oral device. All of the subjects underwent the same visual focusing tests with a Maddox rod and the Berens prismatic bars, from over five meters to 30 centimeters. The results seemed to confirm that the alteration of dental occlusion can induce some fluctuations in visual focusing. The phenomenon occurs after wearing a MORA (Mandibular Orthopedic Repositioning Appliance) for a while. Feedback effects are gradual after removing the mandibular splint.

Occlusion and center of foot pressure variation: is there a relationship?

The influences of head and body posture on the mandibular rest position, the range of functional movements, and the initial tooth contact have been documented. In this investigation, the modifications of the position of the center of foot pressure during natural standing were studied in 30 women. The subjects were divided into three groups: healthy women (control), women with an asymmetric (unilateral) Angle class II malocclusion, and women with temporomandibular disorders. Data were acquired in 30-second trials by use of a force plate that allowed a separate assessment of each foot while the subjects maintained different dental positions: rest position; centric occlusion; maximum clench; occlusion on two cotton rolls placed on the mandibular teeth distal to the canines; and maximum clench on two cotton rolls. Bivariate analysis was used to compute the mean values and relevant variability for the center of foot pressure location during each trial. The results demonstrated that the modifications of foot center of pressure were not influenced by temporomandibular disorders and asymmetric malocclusion or by different dental positions.