Craniomandibular disorders and masticatory muscle function

The heading craniomandibular disorder covers a wide range of abnormal and pathologic conditions accompanied by orofacial pain and impaired mandibular function, the masticatory muscles and the temporomandibular joints being the structures most frequently involved. Prevalences of serve carniomandibular disorder accompanied by headache and facial pain urgently in need if treatment are 1–2% in children, about 5% in adolescents, and 5–15% in adults, with higher values in women than in men. With respect to physiology and ergonomics, masticatory muscles are comparable to other human skeletal muscles, e.g. of shoulder, neck and lower back. Therefore these muscles share pathogenesis, symptoms and signs of muscular disorders caused by prolonged, low-level static contractions or intermittent isometric contractions at higher levels. Since the same elements of performance in the masticatory muscles are influenced by occlusal factors, they link the development of muscular fatigue, discomfort and pain to the dental occlusion. Furthermore, changes of the occulusal surfaces, e.g. due to dental treatment, may influence the performance of the masticatory muscles, and consequently with local muscular function.     

Dental treatment of temporomandibular disorders and masticatory muscle pain.

The treatment of masticatory muscle and temporomandibular joint pain constitutes an important area in dentistry. Current information supports the use of reversible treatments for these disorders. Several recent references are discussed in relation to reversible treatment, the role of occlusion, and appliance therapy for internal derangement.     

Craniomandibular disorders and headaches

Three hundred patients were questioned regarding frequency of headache pain. One hundred forty-one patients were seeking treatment at the University of Kentucky College of Dentistry TMJ Clinic for CMD. A comparison group of 159 was selected from persons being screened for routine dental needs. The following findings regarding incidence and frequency of headache pain were observed: 1. The incidence of headache pain was twice as high in the CMD group than in the comparison group (p less than .001). 2. Of the persons in each group reporting the occurrence of headaches, the frequency of headaches in the CMD group was significantly higher (44%) than in the comparison group (p less than .001). Thirty-three patients with headache pain were treated for a 4-week period with occlusal splint therapy. Patients were questioned regarding the number of headaches per week they had before and after occlusal splint therapy. The following results were observed: 1. Twenty-one (63.6%) patients showed a decrease in the frequency of their headaches. 2. Ten (30.3%) patients showed complete remission of headaches. 3. No patient showed an increase in the frequency of headaches. 4. As a group the average number of headaches per week before treatment was 5.06; after occlusal splint therapy the average number of headaches per week was 2.15 (p less than .001).     

A review of masticatory muscle function

Current reports of the actions of the major muscles of mastication are reviewed for clenching tasks in centric occlusion and eccentric jaw positions, mandibular opening, and unilateral chewing. The relationship of the mandible to the maxillae in the intercuspal position and, consequently, the relationship of the condyle to the fossa of the temporomandibular joint may be controlled by the clinician. Similarly, the number and site of tooth contacts in the intercuspal position and in eccentric jaw positions may be altered. These alterations all produce alteration of muscle activity during functional and parafunctional acts. Some of these alterations are now predictable. Nevertheless, much more study needs to be done before the outcomes of morphologic changes on the muscular system can be accurately predicted. Even now, however, clinicians must understand the nature of clenching and chewing muscle activity and how it can be altered to a more favorable situation for each individual. This review indicates that: The elevator muscles demonstrate maximum activity when even bilateral occlusal contacts occur during clenching in the intercuspal position. The elevator muscles are activated together in the intercuspal zone of tooth contact during chewing when the occlusal contacts are balanced bilaterally in this intercuspal position. Increasing the number of eccentric tooth contacts increases the muscle activity during both chewing and clenching. The medial pterygoid muscle is variable in its action. This variability appears to be related to the chewing pathway and the type of occlusion. Its action is enhanced during laterally directed chewing actions of the mandible. The inferior head of the lateral pterygoid muscle has a reciprocal role with the medial pterygoid muscle during chewing and contributes to forward and lateral bracing of the condyle of the mandible. Although the superior head of the lateral pterygoid muscle appears to be active during mandibular closing, the significance of this finding is not fully understood.     

Craniomandibular disorders in psoriasis

A questionnaire survey of all members of the Psoriasis Society of the Greater Helsinki area was carried out to determine the prevalence of craniomandibular (CM) disorders in psoriasis. 1517 (85%) of the psoriatic members responded; 1050 had skin symptoms (psoriasis; P) and 400 skin and joint symptoms (psoriatic arthritis; PA). The most characteristic CM symptom was pain in the temporomandibular joint area. A high number of subjective symptoms correlated with poor general state of health, stress, pruritus of skin lesions, occlusal parafunctions and impaired chewing ability. Patients with PA had symptoms of CM disorders twice as frequently as patients with P. A high number of symptoms of CM disorders correlated with the number of other joints affected by PA.     

Craniomandibular disorders and general joint mobility

The purpose of the investigation was to study the relationship between general joint mobility and dysfunction among patients with craniomandibular disorders (CMD). Joint mobility was assessed in 74 female patients and 73 controls, using Beighton's modification of the Carter & Wilkinson hypermobility score. Twenty-five (83%) of 30 patients with score greater than or equal to 3 (lax joints) had temporomandibular joint (TMJ) involvement. Eighteen (41%) of 44 patients with score 0-2 (no laxity) had TMJ involvement. The difference between these groups was statistically significant (p less than 0.001). General joint laxity should therefore be taken into consideration in diagnosis and treatment of CMG.     

Sexual dimorphism of murine masticatory muscle function

OBJECTIVE: To determine if gender distinctions of force generating capacity existed in murine masticatory muscles. DESIGN: In order to investigate the effect of sex on force generating capacity in this muscle group, an isolated muscle preparation was developed utilising the murine anterior deep masseter. Age-matched male and female mice were utilized to assess function, muscle fibre type and size in this muscle. RESULTS: Maximum isometric force production was not different between age-matched male and female mice. However, the rate of force generation and relaxation was slower in female masseter muscles. Assessment of fibre type distribution by immunohistochemistry revealed a three-fold decrease in the proportion of myosin heavy chain 2b positive fibres in female masseters, which correlated with the differences in contraction kinetics. CONCLUSIONS: These results provide evidence that masticatory muscle strength in mice is not affected by sex, but there are significant distinctions in kinetics associated with force production between males and females.     

Influence of masticatory muscle function on craniofacial growth in hypocalcemic rats.

The aim of this study was to investigate the influence of low masticatory function on the craniofacial growth pattern in rats fed a low calcium and vitamin D deficient diet. Male growing rats were divided randomly into three groups: the Normal Hard Diet group, the Deficient Soft Diet group, and the Deficient Hard Diet Group. Lateral cephalograms were taken at days 0, 14 and at the end of the experiment, day 28. The craniofacial growth pattern was altered by an upwards rotation of the viscerocranium (orthocranialization) in the Deficient groups and, the total skull lengths were shorter than in the Normal Hard Diet group. The viscerocranium in the Deficient Soft Diet group was in an even more orthocranial position than in the Deficient Hard Diet group and the antegonial notch was shallower. This indicates that an induced disturbance of craniofacial morphology due to metabolic bone disease during growth is accentuated by a low masticatory function.     

Craniomandibular disorders and orthodontic treatment need in children

summary Two hundred and forty subjects (113 boys and 127 girls), divided in three age groups, 7, 11, and 16 years were interviewed and clinically examined to estimate the prevalence of CMDs and the need for functional treatment, and to compare the functional status of the stomatognatic system in two subgroups: those judged to need orthodontic treatment and those judged not to need orthodontic treatment. Signs and symptoms of craniomandibular disorders were quite common and, in most cases, mild. There were significant differences in prevalence of CMDs between sexes. Only 3.7% of the patients were judged to need some functional treatment for CMDs. Trauma to the facial area and headaches were significantly associated with signs and symptoms of CMDs. No indication was found that oral parafunctions produce CMDs. No greater prevalence of CMDs signs and symptoms was found in subjects who needed orthodontic treatment than in subjects who did not need orthodontic treatment. In conclusion, preliminary results of this ongoing study support the contention that the high prevalence of signs and symptoms of CMDs is not really a measure of masticatory dysfunction, and that malocclusion does not appear to cause CMDs and/or to increase craniomandibular treatment need in a young population.     

Masseter muscle fibre changes following reduction of masticatory function

This study evaluated histological changes in masseter muscle fibres following reduced masticatory function by injection of botulinum toxin type A (BTX). Sixty 30-day-old Long-Evans male rats were randomly separated into four groups (15 per group): group I BTX masseter, 25U/ml (0.04ml each muscle) BTX was injected in bilateral masseter muscle whilst bilateral temporalis muscles received an equal amount of normal saline; group II BTX temporalis, 25U/ml (0.04ml each muscle) BTX was injected in bilateral temporalis muscle whilst bilateral masseter muscle received an equal amount of normal saline; group III BTX temporalis and masseter, bilateral temporalis and masseter were given 25U/ml (0.04ml each muscle) BTX; group IV normal saline (control), bilateral temporalis and masseter were given normal saline (0.04ml each muscle). After 45 days, the rats were killed, the muscles dissected and mean muscle mass recorded. The superficial masseter muscles were immunohistochemically analysed. Fibre sizes in group III were bigger than those in other groups. There was a small percentage of type IIa fibres in group III. Reduction in muscle fibre size and transition of muscle fibre subtypes from type IIa to IIx or IIb fibres may occur due to reduced masticatory function.     

骨性Ⅲ类错He畸形患者正颌手术前后咀嚼肌功能变化的初步研究

目的应用肌电图仪评价骨性Ⅲ类错     

Effects of masticatory muscle function and bite-raising on mandibular morphology in the growing rat.

The aim of this series of investigations was to study the effect of masticatory muscle function on the growth pattern and on the internal structure of the mandible during growth. The muscular and dentoskeletal growth adaptation to prolonged bite-raising and the role of the functional state of the masticatory muscles in this adaptation were also to be elucidated. Differences in masticatory muscle function were induced in young rats by altering the consistency of the diet. Bite-raising was produced by the insertion of posterior bite blocks. Morphometric analysis of the internal bone structures of the mandible was performed on microradiographs, and videodensitometric analysis was performed on lateral radiographs and microradiographs. The effect of muscle function and bite-raising on mandibular growth was studied on a series of lateral cephalograms, superimposed on bone markers. Muscle belly, sarcomere and aponeurosis length adaptation to bite-raising was studied in situ with a digital caliper and under a microscope after fluorescent vital staining of the deep masseter muscle. A soft diet altered the pattern of growth of the mandible and reduced bone growth in the angular region. Transversal dimensions and cross-sectional area of the dentoalveolar process were smaller. Bone mass in areas possibly subjected to direct loads or bending forces was smaller. This was due to either less trabecular bone or thinner cortical bone. Only a few sites showed lower bone density. Posterior bite-blocks affected the size of the mandible as well as its growth pattern, and intruded lower molars. The soft diet influenced the effect of bite-blocks and caused less intrusion of upper molars and less inhibition of bone growth at the angular process. The deep masseter muscle adapted to bite-raising by elongation of the aponeurosis, but less in rats on a soft diet. Changes in masticatory muscle function affected the growth of the mandible in both the sagittal and transversal plane. Reduced loads on molars and condyle and smaller bending forces in other regions of the mandible possibly reduced the levels of stimulation of the osteocyte network and osteoblasts, thus inducing less trabecular bone and cortical bone formation in specific areas. In rats fed the soft diet, smaller increase in bone density represented an adaptation process in areas characterised by a lower bone apposition rate. The forces produced by the passive stretching of the masseter muscle affected the skeletal growth pattern and dental eruption. Weaker forces possibly produced by passive stretching of hypofunctional muscles resulted in more eruption of the upper molars and less inhibition of periosteal bone apposition in the angular region. Length adaptation in the masseter muscle through lengthening of the aponeurosis and dentofacial growth adaptation possibly decreased passive forces applied to teeth and skeletal structures, particularly in rats with higher functional demands. This may have caused a gradually decreasing effect of the appliance.     

Craniomandibular disorders management (1) Treatment planning

Various treatment modalities have been reported in the management of the craniomandibular disorders in the half century after Costen reported his hypothesis on the temporomandibular disorders. Recent advances in the basic sciences such as anatomy, histology, pathology, physiology and clinical trials have brought us to this new era. We have been trying to establish our diagnosis and treatment modalities in the management of the craniomandibular disorders over the past fifteen years. In this series of articles we will describe our present concept. We will first discuss diagnosis and treatment planning. After the diagnosis and initial treatment planning craniomandibular management is usually divided into two phases. Phase I is the treatment of the stomatognathic system especially the temporomandibular joint. Behavioral modification and physical therapy and splint therapy are the most common forms of treatment. Sometimes, surgical treatment is required. Phase II is the compensatory phase of the occlusion consisting of occlusal equilibration, occlusal restorations, orthodontic treatment and gnathic surgery if needed. Another phase we like to add is maintenance. In this phase, home therapy, corrective follow-up and long term observation should be emphasized. The motivation of the patient throughout the management of the craniomandibular disorder (phase I, phase II and the maintenance phase) is essential to reach to a successful result.     

Clinical evaluation of protocol for the craniomandibular disorders. 2. Craniomandibular disorders according to new classification

The purpose of this study is to clarify the actual state in the patients with extensive pathological states of craniomandibular disorders (CMDs). 100 patients, with their ages ranging from 11 to 77 years old, were selected for the study and they were divided into 5 groups according to classification of Japanese Society for Temporomandibular Joint. The following results were obtained: 1. By classification type, the ratio was 88, 16, 8 and 2% for Type III, Type I, Type IV and Type II. Type V was not found. 2. 22% of patients were male and 78% were female. The ratio of male and female was 1:4. 3. By age group, the ratio was 34, 23, 18, 12, 11, 1 and 1% for twenties, tens, thirties, fifties, forties, sixties and seventies. CMDs was found highly in younger ages (tens and twenties). 4. The ratio diagnosed Type III was 86.9, 97.0, 88.8 and 83.3% for tens, twenties, thirties and forties. Type III was found high ratio in all ages. 5. In all patients, right TMJ with disorder 37%, left TMJ with disorder 34%, bilateral TMJ with disorder 29%. There were no difference between right and left. 6. As can be seen from the above, young individuals with CMDs were clearly high ratio and many CMDs were diagnosed Type III through all the ages. Therefore, the results of our study suggest that young CMDs patients could be increasing gradually and complicating a pathological state.