Journal of Oral & Facial Pain and Headache, 01/1995

This anatomic study examines the attachment of the lateral muscle to the capsule and disc of the temporomandibular joint. The anatomy of the temporomandibular joint and its surroundings, in particular the insertion of the superior head of the lateral pterygoid muscle, was studied by dissection and conventional histologic techniques. The material consisted of 16 cadaver specimens from individuals 60 years or older. The results showed that only a part of the superior head of the lateral pterygoid muscle is attached to the anterior portion of the capsule, which, in turn, is firmly attached to the disc, giving the impression that the muscle and the disc are directly connected. All specimens showed attachment of the superior head of the lateral pterygoid muscle to the anterior medial portion of the capsule, but they showed varying degrees of attachment to the lateral aspect of the temporomandibular joint capsule. The remaining part of the superior head of the lateral pterygoid muscle attached to the mandibular condyle. Serial sectioning in no instance showed direct insertion into the disc of the fibers of the superior head of the lateral pterygoid muscle.

Controversial topics that influence the etiology and the treatment of temporomandibular disorders include anatomy and function of the lateral pterygoid muscle, and the nature of the disc-muscle connection. To explore whether an agreement has been reached among researchers, a literature survey focusing on the structure, performance, and disc-muscle interface of the lateral pterygoid muscle was performed. Eighty-nine original research articles were identified in the Index Medicus information system from 1879 to 1994 by applying the keyword phrase lateral pterygoid muscle. A majority of references (65%) identified two separate parts of the lateral pterygoid muscle as well as insertions into the disc, the capsule, and the condyle. Seventy-five percent of the articles agreed on three major functions. This literature survey revealed a consensus regarding anatomy, function, and disc connection among the majority of the researchers. However, diverging opinions were persistent and could be identified.

As overview is given of the most commonly investigated signs and symptoms associated with craniomandibular disorders as detected in a population of patients with craniomandibular disorders and in four defined diagnostic subgroups. The information was collected with a questionnaire and during an extensive clinical examination. Comparison of self-report and clinical data indicated that these two methods reveal different aspects of the patient's complaints and should be interpreted in their own way. The results showed that no statistically significant differences could be found between the four diagnostic subgroups with respect to occlusal factors, trauma, and clinically assessed parafunctional habits. The groups differed considerably with respect to general characteristics, pain variables, signs of craniomandibular disorders, self-reported parafunctional habits, psychosocial factors, and general health factors. However, despite the reduction in clinical characteristics of the four subgroups, there was little reduction in the diversity of factors associated with craniomandibular disorders. This implicates that almost all factors associated with craniomandibular disorders may influence the initiation and perpetuation of the different disorders in the individual patient, and therefore, remain of interest in future research.

An overview is given of the following four well-defined diagnostic subgroups of patients who have craniomandibular disorders: those with a mainly myogenous component; those with internal derangement with reduction; this with internal derangement without reduction; and those with osteoarthrosis. Although it was inevitable that the subgroups were not completely homogeneous, symptom profiles differed considerably. There even seemed to be reasons to distinguish two osteoarthrosis groups in future research. Although the identification of clinically significant factors in a given patient with craniomandibular disorders remains a difficult clinical task, the symptom profiles provide a framework that may give more insight into the background of the complaint and into possible contributing factors. The symptom profiles also provide the possibility of a more directed choice of treatment and a treatment evaluation that is more aimed at the specific characteristics of the subgroups. It therefore may be concluded that, to increase insight into craniomandibular disorders, the evaluation of diagnostic subgroups has to be preferred in the assessment of a heterogeneous group of patients with craniomandibular disorders.

The pain-pressure threshold in human tissues such as muscles may be affected by the anatomic location of the recording site and the rate of applied pressure. However, is uncertain how these variables affect the pain-pressure threshold in healthy oral tissues. In 10 subjects, a custom-made algometer was used to apply pressure at a constant rate to 12 sites on the attached gingivae apical to teeth 11 to 16 and 41 to 46. The pain-pressure threshold was measured at three different rates of applied pressure at weekly intervals for 4 weeks. The pain-pressure threshold was consistently higher at maxillary recording sites. There were, however, no differences in the pain-pressure threshold at different recording sites along the tooth row in the maxilla or mandible. The pain-pressure threshold measurements were consistent between recording sessions. The pain-pressure threshold was affected by the rate of pressure application and appeared to increase linearly with increasing rate. This suggests that the pain-pressure threshold may be measured consistently in attached human gingivae. When measurement of deep sensation in the oral mucosa is planned, the location of the recording site and the rate of applied pressure should be verified.

This study examined (1) the relationships between electromyographic-measured nocturnal bruxism, self-reported stress, and several personality variables, and (2) the relationship between belief in a stress-bruxism relationship and self reported stress. One hundred adult bruxers completed a batteryof personality questionnaires, indicated whether they believed in a stress-bruxism relationship, presented for a dental examination, and had dental impressions taken. Subsequentlyu, electromyographic measurements of bruxing frequency and duration were recorded for fifteen consecutive nights. Prior to each night's measurements, subjects indicated their levels of stress for the immediately preceding 24 hours. No overall relationship was established between electromyographic measures and the personality variables nor between electromyographic measures and self-reported stress. Correlations between electromyographic measures and self-reported stress were statistically significant for eight individual subjects. Further, subjects with high levels of stress reported more anxiety, irritability, and depression, and less denial. Subjects who believed in a stress-bruxism relationship reported greater stress.

Pain related limitations in activities of daily living are for 272 patients reporting orofacial pain of the temporomandibular region using the seven-item Pain Disability Index. Results showed that the factor structure for orofacial pain patients differed little from the factor structure for outpatients visiting chronic pain clinic settings. Analysis of pain diagnostic subgroups showed that patients suffering myogenous complaints had higher scores for four of seven daily-living activities that involved pain-related limitations than patients suffering discal disorders. The factor analytical findings indicated that these patients share common pain-related limitations in activities of daily living. These findings are also consistent with previous results indicating greater pain in orofacial pain patients diagnosed with pain complaints primarily myogenous in origin than in pain patients having discal disorders.

Oral motor function (mandibular displacement and velocity) individuals with juvenile chronic arthritis was studied by using an optoelectronic method. The children were compared with two asymptomatic groups: one group with Class I occlusion and the other with Class II malocclusion. The results showed that children with juvenile chronic arthritis and condylar lesions had reduced lateral mandibular masticatory movements. In children with Class II malocclusion, a longer three-dimensional closing distance and a slower closing velocity were found. In children with both juvenile chronic arthritis and Class II malocclusion, and interaction between juvenile chronic arthritis and malocclusion resulted in a longer occlusal time, a shorter amplitude, and a slower velocity. It can be concluded that juvenile chronic arthritis and Class II malocclusion, per se, might have minor influences on the chewing characteristics, but the two factors seem to interact, resultiing in an altered masticatory pattern. An explanation is that children with juvenile chronic arthritis have an increased risk of developing a Class II malocclusion because of the growth disturbances sequelae of condylar lesions. The alteration in occlusion, together with restricted movements in the arthritic condyle, may be the underlying reasons for the findings.

A review of the current literature regarding the interaction of morphologic and functional occlusal factors to TMD indicates that there is a relatively low association of occlusal factors in characterizing TMD. Skeletal anterior open bite, overjets greater than 5 to 7 mm, retruded cuspal position/intercuspal position slides greater than 4 mm, unilateral lingual crossbite, and five or more missing posterior teeth are the five occlusal features that have been associated with specific diagnostic groups of TMD conditions. The first three factors oftenare associated with TMJ arthropathies and may be the result of osseous or ligamentous changes within the temporomandibular articulation. With regard to the relationship of orthodontic treatment performed during adolescence generally does not increase or decrease the odds of developing TMD later in life. There is no elevated risk of TMD associated with any particular type of orthodontic mechanics or with extraction protocols. Although a stable occlusion is a reasonable orthodontic treatment goal, not achieving a specific gnathologically ideal occlusion does not result in TMD signs and symptoms. Thus, according to the existing literature, the relationship of TMD to occlusion and orthodontic treatment is minor. Signs and symptoms of TMD occur in healthy individuals and increase with age, particularly during adolescence; thus, TM disorders that originate during various types of dental treatment may not be related to the treatment but may be a naturally occurring phenomenon.