下颌骨骨折后颞下颌功能紊乱的临床研究

目的 :探讨下颌骨骨折后颞下颌功能紊乱的状况。方法 :按照改良Helkimo指数对 3 6例下颌骨骨折患者和 3 2例正常人的颞下颌功能进行比较分析研究。结果 :骨折组和正常组在主诉症状指数 (Ai)、临床症状指数 (Di)的分布上有显著性差异 (P <0 .0 0 1) ,咬合指数 (Oi) 2组之间无显著性差异。结论 :下颌骨骨折患者比正常人群在一定的时期内更易出现颞下颌功能紊乱     

Temporomandibular joint function and its effect on centric relation

An occlusal analysis in relation to the TMJ radiographs will reveal factors that should be added to the purely clinical definition of centric relation. It has been previously established that bilateral asymmetric TMJ spaces and condylar retrusion or protrusion are most often associated with disc derangement and/or palpable muscle spasm.⁴ Conversely, bilateral TMJ space symmetry and condylar concentricity (condyle centered in the superior portion of the glenoid fossa) are associated with joint and muscle health. All TMJ radiographs are obtained with the teeth in the acquired centric occlusion.Centric relation is considered functional when the magnitude and direction of the centric relation deflective slide to the acquired centric occlusion correlate with the condylar displacement observed on the TMJ radiographs. For example, if the patient has a 2 mm. deflective slide straight forward, the centric relation is considered functional when the TMJ radiographs reveal equal condylar protrusion proportional to the mandibular deflection. In the judgment of the dentist, the occlusal correction of the deflective contacts will result in bilateral condylar concentricity. Conversely, centric relation is dysfunctional when the magnitude and direction of the centric relation deflective slide to the acquired centric occlusiondo not correlate with condylar position in the TMJ radiographs. When no deflective slide is present, both condyles should be concentrically located in each fossa with bilateral symmetrical joint spaces in order for centric relation to be considered functional. Dysfunctional centric, relation is often associated with disc derangement and/or palpable muscle spasm. When the centric relation is functional, the most retruded jaw position should be used. If the centric relation is dysfunctional, a therapeutic or treatment centric occlusion must be established by the dentist, utilizing the TMJ radiographs as a guide. In this situation, the most retruded position would be harmful to the patient.     

Temporomandibular joint function and its effect on concepts of occlusion.

Many of the premises of dentistry that have evolved empirically have been re-evaluated in the light of newly-developed concepts of TMJ function. Centric relation, although duplicable, may not necessarily be correct. A "functional" centric relation exists when the TMJ radiographs can be correlated with the occlusal findings, in which case, the retruded classical centric relation should be used. When a "dysfunctional" centric relation is present (no correlation between the TMJ radiographs and occlusal findings), the most retruded position should not be used and a therapeutic centric occlusion should be created by the dentist. Subclinical TMJ dysfunction occurs more frequently than commonly thought, because TMJ radiographs are not routinely used. Retruded condylar displacements can be easily overlooked, because the lateral pterygoid muscle has relatively few stretch receptors compared to the elevator muscles of the mandible. Condylar retrusion, therefore, would not necessarily cause lateral pterygoid spasm as might be expected. The exact mechanism of the TMJ suspension system is unknown, although experimental evidence has shown that the condyle can be displaced superiorly with posterior unsupported muscle force. This indicates that the immutability of the condylar path under varying clinical conditions is questionable. Due to the superior displacement characteristics of the TMJ, the condyle does not act as the fulcrum in mandibular kinetics. The fulcrum, therefore, shifts to the teeth and/or bolus, depending on the specific situation. In either instance, whether considering bruxism or mastication, for most patients, an occlusion based on group function is preferable to a canine-protected occlusion to insure TMJ health. Scientifically, no one scheme of occlusion or articulation has been proven to be superior to any other scheme; therefore, the choice is a matter of the personal preference of the dentist.     

Temporomandibular Joint Osteoarthrosis and Temporomandibular Joint Hypermobility

For studying the relationship between condylar hypermobility of the temporomandibular joint (TMJ) and osteoarthrosis (OA), 13 patients with bilateral condylar hypermobility were evaluated clinically and radiographically, 30 years after non-surgical treatment. The evaluation included range of motion, joint and muscle tenderness to palpation, joint sounds and masticatory function. Radiographs of the TMJs were evaluated for the absence or presence of degenerative changes. The hypermobile group (HG) was compared with a control group (CG) (n= 13). The CG was evaluated in the same way as the HG. Statistics included t-tests (to compare ranges of motion in the HG over time and to compare ranges of motion in HG and CG), non-parametric tests (to compare tenderness of muscles and joints, joint sounds, masticatory function and radiographic changes over time in the HG). The tests were also used to compare the same variables between the HG and CG group. The groups' only difference was the presence of radiographic signs of OA. In the HG the number of joints with radiographic degenerative changes increased significantly over time and was significantly higher than the CG. Clinically and functionally, the HG and CG did not differ. Therefore, it is concluded that TMJ hypermobility is a subsidiary factor in the development of TMJ OA.     

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Temporomandibular joint meniscectomy--effects on joint structure and masticatory function in macaca fascicularis.

The postoperative effects of unilateral temporomandibular joint meniscectomy on joint structure and masticatory function were evaluated in four mature Macaca fascicularis and compared with one control. Mandibular movement during mastication was monitored objectively with an optoelectronic tracking system within four months and again within twelve months postmeniscectomy in each animal. Temporomandibular joint structure was documented radiographically and histologically. Results showed that degenerative joint disease was produced in the postsurgical joint, and that the morphological changes were location-dependent. Fibrous ankylosis was observed histologically in three animals. The contralateral joints were not affected morphologically, except for bony resorption of the articular eminence noted microscopically in one animal. Radiographically, however, the joint appeared normal. Variable alterations in masticatory patterns were observed following unilateral meniscectomy. While there appeared to be an association between temporomandibular joint structure and masticatory function, radiographic and microscopic observation of morphological alterations in the joint did not result in predictable functional limitations in chewing pattern.     

Understanding Temporomandibular Biomechanics

In all synovial joints normal function demands that sharp surface contact of the moving parts be maintained at all times. This is termed joint stability. Ordinary masticatory function imposes on the craniomandibular articulation a variety of mechanical forces which, if not counteracted, would separate the articulating parts and create a state of instability. An essential role of the articular discs is to maintain sharp contact of the joint surfaces during the full range of function—at rest as well as during empty-mouth movements, power strokes, and maximum intercuspation.

The mechanism by which stability is maintained in the temporomandibular joints is unique and complex. A full understanding of mandibular function (and dysfunction) depends largely on accurate knowledge of the biomechanics by which the articular discs maintain joint stability. Applying such information at a clinical level brings new meaning to symptoms that identify disc interferences. This knowledge improves diagnosis and makes therapy more effective.