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.     

Anterior condylar displacement: Its diagnosis and treatment

A deflective slide in centric relation to centric occlusion does not necessarily mean anterior condylar displacement. Its diagnosis and treatment depend on the correlation of three factors: the direction and magnitude of the mandibular slide from centric relation to centric occlusion, the change in vertical dimension of occlusion during the slide, and the position of the condyles in the fossae when the teeth are in the maximum occlusion (centric occlusion).When the change in vertical dimension almost equals the amount of slide from the deflective contact in centric relation to maximum intercuspation, very little anterior condylar displacement would be expected. Conversely, with proportionately little change in vertical dimension, more anterior condylar translation is required for a given degree of anterior slide. Examples of each type of anterior slide were related to the TMJ radiographs of the condylar position. If the direction and magnitude of the deflective occlusal contact can be correlated with the TMJ radiographs, the centric relation is “functional,” and the clinically retruded mandibular position should be used. When this correlation does not exist, the centric relation is “dysfunctional,” and the terminal hinge position (retruded mandibular position) shouldnot be used for restorative or corrective procedures. Examples of anterior condylar displacement were given, including lateral deviation, with a comparison of “before” and “after” TMJ radiographs.     

An evaluation of occlusal factors in TMJ dysfunction-pain syndrome.

TMJ dysfunction-pain has four main sources: intrajoint, muscle spasm, joint/muscle, and referred. Electromyographic evidence has been cited to show that there is a direct cause-and-effect relationship between occlusal deflective contacts and muscle spasm. In some patients emotional stress can be the primary etiologic agent in TMJ dysfunction-pain syndrome, but it works indirectly through the tension-relieving mechanism of bruxism. The controversy over the relative importance of stress and occlusion as a primary etiologic agent remains active. It has been suggested that the reason this conflict has remained unresolved is because the criteria for “malocclusion” is indefinite.The clinical assumption that “when the mandible is in the most retruded position of centric relation, both condyles are in correct alignment in the glenoid fossa” has been challenged. The centric relation of each patient should be individually evaluated by comparing the clinical occlusal findings with the TMJ radiographs. Sometimes the clinical centric relation is not healthy (dysfunctional) and the suspension mechanism of the TMJ is faulty. Condylar displacements are caused by a lack of harmony between the occlusion and the resulting orientation of the mandible. The absence of posterior tooth support can also lead to posterior or superior condylar displacement. The evaluation of occlusal factors in TMJ dysfunction-pain syndrome should not be a mere tabulation of the “hit and slide” but should contain an evaluation of the relative health of the suspension mechanism of centric relation itself.Recent research into the functional parameters of the condylar suspension mechanism indicates that muscles rather than ligaments determine posterior and inferior condylar position. Superior condylar position is influenced by the posterior teeth and meniscus. These observations and experiments have produced a “biophysical” concept of the condylar suspension mechanism. The teeth, muscles, and disc support and guide the condyle in its suspension within the fossa.In adults, alterations in mandibular position will not produce a “corrective remodeling” of the TMJ, and pathologic changes can take place. The TMJ will attempt to physiologically accept condylar displacement; however, in most people, joint and/or muscle dysfunction develops. The level of dysfunction in many patients remains subclinical.The objective of treatment is to correct the occlusion so that the displaced condyles can be repositioned in the middle of the fossa evenly (symmetrically) on both sides. The therapeutic procedure is different in each patient, depending on the type of condylar displacement involved so that a balanced biophysical relationship is established between the teeth, muscles, and TMJ.     

Practical evaluation of the lateral temporomandibular joint radiograph

The reevaluation of the lateral transcranial radiograph is needed because of the confusion that surrounds the diagnosis and treatment of TMJ dysfunction-pain. The lack of universal acceptance of the validity of the lateral TMJ radiograph contributes to the lack of progress of TMJ dysfunction-pain treatment and improved methods for the treatment of prosthodontic patients. The lateral transcranial TMJ radiograph was reevaluated for its duplicability (+/- 0.2 mm). The image was found to be a cross section of the lateral third of the condyle rather than a composite view of the condyle made at an angle. The condylar position in the fossa can be correctly evaluated in transcranial radiographs, because the relative condylar position in the fossa is similar in all sagittal views and the image is always of the same sagittal plane (lateral third). Soft tissue within or lining the fossa does not affect the evaluation of condylar position. Chronic osteoarthritic TMJ pathology can exist without subjective pain; therefore, routine use of initial TMJ radiographs with subsequent radiographs at 5-year intervals is suggested for all patients. Because condylar repositioning may be indicated before subjective pain symptoms appear, condylar repositioning should be contemplated whenever extensive prosthodontic treatment is needed. In addition, if chronic osteoarthritic lesions are observed initially, radiographs are indicated at more frequent intervals and anti-inflammatory agents should be considered for routine use depending on the rate and extent of the pathologic development. The existence of osteoarthritic lesions was confirmed by serial radiographs over 5 to 10 years. If an osteoarthritis is present, condylar repositioning (when condylar displacement is present) or changes in occlusion should be considered. There is some clinical evidence that condylar displacement is associated with pathologic remodeling and/or osteoarthritic lesions of the condyle and that condyle repositioning arrests the pathologic process. The principle of condylar concentricity , previously established for the treatment of TMJ dysfunction-pain syndrome and for functional centric relation in prosthodontics, was formulated by associating condylar position in the fossa with TMJ dysfunction-pain in many patients. This article suggests the value of the lateral TMJ radiograph as an important practical aid in the diagnosis and treatment of TMJ dysfunction pain and in the establishment of functional centric relation in prosthodontics.     

The role of stress,occlusion, and condyle position in TMJ dysfunction-pain

Lateral transcranial TMJ radiographs are duplicable within ±0.2 mm and are cross-sectional views of the lateral third of the condyle and fossa. The innate asymmetry of humans, when the right and left sides of the fossa and condyle are compared, was clinically insignificant. Tomograms are not indicated because they lack appropriate resolution and detail to evaluate qualitative bone changes; and because they are not an in-office procedure, the condylar position in the fossa is completely unreliable.A correlation was reported between condylar position in the fossa and TMJ dysfunction in over 320 patients. This observation suggests that a new definition of centric relation is indicated, a definition that differentiates whether it is functional or dysfunctional. The criterion is the correlation between the occlusal findings and the condylar position in the fossa as recorded by the lateral TMJ radiographs (when the teeth are in maximum occlusion).Stress response was found to be greater in males than in females (in all vertebrates, including humans); therefore stress cannot be a direct cause of craniomandibular pain since more women have the disorder. It was concluded that stress is an indirect contributing factor that usually works through the medium of clenching. The role of the neuromuscular mechanism in craniomandibular pain was discussed. Proprioception reflex activity forms the basis for muscle length, mandibular positional sense, as well as masticatory function. Occlusal disharmonies increase noxious input to the neuromuscular system, as well as stress-induced clenching, causing increased muscle activity and spasm-pain.Condylar displacement also contributes to TMJ dysfunction-pain, depending on its direction. Anterior condylar displacement can initially affect the muscles by inducing overfunctional response in the proprioceptive system. Posterior condylar displacement usually results in an intrajoint response consisting of a disk derangement, reciprocal clicking, possible anterior disk dislocation, possible pathologic swallowing pattern, and noxious stimulation to the proprioceptive system. These factors contribute to subsequent trismus, muscle spasm and pain, and long-term pathologic remodeling of the joint. A detailed history is necessary to evaluate the role of stress. The physical occlusal findings are correlated with the condylar displacement observed in the TMJ radiographs to diagnose and plan corrective treatment.     

Posterior unilateral condylar displacement: its diagnosis and treatment.

The treatment procedure for posterior unilateral condylar displacement has been described. An acrylic resin repositioning prosthesis may be used to decrease trismus. Occlusal adjustment permits lateral freedom for mandibular movement to the opposite side which provides a dual, or a therapeutic, centric occlusion as well as the existing dysfunctional centric relation. This permits the patient's physiologic adaptive mechanism to choose between the existing dysfunctional centric relation, which resulted in unilateral condylar retrusion and pain, or a therapeutic centric occlusion which is aimed at anterior unilateral condylar repositioning. Over long period of time, muscle reprogramming produces maximum intercuspation of teeth in the planned therapeutic centric occlusion rather than in the original dysfunctional position. No explanation has been established for this phenomenon. It is important, however, to provide a technique that permits physiologic adaptability over a period of time. It should be emphasized that this is not TMJ "remodeling" but a functional change in the position of the jaw. The treatment objectives of bilateral and unilateral posterior condylar displacement are similar, but the clinical techniques are completely different. In either instance, TMJ radiographs are necessary to establish the diagnosis and treatment, as well as to document the postoperative results.     

Treatment prostheses in TMJ dysfunction-pain syndrome

Various types of acrylic resin therapeutic prostheses commonly used in the treatment of TMJ dysfunction-pain syndrome were described. Each design was related to recent data concerning optimum condylar positions in the fossae, the physiologic condylar suspension system, and individual treatment objectives for repositioning the mandibular condyles. For example, alteration of the vertical dimension of occlusion is a popular treatment procedure that is empirical in nature and is usually used without TMJ radiographs or a differential diagnosis. It can violate the physiologic requirements of the interocclusal distance or the speaking space and does not necessarily move the condyles forward as has been commonly thought. The dangers of empirical treatment procedures for a multicausal dysfunction syndrome have been pointed out. An example was cited where the mandible was moved forward for a long period of time with a repositioning prosthesis; this produced pathologic TMJ remodeling and continued pain. It was recommended that specific mandibular repositioning be based on the type of condylar displacement observed on the radiographs. Sometimes the condyles should be retruded, and other times they should be repositioned anteriorly or occasionally inferiorly on one side. Long-standing use of any acrylic resin repositioning prosthesis is contraindicated, particularly without close supervision. Acrylic resin anterior bite plates (with a minimum opening of 1 mm) were recommended for the relief of acute trismus or intractable pain. Usually the prosthesis is used in conjunction with heat and drug therapy. This type of prothesis can also be utilized to deprogram the muscles when a strong habit of eccentric occlusion develops as a result of missing teeth. (This should be confirmed by TMJ radiographs.) Occasionally atypical pain is present and a differential diagnosis can be established between TMJ dysfunction or neurologic etiology by the physiologic response to bite plate therapy. When it is necessary to reposition the mandibular condyles anteriorly the occlusion is adjusted to provide the planned anterior movement without increasing the vertical dimension of occlusion. A temporary acrylic resin prosthesis is used to retrain the muscle programming to the anterior therapeutic mandibular position. When the symptoms are relieved and the corrective condylar position is confirmed with TMJ radiographs, a more permanent repositioning prosthesis is made. The treatment of TMJ dysfunction-pain syndrome should be based on documented data including the pain history, TMJ radiographs, condylar position in the fossae, electromyographic evidence, and occlusal analysis. This information will help determine if the patient's centric relation is functional or dysfunctional and will indicate the recommended treatment procedures.     

Posterior bilateral condylar displacement: its diagnosis and treatment.

One type of condylar displacement (posterior bilateral) was discussed as an etiologic factor in TMJ dysfunction. Joint noise, tenderness on muscle palpation, and acute TMJ pain are all considered signs of TMJ dysfunction. Any joint noise is considered to be an early dysfunctional symptom because of its higher incidence in association with palpable muscle pain or acute TMJ dysfunction. Sometimes the joint noise will immediately precede acute muscle pain and/or fluctuate with the painful symptoms. The treatment of bilateral posterior condyle displacement has been described. The mandibular anterior teeth were shortened and the maxillary posterior occlusion adjusted so that the mandible could be respositioned in an anterior position without increasing the vertical dimension of occlusion. A silver-plated maxillary cast was obtained and mounted on a semiadjustable articulator (Hanau) with a face-bow. The mandibular cast was mounted in the dysfunctional (retruded) centric relation. The articulator was moved into a protrusive position by the amount of anterior correction that is needed to reposition the condyles into the middle of the fossae symmetrically on both sides. The original TMJ radiographs provide the necessary information for this clinical judgment. Acrylic resin was placed in the space created between the condylar sphere and stop on the articulator. An acrylic resin temporary repositioning prosthesis constructed on the metal cast has two functions. It provides a therapeutic trial for the anterior condylar respositioning, and it holds the mandible in the therapeutic position while TMJ radiographs confirm the corrective position of the condyles in the fossae. After a successful 6 to 8 week trial period with remission of symptoms, a gold prosthesis was constructed on the same cast in the same therapeutic position. It remains to be seen whether, after several years, the condylar suspension system changes from a dysfunctional centric relation to a new functional centric relation in which the patient can no longer return to the posterior displaced condylar position in the fossa. Only with painstaking observations, accurate TMJ radiographs, complete documentation, and after-care can a more scientific approach to the diagnosis and treatment of TMJ dysfunctional pain syndrome be achieved.     

Optimum temporomandibular joint (TMJ) condylar position

Controversy exists over the value of the TMJ condylar position in the fossa. Many clinicians associate the concentric position to the normal individuals and the retruded position to the dysfunctional condition. It is also recommended that therapeutically, the condyle should be placed on the posterior slope of the articulating eminence. Different groups of investigators claim that the condylar position, centric, retruded or protruded has little or no value and is not correlated with dysfunctional situations. This controversy is attributed to the inconsistency of research methodology. Using a large number of subjects, defining age and sex, careful selection of subject, using tomographic analysis with similar section locations and excluding individuals with disturbed occlusal condition are recommended for a research of this type. The conclusion is that the condylar position is an end product of many dynamic changes such as growth and remodeling, functional matrix activities, occlusal alteration, functional adaptation and individual variation. It is suggested that diagnosis and treatment of TMJ disorders should not be based solely on the radiographic position of the condyle. Consideration of general body conditions is an essential part of total patient management. TM joint condylar position has been explained as the position of the mandibular condyles in the glenoid fossa when teeth are in maximum intercuspation. Clinicians have based their diagnosis and treatment of temporomandibular joint disorder on this position. The optimal condylar position has been a controversial matter in dentistry for many years. The purpose of this paper is to review the literature pertaining to condylar position and to discuss its significance in clinical practice.     

Role of condylar position in TMJ dysfunction-pain syndrome

TMJ dysfunction-pain syndrome is multicausal, and each patient has an individual “TMJ dysfunction profile.” Stress has been shown to be a correlated factor as well as occlusion. Strong stress etiology and a placebo effect have been reported in MPD. It was emphasized, however, that MPD does not involve pain or pathology of the TMJ itself, by definition, and that research (for MPD) is not valid for TMJ dysfunction-pain syndrome which does involve the joint itself, by definition.Condylar position in the fossae of 116 patients was reported, 55 acute TMJ dysfunction-pain and 61 general practice controls. The main findings were that the incidence of condylar retrusion in the acute TMJ patients was 70.9% and condylar concentricity (in the middle of the fossae) was only 3.6%. In the general practice control group, the incidence of condylar retrusion was 36% and condylar concentricity 23%. The incidence of condylar retrusion in the acute TMJ group was twice that in the control

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group. Conversely, the incidence of condylar concentricity in the general practice control group was 6.4 times the occurrence in the acute TMJ group.It can be concluded that condylar position in the fossae is a significant factor in TMJ dysfunction-pain syndrome. Furthermore, condylar retrusion occurs much more frequently (71%) than other types of displacement in acute TMJ dysfunction-pain. Condylar retrusion also occurs with enough frequency in the general practice control (36%) to indicate that the “classical” retruded mandibular position of centric relation does not necessarily orient the condyles correctly in the fossae, as is commonly thought. The fact that condylar concentricity (middle of the fossae) was 6.4 times more prevalent in the general practice control group, together with previously reported evidence, confirms (that it is the optimum position in the glenoid fossae. Since the condylar position in the fossae is significant, and even in asymptomatic patients one third can be retruded, TMJ radiography and occlusal evaluation are indicated in almost all patients.     

A technique for evaluation of centric relation tooth contacts. Part II: Following use of an occlusal splint for treatment of temporomandibular joint dysfunction

The purpose of this study was to determine the effect of TMJ dysfunction on the recording of centric relation. Centric relation was recorded using an anterior occlusal stop and by bimanual manipulation. Changes in occlusal contacts were recorded before and after occlusal splint therapy in six subjects with TMJ dysfunction. The pantographic reproducibility index and clinical signs and symptoms were used to determine the presence or absence of dysfunction. Use of the anterior occlusal stop resulted in a more posterior, superior initial tooth contact position when compared with bimanual manipulation. Occlusal contact positions were less consistent in TMJ dysfunction subjects than in control subjects. Initial occlusal contacts changed toward centric relation as the dysfunction disappeared. Final occlusal contact was found on the side where clinical signs and symptoms occurred. The condyle on the affected side appeared to be repositioned posteriorly and superiorly in most instances. Occlusal splint therapy was more effective when the splint was adjusted weekly. This study indicates the need to eliminate TMJ dysfunction before recording centric relation or adjusting the occlusion. Occlusal interferences found with TMJ dysfunction are not the same as occlusal interferences found when TMJ dysfunction is absent. Abnormal features on pantographic tracings may aid in indicating the presence of occlusal interferences. Occlusal adjustment in the presence of TMJ dysfunction would result in erroneous occlusal reduction.     

Condylar remodeling after occlusal therapy

Seven men and 15 women with TMJ pain dysfunction syndrome were selected. After clinical examination, polytomography of the TMJ was performed in centric occlusion in different planes. Open-mouth projections were also made in three patients, frontal tomography in one patient, and transcranial radiographs in 16 patients. Occlusal analysis was performed on the articulator. Twenty patients showed various patterns of condylar displacement with flattening of the anterior, superior, or posterior condylar walls in 11 patients, including three with arthritic lesions. Therapy included occlusal splints (21 patients), selective grinding (seven patients), prosthodontic rehabilitation (10 patients), and orthodontic treatment (two patients). After therapy, tomographic examination was repeated at intervals of 9 to 44 months. A distinct reshaping of the condyle was seen in seven patients. The new shape tended to be rounded. The three patients with degenerative changes before treatment showed regression of the lesions. No change was seen in condyles which were rounded before therapy.     

Superior condylar displacement: Its diagnosis and treatment

Superior condylar displacement was induced with the application of unilateral unsupported muscle force, ¹⁹ an example of which was shown in Figs. 1 to 4. This superior displacement occurs in functional as well as dysfunctional temporomandibular joints. It is the contention of this article that superior condylar displacement can also take place by iatrogenic or natural causes and that it should be diagnosed and subsequently treated by inferior condylar repositioning. This condition is only one of the three basic types of condylar displacement (superior, anterior, and posterior) that can contribute to TMJ dysfunction.The diagnosis of superior condylar displacement should be made only with both condyles in the middle of their respective fossae. When the opposite condyle is retruded, the casts are mounted on an adjustable instrument, and a stent is fabricated to reposition the retruded condyle to a more concentric position in its fossa. New left and right TMJ radiographs will allow a comparison of the joint spaces to be made with both condyles in the middle of their fossae. When the joint space of the symptomatic side is obviously narrower than that of the previously retruded side, then superior condylar displacement of the painful side is likely.The condylar mechanism of the articulator is moved to almost a vertical position and an appropriate shim placed between the condylar sphere and stop. A unilateral acrylic resin stent is fabricated and placed over the teeth. Inferior condylar repositioning of the affected side should be immediate, with contact of the anterior teeth almost complete. Anterior opening indicates a misdiagnosis, and the stent should be removed. The diagnosis is confirmed and documented with TMJ radiographic evidence of inferior condylar repositioning and reduction of the patient's symptoms. The procedure was tried on healthy temporomandibular joints, and inferior condylar repositioning was not induced. The final conclusions can be drawn that the condylar mechanism permits superior displacement with unsupported muscle force but does not allow inferior displacement of the condyle in a healthy joint with muscle force. Naturally occurring superior condylar displacement results in pain and is diagnosed by observing the reduced joint space when compared to the opposite asymptomatic side. This comparison should be made only when both condyles are in the middle of their fossae. The treatment is to fabricate a stent on an articulator which has been set for inferior condylar repositioning. After a therapeutic trial of eight weeks, the acrylic resin stent should be duplicated in a simple unilateral full-arch gold onlay. Extensive reconstruction should be delayed usually for one year for further observation of the patient.     

The influence of altered occlusal guidance on condylar displacement

This study investigated mandibular displacement and masticatory muscle activity during clenching in lateral occlusal position in relation to the lateral occlusal pattern. Twenty healthy human subjects (mean = 26.5 years) volunteered for this study. Metallic occlusal overlays were fabricated for the lower working side canine to second molar and non-working side second molar in order to simulate a canine protected occlusion, group function occlusion and bilateral balanced occlusion (balancing contact). Three-dimensional displacements of the bilateral condyle and electromyography (EMG) activities in the bilateral masseter, anterior and posterior temporalis were recorded during maximal clenching. The experimental occlusal pattern was revealed to have statistically significant effects on both condylar displacement and EMG activity (P < 0.001 and P < 0.001, respectively). When compared to the simulated group function occlusion, the simulated canine protected occlusion and balancing contact caused statistically significant smaller superior displacements of the non-working side condyle, which suggests that they may result in reduced temporomandibular joint (TMJ) loading. Furthermore, the simulated canine protected occlusion was associated with the lowest EMG activity, which suggests that this occlusal pattern has the capacity to reduce the level of parafunctional activity.     

Centric relation. Its effect on occluso-muscle harmony.

The most common cause of pain in the region of the temporomandibular joint is occluso-muscle imbalance. This results most often from disharmony between the articulation of the teeth and the centric relation of the condyles. Muscle tenderness of palpation indicates that muscle is involved. An examination must then be done to determine the cause of the muscle tenderness. Before the condyle-occlusion relationship can be evaluated, an accurate centric relation must be determined and verified. The condyles are in centric relation when they are in the most superior position possible in the fossae. From that apex of force position, the condyle can travel neither forward nor backward without moving downward. This position can be located with careful bilateral manipulation and then verified if it can resist firm pressure with no tension or tenderness. Until this correct centric relation is located and verified, it is not possible to properly evaluate the occlusal relationship to the temporomandibular joints. If the occlusion is harmonized to a centric related condyle that can resist firm pressure with pressure with no discomfort, there will be no reason for the muscles to protect either the teeth or the joints. If an occlusion is adjusted to a malrelated condylar position, the occluso-muscle imbalance will be perpetuated and often intensified. Centric relation is the starting point of occlusal contact. Incline interferences in excusive movements must also be eliminated and the occlusion must be harmonized to the envelope of function for each patient. If centric relation is not properly located, occlusal interferences will remain regardless of what procedures are used to record or adjust excursive movements.     

An electromyographic and roentgen cephalometric study of occlusal morphofunctional disharmony in children.

In a sample of children with dual bite and symptoms in the masticatory system, the activity of the anterior temporal and masseter muscles was studied electromyographically during clench and light tapping in the posterior occlusal contact position and centric occlusion and in protrusive bite on the incisors. The findings indicated that the optimal muscle function during maximal clench and tapping with displayed in the posterior occlusal contact position, which in the present subjects was situated, on the average, 0.5 to 1 mm. anterior to the centric jaw relation. It should therefore be recommended that, in orthodontic treatment of children with dual bite, the intercuspal position (centric occlusion) should be established in the posterior occlusal relationship. This is in accordance with the opinion of several authors who have emphasized the use of the retruded contact position (the centric jaw relation) as key reference position in orthodontic treatment and occlusal rehabilitation. These authors have further emphasized the importance of stable occlusal contacts in centric relation, centric occlusion, and the various jaw excursions in obtaining and maintaining a harmonious function between the dentition, the temporomandibular joints, and the neuromuscular system.     

口腔治疗中不同颌位与髁突位置

在口颌系统中,与颌位稳定相关的因素分别是、颞下颌关节和神经肌肉的稳定,其中髁突在关节窝中的位置与获得一个稳定的颌位密切相关。但口腔治疗中涉及到颌位的选择时,不同学者持不同的观点,对于髁突在关节窝中应处的位置也一直处于争议之中。本文对口腔修复和正畸治疗中颌位选择及“髁突前上位”、“髁突前下位”、“治疗性颌位”的适应证、理论基础及临床应用作一综述。文献复习结果提示,当关节无器质性改变或髁凹关系稳定时,髁突前上位即正中关系为传统建的理想颌位。当关节盘增生、变形、盘突关系紊乱无法寻找理想的髁突前上位时,可选择髁突前下位,缓解关节症状的同时促进骨质改建获得良好的稳定性;甚至对于部分安氏Ⅱ类高角或者轻度骨性错的病例,亦可以尝试利用髁突改建的潜力,前下定位髁突,通过掩饰性矫治简化正畸正颌手术方案;而“治疗性颌位”是针对颅下颌功能紊乱症导致的最大牙尖交错位异常或偏斜、肌肉症状和关节功能异常、颌位不稳定等,通过改变原有咬合或关节的异常引导,在有咬合支持和新的引导的基础上,建立并且稳定一个新的牙尖交错位。它摆脱了髁突定位的争论,但此颌位下髁突具体位置未见报道。不同颌位及髁突位置有不同的适用范围,临床选择时应根据患者关节是否有器质性改变及颌位的稳定性进行综合判断。但对于采用不同颌位和髁突位置进行口腔治疗的远期效果未来还需临床对照试验进一步验证。     

Post‐traumatic bifid condyle: the pathogenesis analysis

Abstract – This study investigated the characteristic of bifid condyle secondary to temporomandibular joint (TMJ) trauma, aiming to analyse the pathogenesis of post‐traumatic bifid condyle. Four cases identified as having bifid condyle secondary to TMJ trauma were involved in this study. The relative information extracted from the case records included patients’ complaint, history of injury and radiographic appearance, which were used to analyse the characteristic and pathogenesis of post‐traumatic bifid condyle. The results indicated that there was a correlation between condylar trauma degree and bifid condylar head appearance after trauma. For severe condylar fracture, it might result in Y‐shaped condyle associated with TMJ ankylosis; and condylar groove could be associated with the slight trauma in condyle articulating surface. In conclusion, as a specific entity, post‐traumatic bifid condyle may develop in cases with insufficient remodelling capacity after condyle trauma, and it seems that the severity degree of trauma, the site of trauma and its relation to the insertion of the lateral pterygoid muscles are factors associated with the appearance and orientation of bifid condyle.     

Definitive prosthodontic therapy for TMJ patients. Part I: Anterior and posterior condylar displacement

The final prosthodontic treatment procedure for anterior condylar displacement (functional centric relation) has been described. Deflective interferences in centric relation were removed and a removable partial denture constructed to the classical most retruded centric relation position of the mandible. Several patients with posterior condylar displacement (dysfunctional centric relation) have been documented. Anterior condylar repositioning was accomplished on a denture patient by merely establishing the correct vertical dimension of occlusion. Another patient required an increase in vertical dimension as well as anterior condylar repositioning.     

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.