Radiographic study of condylar position in centric relation and centric occlusion

The present study was conducted to compare the spatial relationship of the condyles to their fossae in the centric occlusion and centric relation positions. Right and left TMJ radiographs were obtained on 40 young adults in the two positions. Direct measurements of the anterior, posterior, and superior spaces between the condyles and their fossae were made on the radiographs. Results were statistically analyzed; the following findings and conclusions were derived: (1) In the centric relation position, both condyles were placed more posteriorly and superiorly in their fossae than in the centric occlusion position. (2) In the centric occlusion position, both condyles were symmetrically placed in their fossae with equal spatial distances anteriorly and posteriorly. (3) Greater spatial differences existed between the centric occlusion and centric relation positions on the left side, which was the orbiting (balancing) side in most subjects. (4) Further studies are needed to develop a more physiologic approach for correctly relating the mandible to the maxillae when reconstructing the occlusion in both dentulous and edentulous patients.     

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.     

Locating centric relation with a leaf gauge

A device called a leaf gauge consists of a number of leaves of plastic and can be used to locate the mandible in centric relation.The leaf gauge, when placed between the anterior teeth, aids the patient in retruding the mandible. The biting force tends to move the condyles against their menisci. Since the patient is applying all pressures, the position of the mandible is not likely to exceed physiologic limits.     

Occlusion and orthodontics.

The importance of considering the functional aspects as well as the static concepts of an occlusion was demonstrated in the case of an 11-year-old girl with postorthodontic temporomandibular joint muscle pain dysfunction. The following characteristics of an ideal occlusion were discussed as they relate to the entire masticatory system: 1. There should be no slide in centric; that is, there should be a stable jaw relationship when occlusal contact is made in centric relation closure. 2. There should be freedom in centric, that is, freedom for the mandible to move from centric relation to centric occlusion and slightly anterior to centric occlusion without interference. 3. Centric relation should be at the same contact vertical dimension as centric occlusion. 4. There should be no buccolingual thrust or impact to any tooth on closure to contact in centric relation or to centric occlusion. 5. Between centric relation and centric occlusion there should be an unrestricted glide with maintained occlusal contact. 6. Complete freedom for smooth-gliding occlusal contact movements in various excursions from both centric occlusion and centric relation. 7. Occlusal guidance should be on the working or functioning side rather than on the balancing or nonfunctioning side. 8. There should be no soft-tissue impingment from occlusal contacts. In effect, the occlusion should be related to centric relation and centric occlusion prior to, during, and at the completion of active treatment. The final occlusion should provide unhindered closure in centric relation, smooth-sliding lateral and protrusive movements, and an optimal bilateral vertical contact dimension. Orthodontic treatment must include proper occlusal adjustment procedures to obtain the goals of an ideal occlusion in most instances.     

Accuracy of perioperative mandibular positions in orthognathic surgery

Mandibular position is an important parameter used for the diagnosis of dentofacial deformities, as well as for orthognathic surgery planning and execution. Centric relation (anterior and superior relationship of the mandibular condyles interposed by the thinnest portion of their disks against the articular eminencies), centric occlusion (when lower teeth contact upper teeth at centric relation), and maximal intercuspation (complete interdigitation of lower and upper teeth) are not often addressed as factors that influence the results of orthognathic surgery, although these relationships are critical to ensure accuracy during the surgery. The present study assessed occlusal measurements taken before and after the induction of general anaesthesia from consecutive orthognathic surgery subjects. The variables assessed included the differences between these occlusal measurements, patient age, gender, type of deformity, and type of proposed orthognathic surgical procedure. The results demonstrated statistically significant differences for mandibular retrusion from maximal intercuspation to centric occlusion position, whereas the mandible appeared not to change significantly from centric occlusion after the induction of general anaesthesia. Patient age and the type of deformity appeared to influence the results. While in most instances centric occlusion can be adequately reproduced under general anaesthesia, for some specific orthognathic cases more accurate results might be obtained if the mandible-first sequence is used.     

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.     

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.     

Radiographic comparisons of condyle-fossa relationships during maxillomandibular registrations made by different methods

The condyle-fossa relationships were compared when maxillomandibular registrations were made in centric relation, with the teeth intercuspated and by muscular stimulation methods. The relationships of the condyles to the glenoid fossae established by each method were determined radiographically and compared on composite tracings. Analysis of the tracings indicated that the condyles were in a central position in the glenoid fossae in 21 of the 30 tracings. Both the intercuspation and centric relation methods caused the condyles to be centered in the fossae in eight of ten subjects. The muscular stimulation method caused the condyles to be centered in the fossae in five subjects and positioned anteriorly in the fossae in five subjects.     

Three-dimensional finite element analysis of the mandible and temporomandibular joint on simulated occlusal forces before and after vertical ramus elongation by distraction osteogenesis

Distraction osteogenesis has recently become a mainstay for treatment of mandibular hypoplasia. Thorough knowledge about changes in the temporomandibular joint (TMJ) and the surrounding parts of the mandible and the skull after mandibular distraction is still lacking. The purpose of the current study was to investigate the stress distribution in the mandible and the TMJ before and after skeletal correction by intraoral unilateral vertical mandibular ramus distraction, using a finite element (FE) model. The FE models were based on computed tomography scans and magnetic resonance imaging scans of a patient with unilateral hypoplasia of the right mandibular ramus caused by juvenile idiopathic arthritis. The character of stress distribution in the mandible and TMJ before and after skeletal correction by 15 mm of vertical distraction of the mandibular ramus was analyzed quantitatively and compared during centric occlusion. Before the distraction osteogenesis treatment, the condyles, articular discs, and glenoid fossa regions are loaded with a different stress pattern. The affected right condyle, disc, and fossa are loaded diffusely and externally in comparison with the anterior and with centralized loading on the normal left side. After unilateral mandibular distraction osteogenesis, the load became more centric and symmetrical. The results suggest that correction of the mandibular deformity by distraction osteogenesis tends to normalize the stress patterns in the TMJ.     

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.     

The role of the general practitioner in restoring patients with temporomandibular joint dysfunction

Treatment of temporomandibular joint pain, resulting from occlusal dysfunction, is divided into two phases. First, occlusal splint therapy is used to eliminate the initial signs and symptoms and to achieve stability in centric relation. In the second phase of treatment the occlusion is adjusted and, if indicated, restored by means of crown and bridge procedures. Casts, properly mounted in a semi-adjustable articulator, with the lower cast mounted in centric relation, can be extremely helpful for an occlusal analysis and a diagnostic occlusal adjustment in the articulator. Each occlusal adjustment procedure in the mouth should be preceded by an initial study, occlusal analysis and occlusal adjustment on articulator mounted casts. The two main criteria for restoring the occlusion are: maximum intercuspation occurring in centric relation and disocclusion of the posterior teeth during excursive movements by means of anterior guidance. Patients with a history of temporomandibular joint pain and dysfunction usually have a limited adaptive capacity of even the smallest occlusal imperfection. In order to cope with the occlusal restoration of patients with such a low level of occlusal tolerance the final crowns and bridges should be cemented temporarily for a period of at least 3 months. A matt gold surface will be very helpful to locate undesirable occlusal contacts during temporary cementation.     

Comparison of the replicability of routinely used centric relation registration techniques

PURPOSE: This study was conducted to determine statistically the most repeatable mandibular position of 3 centric relation methods. MATERIALS AND METHODS: Three centric relation recording methods commonly reported in the literature were selected: bimanual mandibular manipulation with a jig, chin point guidance with a jig, and Gothic arch tracing. Fourteen healthy adult volunteers (7 males and 7 females), with an average age of 26.61 +/- 4.20 years and no history of extractions, temporomandibular joint dysfunction, or orthodontic treatment, were selected for the study. Accurate casts were mounted on an articulator (Denar D4A) by means of a facebow and maximum intercuspation silicone registration record. A mechanical 3-dimensional mandibular position indicator was constructed and mounted on the articulator enabling the operator to analyze the mandibular positions in 3 spatial axes (x, anteroposterior; y, superoinferior; z, mediolateral shift). Each centric relation method was recorded four times on each subject (at baseline, 1 hour, 1 day, and 1 week at approximately the same time of day). Records were transferred to the articulator, and data were extracted using a stereomicroscope modified to accept the mandibular position indicator. RESULTS: Variability within subjects ranged from 0.03 mm (left-side z axis for the bimanual method) to 1.6 mm (left-side y axis for the Gothic arch method). To indicate the least variable (most repeatable) method a comparison was made using the F test. The bimanual method was the most consistent, showing between 10.11 (p = 1) and 0.438 (p = 0.005) times less variation than the Gothic arch method (the least consistent). The repeatability of the chin point guidance method was somewhere between the other 2 methods. CONCLUSIONS: The results of this study showed that of the 3 centric relation methods evaluated, the bimanual manipulation method positioned the condyles in the temporomandibular joint with a more consistent repeatability than the other 2 methods, whereas the Gothic arch was the least consistent method.     

Electrognathographic and electromyographic observations on jaw depression during neck extension

Albeit never substantiated through experimental and clinical evidence, the theoretical linchpin of the mechanics of a so-called whiplash injury of the temporomandibular joint (TMJ) is the postulate that a pre-existing depressor force (continual anchoring force), generated by the anterior suprahyoid (SH) muscles, will always act on the mandible and cause traumatic mouth opening (anterior acceleration of the TMJ condyles) when the neck is extended (posterior acceleration of the head). To test aspects of this postulate, six subjects assumed the positions of neutral (0 degrees ), medium (32 degrees ) and maximum (58 degrees ) neck extension while the mandible was in its postural positions of rest and light centric occlusion. By means of surface electromyography, it was shown that the relative contractile activities of the anterior SH muscles never exceeded 7.3% of the contractile activity required to anchor the mandible in a position of maximum depression. By means of electrognathography, it was shown that the maxillary and mandibular incisors were never separated by more than 2.6 mm during neutral, medium, and maximum extension of the neck. In other words, during neck extensions there was no evidence of a continual or induced voluntary or involuntary depressor force that would and could anchor the mandible in a position of traumatic mouth opening. Accordingly, and in agreement with other biophysical and biomedical evidence, it was concluded that there is no foundation for the pseudoscientific speculations and unsubstantiated opinions offered in support of a concept and diagnosis of a so-called TMJ whiplash injury. Additionally, this study found co-activation of cervical flexor muscles and mandibular elevator as well as depressor muscles.     

Replicability of chinpoint-guidance and anterior programmer for recording centric relation.

The chinpoint-guidance technique, using an anterior programmer, as performed in this study, seems to be a replicable method of locating centric relation. Sequential registration of centric relation was repeatable in 60% of the patients studied. The average variability found in 40% of the patients of this study was about +/- 0.20 mm at the level of the condyles.     

"Myo-Monitor centric": an evaluation

Ten patients had three “Myo-Monitor centric” records made at each of three appointments. Terminal hinge axis determination and interocclusal registration of centric relation were used to accurately mount maxillary and mandibular casts on a modified articulator. The characteristics of “Myo-Monitor centric” were investigated by: evaluation of the reproducibility of “Myo-Monitor centric” records; comparison of “Myo-Monitor centric” position to centric relation contact position and centric occlusion; comparison of the tooth contact on hinge closure from “Myo-Monitor centric” with centric relation contact; evaluation of the effect of the anteroposterior head position on the number and location of tooth contacts during “Myo-Monitor centric” mandibular closure; and a comparison of the anteroposterior relationships among “Myo-Monitor centric,” centric relation, and centric occlusion.Examination and appropriate statistical analysis of the data revealed several characteristics of “Myo-Monitor centric”: The axis of rotation determined by “Myo-Monitor centric” was always anterior and inferior to the patient's terminal hinge axis; “Myo-Monitor centric” registrations within individuals were non-reproducible; with “Myo-Monitor centric” registrations, centric relation contacts on the mandible were anterior to both centric relation and centric occlusion contacts on the maxillae; variation of anteroposterior head position affected Myo-Monitor-produced mandibular closure; and eight of ten patients had “Myo-Monitor centric” contact anterior to their centric relation contact.     

A Tomographic Study of the Condyle/Fossa Relationship in Patients with TMJ Dysfunction

The authors undertook a tomographic study to evaluate the positional relationship of the bony components of the temporomandibular articulation. The sample group consisted of 35 patients with symptoms involving the temporomandibular joint. These were compared to a control group of 19 asymptomatic subjects who had “normal” occlusions. The condylar positions of the symptomatic and the asymptomatic TMJs of the sample group were compared with each other and with those of the control group.

Each of the subjects gave a complete dental history and underwent thorough intra- and extraoral examination. The authors used a submental vertex radiograph to determine the center of each condyle and the horizontal condylar angulation for each subject. The two values obtained from this were used to take a selective tomogram, in centric relation, of the condyles of all the subjects. An anterior prosthesis was used to obtain centric relation in each case.

The tomograms obtained from these subjects were enlarged ten times. Tracings and measurements were made of the enlarged images, and the measurements obtained were reduced by a factor of ten for recording. The authors then evaluated the position of the condyle within the glenoid fossa by comparing joint space measurements and by using a proportional analysis.     

A computer analysis of condylar movement as determined by cuspal guidances

In 1926 Hanau proposed a link between incisal, condylar, and occlusal guidances of the stomatognatic system. This work has been extended by undertaking a computer simulation of the movement of the mandible between centric occlusion and centric relation in an effort to establish a possible mathematical relationship between the variables in Hanau's "Quint." One scheme is proposed by which the geometry of the guidances might be analyzed. The results of the analysis show that there could be a direct link between an altered occlusal guidance and one of the factors involved in the initiation of the temporomandibular joint dysfunction syndrome.     

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.     

Comparison of Myo-Monitor centric position to centric relation and centric occlusion.

Twenty dentulous subjects were selected at random. A Hight tracer, fixed on the labial surface of the teeth by special clutches, was used to indicate a record of centric relation and centric occlusion. The Myo-Monitor centric position was recorded and compared to centric occlusion and centric relation in anteroposterior and lateral dimensions. This study indicated that: 1. Myo-Monitor centric position is always anterior to centric relation, with an average of 3.8 min. 2. Myo-Monitor centric position is always anterior to centric occlusion, with an average of 1.8 mm. 3. In 18 of 20 subjects, the Myo-Monitor registration was to the right or to the left side of the line between centric relation and centric occlusion. 4. In all subjects, centric occlusion was an average of 2.2 mm. anterior to centric relation.     

Comparing condylar positions achieved through bimanual manipulation to condylar positions achieved through masticatory muscle contraction against an anterior deprogrammer: a pilot study

STATEMENT OF PROBLEM: The condylar position can vary depending on several factors. One factor is the influence of occluding teeth. If the influence from occluding teeth could be eliminated, it might be possible to evaluate the condylar position obtained from masticatory muscle contraction. PURPOSE: The purpose of this pilot study was to determine the placement of the condyles by contracted masticatory muscles without influence from occluding teeth. MATERIAL AND METHODS: For a group of 11 participants, 3 dentists were assigned, in turn, to fabricate a centric relation interocclusal record using bimanual manipulation on each member of the group. After obtaining the centric relation interocclusal records using bimanual manipulation, the records were stored in room temperature water. Subsequently, each of the 11 patients had an anterior deprogrammer fabricated and were given instructions to wear the anterior deprogrammer for 60 minutes. The anterior deprogrammer was designed with the contacting surface perpendicular to the arc of close of the mandibular incisors. In addition, the anterior deprogrammer was relined to eliminate any movement under force, and the occluding surface of the deprogrammer was free of any indentations. After wearing the deprogrammer, 4 interocclusal records (3 in a reclined position and 1 in an upright position to ensure the condylar position did not change in the upright position) were made by having the patient squeeze and close into a properly adapted, trimmed, and warmed interocclusal record. The condylar position in centric relation recorded in interocclusal records using bimanual manipulation was compared to the condylar position recorded by the contraction of the masticatory muscles against an anterior deprogrammer using a condylar position indicating device. The data were analyzed with a 2-independent-samples test of proportions, alpha=.05 (1-tail). RESULTS: The condylar positions obtained using bimanual manipulation repeated the condylar position within the 0.11-mm tolerance of the Centri-Check instrument in 33 out of 33 opportunities (100%). The condylar positions obtained by using the anterior deprogrammer technique repeated the condylar position within the 0.11-mm tolerance of the Centri-Check in 43/44 opportunities (97.7%). The sample size used in this pilot study was not large enough to detect a very small actual difference (5 percentage points or less) between the 2 methods, should such a difference exist. CONCLUSION: The results of this pilot study indicate that, without influence from occluding teeth, the contraction of the masticatory muscles places the condyles into the same position as centric relation.