Centric Position Research Articles

Relationship of condylar position to disc position and morphology

Introduction/objective: The purpose of this study was to assess whether condylar position, as depicted by magnetic resonance imaging, was an indicator of disc morphology and position. Methods and material: One hundred and twenty two TMJs of 61 patients with temporomandibular joint disorder were examined. Condylar position, disc deformity and degree of anterior disc displacement were evaluated by using magnetic resonance imaging. Results and discussion: Posterior condyle position was found to be the main feature of temporomandibular joints with slight and moderate anterior disc displacement. No statistical significance was found between the condylar position, and reducing and nonreducing disc positions. On the other hand, superior disc position was found to be statistically significant for centric condylar position. Conclusion: It was concluded that posterior condyle position could indicate anterior disc displacement whereas there was no relation between the position of condyle and the disc deformity.

Commentary

Commentary

Morphological and positional asymmetries of young children with functional unilateral posterior crossbite.

This prospective clinical study evaluated the morphological and positional mandibular asymmetry of young patients with functional unilateral posterior crossbite. The sample included 9 girls and 6 boys (8.8 +/- 1.0 years of age), evaluated at the initiation of treatment and approximately 6 months after the retention phase (1.1 +/- 0.2 years after initiation of treatment). Each patient had a complete unilateral posterior crossbite involving 3 or more posterior teeth, a functional shift from centric relation-intercuspal position, and no signs or symptoms of temporomandibular disorder. A bonded palatal expansion appliance was used to rapidly expand the maxilla (1 month) and retain the treatment changes (6 months). Zonograms were used to assess articular joint spaces, and submental vertex radiographs were used to assess morphological and positional asymmetry. The results showed that the mandible was significantly longer on the noncrossbite side than it was on the crossbite side. The asymmetry was most evident for the ramus and involved both the condylar and the coronoid processes. The posterior and superior joint spaces were larger on the noncrossbite side than they were on the crossbite side. After treatment and retention, the mandible showed no significant morphological asymmetries. Mandibular growth was greater on the crossbite side than it was on the noncrossbite side, and the mandible had been repositioned; the crossbite side had rotated forward and medially toward the noncrossbite side. We concluded that unilateral posterior crossbites produce morphological and positional asymmetries of the mandible in young children, and that these asymmetries can be largely eliminated with early expansion therapy.

表情筋が下顎位に及ぼす影響

It is generally known that the centric position was used to take bite registration and adjust occlusion. However, mandibular position is influenced not only by opening muscles and elevating muscles, but also by the muscles of facial expression. The purpose of this study was to examine the influence of the muscles of facial expression on centric position. The subjects were 3 normal adults using the Gnathohexagraph measuring system. They were required to track their angles of the mouth posteriorly from the centric position. The deviations of the condyler position were recorded. The results showed that the level of tension of the muscles of facial expression were responsible for posterior/upwards deviations of the mandibular position.

Overview of articulation materials and methods for the prosthodontic patient

Statement of problem. Many methods and materials are available for registering the centric relation position, with various degrees of accuracy. Once the centric relation position is recorded, many instruments are available for cast articulation. These articulators range from simple to complex devices that generate different mandibular movements depending on the sophistication of the instrument.Purpose. This review evaluated the methods and materials used to record the centric relation position and eccentric maxillomandibular relations, and to compare the articulators available for mounting casts.Methods.A MEDLINE search was completed (from 1966-present) along with personal searches of selected journals to find additional publications that addressed these materials, methods of registration, and available instrumentation.Conclusion. Potential applications of this review are as follows: (1) to allow the reader to examine the various methods for recording the centric relation position that have been studied and described, and (2) to observe how the accuracy of recording materials have changed over time. The reader will also realize the types of simple and complex articulators that exist, along with the different degrees of simulated mandibular movements that may be accomplished.

Incidence of occlusal contacts with complete dentures during mastication using a 6-channel telemetry system: preliminary measurements.

The purpose of this study was to observe the incidence of occlusal contact with complete dentures during mastication using a 6-channel telemetry system whose accuracy had been improved. The telemetry system consisted of the transmitter unit and the receiver unit. The transmitter unit was embedded in the lower complete denture. This system detects occlusal contacts by the shift of frequency in 100 kHz. The transmitter allowed 6 channels for the occlusal contacts. The data was telemetered by a time division multiplex communication method. A special switch was designed to measure excursive movement on the occlusal surface. After careful occlusal adjustment, the special switches were inserted in the lower first molars. On the basis of preliminary measurements on a 64-year-old edentulous male, it appears that the width of the gliding on the occlusal surface at the lower first molar was mostly 0.2-1.2 mm and the majority of the excursive movements ended at the centric occlusal position.

Association between the accuracy of intermaxillary relations and complete denture usage

Statement of problem. Previous studies have investigated possible associations between the accuracy of intermaxillary relations and complete denture usage with variable results. Purpose. This study investigated the association between the intermaxillary relations in new complete dentures and the use of these dentures for daily wear and eating. Methods. A prospective study of patients (n = 523) attending Guy’s Dental Hospital for complete dentures was undertaken. Patients were examined at the beginning of treatment and at the first post insertion visit. Rest vertical dimension and vertical dimension of occlusion were measured with a Willis gauge. Quality of registration of centric relation position was assessed and, 3 months later, a postal questionnaire was sent to investigate patients’ use of dentures. Data were analyzed with Pearson’s chi-squared test with exact nonparametric inference. Results. Adequate interocclusal rest space was associated with daily wear of dentures (χ 2 = 7.97, P =.018). Quality of registration of centric relation was associated with daily wear (χ 2 = 32.43, P <.001) and use of dentures for eating (χ 2 = 20.23, P =.003). Conclusion. Positive associations were found between the accuracy of intermaxillary relations and complete denture usage. (J Prosthet Dent 1999;81:520-5.)

Learning a clinical method to identify a mandibular reference position.

The teaching of clinical maxillomandibular relationships is an area of weakness in dental school curricula. Most difficulties arise when a reference position is required to adjust or reconstitute the maximum intercuspation of the dentition. The dentist-derived concept of the centric maxillomandibular relation position is used to solve this problem. There is no consensus on the definition of this term. In the descriptions of clinical technique for recording the centric maxillomandibular relation position, clinical criteria to judge whether or not the position required has been achieved usually are not given. The dorsal border paths of the envelope of movement were used to develop a clinical criterion to identify the centric maxillomandibular relation position. Force or "guidance" is not used in this method. Test-patients with normal masticatory systems were randomly selected and fitted with a mechanical tracking apparatus. 50 undergraduate dental students and dental nurses were randomly selected and given instruction in the clinical technique to identify the centric maxillomandibular relation position. The ability of these students to identify the reference position was assessed by having them perform the technique blindfolded on the test-patients on whom tracking apparatus was fitted. Sixty eight percent of the test-clinicians succeeded in using the method to identify the reference position. There was no significant difference in the abilities of subgroups to use the method successfully, e.g., women compared to men, 2nd year students to 3rd year students. It was concluded that the method was a satisfactory way of learning how to identify the centric maxillomandibular relation position in a gentle, non-invasive fashion.

臼歯部人工歯排列位置による上顎総義歯の動揺に関する研究

Although a lot of artificial posterior tooth positioning techniques have been proposed, correlation between complete denture stability and posterior tooth position during mastication has not yet been clarified.This study was conducted to analyze the behavior of complete maxillary dentures that have two posterior tooth positions by the simulation method. Three-dimensional mobility of these dentures was measured during biting two sizes of simulated foods on centric and eccentric positions. One of two artificial posterior teeth arrangements was based on the alveolar crest (A-denture) and the other was in a neutral zone of muscular activity (N-denture).The results were as follows:1. The working side point of two complete maxillary dentures moved downward, forward, and outward when they were loaded on one side.2. The mobility of complete maxillary dentures was changed by posterior tooth position, simulated food size, mandibular position, and tooth contact on the balancing side.3. When biting thick food, there was no tooth contact on the balancing side. In this condition, the mobility of A-denture was less than that of N-denture.4. When biting thin food, there was tooth contact on the balancing side. This contact limited the mobility of two dentures. In this condition, however, the mobility of N-denture was less than that of A-denture.

顎関節症の発症に関与するこう合因子に関する臨床的研究

The purpose of this study was to clarify the relationship between TMD and occlusal contacts on dental arch. Fourty TMD patients and 12 healthy subjects as controls were examined. TMD patients were cured by occlusal adjustment of the occlusal interferences detected by biofeedback occlusal analysis. The occlusal contacts of the subjects were examined at two different occlusal positions. One was the intercuspal position (ICP), and the other was the physiological centric position (PCP) that was an extremely light tooth tapping position with the aid of EMG biofeedback.1. No significant difference was observed in the number of occlusal contacts at ICP between before and after treatment. The number at PCP was 4.2 before and 12.2 after treatment, increasing significantly after treatment (p<0.01).2. No significant differences were observed in the asymmetry index (Al) of occlusal contacts at ICP among TMD patients and healthy subjects. AI at PCP was 54.3% before and 10.8% after treatment, decreasing significantly after treatment (p<0.01). AI after treatment was not different from that (10.1%) of healthy subjects.3. In cases of palpation pains on one side, 21 (72.4%) out of 29 cases were found to be occlusal interferences on the same side observed palpation pain. Occlusal interferences were high frequently found to be in inclines that demonstrated a posterior direction of the occlusal force on mandible with signs and symptoms.These findings clearly showed that the acquisition of bilateral balanced distribution of occlusal contacts at PCP is important for the cure of TMD. It was suggested that bilateral balanced distribution of occlusal contacts is one of the normal occlusal contact patterns and there is a close relation between the location of occlusal interference and prevalence of signs and symptoms of TMD.

Studies of changes in occlusion after the insertion of complete dentures (part II).

The aim of this clinical experimental study was to investigate whether, and what, changes in occlusion occur between 3 weeks and 1 year after insertion of complete dentures. Twenty-six edentulous patients, who already had their jaw relation registered for part I of this study some 357 days before, were re-examined. The same special non-arcon measuring articulator was used for determination of any positional differences between the presently recorded central condylar position with inter-occlusal gap and the equilibrated intercuspal position, from approximately 1 year previous. Differences were recorded electronically in the condylar area in three dimensions. The position of the condylar balls of the measuring articulator in maximum intercuspation had shifted, since the previous recording, by about 0.62 +/- 0.04 mm (0.04-1.76 mm) in the sagittal and 0.89 +/- 0.72 mm (0.01-3.06 mm) in the vertical direction. Whereas the differences measured in maximum intercuspation scattered in the sagittal plane uniformly around the centric condylar position, in the vertical plane they were shifted cranially about an average of 0.77 +/- 0.85 mm (1.06 mm caudally to 3.06 mm cranially). The results indicate that in half of the patients from the present sample the occlusion did not remain stable, which is assumed to be mainly caused by resorption of alveolar bone and abrasion of the acrylic teeth. Therefore, at each check-up visit not only the health of the denture-bearing tissues and the fit of the dentures, but also the mandibular posture and the occlusion should be examined carefully.

Geometric analysis of occlusal plane orientation using simulated ear-rod facebow transfer.

Ear-rod facebow techniques may position casts high or low between the upper and lower members on the articulator when using orbitale or nasion as anterior reference positions. This study assessed the effect of changing the anterior reference position on simulated mountings utilizing simulated ear-rod facebow. Tracings from latoral cephalographs made on seven subjects were superimposed with an outline model of a semiadjustable articulator. Three simulated mountings were performed for each subject in which the plane of occlusion was positioned (1) high, (2) midway, and (3) approaching the lower member (low). Maxillary and mandibular occlusal planes representing intercuspal position were determined from the cephalographs and positioned on the articulator model in a simulated centric relation position for each mounting. Condylar guidance was determined from a simulated protrusive position. Analysis of the three mounting positions demonstrated no change in intercuspal position within subjects; however, angles formed between upper member and condylar guidance were 14.9% smaller for the mid-distance mounting, 42.9% smaller for the high mounting, and 13.4% higher for the low mounting positions when compared with a standard Frankfort horizontal plane reference. The cephalographs showed extreme variability in the position of the ear piece to bony structures of the skull, but this deviation appeared to be compensated by a change in the horizontal condylar guidance relative to mounting. Results also suggest that casts may be mounted in a convenient mid-position for routine articulation.

Cephalometric study of long-term airway changes after orthognathic surgery

Purpose: This study investigated the differences in centric occlusion (intercuspal-CO) and centric relation contact position (CR) in patients in an upright and supine posture when conscious and when supine under general anesthesia to rationalize planning for complex bimaxillary osteotomies.Patients and Methods: Twenty-four men and 37 women, with a mean age of 24.7 ± 4.5 years were included in this study. Occlusal records on each patient included 1 in CO and 3 in CR in each of the following postures: conscious upright, conscious supine, and anesthetized supine. Casts were mounted in the Denar Mark II articulator and transferred to the Denar Vericheck (Denar Corp, Anaheim, CA) recording tool for measurements. The centric relation displacement vectors (CO-CR) were projected in various axes by 3D graphics.Results: The upright conscious CO-CR (mm) vectors were significantly different from both the supine conscious and anesthetized positions in the anteroposterior plane. The difference in the vertical plane was only significant in Class II division 1 patients.Conclusion: The posterior change in centric relation explains the apparent occlusal discrepancies created by rigid fixation of the mandible applied in the supine anesthetized position. By taking the CR records in the supine conscious position, the “loss” of maxillary advancement can be avoided.

Verifiable method for registering the centric relation position in dentulous arches with a central bearing point

Verifiable method for registering the centric relation position in dentulous arches with a central bearing point

咬合育成の重要性

In clinical practice, we encounter many patients with various degrees of malalignment.Malalignment causes impaired perfusion of saliva, inappropriate physical stimulation by the cheeks and tongue, food retention, or difficulty in oral cleansing, resulting in dental caries and periodontal diseases.Depending on the degree of malalignment, problems arise in terms of mastication, talking, aesthetics, and function. In addition, shift in the intercuspal position and the centric position is observed in many patients, making the mandibular position unstable.In the repair of malalignment in adult patients, active use of orthodontic treatment under appropriate conditions of the patient is useful for attaining a more stable intercuspal position and a stable mandibular position and also facilitates repair. A stable state can be maintained for long years.However, since growth of the jaw bone has been completed in adults unlike children in the growth period, orthodontic treatment in adults involves only treatment of the teeth. In addition, translation requires time. Therefore, caution is necessary for the application of orthodontic treatment. Informed consent after adequate explanation should be obtained from the patient when surgical orthodontic treatment beyond treatment of the teeth alone is performed.Since the application of orthodontic treatment to adults is difficult, guidance and management in the early stage of growth are important for appropriate function such as mastication and phonation.

Condylar movement and centric relation in patients with internal derangement of the temporomandibular joint

This study was designed to compare the reproducibility of the condylar translation pathway and the centric relation position in patients with and without internal derangement of the temporomandibular joint. Reproducibility of condylar movement and variability of the axis point of condylar rotation in centric relation was studied in 15 patients with internal derangement of the temporomandibular joint and 15 patients with no history or clinical signs of mandibular dysfunction. Condylar movement and axis point location were recorded with a sagittal recording device at three separate recording sessions. Lead markers were placed on the skin over the axis and orbital points, and lateral cephalometric radiographs were taken at each session. Analysis of cephalometric and axiographic recordings included both linear and angular measurements. Analysis of the condylar movement pathway revealed greater within-subject reproducibility in the control group for both the right and left condyles ( p < 0.0005 and p < 0.0003 respectively). The axis point of condylar rotation in centric relation, as shown by cephalometric analysis, had significantly more within-subject variability in the horizontal plane for the control group ( p < 0.003). There was no significant difference between groups for within-subject variability of condylar position in the vertical direction. These findings are consistent with the contemporary concept of centric relation that a vertically stable condyle with a disk interposed against the anterior eminence is capable of functional adaptation in the horizontal plane. The results have implications with regard to treatment and rehabilitation of patients with temporomandibular joint internal derangement.

Angle of the articular eminence in patients with temporomandibular joint dysfunction and asymptomatic volunteers

The purpose of this study was to compare structural variations of the temporomandibular joint anatomy between symptomatic patients with temporomandibular joint dysfunction and asymptomatic controls. There were 74 symptomatic patients with temporomandibular joint dysfunction, 29 asymptomatic volunteers with normal joints, and 6 asymptomatic volunteers with disk displacement with reduction included in this study. All subjects had bilateral high resolution magnetic resonance imaging scans performed in the sagittal (closed and opened) and coronal (closed) positions. All subjects had right and left full profile laminagraphs, one in the centric occlusal position, and one with the incisors edge to edge. Student-Newman-Keuls tests demonstrated no significant angular or linear differences for depth of the articular fossa, angle of the articular eminence, horizontal and vertical overlap of the incisor teeth, and linear condylar translation. This study concludes that there are no significant differences in angular and linear measurements in the articular fossa of asymptomatic volunteers and symptomatic subjects with temporomandibular joint dysfunction.

Condyle position in the temporomandibular joint: Comparison between asymptomatic volunteers with normal disk position and patients with disk displacement

Though the significance of condyle-fossa relationship in the temporomandibular joint has not yet been clarified and normal condyle position not yet defined, efforts have been made to guide the mandibular condyle into a centric position in the glenoid fossa with the aim of relieving the symptoms in patients with orofacial pain and temporomandibular joint internal derangement. The present study investigated the mandibular condyle position in 34 joints in asymptomatic volunteers with normal disk position as verified by arthrography and compared it with the mandibular condyle position in 85 joints in patients with different stages of internal derangement. The results showed that in the volunteers with normal joints including normal superior disk position, the condyles were almost randomly distributed in anterior, centric, and posterior positions in the glenoid fossa. Of the joints with anterior disk displacement approximately half of the number of joints with reducing disks and two thirds of the joints with nonreducing disks appeared to have posterior condyle position. Posterior condyle position cannot, however, be used to diagnose internal derangement because the condyle was found to be either in anterior or centric position in many joints with a displaced disk. The variety in condyle position in the healthy joints ought to be taken into consideration if treatment is chosen to normalize the mandibular condyle position by bringing it into a centric position in the glenoid fossa.

全部床義歯床下組織の負担圧分布に関する基礎的研究 第２報 こう合器の切歯路指導板の傾斜が負担圧分布に及ぼす影響

When making a complete denture, the horizontal and sagittal inclination of the incisal guide plate of the semi-adjustable articulator have to be determined by denture stability and the anterior arrangement of the denture teeth.The purpose of this' study was to investigate the influence of the inclination of the incisal guide plate on the pressure distribution under a complete denture and to obtain a guideline for adjustment thereof.The results were as follows:1. When the sagittal inclination of the incisal guide plate increased, the pressure distribution under the upper and lower complete denture did not change in the centric occlusion.2. When the horizontal inclination of the incisal guide plate increased, the pressure distribution on the supporting tissue did not change remarkably.3. In one-sided occlusion, the pressure value increased as the horizontal inclination in the buccal region of the upper molar on the working side and lingual region of the lower molar increased. Reduction of pressure was observed in the palatal region of the upper molar and buccal region of the lower molar.4. In one-sided occlusion at the eccentric position, the pressure values increased as the horizontal inclination in the upper buccal region on the working side and lower lingual region increased. Reduction of pressure was seen in the palatal region and lower buccal region. These pressure changes were larger than those in one-sided occlusion at the centric position.

Preliminary study of electromyographic characteristics for distinguishing centric relation and protrusion in edentulous patients

The mean voltages of the masseter and anterior temporal muscles of 30 Chinese edentulous patients were recorded in centric relation and protrusive positions (from 1 mm to 4 mm anterior to centric relation) under two given occlusal force conditions. It was found that the mean ratio of individual voltages of the anterior temporal muscles to the masseter muscles was equal to or greater than 1.2 in centric relation, but the ratio was less than 1.2 in protrusive positions in most of the subjects. The results demonstrated that the ratio of voltages of the anterior temporal muscles to masseter muscles may be a reliable parameter for distinguishing centric relation from protrusion in Chinese edentulous patients.