Purpose: We have made several new types of jaw-tracking devices to perform kinematic analyses of dental occlusion. The present paper discusses the research history behind the development of sixdegree-of-freedom movement detectors. The current status and future directions of jaw-movement research are also discussed.
Study selection: One of the best ways to evaluate the kinematic aspects of dental occlusion is three-dimensional computer analysis. Research in this area has linked three-dimensional tooth-and jaw-shape data with six-degree-of-freedom movement data. The main features and research outcomes of previously reported jaw-tracking devices are introduced herein. Several studies evaluating the effect of different heights of occlusal restoration have suggested fundamental ideas for the accuracy required in clinical occlusal adjustments. Progress of our new movement detector, which applies magnetic phase fields, and the prospects of computer technologies for visualizing kinematic occlusion, are also reported.
Results: When occlusal adjustment was performed for the level of 10μm, clinical problems of stomatognathic function caused by occlusal problems could be prevented. This finding suggests that performance of jaw-tracking devices should be finer than the level of 10μm. Sampling frequency of the measuring system should be faster than 300Hz.
Conclusions: Computer visualizing systems for dental occlusion have the potential to resolve various theoretical issues in dental research and clinics. Six-degree-of-freedom movement detectors with high specifications seem to offer an essential component for such research.

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Purpose: The purpose of this study was to investigate the relationship among the position of the mandible, cervical vertebra alignment, and body posture in temporomandibular disorders patients.
Materials and Methods: Subjects consisted of 10 patients with temporomandibular disorders (eight females and two males; average age, 36.4 years old). The position of the mandible and the inclination of cervical vertebrae (C2, C4) were analyzed with lateral cephaolograms, and the body posture was analyzed with side-view photographs. The relationship among the position of the mandible, cervical vertebra alignment, and body posture was examined by means of correlation coefficient and principal component analysis.
Results: 1. The angle of the SN plane to the mandibular plane showed a positive correlation with the inclination of C2, and a negative correlation with the angle of C2 to C4 (p<0.05). 2. The head posture showed a negative correlation with both ANB angle and the inclination of C2 (p<0.05). 3. Subjects were classified into two groups according to the position of the mandible by means of principal component analysis. 4. The subjects who demonstrated a retro-and inferior-mandibular position showed a forwarded inclination of C2 and C4 and straight alignment of C2 to C4.
Conclusion: It was suggested that the relationship between the mandibular position and the body posture was intervened by the alignment of cervical vertebrae.

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Purpose: Temporomandibular disorder (TMD) patients often complain of various accompanying symptoms, such as headache, shoulder stiffness, or low back pain, in addition to masticatory muscleand TMJ-related TMD symptoms. Currently available TMD sub-categorization systems sometimes fail to include patients' complaints relating to such accompanying symptoms. In the present study, we investigated the relationship between TMD sub-categorization and patients' complaints at the initial visit.
Methods: A total of 393 consecutive TMD patients (mean age: 34.5±16.5, 89 males and 304 females), who visited our TMD clinic from April 1994 to March 1998, were included. These patients were classified according to a masticatory muscle- and TMJ-related TMD sub-categorization system, and they were also classified into three groups based on their chief complaints: a group with masticatory muscle- and TMJ-related complaints only, a group with accompanying complaints only, and a group with both of them. Then, the distributions of chief complaints were investigated in each TMD sub-categorization.
Results: In every TMD sub-categorization, masticatory muscle-and TMJ-related complaints (e. g. TMJ pain, 49.6%; difficulty in mouth opening, 32.6%; TMJ noise, 30.8%) were major complaints, while other complaints (e.g. headache, 6.9%; masticatory disturbance, 6.1%; shoulder or neck stiffness, 5.9%) were also substantial.
Conclusions: A considerable number of TMD patients complained of other accompanying complaints with or without masticatory muscle-and TMJ-related complaints. This finding supports the proposal that the classical TMD sub-categorization system should be changed to a multi-axes diagnostic system.

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Purpose: To grasp the membrane thickness of the lower alveolar crest and different areas of membrane as classified by prosthodontics, contributing to prosthodontics based on EBD.
Method: After obtaining informed consent from 31 individuals with mandibular free-end, we measured their oral mucous membrane at the four regions of the second premolar, the first molar, the second molar of the alveolar crest, and on the lingual side of the central incisor, with SDM (Schleimhaut-Dicken-Meβ). Measurement was done five times, and the thickness of membrane was worked out. For reference, measurements were also taken by palpation in the fixed, movable, hard-fixed, and flabby areas of membrane, as classified by prosthodontists.
Results: 1. The reliability of SDM was confirmed experimentally with the use of specimens of hog membrane, 2mm and 3mm thick. 2. The measurements of membrane thickness varied from site to site. Values showed a tendency to be lower in the membrane on the lingual side of the central incisor than in the membrane lining the alveolar crest.
Conclusions: 1. Values obtained with SDM showed a tendency to be lower in the membrane on the lingual side of the central incisor than in the membrane lining the alveolar crest. 2. The areas of membrane divided according to the prosthodontic classification: the thickest and thinnest membranes were found in the flabby and the hard-fixed area, respectively.

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Purpose: To investigate the intra-rater reliability of the occlusal contact area measured with an occlusal examination device of a pressure-sensitive sheet (Dental Prescale System ^(®) ) by using generalizability theory.
Methods: Two occlusal conditions: medium clenching (MEC) and maximum (MAC), were selected. Subjects were ten males with healthy complete dentition. Measurement variability was estimated both among repetitions and between days using a repeated-measures study design, which provided 3 measurements during the same test, and 3 additional clenchings at a second test 7 days after the initial measurement. Generalizability study was used to assess the relative contribution of identified error sources (subject, occasion, and repetition) to the total measurement error. For intra-rater applications, an index of dependability, the standard error of measurement (SEM), and the smallest detectable difference (SDD) at the 0.05 level were estimated using decision study.
Results: The measurement variability included two-way interaction components and a residual component, indicating that these interaction effects were important sources of measurement error. At least six measurements in MEC taken on two occasions (three measurements per occasion), and three measurements taken on a single occasion, or four measurements taken on two occasions (two measurements per occasion), for MAC, were necessary to obtain an index of dependability over 0.9. The SEM for an index of dependability over 0.9 was below 1.17mm² for MEC and 1.89mm² for MAC. Again, the SDD was below 3.24mm² for MEC and 5.24mm² for MAC.
Conclusions: The clinical implication of these findings was that intra-rater reliability for occlusal contact area measurements could best be enhanced by averaging multiple measurements rather than by using a single measurement.

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Purpose: The purpose of this study was to estimate the influence of the inter-coronal freeway of lingualized occlusion on masticatory function.
Methods: Two male and 4 female edentulous subjects were studied. The masticatory performance, masticatory movement, and subjective chewing sensation were studied using complete dentures that could be changed to 0.5, 1.0, 1.5and2.0mm of the inter-coronal freeway. The masticatory performance on chewing each test food of boiled fish-paste, peanuts, and raw carrot was measured, using the sieve method. The masticatory movement on chewing each test food of boiled fish-paste, peanuts, raw carrot and pickled Japanese radish was measured, using the MKG (Mandibular kinesiograph). The subjective chewing sensation of each test food of boiled fish-paste, peanuts, raw carrots, and pickled Japanese radish, and general foods in daily life, was evaluated by a visual analogue scale (VAS).
Results: On 10, 20, and 30 repetitions of the chewing test of boiled fish-paste and peanuts, the masticatory performance was highest with 0.5mm of inter-coronal freeway. A higher inter-coronal freeway tended to have a slower closing time and cycle time. In the subjective chewing sensation of each test food and general foods in daily life, the values of a VAS were highest with 0.5mm of inter-coronal freeway.
Conclusions: From these results, it was demonstrated that the masticatory function is most effective in 0.5mm of the inter-coronal freeway.

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Purpose: This study investigated pronunciation disorders regarded as a disadvantage in cross-bite arrangement of complete dentures.
Methods: An articulation test of pronouncing 67 single sounds (62 consonants and 5 vowels) was applied to a dentulous subject group, and a complete denture-wearer group subdivided into a cross-bite group, and a normal-bite group. The rate of mishearing and the rate of mishearing each sound in each subject, and the average mishearing rate and the average mishearing rate of each sound in each group, were calculated. The test sounds that demonstrated a higher-than-average mishearing rate were sorted out and evaluated according to the place of articulation.
Results: 1. Rate of mishearing. 1) In both the cross-bite group and the normal-bite group, there were significant differences among subjects. 2) In the complete denture-wearer group, there was a significant negative correlation between the rate of mishearing and the duration of having used the present complete denture. 3) There was no significant difference among groups. 2. Sorted misheard sounds according to the place of articulation. 1) The number of sorted misheard sounds involving alveolars and glottals in the cross-bite group was greater than in the normal-bite group. 2) In the cross-bite group, dentals, alveolars, and velars tended to be misheard as sounds with a different place of articulation, and glottals tended to lack the preceding consonant. However, there was no significant difference in comparison with the normal-bite group.
Conclusions: Articulation testing in pronunciation indicated that there was no significant difference between the cross-bite group and the normal-bite group, but there was a significant negative correlation between the rate of mishearing and the duration of having used the present complete denture in the complete denture-wearer group. Therefore, it was suggested that pronunciation disorders can be recovered by experience with a denture.

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Purpose: We previously reported that an oxidation layer and space (black layer) were observed between the keeper and 12% Au-Ag-Pd alloy in a basic study. The black layer was affected by the mold temperature and casting method. In this report, conditions of casting dental alloys to an embedded keeper of magnetic attachment in clinical cases were investigated.
Methods: Seven extracted teeth were investigated. These teeth were extracted due to periodontal disease. A 12% Au-Ag-Pd alloy was used as a casting alloy. Coping was cast by a centrifugationtype casting machine. The interface between the keeper and casting alloy was observed by light microscopy and scanning electron microscopy. Additionally, this interface was analyzed with an Xray electron microprobe. These resulting data were compared with those of a previous report.
Results: By microscopic observation, the black layer was observed between the keeper and casting alloy in all specimens. By scanning electron microscopy and X-ray electron microprobe analysis, the black layer was composed of an oxidation layer and a casing defect. These black layers were larger than those of the bench test, and they had irregular thicknesses.
Conclusions: The proper casting conditions are needed for casting Au-Ag-Pd alloy to an embedded keeper of magnetic attachment.

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Purpose: The purpose of this study was to compare the flexural strength, compression strength, Vickers hardness, and water sorption test among light-heat curing highly crosslinked plastic, Targis, light curing highly crosslinked plastic, Spectrasit, Cesead, New META COLOR INFIS, heat curing highly crosslinked plastic, Chromasit, and fiber-reinforcing material (Vectris). The effect of reinforcing materials of Targis was investigated.
Methods: Rectangular test specimens were modified by incorporating an additional fiber reinforcement of treated glass fibers (Vectris) in the test specimens. Control specimens were the same size as the test specimens, without any reinforced fibers. Flexural strength testing and compression testing of the specimens were done using a Computer Control System Autograph (AUTO GRAPH AG-5000 D). Vickers hardness testing of the specimens was done using a Micro Hardness Tester (HMV-2000), after the specimens had been stored in water at 37°C for 2 weeks. The additional reinforcing materials of the test specimen did not affect the flexural strength.
Results and Conclusions: The results of this study suggest that fiber-reinforcing material reinforcement enhanced the flexural strength of highly crosslinked plastic, while the use of additional fiber reinforcement, made of glass fibers, in the test specimens, did not have an effect on the flexural strength.

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