The purpose of this study was to measure linear distortions (the vertical direction) and rotational distortions in indexing a three-unit fixed partial denture. The three-unit was assembled with the second premolar and molar as abutments and the first molar as a pontic on the left mandible.
The two types of self-polymerizing acrylic resin (the Unifast, the Pattern Resin) and bar for reinforcing were used, and four types specimens (1. only the Unifast, 2. only the Pattern Resin, 3. the Unifast and bar, 4. the Pattern Resin and bar) were prepared.
The following results were obtained.
1. The linear distortions and rotational distortions of specimens fixed with only the Unifast were smallest.
2. The standard deviation of the linear and rotational distortions of the specimens fixed with the Pattern Resin and bar was the smallest.

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The purpose of this research was to investigate the horizontal dimensional variations in maxillary complete dentures fabricated with Polyethersulfone (PES) using compression molding. Dimensional changes were compared for the three different materials PES, Polysulfone (PSF), and PMMA.
The results were as follows:
1. In the case of the occlusion rim, all three materials displayed horizontal shrinkage both in the anteroposterior and in the left/right directions. PMMA had the largest shrinkage, followed by PSF and PES in that order.
2. In the case of the denture, PSF had the largest horizontal shrinkage in the anteroposterior direction, followed by PES and PMMA in that order. In the left/right direction the shrinkage was largest for PMMA, followed by PES and PSF in that order.
3. PES, like PMMA displayed a uniform shrinkage in the anteroposterior direction, with little difference observed between shrinkage in the anterior and posterior region. However, PES, like PSF, had greater shrinkage in molar region than the anterior region.

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Numerous devices to improve various components of removable partial denture have been made to meet two requirements, i. e., retoration of defective function and protection residual tissue. The artificial tooth, as a denture prosthesis, has gradually progressed from a simple anatomical structure complementing defect and changed to a non-anatomical artificial tooth, an articulation or a tooth arrengement mechanically stabilizing a removable partial denture. Most, however, aim at improving mastication, but little attention has been paid to the influence on residual tissue, in particular on abutment.
We therefore measured effect of the articulation force imposed on either the lingual or buccal side of a denture site on the horizontal movement of an abutment tooth long axis. This was determined as the flexing strain by a bridge circuit based on the 2 gauge Active-Active method during function of a lower free end removable partial denture using experimental Kennedy's II model.
Our conculusions are as follows:
The load on the lingual side of the defect, in comparison with the load on buccal one, reduced horizontal stress on direct and indirect abutment and increased the effect of crossarch stabilization, thus was a more beneficial condition for protection of abutment.

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Structural study of the temporomandibular joint is a key issue in prosthodontics because the T. M. J. is the most important element of mandibular movement. As threedimensional investigation is needed in this field, I recently developed a personal computer system that can form three-dimensional images of the T. M. J.. The use of three-dimensional images created by the computer system is effective to research the shape of the T. M. J. and mandibular movements. Using this system, I studied condyle behavior and the relationship between mandibular fossa and condyle.
The results are as follows:
1. In an intercuspal position, each distance between forssa and condyle at its middle, inner and outer part is almost the same. The distance between the fossa and condyle at its center, front and rear is nearly equal.
2. Rige lines of fossa, condyle and articular tubercle have similar form.
Three-dimensional images of the T. M. J. can be reconstructed from successive sections of a T. M. J. of a dry skull. The images can be sectioned at arbitrary positions in sagittal, frontal and horizontal planes, and by the addition of movement data, mandibular movement can be simulated.

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The radiograph stress measurement method is the only known means of a nondestructive measurement, and this method is used to assess the residual stresses of variousmetals.
This study was made to evaluate the effect of cutting and spraying on the residual stress of the metallic denture base formed by the wire explosion energy. We cannot neglect the effect of cutting and spraying, but the metallic denture base can fit well after reforming.

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The objective of this study was to clarify the casting rate, the surface roughness and acuracy of ethyl silicate by comparing those of other investments.
The accuracy here means those of simple gypsum model and the metal plate.
The results obtained were summarized as follows:
1. In the experiment of the casting rate, ethyl silicate was effective in using chromiumcobalt alloy.
2. In making of the test piece, it was possible to reduce the working hours considerably in case of ethyl silicate. The surface roughness of the test piece by using ethyl silicate was almost the same or less compared to the conventional ones.
3. Judging from the results of the first and the second experiments, the capacity of ethyl silicate was effective in many points. But in the experiment of the accuracy, it showed that there was mainly a little shrinkage toward X-axis, Y-axis and had a tendancy to rise to the surface toward Z-axis. That is, ethyl silicate was not so good in the accuracy.

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The purpose of this study is to show the guideline for incisal table adjustment of the semi-adjustable articulator LL-85^®. In this report, we discuss the influence of the guide plane of the articulator on the pathway of the upper first molar determined by geometrical method.
The following results were obtained:
1. The sagittal condylar path inclination affected the pathway of the upper first molar in the frontal and the sagittal planes at the balancing side. The lateral condylar inclination affected the pathway at both the balancing and the working sides but not so much.
2. The sagittal incisal guide angle affected the pathway in the sagittal plane more significantly at the working than balancing side. The inclination of lateral wing was the most impotant factor in guidance of the articulator.
3. The pathway of the upper first molar was almost independent of its position in the horizontal distance of 15 to 18mm from the incisal pin.

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The purpose of this study is to show the guideline for incisal table adjustment of the semi-adjustable articulator LL-85^®. The inclination of lower artificial teeth in the frontal plane was calculated from pathway of the upper first molar, and the direction of the combinated occlusal force was obtained by mechanical technique.
We showed the guideline for incisal table adjustment of the articulator in the case of the tooth arrangement by interalveolar crest line.
The following results were obtained:
1. The direction of combinated force was not affected very much by the sagittal incisal guide angle. On the other hand, it was affected significantly by the inclination of lateral wing.
2. The direction of the combinated force was affected by the occlusal morphology and form of the artificial teeth.
3. The guideline for incisal table adjustment of the semi-adjustable articulator LL-85^®and the guideline for selecting the occlusion form in complete denture were shown.

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The standards for the shape of the metal framework of resin-veneered crowns mentioned in various textbooks seem to be only experiential models. There may be no theory to ensure the safety or durability of crowns.
The purpose of the present study is to establish a structural principle for the shape of the metal framework of resin-veneered crowns. Thus, the influence of the differences in shape of metal frameworks was examined by measuring the strain on several parts of the crowns caused by static pressure.
The results of the investigation are as follows:
1. The thick visor is better than the thin one. A thickness of 0.5mm is insufficient for a visor made from 12% Au-Ag-Pd alloy.
2. With regard to the underlying metal, it is more rational to make it thicker from the cervical to the cuspate side.
3. The presence of a metal collar slightly decreases the degree of the elastic transformation of the crown cervical portion. But its usefulness is not yet clearly established.

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The purpose of this study was to investigate the influence of the vertical dimension on pronunciation.
Tongue pressures, mandibular movements and speech sounds were simultaneously recorded and analyzed for the following sounds:/asa/, /asi/, /ahi/, /aci/, /aki/, /ake/ and /ari/ when the vertical dimension was normal and increased by 4mm, 8mm and 12mm beyond the normal vertical dimension at the incisor.
The results were as follows:
1. The maximum tongue pressures tended to be smaller on for /asa/ than other sounds and be greater in more posterior palate in the normal vertical dimension.
2. The maximum tongue pressures changed differently among subjects, sounds and measuring sites, but tended to decrease in anterior palate for any sounds and increase in posterior palate with increases in vertical dimensions.
3. Tongue contacts usually started from posterior palate to anterior palate before the end of the preceding vowel, and tongue pressures usually came up to maximum between the end of the preceding vowel and the start of the following vowel. But the timings between sounds and tongue pressures were not evidently influenced with increasing vertical dimensions.
4. It was found that changes in maximum tongue pressures with increasing vertical dimensions were related to those of simultaneous mandibular movements.

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The excellent success through many implant systems such as the osseointegrated and others have been directed toward reducing the interest and research effort for removable prosthesis over the past few years.
The need to improve the quality of removable partial dentures through research, however, will remain at a high level because the implant procedures will never eliminate removable prosthodontics at an early date.
The research for the removable prosthesis, especially the movement of the abutment tooth, has been investigated in various ways such as by strain gauge, photoelastic and finite element methods, including a few experiment executedin vivo. All of them, however, have disadvantages respectively, so more effective methods for observation of the abutment tooth behaviors have been waiting for.
Authors have undertaken some experiments on the abutment teeth behaviors under loading by a new analysing method that combined with MKG to the Frechette's method.
This study was to analyse and evaluate the movements of the mesial abutment tooth in the tooth-supported segment on Kennedy Class II Modification 1 simulation model by the same method.
The results were as follows;
1. As the constructred factors were reduced from the original design of the RPD, the abutment tooth movements increased gradually.
2. The greatest movements were recognized under the lingual load, and the minimum ones under the vertical load.
3. Few movements toward the mesial direction were observed in every design.
4. Movements toward the linguo-distal direction were remarkably noticed on almost designs.

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Effects of head positions on the activity of masseter and temporal muscles during voluntary contraction were evaluated on six subjects with normal jaw-function. The subjects in the upright body position were asked to perform maximum voluntary contractions in three head positions; full dorsal flexion, full ventral flexion, and normal head position. EMG recordings of the muscles as myoelectrical activity and bite force as myomechanical activity were taken simultaneously. Acquired data were analyzed by four parameters; 1) integrated EMG, 2) bite force, 3) median frequency of EMG power spectra, and 4) EMG/force ratio.
Integrated EMG of masseter muscle in the dorsal flexion increased in activity by 30% over the normal position and decreased in the ventral flexion. On the contrary, bite force was not influenced by head positions, thus resultant EMG/force ratio changed in the same manner as integrated EMG did. These effects of head positions were greater in the masseter than in the temporal muscle.
No evidences of muscular fatigue such as contractile failure, increasing EMG/force ratio, or spectral shift to lower frequency in the normal head position were observed in the study. These results suggest that changing head position generates antagonistic or synergistic force to masticatory contraction force.

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The development of new dental materials and methods has enlarged the possibilities of composite resin cores. In this study we examined effects of prefabricated metal posts on reinforcement of composite cores and effects of post length and diameter on core retention. First, the bending test of both various prefabricated posts only and composite cores in which the stainless parallel posts (AD Post^®) were embedded was carried out. Then, pull-out test of AD Posts which were built up with Panavia EX^®in root canals of extracted human teeth was carried out.
The following conclusions were drawn:
1. The bending strengths of prefabricated posts were greatly different from the kind of metal to its shape. The tapered self-threading posts provided the weakest bending strength because they have deep grooves, whereas the stainless parallel posts provided the biggest.
2. It was confirmed by bending test that the prefabricated metal post reinforced composite resin core significantly.
3. The surface treatment, i.e. sandblasting with almina and/or application of resin adhesive, on the metal post had no significant effect on the reinforcement of composite cores.
4. The retentive force of AD Post increased gradually with increasing both its length and its diameter. Especially, the increase of diameter was more effective for increasing the retention.

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Examining of the compressibility of the denture foundation is very important for construct of a denture. The areas, especially the torus palatinus area, should not be pressured excessively by a denture and relief is usually necessary for such specific areas.
However, to determine the amount of relief in thickness depends on a clinician's experience.
The purpose of this study was to investigate the compressibility of the denture foundation and to determine the amount of relief in thickness over the specific area.
In this report, the mucosal thicknesses of 60 complete denture wearers were measured with 20MHz B-Mode Ultrasonic Diagnostic Equipment, under both non-occlusal load and maximum occlusal force. Moreover, the mucosal thicknesses of 15 complete denture wearers whose dentures were relieved by 0.25, 0.50, 0.75, 1.00 mm over the areas of incisive papilla, torus palatinus and median palatine suture were also measured by the same manner.
The main results were as follows:
1. Decrease in the mucosal thickness under maximum occlusal force was about 0.3mm in averages.
2. Decreasing rate in the mucosal thickness under maximum occlusal force was greater in a mandible than in a maxilla.
3. Judging from the decrease in the mucosal thickness by relief procedures, it was found that 0.50mm relief in thickness was necessary in a case of a severe torus palatinus and 0.250.50 mm relief in a moderate one.
4. Even in a case without the existance of torus palatinus, about 0.25mm relief in thickness was desirable over the incisive papilla and median palatine suture areas.

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Preparation of teeth is an important treatment which is initially performed in crown and bridge procedures. The quality of preparation affects not only the subsequent treatment but also the clinical value of completed prostheses. In order to effectively train students in the proper administration of such preparation in a limited period, it is necessary to improve models for preparation and manikin heads according to clinical conditions. Basic evaluative criteria are also required for assessing students ability in this procedure. We have been examining the preparation of teeth from this point of view.
We report how students developed their technique during a one-year period of polyclinical practice, comparing basic items and regions which frequently resulted in poor preparation with those in previous reports.
As a result, we concluded that
1. Almost items and regions identical to those indicated in the previous reports in poor preparation.
2. A slight difference was seen in the finish of preparation performed before and after polyclinical practice. Progress was recognized for most items after polyclinical practice; however, degression rather than progress was observed for some items. The technical level of the students was found to be uneven.

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The denture dislocation during function is inevitable since the retention and the support of the complete denture depend on the mucoperiosteum covering the bone. It is important to minimize the denture dislocation to restore the oral function and protect against the ridge absorption.
The final goal was to investigate the effects of the balancing contact on the denture dislocation. The purpose of this study was to develop a measuring system for the maxillary complete denture mobility by a Video Tracker and measure the mobility of that denture and the occlusal force in the lower artificial posteriors.
The results were as follows:
1. The resolution of the measuring system was 65×65μm. The measure was carried out in the area of 12×16mm with the working distance of 210mm and with frequency of 60Hz.
2. The denture on clinical normal ridges dislocated upward by 330 to 700μm during tapping movements.
3. The occlusal force was not an influential factor in the denture mobility during tapping movements.
4. The denture shifted laterally toward the nonworking side in the nine of the ten patients during chewing movements.
5. The occlusal contact on the nonworking side reduced the lateral denture mobility statistically.

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For the purpose of clarifying the functions of each articulator following the insertion of a denture and the state of self-compensation of these organ, the experimental palatal plates were inserted on 13 subjects with natural dentition, assuming that they were inserted with complete denture. The muscular discharge of facial muscles and the tongue pressure of each subject during pronunciation following the insertion was evaluated longitudinally with the pre-insertion of a palatal plate as basis.
As the result of this study, the following conclusions were obtained. The results of this study clearly showed that the lips and the tongue, major articulators, come under the influence by insertion of the denture. They appear to adapt to the new oral cavity environment earlier than before pronunciation.

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The aim of this study was to evaluate the sliding-induced wear of five commercial resin materials for reconstructing occlusion opposing an Au-Ag-Pd alloy. A polymethylmetacrylate (PMMA) resin and enamel were used as the control. The evaluation of the wear was to measure the volume and depth of wear of resin materials and the volume of wear of Au-Ag-Pd alloy.
There was a great variation in the wear of tested resin materials. A light curing composite resin for inlay (ES) and a light curing veneering hard resin (CE) had a wear near that of the PMMA resin (UN). Wear of a heat curing composite resin for inlay and a light curing composite resin for filling were less than that of UN, ES and CE, and were greater than that of a hard resin denture tooth and enamel. The smallest wear was shown by the hard resin denture tooth. The difference of wear between the hard resin denture tooth and enamel was not statistically significant.

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A dental magnetic attachment has recently attracted vivid attentions from many prosthodontists for their clinical availabilities as a retainer for prostheses. Several types of dental magnetic attachments are commercially available at the moment. However none of them are clinically satisfactory. They must possess strong retention and complete corrosion resistance, since the available space is limited and the exposed magnet is easily corroded in the oral cavity.
A very small and powerful attachment has been developed by devising a sandwich typed construction and the elliptic cross-section with the aid of three dimensional FEM magnetic field analysis. The attachment is sealed up with a stainless steel cap laser-welded to the yoke. It has shown sufficient attractive force (560 gf) and stability in various fundamental tests.

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This study was made to investigate the influence of gum texture on the chewing motion. The textures of chewed gum (Green gum, LOTTE Co.), the hardness, the cohesiveness, the gumminess, the stickiness and the adhesiveness, were quantified by a texturometer (Zenken Co.), and also the weight measured for 10, 20, 30, 60, 90, 120, 180, 240, 300 and 600 sec in 8 normal subjects and 2 patients with craniomandibular disorders (CMD). Using a kinesiograph (Model K 6, Myo-tronics Co.), the jaw movement of mandible was recorded three-dimensionally during 10min. habitual gum chewing. Multiple regression analysis was applied for investigating the effects of the change of gum texture and weight on chewing motion (criterion variables: chewing movement parameters, explanatory variables: texture and weight factors).
The results obtained were as follows:
1. In normal subjects, the closing and the occluding phases were observed high correlations with the hardness and the cohesiveness. On the other hand, the opening phase and the cycle time were not observed correlations with any texture and weight factors.
2. In CMD patients, all parameters of chewing movement were observed high correlations with texture and weight factors.
In conclusion, a central pattern generator (CPG), somewhere in the brain stem, is suggested to be responsible for rhythmical jaw movement in normal subjects. In CMD patients, however, jaw movement was easy to be affected by peripheral factors such as gum texture and weight.

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The purpose of this study was to investigate the relationship between the stomatognathic system and physical exercise. Intensive physical exercise is often accompanied by a clenching of the jaws and the teeth. In the present study, frequency of clenching during physical exertion was investigated in one hundred young adults. Measurement of back strength was used as physical exertion. Clenching during physical exertion was evaluated using Photoocclusion^TM(rocky mountain orthodontics).
The following results were obtained
1. Centric clenching was shown in fifty eight percent of the subjects during physical exertion.
2. Eccentric tooth contacts were shown in eleven percent of the subjects, but thirty one percent did not show any occlusal contacts during physical exertion.
3. Although there were individual variation, physical exertion had some effect to stomatognathic system.
Those results suggest that the stomatognathic system may play a significant role in the physical exertion.

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I spatulated dental stone with slurry water and mounted the cast on the articulator with that plaster. In consequence I had the following results.
1. Using slurry water mixed sediment and water (the top clean part) at the rate of 1:1, if I add water powder ratio, the vertical displacement of cast and upper frame was little.
2. Using slurry water mixed sediment and water at the rate of 1:2, the displacement was as little as the one at the rate of 1:1 in the high water powder ratio.
3. Compared 1:1 with 1:2, using high water powder ratio minimized the displacement.
Last time I reported, using low water powder ratio and bad liquidity plaster and moist cast, it get large setting expansion, and if not loading upper frame, it is hard to restore incisal pin to the original state of the incisal table. It is similar to use slurry water. Using slurry water with high water powder ratio, I get good precision compared with using usual plaster. Still more it is related to the shortening time of mounting cast, and to improve the efficiency of dental technical work.

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