Structural deformation and fracture analyses of complete dentures were made by use of a strain gauge. A variety of methods-brittle coating, photoelastic, strain gauge, finite element, and laser holography interference have been used to analyze dynamic movements in prostheses. Since strain gauge is very accurate and demonstrates linearity in stress vs. load, such gauges were used in these experiments.
Preliminary experiments were designed to study principal strain, maximum shear strain, principal stress, maximum shear stress, and surface strain at breaking point in experimental bite rim models. A fracture test for breaking strength in the experimental bite rim model was first carried out breaking occurred at a 127 kgf concentrated load. Next, rosette analysis of this model was performed using rosette gauges. Rosette analysis was done to determine various strain/stress parameters at the breaking point. Larger strain-stress dynamic movements appeared in the palatal than in the labio and buccal regions, with the largest deformation occurring in the molar and posterior palatal part upon median sagittal line. Rosette gauges were also concentrically arranged on the palatal area was done. The principal strain and stress were observed in the posterior palatal part of the median sagittal line; tensile strain and stress were much the same at right angles to the median sagittal line. Maximum shear strain and stress were observed in the same area on a large at the breaking point scale. Observations were made with strain gauges on surface strain along a single axis; large tensile strain was observed in the posterior palatal part of the median sagittal line.
Following the preliminary experiments using bite rim models, experiments were done using complete dentures. Firstly fracture testing at centric occlusion was done using uniformly distributed and concentrated loads. After this step, principal strain, maximum shear strain, principal stress, maximum shear stress, and surface strain at breaking point were measured and analyzed under a breaking load. Principal strain and stress were observed in premolar and posterior palatal area along the median sagittal line; tensile strain and stress were much the same right angles to the median sagittal line. And the maximum shear strain and stress were observed in the same areas on a larger scale. When a concentrated load was used, principal strain, maximum shear strain, principal stress, and maximum shear stress were also observed mainly in the molar and posterior palatal areas along the median sagittal line. The complete denture behaves like a shell structure which is subject to tensile stress and shear stress according to the membrane theory. It was concluded that deformation and fracture result from tensile and shear stress working in the median palatal region. Following rosette analysis, experiments were designed to measure the surface strain at breaking point by concentrated stress strain gauges using both uniformly distributed and concentrated loads. Dynamic movements in the posterior palatal region appeared to result from large tensile strain. It was concluded that initial destruction begins in this area. The tensile strain observed at the upper labial frenulum notch is thought to be a result of this palatal region tensile strain.
Evidence has been presented:
1) that deformation and fracture of complete upper dentures appears in the median palatal region
2) that initial destruction was caused by tensile stress and shear stress, and
3) that deformation and fracture progresses from the posterior palatal region foward to the upper labial frenulum notch.

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Study on the Bonding between Ni-Cr Alloys and Porcelain and the Fitness of Metal Coping to Metal Die.
The base metal alloys for porcelain firing have recently been used because of the increase in the cost of precious metal alloys. And also, these alloys were prefered in the mechanical strength.
The base metal alloys remain unknown problems in bonding between the porcelain and alloys. Furthermore, in the case of base metal alloys, the fitness of metal coping to prepared teeth are less than in precious metal alloys.
The purpose of this study was to investigate the element behavior at the porcelain metal interface after firing, and to measure bonding strength and the deformation of metal coping obtained by firing.
The results were as follows:
1. The bonding between Ni-Cr alloy and porcelain.
1) It was not concluded that roughness contributes mechanical interlocking or increse of reaction area from this experiment.
2) The segregation of Sn, Al was marked at the porcelain/metal interface.
3) Shear strength at the interface was not significant between Ni-Cr alloy and precious alloy.
2. The metal coping was considerably deformed by repeated firing.
3. The space for cementation of metal coping to metal die was 300-350μm at marginal shoulder, 35-60μm at labial side, 300-350μm at edge, 20-45μm at lingual side.

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The introduction of air-turbines has resulted in improved dental treatment and, consequently, the sitting dentistry has been designed and recommended in view of work simplification and the dentists' health. Studies and observations, however, are rare as to the influence of dentists' sitting positions on the external prepared abutment in crown and bridge procedures. The present paper was intended to evaluate the influence of the dentists' sitting positions on the abutment preparation of full cast crowns and then the author classified the sitting positions into two categories as follow:
1. Home Position (abbreviated as H. P.)
This dental treatment system arranges the dentist in a sitting position and the patient in a supine position and all the basic postures of a dentist is regulated exactly.
2. Random Position (abbreviated as R. P.)
This position allows the various sitting positions up to the maximum range and most dentists usually practise in this posture.
The author here studied the tendency of the upper left first molar prepared at H.P. of five dentists with clinical experiences of one to four years.
1) At occlusal surface, distobuccal and mesiolingual cusps were reduced deeper than the direction (1.3mm) of occlusal preparation, on the contrary the central pit had less reduction.
2) In four axial walls, particularly in the buccal and lingual grooves were reduced much shallower than the direction (0.6mm) in axial walls and the errors in depth were from half to one third of the direction.
3) In spite of the direction for the subgingival reduction (1.0mm), almost all the points were less than 1.0mm in depth. And clear outlines of the lingual margin became scarecely observable.
4) The convergence angles of each axial wall were larger than 3°, that indicated the cutting instrument's angle. And the lingual and distal walls on any abutment showed more inclination (15-20°).
5) In view of the regular depths of preparation, abutment preparation at H.P. attained its object except the convergence angles.
6) The increase of the number of the abutment preparations did not indicate morphological difference. While the total time to finish preparations decreased, the time to confirm the preparation tended to increase.
7) H. P. system, therefore, should be given more credits and popularity as one of the efficient methods to assure constant tooth preparation.

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Observing the effect of the anchor teeth on the masticatory function in full overdenture used “O'ring” stud attachment on bilateral mandibular canines, the author studied with the masticatory force and electromyogram at the same time. As the results of these studies, the author arrived at the following conclusions.
1. The masticatory forces were largest on the pickled radish. In foods, the largest masticatory forces were measured in 3rd period and the smallest in 5th. The antagonistic forces were smaller. The significant F factors were found for the food, the masticatory period, the interaction of them and the interaction between the side and the masticatory period.
2. According to the rhythm of masticatory force and swallowing pattern, the duration (D), the interval (I), and the term (T) were largest on the peanut. In foods, the largest rhythms were measured in 1st period and the smallest in 4th. The swallowing pattern was larger. Further, the ratio of the duration to the term (D/T) were largest on the peanut. The significant F factors were found for the food, the side, the masticatory period and the interaction of them.
3. As for the rhythm of electric discharge of masticatory muscles, the D, the I and the T were largest on the peanut. In foods, the largest rhythms were on 1st period and the smallest in 4th. The swallowing pattern was larger. However, the D/T showed the same values in mastication. The swallowing value was smaller. The significant F factors were found for the food, the side, the masticatory period and the interaction of them.
4. The integrated amounts of masticatory forces were largest on the ham. In foods, the largest values were measured in early period and the smallest in late. The significant F factors were found for the food, the side, the masticatory period and the interaction of them, but except the side and the interaction between the side and the masticatory period.
5. In terms of the integrated amounts of muscular activity, the largest values were on the ham. In foods, the largest values were measured in 3rd period and the smallest in 5th. The swallowing was larger. The significant F factors were found for the food, the side, the masticatory period and the interaction of them.
6. The integrated amounts of muscular activity required per unit of the integrated amounts of the masticatory forces were largest on the pickled radish. In foods, it's values were larger in early period and smaller in late. The swallowing was larger. The significant F factors were found for the food, the masticatory period and the interaction of them.
7. In numbers of masticatory stroke, the peanut were most. However, the significant F factor was not found for the food.
From these studies, it was given a suggestion that the full overdenture wearers masticate more efficiently and harmoniously than the full denture. It was estimated that the reasons were the rich sensation from the mechanoreceptor in periodontal ligament, the remaing the alveolar ridge and the improvement of denture stability and retention from the attachment.

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In recent years cast plates using high-fusing alloys like cobalt-chromium alloys are being used widely in clinical work for making removable partial dentures. This has been made possible though the development of highmelting dental casting method sustaind by the development and progress of dental equipment. The author, therefore, assuming the state of the inner surface of the clasps of the cast plates made of cobalt-chromium alloys and the surface of the mucous membrane, examined how the surface roughness of the investment materials will affect the surface of the cast plates in the process of its manufacture. The author further examined how sand blasting will affect the surface roughness of the cast structures.
As a result, the author has obtained the following information:
1. Among the three types of duplicating materials, a significant difference was found between the alginate impression material and the silicone base impression material, and also between the agar-agar impression material and the silicone base impression material. The silicone base impression material showed the lowest value.
2. The effect of the duplicating materials showed a similar trend on all of the three investment materials.
3. The surface roughness of the cast structures obtained by manual casting was about the same as that of the surface of the investment material models, but with the cast structures obtained by auto casting, the effect of the penetration phenomenon was stronger than that of the duplicating operation.
4. Where the roughness was marked, sand blasting treatment reduced the roughness, but with the surface having slight roughness, it increased on the contrary.
5. In the sand blasting treatment, the surface roughness of the cast structures became almost uniform after 2 to 4 seconds of blasting, showing 12-13μm under the ten-point height roughness scale.
6. The optimum conditions in the present experiment consisted of the use of silicone base impression material as the duplicating material, manual casting and 2-4 seconds of sand blasting treatment.

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