Ryozo Hirayasu

Radiograph stress measurement of metallic denture base formed by wire explosion energy. Part 2. Effect of cutting and spraying after formed by wire explosion energy.

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.

Stress analysis of posterior bridge. Case of abutment teeth with reduced periodontal supporting tissue. (Part II). Stress distribution of 3-dimensional finite element model and 2-Demensional finite element model on the single rooted tooth.

In the first report, the two dimensional finite element analysis was performed on the bridge model through a computer in order to learn the effect of such two factors as the resorption of the alveolar bone and the number of abutment teeth against the stress distribution of the supporting tissue of the brige whitch is subject to the occlusal force. Furthermore, the results of the finite element analysis under vertical load were compared between the three and the two dimensional models of single rooted tooth in order to study the relation between the threedimensional resorption state of the alveolar bone and the two dimensional model.The models used in study, however, were extremely simplified. Moreover, the periodontal membrane was not modeled and the influence of the lateral load was not considered. Based on these background, in this report, more practical three dimensional model was created including the periodontal membrane. In addition, two two-dimensional models of bucco-lingual and mesiodistal cross sections of three dimentional one were created.The loading direction and the degree of alveolarbone defect were varied by each model. The load was given vertically, bucco-laterally and lingual-laterally. Alveolar bone defect were three cases of 0, 1/3 and2/3 defect of the root length. The comparison of the results of the finite element analysis performed on the total of 18 cases and those of first report resulted in as follows.1. The periodontal membrane has stress breaking effect on the alveolar bone surrounding teeth.2. In the extremely-stressed part, the three dimensional model tends to show higher stress value than the two dimensional one.3. In the laterally loaded case, the load part generates tensile stress and opposite side, compressive stress around the ceavical part. Around the apical part, the two stresses are reversed.4. As bone defect progresses, the stress to be generated increases. For exsample, equivalent stresses generated atthe periodontal membrane in the vertically-loaded three dimensional model were 1.0, about 1.5 and about 2.3 in terms of 0, 1/3 and 2/3 defect respectively.

Radiograph stress measurement of metallic denture base formed by wire explosion energy. 1. Stress changes during various stages of manufacturing metallic denture base

The radiograph stress measurement method is the only known means of a non-destructive measurement, and this method is used to assess the residual stresses of various metals. This study was made to evaluate the possibility of radiograph stress measurement of the metallic denture base formed by the wire explosion energy. Radiograph stress measurements of stress changes during various stages of manufacturing metallic denture base were successfully obtained.

Chromatic studies of porcelain veneered crown. Influence of the dentin porcelain on the color of opaque porcelain fused on the metal substructure

The metals for porcelain fusing used in this study were gold alloys and nickel-chromium alloys. Chromatic characteristics were compared between samples of 0.1, 0.2 and 0.3 mm thickness. The dentin porcelain was fused on the opaque surface. Chromatic analyses were then carried out at each stage of 0.1 mm-incremental reductions of the dentin thickness starting from 0.5 mm. In conclusion, the metallic color was not sufficiently hidden by opaque porcelain 0.1 mm thick for both the gold alloy and nickel-chromium alloy samples. The metallic color was sufficiently hidden by opaque porcelain of 0.2 mm thick for the gold alloy sample but was not sufficiently for the nickel-chromium alloy sample.

[Non-destructive stress analysis of porcelain-fused-to-metal crown. 2. X-ray diffraction and radiograph stress measurement of various gold alloys for porcelain fusing].

Porcelain-fused-to-metal crowns though having a better aesthetic appearance, are admittedly inferior in strength, as compared with full cast crowns. We have used the X-ray stress measurement method that is the means of a non-destructive measurement, and this method is used to assess the residual stresses of various metals. X-ray diffraction examinations were made to evaluate the possibility of X-ray stress measurement of precious metals. Precious metal strips were then prepared to determine the change in the stress value during the porcelain firing process. The high compression stress produced by polishing was reduced by degassing. X-ray stress measurement of precious metals were successfully obtained.

Chromatic studies of porcelain veneered crown. Application of ceramco opaque porcelain

Chromatic characteristics were compared between the porcelain fused metal substructures using a gold alloy and a nickel-chromium alloy with or without superficially sprayed with gold alloy. From the stand point of the hiding efficiency for the metallic color of the substructure by opaque porcelain fusing, the gold alloy and the sprayed nickel-chromium alloy were superior to the nickel-chromium one as a metal for the porcelain-fused-to-metal crown. The likeness in color of the gold alloy and the sprayed one was also shown. As the conclusion, the application of wire explosion spraying technique which combines the advantages of the gold alloy and the nickel-chromium one appears to be quite useful for providing an excellent substructure for porcelain-fused crowns.

A Study of Marginal Shapes on Abutment Teeth of All Ceramic Crown

The purpose of this study is to investigate the influence of two marginal shapes of abutment teeth (shoulder type and chamfer type) on the toughness of all ceramic crowns, by means of finite element method and the model tests.The following results were obtained;1. Tensile, bending and shear strengths of the Cerestore materials used in the model tests were higher than those of conventional porcelain materials.2. In the model tests for breaking loads of all ceramic crowns, the models corresponding to abutment teeth with metal core showed higher effect than those corresponding to vital abutment teeth.On the marginal difference, the strength of full shoulder types were higher than those of chamfer types in the models corresponding to vital abutment teeth, while there was no significant difference between two types in the models corresponding to abutment teeth with metal core.3. Using finite element method, there was the heavy tensile stress around the loading point of all ceramic crown with vital abutment teeth, which approximated to tensile strength of Cerestore material, the value was approximately three times of that in abutment teeth with metal core.

Stress analysis of porcelain laminate veneers

For this purpose, the stress distribution produced on the porcelain and resin cement layer of prosthetic porcelain laminate veneer crown on upper central incisor, under the different loads were applied to the normal coverage portion and the incisal edge portion at an angle of 45° or 0° to the tooth axis, were estimated in the present study with respect to the shape of the abutment tooth for the laminate veneer crown, by means of finite element method as well as model tests.The results obtained were as follows:1. When the load force was applied to the incisal edge of abutment tooth covered over the incisal edge by porcelain, the tensile stress in the porcelain and the maximum shear stress at resin cement layer were most distinct.Furthermore load distribution was parrarel to the tooth axis, the highest tensile stress was produced in the porcelain.2. The maximum shear stress at resin cement layer were dependented on the sites of the prosities in resin cement layer rather than the amount of them.3. As for a model test, there was no risk of fracture of the porcelain under the load within 15 kg.

A compact system for analyzing mandibular movements with the application of an infrared sensor. Outline and precision of the system

We developed a compact system for analyzing mandibular movements with the application of an infrared sensor, and examined factors which affected e its precision in order to determine the precision numerically.The essential points were as follows;(1) We were able to pick out the following three factors which affected the system.(i) The distance between the LED and the infrared sensor (repressented as “L”)(ii) The angle formed between the axis of the LED and the axis of the infrared sensor (called the angle of “deviation”; component of X axis:θx, component of Y axis:θy)(iii) The rotation of the infrared sensor (termed the “rotation”:δ)(2) According to the regression analysis, under the condition that L (=Lo+ΔL: Lo=100.0mm) was in the range (90.0≤L≤110.0), the maximum errors of the X and Y axes components were both 0.04mm when ΔL was neglected.(3) Under the condition of the range (|θx|≤10° and |θy|≤10°), the standard error of the X axis component was 8.7 percent and that of the Y axis component was 9.7 percent.We were then able to determine that δ was zero in the sagittal view.(4)According to experiments involving trial and error, we could fulfill the requirements of 90.0≤L≤110.0mm, |θx|≤10°, |θy|≤10°, and δ=0°.(5)Under the conditions indicated above, the precision of this system was estimated to be 0.15mm.

[Non-destructive stress analysis of porcelain-fused-to-metal crowns (1). X-ray stress measurement and X-ray diffraction of gold alloys used for porcelain fusing].

Porcelain-fused-to-metal crowns, though having a better aesthetic appearance, are admittedly inferior in fitness, as compared with full cast crowns. As compression stress is applied to porcelain after firing, porcelain is prepared with a slightly lower thermal expansion coefficient than is metal. This contributes to an increased strength of porcelain, but disturbs the fit due to tension stress, under conditions of an inadequate thickness of the metal.The X-ray stress measurement method is the only known means of a non-destructive measurement, and this method is used to assess the residual stresses of various metals.X-ray diffraction examinations were made to evaluate the possibility of X-ray stress measurement of precious metals.Precious metal strips 6mm widetimes;18mm long were then prepared to determine the change in the stress value during the porcelain firing process. The high compression stress after both the specimens had been polished was reduced by degassing.X-ray stress measurements of precious metals were successfully obtained.