A study was made of interpulpal the rmal changes of various restorations, under the rmal irritations applied externally, with the use of a 2-dimensional steady state heart conductive analysis following the finite element method.
The results obtained were as follows:
1. No marked differences were found between the interpulpal the rmal changes of the inlay and amalgam restorations with the same cavity depth. Interpulpal the rmal changes of the metal crown were slightly higher than those of the natural tooth.
2. An insulation effect of cement bases in the inlay cavity was increased, as the cement base became thicker and the the rmal conductivity of cement became lower.
3. Secondary dentin 0.5mm in thickness was significantly effective for decrease of interpulpal the rmal changes.
4. A temporary resin crown and ZOE cement dressing in the inlay cavity provided a most favorable treatment for the protection from the rmal irritation.
5. When temperatures externally applied to various restored teeth were adjusted toward body temperature in 3°C-7°C, interpulpal the rmal changes of those specimens bacame favorable, as compared with interpulpal the rmal changes of the natural tooth.
6. The rmal irritation during desiccation was more, influential to the prepared teeth than during reversible hydrocolloid impression.
7. Marked interpuipal the rmal changes were found during polymerization of a temporary resin crown made by a direct method.

View full abstract

In prosthodontics, the discussion in recent years has been as to whether the occlusal position would be made to agree with what part of the jaw. It still remains controversial whether the occlusal position at the terminal hinge inter-occlusal position (to be referred to as t. h. i. o. p. in the following) is functional or will be subjected to changes, the problem requiring a further elucidation.
In the present study, therefore, the author was concerned with 4 subjects selected from those employed at Nihon University School of Dentistry, consisting of 3 males and 1 female samples who volunteered for the study, who were diagnosed as having the normal dental arch clinically, having the definite normal occlusal position (to be referred to as i. o. p.) and, further, who were found to have no abnormal findings in the oral cavity. With these carefully selected subjects, analytical observations were made as to the number of occlusal points, occlusal point surface and food masticating efficiency (rice grains) between i. o. p. before the occlusal adjustment and t. h. i. o. p. after the occlusal treatment. The data of observations were carefully compared and analyzed.
As a result of the study, the author arrived at the following conclusions:
1. Although there were observed some changes in the occlusal point in terms of t. h. i. o. p., there was seen no functional disturbance whatsoever as to the food masticatory efficiency.
2. For this reason, it may be concluded that the use of the above jaw position in prosthodontics has been academically confirmed.

View full abstract

The clasps, as retainers, are an essential component of removable partial denture and have various features dependent on the form of abutment tooth crown, on the relative position of teeth and of a tooth and its alveolar bone.
These clasps has mostly been manufactured by casting method for cast clasps or soldering method for wire clasps. Yet recently a new technique of simplifying laboratory procedures was introduced for making combination clasps and attachments: a technique of casting metal onto the wire, and, in effect, the wire is soldered to the metal (Cast-Soldering Method hence).
Studies of this Cast-Soldering Method, however, are comparatively fewer than those of microscopic observation of the microstructure and affinity of metals, and they need much to be studied.
The present author analyzed the joint area of combination clasps made by Cast-Soldering Method with the help of Electron Probe X-ray Microanalyzer, and examined the changes in metal composition for the purpose of ascertaining the influence on the joint area, of different wire length and features of embedding in the casting mass, the kinds of investment material, and mold temperature. He obtained the following results.
1. The factors that governed the tensile strength of 18k gold alloy by Cast-Soldering Method were the length and feature of embedding part, the kind of investment material, and mold temperature, with the interaction of investment material and mold temperature.
2. The factors that governed the tensile strength of Au-Ag-Pd alloy were the length and feature of embedding part, the kind of investment material, and mold temperature, with the interaction of the length and feature of embedding part and mold temperature, of investment material and mold temperature, and the interaction among the length and feature of embedding part, investment material, and mold temperature.
3. The tensile strength of the two kinds of alloy above examined increased, in the case of the length and feature of embedding: 4mm or L-featured embedding. The tensile strength also was found to increase, dependent on the kinds of investment material: Cristobalite and Real Vest; it also increased in inverse ratio with the mold temperature.
4. The analyses by Electron Probe X-ray Microanalyzer proved that the tensile strength of the joint area depended on the degree of interlocking of the surface of wire and casting body (a part of joints revealed the fused condition and the diffusion of Pt was ascertained).
5. The analyses by Electron Probe X-ray Microanalyzer indicated that the tensile strength decreased in proportion to the degree of fusion of the embedded dental gold (Pt-Au) wire, and when complete fusion was attained, the diffusion of Pt was distinctly observed.
6. The analyses of Electron Probe X-ray Microanalyzer indicated that the extent of Pt diffusion increased in proportion to the mold temperature and the melting temperature.
7. The above results indicates the necessity of cautions laboratory procedure because there exists more cases of interaction of factors in the application of Cast-Soldering Method to dental gold (Pt-Au) wire and Au-Ag-Pd alloy than to dental gold (Pt-Au) and 18K gold alloy.

View full abstract

Much, so far, has been reported on the amount of residual monomer in heat curing acrylic resin denture bases, which has supposedly undesirable influence on oral mucosa or on the physical properties of a denture base after curing. These reports, however, mostly have dealt with standardized models and few reported on the basis of casts clinically applicable. Further, in these reports, the methods of conducting examinations usually very in each student: ie. the methods of mixing and curing of monomer and polymer. Most of such models have simplified features, which, unfortunately, makes it impossible to make investigation of the difference in the heat emitted from resin, and also of the influence of different heat thus emitted, on the amount of residual monomer.
The present author examined the mixing methods of monomer and polymer by the use of generally employed eduntlos practice casts, which had been completed-from the arrangement of artificial teeth to flasking. This process was for the purpose of obtaining the same condition of the casts which had undergone identical process from mixing to filling of dough-stage resin. The amount of residual monomer and heat inside an acrylic resin denture base was measured on each cast by different curing methods and the following results were obtained:
1. The distribution of polymer size was examined among three kinds of resin-Acron, L-resin, and Hircoe-and a fact was obtained that the area of their distribution was less than 130μ. Acron had its most distributed area in from 60μ to less than 70μ, L-resin in from 20μ to less than 50μ, and Hircoe in from 50μ to less than 60μ.
2. After surveying monomer and polymer mixing methods of the three cases above mentioned, a tendency was observed that, in order to mix polymer more efficiently, mixing time should be 60 seconds rather than 30 seconds, and that in case of employing vibrators the amount of mixed polymer increased in proportion to the degree of vibration.
3. Most efficient mixing ratio of polymer and monomer (P/L ratio) varied from 2:1 to 2.5:1 in Acron and L-resin, and from 2.5: 1 to 3:1 in Hircoe.
4. Time duration necessary for reaching dough-like stage was about 20 minutes for Acron, about 15 minutes for L-resin, and about 8 minutes for Hircoe. Time duration after reaching dough-like stage was longest in L-resin, and next came Acron, Hircoe being shortest.
5. The author examined the changes in temperature of resin in curing process. With the flask submerged in the water 70°C or 60°C, the temperature of upper and lower dentume bases of the three kinds of resin tended to rise, first at the labial side of anterior area, next the buccal side of posterior area, and then at the lingual side of posterior area showed rise in temperature.
6. In the curing process of the upper and lower denture bases of the three kinds of resin, the elapsed time for the temperature inside the flask to reach curing temperature 70°C or 60°C-tended to be shortest in the labial side of anterior area, next the buccal side of posterior are, and then the lingual side of posterior area reached the temperature necessary for curing.
7. He next measured the residual monomer in the denture bases which had been completed according to two curing methods, one method being to submerge flask in the water 70°C in temperature for 90 minutes and then into boiling water for 30 minutes (70°C Curing Method hence), and the other to submerge flask in the water 60°C in temperature for 9 hours and then into boiling water for 30 minutes (60°C Curing Method hence). By 70°C Curing Method the amount of residual monomer showed in Acron to be between 0.44 and 0.46%, in L-resin between 0.35 and 0.36%, in Hircoe 0.73 and 0.86%; by 60°C Curing Method, the amount was in Acron between 0.26 and 0.30%, in L-resin between 0.23 and 0.27%, in Hircoe between 0.52 and 0.60%.

View full abstract