Kazuhiro Mizukawa

Adhesion of composite to porcelain with various surface conditions.

This study evaluated the adhesion of composite resin to five different surface conditions of porcelain samples that were treated with three kinds of silane agents. Two of these were commercially available Porcelain Liner M and Tokuso Ceramic Primer, and one was an experimental agent. The commercially available silane agents gave high bond strengths without hydrofluoric acid etching, which gave the greatest roughness on the porcelain surface. One component of these commercially available silane agents was gamma-methacryloxypropyl trimethoxysilane, and the other was the carboxylic acid. As a result of the effective formation of siloxane bonds by mixing with acid solution, porcelain surface conditions did not affect the bond strengths.

Microbial Flora in Periodontal Pockets Involved with Occlusal Trauma.

The purpose of this study was to clarify the relationship between the frequency of Gram-negative anaerobic black-pigmented rods and periodontal disease-inducing occlusal trauma. The occlusal trauma group had a markedly higher level of gingival exudates and higher numbers of bacteria in gingival exudates than the normal control group. The rate of total numbers of bacteria against a definite amount of gingival exudates were found remarkably higher in all subjects with occlusal trauma than normal controls. Facultative anaerobes showed the highest frequency, in which the Gram-positive coccamount isolation rate of bacteria was predominant in all subjects. The frequency of obligate anaerobes increased in the group with occlusal trauma. The frequency of obligate anaerobic Gram-negative rods was observed to have no significant difference between occlusal trauma and normal control groups. All obligate anaerobic Gram-negative black-pigmented rods in the periodontal pockets isolated from patients with occlusal trauma and normal controls were identified with Prevotella intermedia by a biochemical test. Prevalence of obligate anaerobic Gram-negative black-pigmented rods isolated from occlusal trauma maintained a low level throughout the experimental period. These results indicate that alveolar bone loss in occlusal trauma may have no relation to obligate anaerobic Gram-negative black-pigmented rods.

A Core for Casting on One Peace Casting Dowel-Core.

The rebuilding abutment teeth with metal casting had been applied mainly for thesingle root teeth down to 1970. On the other hand, carbon rod, investment materials, and the split method by using the metal casting have been applied for the rebuilding abutment teeth of the divergent and multi-rooted teeth.On and after the 1970s, the study on the rebuilding abutment teeth of the multi-rooted teeth has been initiated to realize the practical application of the core for casting.Co-Cr, Cu, Ni-Cr, brass, Ni-Ag, and graphite were used for the preliminary examination, since it was difficult to get the prescribed material which was previously designed by the other researchers. But, the results from the combined method of these materials and the precise readymade post did not seem to satisfy the object of this study.6 years ago, it was easy to get the carbon steel by which the good fitness could be obtained in the combined method with ready-made post. The laboratory procedure on this technique was presented at the 42 nd meeting of Nihon University School of Dentistry by the author. Thereafter, the study on the development of the new materials was initiated, since it became difficult to get the carbon steel.The experiments by using some materials for this technique indicated that the stainless steel and Co-Cr plated with Cu had a good fitness to the post channel.

Three-dimensional Photoelastic Investigations of Bite Stresses on the Abutment Tooth, the Alveolar Socket and Plate-supporting Alveolar Ridge Bones.(Part 1)

The present study is concerned with a consolidated analysis through the photoelastic method of mechanical properties of physical stresses which are responsible for pathohystological changes on the abutment tooth, alveolar socket and plate-supporting alveolar ridge bones due to bite stresses when a partial denture is inserted in a patient. By the use of Epoxy resin B hardener 901 product of Ciba Company, Switzerland, the author constructed through a casting method of his own design study models which would fit intercalary denture (56 missing), one-side free-end denture (76 missing), as well as both side free-end denture (76 67 missing). On these models there were constructed one-piece cast denture bases and clasps of platinum-gold having an elastic coefficient of 12, 300Kg/mm2, on which dentures were completed with artificial porcelain teeth and resin gingiva. On the other hand, the upper jaws were made of hard plaster on which were planted artificial teeth made of cobalt-chrome alloy having an elastic coefficient of 12, 000Kg/mm2. When the upper and lower jaws were firmly mounted on the articulator in the position of centric and lateral occlusion, bite load was administered to them while they were placed in the stress freezing apparatus. Then, sections were prepared of the jaws and a three dimensional photoelastic analysis was conducted on them by means of photographic fringe method. As a result of these experiments, the following findings came to light.1) As regards bite load working on the abutment teeth, a stress concentration on a load point on the tooth crown, and a stress distribution on the tooth surface except the load point were observed. With reference to the roots and alveolar socket bones, stresses were dispersed by the stress braking action of the periodontium. Therefore, under these conditions the uniform load was obtained which gave little fatigue on the abutment teeth.2) When bite load was exerted on the single-rooted abutment teeth in the axial direction, there was produced an equilibrium between a load point on the crown and the root apex, and thus stresses were uniformly distributed all over the surface of root and alveolar socket bone. In case more than two stresses in different directions acted on one another and consequently in balance, the working center of force took place inside the dental substance of the root portion. The posion of the working center of force varied in terms of the direction, angle and size of stresses. As the working center of force acted as a fulcrum of inclination of the abutment tooth, a compression stress was distributed locally on the surface of the abutment tooth as well as on the alveolar socket bone surface in the inclined direction of the tooth.3) When bite load was exerted on the multirooted abutment teeth in the axial direction of the one root, an equilibrium was produced between a load point on the crown and the apex of the root. Moreover, when more than two loads were experted in different directions and they were in balance, the working center of force was produced inside the dental substance of the crown center portion. On the other hand, when more than two loads working in different directions were out of balance, the working center of force tended to be located inside the dental substance of the side portion of the crown on which a stronger stress acted, a compression stress being distributed locally on the surface of multiroots in the direction of that stress and the opposing surfaces of alveolar sockets and the inter-alveolar septum.4) As compared with the single-rooted abutment teeth, the multirooted abutment teeth had a larger surface to bear a stress because of inter-alveolar septum and, for this reason, a load on the alveolar socket bone becomes less. Also the resistance against torsion was correspondingly large.