New types of composite resins for crown and bridge were recently developed and put on the market. One of them is a highly filled hybrid resin (ESTENIA, Kuraray) including 92 wt% (82 vol%) of ceramic particles. It is claimed that the resin much improved in hardness and strength is available for posterior crown and bridge. The present study examined the wear behavior of this resin when opposed by tooth enamel by means of impacting-sliding wear test, comparing with three kinds of materials for posterior use, porcelain, Au-Ag-Pd alloy and restorative composite resin. A hemispherical upper specimen and a flat lower specimen were prepared with each of the material and tooth. The upper specimen made of each material dropped and slid on the lower specimen made of tooth, or vice versa, for 10,000 times under a given load of 500 gf in artificial saliva. The Knoop hardness number was the largest in porcelain and the next in tooth enamel, Au-Ag-Pd alloy, hybrid resin and restorative resin, in that order ; however, the wear resistance was not dependent on the hardness in this test. The combination of porcelain and tooth showed significantly severe wear in both the specimens. The observation of the worn surface aspects revealed that the superficial cracking of them might induce their wears. There were no significant differences in wear among Au-Ag-Pd alloy-enamel, restorative resin-enamel and tooth-tooth. The highly filled hybrid resin exhibited the mixed wearing modes of porcelain and restorative resin. The combination of highly filled hybrid resin and tooth showed larger wears than tooth-tooth but significantly smaller than porcelain-tooth, and the hybrid resin seemed to be more favorable than porcelain for esthetic posterior crown and bridge.

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We isolated the predominant indigenous bacteria from the saliva of non-immune rabbits. The presence of naturally occurring antibodies to the isolated bacteria and the induction of these antibodies were then studied. The bacteria in the saliva was identified as Staphylococcus lentus using a commercial identification kit, and found to have 1.5 (±2.2) × 10⁶ cells/ml and to account for 16.1 (±5.6)% of the bacteria grown under aerobic condition. The concentration of anti-S. lentus antibodies in the saliva of non-immune rabbits was higher than that of the other kinds of staphylococci in ELISA. In non-immune rabbits, the anti-S. lentus IgA antibodies in the saliva was higher than that in the nasal wash and the intestinal fluid, while the anti-S. lentus IgA antibodies in the saliva, the nasal wash and the intestinal fluid were similar in level. When the suspension of fluorescence-labeled isolated Sta. lentus cells in saliva was applied to palatine tonsil of rabbits, many spots of the fluorescence were found in the cortex of the tonsil. Weekly tonsillar application of 10¹⁰ isolated Sta. lentus cells in one ml PBS caused an increase in the concentration of anti-S. lentus IgA antibodies in saliva the and the IgG antibodies and IgM antibodies in the blood plasma. Even one week following the first application of isolated Sta. lentus, the antibodies in the saliva were found to have increased. The anti-S. lentus antibodies was induced by the application of 10⁸ cells or 10⁶ cells. The antibody level after six weeks of these applications was similar in level to that applied 10¹⁰ cells. The above results show that naturally occurring antibodies to the predominant indigenous oral bacteria were induced in the saliva of rabbits through the stimulation of the palatine tonsil.

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The orthodontic bonding characteristics were evaluated for the two types of orthodontic resin-modified glassionomer cements involving a chemical-activating cement (Fuji Ortho, GC) and a light-activating cement (Fuji Ortho LC, GC). Plastic, metal and ceramic brackets having individual irregularities for mechanical retention at their basal planes were bonded to tooth enamel with each of the cements. Their bond strengths were examined by means of shear and tensile tests and the fracture surfaces were also observed. The results obtained were as follows.
1. Both the cements showed no or little bonding to plastic bracket.
2. The bond strength between metal bracket and enamel was around 6 MPa in shear test and 5.5 MPa in tensile test. The fracture mode was cohesive failure in the cement, adhesive failure at the enamel-cement interface or their mixture.
3. When ceramic bracket was used, the tensile bond strength was significantly (p<0.05) larger than that of metal bracket showing complicatedly mixed fracture mode although there was no significant difference in shear bond strength between them. It suggests that the ceramic bracket may be favorable for tensile force bearing use.
4. In rebonding the surface retreatment with polyacrylic acid solution seemed to be one of the means effective for bonding.
5. There were little significant differences in bonding characteristics between the chemical- and light-activating cements used.
The foregoing results indicate that the resin-modified glassionomer cements may be desirable for orthodontic use on account of their reasonable bond strength satisfying the proposed values in service and rebonding so long as the proper bracket is selected.

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The purpose of this study is to examine how newly formed bone and degenerated periodontal ligament will react to orthodontic force in reversed tooth movement. After moving the maxillary first premolars in ten adult dogs with a continuous force of 100 grams in a distal direction for three weeks, the teeth were subsequently moved in a mesial direction for five days. Light and fluorescence microscopes, and microradiography were used for histological investigation.
On the pressure side, new bone created during distal movement was cancellous and not well calcified. In five days, the new bone was undermined from the numerous marrow spaces and was more readily resorbed than old one when it was subjected to pressure. On the tension side, there were extensive bone resorption on the periodontal surface and marrow space of old bone by osteoclasts, whereas hyalinized area still remained. When subjected to tension, the hyalinized tissue was extended and osteoclasts migrated away from Howships lacunae. However, resorptive process persisted in the marrow space up to five days. Mineralization was found on the stretched periodontal ligament at one and three days, and it disappeared at five days.
From these findings, we concluded that newly formed bone during distal movement will not resist against orthodontic force, because the reversed tooth movement will bring about comprehensive bone remodeling within the periodontal tissue. We must take into consideration that reversed tooth movement is likely to result in calcification or mineralization of the periodontal ligament.

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The purpose of this study was to compare the magnitude and direction of displacement that arose in two groups of complete dentures when occluding unilaterally test food ; those for one group (FD, FG and FL) were made by flange techniques, which are generally said as showing an excellent stability during non-occlusal function like laugh and speech, while those for the other group (A) were made according to the law of the interalveoler ridge line, which shows an excellent stability especially during unilateral occlusion.
Eight edentulous patients (male : 3, female : 5, age : 74.9±8.1) whose oral mucosa, the function of tongue and temporomandibular joints were normal, were used in this experiment, and the displacement of complete dentures were respectively measured by using measurement analyzing system in six degrees of freedom.
The results obtained were as follows :
1) By utilizing this measurement analyzing system in six degrees of freedom, behavior analysis of the complete dentures could be gained easily and with accuracy.
2) When unilateral occluding tightly test food, every lower dentures tended to move toward the balancing side and lower-backward, and upper dentures except for FD the working side and upper-forward. Only the FD directed to upper-forward direction, and the molar region of the balancing side to lingual direction, and the frontal position rotatively moved to the working side.
3) To evaluate stability of the dentures, vertical displacement of the upper and lower dentures were respectively measured at the first molar of the balancing side when occluding unilaterally. The result was A>FG>FL in the upper and the lower dentures, but the vertical displacement of the only upper FD could not be evaluated with accuracy because it showed remarkable rotation and unstable equilibrium. Lower FL and FG were significantly smaller than FD (respectively p<0.05, p<0.01), and there was statistically significant association (p<0.05) between upper A and upper FL, too.
4) Vertical displacement ratio to the denture A was only one from some 0.65 to 0.85 in upper dentures and 0.75 in lower dentures, although one of lower dentures for the flange technique (FD) showed twice the ratio of the denture A.
5) The denture A did not show the most excellent stability in unilateral occluding tightly test food. It was therefore suggested that the dental molar arrangement method according to the law of interalveolar crest line, which was used in daily clinic, would be necessary for improvement.
On the basis of the foregoing findings, the linguarized occlusion was proved most effective in order to insure more excellent stability of complete dentures constructed by the flange technique.

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The shapes and structures of teeth are associated with mastication and swallowing. Morphologically, the premolars may be regarded as “intermediate” or “transitional” forms between canines and molars. Lesions of the hard tissues, which might have been induced by occlusal force, are often observed on premolars, especially on first premolars. In the present study, therefore, the effects of the occlusal loading point and direction on the stress generation in the root cervical surface of maxillary premolar were examined using strain gages.
In the first experiment, the strains on the four root cervical regions involving buccal, palatal, mesial and distal surfaces were measured for extracted intact human maxillary first and second premolars when one concentrated load was applied perpendicularly to each of the prescribed occlusal surfaces. The compressive component of the load generally yielded axial shortening and barreling, and lateral bending toward the loading side. The strain values increased as the loading point located farther and outer from measuring area. It suggests that the shortening of the crown or outward shifting of occlusal contacts by attrision may have a risk of injuring teeth and periodontal tissues.
Second, a load of 7 kg was applied to epoxy resin models duplicating first premolars mesially in sagittal plane at an angle of -10, 0, 10 or 20 degree. In addition, the same experiment carried out for the columnar epoxy resin model. Excessive mesial inclination seemed to make the teeth bend to mesial direction and induce unusual tensile stress on the opposite side of the loading. It was confirmed from the finding that the cervical one-third exhibited a deep depression and the mesial concavity extends from the crown down to the root surface.
Third, a load of 7 kg was applied to the epoxy resin model on the 3 points (palatal cusp, mesial and distal marginal ridges) of the occlusal surface at the same time. The compressive strain became smaller than that in 1 point loading.
The foregoing results suggest that the imbalanced loading, even though the magnitude of the occlusal force is adequate, may give some effect on the teeth aspects, if the shape of teeth and the directions of loading are varied by attrisions. It is necessary to consider the configuration of teeth and the occlusal direction on this basis in the occlusal reconstruction.

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Amino acids in mammalian tissues and body fluids have been considered to consist solely of L-enantiomer. However, the recent studies have reported the presence of several free D-amino acids, exclusively D-serine (D-Ser) and D-aspartic acid (D-Asp), in mammalian tissues. D-Ser specifically exists in the brain and plays a genuine ligand for NMDA receptor. The high concentration of D-Asp was found in rat pituitary gland, pineal gland, adrenal gland and testis. These suggest that free D-amino acids may play some important roles in mammals.
The present study was arranged to investigate the occurrence of D-Asp in rat salivary glands by using a high-performance liquid chromatography technique. The concentration of D-Asp was high in the parotid gland (PG) (0.212±0.068μmol/g) and the submandibular gland (SMG) (0.233±0.034μmol/g) of 7-week-old rats, but the low in the sublingual gland (0.038±0.020μmol/g). A transient increase of D-Asp concentration was observed in 3-week-old rat PG. On the other hand, D-Asp content in the SMG was held at a high level in and after 7-week-old. These results suggested that free D-Asp may play different roles in rat PG and SMG.

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In order to investigate the mechanical effects of the design of osseointegrated dental implant on the surrounding bone, the present study adopted more realistic approach by 3D FEM for stress analysis. An osseointegrated, screw type implant for molar region was selected, and the standard model and modified models in which the cusp inclination was increased to 40°, the abutment inclination was increased to 20° or the occlusal plane was buccolingually expanded were constructed. The results showed that the alteration of the configuration of superstructure, the occlusal contact positions or the occlusal relief variously changed the aspects of the stress distribution. However, any arrangement of these factors could not drastically relieve the stress concentration at the marginal crest of interfacial cortical bone so long as the occlusal contacts were limited to two points. An additional contact on the distal fossa to form three-point occlusal contacts could significantly reduce the maximum principal stresses and relieve the stress concentration.
It was reconfirmed through the 3D FEM analyses that the proper design of superstructure, occlusal contour and balanced disposition of occlusal contacts would minimize the stress concentration on surrounding bone in centric occlusion, lateral sliding or mastication of foods and contribute to the good performance of implant restorations.

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Chewing movements were analyzed using mandibular movement analyzers ; Gnathohexagraph with some modifications and Syrognathograph, in order to restore appropriate occlusal morphology for chewing movements.
In addition to the analysis of subjects with typical chewing patterns, effects of occlusal morphology on chewing movements were studied by making occlusal adjustments, creating occlusal interferences, etc.
The results showed that there were two types of chewing movements, chopping type and grinding type, and that the latter consists of two subtypes, one with inadequate guidance and the other with no guidance.
The mandible was found to move backward and downward upon opening in chewing movements unlike border movements, resulting in occlusal interferences in the areas regarded as interference-free in traditional occlusion theories. The study also demonstrated that ICP was reached with a time lag between the right and left side rather than simultaneously on both sides. The study thus provided detailed information on chewing movements.
The results obtained in this study differed in several aspects from the existing occlusion concepts based on the observations and measurements made on mounted models, which may be attributable to the failure of articulators to accurately reproduce movements of the living system.

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