This study was performed to evaluate the clinical performance of resin-bonded fixed partial dentures (FPDs) for various service periods. FPDs were divided into two groups: A, seated from 1982 to 1988 and B, seated from 1989 to 1996. The failure rate for each group was compared periodically, and the factors affecting the service period were considered. Group A consisted of 504 FPDs seated in 335 patients, whereas group B consisted of 331 FPDs in 275 patients.
The follow-up rate was 51% for group A, and 61% for group B. The failure rates after the specific service period observed in group B were 5% for 0-2 years, 9% for 3-5 years, and 22% for 6-8 years. The total group B failure rate was 9%, which was only one-fourth that of group A.
Two major factors were considered for improvement in the retentive rate of FPDs. One was decrease in original retainer design without retentive form. Specifically, the so-called Maryland retainer considerably reduced to less than 33%, while retainers with sufficient retentive structure such as proximal or incisal groove increased. The other factor was development of a new metal conditioner for noble metal alloys used in the majority of FPDs in group B.
The remaining problem to be solved was undoubtedly improvement in the survival rate after a longer service period.

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Immediately after development of composite resin, it was used not only as filling material but also as the core material. Clearfil core, which came on market in 1980, was widely accepted in dental practice, resulting in many failures because of insufficient bond strength to dentin.
Since then, high polymer science has made rapid progress, and now a lot of adhesive resin core materials are available with high bond strength to dentin. It is time to check the efficiency of these materials in practice.
In this study, each component and its mutual relationship of the composite resin core with prefabricated metal posts were examined. As a result, the resin core with prefabricated posts indicated the same bonding strength as the cast post and core. In addition, core resin could be used as luting materials with better bond strength than conventional adhesive resin cements.

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SiO₂ type glass ceramics (OCC), which educe mica and -spodiumen crystals, were developed in the 1980 s and clinically applied in 1986. On a commercial basis, some of the clinical failure cases developed, and since 1995, properties of the material and technique have been reexamined. OCC restorations are now cemented by Panavia 21, a luting agent.
Some of the main improvements of OCC to prevent failure are as follows: Currently used pellet type was changed to powder type and stabilization of the material was attempted. In the laboratory technique, polishing of OCC restorations, which has been done after ceraming, was done before ceraming, in the state of as-cast because processed micro cracks became obtuse angles or diminished. The crystalization schedule was examined, and a modified schedule was found to be useful for obtaining small, constant sized crystal grains.
Furthermore, applications of OCC to the artificial denture teeth or implant prosthesis and so on were discussed.

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Adhesive luting cement for restorative and prosthetic procedure has been used in our department since 1980 because its use was expected to contribute to decreasing the marginal leakage between tooth and prosthesis and resultantly increasing the longevity of teeth. In this study, the survival rate of resin and cast posts and cores, conventional crowns and bridges, and resin-bonded fixed bridges were investigated by the Kaplan-Meier method in randomly selected patients who had been treated in our department for 15 years from April 1982 to February 1997. The 15-year survival rates were 86.7% for resin posts and cores, 80.1% for full coverage crowns, 59.8% for bridges, and 59.8% for resin-bonded fixed bridges including early ones which showed a high frequency of dislodgment. The survival rate of resin-bonded bridge increased to 90.1% if it was refabricated. These results suggested that the use of adhesive luting resin contributed both to increasing the longevity of teeth and to conservation of abutment teeth.

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The purpose of this study was to investigate the condition of a magnetic attachment, Hicorex MD, inserted in the oral cavity. The materials used were investigation cards regarding 1719 teeth for 1123 cases, offered from 261 dental offices in Japan where the Hicorex MD was used from Nov. 1992 to Mar. 1994. The results were as follows:
1. As for sex, there were 459 males (695 teeth), and 616 females (945 teeth), and 48 unknown cases (79teeth).
2. As for the site of maxillary tooth, the most common was the canine, the second was the 1 st premolar, the third was the 2 nd premolar, and the fourth was the central incisor. As for the mandible, the most common was the canine, the second was the 1 st premolar, the third was the 2 nd premolar, and the fourth was the lateral incisor.
3. As for the side effects, 5 out of 1, 123 cases were reported. The substances were color change of the keeper, swelling, and erosion of the gingiva. Only these 5 cases had all of the side effects. These could have been caused by the abutment teeth themselves not the magnetic attachment.

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The purpose of this study was to examine the effect of heat denaturation of dentinal protein onadhesive strength. In this study, a model system for resin-impregnated layers (RILs) was proposed, andcompression test was tried in order to clarify the relationship between RIL and adhesion strengths. Bovineincisors were heated in 93+1°C water for 1 hr to denature the dentinal protein uniformly (heat-treated).Superbond (SB) and Panavia 21 (PA) were used as the resin adhesives. Heat-treated and untreated dentinswere powdered respectively, decalcified by hydrochloric acid, washed with distilled water, and dried. Dentinpowder thus prepared and resin adhesive were mixed, then specimens of 3 mm in diameter and 4 mm in heightwere fabricated in Teflon molds. They were allowed to set at room temperature for 24 hrs. Compressiontests were performed on ten specimens for each group. The compressive strength and elastic modulus weresubjected to the Student's t-test to determine the statistical significance of any difference. Compressivestrength of the heat-treated group was significantly weaker than that of the untreated group (SB: p<0.01, PA: p<0.001). The elastic modulus of the heat-treated group was significantly smaller than that of theuntreated group (SB: p<0.001, PA: p<0.01).

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The purpose of this study was to investigate the characteristics of tooth preparation and the relation among the evaluative criteria by applying multivariate analysis (cluster analysis, principal component analysis).
The results were as follows:
1. Cluster analysis showed that tooth preparation by the students could be classified into 3 clusters.
2. Principal component analysis of each cluster and examination of actual tooth preparations showed the following.
1) In the first cluster, the first component was related to “the quantity of occlusal reduction” and the second component was related to “the location of the margin” and “the width of the gingiva wound”.
2) In the second cluster, the first component was related to “the quantity of occlusal reduction” and the second component was related to “the balance of the quantity of occlusal reduction between cusps and fossae”.
3) The third cluster was singular, and principal component analysis could not be carried out.
3. Principal component analysis and the correlation coefficients between evaluative regions showed that the first cluster was characterized as being comparatively well-balanced and the second was imbalanced due to the increased amount of preparation.
4. This study suggested that a concrete guidance method for each cluster would enable educating students more efficiently.

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Recently, multimodal radiography system “Scanora^®” was introduced to Japan. Scanora is small enough to set in the dental office. In this paper, the images of the temporomandibular joint by Scanora were compared to images by multidirectional tomography.
It was possible to observe the morphology of the temporomandibular joint and joint spaces by Scanora. There were no differences of images between the multidirectional tomography and Scanora in most clinical cases.
These results suggested that the tomograms of the temporomandibular joint by Scanora can be used clinically.

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Postmenopausal estrogen deficiency results in bone loss (osteoporosis) in humans and experimental animals. The acute and significant loss of trabecular bone in the ovariectomized (OVX) rat provides a useful experimental model of postmenopausal osteoporosis. Five months after ovariectomy of 3-month-old female rats, the mid and distal femurs, maxillae, and mandibular condyles were dissected and processed for light and backscattered electron microscopic examinations. Net trabecular bone values of femurs in OVX ats showed significant loss of trabecular (but not cortical) bones compared to those in sham-operated controls. Net bone volume in the maxillae of OVX rats was similar to that of controls. In mandibular condyles, OVX caused prominent bone loss similar to that in femurs. Throughout the observations, active osteoclastic bone resorption was rarely recognized, presumably due to the fact that the rats had been in the statistic post-OVX phase. These results suggested that, in this animal model of postmenopausal steoporosis, the bone loss is more prominent in trabecular bone areas formed by endochondral ossification such asmetaphyses of femurs and mandibular condyles than cortical bone areas formed by intramembranous ossification such as mid-diaphyses of femurs and maxillae.

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Experimental studies on clinical use of removable partial dentures with a clasp that is rigidly supported by the abutment were conducted. In order to clarify the effects of denture-wearing, 108 cases of partial denture operation performed on 71 patients were followed up. The partial dentures included dentures with a cone-crown telescope, precision attachments, a conventional clasp, and a clasp rigidly supported by the abutment, as well as overdentures.
The results were as follows:
1. Of the cases examined, 25.7% were dentures with a cone-crown telescope, 31.9% were dentures with a clasp rigidly supported by the abutment, 17.7% were dentures with a conventional clasp, 12.3% were overdentures, and the remaining 12.4% were other types of dentures.
2. Problems were most frequently experienced in patients with 13-16 missing teeth, patients in groups B-1 and B-3 of Eichner's classification, and in patients with 7-8 or 1-2 occlusal contact sites.
3. Patients who wore dentures retained by a cone-crown telescope or conventional clasp experienced more problems than those who wore dentures retained by a clasp that was rigidly supported by the abutment.

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The color of laminate veneer crown is affected strongly by underlying cements. Therefore, if color of the mixed resin cements can be predicted, color resin cement is efficient to adjust the color of laminate veneer crown. The purpose of this study was to establish color prediction of cement mixtures based on the Kubelka-Munk theory. Absorption and scattering coefficients of monotone-opaque (OP), -light (L), -red (R), and -blue (B) shades were measured with white and black backings using a spectrophotometer (CASID 1). Then, reflectivity (R∞) of 1: 1 mixtures of OP+L, OP+B, and OP+R were predicted from the calculated coefficients of respective monotone values. These predicted values were compared with R∞ calculated from measured absorption and scattering coefficients of the mixed resin samples. The color differences (dE) between the predicted R∞ and measured R∞ were very small, and can not be clinically discriminated. In conclusion, precise prediction of mixed color resin cement was achieved. The color prediction of the cement is considered to be effective for color adjustment of laminate veneer crowns.

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This study was conducted to investigate how the sounds of TMJ movement were changed by TMJ loading. Sounds of TMJ movement were recorded by contact microphones in 7 normal subjects, and amplified with filtered bioelectrical amplifiers. The filter was a high-pass with a cut-off frequency at 40Hz and a slope of 6 dB/octave as an equalizer. Joint sounds and mandibular movements were simultaneously recorded on a data recorder. Sound recordings from two measurement sites in four different mandibular positions and three different speeds of jaw opening were set.
The results were as follows:
. Recordings made 20mm anterior to the average condylar position clearly caught the changing conditions of the TMJ.
2. Observing changes in the frequency was informative. It was desirable for the jaw opening speed to be slow or moderate.
3. Loading the front of the TMJ increased the high frequency of the sounds generated by TMJ movement. One method for diagnosing mild cases of TMD was considered to be to observe the range of frequencies between those of normal and abnormal subjects.

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Various attempts have been made to investigate what effects the constitutional elements of a partial denture have on the abutment teeth and how the difference in its design, retention and supporting method affects the abutment teeth. However, no analysis seems to have been reported as to the difference in the capacity of load that the abutment teeth have and the force on the periodontal tissues, which have different dental root shapes.
Therefore, the strain in the periodontal membrane of the straight root and curving root shapes were investigated by using the 3-dimensional strain gauge system. The results were as follows:
1. In both root shapes, the greater the load, the greater the strain on the periodontal membrane.
2. There was a difference in the value and direction of strain between straight root and curving root shapes. Furthermore, the strain on the curving root shape was greater than that on the straight one.

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The purpose of this study was to investigate the accuracy of interocclusal recording materials that reproduced intercuspation on mounting stone casts. A bridge type reference model, which could not maintain stable intercuspation without interocclusal records, was selected. The reference model was mounted on an articulator. Interocclusal records were taken on the reference model. The reference model could be separated from the articulator when interocclusal records were measured. For interocclusal records, which were made from PRESIDENT JET BITE, EXABITE, RAMITEC, Xantano, and NEW PLASTONE between the upper and lower reference models, the occlusal heights of the reference model on the left molar of the abutment side, anterior teeth, and right molar were measured using an IP-Checker. The PRESIDENT JET BITE, EXABITE, and RAMITEC elastic materials were studied to determine the influence on the recording range.
The results were as follows:
1. The occlusal height was higher for the left molar than the other sides when the recording range was the abutments; the occlusal height was higher for the left molar and the anterior teeth than for the right molar when the recording range was 1/3 dentition.
2. The occlusal height of the elastic materials was lower than the nonelastic materials.
3. The results suggested that interocclusal records made from addition type silicone rubber impression materials have the best reproducibility of intercuspation and a smaller recording range has greater reproducibility of intercuspation.

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The formation processes of the denture plaque and calculus were studied by means of transmission electron microscopy and EPMA. The dentures worn experimentally for 6 hours and 3 days and the dentures obtained from patients were used.
For the electron microscopy, the pieces cut from the dentures were embedded in Epok 812 after fixation, and the ultrathin sections were examined without staining. For EPMA, the cut pieces were immediately frozen in liquid nitrogen, and the freeze-dried sections were prepared and examined.
Amorphous electron dense materials appeared in the spaces between the loosely bound microorganisms on the denture surface at 3 days, although the denture plaque was not observed at 6 hours. The relatively high X-ray peak of calcium was detected from the plaque. The lamellated substance appeared on the surface of the denture from the patients, and the substance was heavily mineralized. The initial mineral crystals appeared along the plasma membrane of microorganisms, the intermicrobiol matrix, and the lamellated substance.
These results suggested that the denture plaque facilitates the calcium accumulation and the formation of the denture calculus is initiated by the intermicrobiol matrix, the cell membrane, and/or the lamellated substance.

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The purpose of this study was to examine the role of protein of human submandibular-sublingual saliva in the retention and stability of dentures. This study was performed by analyzing how changes in protein affect viscosity.
Submandibular-sublingual saliva samples obtained from 15 subjects, each with a healthy oral cavity and good general condition, were studied. A Kuette type rotary viscometer Low-Shear 30 (Contraves) was used to determine viscosity. The analysis of salivary proteins was achieved by combining microscale twodimensional SDS-PAGE with silver staining.
In high viscosity saliva, 44 protein spots were detected. These spots appeared in the range of pI 3.8-10.0 and estimated molecular weight of 15, 000-1, 000, 000. In low viscosity saliva, approximately 30 protein spots were detected. These spots appeared in the range of pI 3.8-10.0 and estimated molecular weight of 15, 000-1, 000, 000.
There was a significant correlation between the concentration of high molecular weight proteins with an estimated weight of more than 700, 000 and viscosity (r=071, p<0.01). High molecular weight proteins (with an estimated weight of more than 700, 000) were characterized into five groups to the isoelectric point. The two groups (more than pI 7.0 and pI 4.1-5.1) showed significant correlations with high viscosity of human submandibular-sublingual saliva (r=0.73 and p<001 for both groups).

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The purpose of this study was to examine the role of protein of human submandibular-sublingual saliva in the retention and stability of dentures. This study was performed by analyzing how changes in protein affect viscosity.
Submandibular-sublingual saliva samples obtained from 15 subjects, each with a healthy oral cavity and good general condition, were studied. A Kuette type rotary viscometer Low-Shear 30 (Contraves) was used to determine viscosity. The analysis of salivary proteins was achieved by combining microscale twodimensional SDS-PAGE with silver staining.
In high viscosity saliva, 44 protein spots were detected. These spots appeared in the range of pI 3.8-10.0 and estimated molecular weight of 15, 000-1, 000, 000. In low viscosity saliva, approximately 30 protein spots were detected. These spots appeared in the range of pI 3.8-10.0 and estimated molecular weight of 15, 000-1, 000, 000.
There was a significant correlation between the concentration of high molecular weight proteins with an estimated weight of more than 700, 000 and viscosity (r=071, p<0.01). High molecular weight proteins (with an estimated weight of more than 700, 000) were characterized into five groups to the isoelectric point. The two groups (more than pI 7.0 and pI 4.1-5.1) showed significant correlations with high viscosity of human submandibular-sublingual saliva (r=0.73 and p<001 for both groups).To standardize the reproducibility of the color of composite resin, the color range and tendency of photopolymerized composite resin were investigated. The color of single and multiple layer A 1 and A 3.5 were compared and analyzed using the L*a*b* color system. The results were as follows:
1. The color range of the single layer photopolymerized composite resin was Opaque: L*=73.78 to 84.50, a*=0.47 to 4.01, and b*=11.96 to 19.59; Dentine: L*=50.47 to 63.95, a*=-3.75 to -1.68, and b*=-2.65 to 6.92; and Enamel: L*=38.02 to 42.33, a*=-1.67 to -0.51, and b*=-14.56 to -12.49.
2. The color of triple-layer resin measured by L* and a* decreased when the thickness of dentine was increased from 0.4 mm to 1.0 mm and that of enamel was increased from 0.1 mm to 0.3 mm. However, the color of A 3.5 measured by a* was high when the thickness of enamel was between 0.1 and 0.2 mm. H^ab° fluctuated within the YR and Y range in A 1 and within the YR range in A 3.5.
3. The thickness of resin that is required for color expression in triple-layer photopolymerized composite resin was more than 0.6 mm of dentine and more than 0.2 mm enamel in A 1, and more than 0.6 mm of dentine and more than 0.1 mm of enamel in A 3.5.

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