We tried to improve the color, surface hardnesses and wear resistances of titanium and titanium casting irradiation with pulsed and continuous wave YAG lasers in a nitrogen gas atomosphere. The effects on formation of the TiN layer were investigated for various irradiation conditions, such as device selection, type of fiber, speed of the specimen, and defocused distance. We found that the surfaces of pure titanium and titanium casting were discolored to a golden color by laser irradiation. Irradiation by the YAG laser produced TiN crystals on the surface of the titanium and titanium castings. A TiN layer was observed on the surface and a nitrogen-rich α-titanium layer was found under the TiN layer. Irradiation by the continuous wave laser formed a thicker TiN layer than irradiation by the pulsed laser. Use of the GI-fiber formed a deeper TiN layer than did the SI fiber. Decreasing the speed of the work table increased the width and depth of the TiN layer. In the case of Ti castings, some elements from the investment diffused into the fusion zone.

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I investigated whether differences in occlusal support position affect the craniofacial growth pattern in the rat. Two hundred and four 3-week-old male F344/Jcl rats were randomly divided into three groups. Group A (n=72) served as the anterior occlusal support group, where the vertical dimension of occlusion was raised 1mm at the maxillary first molar, group P (n=72) served as the posterior occlusal support group, where the vertical dimension of occlusion was raised at the third molar, and group C served as controls (n=60). Raisting the occlusion was carried out at 5 weeks of age, when eruption of the third molar is complete. Skull morpholgy, and dry weight of the masticatory muscle were observed and analyzed statistically using EXT-T procedures of multiple comparison cross-sectionally at 7, 9, 12, and 15 weeks of age.
      Cephalometric results showed the facial type was hyperdivergent in group P whereas it was hypodivergent in group A. These changes were due to rotational changes in the viscerocranqum (p<0.001) and mandibular ramus (p<0.001). However, dried masticatory muscle weights were not significantly different between groups A and P. These results indicate that the occlusal support position influences the rotational growth pattern of the rat face. This may result from functional pressure on the temporomandibular joint.

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I investigated nitride Ti plating by yttrium aluminum garnet (YAG) laser irradiation in nitrogen atmosphere. Ti nitriding treatment of dental prosthesis by ion-plating and furnace heating has been used to improve esthetics and the biocompatibility. The disadvantages of these surface treatments is that they have a thin nitrided layer, long plating time and unlimited treatment area. Using X-ray defractometer tests, surface roughness, Vicker's hardness, wear resistance and the three point-bending test, laser nitrided specimens were compared to those obtained by ion-plating and furnace heating. All treatments resulted in the appearance of a gold color to the naked eye. X-ray defractometer tests revealed Ti and TiN peaks for laser nitriding and ion-plating, while furnace heating produced Ti₂N peaks. The surface of laser nitrided Ti specimens was rougher than that of pure Ti processed by sand-blasting. The laser nitriding technique was better than the others in terms of Vicker's hardness and wear resistance. The three point-bending test created cracks in all specimens.

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I studied three-dimensional masticatory forces in humans while they chewed test foods of various textures. Measured amounts of beef jerky, peanuts, raw apples, boiled fish paste, sponge cake and cheese were used. Forces were measured using a small sensor on one of the mandibular first molars while electoromyograms were recorded for both masseter muscles. The data was analyzed by a masticatory force analyzing system developed for this experiment. Analyses were done for each element of force, the resultant masticatory force, impulses of these forces, electoromyograms of the masseter muscles, and combinations of all of these factors.
      I found that the texture of the food influenced masticatory force, which was modified in response to changes in the condition of the food between the occlusal surfaces.

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I investigated effects of the inhibition of unilateral craniomaxillofacial growth on the condyle in 80 male Wistar rats. A spring appliance made of orthodontic wire was inserted in the left infraorbital fissure of the maxilla and occipital bone at 5 days of age, and the rats were sacrificed at ages 4, 6, 10 and 15 weeks. Effects on the condylar cartilage were examined by histological and histometric methods.
      The craniomaxillofacial complex and mandible shifted to the left in the experimental group. Thickness and chondrocyte density of each cartilage layer of the temporomandibular joint decreased with age in the control group and in the anterior region of the experimental group. Thickness of the intermediate and hypertrophic zones and the total thickness of all layers in the central region on the left side (shift side) were greater than those of the controls. Thickness of the hypertrophic zone and the total thickness of all layers in the posterior region on the right side (non-shift side) were greater than those in the controls. In the later stages, cartilage matrix metachromasia was clearly observed in the central region of the shift side and in the posterior region of the non-shift side.
      Sagittal inhibition of the craniomaxillofacial complex on the left side resulted in superior acceleration of condylar growth on the left. Since the craniomaxillofacial complex shifted to the left, posterior growth of the condyle was accelerated on the right side.

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Using electromyograpy, I evaluated the adaptation of patients to recently placed dentures. Electromyograms (EMG) of the bilateral anterior temporal and masseter muscles were recorded in five patients together with mandibular kinesiograph (MKG) motions during mastication at the time of insertion of new dentures and for four weeks thereafter. The same recordings were made for patients who had dentures that had been in use for some time. EMG bursts during mastication were recorded before and after tooth contact, and duration and integrated values were measured. The results suggested that EMG time parameters and burst activities were effective factors in evaluating patient adaption to dentures.

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I studied three-dimensional masticatory forces in humans while they chewed test foods of the various textures. Measured amounts of beef jerky, peanuts, raw apples, boiled fish paste, sponge cake and cheese were used as the test foods. Forces were measured using a small sensor on one of the mandibular first molars while electoromyograms were recorded for both masseter muscles. I found that the texture of the food influenced masticatory force which was modified in response to changes in the condition of the food between the maxillary and mandibular occlusal surfaces.

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In order to elucidate the effect of basic fibroblast growth factor (bFGF) on the healing process after tooth extraction, I investigated the localization of bFGF, FGF-receptor (FGF-R) and alkaline phosphatase (ALP) activity, and studied new bone formation in the socket by laser scanning microscopy (LSM). Angiogenesis with intense localization of bFGF was initiated three days after extraction and new bone formation was evident by LSM after 7 days. Localization of ALP activity and FGF-R increased gradually with time from the socket bottom toward the surface. These results indicated that the greatest decrease in bFGF result from consumption by fibroblasts, followed by consumption by endothelial cells and osteoblasts in that order. In other words, the amount of FGF-R tended to increase, along with increasing ALP activity. After that, osteoblasts promoted bone formation.

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We studied the radiographic characteristics of 71 odontogenic keratocysts (OKC) from 65 patients (44 males and 21 females). The peak incidence was in the third and fourth decades of life, and the occurrence in the mandible was 1.6 times more common than in the maxilla, with the mandibular molar-ramus region being the most common site. Radiographically 65% of the OKC appeared as unilocular radiolucencies with smooth margins, while 22% were unilocular with scalloped margins and 13% exhibited a multilocular appearance. Most of the OKC were lined by parakeratinized epithelium, but a few lined with orthokeratin were also observed.

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Acid treatment prior to dentin bonding is believed to cause structural changes in the dentin surface collagen. I attempted to elucidate this chemical change using IR and NMR spectrometers. The IR spectrum obtained after treating collagen with phosphoric or hydrochloric acid indicated a decrease in absorption based on the vibration of the secondary amido N-H. This suggests a cleavage of the peptide C-N bond containing a glycine or alanine N terminus. The NMR study using a collagen model, i.e., (Pro-Pro-Gly)_5, strongly supported the above result.

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I investigated the effect of positional differences in the center of occlusal force on the craniofacial growth in rats. Two hundred and four 3-week-old male F344/Jcl rats were divided into three groups. The vertical dimension of occlusion was raised 1mm at the first molar in group A, and 1mm on the third molar in group P, while group C was untreated controls. At 15 weeks of age, cephalometric analysis showed a hyperdivergent facial type in group P and a hypodivergent type in group A. The mandibular condyle in group P was smaller and rounder than in group A. The weight of the masticatory muscles was not significantly different. These results indicate that occlusal position influences the rotational growth pattern of the face in rats.

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I investigated changes in the periodontal ligament (PL) blood flow after application of external forces on the maxillary canine of adult cats. The blood flow was measured by a laser Doppler flowmeter at five points each on the mesial and distal of the root when force was applied in the mesial direction. There were significant changes in the mean blood flow at all measurement points after application of the force. However, there were no significant changes in the blood flow wave forms except in the most cervical region on the mesial of the tooth. This indicates that blood vessels in the most cervical region of the PL on the compression side were subjected to forces exceeding their capacity to adapt.

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I investigated Ti nitride plating by yttrium aluminum garnet (YAG) laser irradiation in a nitrogen atmosphere. The results were compared to those obtained by ion-plating and furnace heating. Although all treatments resulted in the appearance of a gold color to the naked eye, color measuring instruments revealed minor differences. X-ray defractometer tests revealed Ti and TiN peaks for laser nitriding and ion-plating, while furnace heating produced Ti_2N peaks. The laser nitriding technique was better than the others in terms of Vicker's hardness and wear resistance. Three point-bending created cracks in all specimens.

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I attempted to establish an objective diagnostic method for occlusal splint therapy using the pressure pain threshold (PPT) measuring system, which records signals on the muscles of mastication. Pressure sensors were placed on the skin over the muscle and the subject instructed to release pressure when he felt pain on clenching. Values were recorded for 340 normal subjects between 15 and 77 years of age and four CMD patients before and after occlusal splint therapy. Although all the CMD patients had PPT valves outside normal ranges before treatment, they were within normal intervals after treatment. The PPT measuring system produced objective information on the effect of occlusal splint therapy.

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I studied the influence of occlusal vertical dimension on the muscle fiber conduction velocity (MFCV) and muscle fatigue in the human temporal and masseter muscles of six normal subjects between 22 and 30 years of age. The vertical dimension of occlusion was changed from the intercuspal position to a maximum opening of 21.0mm using three different occlusal splints. The subjects were asked to fatigue the muscles by contracting at each occlusal vertical dimension. EMG responses were evoked by electrical stimulation, and the EMG signals were detected by a linear array of surface electrodes placed along the muscle fibers. The MFCV was calculated from the time delay between adjacent EMG signals. I found that the higher the vertical dimension of occlusion, the lower the MFCV. In addition, at a given vertical dimension, the greater the muscle fatigue, the lower the MFCV. The endurance time also decreased with increases in vertical dimension. These results indicate that vertical dimension is an important parameter in the propagation velocity of action potentials and in the development of static muscle fatigue.

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I studied whether splinting of healthy teeth affected the viscoelasticity of the periodontal tissue. Teeth were splinted either with each other or with tianium IMZ implants. The splinting device did not affect occlusal contacts and could be removed by the operator. Horizontal mechanical mobility of the individual teeth and implants was measured over a period of about two months with an automatic diagnostic system. I found that when the difference in tooth mobility between two teeth was large, this difference was decreased with splinting. There was a greater percentage change in the mechanical mobility of teeth that initially had smaller mobility than was the case for teeth that initially had greater mobility. However, the mechanical mobility of teeth did not decrease significantly after splinting with implants.

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We investigated the EMG profiles of masticatory muscles in orthognathic surgery patients with mandibular prognathism during gum chewing. Vertical jaw movement and EMG activities from the bilateral anterior temporal, the masseter and the anterior belly of the digastric muscles were recorded simultaneously in 12 healthy adults and 12 patients. Normalization was achieved by setting the mean value of each EMG over the chewing cycle to 100%. The degree of similarity and time lag for each EMG profile between normal subjects and patients were investigated using the cross-correlation technique. The EMG profiles for the normal subjects were similar in shape and had little time lag. However, on the working side the profiles for patients were similar in shape but had considerable time lag. On the non-working side, the shape was not similar, but there was no time lag.

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Prevotella intermedia strain E18 possesses non-fimbriated hemagglutinin that is closely related to pathogenicity. We found several strains subcultured from strain E18 (1801, 1802 and 1803) that lost the ability to produce black pigment on blood agar plates. We examined the pheno- and geno-typic characteristics of these strains. Non-black pigmented strains showed similar phenotypic characteristics with the parent strain, including production of hydrolytic enzymes and hemagglutinating activity. Cell suspensions of each of these strains reacted with antisera against vesicles (hemagglutinin) from strain E18. SDS-PAGE revealed that the protein patterns of all strains tested were quite similar. Bacteriophage similar in morphology and size were induced in these strains after irradiation by ultraviolet light. These results indicate that 1801, 1802 and 1803 are mutants derived from strain E18.

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