We investigated changes in masticatory performance during retention in Angle Class I crowding cases. The color-changeable chewing gum method was used to investigate masticatiory performance at four stages during treatment : debonding, and 1, 3 and 6 months after treatment. The color of the chewing gum was measured and transformed using the CIE-LAB coloring system. The values of a* were evaluated at each stage.
     We found that masticatiory performance increased up to 3 months after retention, but did not change after that.
     These results indicate that masticatory performance is stable at 3 months after retention in adult crowding cases.

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We used three-dimensional finite element analysis to investigate how the shape of the screw-type temporary anchorage device (TAD) affected stress distribution in the bone during removal. Two different shapes of titanium screws were tested. The simulated alveolar bone had 1 mm of cortical bone, with the remainder being cancellous bone. Finite element models were prepared for both the straight and taper type screws and torque loading during removal was im- parted on either the top of head or the top of the screw.
     The results demonstrated that the different TAD shapes and loading positions produced significantly different results. The taper type screw and gripping the top of the screw produced distinctly superior results. The shape of the TAD and how it is gripped are important factors for its safe removal.

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Temporary anchorage devices (TAD) have recently been employed for orthodontic treatment. I attempted to find the safest position for placing the screw-type TAD in the maxillary molar region. Using reconstructed CT images, I investigated the buccolingual and mesiodistal lengths of the interalveolar septums between the maxillary first premolar, second premolar, first molar, and the second molar. For the first and second molars, I measured the distance from the alveolar crest to the maxillary sinus. The results indicated that the safest position for placing a screw-type TAD was the interalveolar septum between the maxillary first molar and the second premolar at about a depth of 4〜6 mm from the alveolar crest on the buccal side, and at about a depth of 2〜6 mm from the alveolar crest on the palatal side.

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We used three-dimensional computed tomography (3 D-CT) to investigate differences in the amount of mandibular deviation and the position of the mastoid processes at the insertion of the sternocleidomastoid muscle in subjects who had jaw deformities with mandibular deviation. We measured the distance from the Frankfort horizontal (FH), frontal and sagittal median planes to the mastoid processes. We also measured mandibular deviation as the distance from the sagittal median plane to Me (Me deviation distance), the angle of the FH plane to Ag line (vertical mandibular deviation angle), as well as the angle of the sagittal median plane to Ag line (axial mandibular deviation angle). We calculated the ratios of the vertical, anteroposterior and lateral distances from each plane to the bilateral mastoid processes.
     Significant correlation was found between the Me deviation distance and the ratio of the vertical distance to the bilateral mastoid processes. Significant correlation was also found between the aial mandibular deviation angle and the ratio of the vertical distance to the bilateral mastoid processes. 0ur results suggest that in patients with jaw deformities there is a correlation between deviation of the mandible from the body axis and the position of the mastoid processes.

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We measured the maximum lip closure pressure of 295 elementary school children using a lip pressure gauge. The mean value and standard deviation were calculated for each grade. In addition, the same measurements were made for 36 elementary school children longitudinally from the second through the sixth grades.
     The mean values and standard deviations of maximum lip closure pressure for the children in the first through sixth grades were 2.5±15 N, 3.1±1.9 N, 47±2.3 N, 4.8±3.1 N, 7.0±3.3 N, and 7.9±4.2 N, respectively. For the longitudinal measurements, the figures were 2.9±3.1 N, 3.1±3.4 N, 4.8±3.1 N, 9.5±3.1 N, and 10.1±3.1 N, for the second through sixth grades.
     The results showed a gradual increase in the lip closure pressure with age, with the qreatest change seen between the fourth and fifth grades. These results suggest that the functional forces of the orbicularis oris muscle change during growth.

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I analyzed the stress distribution in bone during tooth movement using a new heterogeneously constructed three-dimensional finite element model. The results for the new model were compared with those of a model constructed homogeneously. Although the stress concentrated locally when it was applied on the conventional model, the stress was dispersed to the surrounding bone on the new model. These results indicate that the heterogeneously constructed three-dimensional finite element model is more suitable for analysis of stress distribution in teeth and supporting tissues than the model constructed homogeneously.

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We created periodontal defects on the palatal roots of rat maxillary first molars in order to examine the relation between Enamel Matrix Derivative(EMD) and type III collagen. EMD was applied on the defect which was created by removing bone after reflecting a gingival flap.
     The animals were euthanized at 1, 3, 5 and 7 days after the surgical operation. The periodontal defects were then observed using the reticular silver impregnation technique and immunohistochemistry for type III collagen.
     Application of EMD induced formation of eosinophilic substances in the clot of the periodontal defects. lt inhibited epithelial growth on the defect and precipitated production of type III collagen and cell growth. The type III collagen created a scaffold for migration of capillaries and cells. Findings on the fifth day after surgery when EMD had been applied were similar to those on the seventh day when EMD had not been used. These results suggest that EMD promotes periodontal regeneration and wound healing by enhancing collagen formation and suppressing epithelial growth.

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We evaluated the adhesive properties of composite resin to the pulpal side of dentin after endodontic treatment. Pulpectomies were done on extracted human teeth, and dentin surfaces on the pulpal side were treated with one of three medicaments used in endodontic treatment : EDTA solution (Smear Clean^® (SC)), NaOCI solution (Neo Cleaner^®)(NC)) or a mixture of formaldehyde and cresol (FC). The treated dentin was then coated with either Single Bond (SB), Mega Bond (MB) or tri-S Bond (TB), and a composite resin was applied.
     After the specimens were stored in water at 37℃ for 24 hours, they were trimmed into a dumbbell shape and the microtensile bond strength (μ-TBS) was determined. The obtained data was analyzed by Student's t-test and Scheffè's test (α<O.05). The debonded surface was also observed by SEM.
     The μ-TBS to the pulpal side of the dentin was significantly lower than that on the enamel side, irrespective of the medicament or bonding system. The bond strength tended to decrease as the exposure time to the medicament increased. With SB and MB, the remaining demineralized dentin was observed on the fractured dentin surface. We found that a shorter exposure time of the medicaments favored the bonding durability of the composite resin restoration to the endodontically treated teeth.

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We investigated primary cultured cells derived from three cases of follicular type ameloblastoma, in order to search for a new therapy for this disease. We used to immunohistochemical methods and reverse transcriptase-polymerase chain reaction (RT-PCR) to examine whether ameloblastoma-like cells treated with or without ratinoic acid and vitamin D₃ would differentiate.
    The primary cultured cells derived from ameloblastoma, spread in monolayers or double layers of ameloblastoma-like cells having nuclei that stained with hematoxillin. Proliferating cell nuclear antigen (PCNA) was observed in the perphery of the ameloblastoma colony. Ratinoic acid (RA) induced upregulation of the transcription level of amelogenin andenamelin mRNA. Vitamin D₃ (VD) induced upregulation of the translation of cytokeratin.
    These results suggest that the cells derived from ameloblastoma differentiate to more mature cells when induced by ratinoic acid and vitamin D₃.

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In order to clarify the role of stomatognathic function during physical activity, we investigated the occlusal contact and muscle activities of five healthy dentulous individuals during bench press of weights by simultaneously measuring dynamic occlusal contact area, occlusa force distribution, and electromyography. Measurement of muscle activity was conducted for the anterior temporalis, the masseter, and digastric muscles on the dominant-hand side. A custombuilt sensor sheet was used to measure the occlusal contact area and occlusal force distribution. These measurements were taken for each subject as he was instructed to clench as hard as possible and open his mouth as wide as possible. Mean maximum occlusal contact force, occlusal contact area and the mean envelope curve of the maximum electromyography signal were calculated as reference values (100%). After determining the heaviest weight that he could bench press (maximum weight), each subject was instructed to bench press different weights less than the maximum as quickly as possible after a light signal (switch). During each bench press, ratios for the temporalis, masseter, and digastric muscle activities were calculated relative to the maximum activity.
     We found that during bench press of approximately 95% the maximum weight, the expression of masseter muscle action potential exceeded 20% in all subjects. During bench press of less than 50% the maximum weight, the expression of temporalis and masseter muscle action potential was less than 10% in all subjects. We found that the muscle activity of the digastric muscle was comparable to that at maximum mouth opening. However, the occlusal contact as- sociated with maximum clenching was not seen in any of the subjects at any time during the study. The above findings suggest that during bench press of weight close to an individual's maximum capacity, the masticatory muscles coordinate to stabilize the mandible irrespective of occlusal contact.

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We fixed two appliances of 100μm and 2 mm height in five adults to produce occlusal interferences, and studied their influence on the function of the autonomic nervous system. We also attempted to understand the mechanism of the effect produced by the appliances.
     Autonomic nervous system function was measured by videopupillography. The experiment was performed under the two conditions of the mandible at rest and at maximum clenching with the appliances in place. We measured the initial pupil diameter and the maximum constriction velocity as parameters for function of the sympathetic and parasympathetic nervous systems. respectively.
    We found significant differences in the initial pupil diameter and maximum constriction velocity in all subjects between rest and clenching with the 2 mm interference. A significant difference was noted in the initial pupil diameter and maximum constriction velocity in only one subject between rest and clenching with the 100μm interference. Based on the above findings, we concluded that the 2 mm interference altered function of the sympathetic and parasympathetic nervous systems in all subjects. However individual differences were noted in the response to the 100μm interference, suggesting that not periodontal sensation but temporomandibular sensation affect function of the autonomic nervous system.

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We previously developed and reported the potential clinical application of a simple, rapid porcelain firing method for the production of copings that does not require special equipment or refractory casts. However, the production method described in that report was based on conventional methods, and had not been evaluated in detail. In this study, we attempted to optimize the production method. We evaluated the powder-liquid ratio, composition of mixed powder, taper angles on the axial plane, holding temperature at firing, and the relationship between the marginal space and firing conditions. We also examined changes in the crystal structure of lithium silicate glass created by the firing, the effect of the sintering conditions on the distance between alumina particles, and the bending strength of the crown at different stages of production. We found the optimal conditions for firing of the porcelain by evaluating the production processes. We were able to produce all-ceramic coping crowns with a marinal gap comparable with conventional coping crowns, and do this within a production time of 160 min.

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