Structural changes of human dentin by brushing with several kinds of commercial dentifrices in vitro were observed with scanning electron and scanning laser microscopes. Their gel, fluid, and paste-type dentifrices for gingivitis, sound enamel, or sensitive teeth contained no abrasives, crystallized sodium chloride (NaCl) which has not been noted as abrasive, abrasive silica, or several abrasives containing silica. Automatic toothbrushing rotated two-dimensionally was performed on the tangential ground surfaces of the cervical sound dentin for 10 min. The brushing with dentifrice containing abrasive silica or silica-containing abrasives caused dentin abrasion although the abrasivity of dentifrice containing NaCl and fluid-type dentifrices containing silica was weakened, while most of their dentinal tubules were occluded. Similar data have been obtained in our previous study using paste-type abrasive dentifrices for sensitive teeth or nicotine removal. Under brushing with a gel-type dentifrice containing no abrasives for gingivitis, the abrasivity was significantly lower than that of abrasive dentifrices. However, the dentifrice caused all the dentinal tubules to open following the erosion of the peritubular matrix because the pH range was 5 to 6. Such a patency of the tubules will cause dentin hypersensitivity in a case of in situ. Therefore, one must be cautious about the abrasivity of NaCl as well as abrasive silica and also the pH range in dentifrice even if dentifrice has no abrasives, when the cervical regions of teeth exposed to the oral cavity are brushed with commercial dentifrice.

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This study determined the mechanical properties of seven interocclusal recording addition-type silicone rubber impression materials, namely, Exabite, President Jet Bite, Bitesil, Memosil C. D., Stat·BR, Mushprint and Express, and one polyether rubber impression material, Ramitec, which was contrasted with the addition-type silicone rubber impression materials. The strain in compression, the compression set and the dimensional change were measured according to American Dental Association (ADA) Specification No.19. The dimensional change was obtained at not only 24 h but 72 h after the start of mixing.
The strain in compression of interocclusal recording addition-type silicone rubber impression materials was smaller than that of the addition-type silicone rubber for impression. The strains in compression of Memosil C. D. and Express were larger than those of the other materials. The compression set and the dimensional change of interocclusal recording addition-type silicone rubber impression materials were the same as those of the addition-type silicone rubber for impression. The compression sets of Bitesil, Memosil C. D. and Ramitec were larger than those of the other materials. The dimensional change was not different from 72 h after the start of mixing. The dimensional change of Memosil C. D. was larger than that of the other materials, and the dimensional change of Stat·BR was smaller than that of Exabite, President Jet Bite, Bitesil and Memosil C. D.

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The change of the microstructure in a gypsum-bonded investment after heating was investigated by thermal analysis, x-ray diffraction analysis, compressive test, and SEM observation. Both thermal and x-ray diffraction analyses showed the binder CaSO₄·2H₂O changed to CaSO₄ after releasing water due to elevated temperature. SEM observation revealed needle-like crystals of gypsum with some cracks and contracting due to elevated temperature. Since the compressive strengths of heated materials up to 800°C were significantly smaller than those of set material, we suggest that change in the microstructure by dehydration lowered the strength of the mold. On the other hand, when there was no change in the x-ray diffraction patterns between 800 and 1,000°C, the SEM observation at 1000°C revealed that the needle-like crystals at 800°C disappeared and a fusion of the microparticles. Since the compressive strength of heated material at 1,000°C was higher than that at 800°C, we suggest that the sintering process strengthened the mold.

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One of the reasons for the excellent bone biocompatibility of titanium is the capacity of selective precipitation of very thin calcium phosphate film on the surface when immersed in neutral electrolyte solution. This capacity is influenced by the surface chemical conditions of titanium plates. The aim of this study was to evaluate the capacity of the titanium plates treated by wire-type electric discharge machining (EDM plates) with much thicker surface oxide films on the surface with the structure changing from TiO₂, TiO and Ti₂O gradiently. EDM plates and conventionally polished titanium plates as a control (P plate) were immersed in Hanks solution at 37°C for 30 days. Surfaces were characterized by XPS and FTIR and observed by a microscope. XPS revealed that the Ca/P value increased with increase in immersion time and reached to similar level on both plates. The binding energy of Ca and P indicated the presence of apatite like calcium phosphate. FTIR also indicated that the film on the P plate was apatite-like calcium phosphate. Microscopically, the surface of the P plate was covered with a uniform opaque thin film, and that of the EDM plate was covered with fur thicker opaque film with crystalline precipitation. Microscopic observation of the sectioned surface revealed the thickness of the precipitated film on the EDM plate was in the pm order and the P plate in the nm order. These results suggest the titanium plates treated by wire-type electric discharge machining promote the precipitation of calcium phosphate on their surfaces in electrolyte solution and have excellent biocompatibility with bone.

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Presently there are two types of root form implants, cylinder and screw, available for clinical application. The initial stability of implants after insertion into the prepared bone cavity is important to achieve osseointegration. The aim of this study was to investigate the mechanism of initial stability of root form implants, especially cylinder implants that were usually press-inserted into the bone cavity to fit clinical situations. The models of a typical cylinder and screw were analyzed by computer finite element analysis. The friction coefficient of the cylinder was fixed, 0-0.3. The gap between the diameter of the implant and that of the bone cavity was also fixed, 0, 10, and 20μm (diameter of implant ? diameter of bone cavity). Relative displacement between the inserted implant and bone under load was evaluated to understand initial stability.
In addition, stress produced inside bone around the implant was also evaluated. The results indicated that screw implants showed excellent stability even with a friction coefficient of zero and gap of zero. On the other hand, cylinder implants had worse stability under the same conditions. However, stability of the cylinder implant increased with the increase of friction coefficient and gap, and reached a similar level to that of the screw implant. Considering the internal stress produced in bone, we suggest to inserting a cylinder with a higher friction coefficient into the bone cavity, of which the diameter is prepared a little smaller than that of the implant. Therefore, the key of success to cylinder implants is the accuracy of bone preparation and the surface texture of the implant body.

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The accuracy of bone cavity preparation for the insertion of cylinder implants is an important factor to achieve clinical success in implant treatment. We developed a series of drills for the newly developed titanium cylinder implant system (IAT Fit II system) that consists of a pilot drill (1.6 mm), twist drill (2.75 mm), countersink drill (3.60 mm) and cannon drill (3.8 mm). The aim of this study was to evaluate machinability and cutting accuray of these drills. As a control, a twist drill, countersink drill, and cannon drill with the same dimension were prepared by a Japanese dental implant tool maker with conventionally available standards. We fixed drills to a compact machining center to prepare holes on an acrylic resin plate with a rotational speed of 1000 rpm, penetration of 100 mm/min and depth of 8 mm. The difference between the diameter of the drill and that of the prepared hole was evaluated as the cutting accuracy. We also detected the cutting force produced on the work with X, Y and Z axes and rotational direction using a cutting force device. We also machined aluminium plates with penetration of 20 mm/min to measure the cutting force. Measuring the cutting force was useful to evaluate machinability and cutting accuracy. Continuous usage of a series of drills was effective to improve machinability and accuracy. Among the tested drills, the countersink drill and cannon drill of the IAT Fit II system were superior to those from the control in both machinability and cutting accuracy. Especially, we suggest that the excellent accuracy of the cannon drill from the IAT Fit II system is promising for bone cavity preparation in clinics.

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The aim of this study was to evaluate the cutting efficiency and accuracy of the newly developed TiN-coated pilot drills (TiN drill) for bone cutting. Commercial drills for the same application, without TiN coating, were used as a control. We fixed drills to a compact machining center and machined holes on cast aluminium plates at a rotational speed of 1000 rpm, penetration of 20 mm/min and depth of 8 mm. We detected the cutting force produced on the work with X, Y and Z axes and rotational direction using a cutting force device. We repeated hole preparation 100 times with the same drill. We found that the TiN drill was excellent in cutting accuracy up to the preparation of 100 holes and in durability up to at least 90 hole preparations. On the other hand, the control was a inferior to the TiN drill in machinability and especially durability. SEM observation revealed gross wear on the edges of the control. These results suggest the composition of tool steel, TiN coating and the profile of the edge of the newly developed pilot drill contribute to excellent machinability and durability.

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We compared normal and deformed mandibular condyles in regard to structural changes in the articular components of the condyle using light microscopic and scanning electron microscopic techniques. Human adult bodies for anatomical dissection were used for this study. The normal condyle had articular components containing some zones : the condylar cartilage consisting of fibrous, proliferative, and cartilaginous zones and subchondral bony plate. The articular surface of the fibrous zone had undirectionally interlaced fibril bondles covered with irregularly oriented fibrils. Lumps interwoven with fibrils appeared on the articular surface in both normal and deformed condyles. In the rugged articular surface of the deformed condyle, convex portions coincided with chondroid tissue replenished on the subchondral body plate with partial thickening. Concave portions consisted of fibrous and subchondral body plate showing serrated contours in the uppermost surface. Subchondral bony plate showing serrated contour was also seen in the eroded articular surface of the condyle. The proliferative and cartilaginous zones lacked in these portions. The serrated contours appeared to be composed of many resorption lacunae by osteoclastic bone resorption. Articular remodeling is an adaptive change in the temporomandibular joint, and allows them to morphologically adapt to various biomechanical circumstances and functions. The structural changes present in the rugged or eroded surfaces of the condyle might be considered an adaptation process of articular remodeling.

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Relationships between the hand grasp force and occlusal pressure were investigated in young male adults during static teeth clenching and nonclenching. The hand grasp forces of left and right sides during static teeth clenching (L : 37.6±1.89 kg, R : 42.8±1.89 kg) were significantly greater than those during nonclenching (L : 35.7±1.16 kg, R : 40.5±1.06 kg). The findings indicated that the bite force influenced increase in hand grasp force.

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The purpose of this study was to investigate in three dimensions the differences in face form between Filipino females, who belong to Sundadont, and Japanese females, who belongs to Sinodont, using moiré Topography.
The Subjects were 70 adult Filipino females of ages 17-38 years and 70 Japanese females of ages 14-24 years.
The width, height and depth of each facial part were measured and statistically compared.
1. The Japanese females had a broad and long middle face and a long nose, whether relatively or absolutely. The Filipino females had long mouths, broad noses, and large and protruding lips. These lip features are also identified in the Negroid, and are thought to be an adaptation to Southern migration.
2. Though a few items were large in the right face, the left face was relatively large in the Japanese female. In the Filipino female, no items were large in the right face and most were large in the left face. There seemed to be tendency for the left face to be large in general, although there was some difference between the groups.

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