It has been reported that the fissures of rat molar teeth are apt to cause dental caries. In this study, we observed enamel lamellae in the fissures of caries-free molar teeth of rats, 2 and 4 weeks after birth, by transmitted light microscopy with decalcified sections and by scanning electron microscopy with EDTA-treated samples. Enamel lamellae were always present buccolingually in the fissure enamel. In unerupted teeth, the organic lamellae showing an intermittent structure were composed of the organic matrix, derived from ameloblasts and reduced enamel epithelium, occasionally with these epithelial cells. After eruption, the thin organic membrane of enamel lamellae was probably derived from saliva as well as the organic matrix formed during the enamel formation. The lamellae also contained oral microorganisms and fibrous structures, some of which were formed from microorganisms, under the widely opened fissures containing the deposits of oral microorganisms and diet remnants. Thus, we strongly suggest that such fissure lamellae of rat molar teeth are apt to become the passing point in the way to inducing the dentin caries.

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It has been reported that the fissures of rat molar teeth are apt to cause dental caries. In this study, we observed the fissure enamel in caries-free molar teeth of rats, 4 weeks after birth, by scanning electron microscopy with ground and fractured samples. On the fissure floors of first molar teeth, dome-shaped prism ends, which were slightly and clearly elevated, were observed, although the fissure floors of second molar teeth were scattered with incompletely prism-end pits in some dome-shaped prism ends. When the fissure enamel was compared with the other enamel regions, the hypocalcified areae, previously reported, showed a low microhardness and a low resistance to grinding. The enamel prisms, occasionally containing short crystals, had thin crystals in diameter with a smooth surface, and the prism boundaries showed a loose connection. Therefore, it is revealed that the fissure enamel shows a lower crystal density with a porous structure within and among prisms than the other enamel regions. Thus, we strongly suggest that the fissure enamel structure of rat molar teeth is apt to cause enamel caries and to become the passing point in the way to inducing the dentin caries as well as fissure lamellae.

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Sonography has recently been applied to studies concerning the central grooving of the tongue surface during swallowing.
The purpose of this study was to investigate the influence of bolus quantity upon the grooving of the tongue surface during swallowing using standardized scanning methods with a sono-graph.
Measuring regions were on a coronal plane passing through the distal surfaces of both right and left lower second premolar (5D), canine (3D) and first molars (6D).
We studied the quantitative features of grooving depth, grooving width, grooving duration and groove appearance and disappearance speed during swallowing.
The subjects were 12 healthy adult volunteers aged 19-31 years (average age of 27.5 years) with normal occlusion. They were given different volumes of yoghurt (2 g, 5 g).
The results obtained were as follows :
1) The mean value of grooving depth in every measuring regions when swallowing 5 g of yoghurt significantly increased as compared to the 2 g volume.
2) The width of central grooving in the 5D and 6D regions of the tongue when swallowing 5 g of yoghurt significantly increased as compared to the 2 g volume.
3) The grooving durations in the 3D and 6D regions when 5 g swallowing 5 g of yoghurt were longer than those when 2 g of yoghurt was swallowed.
4) The mean values of groove appearance and disappearance speed by increased bolus quantity did not show a significant difference in every measuring region.
In comparison of grooving speed with groove disappearance speed, the groove disappearance speed when swallowing 5 g and 2 g of yoghurt was significantly faster than the appearance speed in every measuring region.
5) The grooving depth in most subjects increased according to the increase of blus quantity, and one-half of subjects showed a change in depth, width, duration, appearance speed and disappearance speed.

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Methods : Oral movement trajectories were studied by monitoring orofacial movements during mastication to obtain basic data on masticatory capability. Eleven dentulous young adults chewed a color-developing chewing gum that becomes redder as it is chewed, with the intensity of the red color serving as an indicator of masticatory capability. Light-emitting markers that were recorded as reflective points with clear outlines when illuminated with infrared strobe lights provided trajectory data for the monitoring of orofacial movements at the following reference points : the modiolus (Mo), menton (Me) and incisal point (IP), which was represented by a point on a wire extending from the lower incisor teeth to outside of the mouth.
The subjects' facial markers were located and automatically tracked while chewing using six video cameras from six different perspectives, and the video data were collected using a datastation (VICON 370 Datastation, Oxford Metorics Ltd.). After every 20 masticatory strokes, the color of the chewing gum was assessed using a Chroma Meter (CR-300, Minolta Co.) with respect to degree of redness or a* value, which is one of the coordinates in the L*a*b* color evaluation system. The same piece of chewing gum was continuously chewed for a total of 100 strokes. Digitally recorded video data at the start of the first period (1F) and at the end of each period (1L-5L) were analyzed using a workstation (VICON 370 software), and three-dimensional (3D) maker trajectories were reconstructed. The results of photogrammetric measurements were analyzed using a 3D analyzer (Movias 3D, nac Co.) with reference to the following parameters : total length of the trajectory from start to finish (TL), distance between the start and finish of the trajectory (SL), TL to SL ratio (T/S), volume of the rectangular solid encompassing the entire trajectory (cubic range [Cub]), and the mean of the 3D angles created by differences in the direction of the preceding and subsequent trajectories for each measured time (TH).
Results : The time required for one chewing cycle and closing phase decreased geadually from 1F to 5L. Similarly, the Cub and TL of the occluding phase in both the IP and Me also gradually decreased, while the TH of the IP and Me increased. In the closing phase of the Mo, the Cub, SL, and velocity on the working side were greater than on the nonworking side, However, the T/S and TH on the working side were smaller than on the nonworking side. These findings indicate that as mastication proceeds, the range of orofacial movements in the closing phase becomes narrower and that all trajectories become smoother.

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The precise accuracy of a mica-containing commercial castable ceramic was evaluated by examining the reproducability of the apical morphology of the acryl pattern and measuring the discrepancy between the tapered cylinder master die and the caramic ring, which was prepared by experimental casting methods. The wax ring, 1.5mm in thickness prepared on a stainless die was, invested using a paper ring and a commercial phosphate bond investment (Maizoudon) mixed with various concentrations of the special liquid equipped in this material. In addition, adaptation of the ceramic ring produced by the die-investing technique using a magnesia-containing investment was evaluated.
The apical morphology of the acryl pattern was well reproduced on the ceramic when the apical angle was greater than 60 degrees. The discrepancy between the top surface of the ceramic ring and master die was minimized when the ceramic was produced using the investment mixed with the 75 and 50 vol% of the special liquid. It was concluded that this castable ceramic system still requires some improvements, especially in the step of reheating (ceraming) after casting because the ceramic ring is possibly distorted in this procedure.

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Recently, there is increasing the interest in the dental diseases of physically and mentally handicapped persons. The purpose of this survey was to learn the actual conditions of handicapped patients who were managed in our department of Showa University Dental Hospital and had permanent dentition.
The subjects consisted of 171 patients (average age, 18 years 4 months) who were mainly physically or mentally handicapped.
The mean DMFT of the subjects was 10.94, a relatively high score, but filled teeth occupied 88.7%. Mean DMFT was different by dental stage at first visit : Group I, who visited our clinic in the primary dentition stage, showed lower DMFT than groups II and III, who visited in the mixed or permanent dentition stage.
The patients who had the experience of treatment under general anesthesia showed high DMFT, but they already had high DMF (def) at first visit.
With patients managed over a long term, dental caries of permanent teeth had increased after III B stage, so a more effective approach seems to be necessary for patients in this stage.

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The use of free flap transfer has recently gained increasing popularity in reconstructive surgery to the head and neck regions. However, there are few clinicoanatomical studies of the neck. Morphometric investigation of the vessels in the neck region were carried out on 21 cadavers from the dissection room in order to gain more knowledge of the anatomy for microvascular surgery. Our results briefly :
1.The largest diameter (1.7 mm) was measured in the facial artery except for the external carotid artery.
2.The largest diameter (3.6 mm) was measured in the external jugular vein except for the internal jugular vein.
3.The longest arterial section (5.9 cm) was measured in the superficial cervical artery.
4.There were no significant differences between the diameter and length of the vessels on the right and left sides in the cervical and facial regions.
From these results, it was found that some of the clinicoanatomical considerations of vessels in the neck region which will form the clinicoanatomical basis for free flap transfer should be clarified.

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