Temporomandibular joint disc, located between temporal bone and mandibular condyle, consists mainly of collagen fibers and proteoglycans constrained in the interstices of collagen fiber mesh. These components result in a viscoelastic characteristic of the disc and enable the disc to play an important role as a stress absorber during function. The viscoelastic properties depend on the direction, magnitude, rate and type of the applied loading. In addition, these properties change as a result of various intrinsic and extrinsic factors in life such as aging, trauma, and pathology. Information about the unique behavior of the disc is required for tissue engineering of the disc. In this review, I introduce the biomechanical behavior of the disc in response to various biomechanical environments and discuss the possibility of a suitable TMJ replacement and disc tissue engineering.

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In 1960s, several regimes for the joint lubrication were proposed. In 1980s, they were integrated in the multimode lubricating mechanism containing the fluid film lubrication and the boundary lubrication. Our recent study using a robotic system for the measurements of joint friction showed that there is none of boundary lubricating effect in joint mechanics.

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‹Objective› The objective of this study was to investigate the relation between the length a dental implant was embedded in bone and its mobility in two different models, one with cortical anchorage and one without.
‹Methods› Two dental implant models were made, one with cortical anchorage and one without. The implants were made of brass cylinders with a diameter of 4mm, which were embedded vertically 7, 9, 11, 13, 15 and 17mm into a resin model of bone (70 × 70 × 40mm) . The surfaces of the implants were treated by sand-blasting with glass beads (75pm) . The part of cortical bone was made of resin (Araldite^®) . The layer of cortical bone was 2mm in thickness. The part of cancellous bone was made of different resin (Rigolac^®) . Three models were made per each condition. The dental implant models were fixed under the same condition by using a vise. IM score was measured in a horizontal direction by means of IM checker. Parametric comparisons of IM score used two-factor analysis of variance. Significances of individual differences were evaluated by using the Tukey-Kramer test if ANOVA was significant.
‹Results and discussion› About models without cortical anchorage, no significant difference was observed among data of 13, 15 and 17mm. About models with cortical anchorage, no significant difference was observed among data of 11, 13, 15 and 17mm. Additionally, IM scores of models with cortical anchorage were less than those without significantly (p<0.01) .
‹Conclusions›
1. The IM checker could quantify the mobility of dental implants which had various embedded lengths.
2. Cortical bone was very important for implant stability.
3. The embedded lengths which did not change IM score significantly were observed.

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It is necessary to observe all processes from food crushing to formation of swallow-able food bolus in order to evaluate the whole masticatory function. Many researchers reported various evaluation of chewing function. But, most of these reports discussed only the evaluation of crushing function. Therefore, this study is designed to develop a method to evaluate the masticatory function including bolus formation.
The bolus formation is thought to be related to two functions, one is the saliva secretion function, and the other is the lingual transport function. In this study, therefore, the relation between the bolus formation function and the number of chewing strokes until swallowing rice crackers with different absorbency was examined. Twenty-one normal healthy subjects (14 male, 7female) were selected for this study. The lingual transport ratio and the degree of crushing were measured using 3-gram peanuts. Moreover, the numbers of chewing strokes until swallowing a piece of rice cracker was counted. The amount of saliva was measured using a piece of wax stick for saliva secretion test. The correlation between the number of chewing strokes and the amount of saliva was analyzed. The correlation between the number of chewing strokes and the lingual transport ratio was also analyzed.
The results were as follows: 1) A negative correlation was proven between the amount of saliva and the number of chewing strokes until swallowing, and a little number of chewing strokes tended to be recorded in the subjects with high saliva secretion ability; 2) A negative correlation was proven between the lingual transport ratio and the number of chewing strokes until swallowing. In the subjects with high lingual transport ratio a few number of chewing strokes tended to be recorded; 3) The above-mentioned relations were remarkable in the rice cracker with large amount of water absorption.
From these results, the saliva secretion and lingual transportation that are related to the bolus formation were able to be predicted by this method, counting the number of chewing strokes until swallowing of water absorbing rice crackers. This means that the evaluation of masticatory function, including bolus formation, can be achieved by this method.

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