Wataru Yoshioka

An in vitro investigation of the tooth strains associated with four different restorations in Class II cavity

The purpose of this study was to examine tooth strains in Class II preparations. A Class II cavity was prepared in 16 permanent premolars, and a strain gauge was attached to the buccal surface of each tooth. Each cavity was then restored with bonded amalgam, bonded gallium, composite, or composite with a resin liner. The tooth strains created by these four restorations were determined and evaluated with a strain indicator. The results of this study indicated that composite restorations with and without resin liner created much greater strains to tooth structure than did bonded amalgam and bonded gallium restorations. The application of resin liner before placement of the composite was effective for decreased tooth strain.

Induction of bleomycin resistance in a human oral squamous carcinoma cell line and characterisation of bleomycin-resistant and -sensitive clones

We examined the change of sensitivity to antitumour agents by repeated treatment with bleomycin (BLM) using two oral squamous carcinoma cell lines, SCCTF and SCCKN. SCCTF exhibited minimal sensitivity to BLM and strong heterogeneity in BLM sensitivity, whereas SCCKN was highly sensitive to BLM and showed weak heterogeneity. When SCCTF was treated continuously with low-dose BLM (0.1 microgram/ml) but not intermittently with high-dose BLM (1 microgram/ml), the BLM sensitivity was rapidly decreased to acquire drug resistance. On the other hand, SCCKN was completely killed by the same treatments. To investigate the mechanism of induction of resistance in SCCTF, BLM-sensitive and -resistant clones, TF-S and TF-R, were isolated and analysed. Consequently, TF-R showed decreased cellular accumulation and retention of BLM, increased BLM hydrolase activity and elevated DNA repair activity concomitant with increased poly(ADP-ribose) polymerase activity as compared with TF-S. Therefore, it was suggested that antitumour drug-resistant clones were selectively grown from heterogeneous tumour cell population.

An experimental study of the sealing ability of a dentinal apical plug treated with bonding agent

The purpose of this study was to evaluate the sealing ability of a dentinal apical plug treated with a bonding agent. Ninety human lower premolars were used. The teeth were divided into three groups. in groups 1 and 2, to prepare an apical isthmus of 1 mm in length, the first apical seat was prepared with a #45 K file 1 mm short of the anatomical apex and with a #60 K file 2 mm short for the second apical seat. Dry dentin fillings were packed in the apical isthmus with a #60 K file. In group 1, the root canal was obturated with gutta-percha and Canals root canal sealer by the lateral condensation method. In group 2, following an application of the bonding agent to the plug, the root canal was obturated in the same way. In group 3 (control), a single apical seat was prepared with a #60 K file 1 mm short of the apex and the root canal was obturated similarly. The teeth of three groups were immersed in a 1% methylene blue solution for 1, 2, and 4 wk. Dye penetration depth from the apical foramen was determined. Group 2 showed no leakage after 4 wk. Groups 1 and 3 showed dye penetration into the root canal, and in these two groups dye penetration increased with time.