ABC multidrug transporters play the main role in multidrug resistance(MDR) of cancer cells.RNA interference(RNAi) has been applied in the study of the mechanism and reverse of multidrug resistance of cancer cells.MDR cell lines of human salivary gland adenoid cystic carcinoma(ACC) and mucoepidermoid carcinoma(MEC) were established.MDR of the cells may be related to multigenes and MDR1 gene or ABCC1 gene may be most important.The expressions of MDR1 or ABCC1 gene and proteins of the cells can be silenced and the MDR can be overcome by RNAi.

Objective: To develop a grinding intrument for removing the remaining bonding material and polishing the dental enamel after orthodontic treatment. Methods: A dental griding instrument was made based on ultrasonic principle with the frequency of 25～45 kHz. 60 premolars extracted for orthodontic purpose were used in the experiment, before treatment the surface roughness was measured and recorded as Ra 1. Brackets were adhered to the premolars, and then debonded. The surface enamel of 30 teeth were polished by the ultrasonic grinding instrument (group of GI), that of another 30 by conventional technique(group of CT) , the roughness was measured and recorded as Ra 2. Results: In group GI Ra 1 and Ra 2 were 0.846 6?0.428 2 and 0.740 5?0.372 1(P0.05), respectively. After treatment Ra 2 in group GI was smaller than that in group CT(P