To adapt interns to the stage of clinic dentist as soon as possible and to increase the efficiency of internship,we have applied problem-based learning(PBL) model to the clinic practice of prosthodontics in the students of Grades 2002 and 2003.Such a teaching reform cultivates their interests in autonomous study,increases their confidence,improves the relationship with patients and trains their re-learning ability.

BACKGROUND:The morphological structure of nanofiber scaffold which fabricated by electrospinning technique is similar to the natural extracelular matrix, which provides a good microenvironment for cel growth and proliferation, and can also enhance cel adhesion, migration, proliferation and differentiation. OBJECTIVE: To observe the biocompatibility of double-layer poly(L-lactic acid) electrospun nanofiber scaffold and human periodontal ligament cels. METHODS: Electrospinning technique was used to prepare double layers poly(L-lactic acid) electrospun nanofiber scaffold. The toxicity of different concentrations of (100%, 75%, 50%, 25%) double-layer poly(L-lactic acid) electrospun nanofiber scaffold extracts to human periodontal ligament cels was evaluated by MTT assay. The double-layer poly(L-lactic acid) electrospun nanofiber scaffold was co-cultured with human periodontal ligament cels. The cel adhesive capacity in early stage was determined by MTT assay. The growth of cels on the scaffold was observed by scanning electron microscopy. RESULTS AND CONCLUSION: Different concentrations of double-layer poly(L-lactic acid) electrospun nanofiber scaffold extracts did not create any toxicity to human periodontal ligament cels. After co-culture for 2, 6, 24 hours, human periodontal ligament cels were poorly adherent onto the double-layer poly(L-lactic acid) electrospun nanofiber scaffold. After 7 days of co-culture, human periodontal ligament cels adhered wel on the loose surface of scaffold, maintained the original shape, stretched wel, and interconnected processes were observed; on the dense surface of the scaffold, multi-layer cels were observed. The cels showed fusiform or polygonal appearance and were connected together. These results demonstrate that the double-layer poly(L-lactic acid) electrospun nanofiber scaffold has good biocompatibility with human periodontal ligament cels.

BACKGROUND: BACKGROUND: Studies have found that surface treatment agents containing 10-methacryloyloxy decyl dihydrogen phosphate may be chemical y bonded to the oxide on the surface of zirconia, thereby notably improving the bonding performance of zirconia. OBJECTIVE: To study the effects of Mondbond N and Single bond Universal Adhesive on microtensile bond strength between zirconia and composite resin. METHODS: Sixty pieces of zirconia were randomized into three groups: in group 1, conventional Bis-GMA resin cement was used to bond zironia and composite resin; in group 2, conventional Bis-GMA resin cement was used to bond zironia and composite resin fol owing Mondbond N treatment; in group 3, conventional Bis-GMA resin cement was used to bond zironia and composite resin fol owing surface treatment with Single Bond Universal Adhesive containing 10-methacryloyloxy decyl dihydrogen phosphate. Microtensile bond strength and microstructure on the bonding interface were compared among three groups. RESULTS AND CONCLUSION: (1) Microtensile bond strength was significantly higher in the groups 2, 3 than group 1 (P < 0.05), and there was no difference between the two former groups. (2) Scanning electron microscope observation of the bonding interface: before microtensile test, there were more fissures on the bonding interface of group 1; in the group 2, there were a few fissures on the bonding interface that was relatively even; in the group 3, the bonding interface was smooth and continuous with few fissures. After microtensile, cohesive failure and bonding interface failure were mainly seen in the three groups, but there was no simple interface failure in the groups 2 and 3. These findings indicate that Monobond N and Single Bond Universal Adhesive can both improve the bonding strength of zirconia with composite resin.