Type Ⅱ root canal was defined that two canals leave the chamber and merge to form a single canal at short of the apex. The aim of this study was to analyse the master apical file (MAF) size according to various instrumentation techniques in the type Ⅱ root canal when each canal was enlarged to working length.Eighty mesial roots of molar with ISO #15 initial apical file (IAF) size in type II root canals were randomly divided into four experimental groups with 20 teeth each. According to enlarging instruments, four groups are: K-FLEXOFILE � (KF), engine-driven Ni-Ti PROTAPER � (PT), HERO Shaper � (HS), K 3 TM (K3). All canals were enlarged to each working length with ISO #30 size: #30 in KF, F3 in PT, .04/30 in HS, and .06/30 in K3. The master apical file (MAF) size was confirmed by tactile sensation and universal testing machine (EZ test, Shimadzu Co., Kyoto, Japan). The mean MAF size was statistically compared using one-way ANOVA and Tukey HSD test at the 0.05 probability level.These results show that the MAF size was appeared one or two sizes larger than the final enlarging instrument when all canal in type Ⅱ configuration were enlarged to each working length. Therefore, the clinician have to confirm the apical stop once more after instrumentation of type Ⅱ root canal. [J Kor Acad Cons Dent 33(5):435-442, 2008]

The purpose of this study was to compare the microtensile bond strength in Class I cavities associated with different light curing modes of same light energy density.Occlusal enamel was removed to expose a flat dentin surface and twenty box-shaped Class I cavities were prepared in dentin. Single Bond (3M Dental product) was applied and Z 250 was inserted using bulk technique. The composite was light-cured using one of four techniques; pulse delay (PD group), soft-start (SS group), pulse cure (PC group) and standard continuous cure (CC group). The light-curing unit capable of adjusting time and intensity (VIP, Bisco Dental product) was selected and the light energy density for all curing modes was fixed at 16 J/㎠. After storage for 24 hours, specimens were sectioned into beams with a rectangular cross-sectional area of approximately 1 ㎟. Microtensile bond strength (μ TBS) test was performed using a universal testing machine (EZ Test, Shimadzu Co.). The results were analyzed using oneway ANOVA and Tukey' s test at significance level 0.05. The μ TBS of PD group and SS group was higher than that of PC group and CC group.Within the limitations of this in vitro study, modification of curing modes such as pulse delay and soft start polymerization can improve resin/dentin bond strength in Class I cavities by controlling polymerization velocity of composite resin. [J Kor Acad Cons Dent 33(5):428-434, 2008]