The purpose of this study was to evaluate the effect of Er,Cr:YSGG laser irradiation with hypersensitivity mode on microtensile bond strength of composite resin. Twenty extracted permanent molars were randomly assigned to six groups, according to the irradiation of Er,Cr:YSGG laser, adhesive system (Optibond FL or Clearfil SE bond) and application time of etchant (15 sec or 20 sec). Then composite resin was build up on each conditioned surface. The restored teeth were stored in distilled water at room temperature for 24 h and twelve specimens for each group were prepared. All specimens were subjected to microtensile bond strength and the fracture modes were evaluated. Also, the prepared dentin surface and laser irradiated dentin surface were examined under SEM.

The results were as follows:

The microtensile bond strength of laser irradiated group was lower than that of no laser irradiated group.

The purpose of this study was to evaluate the effect of different etching times on microtensile bond strength (µTBS) to dentin both initial and after thermocycling with 3 different types of total-etching adhesives.

Fifty four teeth were divided into 18 groups by etching times (5, 15, 25 sec), adhesives types (Scotchbond Multipurpose (SM), Single Bond (SB), One-Step (OS)), and number of thermocycling (0, 2,000 cycles).

Flat dentin surfaces were prepared on mid-coronal dentin of extracted third molars. After exposed fresh dentin surfaces were polished with 600-grit SiC papers, each specimen was acid-etched with 35% phosphoric acid (5, 15, 25 sec) and bonded with 3 different types of total etching adhesives respectively. Then, hybrid composite Z-250 was built up. Half of them were not thermocycled (control group) and the others were subjected to 2,000 thermocycle (experimental group). They were sectioned occluso-gingivally into 1.0 × 1.0 mm² composite-dentin beams and tested with universal testing machine at a crosshead speed of 1.0 mm/min.

Within limited data of this study, the results were as follows

1. There was no statistically significant difference in µTBS between the thermocycled and non-thermocycled groups, except for both SM and SB etched for 25 sec.

2. In thermocycled SM and SB groups, bond strength decreased by extended etching time.

In total etching systems, adhesive durability for dentin could be affected by type of solvents in adhesive and etching time. Especially, extended etching time may cause deteriorate effects on bond strength when ethanol-based adhesive was used.

The objectives of this study was to evaluate the effect of thermocycling on the μTBS (microtensile bond strength) to dentin with four different adhesive systems to examine the bonding durability.

Freshly extracted 3^rd molar teeth were exposed occlusal dentin surfaces, and randomly distributed into 8 adhesive groups: 3-steps total-etching (Scotchbond Multi-Purpose Plus; SM, All Bond-2; AB), 2-steps total-etching (Single Bond; SB, One Step plus; OS), 2-steps self-etching (Clearfil SE Bond; SE, AdheSE; AD) and single-step self-etching systems (Promp L-Pop; PL, Xeno III; XE). Each adhesive system in 8 adhesives groups was applied on prepared dentin surface as an instruction and resin composite (Z250) was placed incrementally and light-cured. The bonded specimens were sectioned with low-speed diamond saw to obtain 1 × 1 ㎜ sticks after 24 hours of storage at 37 °C distilled water and proceeded thermocycling at the pre-determined cycles of 0, 1,000 and 2,000. The μTBS test was carried out with EZ-tester at 1 mm/min. The results of bond strength test were statistically analyzed using one-way ANOVA/ Duncan's test at the α〈 0.05 confidence level. Also, the fracture mode of debonded surface and the interface were examined under SEM.

The results of this study were as follows;

3-step total etching adhesives showed stable, but bond strength of 2-step adhesives were decreased as thermocycling stress.

Within limited results of this study, the bond strength of adhesive system was material specific and the bonding durability was affected by the bonding step/ procedure of adhesive. Simplified bonding procedures do not necessarily imply improved bonding performance.