Effects of Nd:YAG laser irradiation on the hybrid layer of different adhesive systems.

PURPOSE: The aim of this in vitro study was to evaluate the microtensile bond strength (microTBS) and hybrid layer morphology of different adhesive systems, either followed by treatment with Nd:YAG laser irradiation or not. Previous studies have shown the effects of Nd:YAG laser irradiation on the dentin surface at restoration margins, but there are few reports about the significance of the irradiation on the hybrid layer. MATERIALS AND METHODS: The flattened coronal and root dentin samples of 24 bovine teeth were randomly divided into 8 groups, according to the adhesive system used -- Scotchbond Multi Purpose (SBMP) or Clearfil SE Bond (CSEB) -- and were either irradiated with Nd:YAG or not, with different parameters: 0.8 W/10 Hz, 0.8 W/20 Hz, 1.2 W/10 Hz, 1.2 W/20 Hz. The left sides of specimens were the control groups, and right sides were irradiated. A composite crown was built over bonded surfaces and stored in water (24 h at 37 degrees C). Specimens were sectioned vertically into slabs that were subjected to microTBS testing and observed by SEM. RESULTS: Control groups (27.81 +/- 1.38) showed statistically higher values than lased groups (21.37 +/- 0.99), and CSEB control group values (31.26 +/- 15.71) were statistically higher than those of SBMP (24.3 +/- 10.66). There were no significant differences between CSEB (20.34 +/- 10.01) and SBMP (22.43 +/- 9.82) lased groups. Among parameters tested, 0.8 W/10 Hz showed the highest value (25.54 +/- 11.74). Nd:YAG laser irradiation caused dentin to melt under the adhesive layer of both adhesive systems tested. CONCLUSION: With the parameters used in this study, Nd:YAG laser irradiation of the hybrid layer promoted morphological changes in dentin and negatively influenced the bond strength of both adhesive systems.

Microleakage of glass ionomer restoration in cavities prepared by Er,Cr:YSGG laser irradiation in primary teeth.

PURPOSE: The purpose of this study was to evaluate microleakage of cavity preparation in primary teeth made with an Er, Cr:YSGG laser (L) or high-speed drill (HD) and conventional (CGIC) and resin-modified glass ionomer cement (RMGIC). METHODS: One hundred primary teeth were divided into 10 groups (N=10): (a) groups 1 and 2 represented cavities prepared by a no. 1012 diamond bur with HD; (b) groups 3 through 10 represented cavities prepared with an Er, Cr:YSGG laser (with a repetition rate of 20 Hz power settings varying for enamel=2.5 W and 3 W and dentine=1.0 W and 1.5 W). After cavity preparation, samples were restored with CGIC (Ketac Molar Easy Mix) and RMGIC (Vitremer), impermeabilized, thermal cycled, stained, washed, and sectioned. The degree of dye penetration was scored by 3 standardized examiners using a light stereoscope at X30 magnification. RESULTS: The Kruskal-Wallis test detected no statistical differences between the cavity preparation methods (P<.049). Neither of the GICs tested were able to avoid microleakage, and the RMGIC showed the lowest statistical degree of microleakage compared with CGIC for both types of cavity preparation. CONCLUSIONS: The Er,Cr:YSGG laser provided an equivalent method of cavity preparation compared to the high-speed drill. The resin-modified glass ionomer cement showed the lowest degree of microleakage. This restorative material should be considered when choosing the cavity preparation method.