Objectives: One of the diffi culties in restorative dentistry continues to be microleakage around cavities restored with esthetic materials. Microleakage is the factor that most infl uences restoration durability. It is characterized by gap formation due to failure of the restorative material to bond to cavity walls. The aim of this in vitro study was to compare the degree of microleakage of Class V restorations when different instruments are used for cavity preparation. Methods: Class V

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... s were performed in 30 bovine teeth divided into three treatment groups (n = 10): G1, preparation with a diamond bur; G2, preparation with an Er,Cr:YSGG laser (2.78 mm); and G3, preparation with diamond tips and an ultrasonic system (CVDentus). All cavities were restored with composite resin, according to the manufacturer's specifi cations. The specimens were submitted to thermal cycling (700 cycles, 5°C ± 1°C and 55°C ± 1°C) and immersed in 2% methylene blue to evaluate microleakage. The teeth were sectioned longitudinally and images were captured using a stereomicroscope at 50× magnifi cation. Three evaluators examined the images according to the scale proposed by Retief. Data were analyzed by the Kruskal-Wallis and Dunn tests. Results: Statistically signifi cant differences were observed between the treatment groups (p = 0.0007). The highest microleakage rates were found for G2, which differed signifi cantly from those of the other treatment groups. There was no statistically signifi cant difference between G1 and G3. Conclusion: Different cavity preparation techniques may infl uence microleakage in Class V restorations, and the ultrasound technique was found to be an effective alternative.