ER-YAG laser pretreatment effect on in vitro secondary caries formation around composite restorations

This in vitro study determined if Er-YAG laser used in instead of acid-etching influenced artificial secondary caries formation in enamel and root surfaces.

Class V cavities were prepared in buccal and lingual surfaces of 10 extracted caries-free molars, with cervical margins in the root surface and occlusal margins in enamel. The specimens were randomly assigned to 2 groups: Group 1: Enamel and dentin etched with 35% phosphoric acid gel (Scotchbond 15s, rinse 10s; n=5 teeth with 2 cavities per specimen, 10 occlusal and 10 root surface margins at caries risk). Group 2: Enamel and dentin surfaces conditioned using a pulsed Er-YAG laser (KAVO) with 2.94 microm wavelength, 250 micros pulse duration, 300 mJ for enamel and 250 mJ for root surface pulse energy, 2 Hz repetition rate, and water cooling (n=5 teeth with 2 cavities per specimen, 10 occlusal and 10 root surface margins at caries risk). The cavity preparations were restored with a wet-bonding technique (Scotchbond 1 adhesive system) and a hybrid resin, light-cured composite (Z100, A3 shade), according to the manufacturer's instructions. Acid-resistant varnish was applied leaving the restoration and a 1 mm rim of adjacent surface enamel and root surface exposed. The specimens were thermocycled (5-50 degrees C, 500 cycles, dwell time 30s). Following artificial caries formation (2.2 mM calcium, 2.2 mM phosphate, 50 mM acetic acid, 5.0 mg/L fluoride, pH 4.25, 10 days), longitudinal sections (3/tooth, 30 occlusal and cervical caries risk sites per group) were taken for polarized light microscopic examination (water imbibition). Primary surface lesion depth and wall lesion frequency was determined and compared between groups (Student's t-test).

Er-YAG laser irradiation resulted in a 56% reduction in primary enamel surface lesion depth (116 microm mean depth) when compared with the acid-etched group (263 microm mean depth), and a 39% decrease in root surface lesion depth (194 microm mean depth) compared with that (316 microm mean depth) for acid-etching pretreatment (P< 0.05). Wall lesion frequency was similar (P>0.05) between treatment groups.