Bonding to LASER Treated Tooth Structure-effects of Power

LASER removal of dental hard tissues was approved by the FDA in 1997.  Erbium-doped:yttrium-aluminum-garnet (Er:YAG) laser removes caries and sound tooth structure by heating H₂O in tooth apatite, producing water vapor which expands causing a micro-explosion with the removal of a small portion of tissue. Even though the Er:YAG laser could produce a microretentive surface it has been reported that Er:YAG LASER irradiation on enamel caused crystalline changes producing increased acid resistance of dental hard tissue.Objective: This study examined the effects of varying the power of the laser on shear bond strength to enamel compared to a control (not LASER treated enamel). Methods: Freshly extracted human molars were obtained.  The enamel of these teeth was prepared to a flat surface using a polisher grinder to 320 grit.  A Waterlase LASER (Biolase) was used to prepare the tooth surface.  Distance to the tooth, water and air setting were constant.  Power was varied for enamel.  A 15 second etch with 10% phosphoric acid was applied to the bonding area, rinsed and One Coat adhesive was applied following the manufacturer's directions.  A Teflon tube filled with Z 250 composite resin (shade A2) was applied over the adhesive and cured 60 seconds with a curing light (Optilux 500, output 500mW/cm²).  The Teflon tube was removed and the specimens loaded in shear until failure in an Instron (model 1141) crosshead speed 1mm/min. A one-factor ANOVA evaluated power setting Tukey B post-hoc analysis was used to determine group differences. Significance =.05. Results:  Shear bond strength (MPa, n=10)