Er : YAG (lambda=2.94 mu m) laser etching of dental enamel as an alternative to acid etching

Acid etching is widely used in clinical dentistry to facilitate the mechani cal retention of resin-based materials to teeth, in particular enamel surfa ces. Several laser systems have been developed with the aim of modifying de ntal hard tissues and the Er:YAG; (lambda=2.94 mu m) laser may offer a poss ible alternative to the acid etching technique. This study compares the shear bond strengths of composite beads attached to sound enamel surfaces prepared using either (a) no etching (negative contr ol), (b) acid etching (positive control) or (c) Er:YAG laser etching, eithe r with or without water, at one of three fluences: 15 J/cm(2), 18 J/cm(2) o r 24 J/cm(2). A histological appraisal was also conducted using environment al scanning electron microscopy (ESEM) techniques. The mean shear bond strength for acid-etched enamel was 16.6 MPa (SD 4.4, n =10), whereas the best laser-etched mean bond strength obtained was 11.5 MP a (SD 4.1, n=11) using a fluence of 24 J/cm(2) with water. These values wer e significantly greater than those obtained for the negative control (no et ching) of 4.4 MPa (SD 0.9, n=8). There was a significant positive correlati on between the etching fluence and the shear bond strength, but pitting of the enamel surface at fluences above 25 J/cm(2) limited the maximum fluence for etching purposes. Although Er:YAG laser etching enhanced the retention of a resin-based material to an enamel surface when compared to a negative control, the mean shear bond strengths were significantly lower than those obtained using conventional acid etching. The optimal laser etching parame ters in this study were shown to be 24 J/cm(2) in conjunction with water.