Effects of the Nd : YAP laser on coronal restorative materials: Implications for endodontic retreatment

With new wavelengths that allow light transmission by optical fibers, the l aser is now often used in endodontics either during treatment or retreatmen t. The aims of this study were to (i) specify the effects of laser irradiat ion on restorative materials in terms of topographic effects and (ii) descr ibe different protocols for the first steps of retreatment. The laser used in this study was an optical fiber Nd:YAP (Lokki dt, Vienne, France) with a wavelength of 1.34 mu m. Samples of the following restorative materials we re prepared: amalgam, composite, permanent and temporary cements, and prost hodontic alloy. The handpiece of the Nd: YAP laser was fixed perpendicular to the surface of the different preparations. All trials were performed wit h the fiber tip either in contact with or at a distance of 2 mm from the ma terial. The surface effects in all cases were (i) the creation of craters i n the center of the lased areas, (ii) a border of fusion material at the ed ge of the craters, and (iii) cracks or fractures at a distance from the tar get areas. For the cements, amalgam and composite, the effects included a p rojection of material from the center to the edge of the lased area and/or the apparent photovolatization of light particles. For all materials the la ser induced deeper absorption in the areas of direct contact than when it w as held at a distance. This suggests that the fiber should be in contact wi th the restorative material for lasing in the straight part of the canal wh en the objective is either to pass through the material or alongside it bet ween material and tooth. If the practitioner cannot determine the direction of the curve of the canal, lasing should be performed at a distance to wea ken the material and thus permit more efficient use of an ultrasonic device . Lasing should in all cases be performed under close X-ray monitoring. Pro vided that sufficient caution is used, the laser may be helpful in removing restorative materials during retreatment.