AbstractThe purpose of this in vitro study was to evaluate the effects of the Nd:YAG laser either alone or in combination with root planning or air‐powder abrasive treatment on fibroblast attachment to non‐diseased root surfaces. 28. 4x4 mm root specimens and four disc‐shaped root specimens 6 mm in diameter were obtained from unreputed 3rd molars. The root segments were randomly assigned to 4 treatment groups: (1) control: (2) laser‐only treated: (3) laser treated followed by root planning; (4) laser treated followed by air‐powder abrasive treatment. Laser‐treated root specimens were exposed for 1 min with the Nd:YAG laser calibrated at an energy setting of 75 mJ at 20 pulses/s using a 320 μm contact fiber. The contact fiber was held parallel to the root segments and the root segments were kept moist with distilled water. Following the prescribed treatments, the root specimens were incubated with fibroblast cultures and then prepared for SEM examination. Results of cell counts of fibroblasts attached to specimens within each treatment group yielded the following means and standard deviations: control groups. 181.64 ± 44.74; lased only, 78.57 ± 21.35; lased and root planed 125.35 ± 26.13: and lased followed by an air‐powder abrasive, 177.28 ± 55.71. Application of ANOVA followed by the Dunn Multiple Comparison test revealed significant differences (p<0.01) in the number of attached cells between the control and laser‐only treated groups: and between the laser‐only and laser/air‐powder abrasive treated groups. The decreased fibroblast attachment observed in the laser‐only treated group suggests a laser‐induced bio in compatibility of the root surface. Several surface alterations including ablation of cementum with exposure of dentinal tubules and crater formation were observed. Increased numbers of fibroblasts were seen attached to the lased root segments after root planning or after exposure to an air‐powder abrasive, indicating that the laser‐induced bioincompatibility is reversible and most likely a surface phenomena. A pilot study using pholoacoustic Fourier transform infrared spectroscopy revealed reductions in the intensity of the Amide II band between 1500–1550 cm‐1, suggesting the laser exposure denatures surface protein which, in turn, may contribute to