Ultrastructural changes of the tooth root surface by Nd : YAG laser irradiation followed by citric acid and tetracycline

The neodymium:yttrium-aluminum-garnet (Nd:YAG) laser has been used for trea tment of dentinal hypersensitivity, eradicating periodontal pathogens, and facilitating calculus removal. However, Nd:YAG laser irradiation exerts pot entially harmful effects on the tooth root surface. The purpose of this stu dy was to examine the ultrastructural changes of the tooth root surface cau sed by Nd:YAG laser irradiation, and to determine whether chemical and mech anical preparations can correct these ultrastructural changes. Eighteen too th specimens (3 x 3 x 0.5 mm) with healthy root surfaces were prepared and irradiated with an Nd:YAG laser at various power densities. Root surfaces w ere irradiated at 100 mJ at 20 pulses per second (pps) for 2 seconds follow ed by the application of citric acid (pH 1.2) or tetracycline solution (100 mg/mL) for 3 and 5 minutes, respectively, or ultrasonic scaling for 5 stro kes of 3 seconds per stroke. As observed with low-vacuum scanning electron microscopy, (Wet-SEM), Nd:YAG laser irradiation at 70 to 100 mJ, 20 pps for 2 seconds caused surface cratering, areas of porosity, pitting, fissures, and lava-like structures in an area 140 to 280 mu m in diameter. Irradiatio n of 50 mJ, 20 pps for 2 seconds, led to only mild surface charring. No evi dence of morphologic changes was found when root surfaces were irradiated w ith the Nd:YAG laser at 20 mJ, 20 pps for 2 seconds or at 50 mJ, 10 pps for 8 seconds. The laser-induced lava-like structures were partially detached by citric acid (pH 1.2) etching and ultrasonic scaling, but not by tetracyc line (100 mg/mL). These results indicate that chemical and mechanical prepa rations can be used effectively in conjunction with Nd:YAG laser irradiatio n for root surface preparation during both nonsurgical and surgical periodo ntal treatments.