1. Materials and Methods Aim of the work Conclusions Results and Discussion 1-Er:YAG laser device produces some thermal explosive changes of dental hard tissues. 2-Linear and circular surface irregularities (Caterpillar-like impressions ) were observed on the lased dentin. 3-No prism structures are evident. with a molten lava-like appearance were produced on the lased enamel. 4-Phosphoric acid etching is essential for surface modification even after laser irradiation. Topographical characteristics of enamel and dentin after Er:YAG laser ablation versus phosphoric acid etching. Introduction A.Typical enamel etching pattern. Etching of prim cores is predominant. B.Lased Enamel treated with phosphoric acid etchant. Enamel prism are created but not predominant. C.Typical pattern of dentin surface etched with phosphoric acid. Smear layer is completely removed. Dentinal tubules are completely opened. D.Lased dentine treated with phosphoric acid. An irregular structure with many microholes was observed on the lased enamel. There is no etching pattern of prism cores. Scaly and rough surfaces were observed. No prism structures are evident. Molten lava-like appearance were produced. Lased dentine shows irregular and rugged surface aspects with different depths were observed. Smear layer is partially removed. Dentinal tubules are not widely opened. Lasers were first considered for dental use in 1964, researchers have investigated various applications of laser in dentistry. Different studies have evaluated the ruby, CO2, Nd:YAG, Erbium (Er):YAG, excimer, and argon lasers for their effects on hard and soft tissues as well as dental materials. Erbium: yttrium-aluminium- garnet (Er:YAG) laser is the only laser that American Food and Drug administration approved for cavity preparation. Wavelength of Er:YAG (2940 nm) correspond to absorption peak of hydroxyapatite and water. Er:YAG laser has a cutting mechanism different from other lasers. That is, water molecules in microscopic area on an irradiated dental surface absorb energy immediately after laser irradiation. The pressure produced causes microexplosions and vaporization.The potential of the Er:YAG laser to cut hard dental tissues such as enamel, cementum and bone, without significant thermal or structural damage has attracted attention. Er:YAG laser with a wavelength of 2.94 µm is used for tooth cavity preparations, as well as removing restorative materials. When Er:YAG laser (2940 nm) is used to prepare cavities, does the bonding procedure require an acid etching step before application of primer and adhesive? 1-Stock K, Hibst R, Keller U. Comparison of Er:YAG and Er:YSGG laser ablation of dental hard tissues. SPIE 2000 ; 3192:88-95. 2-VSP-Variable Square Technology is a proprietary technology of Fotona d.d. 3-Majaron, D. Šušterčič, M. Lukač, U. Skalerič, N. Funduk. Appl. Phys. B 66, 479- 487. 1998. 4-Curti M, Rocca JP, Bertrand MF, Nammour S. Morpho-structural aspects of Er:YAG-prepared class V cavities. J Clin Laser Med Surg. 2004 Apr;22(2):119-23.Curti MRocca JPBertrand MFNammour S References A B C D EDX