Surface morphology modifications of human teeth induced by a picosecond Nd:YAG laser operating at 532 nm B.M. MIRDAN, 1 H.A. JAWAD, 1 D. BATANI, 2 V. CONTE, 3 T. DESAI, 2 AND R. JAFER 2 1 Institute of Laser for Postgraduate Studies, University of Baghdad, Baghdad, Iraq 2 Dipartimento di Fisica “G.Occhialini,” Universita ` di Milano Bicocca, Milano, Italy 3 Dipartimento di Morfologia Umana, Universita ` di Milano, Milano, Italy (RECEIVED 11 August 2008; ACCEPTED 26 November 2008) Abstract The interaction of an Nd:YAG laser, operating at 532 nm with 40 ps pulse duration, with human teeth was studied. The results show that teeth were significantly modified at an energy fluence of about 11 J/cm 2 . Various surface morphologies of enamel and dentinewere recorded. Features on enamel include crater (conical form) in the central part and cauliflower morphology at the periphery, whereas on dentine the crater looks like a stretched dome between sharp edges. The behavior of the enamel-dentine junction area showed different morphology with respect to both tooth enamel and dentine alone. Finally, the junction channel showed a removal of collagen fibers and the formation of a needle-like bottom structure. Generally, this investigation showed that the picosecond Nd:YAG laser can ablate a tooth surface practically instantaneously, implying that large tooth surfaces can be processed in short time. Keywords: Biomaterials; Crater formation; Endodontics/human teeth; Laser treatment; Picosecond Nd:YAG laser INTRODUCTION Studies on surface modifications of various materials (includ- ing bio-materials) by different types of lasers are almost as old as the laser itself, and the field is constantly growing (Di Bernardo et al., 2003; Bussoli et al., 2007; Alti & Khare, 2006; Bashir et al., 2007; Beilis, 2007; Batani et al., 2003, 2007; Desai et al., 2008, 2007, 2005; Fernandez et al., 2005; Kasperczuk et al., 2008; Schade et al., 2006; Thareja & Sharma, 2006; Trusso et al., 2005; Trtica et al., 2006a, 2006b; Veiko et al., 2006; Wieger et al., 2006; Schreiber, 2005). Various lasers and bio-materials have been used up to now for such studies. For fundamental and application interest, laser surface modification studies of bio-material including human teeth are very importance. The tooth structure is known to be inhomogeneous and birefringent (Carlson & Krause, 1985; Zip & Bosch, 1993; Bhaskar, 1991), the coronal portion of the tooth can be regarded as a bio-mechanical complex of two major tissues: enamel and dentine. Enamel is the outermost layer restricted to the coronal portion of the tooth. It is composed of enamel rods, which are not in direct contact with each other, but are cemented together by inter-prismatic sub- stance. Dentine is the supporting structure and consists of specialized cells and bulky intercellular substance. The latter consists of two components: (1) collagenous fibers and (2) cementing substance mainly composed of polysac- charides (Bhaskar, 1991; Takuma et al., 1982). The specialized cells are the odontoblasts. Each cell con- sists of two parts, the body of the cell that lies in the pulpal side of dentine and the odontoblastic process that extends through the full thickness of the dentine (the so-called, Tom’s fiber) in the dentinal tubules. Each odontoblastic process in the dentine is found in thin walled tubes. The wall (the so-called Newman’s sheath) is not formed by a different membrane, but originates from the differences in the nature of the matrix at the edge of the tubules, or from differences in the orientation of the fibers. The interest in the studies of laser beam interaction with human teeth has risen, especially in the last two decades; Nd:YAG (Serafetinides et al., 1999), Ti:Sapphire (Rode et al., 2003), TEA CO 2 (Makropoulou et al., 1996), and different excimer (Neev et al., 1993; Frankline et al., 2005) laser systems have so far been employed for these purposes. Generally, during laser interaction with tooth surfaces, the laser energy is partially absorbed, and partially reflected. Due 1 Address correspondence and reprint requests to: B.M. Mirdan, Institute of Laser for Postgraduate Studies, University of Baghdad, Baghdad, Iraq. E-mail: balsammardan@gmail.com Laser and Particle Beams, page 1 of 6, 2009. Printed in the USA. Copyright # 2009 Cambridge University Press 0263-0346/09 $20.00 doi:10.1017/S0263034609000159