Thermal Alteration and Morphological Changes of Sound and Demineralized Primary Dentin After Er:YAG Laser Ablation CRISTINA BUENO BRANDA ˜ O, 1 MARTA MARIA MARTINS GIAMATEI CONTENTE, 1 FABRI ´ CIO AUGUSTO DE LIMA, 2 RODRIGO GALO, 1 ALESSANDRA MARQUES CORRE ˆ A-AFONSO, 1 LUCIANO BACHMANN, 2 AND MARIA CRISTINA BORSATTO 1 * 1 Departamento de Clı ´nica Infantil, Odontologia Preventiva e Social, Faculdade de Odontologia de Ribeira ˜ o Preto, Universidade de Sa ˜ o Paulo, Ribeira ˜ o Preto, SP14040-904, Brazil 2 Departamento de Fı ´sica, Faculdade de Filosofia, Cie ˆncias e Letras de Ribeira ˜ o Preto, Universidade de Sa ˜ o Paulo, Ribeira ˜ o Preto, SP 14.040-901, Brazil KEY WORDS temperature; SEM; decidous teeth; laser ABSTRACT The purpose of this study was to assess the influence of Er:YAG laser pulse repeti- tion rate on the thermal alterations occurring during laser ablation of sound and demineralized primary dentin. The morphological changes at the lased areas were examined by scanning elec- tronic microscopy (SEM). To this end, 60 fragments of 30 sound primary molars were selected and randomly assigned to two groups (n 5 30); namely A sound dentin (control) and B demineralized dentin. Each group was divided into three subgroups (n 5 10) according to the employed laser fre- quencies: I–4 Hz; II–6 Hz, and III–10 Hz. Specimens in group B were submitted to a pH-cycling regimen for 21 consecutive days. The irradiation was performed with a 250 mJ pulse energy in the noncontact and focused mode, in the presence of a fine water mist at 1.5 mL/min, for 15 s. The measured temperature was recorded by type K thermocouples adapted to the dentin wall relative to the pulp chamber. Three samples of each group were analyzed by SEM. The data were submitted to the nonparametric Kruskal-Wallis test and to qualitative SEM analysis. The results revealed that the temperature increase did not promote any damage to the dental structure. Data analysis demonstrated that in group A, there was a statistically significant difference among all the sub- groups and the temperature rise was directly proportional to the increase in frequency. In group B, there was no difference between subgroup I and II in terms of temperature. The superficial dentin observed by SEM displayed irregularities that augmented with rising frequency, both in sound and demineralized tissues. In conclusion, temperature rise and morphological alterations are directly related to frequency increment in both demineralized and sound dentin. Microsc. Res. Tech. 75:126–132, 2012. V V C 2011 Wiley Periodicals, Inc. INTRODUCTION New technologies have been developed to replace the conventional restorative procedure, to obtain a more selective and conservative therapy (Hibst and Keller, 1989; Keller and Hibst, 1995; Raucci-Neto et al., in press; Yazici et al., 2010) that is also more comfortable to the patient, and often eliminate the need for anes- thesia (Chaiyavej et al., 2000). The reported advan- tages of laser technology compared to conventional high-speed rotatory instrumentation include, apart from the possibility of treatment without local anesthe- sia, elimination of stress factors such as vibration, pressure, and noise, which cause anxiety in patients, especially children (Chaiyavej et al., 2000; Keller and Hibst, 1997; Liu et al., 2006a). Many researchers have investigated the efficiency of the Er:YAG laser for dental applications, such as cavity preparation (Attrill et al., 2004; Bertrand et al., 2006; Chinelatti et al., 2006; Contente et al., in press; Dosta- lova ´ et al., 1996; Gimbel, 2000; Raucci-Neto et al., 2007; Takamori et al., 2003), periodontal treatment (Crespi et al., 2006), and superficial treatment for caries prevention (Correa-Afonso et al., 2010; Liu et al., 2006b). This laser has an active yttrium-aluminum- garnet crystal doped with erbium ions and emits energy of 2.94 lm wavelength, which coincides with the maximum water and OH absorption peak in tooth hard tissues. Dentin ablation by Er:YAG laser occurs when the organic components of the tissues absorb the radiated energy, causing water and OH to vaporize (Hibst and Keller, 1989). A small portion of this energy is not consumed in the ablation process, causing heating of the dental structures (Hibst and Keller, 1989). Among Er:YAG laser parameters, pulse frequency deserves attention because it is directly related to temperature increment in tissues and dental pulp (Armengol et al., 2000; Attrill et al., 2004; Dostalova ´ et al., 1998; Raucci-Neto et al., 2007; Takamori et al., 2003). According to Zach and Cohen (1965), temperature rises above 5.58C for 1 min may promote irreversible pulp damage. However, thermal *Correspondence to: Maria Cristina Borsatto, Universidade de Sa ˜o Paulo (USP), Faculdade de Odontologia de Ribeira ˜o Preto, Departamento de Clı ´nica Infantil, Odontologia Preventiva e Social, Av. do Cafe ´, S/N Monte Alegre CEP: 14040-904 Ribeira ˜o Preto, SP, Brazil. E-mail: borsatto@forp.usp.br Received 25 January 2011; accepted in revised form 24 April 2011 DOI 10.1002/jemt.21034 Published online 14 July 2011 in Wiley Online Library (wileyonlinelibrary.com). V V C 2011 WILEY PERIODICALS, INC. MICROSCOPY RESEARCH AND TECHNIQUE 75:126–132 (2012)