ORIGINAL ARTICLE In vitro investigation of intra-canal dentine–laser beam interaction aspects: I. Evaluation of ablation capability (ablation rate and efficiency) Nova Hambersom Minas & Joerg Meister & Rene Franzen & Norbert Gutknecht & Friedrich Lampert Received: 6 March 2009 / Accepted: 8 June 2009 / Published online: 28 July 2009 # Springer-Verlag London Ltd 2009 Abstract The aim of this study was to determine the amount of intra-canal dentine removed with an erbium, chromium: yttrium–scandium–gallium–garnet (Er,Cr:YSGG) laser using different endodontic tips and different power settings. Ninety intact extracted bovine teeth were selected as samples. After sectioning the roots and preparing the testing cylinders, we divided the samples into three main groups (A, B, C), with further subdivision of each group to be irradiated with three different powers (1500 mW, 1750 mW and 2000 mW). An Er, Cr:YSGG laser system (2.78 μm, 140 μs, 20 Hz and 65% water to 35% air ratio) was used for irradiation, and the loss of intra-canal dentine mass was calculated by the difference between the initial and final sample masses. Data were analysed with Kolmogorov–Smirnov, analysis of variance (ANOVA) and Tukey tests. At a significance level of α =1%, the results showed statistically significant differences (P < 0.0001) between different tip groups, regarding both the ablation rate and the ablation efficiency criteria. With regard to the three irradiation power settings, statistically significant difference were recorded only between groups C and A, for the ablation rate criteria. The intra-canal ablation ability of the Er,Cr:YSGG laser improved with increasing power and/ or tip diameter. The latter exhibited a stronger influence on ablation rate and efficiency. Laser intra-canal ablation is an important addition to the field of endodontics; nevertheless, further investigations and system improvements are required. Keywords Canal preparation . Canal ablation . Intra-canal laser beam interaction . Root canal enlargement Introduction Conventional endodontic techniques lend themselves to the over-enlargement and shaping of the root canal system to sterilize and obturate the root canal system fully. As contemporary conservative dentistry encourages movement towards more minimally invasive treatment notions and models, dental laser systems have become attractive adjuncts in up to date endodontic therapy. Among a wide range of applications of different laser wavelengths inside the root canal lumen, preparation and shaping of the root canal with erbium lasers have always been issues for debate over more than a decade [1–5]. The most essential aspect associated with previous applications is the intra-canal ablation capability of laser beams. Upon the release of endodontic tips to be used with erbium, chromium:yttrium–scandium–gallium–garnet (Er,Cr:YSGG) laser units, several studies [6–10] investigated the different behaviours of those tips in terms of preparation ability, capability, efficacy and morphology of the resulting treat- ment. Moreover, regarding settings and application advices, studies showed that pulse energy, application duration and water/air ratio are among the most important parameters that seem to be directly related to the efficiency of laser ablation of the canal substrate [11–14]. To date, a consensus has not yet been reached, and, to the best of our knowledge, there are still no data available that demonstrate specific characteristic features of intra-canal ablation rate and efficiency of those tips using different pulse energy and tip diameters. Therefore, this project was N. H. Minas (*) : J. Meister : R. Franzen : N. Gutknecht : F. Lampert Department of Conservative Dentistry, Periodontology and Preventive Dentistry (ZPP), University of Aachen, Pauwelsstr. 30, 52074 Aachen, Germany e-mail: nminas@ukaachen.de Lasers Med Sci (2010) 25:835–840 DOI 10.1007/s10103-009-0701-4