Contents lists available at ScienceDirect Archives of Oral Biology journal homepage: www.elsevier.com/locate/archoralbio Research Paper Effect of laser activated bleaching on the chemical stability and morphology of intracoronal dentin Fabiane Carneiro Lopes a , Renato Roperto b, ⁎ , Anna Akkus b , Ozan Akkus c , Regina Guenka Palma-Dibb a , Manoel Damião de Sousa-Neto a a Department of Restorative Dentistry, School of Dentistry of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil b Department of Comprehensive Care, School of Dental Medicine, Case Western Reserve University, Cleveland, OH, USA c Department of Mechanical and Aerospace Engineering, Case Western Reserve University, Cleveland, OH, USA ARTICLE INFO Keywords: Intracoronal bleaching Raman spectroscopy Laser ABSTRACT Objectives: To evaluate the effect of the bleaching with 35% hydrogen peroxide either activated or not by a 970 nm diode laser on the chemical stability and dentin surface morphology of intracoronary dentin. Methods: Twenty-seven slabs of intracoronary dentin specimens (3 × 3 mm) were distributed into three groups (n = 9), according to surface treatment: HP – 35% hydrogen peroxide (1 × 4’), DL – 970 nm diode laser (1 × 30”/0,8W/10 Hz), HP + DL – 35% HP activated with 970 nm diode laser (1 × 30”/0,8W/10 Hz leaving the gel in contact to the surface for 4′ after activation). Three Raman spectra from each fragment were obtained to calculate the mean intensity of peaks of inorganic component (a.u.), organic collagen content (a.u.), and the ratio of inorganic/organic content, before and after treatment. Analyses of the samples by confocal laser mi- croscopy were performed to evaluate the surface roughness, percentage of tubules, perimeter and area per- centage of tubules, before and after treatment. Data were analyzed by Kruskal-Wallis, Dunn’s, and Wilcoxon test (P < 0.05). Results: Data analysis showed that HP + DL did not change the inorganic content peaks 8.31 [29.78] or the inorganic/organic ratio 3.37 [14.67] (P> 0.05). Similarly, DL did not affect the chemical stability of the dentin surface (P> 0.05). However, HP significantly increased inorganic content peaks 10.87 [22.62], as well as the inorganic/organic ratio 6.25 [27.78] (P< 0.05). Regarding the morphological alterations, all surface treat- ments increase tubules exposure; HP treatment significantly increases perimeter and area percentage; and HP + DL increases surface roughness. Conclusions: Bleaching HP combined with DL offers an improvement in terms of intracoronal dentin surface protection, yielding better maintenance of dentin chemical stability and morphology. 1. Introduction Aesthetic dental problems often result in stained teeth as result of pigment incorporation into tooth structure (Plotino, Buono, Grande, Pameijer, & Somma, 2008). The discoloration process occurs by for- mation of chemically stable structures on dentin (Tredwin, Naik, Lewis, & Scully, 2006). In a non-vital tooth, this process may be associated with pulp tissue decomposition, blood pigments from an intrapulpal hemorrhage, and iatrogenic endodontic treatment, such as roof remains or pulp tissue leftovers in the pulp chamber, insufficient debridement and irrigation, or the presence of restorative and filling materials left in contact with the pulp chamber for long periods of time (Plotino et al., 2008; Baratieri, Ritter, Monteiro, Caldeira de Andrada, & Cardoso Vieira, 1995). Among the cosmetic restorative treatment used to remove these pigments and recover the compromised esthetics, the intracoronal bleaching procedure is the least invasive alternative. This method is widely used due to its relative simplicity and effectiveness, in addition to its low cost and preservation of the dental hard tissue, as compared to prosthetic treatment (Amaral et al., 2008; Joiner, 2006). Despite the advantages offered by this procedure, the underlying effects of bleaching agents on dental hard tissues remain controversial. Bleaching is based on substances that have a high potential for oxygen release. Hydrogen peroxide is the most commonly used bleaching agent in dental practice (Joiner, 2006; Joiner, 2007). Used in high concentrations, hydrogen peroxide whitens teeth simply by oxi- dation of their transparent organic matrices (Eimar et al., 2012). Contemporary approaches have focused on accelerating peroxide https://doi.org/10.1016/j.archoralbio.2017.10.023 Received 13 October 2016; Received in revised form 11 October 2017; Accepted 28 October 2017 ⁎ Corresponding author. E-mail address: rcr67@case.edu (R. Roperto). Archives of Oral Biology 86 (2018) 40–45 0003-9969/ © 2017 Elsevier Ltd. All rights reserved. MARK