Influence of intracoronal bleaching agents on the ultimate strength and ultrastructure morphology of dentine V. Cavalli 1 , M. S. Shinohara 2 , W. Ambrose 3 , F. M. Malafaia 4 , P. N. R. Pereira 5 & M. Giannini 6 1 Division of Operative Dentistry, Department of Dentistry, University of Taubate ´, Taubate ´, SP; 2 Division of Operative Dentistry, Department of Dentistry, State University of Amazonas, Manus, AM, Brazil; 3 School of Dentistry, Electron Microscopy Facility, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; 4 Division of Prosthodontics, Department of Dentistry, University of Taubate ´, Taubate ´, SP, Brazil; 5 Department of Operative Dentistry, School of Dentistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA; and 6 Division of Operative Dentistry, Department of Restorative Dentistry, Piracicaba School of Dentistry, University of Campinas, Piracicaba, SP, Brazil Abstract Cavalli V, Shinohara MS, Ambrose W, Malafaia FM, Pereira PNR, Giannini M. Influence of intracoronal bleaching agents on the ultimate strength and ultrastructure morphology of dentine. International Endodontic Journal, 42, 568–575, 2009. Objective To evaluate the effects of intracoronal bleaching on ultimate tensile strength (UTS) of sound and etched dentine and its ultrastructure morphology. Methodology Bovine dentine specimens with (e) or without previous etching with 37% phosphoric acid for 15 s were used for the intracoronal bleaching exper- iments. Teeth were randomly assigned to five treat- ments (n = 10): (C) control – no bleaching, (SP) sodium perborate, (CP) 35% carbamide peroxide, (25% HP) 25% hydrogen peroxide and (35% HP) 35% hydrogen peroxide. Bleaching was performed four times within a 72 h interval and afterwards, dentine pulp chamber blocks were obtained. The blocks were sectioned in 0.7 mm-thick slices and these were trimmed to reduce the inner dentine to a dumbbell shape with a cross- sectional area of 0.8 mm 2 . Specimens were tested with the microtensile method (0.5 mm min )1 ) and data were analysed (two-way anova-Tukey test, P < 0.05). Additional teeth were prepared for transmission elec- tron microscopy (TEM) to evaluate dentine ultramor- phology. Results The mean values of the UTS (SD) in MPa for sound dentine were: C = 48.3(8.5)a, SP = 34.6 (8.2)b, CP = 32.9 (8.9)b, 25% HP = 28.0(4.6)b, 35% HP = 26.4(6.6)b, and pre-etched dentine: Ce = 38.9(13.8)a, SPe = 31.3 (9.3)ab, CPe = 28.4 (6.2)ab, 25% HPe = 30.0 (7.9)ab, 35% HPe = 19.9(4.6)b. Significant differences between the means are indicated by the letters. TEM observations exhibited demineralization areas for all bleaching treatments. Conclusion Bleaching decreased dentine UTS after treatment. Pre-etched not-bleached dentine (Ce) presented UTS similar to pre-etched bleached dentine, except for 35% HPe. The decrease of UTS of bleached dentine could be attributed to ultrastructural altera- tions such as loss of inorganic components. Keywords: dentine, intracoronal bleaching, ulti- mate tensile strength, ultrastructure. Received 29 February 2008; accepted 17 December 2008 Introduction Root filled teeth may discolour due to the incorporation of degradation products from haemorrhage, incomplete removal of pulpal remnants, or the presence of filling materials and sealers after endodontic procedures Correspondence: Prof. Dr Marcelo Giannini, Faculdade de Odontologia de Piracicaba, Av. Limeira, 901 – 13414-903 Piracicaba, SP, Brazil (Tel.: +55-19-2106-5338; fax: +55-19- 2106-5218; e-mail: giannini@fop.unicamp.br). doi:10.1111/j.1365-2591.2009.01543.x International Endodontic Journal, 42, 568–575, 2009 ª 2009 International Endodontic Journal 568