dental materials 27S (2011) e1–e84 e27 Conclusions: Within the limitations of this in vitro study we can conclude that: 1, only L* and Y are significantly correlated to the 5 opacity parameters; 2, the couple L* black/CR Y gave the highest value of R 2 (=0.97) and must be considered as a standard for future investigations; 3, R 2 values are influenced by the background color. doi:10.1016/j.dental.2011.08.463 61 Remineralizing agents on microhardness of sound and dem- ineralized bleached enamel A.B. Borges * , C.A. Guimarães, C.J. Ramos, A.L.S. Borges, C.R. Pucci, C.R.G. Torres Universidade Estadual Paulista, UNESP, São José dos Campos, Brazil Objectives: To evaluate the effect of calcium and fluoride addition in 35% hydrogen peroxide (HP) bleach- ing gel on microhardness of sound and demineralized enamel. Materials and methods: Cylindrical specimens of bovine enamel (3 mm × 2 mm) were divided in two groups (n = 30): sound enamel (SE) and demineralized enamel (DE). Each group was divided in three subgroups, according to the bleaching gel modified by manufacturer 1 : HP 35%; HP 35% + calcium gluconate; HP 35% + sodium fluoride. Bleach- ing procedures were performed ex vivo. The specimens were fixed in intraoral devices used by 10 volunteers during 7 days in order to evaluate the effect of human saliva on bleached enamel. Surface Knoop Microhardness (SMH) of superficial enamel was measured before and after bleach- ing treatments, as well as after 1 and 7 days of saliva exposure. Results: Data were analyzed by RM-ANOVA (5%) and showed significant difference for time factor, both for SE and DE groups (p =0.001). The application of Tukey’s test in SE groups revealed significant lower SMH mean imme- diately after bleaching compared to baseline and after 7 days. For DE specimens, the lowest means were obtained for baseline period. Bleaching with HP + calcium increased sig- nificantly the SMH means immediately after bleaching and the exposure to saliva resulted in increasing of SMH for all groups. Conclusions: Bleaching with 35% HP caused significant reduction in SE microhardness and did not exacerbate the demineralization of initial artificial caries. The addi- tion of potentially remineralizing agents in the bleaching gels can play an important role in the maintenance of microhardness values of SE and to induce remineralization of DE. doi:10.1016/j.dental.2011.08.464 1 FGM Produtos Odontológicos. 62 A novel at-home bleaching technique modified by a CPP-ACP paste B.C. Borges 1,* , J.S. Borges 2 , C.D. Melo 2 , I.V. Pinheiro 2 , A.J. Santos 2 , R. Braz 1 , M.A. Montes 1 1 University of Pernambuco, Camaragibe, Brazil 2 Federal University of Rio Grande do Norte, Natal, Brazil Objectives: This study was designed to evaluate in vitro the efficacy of a novel at-home bleaching technique using 10% or 16% carbamide peroxides modified by a CPP-ACP paste (MI Paste, GC Corporation) and its influence on the microhardness of bleached enamel. Materials and methods: Forty bovine incisors were divided into four groups (n = 10) according to the bleaching agent uti- lized: 10% carbamide peroxide only; a blend of 10% carbamide peroxide and MI paste; 16% carbamide peroxide only; and a blend of 16% carbamide peroxide and MI Paste. During the 14-day bleaching regimen, the samples were stored in artifi- cial saliva. The Vickers microhardness and color of the teeth were assessed at baseline (T0) and immediately after the bleaching regimen (T14) using a microhardness tester and a spectrophotometer, respectively. The degree of color change was determined by the CIEL*a*b* system (E, L*, a* and b*) and Vita shade guide parameters. The data was analyzed by analysis of variance and Tukey’s test (p < 0.05). Results: The teeth that were bleached with a blend of perox- ides (10% or 16%) and the CPP-ACP paste presented increased microhardness values at T14 compared with T0, whereas the samples that were bleached with peroxides only did not show any differences in their microhardness values. All the bleach- ing agents were effective at whitening the teeth and did not show a statistically significant difference using the CIEL*a*b* system (E, L*, a* and b*) or the Vita shade guide param- eters. Conclusions: The use of a CPP-ACP paste with carbamide peroxide bleaching agents increased the bleached enamel’s microhardness and did not have an influence on whitening efficacy. This improves safety and might even reduce in vivo tooth sensitivity during the bleaching process. doi:10.1016/j.dental.2011.08.465 63 Polymerization stress assessment by crack analysis and mechanical testing R.R. Braga 1,* , T. Yamamoto 2 , K. Tyler 3 , L.C. Boaro 1 , J.L. Ferracane 4 , M.V. Swain 3 1 University of São Paulo, Brazil 2 Tsurumi University, Japan 3 University of Sydney, Australia 4 Oregon Health & Science University, USA Objectives: The aim of this study was to verify the working hypothesis that two methods for determining polymerization contraction stress, analysis of cracks from hardness indents and axial loading, would rank a series of commercial restora- tive composites in a similar order, and that both tests would