Vol 15, No 6, 2013 553 Influence of Two Different Methods of Delivering Fluoride on Bond Strength and Degree of Conversion of an Adhesive After Bleaching Bruna Fortes Bittencourt a / John Alexis Dominguez b / Alessandro D. Loguercio c / João Carlos Gomes d / Osnara Maria Mongruel Gomes e Purpose: To evaluate the influence of fluoride delivery and restoration time point on the microshear bond strength (mSBS) and degree of conversion (DC) values of an adhesive applied on bleached enamel. Materials and Methods: Fifty-four enamel specimens were submitted to bleaching and divided into 3 groups of n = 18: group HP: 35% hydrogen peroxide (HP); group HPF: HP + 1.23% sodium fluoride application (F); group PF: 38% HP with F. A control group of n = 6 was neither bleached nor fluoridated. Subsequently, each group ex- cept the control was subdivided into 3 subgroups (n = 6) to be restored immediately, or at 7 or 14 days. Tygon tubes were filled with composite resin and placed on enamel surfaces, then the mSBS test was performed. The DC of the interface was observed with Raman spectroscopy. The data were submitted to two-way ANOVA and Tukey’s and Dunnet’s post-hoc test (_ = 0.05). Results: The mSBS results showed higher values for groups HP and HPF at 14 days compared with immediate and 7 days (p < 0.05). Lower DC values were obtained in the immediately restored groups HP and HPF, which were significantly different from 7 and 14 days (p < 0.05). mSBS and DC for group PF was similar at all restor- ation time points and to the control group (p > 0.05). Conclusion: Only the use of a fluoridated in-office bleaching agent (Opalescence Boost PF) proved to be effective for immediately reversing the side effects of low mSBS and DC values when in-office bleaching is used. Keywords: tooth bleaching, hydrogen peroxide, dental adhesives, fluoride. J Adhes Dent 2013; 15: 553–559. Submitted for publication: 09.04.12; accepted for publication: 01.02.13. doi: 10.3290/j.jad.a29585 a PhD Student, Department of Dentistry, Ponta Grossa State University, Ponta Grossa, Brazil. Wrote manuscript, performed experiments. b PhD Student, Department of Dentistry, Ponta Grossa State University, Ponta Grossa, Brazil. Contributed to overall manuscript and experiments. c Professor, Department of Dentistry, Ponta Grossa State University, Ponta Grossa, Brazil. Performed statistical evaluation and contributed to overall manuscript. d Professor, Department of Dentistry, Ponta Grossa State University, Ponta Grossa, Brazil. Proofread manuscript. e Professor, Department of Dentistry, Ponta Grossa State University, Ponta Grossa, Brazil. Co-wrote and proofread manuscript. Correspondence: Bruna Fortes Bittencourt, Ponta Grossa State University, Department of Dentistry, School of Dentistry, Carlos Cavalcanti, 4748 Ponta Grossa 84030-900 Brazil. Tel: +55-42-3224-5164, Fax: +55-42-3224-1166. e-mail: brubita@hotmail.com techniques developed for bleaching purposes, the in- office technique is useful for patients who are unable to perform daily at-home bleaching, or for those looking to obtain satisfactory results in a shorter period of time. 29 However, it has been found that in-office treatment is more aggressive than the at-home technique in terms of post-operative tooth sensitivity. 39 This could be ex- plained because with in-office bleaching, higher concen- trations of hydrogen peroxide with lower pH are used for shorter periods; these factors can affect dental tissues in different ways. 26 Hydrogen peroxide in higher concentrations may cause morphological changes in the enamel surface. Studies have shown that bleaching materials can lead to different degrees of enamel mineral loss, 1,8 and consequently decrease enamel microhardness val- ues 4,5,8,10,12,14,15,26,28,42 and increase surface rough- ness. 3,30 Moreover, previous studies have shown a reduction in bond strength values when the restoration was performed immediately after bleaching. 7,24,35,40 Two hypotheses may explain this effect. First, the presence T ooth whitening techniques are the preferred option to treat discolored teeth, because they are a safe, mini- mally invasive and cost-effective treatment, compared with other restorative procedures. 21,22,29 Among several