Dental adhesives hydrolyze in the mouth. this study investigated the water sorption (SoR), solubility (SoL) and cytotoxicity (cYto) of experimental adhesives containing nitrogen-doped titanium dioxide nanoparticles (n_tio 2). Specimens (n = 15/group [SOR, SOL]; n = 10/group [CYTO]) of unaltered Clearfil SE Protect (CSP), OptiBond Solo Plus (OSP), Adper Scotchbond (ASB) and experimental adhesives (OSP + 25% or 30% of N_TiO 2) were fabricated, desiccated (37 °C) and tested for SOR and SOL according to ISO Specification 4049 (2009). CYTO specimens were UV-sterilized (8 J/cm 2) and monomer extracted in growth medium (1, 3 or 7 days). Human pulp cells were isolated and seeded (0.5 × 10 4) for MTT assay. SOR and SOL data was analyzed using GLM and SNK (α = 0.05) and CYTO data was analyzed with Kruskal-Wallis and SNK tests (α = 0.05). SOR and SOL values ranged from 25.80 μg/mm 3 (30% N_TiO 2) to 28.01 μg/mm 3 (OSP) and 23.88 μg/mm 3 (30% N_TiO 2) to 25.39 μg/mm 3 (25% N_TiO 2). cYto results indicated that pulp cells exposed to experimental materials displayed comparable viabilities (p > 0.05) to those of OSP. Experimental materials displayed comparable SOR, SOL and CYTO values (p > 0.05) when compared to unaltered materials. N_TiO 2 incorporation have not adversely impacted SoR, SoL and cYto properties of unaltered adhesives. Resin composite restorations are currently the most prevalent medical intervention in human beings with more than five hundred million restorations placed globally every year 1. Such popularity amongst patients and clinicians precipitates from their mercury-free compositions 2 , outstanding esthetic properties, and their minimally invasive and ultra-conservative restorative techniques 3. Their clinical use involves the removal of demineralized and bacteria-contaminated tooth structure, application of phosphoric acid (37%, 15-30 s), and the subsequent application of a primer and a dental adhesive resin in preparation for the intraoral fabrication of the resin composite restoration 4. The formation of the hybrid layer starts with the penetration of uncured monomers into water-rich, mineraldepleted areas of dentin, followed by the envelopment of exposed collagen fibrils, and the subsequent in situ polymerization by on-demand visible light irradiation 5. Its successful completion 6 should allow for the establishment of a crosslinked 7 and hermetically sealed 3-dimensional polymer-collagen network 6 capable of reducing microleakage, bacterial invasion, marginal staining, secondary caries and pulpal irritation 8. However, because these materials contain both hydrophilic and hydrophobic moieties in a single product 9 , they tend to become chemically unstable when placed in contact with moist dentin 10. The physical manifestation of such instability is translated into materials that phase-separate 11 and display inadequate degrees of conversion 12 .

Thls report was prepared as an account of Government sponsored work. Neither the _ United States, nor the Commission, nor any person acting on behalf of the Commlsslon: i_.A. Makes any warranty or representation, express or Implied, with respect to the ac-ii._ curacy, comp]eteness, or usefulness of the informatlon contained In thls report, or that the ! ,'. 'i": use of any InformaHon, apparatus, method, or pi'ocess disclosed In this report may not In-