Sorption, solubility and cytotoxicity of novel antibacterial nanofilled dental adhesive resins

Abstract

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 .

Medical and Dental Applications of Titania Nanoparticles: An Overview

“…Recently, research incorporating TiO 2 NPs in dental adhesives concluded that they had enhanced biocompatibility with reduced solubility and water sorption when compared to the conventional adhesives used in dentistry. Thus, the usage of these NPs is highly recommended in currently available adhesive dentistry [ 333 ]. Another research work elaborated that TiO 2 NPs added to self-adhesive cements revealed a maximum degree of conversion (DC) when compared to their conventional types [ 334 ].…”

Characterization of Experimental Nanoparticulated Dental Adhesive Resins with Long-Term Antibacterial Properties

“…According to previous studies, current dental adhesive resins are formulated using a combination of hydrophilic and hydrophobic components [ 18 ] that phase-separate when applied onto water-rich tissues [ 19 ]. This chemical instability leads to incomplete envelopment of exposed collagen fibrils and the establishment of porous hybrid layers that are prone to failure by biodegradation, hydrolysis, esterases, and biofilms [ 20 ]. This significant problem has precipitated the execution of several studies to improve the physical, chemical, and biological properties of current polymer formulations.…”

“…Titanium dioxide (TiO 2 , anatase, rutile, or brookite) is known for its relevant physical, chemical, antimicrobial, and biocompatibility properties [ 33 ]. Nanoparticles of TiO 2 (TiO 2 -np) are typically white, have diameters around 25 nm, have high refractive index, are corrosion resistant, display high microhardness values [ 20 , 34 ], and were demonstrated to be effective against numerous microorganisms, including Candida albicans , Staphylococcus aureus , Pseudomonas aeruginosa , Escherichia coli , and Lactobacillus acidophilus [ 35 ]. However, despite these relevant characteristics, TiO 2 -np have large bandgaps (3.2204 eV, for anatase) and require the utilization of UV irradiation to generate different types of reactive oxygen species (ROS) [ 34 ].…”

“…Doping the crystal lattice of TiO 2 -np with metals and non-metals has been previously shown to decrease the bandgap of Titania (2.47 eV) [ 37 ] and allow the utilization of visible light irradiation, which is widely used in dentistry, for the generation of ROS. The synthesis, incorporation, and covalent functionalization of visible light-responsive nitrogen-doped titanium dioxide nanoparticles (N_TiO 2 ) into a commercially available dental adhesive resin (OptiBond Solo Plus, Kerr Corp., USA; OPTB) has been recently reported by Esteban Florez et al [ 34 , 38 , 39 ] Experimental adhesive resins displayed strong antibacterial and biomimetic properties when irradiated with visible light [ 34 ] and were less soluble and more biocompatible [ 20 ], when compared to commercially available materials, which suggests that nanoparticulated materials may hold the promise to decrease the incidence of secondary caries and to extend the service lives of polymer-based adhesive restorations.…”

Influence of TiO2 and ZrO2 Nanoparticles on Adhesive Bond Strength and Viscosity of Dentin Polymer: A Physical and Chemical Evaluation

“…In dentistry, TiO 2 nanoparticles have been used to improve the fracture resistance of endodontically treated teeth [14], osseointegration of dental implants [15], antibacterial potential of a material [13], and bonding to human teeth by incorporating them in the adhesives [16]. In a recent study, the addition of TiO 2 nanoparticles in experimental dental adhesives demonstrated comparable water sorption, solubility, and biocompatibility with unaltered adhesives, advocating the use of these particles in adhesive dentistry [17]. In another study, it was reported that self-adhesive resin cements containing TiO 2 displayed a superior degree of conversion (DC) to their unaltered counterparts [18].…”