Modifying Adhesive Materials to Improve the Longevity of Resinous Restorations

Dental caries is a common disease on a global scale. Resin composites are the most popular materials to restore caries by bonding to tooth tissues via adhesives. However, multiple factors, such as microleakage and recurrent caries, impair the durability of resinous restorations. Various innovative methods have been applied to develop adhesives with particular functions to tackle these problems, such as incorporating matrix metalloproteinase inhibitors, antibacterial or remineralizing agents into bonding systems, as well as improving the mechanical/chemical properties of adhesives, even combining these methods. This review will sum up the latest achievements in this field

Evaluation of the Biocompatibility and Micromechanical Properties of Experimental Dental Adhesives

The purpose of this study was to investigate the biocompatibility and micromechanical properties of newly synthesized antibacterial monomer and cross-linker functional surfactants into a commercially available dental adhesive (Single Bond, 3M ESPE, Saint Paul, MN, USA) at three concentrations (0.05, 0.1, 0.25 mg/mg). All groups were analyzed by evaluation of micro-tensile bond strength, ultimate tensile strength, cell viability, antibacterial properties, and surface micro-hardness. Scanning electron microscopy (SEM) was used for interfacial characterization. Human extracted molars were used as a substrate for bonding adhesives for the micro-tensile bond strength (MTBS) and scanning electron microscopy (SEM) studies. Twenty resin-dentin beams (0.9 ± 0.1 mm2) per group were evaluated at 24 hrs and 6 mos for MTBS. Slabs of ~1 mm were analyzed in the SEM for surface characterization. For the ultimate tensile strength (UTS), ten hour-glass shaped specimens (10 × 2 × 1mm) per group were tested at 24 hrs, 1 wk, and 6 mos. To evaluate toxicity, four disc-shaped specimens (5 × 2 mm) per group were incubated with human gingival fibroblasts (HGF). Antibacterial properties were evaluated by incubating three disc-shaped specimens (8 × 1 mm) per group with a strain of caries-producing bacteria S. mutans. Within the limitations of this in vitro study, it was concluded that incorporation of antibacterial monomer and cross-linker additives may be a viable option to help increase the longevity of tooth-colored adhesive restorations. Single Bond adhesive modified with 0.1 mg/mg monomer appears to provide the optimal balance for biocompatibility and micromechanical properties

Threats to adhesive/dentin interfacial integrity and next generation bio-enabled multifunctional adhesives

Nearly 100 million of the 170 million composite and amalgam restorations placed annually in the United States are replacements for failed restorations. The primary reason both composite and amalgam restorations fail is recurrent decay, for which composite restorations experience a 2.0–3.5-fold increase compared to amalgam. Recurrent decay is a pernicious problem—the standard treatment is replacement of defective composites with larger restorations that will also fail, initiating a cycle of ever-larger restorations that can lead to root canals, and eventually, to tooth loss. Unlike amalgam, composite lacks the inherent capability to seal discrepancies at the restorative material/tooth interface. The low-viscosity adhesive that bonds the composite to the tooth is intended to seal the interface, but the adhesive degrades, which can breach the composite/tooth margin. Bacteria and bacterial by-products such as acids and enzymes infiltrate the marginal gaps and the composite\u27s inability to increase the interfacial pH facilitates cariogenic and aciduric bacterial outgrowth. Together, these characteristics encourage recurrent decay, pulpal damage, and composite failure. This review article examines key biological and physicochemical interactions involved in the failure of composite restorations and discusses innovative strategies to mitigate the negative effects of pathogens at the adhesive/dentin interface

The effect of photoinitiator systems on resin-based composite containing ZnO-nanoparticles

ObjectiveZinc oxide (ZnO) powder possesses antibacterial activity and although white in color, it can severely reduce the depth of cure (DoC) of resin-based composite (RBC). This study investigated the effect of unary and binary photoinitiator systems on the DoC and degree of conversion (DC) of formulated RBC containing ZnO-nanoparticles.MethodsFourteen RBCs (n = 3/group) were formulated consisting of 50 wt% mixture of monomers (Bis-GMA, TEGDMA, and UDMA) and 50 wt% fillers (inert barium glass powder and silica nanoparticles). ZnO-nanoparticles were added at 0 (control), 0.5, 1, 1.5 and 2 wt%. A unary initiator system consists of camphorquinone (CQ) 0.25, 0.5 and 1 wt% and ethyl 4-(dimethylamino)benzoate (EDMAB) 0.75 wt% or a binary initiator system consisting of diphenyliodonium hexafluorophosphate (DPI) 0.25, 0.5 and 1 wt%, CQ 0.25, 0.5 and 1 wt% and EDMAB 0.75 wt% were added to the monomer mixture. To measure the DoC, each specimen was prepared in a custom-made mold with a slot (16 x 8×2 mm) and a top cover plate, irradiated from one end (40 s), stored dry (37° C, 1 d) and measured at increasing depths using Vickers hardness (0.5 mm intervals). 1 mm thick specimens were prepared to measure DC continuously using FTIR, from zero up to 24 h post-irradiation.ResultsIncreasing the concentrations of ZnO led to a significant reduction of DoC (p < 0.05). But most of the binary initiator groups showed significantly higher DoC (p < 0.05). Depth, at 80 % of max VHN, of unary initiator groups reduced from 6.8 mm (ZnO at 0 wt%) to 2.1 mm (ZnO at 2 wt%) and in binary initiator groups from 8.4 mm to 2.3 mm. Groups with lower photoinitiator concentrations (0.25 wt%) showed a significant increase in DoC compared with groups with higher concentrations (1 wt%) (p < 0.05). DC after 24 h was independent of either ZnO concentration or the photoinitiator system (p > 0.05). However, faster conversions were observed in binary initiator groups. The RPmax of binary groups ranged from 8.1 % to 10.1 %/s, and unary groups ranged from 5.2 % to 7.2 %/s.SignificanceThe addition of DPI resulted in an overall increased curing depth, which was enhanced when lower concentrations of photoinitiators were used. Also, DPI resulted in faster conversions. This is desirable in designing antibacterial RBC containing ZnO

Synthesis and evaluation of a novel co-initiator for dentin adhesives: polymerization kinetics and leachables study

The final publication is available at Springer via http://dx.doi.org/10.1007/s11837-015-1335-6.A new tertiary amine co-initiator (TUMA) containing three methacrylate-urethane groups was synthesized for application in dentin adhesives. The photopolymerization kinetics and leaching of unreacted components from methacrylate-based dental polymers formulated with this new co-initiator were determined. The newly synthesize co-initiator showed good chemical stability and decreased amine release from the initiator system. This study provides important information for the future development of biocompatible dentin adhesives/composites

Bacterial Interactions with Dental and Medical Materials

The interaction of bacteria with biomaterials’ surfaces has critical clinical implications on the development and progression of biofilm-related diseases. In this book "Bacterial Interactions with Dental and Medical Materials", encouraging findings on tissue-contacting biomaterials to control biofilms, enhanced understanding of key mechanisms, and clinical perspectives are discussed toward improving healthcare

Towards enhancing the durability and strength of dentin-resin bond : the role of dimethyl sulfoxide (DMSO) as an alternative solvent in dental adhesives

One of the main goals in adhesive dentistry is the preservation of the hybrid layer, a unique biological composite layer, formed by the impregnation of collagen fibrils in the dentin structure with adhesive resin. Different adhesive strategies have been used to achieve this. One strategy focuses on the inhibition of endogenous protease activity, and the other strategy on improving the penetration and impregnation of the adhesive monomers in demineralized dentin. Dimethyl sulfoxide (DMSO; (CH3)2SO) is a polar aprotic solvent which dissolves polar and nonpolar compounds. It has the ability to penetrate biological tissues and has been used to solvate dental resin monomers. It has recently been suggested to improve the durability and longevity of bonding, by enhancing the penetration of resin monomers in dentin. Four studies were designed to evaluate the impact of DMSO on the durability of resin-dentin bonding, to evaluate the effects of incorporating DMSO into experimental adhesives with different hydrophilicities on mechanical and physical properties, as well as the biological effects on cells. The aim of this series of studies is to evaluate the effect and mechanism of action of DMSO on resin-dentin bonding, to find one optimal concentration or range of concentrations of DMSO that can be safely incorporated into resin adhesive systems to improve the integrity and stability of bonding to dentin. Results of these studies showed that pre-treating dentin with low DMSO concentrations (1–5 vol. %) preserve the integrity of adhesion and enhance the permeability of small-molecule monomers in dentin. Results also showed thatincorporation of 1 w/w % or less DMSO to adhesive did not impair the mechanical and physical properties of hydrophobic and hydrophilic adhesives. Results also showed that incorporation of DMSO into hydrophobic adhesive did not increase the cytotoxicity, while 1 w/w % and more DMSO incorporation into hydrophilic adhesive showed an increase of cytotoxic effects. These results suggested that when DMSO (1–5 vol. %) used as dentin- pretreatment, it improves the durability and quality of resin-dentin bonding. Results also suggested that the addition of DMSO to hydrophobic and hydrophilic adhesives (up to 1 % w/w), did not negatively affect their physical or mechanical properties. Addition of DMSO (up to 10 % w/w) to hydrophobic or hydrophilic adhesives did not increase the cytotoxicity from eluates, while the addition of DMSO (1 w/w %) to hydrophilic resin caused an increase in the transdentinal cytotoxic effects