Release of Interface Confined Water Significantly Improves Dentin Bonding

New Monomer Capable of Dual Chemical Binding with Dentin to Improve Bonding Durability

The water-rich nature of the dentin bonding microenvironment, coupled with the stresses on the bonding interface, contributes to the hydrolytic degradation of the hybrid layer, resulting in a decline in bonding durability and, ultimately, restoration failure. Currently, the 3-step etch-and-rinse technique remains the gold standard for dentin bonding, and the bonding mechanism mainly involves a physical interaction with little chemical bonding. In this study, we have developed a siloxane-modified polyurethane monomer (SPU) with acrylate and siloxane modifications that chemically binds to both collagen and hydroxyapatite in dentin. Formulated as a bisphenol A-glycidyl methacrylate alternative, the SPU monomer-based adhesive was designed to improve dentin bonding quality and durability. Attenuated total reflection Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscope, and hydroxyproline release assays were performed on SPU-treated collagen, hydroxyapatite, and acid-etched dentin slices to dentin. The physicochemical properties of the configured SPU adhesives were profiled for polymerization behavior, water contact angle, and tensile strain and strength. The bonding effectiveness was assessed through micro-tensile strength, nano-leakage tests conducted on the bonded samples before and after thermal cycle aging. Finally, we further conducted in vivo and in vitro experiments to assess the biocompatibility of adhesives. The results showed that the siloxane groups of SPU monomer could covalently bind to dentin collagen and hydroxyapatite. The incorporation of SPU in the adhesive led to a significant increase in adhesive polymerization (P < 0.05) and tensile strain at break up to 134.11%. Furthermore, the SPU adhesive significantly improved dentin bond strength (P < 0.05), reduced interfacial nano-leakage (P < 0.05), and displayed good biocompatibility. In conclusion, the application of SPU, which achieves dual chemical bonding with dentin, can improve the quality of the hybrid layer, buffer the interfacial stresses, enhance the interfacial resistance to hydrolysis, and provide a feasible strategy to extend the service life of adhesive restorations.

A glycol chitosan derivative with extrafibrillar demineralization potential for self-etch dentin bonding

OBJECTIVES

Extrafibrillar demineralization is an etching technique that removes only minerals from around the collagen fibrils for resin infiltration. The intrafibrillar minerals are left intact to avoid their replacement by water that is hard for adhesive resin monomers to displace. The present work reported the synthesis of a water-soluble methacryloyloxy glycol chitosan-EDTA conjugate (GCE-MA) and evaluated its potential as an extrafibrillar demineralization agent for self-etch dentin bonding.

METHODS

Glycol chitosan-EDTA was functionalized with a methacryloyloxy functionality. Conjugation was confirmed using Fourier transform-infrared spectroscopy. The GCE-MA was used to prepare experimental self-etch primers. Extrafibrillar demineralization of the primers was evaluated with scaning electron microscopy and transmission electron microscopy. The feasibility of this new self-etch bonding approach was evaluated using microtensile bond strength testing and inhibition of dentin gelatinolytic activity. The antibacterial activity and cytotoxicity of GCE-MA were also analyzed.

RESULTS

Conjugation of EDTA and the methacryloyloxy functionality to glycol chitosan was successful. The functionalized conjugate was capable of extrafibrillar demineralization of mineralized collagen fibrils. Tensile bond strength of the experimental self-etch primer to dentin was comparable to that of phosphoric acid-etched dentin and the commercial self-etch primer Clearfil SE Bond 2. The GCE-MA also inhibited soluble rhMMP-9. In-situ zymography detected minimal fluorescence in hybrid layers conditioned with the experimental primer. The GCE-MA was noncytotoxic and possessed antibacterial activities against planktonic bacteria.

SIGNIFICANCE

Synthesis of GCE-MA brought into fruition a self-etch conditioner that selectively demineralizes the extrafibrillar mineral component of dentin. A self-etch primer prepared with GCE-MA achieved bond strengths comparable to commercial reference adhesive systems.

A polyhexamethylene biguanide-assembly assisted strategy of dentin bonding greatly promotes bonding effects and caries treatment

Structural degeneration of a hybrid layer composed of a demineralized dentin matrix (DDM) and adhesive causes unsatisfactory functional outcomes in terms of bonding repair and caries treatment and is accompanied by high prevalence of secondary caries. Clinically, defects in the hybrid layer from insufficient adhesive infiltration, bacterial load from retained infected-dentin, and bacterial attack from the oral cavity are the main threats to degeneration. Currently, there is no strategy to simultaneously address adhesive penetration and bacterial infection. Herein, based on the core role of the strongly-polar hydrated DDM interface in dentin bonding, an interface-reconstructed bonding strategy assisted by electrostatic assembly of broad-spectrum germicidal polyhexamethylene biguanide (PHMB) is proposed that kills two birds with one stone. PHMB is absorbed onto the anionic 3D DDM forming a PHMB/DDM complex. The surface potential of the DDM increases by about 100 mV, the anion content decreases by 20%, and the interface water content decreases by nearly 40%. All of these changes contribute to the penetration of the adhesive, thereby improving the bonding strength and durability. After thermal cycling aging, the bonding strength of the PHMB group was 1.45-1.65 times that of the control group. In terms of antibacterial properties, PHMB treatment not only has a bacterial-killing ability due to the already formed biofilm but also significantly reduces the adhesion of bacteria, thereby delaying the occurrence of secondary caries. In summary, PHMB treatment reconstructed the DDM interface, resulting in a defect-low and inherent antibacterial hybrid layer that improves the bonding effect, treatment of caries and even prevention of secondary caries.