In vitro enzymatic biodegradation of adhesive resin in the hybrid layer

Effect of matrix metalloproteinase inhibitors on bonding durability of universal adhesives

This study aimed to evaluate the effect of different matrix metalloproteinase inhibitors (MMPIs) on the microtensile bond strength (μTBS) and nanoleakage of universal adhesives. One hundred twenty non-carious human molars were prepared and randomly assigned to two groups: Scotchbond Bond Universal (SBU) and Gluma Bond Universal (GBU). The samples in each group were assigned to five subgroups (n=12) based on one control (water) and four MMPIs (Benzalkonium-chloride (BAC), Batimastat (BB94), Chlorhexidine (CHX), and Epigallocatechin-gallate (EGCG)). Each adhesive was applied in self-etch (SE) mode or etch-and-rinse (ER) mode. Dentin/composite sticks were fabricated and subjected to the μTBS test after 24 h or 6 months. At 6 months, MMPIs did not affect the μTBS of the adhesives, regardless of etching mode. Nanoleakage was more pronounced in ER mode than in SE mode for all subgroups. All MMPIs, with the exception of CHX, decreased the nanoleakage of GBU in ER mode.

Biodegradation of Dental Resin-Based Composite—A Potential Factor Affecting the Bonding Effect: A Narrative Review

In recent years, although resin composite has played an important role in the restoration of tooth defects, it still has several disadvantages, including being biodegraded by saliva, bacteria and other enzymes in the oral cavity, which may result in repair failure. This factor is not conducive to the long-term survival of the prosthesis in the mouth. In this article, we review the causes, influencing factors and prevention methods of resin biodegradation. Biodegradation is mainly caused by esterase in saliva and bacteria, which breaks the ester bond in resin and causes the release of monomers. The mechanical properties of the prosthesis can then be affected. Meanwhile, cathepsin and MMPs are activated on the bonding surface, which may decompose the dentin collagen. In addition, neutrophils and residual water on the bonding surface can also aggravate biodegradation. Currently, the primary methods to prevent biodegradation involve adding antibacterial agents to resin, inhibiting the activity of MMPs and enhancing the crosslinking of collagen fibers. All of the above indicates that in the preparation and adhesion of resin materials, attention should be paid to the influence of biodegradation to improve the prosthesis’s service life in the complex environment of the oral cavity.

Evaluation of resveratrol-doped adhesive with advanced dentin bond durability

OBJECTIVES

This paper aimed to evaluate the influence of resveratrol-doped adhesive on the durability and antibiofilm capability of dentin bonding.

METHODS

Experimental adhesives were prepared by incorporating resveratrol into a universal adhesive at concentrations of 0 (control), 0.1, 1, and 10 mg/mL. The microtensile bond strength, fracture modes, and adhesive-dentin interface nanoleakage were assessed after 24 h of water storage, 10,000 times of thermocycling or 1-month of collagenase ageing. Relevant antibiofilm capability on Streptococcus mutans (S. mutans), in situ zymography, degree of conversion, and cytotoxicity of resveratrol-doped adhesives were also determined.

RESULTS

Irrespective of thermocycled or collagenase ageing, the resveratrol-doped adhesive (1 mg/mL) maintained the bond strength and reduced the nanoleakage expression. Meanwhile, the inhibitory ability on endogenous protease activity and S. mutans biofilm formation with acceptable biocompatibility were obtained.

CONCLUSIONS

This study suggested that the resveratrol-doped adhesive achieved effective improvement on dentin bond durability and secondary caries management.

CLINICAL SIGNIFICANCE

The application of the resveratrol-doped adhesive indicates promising benefits to increase the lifetime of composite restorations.

A Review of Mechano-Biochemical Models for Testing Composite Restorations

Due to the severe mechano-biochemical conditions in the oral cavity, many dental restorations will degrade and eventually fail. For teeth restored with resin composite, the major modes of failure are secondary caries and fracture of the tooth or restoration. While clinical studies can answer some of the more practical questions, such as the rate of failure, fundamental understanding on the failure mechanism can be obtained from laboratory studies using simplified models more effectively. Reviewed in this article are the 4 main types of models used to study the degradation of resin-composite restorations, namely, animal, human in vivo or in situ, in vitro biofilm, and in vitro chemical models. The characteristics, advantages, and disadvantages of these models are discussed and compared. The tooth-restoration interface is widely considered the weakest link in a resin composite restoration. To account for the different types of degradation that can occur (i.e., demineralization, resin hydrolysis, and collagen degradation), enzymes such as esterase and collagenase found in the oral environment are used, in addition to acids, to form biochemical models to test resin-composite restorations in conjunction with mechanical loading. Furthermore, laboratory tests are usually performed in an accelerated manner to save time. It is argued that, for an accelerated multicomponent model to be representative and predictive in terms of both the mode and the speed of degradation, the individual components must be synchronized in their rates of action and be calibrated with clinical data. The process of calibrating the in vitro models against clinical data is briefly described. To achieve representative and predictive in vitro models, more comparative studies of in vivo and in vitro models are required to calibrate the laboratory studies.

Mechanical-physicochemical properties and biocompatibility of catechin-incorporated adhesive resins

Several anti-proteolytic dentin therapies are being exhaustively studied in an attempt to reduce dentin bond degradation and improve clinical performance and longevity of adhesive restorations.

A novel dry-bonding approach to reduce collagen degradation and optimize resin-dentin interfaces

In dentistry, the wet-bonding approach relies on water to maintain demineralized collagen expanded for proper resin infiltration; nevertheless, hydrolytic instability of the resin-dentin interface is inevitable with current bonding techniques. Considering dimethyl sulfoxide’s (DMSO) ability to “biomodify” collagen and precipitate enzymes, the aim was to test whether the use of DMSO would permit adequate resin bonding to H₃PO₄-etched dehydrated dentin and assess its impact on collagen degradation by host-derived enzymes. Etched dentin surfaces from extracted sound human molars were randomly bonded in wet or dry conditions using aqueous or ethanolic DMSO solutions as pretreatments and bonding resins with or without DMSO. Bonded teeth were sectioned into resin-dentin slabs for confocal in situ zymography and beams for microtensile bond strength test. Demineralized powdered dentin was incubated in the tested DMSO -media and a hydroxyproline assay evaluated dissolution of collagen peptides. Zymography was performed on protein extracts obtained from dry and wet H₃PO₄-ecthed dentin powder treated with the DMSO- media. The correlative biochemical analysis demonstrated that reduction of water content during dentin hybridization by the innovative dry-bonding approaches with DMSO is effective to inactivate host-derived MMP-2 and MMP-9 and thus reduce collagen degradation while simultaneously optimizing resin-dentin bonding.

Modulating pH through lysine integrated dental adhesives

OBJECTIVES

The objective of this study was to explore the effect of lysine integration to dental adhesives with respect to the polymerization kinetics, neutralization capacities in the acidic microenvironment, dynamic mechanical properties, and thermal properties.

MATERIALS AND METHOD

Lysine was incorporated into liquid resin formulations at 2.5 and 5.0wt % with additional water/ethanol co-solvents. The co-monomer system contained 2-hydroxyethyl-methacrylate (HEMA) and Bisphenol A glycerolate dimethacrylate (BisGMA) with a mass ratio of 45/55. The kinetics of photopolymerization, neutralization capacities, lysine-leaching, dynamic mechanical properties and thermal properties of the control and experimental adhesives were analyzed.

RESULTS

The degree of conversion of the experimental adhesive was increased substantially at 2.5wt% lysine as compared to the control. The experimental polymers provided acute neutralization of the acidic microenvironment. Approximately half of the lysine was released from the polymer network within one month. Under dry conditions and physiologic temperatures, the incorporation of lysine did not compromise the storage modulus. Comparison of the thermal properties suggests that the more compact structure of the control adhesive inhibits movement of the polymer chains resulting in increased T_g.

SIGNIFICANCE

Incorporating lysine in the adhesive formulations led to promising results regarding modulating pH, which may serve as one aspect of a multi-spectrum approach for enhancing the durability of composite restorations. The results provide insight and lay a foundation for incorporating amino acids or peptides into adhesive formulations for pH modulation or desired bioactivity at the interfacial margin between the composite and tooth.

Quercetin as a simple but versatile primer in dentin bonding

A quercetin/ethanol solution may serve as a simple but versatile primer to obtain desirable bonding stability and prevent secondary caries.

Self-Strengthening Hybrid Dental Adhesive via Visible-light Irradiation Triple Polymerization

A self-strengthening methacrylate-based dental adhesive system was developed by introducing an epoxy cyclohexyl trimethoxysilane (TS) which contains both epoxy and methoxysilyl functional groups. The experimental formulation, HEMA/BisGMA/TS (22.5/27.5/50, wt%), was polymerized by visible-light. Real-time Fourier transform infrared spectroscopy (FTIR) was used to investigate in situ the free radical polymerization of methacrylate, ring-opening cationic polymerization of epoxy, and photoacid-induced sol-gel reactions. Among the three simultaneous reactions, the reaction rate of the free radical polymerization was the highest and the hydrolysis/condensation rate was the lowest. With 40s-irradiation, the degrees of conversion of the double bond and epoxy groups at 600 s were 73.2±1.2%, 87.9±2.4%, respectively. Hydrolysis of the methoxysilyl group was initially <5%, and increased gradually to about 50% after 48 h dark storage. Photoacids generated through the visible-light-induced reaction were effective in catalyzing both epoxy ring-opening polymerization and methoxysilyl sol-gel reaction. The mechanical properties of copolymers made with TS concentrations from 5 to 35 wt% were obtained using dynamic mechanical analysis (DMA). In wet conditions, the storage moduli at 70 °C and glass transition temperature were significantly higher than that of the control (p<0.05); these properties increased with TS concentration and storage time. The post reaction of hydrolysis/condensation of alkoxysilane could provide persistent strengthening whether in a neutral or acidic environment and these characteristics could lead to enhanced mechanical properties in the oral environment. The cumulative amount of leached species decreased significantly in the TS-containing copolymers. These results provide valuable information for the development of dental adhesives with reduced leaching of methacrylate monomers and enhanced mechanical properties under the wet, oral environment.

Optimization of direct currents to enhance dentine bonding of simplified one-step adhesive

The aim of this study was to investigate the effects of different direct current intensities on dentine bonding effectiveness of Clearfil S(3) Bond and on cell viability of human dental pulp cells (HDPCs). Thirty-five-third molars were sectioned and ground to provide flat surfaces. Clearfil S(3) Bond was applied under different current conditions for 30 s and then resin composite was built up. Specimens were processed for microtensile bond strength (µTBS) testing and for nanoleakage investigation using scanning electron microscopy. Primary HDPCs isolated from premolars were stimulated with different intensities of electric current for 30 s. Then, cell viability was tested using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Specimens bonded with application of electrical current intensities of 50, 60, 70, and 90 µA exhibited a significant increase in immediate µTBS compared with all other groups. Bonded interfaces prepared using electrically assisted current application showed reduced interfacial nanoleakage upon scanning electron microscopy. Electric current application, from 20 to 70 µA, had no effect on the viability of HDPCs. This study provides further evidence for its future clinical use.

Proanthocyanidins alter adhesive/dentin bonding strengths when included in a bonding system

PURPOSE

To determine the effect of proanthocyanidins (PA) incorporation into a bonding system on dentin/adhesive bond stability following long-term storage in buffer and collagenase.

METHODS

Human dentin surfaces were bonded with no PA (0-PA), PA incorporated in the primer (PA-primer), or PA incorporated in the adhesive (PA-adhesive), and composite build-ups were created. Following sectioning into beams, bonded specimens were stored in buffer or collagenase for 0, 1, 4, 26, or 52 weeks before being tested for microtensile bond strength (muTBS). ANOVA and Tukey's HSD post-hoc were performed. Fractured surfaces were viewed with scanning electron microscopy (SEM).

RESULTS

Both bonding system and storage time but not storage medium significantly affected muTBS. Initially, 0-PA and PA-primer were superior to PA-adhesive, and after 1 week both PA groups were inferior to 0-PA. However, after 4 weeks PA-adhesive had significantly increased and 0-PA significantly decreased such that all three groups were equal. Thereafter, both PA-primer/adhesive groups trended with an increase (the 0-PA group remaining consistent) such that at 52 weeks PA-primer samples were significantly stronger (P < 0.001) or nearly so (P = 0.08) when compared to 0-PA samples. SEM revealed that initial fractures tended to occur at the middle/bottom of the hybrid layer for 0-PA and PA-primer groups but at the top of the hybrid layer/in the adhesive for PA-adhesive. After 4 weeks, however, all groups fractured similarly at the middle/bottom of the hybrid layer.

Epigallocatechin-3-gallate (EGCG) enhances the therapeutic activity of a dental adhesive

OBJECTIVES

The purpose of this study was to evaluate the antibacterial potential and physicochemical properties of a dental adhesive incorporated with epigallocatechin-3-gallate (EGCG) in different concentration over time.

METHODS

EGCG was incorporated at a ratio of 100, 200, and 300 μg/ml into a dental adhesive. The effects of the cured adhesives on the growth of Streptococcus mutans were determined by direct contact test immediately or one month later and by scanning electron microscopy (SEM), respectively. Microtensile bond strength (μTBS) test was used to test the mechanical property of the adhesives immediately or six months later. The degree of conversion (DC) of the adhesives was evaluated by Fourier transform infrared spectroscopy (FTIR).

RESULTS

Compared with negative control, the 200 μg/ml and 300 μg/ml EGCG-incorporated dental adhesive were found to exhibit inhibitory effect on the growth of S. mutans. The μTBS of the EGCG-incorporated dental adhesive was higher than the control. The DC of the adhesive system was not affected by the addition of EGCG.

CONCLUSIONS

200 μg/ml EGCG incorporated dental adhesives could accomplish therapeutic goals that play in antimicrobial function whilst keeping the durability of resin-dentine bond.

Durability of bonds and clinical success of adhesive restorations

Resin-dentin bond strength durability testing has been extensively used to evaluate the effectiveness of adhesive systems and the applicability of new strategies to improve that property. Clinical effectiveness is determined by the survival rates of restorations placed in non-carious cervical lesions (NCCL). While there is evidence that the bond strength data generated in laboratory studies somehow correlates with the clinical outcome of NCCL restorations, it is questionable whether the knowledge of bonding mechanisms obtained from laboratory testing can be used to justify clinical performance of resin-dentin bonds. There are significant morphological and structural differences between the bonding substrate used in in vitro testing versus the substrate encountered in NCCL. These differences qualify NCCL as a hostile substrate for bonding, yielding bond strengths that are usually lower than those obtained in normal dentin. However, clinical survival time of NCCL restorations often surpass the durability of normal dentin tested in the laboratory. Likewise, clinical reports on the long-term survival rates of posterior composite restorations defy the relatively rapid rate of degradation of adhesive interfaces reported in laboratory studies. This article critically analyzes how the effectiveness of adhesive systems is currently measured, to identify gaps in knowledge where new research could be encouraged. The morphological and chemical analysis of bonded interfaces of resin composite restorations in teeth that had been in clinical service for many years, but were extracted for periodontal reasons, could be a useful tool to observe the ultrastructural characteristics of restorations that are regarded as clinically acceptable. This could help determine how much degradation is acceptable for clinical success.

Effects of pH, ionic strength, and applied voltage on migration of dental monomers in an organic matrix

OBJECTIVES

The application of an electric field has been shown to positively influence the bonding of dentin bonding systems (DBS) by improving adhesive impregnation into dentin. However, the mechanism responsible for this phenomenon has not been completely elucidated. The aim of this study was to clarify the effects of pH, matrix ionic strength, and applied voltage on the migration of commonly used DBS monomers in a model matrix (agarose gel).

METHODS

Some common monomers examined were bis-GMA (2,2-bis[4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane); HEMA (2-hydroxyethyl methacrylate); 2-MP (bis[2-(methacryloyloxy) ethyl] phosphate); TCDM [di(hydroxyethyl methacrylate) ester of 5-(2,5,-dioxo tetrahydrofurfuryl)-3-methyl-3-cyclohexenyl-1,2-dicarboxylic acid]; and TEGDMA (triethylene glycol dimethacrylate). Agarose gels poured into a horizontal 10-well electrophoretic cell were used to mimic the collagen fibrils of the dentin organic matrix. The role of pH, matrix ionic strength, and voltage on monomer migration was assayed by modifying the experimental conditions.

RESULTS

Results of experiments performed at pH 3.1, 6.3, 8.5, and 12.3; at low, medium, and high ionic strength; and at 50 and 100 V clearly showed that DBA monomer migration toward both the anode and the cathode can be affected by each of these parameters.

SIGNIFICANCE

Migration of acrylic monomers toward the anode or cathode can be achieved as desired by selective choice of pH, ionic strength, and applied voltage. Additional studies are needed to evaluate the synergistic effects of DBS monomer blends on migration in an electric field.

Long-term nano-mechanical properties of biomodified dentin-resin interface components

Failures of dental composite restorative procedures are largely attributed to the degradation of dentin-resin interface components. Biomodification of dentin using bioactive agents may improve the quality and durability of the dentin-resin bonds. The aim of this study was to nanomechanically assess the reduced modulus of elasticity (Er) and nano-hardness (H) of major components of the dentin-resin interface (hybrid layer, adhesive layer and underlying dentin) biomodified by collagen cross-linkers at 24h, 3 and 6 months following restorative procedure. Demineralized dentin surfaces were biomodified with 5% glutaraldehyde (GD) or 6.5% grape seed extract (GSE) prior to placement of adhesive systems and composite resin. Nano-measurements of the interface components in a fluid cell showed that both agents increased the Er and H of underlying dentin after 3 and 6 months when compared to a control. The mechanical properties of the adhesive and hybrid layers decreased over time. Biomodification of the dentin-resin interface structures using GD and GSE can increase the mechanical properties of the interface over time and may contribute to the long-term quality of adhesive restorations.