Ultrastructural Correlates of in vivo/in vitro Bond Degradation in Self-etch Adhesives

Effect of MMP Inhibitors on the Bond Strength of Fibre Posts After Ageing

AIM

This in vitro study aimed to evaluate the effect of matrix metalloproteinase (MMP) inhibitors on the bond strength of resin-cemented fibre posts to radicular dentin under an aged-loaded condition.

MATERIALS AND METHODS

Radicular dentin was prepared and irrigated by MMP inhibitor solution after root canal obturation in 60 extracted single-rooted teeth based on 6 groups: (1) 2% chlorhexidine (CHX) + loaded; (2) CHX + unloaded; (3) 0.5% benzalkonium chloride (BAC) + loaded; (4) BAC + unloaded; (5) 17% ethylenediaminetetraacetic acid (EDTA) + loaded; and (6) EDTA + unloaded. After final rinsing, all specimens were sliced cross-sectionally and kept in a water bath for 12 months of ageing. Groups 1, 3, and 5 were subjected to cyclic loading. Push-out tests were conducted using a universal testing machine, and failure mode was examined. The data were analysed using 3-way analysis of variance and post hoc tests at α = 0.05.

RESULTS

BAC + unloaded demonstrated the highest mean bond strength (3.12 ± 0.18 MPa; P < .001), while the BAC + loaded and CHX + loaded groups showed a significantly lower push-out bond strength than their unloaded counterparts. Mixed adhesive-cohesive failure was the most common failure mode observed.

CONCLUSIONS

Without cycling loading, BAC was superior to CHX and EDTA in preserving the bond strength of resin-cemented fibre posts after 12 months of ageing. Loading significantly weakened the effectiveness of BAC and CHX in preserving the bond strength.

Comparative Evaluation of Retention of Fiber Posts in Different Dentin Regions Using Various Bonding Techniques: An In Vitro Study

Aim This study aims to evaluate the retention of fiber posts in the coronal, middle, and apical dentin regions with various bonding techniques by using fifth, sixth, and eighth-generation bonding agents and self-etch adhesive cement. Materials and methods For this study, 96 freshly extracted human incisors with straight roots were selected. Endodontic treatment of the specimens was performed. The post spaces were created immediately after obturation and the posts were luted with three different bonding agents and self-adhesive resin cement and the specimens were divided into four groups. Approximately 3 mm thick sections were made from different dentin regions of the post space and were tested for three subgroups: Subgroup I: Coronal, Subgroup II: Middle, Subgroup III: Apical. The specimens were tested on a universal testing machine. Results Statistical analysis was done using one-way analysis of variance (ANOVA) and Tukey's post hoc test using SPSS software version 17.0 (SPSS Inc., Chicago ). The intra-group comparison showed that the bond strength was more in the fifth-generation bonding agent (Cervical- 8.2574± 1.49034, Middle- 11.4800± 2.59938, Apical- 14.7108±1.82931), followed by the sixth (Cervical- 9.102± 2.76119, Middle-9.3152±2.11585, Apical- 12.9478±4.69404) and eighth-generation bonding systems (Cervical- 9.0938±2.77537, Middle- 7.1585±1.97601, Apical- 9.3726±0.73720) and the self-etch adhesive dental resin cement (Cervical- 5.1004±2.17389, Middle- 4.1574±1.28664, Apical-7.8884±1.90078). The inter-group comparison showed that the bond strength was higher in the fifth-generation bonding agent followed by sixth-generation, eighth-generation, and self-adhesive resin cement. Conclusion The present study reveals that the highest push-out bond strengths were obtained in apical sections followed by the middle and cervical areas. The bond strength was higher when using the fifth-generation bonding agent followed by the sixth, eighth, and self-adhesive resin cement. Despite many advancements, the fifth-generation bonding agent still showed superior retention in different dentin regions among various other bonding techniques.

Clinical Outcomes and Quantitative Margin Analysis of a Universal Adhesive Using a Randomized Clinical Trial over Three Years

The effectiveness of a universal adhesive applied in different application modes for the preparation of Class V composite restorations was evaluated both clinically and by quantitative marginal analysis (QMA). In each of the 22 patients, four non-carious cervical lesions (NCCL) were restored with Filtek^™ Supreme XTE (3M). The adhesive Scotchbond^™ Universal (SBU, 3M) was applied in self-etch (SE), selective-enamel-etch (SEE) or etch-and-rinse (ER) modes. The etch-and-rinse adhesive OptiBond^™ FL (OFL, Kerr) served as a control. The restorations were clinically evaluated (FDI criteria) after 14 days (BL), 6, 12, 24, and 36 months. Additionally, QMA was conducted on all restorations of 11 randomly selected patients. The FDI criteria and marginal gap were statistically compared between the groups at each recall as well as for the time periods between recalls. The cumulative failure rate was non-significantly higher in the OFL group when compared to all of the SBU groups. Marginal adaptation in the OFL and SBU-SE/ER groups was significantly decreased (BL-36 m, p: 0.004) in comparison to the SBU-SEE group (BL-36 m, p: 0.063). More marginal gaps were found in the OFL group than in the SBU-SEE (BL to 36 m, p: 0.063-0.003) and SBU-ER (24/36 m, p: 0.066/0.005) groups as well as in the SBU-SE group when compared to the SBU-SEE (12-36 m, p_i ≤ 0.016) and SBU-ER (24/36 m, p: 0.055/0.001) groups. SBU-SEE performed most effectively. The clinical evaluation and QMA corresponded, yet QMA detected group differences earliest after 6 months and is thus a valuable extension to clinical evaluations.

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.

A Novel Evaluation Method for Detecting Defects of the Bonded Orthodontic Bracket-Tooth Interface

Background

Orthodontic patients are at high risk to develop caries. This study is introducing a clinical method detecting interfacial defects between ceramic brackets and enamel utilizing optical coherent tomography in addition to using the nanoleakage expression in vitro test.

Methods

Transbond XT primer and moisture insensitive primer (MIP) were bonded to 75 human premolar enamel surfaces and divided into (XTD), (MIPD), and (MIPW) groups. The (XTD) and (MIPD) groups had ceramic brackets bonded to dry enamel surfaces using TransBond and moisture insensitive primers, respectively, while the (MIPW) samples were bonded to moist enamel using moisture insensitive primer. All specimens were examined under crosspolarization optical coherence tomography. Debonding forces of the brackets to 45 teeth (15 teeth/group). 30 bonded specimens (15 specimens/group) were cross-sectioned to detect the nanoleakage expression using scanning electron microscope equipped with energy-dispersive spectroscopy (SEM/EDS). The degree of conversion of the specimens in the experimental groups was tested using attenuated total reflectance Fourier transform infrared spectroscopy (FTIR/ATR).

Results

Optical coherence tomography detected the interfacial defects between the ceramic brackets and tooth structure. One way ANOVA showed that (XTD) and (MIPD) groups recorded significantly higher bond strength values and less nanoleakage expression when compared to MIPW (p > 0.05).

Conclusions

Optical coherence tomography can be utilized to detect interfacial adhesive-tooth defects. Dry enamel surfaces improve the quality of the enamel/primer interface (200 words).

Bioinspired multifunctional adhesive system for next generation bio-additively designed dental restorations

Resin-based composite has overtaken dental amalgam as the most popular material for the repair of lost or damaged tooth structure. In spite of the popularity, the average composite lifetime is about half that of amalgam restorations. The leading cause of composite-restoration failure is decay at the margin where the adhesive is applied. The adhesive is intended to seal the composite/tooth interface, but the adhesive seal to dentin is fragile and readily degraded by acids, enzymes and other oral fluids. The inherent weakness of this material system is attributable to several factors including the lack of antimicrobial properties, remineralization capabilities and durable mechanical performance - elements that are central to the integrity of the adhesive/dentin (a/d) interfacial seal. Our approach to this problem offers a transition from a hybrid to a biohybrid structure. Discrete peptides are tethered to polymers to provide multi-bio-functional adhesive formulations that simultaneously achieve antimicrobial and remineralization properties. The bio-additive materials design combines several functional properties with the goal of providing an adhesive that will serve as a durable barrier to recurrent decay at the composite/tooth interface. This article provides an overview of our multi-faceted approach which uses peptides tethered to polymers and new polymer chemistries to achieve the next generation adhesive system - an adhesive that provides antimicrobial properties, repair of defective dentin and enhanced mechanical performance.

Effects of remaining dentin thickness, smear layer and aging on the bond strengths of self-etch adhesives to dentin

This study evaluated the effects of remaining dentin thickness (RDT), different smear layers, and aging on the microtensile bond strength (µTBS) of universal adhesives to dentin when applied in self-etch mode. Ninety-six human third molars were randomly allocated to 12 groups (n=8) based on adhesives: Clearfil^TM SE Bond 2 (SE, control), Clearfil^TM Universal Bond (CU) and ScotchBond^TM Universal Adhesive (SB); smear layers: prepared either with 600-grit SiC paper (P) or regular diamond bur (B); and aging: stored in distilled water at 37ºC for 24 hours (24h) or 1 year (1y). µTBS was significantly affected by the type of adhesives, smear layers, and aging (p<0.001). A statistically significant and positive linear relationship was also observed between µTBS and RDT (p<0.05) in all the tested groups, except for SEB1y and CUB24h (p>0.05). RDT, smear layer types, and aging can influence the bonding performances of universal adhesives when applied in self-etch mode.

Current perspectives on dental adhesion: (3) Adhesion to intraradicular dentin: Concepts and applications

Adhesion science is one of the greatest contributions to restorative dentistry. Adhesion not only established the current principles of tissue preservation, but also allowed for the production of more hermetic and long-lasting restorations. Although adhesive strategies are routinely used in most clinical situations, adhesion to root dentin is still a major challenge. The presence of humidity together with less intertubular dentin are factors that limit the adhesive potential of root dentin. This situation is more unfavorable in endodontically treated teeth prepared for prefabricated or custom-made intraradicular posts; these procedures may alter the mechanical properties of teeth by modifying the viable dentin surface for adhesion. Also, contaminants deposited on the dentin surface are difficult to remove through conventional techniques. Moreover, root canal morphology has a very unfavorable C-factor, bringing undesirable effects resulting from polymerization contraction of resin-based materials. However, the differences between coronal and root dentin are not a barrier for dentin adhesion. Standardization of procedures and care during clinical steps are fundamental to the success of adhesion to coronal or intraradicular dentin. Thus, it is essential to know the anatomy of the root structure, the factors that interfere with intraradicular adhesion, as well as the current adhesive materials and techniques.

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's 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. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2466-2475, 2019.

Effect of a novel quaternary ammonium silane cavity disinfectant on cariogenic biofilm formation

OBJECTIVE

Evaluate effect of quaternary ammonium silane (QAS) cavity disinfectant on cariogenic biofilm.

MATERIALS AND METHODS

Single- (Streptococcus mutans or Lactobacillus acidophilus), dual- (Streptococcus mutans/Lactobacillus Acidophilus), and multi-species (Streptococcus mutans, Actinomyces naeslundii, and Streptococcus sanguis) biofilms were grown on acid-etched dentine discs. Biofilms were incubated (120 min/37 °C) and allowed to grow for 3 days anaerobically. Discs (no treatment) served as control (group 1). Groups II, III, IV, and V were then treated with 2% chlorhexidine, and 2%, 5%, and 10% QAS (20 s). Discs were returned to well plates with 300 μL of bacterial suspension and placed in anaerobic incubator at 37 °C and biofilms redeveloped for 4 days. Confocal microscopy, Raman, CFU, and MTT assay were performed.

RESULTS

Raman peaks show shifts at 1450 cm^-1, 1453 cm^-1, 1457 cm^-1, 1460 cm^-1, and 1462 cm^-1 for control, 2% CHX, 2%, 5%, and 10% QAS groups in multi-species biofilms. There was reduction of 484 cm^-1 band in 10% QAS group. CLSM revealed densely clustered green colonies in control group and red confluent QAS-treated biofilms with significantly lower log CFU for single/dual species. Metabolic activities of Streptococcus mutans and Lactobacillus acidophilus decreased with increasing QAS exposure time.

CONCLUSION

Quaternary ammonium silanes possess antimicrobial activities and inhibit growth of cariogenic biofilms.

CLINICAL SIGNIFICANCE

Available data demonstrated use of QAS as potential antibacterial cavity disinfectant in adhesive dentistry. Experimental QAS can effectively eliminate caries-forming bacteria, when used inside a prepared cavity, and can definitely overcome problems associated with present available cavity disinfectants.

Two-year Effects of Chlorhexidine-containing Adhesives on the In Vitro Durability of Resin-dentin Interfaces and Modeling of Drug Release

OBJECTIVES

To evaluate the effects of addition of diacetate chlorhexidine (CHX) at different concentrations into two etch-and-rinse adhesive systems on CHX release, as well as the immediate (IM) and two-year (2-Y) resin-dentin microtensile bond strength (μTBS) and nanoleakage (NL).

METHODS

CHX was added to XP Bond (XP) and Ambar (AM) at concentrations of 0.0 wt% (control); 0.01 wt%; 0.05 wt%; and 0.1 to 0.2 wt%. To assess the cumulative CHX release, adhesive disks were made in a metallic matrix and after light-curing were stored in water. Ultraviolet spectrophotometric measurements of the storage solution were performed to examine the release kinetics of CHX. For μTBS and NL, the occlusal enamel of molars was removed and the adhesives were applied to the dentin surface after acid etching. After composite resin build-up, specimens were sectioned to obtain μTBS sticks. The specimens were subjected to μTBS and NL at IM and after 2-Y. In addition, specimens underwent examination for CHX using micro-Raman spectroscopy. All data were submitted to statistical analysis (α=0.05).

RESULTS

With regard to CHX release, AM showed a slower and gradual release of CHX while XP released CHX more quickly ( p<0.05), and CHX was still present in the hybrid layers after 2-Y. Both adhesives showed CHX release at 2-Y water storage. Both CHX-containing adhesives showed higher μTBS values than did the control group ( p<0.05).

Is Optical Coherence Tomography a Potential Tool to Evaluate Marginal Adaptation of Class III/IV Composite Restorations In Vivo?

OBJECTIVE

Margin analysis of Class III and IV composite restorations in vitro and in vivo occurred by scanning electron microscopy (SEM) and optical coherence tomography (OCT). The results were compared and related to clinical evaluation.

METHODS AND MATERIALS

Eight Class III composite restorations were imaged in vitro using OCT and SEM. The margins were analyzed quantitatively. OCT signals were verified by assignment to the criteria perfect margin, gap, and positive/negative ledge. In vivo quantitative margin analysis of Class III/IV composite restorations made of the micro-hybrid composite Venus combined with the self-etch adhesive iBond Gluma inside (1-SE) or etch-and-rinse adhesive Gluma Comfort Bond (2-ER) (all Heraeus Kulzer) was carried out using OCT and SEM after 90 months of clinical function. The results were compared with clinical evaluation (US Public Health Service criteria; marginal integrity, marginal discoloration).

RESULTS

In vitro, the correlation between OCT and SEM was high for all four margin criteria (Kendall tau b [τ_b] correlation: 0.64-0.92, p_i≤0.026), with no significant differences between OCT and SEM (p_i≥0.63). In vivo, a moderate correlation was observed (τ_b: 0.38-0.45, p_i<0.016). Clinically, the cumulative failure rate in the criterion marginal integrity was higher for the 1-SE group (baseline 90 M, p=0.011). Similarly, OCT and SEM detected higher percentages of the criterion gap in the 1-SE group (p: 0.027/0.002), in contrast to perfect margin. Both, gap and perfect margin ranged widely between 0.0% and 88.7% (OCT) and between 0.0% and 89.0% (SEM).

CONCLUSION

Despite the positive selection bias after 90 months with only a few patients left, quantitative margin analysis allows for differentiation between the two adhesives at this specific date. OCT in particular offers the possibility to evaluate marginal integrity directly in vivo.

Bioactive Dental Composites and Bonding Agents Having Remineralizing and Antibacterial Characteristics

Current dental restorative materials are typically inert and replace missing tooth structures. This article reviews efforts in the development of a new generation of bioactive materials designed to not only replace the missing tooth volume but also possess therapeutic functions. Composites and bonding agents with remineralizing and antibacterial characteristics have shown promise in replacing lost minerals, inhibiting recurrent caries, neutralizing acids, repelling proteins, and suppressing biofilms and acid production. Furthermore, they have demonstrated a low cytotoxicity similar to current resins, with additional benefits to protect the dental pulp and promote tertiary dentin formation. This new class of bioactive materials shows promise in reversing lesions and inhibiting caries.

Effects of water-aging for 6 months on the durability of a novel antimicrobial and protein-repellent dental bonding agent

Biofilms at the tooth-restoration bonded interface can produce acids and cause recurrent caries. Recurrent caries is a primary reason for restoration failures. The objectives of this study were to synthesize a novel bioactive dental bonding agent containing dimethylaminohexadecyl methacrylate (DMAHDM) and 2-methacryloyloxyethyl phosphorylcholine (MPC) to inhibit biofilm formation at the tooth-restoration margin and to investigate the effects of water-aging for 6 months on the dentin bond strength and protein-repellent and antibacterial durability. A protein-repellent agent (MPC) and antibacterial agent (DMAHDM) were added to a Scotchbond multi-purpose (SBMP) primer and adhesive. Specimens were stored in water at 37 °C for 1, 30, 90, or 180 days (d). At the end of each time period, the dentin bond strength and protein-repellent and antibacterial properties were evaluated. Protein attachment onto resin specimens was measured by the micro-bicinchoninic acid approach. A dental plaque microcosm biofilm model was used to test the biofilm response. The SBMP + MPC + DMAHDM group showed no decline in dentin bond strength after water-aging for 6 months, which was significantly higher than that of the control (P < 0.05). The SBMP + MPC + DMAHDM group had protein adhesion that was only 1/20 of that of the SBMP control (P < 0.05). Incorporation of MPC and DMAHDM into SBMP provided a synergistic effect on biofilm reduction. The antibacterial effect and resistance to protein adsorption exhibited no decrease from 1 to 180 d (P > 0.1). In conclusion, a bonding agent with MPC and DMAHDM achieved a durable dentin bond strength and long-term resistance to proteins and oral bacteria. The novel dental bonding agent is promising for applications in preventive and restorative dentistry to reduce biofilm formation at the tooth-restoration margin.

Nanostructured Polymeric Materials with Protein-Repellent and Anti-Caries Properties for Dental Applications

Dental caries is prevalent worldwide. Tooth cavity restorations cost more than $46 billion annually in the United States alone. The current generation of esthetic polymeric restorations have unsatisfactory failure rates. Replacing the failed restorations accounts for 50–70% of all the restorations. This article reviewed developments in producing a new generation of bioactive and therapeutic restorations. This includes: Protein-repellent and anti-caries polymeric dental composites, especially the use of 2-methacryloyloxyethyl phosphorylcholine (MPC) and dimethylaminododecyl methacrylate (DMAHDM); protein-repellent adhesives to greatly reduce biofilm acids; bioactive cements to inhibit tooth lesions; combining protein-repellency with antibacterial nanoparticles of silver; tooth surface coatings containing calcium phosphate nanoparticles for remineralization; therapeutic restorations to suppress periodontal pathogens; and long-term durability of bioactive and therapeutic dental polymers. MPC was chosen due to its strong ability to repel proteins. DMAHDM was selected because it had the most potent antibacterial activity when compared to a series of antibacterial monomers. The new generation of materials possessed potent antibacterial functions against cariogenic and periodontal pathogens, and reduced biofilm colony-forming units by up to 4 logs, provided calcium phosphate ions for remineralization and strengthening of tooth structures, and raised biofilm pH from a cariogenic pH 4.5 to a safe pH 6.5. The new materials achieved a long-term durability that was significantly beyond current commercial control materials. This new generation of bioactive and nanostructured polymers is promising for wide applications to provide therapeutic healing effects and greater longevity for dental restorations.

Recent Advances in Adhesive Bonding - The Role of Biomolecules, Nanocompounds, and Bonding Strategies in Enhancing Resin Bonding to Dental Substrates

PURPOSE OF REVIEW

To present an overview on the main agents (i.e., biomolecules and nanocompounds) and/or strategies currently available to amplify or stabilize resin-dentin bonding.

RECENT FINDINGS

According to studies retrieved for full text reading (2014-2017), there are currently six major strategies available to overcome resin-dentin bond degradation: (i) use of collagen crosslinking agents, which may form stable covalent bonds with collagen fibrils, thus strengthening the hybrid layer; (ii) use of antioxidants, which may allow further polymerization reactions over time; (iii) use of protease inhibitors, which may inhibit or inactivate metalloproteinases; (iv) modification of the bonding procedure, which may be performed by using the ethanol wet-bonding technique or by applying an additional adhesive (hydrophobic) coating, thereby strengthening the hybrid layer; (v) laser treatment of the substrate prior to bonding, which may cause specific topographic changes in the surface of dental substrates, increasing bonding efficacy; and (vi) reinforcement of the resin matrix with inorganic fillers and/or remineralizing agents, which may positively enhance physico-mechanical properties of the hybrid layer.

SUMMARY

With the present review, we contributed to the better understanding of adhesion concepts and mechanisms of resin-dentin bond degradation, showing the current prospects available to solve that problematic. Also, adhesively-bonded restorations may be benefited by the use of some biomolecules, nanocompounds or alternative bonding strategies in order to minimize bond strength degradation.

[Progress on matrix metalloproteinase inhibitors]

Continuing advances in dentin bonding technology and adhesives revolutionized bonding of resin-based composite restorations. However, hybrid layers created by contemporary dentin adhesives present imperfect durability, and degradation of collagen matrix by endogenous enzymes is a significant factor causing destruction of hybrid layers. Bond durability can be improved by using enzyme inhibitors to prevent collagen degradation and to preserve integrity of collagen matrix. This review summarizes progress on matrix metalloproteinase inhibitors (including chlorhexidine, ethylenediaminetetraacetic acid, quaternary ammonium salt, tetracycline and its derivatives, hydroxamic acid inhibitors, bisphosphonate derivative, and cross-linking agents) and suggests prospects for these compounds.

Monitoring of cariogenic demineralization at the enamel-composite interface using swept-source optical coherence tomography

OBJECTIVES

The aim of this study was to evaluate enamel demineralization at composite restoration margins caused by cariogenic biofilm using swept-source optical coherence tomography (SS-OCT).

METHODS

Sixty round-shaped cavities were prepared on the mid-buccal enamel surface of extracted human molars. The cavities were restored with Estelite Flow Quick flowable composite using either Clearfil SE Bond or Clearfil Tri-S Bond ND bonding agents. Streptococcus mutans suspension was applied to form a cariogenic biofilm on the surface. After 1, 2, or 3 weeks of incubation (n=10), the biofilm was removed to observe the carious demineralization at the cavosurface margins using SS-OCT. The gap along the enamel-composite interface was recorded on each adhesive system. Confirmatory direct observation was accomplished at the same location using confocal laser scanning microscope.

RESULTS

The demineralized enamel around the restorations was observed as a zone of intensified brightness in SS-OCT. The demineralized lesion on the cervical enamel was significantly deeper than that on the occlusal enamel (p<0.05). However, the extension of enamel demineralization at the enamel-composite interface was significantly deeper at the occlusal wall than the cervical wall (p<0.05). The extension in Tri-S Bond ND group was significantly deeper than in SE Bond group (p<0.05). A significant increase in gap formation was found after the extension of demineralization compared with the baseline.

SIGNIFICANCE

The carious demineralization around composite restorations were observed as a bright zone in SS-OCT during the process of bacterial demineralization. SS-OCT appears to be a promising modality for the detection of caries adjacent to an existing restoration.

In Vivo and In Vitro Effects of Chlorhexidine Pretreatment on Immediate and Aged Dentin Bond Strengths

This study evaluated the effect of 2% chlorhexidine (CHX) pretreatment of dentin on the immediate and aged microtensile bond strength (μTBS) of different adhesives to dentin in vivo and in vitro. Class I cavities were prepared in 80 caries-free human third molars of 40 patients in a split-mouth fashion. In each tooth pair, one tooth received 2% CHX pretreatment after which both teeth were randomly assigned to one of the following groups with respect to the type of adhesive system applied: Adper Single Bond 2 (etch-and-rinse), Clearfil SE Bond (two-step self-etch), Clearfil S(3) Bond (one-step self-etch), and Adper Prompt-L-Pop (all-in-one self-etch). The teeth were restored with resin composite and extracted for μTBS testing either immediately or after six months in function. In vitro specimen pairs were prepared as with the clinical protocol in intact, freshly extracted human molars, and thereafter, subjected to testing immediately or after 5000× thermocycling. Data were analyzed with four-way analysis of variance (ANOVA). Bonferroni test was utilized for pair-wise comparisons. The immediate bond strength values were significantly higher than "aged" ones for all tested adhesives (p=0.00). The in vitro immediate bond strength values were statistically higher than in vivo bond strength values (p<0.05). While the bond strength of in vitro aged, CHX-treated samples were higher than their in vivo counterparts (p<0.05), no difference was observed in non-CHX treated groups (p>0.05). In the absence of CHX pretreatment, all adhesives showed significantly higher immediate bond strength values than CHX-treated groups, while all "aged", non-pretreated adhesives exhibited significantly lower bond strength values (both p<0.05). By contrast, chlorhexidine pretreatment resulted in significantly higher aged bond strengths, regardless of the adhesive system and testing condition. Aging-associated decline in dentin bond strength of etch-and rinse and self-etch adhesives can be counteracted by chlorhexidine application.

Submicron-to-nanoscale structure characterization and organization of crystals in dentin bioapatites

The aim of this study was to ascertain the crystal morphology and to assess the ultrastructure and texture changes of sound (SD) and caries-affected dentin (CAD) after being restored with Zn-free and Zn-containing amalgam.

Effects of remineralization procedures on shear bond strengths of brackets bonded to demineralized enamel surfaces with self-etch systems

OBJECTIVE

To compare the effects of different remineralization procedures on the surface roughness of teeth, shear bond strengths (SBSs), and Adhesive Remnant Index scores of self-etching primer (SEP) used to bond orthodontic brackets to previously treated demineralized enamel surfaces.

MATERIALS AND METHODS

A total of 140 extracted human premolar teeth were randomly divided into seven equal groups. Group I was the control group. A demineralization procedure was performed in the other six groups. A remineralization procedure was performed before bonding by using casein phosphopeptide-amorphous calcium phosphate, fluoride, a microabrasion mixture (18% hydrochloric acid-fine pumice), a microabrasion agent, and resin infiltration in groups III to VII. Brackets were bonded using a self-etching primer/adhesive system. The specimens were tested for SBS. The roughness and morphology of the enamel surfaces were analyzed using profilometer and scanning electron microscopy. Data were analyzed with analysis of variance, Tukey, and G-tests at the α  =  .05 level.

RESULTS

Significant differences were found in the SBS values among the seven groups (F  =  32.69, P  =  .003). The lowest SBS value was found in group II (2.62 ± 1.46 MPa). No significant differences were found between groups I, III, and VII, between groups III and IV, or between groups V and VI. The differences in the roughness values were statistically significant among the groups (P  =  .002).

CONCLUSIONS

Remineralization procedures restore the decreased SBS of orthodontic brackets and decrease surface roughness caused by enamel demineralization. SEPs provide clinically acceptable SBS values for bonding orthodontic brackets to previously treated demineralized enamel surfaces.

Effects of different pre-treatment methods on the shear bond strength of orthodontic brackets to demineralized enamel

OBJECTIVE

To compare the effects of different treatment methods used for the enamel damage, on the shear bond strength (SBS) and fracture mode of orthodontic brackets.

MATERIALS AND METHODS

Freshly-extracted 140 premolars were randomly allocated to seven groups: Group I was considered as the control of other groups. The remaining groups were exposed to demineralization. In group II, brackets were directly bonded to the demineralized enamel surface. CPP-ACP paste (GC Tooth Mousse), fluoride varnish (Bifluorid 12), microabrasion with a mixture prepared with 18% hydrochloric acid and fine pumice powder, microabrasion with an agent (Opalustre) and resin infiltrant (Icon®) were applied in Groups III, IV, V, VI and VII, respectively. The specimens were tested for SBS and bond failures were scored according to the Adhesive Remnant Index (ARI). Analysis of variance and Tukey tests were used to compare the SBS of the groups. ARI scores were compared with G-test. The statistical significance was set at p < 0.05 level.

RESULTS

Statistically significant differences were found among seven groups (F = 191.697; p < 0.001). The SBSs of groups I (mean = 18.8 ± 2.0 MPa) and VII (mean = 19.1 ± 1.4 MPa) were significantly higher than the other groups. No statistically significant difference was found between groups IV (mean = 11.5 ± 1.2 MPa) and V (mean = 12.6 ± 1.5 MPa). The differences in ARI scores of the groups were statistically significant (p < 0.01).

CONCLUSIONS

All demineralization treatment methods improve bonding to demineralized enamel. Resin infiltrant application after demineralization showed similar bond strength values as intact enamel.

Effect of fluoride concentration in adhesives on morphology of acid-base resistant zones

This study aimed to investigate the effect of fluoride concentration in adhesives on morphology of acid-base resistant zone (ABRZ). Seven experimental adhesives with different concentrations of NaF (0 wt%; F0 to 100 wt%: F100) were prepared based on the formulation of a commercially available adhesive (Clearfil Protect Bond, F100). The resin-dentin interface of the bonded specimen was subjected to demineralizing solution and NaOCl, sectioned, polished and argon-ion etched for SEM observation. Fluoride release from each adhesive was measured using an ion-selective electrode. Fluoride ion release from the adhesive linearly increased with higher NaF concentration. The ABRZ area increased significantly with higher NaF concentration except for F0, F10, and F20 (p<0.05). F100 showed the largest ABRZ, where a slope of acid-resistant dentin was clearly observed at the bottom of the ABRZ. The concentration of NaF in the two-step self-etching adhesive resin influenced the amount of dentin structure remaining after acid-challenge.

Inhibition of matrix metalloproteinase activity in human dentin via novel antibacterial monomer

OBJECTIVE

Dentin-composite bond failure is caused by factors including hybrid layer degradation, which in turn can be caused by hydrolysis and enzymatic degradation of the exposed collagen in the dentin. The objectives of this study were to investigate a new antibacterial monomer (dimethylaminododecyl methacrylate, DMADDM) as an inhibitor for matrix metalloproteinases (MMPs), and to determine the effects of DMADDM on both soluble recombinant human MMPs (rhMMPs) and dentin matrix-bound endogenous MMPs.

METHODS

Inhibitory effects of DMADDM at six mass% (0.1% to 10%) on soluble rhMMP-8 and rhMMP-9 were measured using a colorimetic assay. Matrix-bound endogenous MMP activity was evaluated in demineralized human dentin. Dentin beams were divided into four groups (n=10) and incubated in calcium- and zinc-containing media (control medium); or control medium+0.2% chlorhexidine (CHX); 5% 12-methacryloyloxydodecylpyridinium bromide (MDPB); or 5% DMADDM. Dissolution of dentin collagen peptides was evaluated by mechanical testing in three-point flexure, loss of dentin mass, and a hydroxyproline assay.

RESULTS

Use of 0.1% to 10% DMADDM exhibited a strong concentration-dependent anti-MMP effect, reaching 90% of inhibition on rhMMP-8 and rhMMP-9 at 5% DMADDM concentration. Dentin beams in medium with 5% DMADDM showed 34% decrease in elastic modulus (vs. 73% decrease for control), 3% loss of dry dentin mass (vs. 28% loss for control), and significantly less solubilized hydroxyproline when compared with control (p<0.05).

SIGNIFICANCE

The new antibacterial monomer DMADDM was effective in inhibiting both soluble rhMMPs and matrix-bound human dentin MMPs. These results, together with previous studies showing that adhesives containing DMADDM inhibited biofilms without compromising dentin bond strength, suggest that DMADDM is promising for use in adhesives to prevent collagen degradation in hybrid layer and protect the resin-dentin bond.

Aging of adhesive interfaces treated with benzalkonium chloride and benzalkonium methacrylate

Inhibition of endogenous dentin matrix metalloproteinases (MMPs) within incompletely infiltrated hybrid layers can contribute to the preservation of resin-dentin bonds. This study evaluated the bond stability of interfaces treated with benzalkonium chloride (BAC) and benzalkonium methacrylate (MBAC), and the inhibitory properties of these compounds on dentin MMP activity. Single-component adhesive ALL-BOND UNIVERSAL, modified with BAC or MBAC at concentrations of 0, 0.5, 1.0, and 2.0%, was used for microtensile bond strength (μTBS) evaluation after 24 h, 6 months, and 1 yr. Beams produced from human dentin were treated with 37% phosphoric acid, dipped in 0.5% BAC, 1.0% BAC, or water (control) for 60 s, and then incubated in SensoLyte generic MMP substrate to determine MMP activity. A significant decrease in the μTBS after 6 months and 1 yr was observed for the control group only. No significant differences among groups were shown at 24 h. After 6 months and 1 yr, the control group demonstrated significantly lower μTBS than all treatment groups. When applied for 60 s, 0.5% BAC inhibited total MMP activity by 31%, and 1.0% BAC inhibited total MMP activity by 54%. Both BAC and MBAC contributed to the preservation of resin-dentin bonds, probably because of their inhibitory properties of endogenous dentin proteinases.

Dentin bonding: can we make it last?

In dentin bonding, contemporary dental adhesive systems rely on formation of the hybrid layer, a biocomposite containing dentin collagen and polymerized resin adhesive. They are usually able to create at least reasonable integrity of the hybrid layer with high immediate bond strength. However, loss of dentin-bonded interface integrity and bond strength is commonly seen after aging both in vitro and in vivo. This is due to endogenous collagenolytic enzymes, matrix metalloproteinases, and cysteine cathepsins, responsible for the time-dependent loss of hybrid layer collagen. In addition, the hydrophilic nature of adhesive systems creates problems that lead to suboptimal hybrid layers. These problems include, for example, insufficient resin impregnation of dentin, phase separation, and a low rate of polymerization, all of which may reduce the longevity of the bonded interface. Preservation of the collagen matrix integrity by inhibition of endogenous dentin proteases is key to improving dentin bonding durability. Several approaches to retain the integrity of the hybrid layer and to improve the long-term dentin bond strength have been tested. These include the use of enzyme inhibitors, either separately or as incorporated into the adhesive resins; increase of collagen resistance to enzymatic degradation; and elimination of water from the interface to slow down or eliminate hydrolytic loss of the hybrid layer components. This review looks at the principles, current status, and future of the different techniques designed to prevent the loss of hybrid layer and bond strength.

Dentin Bond Strength of a Fluoride-Releasing Adhesive System Submitted to pH-Cycling

To evaluate the microtensile bond strength (µTBS) of a fluoride-containing adhesive system submitted to a pH-cycling and storage time regimen for primary outcomes. As secondary outcomes the fluoride released amount was evaluated. Twelve dentin surfaces from sound third molar were divided into 2 groups according to adhesive systems: Clearfil SE Protect (PB) and Clearfil SE Bond (SE). Sticks obtained (1.0 mm2) from teeth were randomly divided into 3 subgroups according to storage regimen model: immediate (24h); 5-month deionized water (W); and pH-cycling model (C). All sticks were tested for µTBS in a universal testing machine. Fluoride concentration was obtained from 1-4 days and 30-day in W and 1-4 days in demineralization (DE)/remineralization (RE) solutions from C, using a fluoride-specific electrode. µTBS and fluoride released data were, respectively, submitted to ANOVA in a split plot design and Tukey, and Friedman' tests (a=0.05). There was no significant interaction between adhesive system and storage regimen for µTBS. W showed the lowest µTBS values. There was no significant difference between 24 h and C models for µTBS. There was no significant difference between adhesive systems. Failure mode was predominantly cohesive within composite for the 24 h and W, for the C group it was mixed for SE and cohesive within composite for PB adhesive system. Fluoride concentrations in the DE/RE solutions were less than 0.03125 ppm and not detected in W. In conclusion, the fluoride-containing adhesive system performed similarly to the regular one. Hydrolytic degradation is the main problem with both adhesive systems, regardless of fluoride contents.

The reparability of contemporary composite resins

Objective:

The objective was to investigate the way that various surface treatments could influence the bond strength of the repair of methacrylate (MC) and silorane (SIL) composites.

Materials and Methods:

A total of 160 MC and SIL cylindrical specimens were polymerized and aged in artificial saliva solution for 7 days. Depending on the following surface treatment (diamond bur or air abrasion), and the conditioning procedure (orthophosphoric acid or sodium hypochlorite), 16 groups were formed and repaired either with MC, either with SIL composite. Repaired specimens were subjected to an additional aging procedure in artificial saliva for 7 days, followed by thermo-cycling and then stressed in shear at a rate of 0.5 mm/min until failure. Failure patterns were analyzed using stereomicroscope and scanning electron microscopy.

Results:

MC composite showed statistically significant higher bond strength both as a base or repair material than SIL (P < 0.001). Statistically significant differences were not observed, when grinding and conditioning procedures was compared. Pretest failures were observed when aged MC-based composite was repaired with SIL-based.

Conclusions:

Type of composite seems to be the main factor influencing the bond strength of the repair. MC-based composite showed better repairability than SIL composite. Optimum repair conditions should include knowledge of the composite's composition.

Proteins, pathogens, and failure at the composite-tooth interface

In the United States, composites accounted for nearly 70% of the 173.2 million composite and amalgam restorations placed in 2006 (Kingman et al., 2012), and it is likely that the use of composite will continue to increase as dentists phase out dental amalgam. This trend is not, however, without consequences. The failure rate of composite restorations is double that of amalgam (Ferracane, 2013). Composite restorations accumulate more biofilm, experience more secondary decay, and require more frequent replacement. In vivo biodegradation of the adhesive bond at the composite-tooth interface is a major contributor to the cascade of events leading to restoration failure. Binding by proteins, particularly gp340, from the salivary pellicle leads to biofilm attachment, which accelerates degradation of the interfacial bond and demineralization of the tooth by recruiting the pioneer bacterium Streptococcus mutans to the surface. Bacterial production of lactic acid lowers the pH of the oral microenvironment, erodes hydroxyapatite in enamel and dentin, and promotes hydrolysis of the adhesive. Secreted esterases further hydrolyze the adhesive polymer, exposing the soft underlying collagenous dentinal matrix and allowing further infiltration by the pathogenic biofilm. Manifold approaches are being pursued to increase the longevity of composite dental restorations based on the major contributing factors responsible for degradation. The key material and biological components and the interactions involved in the destructive processes, including recent advances in understanding the structural and molecular basis of biofilm recruitment, are described in this review. Innovative strategies to mitigate these pathogenic effects and slow deterioration are discussed.

Evaluation of the bond strength of resin cements used to lute ceramics on laser-etched dentin

OBJECTIVE

The purpose of this study was to investigate the shear bond strength (SBS) of two different adhesive resin cements used to lute ceramics on laser-etched dentin.

BACKGROUND DATA

Erbium, chromium: yttrium, scandium, gallium, garnet (Er,Cr:YSGG) laser irradiation has been claimed to improve the adhesive properties of dentin, but results to date have been controversial, and its compatibility with existing adhesive resin cements has not been conclusively determined.

MATERIALS AND METHODS

Two adhesive cements, one "etch-and-rinse" [Variolink II (V)] and one "self-etch" [Clearfil Esthetic Cement (C)] luting cement, were used to lute ceramic blocks (Vita Celay Blanks, Vita) onto dentin surfaces. In total, 80 dentin specimens were distributed randomly into eight experimental groups according to the dentin surface-etching technique used Er,Cr:YSGG laser and Er:YAG laser: (1) 37% orthophosphoric acid+V (control group), (2) Er,Cr:YSGG laser+V, (3) Er,Cr:YSGG laser+acid+V, (4) Er:YAG laser+V, (5) Er:YAG laser+acid+V, (6) C, (7) Er,Cr:YSGG laser+C, and (8) Er:YAG laser+C. Following these applications, the ceramic discs were bonded to prepared surfaces and were shear loaded in a universal testing machine until fracture. SBS was recorded for each group in MPa. Shear test values were evaluated statistically using the Mann-Whitney U test.

RESULTS

No statistically significant differences were evident between the control group and the other groups (p>0.05). The Er,Cr:YSGG laser+A+V group demonstrated significantly higher SBS than did the Er,Cr:YSGG laser+V group (p=0.034). The Er,Cr:YSGG laser+C and Er:YAG laser+C groups demonstrated significantly lower SBS than did the C group (p<0.05).

CONCLUSIONS

Dentin surfaces prepared with lasers may provide comparable ceramic bond strengths, depending upon the adhesive cement used.

Polymerization- and solvent-induced phase separation in hydrophilic-rich dentin adhesive mimic

Current dental resin undergoes phase separation into hydrophobic-rich and hydrophilic-rich phases during infiltration of the over-wet demineralized collagen matrix. Such phase separation undermines the integrity and durability of the bond at the composite/tooth interface. This study marks the first time that the polymerization kinetics of model hydrophilic-rich phase of dental adhesive has been determined. Samples were prepared by adding varying water content to neat resins made from 95 and 99 wt.% hydroxyethylmethacrylate and 5 and 1 wt.% (2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl1]-propane prior to light curing. Viscosity of the formulations decreased with increased water content. The photopolymerization kinetics study was carried out with a time-resolved Fourier transform infrared spectrometer. All of the samples exhibited two-stage polymerization behavior which has not been reported previously for dental resin formulation. The lowest secondary rate maxima were observed for water contents of 10-30 wt.%. Differential scanning calorimetry (DSC) showed two glass transition temperatures for the hydrophilic-rich phase of dental adhesive. The DSC results indicate that the heterogeneity within the final polymer structure decreased with increasing water content. The results suggest a reaction mechanism involving both polymerization-induced phase separation and solvent-induced phase separation for the model hydrophilic-rich phase of dental resin.

Can demineralized enamel surfaces be bonded safely?

OBJECTIVE

To evaluate and compare the effects of enamel demineralization, microabrasion therapy and casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) application on the shear bond strength (SBS) of orthodontic brackets bonded to enamel surfaces and enamel color.

MATERIALS AND METHODS

Eighty freshly extracted human maxillary premolar teeth were allocated to one of the four groups. Brackets were bonded directly to non-demineralized enamel surfaces in Group I (control group), directly to the demineralized enamel surfaces in Group II, to demineralized enamel surfaces after CPP-ACP application in Group III and to demineralized enamel surfaces after microabrasion therapy in Group IV. The samples were stored in water for 24 h at 37°C and then underwent thermocycling. The SBS in megapascals (MPa) was determined by a shear test with 0.5 mm/min crosshead speed and failure types were classified with modified adhesive remnant index scores. The data were analyzed with one-way analyses of variance (ANOVA), Tukey and chi-square tests at the α = 0.05 level.

RESULTS

Significant differences were found among the four groups (F = 21.57, p < 0.01). No significant difference was found between Group I and III (17.12 ± 2.84 and 15.08 ± 3.42 MPa, respectively) or between Group III and IV (12.82 ± 2.64 MPa). The lowest SBS value was determined in Group II (5.88 ± 2.12 MPa). Enamel demineralization, microabrasion therapy and CPP-ACP application affected enamel color significantly.

CONCLUSION

CPP-ACP application and microabrasion therapy are able to increase the decreased SBS of orthodontic brackets because of enamel demineralization.

Pre-treatment of radicular dentin by self-etch primer containing chlorhexidine can improve fiber post bond durability

We evaluated whether the pre-treatment of radicular dentin by ED Primer containing different concentrations of chlorhexidine can improve the bond durability of fiber post to radicular dentin. Experimental ED primers containing different concentrations of chlorhexidine (0%, 0.5% and 1.0%) were prepared. Thirty extracted maxillary anterior teeth were divided into 3 groups, each group corresponding to different chlorhexidine concentrations. Fiber posts were cemented in endodontically treated teeth with experimental ED primers and Panavia F. The bonded teeth were transversally sectioned into six slices and then were processed for thin slice push-out test 24 h later or after 18-months water storage. Eighteen-month storage resulted in significant bond strength reduction of all groups (p<0.05). The bond strength reduction of 1.0% group was significantly lower than that of control group and 0.5% group (p<0.05). In conclusion, the incorporation of 1.0% chlorhexidine into ED primer can extend the bond longevity of fiber post to radicular dentin.

Characterization of Acid-neutralizing Basic Monomers in Co-solvent Systems by NMR

Metabolic activity of the oral microbiota leads to acidification of the microenvironment and promotes demineralization of tooth structure at the margin of composite restorations. The pathogenic impact of the biofilm at the margin of the composite restoration could be reduced by engineering novel dentin adhesives that neutralize the acidic micro-environment. Integrating basic moieties into methacrylate derivatives has the potential to buffer against acid-induced degradation, and we are investigating basic monomers for this purpose. These monomers must be compatible with existing formulations, which are hydrophobic and marginally miscible with water. As such, cosolvent systems may be required to enable analysis of monomer function and chemical properties. Here we present an approach for examining the neutralizing capacity of basic methacrylate monomers in a water/ethanol co-solvent system using NMR spectroscopy. NMR is an excellent tool for monitoring the impact of co-solvent effects on pKa and buffering capacity of basic monomers because chemical shift is extremely sensitive to small changes that most other methods cannot detect. Because lactic acid (LA) is produced by oral bacteria and is prevalent in this microenvironment, LA was used to analyze the effectiveness of basic monomers to neutralize acid. The ¹³C chemical shift of the carbonyl in lactic acid was monitored as a function of ethanol and monomer concentration and each was correlated with pH to determine the functional buffering range. This study shows that the buffering capacity of even very poorly water-soluble monomers can be analyzed using NMR.

Effect of accelerated aging on the bonding performance of fluoridated adhesive resins

The purpose of this study was to investigate the dentin bond durability of a one-step, fluoride-containing, glass ionomer-based adhesive system, Reactmer Bond (RB), and that of a two-step, fluoride-containing, self-etch adhesive system, Clearfil Protect Bond (CPB). Enamel was removed from the occlusal surfaces of teeth, and flat dentin surfaces were entirely covered with a composite resin following the application of an adhesive material (n=10). After specimens were sectioned into rectangular sticks of 0.87 ± 0.03 mm(2), the sticks were randomly assigned into two accelerated aging time period groups: 1 week or 1 year. Microtensile bond strengths were determined. Bond strength of RB increased significantly after 1 year (1 week=27.80 ± 10.57 MPa versus 1 year=36.93 ± 14.38 MPa) (p<0.05). In contrast, there was no significant difference in bond strength between the two time periods for CPB (1 week=51.74 ± 17.8 MPa versus 1 year=56.03 ± 18.85 MPa) (p>0.05). Both fluoride-containing adhesives seemed to demonstrate reliable bonding performance after 1 year of accelerated aging in water.

Degradation in the dentin-composite interface subjected to multi-species biofilm challenges

Oral biofilms can degrade the components in dental resin-based composite restorations, thus compromising marginal integrity and leading to secondary caries. This study investigates the mechanical integrity of the dentin-composite interface challenged with multi-species oral biofilms. While most studies used single-species biofilms, the present study used a more realistic, diverse biofilm model produced directly from plaques collected from donors with a history of early childhood caries. Dentin-composite disks were made using bovine incisor roots filled with Z100(TM) or Filtek(TM) LS (3M ESPE). The disks were incubated for 72 h in paired CDC biofilm reactors, using a previously published protocol. One reactor was pulsed with sucrose, and the other was not. A sterile saliva-only control group was run with sucrose pulsing. The disks were fractured under diametral compression to evaluate their interfacial bond strength. The surface deformation of the disks was mapped using digital image correlation to ascertain the fracture origin. Fracture surfaces were examined using scanning electron microscopy/energy-dispersive X-ray spectroscopy to assess demineralization and interfacial degradation. Dentin demineralization was greater under sucrose-pulsed biofilms, as the pH dropped <5.5 during pulsing, with LS and Z100 specimens suffering similar degrees of surface mineral loss. Biofilm growth with sucrose pulsing also caused preferential degradation of the composite-dentin interface, depending on the composite/adhesive system used. Specifically, Z100 specimens showed greater bond strength reduction and more frequent cohesive failure in the adhesive layer. This was attributed to the inferior dentin coverage by Z100 adhesive, which possibly led to a higher level of chemical and enzymatic degradation. The results suggested that factors other than dentin demineralization were also responsible for interfacial degradation. A clinically relevant in vitro biofilm model was therefore developed, which would effectively allow assessment of the degradation of the dentin-composite interface subjected to multi-species biofilm challenge.

Strategies to prevent hydrolytic degradation of the hybrid layer-A review

OBJECTIVE

Endogenous dentin collagenolytic enzymes, matrix metalloproteinases (MMPs) and cysteine cathepsins, are responsible for the time-dependent hydrolysis of collagen matrix of hybrid layers. As collagen matrix integrity is essential for the preservation of long-term dentin bond strength, inhibition of endogenous dentin proteases is necessary for durable resin-bonded restorations.

METHODS

Several tentative approaches to prevent enzyme function have been proposed. Some of them have already demonstrated clinical efficacy, while others need to be researched further before clinical protocols can be proposed. This review will examine both the principles and outcomes of techniques to prevent collagen hydrolysis in dentin-resin interfaces.

RESULTS

Chlorhexidine, a general inhibitor of MMPs and cysteine cathepsins, is the most tested method. In general, these experiments have shown that enzyme inhibition is a promising approach to improve hybrid layer preservation and bond strength durability. Other enzyme inhibitors, e.g. enzyme-inhibiting monomers, may be considered promising alternatives that would allow more simple clinical application than chlorhexidine. Cross-linking collagen and/or dentin matrix-bound enzymes could render hybrid layer organic matrices resistant to degradation. Alternatively, complete removal of water from the hybrid layer with ethanol wet bonding or biomimetic remineralization should eliminate hydrolysis of both collagen and resin components.

SIGNIFICANCE

Understanding the function of the enzymes responsible for the hydrolysis of hybrid layer collagen has prompted several innovative approaches to retain hybrid layer integrity and strong dentin bonding. The ultimate goal, prevention of collagen matrix degradation with clinically applicable techniques and commercially available materials may be achievable in several ways.

Therapeutic polymers for dental adhesives: loading resins with bio-active components

OBJECTIVES

Many recent adhesives on the market exhibit reasonable clinical performance. Future innovations in adhesive materials should therefore seek out novel properties rather than simply modifying existing technologies. It is proposed that adhesive materials that are "bio-active" could contribute to better prognosis of restorative treatments.

METHODS

This review examines the recent approaches used to achieve therapeutic polymers for dental adhesives by incorporating bio-active components. A strategy to maintain adhesive restorations is the focus of this paper.

RESULTS

Major trials on therapeutic dental adhesives have looked at adding antibacterial activities or remineralization effects. Applications of antibacterial resin monomers based on quaternary ammonium compounds have received much research attention, and the loading of nano-sized bioactive particles or multiple ion-releasing glass fillers have been perceived as advantageous since they are not expected to influence the mechanical properties of the carrier polymer.

SIGNIFICANCE

The therapeutic polymer approaches described here have the potential to provide clinical benefits. However, not many technological applications in this category have been successfully commercialized. Clinical evidence as well as further advancement of these technologies can be a driving force to make these new types of materials clinically available.

Posterior composite restoration update: focus on factors influencing form and function

Restoring posterior teeth with resin-based composite materials continues to gain popularity among clinicians, and the demand for such aesthetic restorations is increasing. Indeed, the most common aesthetic alternative to dental amalgam is resin composite. Moderate to large posterior composite restorations, however, have higher failure rates, more recurrent caries, and increased frequency of replacement. Investigators across the globe are researching new materials and techniques that will improve the clinical performance, handling characteristics, and mechanical and physical properties of composite resin restorative materials. Despite such attention, large to moderate posterior composite restorations continue to have a clinical lifetime that is approximately one-half that of the dental amalgam. While there are numerous recommendations regarding preparation design, restoration placement, and polymerization technique, current research indicates that restoration longevity depends on several variables that may be difficult for the dentist to control. These variables include the patient’s caries risk, tooth position, patient habits, number of restored surfaces, the quality of the tooth–restoration bond, and the ability of the restorative material to produce a sealed tooth–restoration interface. Although clinicians tend to focus on tooth form when evaluating the success and failure of posterior composite restorations, the emphasis must remain on advancing our understanding of the clinical variables that impact the formation of a durable seal at the restoration–tooth interface. This paper presents an update of existing technology and underscores the mechanisms that negatively impact the durability of posterior composite restorations in permanent teeth.