Rational Designs of Biomaterials for Combating Oral Biofilm Infections.

Oral biofilms, which are also known as dental plaque, are the culprit of a wide range of oral diseases and systemic diseases, thus contributing to serious health risks. The manner of how to achieve good control of oral biofilms has been an increasing public concern. Novel antimicrobial biomaterials with highly controllable fabrication and functionalization have been proven to be promising candidates. However, previous reviews have generally emphasized the physicochemical properties, action mode, and application effectiveness of those biomaterials, whereas insufficient attention has been given to the design rationales tailored to different infection types and application scenarios. To offer guidance for better diversification and functionalization of anti-oral-biofilm biomaterials, this review details the up-to-date design rationales in three aspects: the core strategies in combating oral biofilm, as well as the biomaterials with advanced antibiofilm capacity and multiple functions based on the improvement or combination of the abovementioned antimicrobial strategies. Thereafter, insights on the existing challenges and future improvement of biomaterial-assisted oral biofilm treatments are proposed, hoping to provide a theoretical basis and reference for the subsequent design and application of antibiofilm biomaterials.

Corrigendum to "Epigallocatechin-3-gallate/mineralization precursors co-delivery hollow mesoporous nanosystem for synergistic manipulation of dentin exposure" [Bioact. Mater. 23 (2023) 394-408].

[This corrects the article DOI: 10.1016/j.bioactmat.2022.11.018.].

Epigallocatechin-3-gallate/mineralization precursors co-delivery hollow mesoporous nanosystem for synergistic manipulation of dentin exposure.

As a global public health focus, oral health plays a vital role in facilitating overall health. Defected teeth characterized by exposure of dentin generally increase the risk of aggravating oral diseases. The exposed dentinal tubules provide channels for irritants and bacterial invasion, leading to dentin hypersensitivity and even pulp inflammation. Cariogenic bacterial adhesion and biofilm formation on dentin are responsible for tooth demineralization and caries. It remains a clinical challenge to achieve the integration of tubule occlusion, collagen mineralization, and antibiofilm functions for managing exposed dentin. To address this issue, an epigallocatechin-3-gallate (EGCG) and poly(allylamine)-stabilized amorphous calcium phosphate (PAH-ACP) co-delivery hollow mesoporous silica (HMS) nanosystem (E/PA@HMS) was herein developed. The application of E/PA@HMS effectively occluded the dentinal tubules with acid- and abrasion-resistant stability and inhibited the biofilm formation of Streptococcus mutans. Intrafibrillar mineralization of collagen fibrils and remineralization of demineralized dentin were induced by E/PA@HMS. The odontogenic differentiation and mineralization of dental pulp cells with high biocompatibility were also promoted. Animal experiments showed that E/PA@HMS durably sealed the tubules and inhibited biofilm growth up to 14 days. Thus, the development of the E/PA@HMS nanosystem provides promising benefits for protecting exposed dentin through the coordinated manipulation of dentin caries and hypersensitivity.

Dental plaque-inspired versatile nanosystem for caries prevention and tooth restoration.

Dental caries is one of the most prevalent human diseases resulting from tooth demineralization caused by acid production of bacteria plaque. It remains challenges for current practice to specifically identify, intervene and interrupt the development of caries while restoring defects. In this study, inspired by natural dental plaque, a stimuli-responsive multidrug delivery system (PMs@NaF-SAP) has been developed to prevent tooth decay and promote enamel restoration. Classic spherical core-shell structures of micelles dual-loaded with antibacterial and restorative agents are self-assembled into bacteria-responsive multidrug delivery system based on the pH-cleavable boronate ester bond, followed by conjugation with salivary-acquired peptide (SAP) to endow the nanoparticle with strong adhesion to tooth enamel. The constructed PMs@NaF-SAP specifically adheres to tooth, identifies cariogenic conditions and intelligently releases drugs at acidic pH, thereby providing antibacterial adhesion and cariogenic biofilm resistance, and restoring the microarchitecture and mechanical properties of demineralized teeth. Topical treatment with PMs@NaF-SAP effectively diminishes the onset and severity of caries without impacting oral microbiota diversity or surrounding mucosal tissues. These findings demonstrate this novel nanotherapy has potential as a promising biomedical application for caries prevention and tooth defect restoration while resisting biofilm-associated diseases in a controlled manner activated by pathological bacteria.

Sodium carboxymethyl cellulose-based extrafibrillar demineralization to optimize dentin bonding durability.

OBJECTIVE: To investigate the effects of a sodium carboxymethyl cellulose (SCMC)-based extrafibrillar demineralization conditioner on dentin bonding durability and explore the possible mechanisms. METHODS: The SCMC-based extrafibrillar demineralization conditioner was facilely developed by dissolving SCMC into deionized water at an appropriate concentration. A single layer collagen mineralization/demineralization model was designed to visualize extrafibrillar demineralization in detail. Dentin surfaces of human third molars were conditioned with 3 % SCMC or 37 % phosphoric acid (PA). The morphology, composition, and mechanical properties of conditioned dentin from each group were characterized. To evaluate dentin bonding performance, SCMC- and PA- conditioned dentin were applied with adhesive restoration using the dry-bonding technique. The microtensile bond strength (MTBS), interface nanoleakage, and in situ zymography were measured after 24 h of water storage, 10,000 thermocycles, or one month of collagenase aging. The inhibitory effect of SCMC on recombinant human matrix metalloproteinase-2 (rhMMP-2) and cell toxicity were also investigated. RESULTS: After SCMC conditioning, both demineralization of extrafibrillar minerals and retention of intrafibrillar minerals were observed in the single layer collagen model and the dentin ultrastructure. The mechanical properties of SCMC-conditioned dentin were largely preserved. Compared with PA, SCMC conditioning produced greater MTBS values and less nanoleakage expression after aging. Endogenous gelatinolytic activity was suppressed in SCMC-conditioned dentin. In addition to being nontoxic, the inhibition of rhMMP-2 by SCMC was confirmed to be dose-dependent. SIGNIFICANCE: From the perspective of minimal intervention, the SCMC-based extrafibrillar demineralization conditioner could improve dentin bonding durability, suggesting a promising strategy to extend the service life of adhesive restorations.

Enhancing adhesive-dentin interface stability of primary teeth: From ethanol wet-bonding to plant-derived polyphenol application.

OBJECTIVES: To investigate whether the adhesive-dentin interface stability of primary teeth would be enhanced by epigallocatechin-3-gallate (EGCG) with ethanol wet-bonding. METHODS: Non-caries primary molars were sliced to achieve a flat dentin surface and etched then randomly distributed into five groups in accordance with different treatments: group 1, no treatment; group 2, applying absolute ethanol wet-bonding for 60 s; groups 3-5, applying 0.1%, 0.5%, and 1% (w/v) EGCG-incorporating ethanol wet-bonding (0.1%, 0.5%, and 1% EGCG) for 60 s. Singlebond universal adhesive was then applied followed by resin composite construction. Microtensile bond strength, fracture mode, and nanoleakage at adhesive-dentin interface were evaluated after 24 h of water storage or 10,000 times of thermocycling. Zymography of hybrid layer, biofilm formation of Streptococcus mutans by CLSM, FESEM, and MTT test, and cytotoxicity by CCK-8 assay were respectively assessed. RESULTS: Irrespective of thermocycling, the dentin bond strength was preserved with reduced nanoleakage in the 0.5% and 1% EGCG groups. Furthermore, the activity of endogenous proteases and the growth of Streptococcus mutans biofilm were inhibited after treatment with 0.5% and 1% EGCG/ethanol solutions (groups 4 and 5). CCK-8 results of the 0.1% and 0.5% EGCG groups showed acceptable biocompatibility. CONCLUSIONS: Treatment by EGCG/ethanol solutions effectively enhanced the bond stability of primary teeth at the adhesive-dentin interface. CLINICAL SIGNIFICANCE: Synergistic application of EGCG and ethanol wet-bonding suggesting a promising strategy to improve dentin bonding durability with bacterial biofilm inhibition, thus increasing resin-based restorations' service life in primary dentition.

Evaluation of Retention Forces of Implant-Supported Zirconia Copings on Titanium Abutments Coated with Metal Opaquers Using Different Cements.

PURPOSE: To evaluate the use of a new resin metal opaquer on the surface of titanium abutments, in combination with two luting agents, and its effect on the retentive strength of implant-supported zirconia copings. MATERIALS AND METHODS: Sixty customized titanium abutments were designed and fabricated with virtual design software and a milling machine. Thirty abutment specimens were coated with metal opaquers, and the others were not coated. Then, the titanium abutments were fitted into the implant analogs, and the abutment-implant analog complexes were embedded in acrylic resin blocks. Sixty CAD/CAM-fabricated zirconia copings were seated on the abutments and secured with glassionomer cement or self-adhesive resin cement. The specimens were stored in 100% humidity for 1 hour and artificial saliva for 23 hours at 37°C before thermocycling for 5,000 cycles of 5°C to 55°C with a 30-second dwell time. The retentive strength was measured using a pull-out test with a universal testing machine. The dislodgment forces were statistically analyzed via two-way analysis of variance (ANOVA). The failure modes were evaluated and categorized by examining the fracture surface. RESULTS: The metal opaquer material had a significant negative effect on retention of zirconia copings. The nonopaquer titanium abutments showed significantly (P < .05) higher retentive strength than the metal opaquer abutments. Comparing the cements, the retentive strength values of self-adhesive resin cement were significantly higher than those of glass-ionomer cement. The metal opaquer groups exhibited mostly mixed-type failures, a combination of adhesive failures and cohesive failures, whereas the nonopaquer groups showed mostly adhesive-type failures. CONCLUSION: The titanium abutments coated with the new metal opaquer material resulted in a reduction of retentive strength. Self-adhesive resin cements exhibited significantly higher retention than glass-ionomer cements.

An MSN-based synergistic nanoplatform for root canal biofilm eradication via Fenton-enhanced sonodynamic therapy.

The validity and biocompatibility of irrigating agents are imperative for the success of root canal therapy. The imperfections in the currently available irrigants highlight the fact that more advanced technologies and strategies are required for complete disinfection in endodontic treatments. In the present study, a Fenton reaction-enhanced antimicrobial sonodynamic therapy (SDT) platform was fabricated for root canal disinfection. Firstly, mesoporous silica nanoparticles (MSNs) were synthesized, grafted with an amino group and then conjugated with sonosensitizer protoporphyrin IX (PpIX). Iron ions were then anchored (M@P-Fe) to initiate a Fenton reaction. Nanoparticle characterization by size and zeta potential measurements, scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis confirmed that the platform was successfully developed. Reactive oxygen species (ROS) generation assessment, methylene blue degradation and electron spin resonance assays illustrated upon ultrasound (US) irradiation, that augmented ROS, can be produced by US activated PpIX and iron mediated Fenton reactions from low concentration H2O2 (0.01%). In vitro anti-Enterococcus faecalis efficacy was demonstrated by growth curve and colony forming unit measurements. Confocal laser scanning microscopy and scanning electron microscopy observations illustrated the effectiveness of the platform on in situ biofilm eradication in root canal. Owing to the stronger oxidizing capability and short lifetime of ROS, the Fenton reaction-enhanced SDT can induce detrimental oxidative damage to bacteria upon activation of US while avoiding nonspecific toxicity to cells, which was verified by cytotoxicity evaluations using CCK-8 assay and morphology observation of MC3T3-E1 cells. Compared to commonly used NaClO, this nanoplatform displayed desirable anti-bacterial, anti-biofilm abilities and better biocompatibility. These results highlight that the integrated M@P-Fe + US + H2O2 platform is a promising candidate for US enhanced root canal irrigation and disinfection.

The Stability of Dentin Surface Biobarrier Consisting of Mesoporous Delivery System on Dentinal Tubule Occlusion and Streptococcus Mutans Biofilm Inhibition.

BACKGROUND: The dentin exposure always leads to dentin hypersensitivity and/or caries. Given the dentin's tubular structure and low mineralization degree, reestablishing an effective biobarrier to stably protect dentin remains significantly challenging. This study reports a versatile dentin surface biobarrier consisting of a mesoporous silica-based epigallocatechin-3-gallate (EGCG)/nanohydroxyapatite delivery system and evaluates its stability on the dentinal tubule occlusion and the Streptococcus mutans (S. mutans) biofilm inhibition. MATERIALS AND METHODS: The mesoporous delivery system was fabricated and characterized. Sensitive dentin discs were prepared and randomly allocated to three groups: 1, control group; 2, casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) group; and 3, the mesoporous delivery system group. The dentin permeability, dentinal tubule occlusion, acid and abrasion resistance, and S. mutans biofilm inhibition were determined for 1 week and 1 month. The in vitro release profiles of EGCG, Ca, and P were also monitored. RESULTS: The mesoporous delivery system held the ability to sustainably release EGCG, Ca, and P and could persistently occlude dentinal tubules with acid and abrasion resistance, reduce the dentin permeability, and inhibit the S. mutans biofilm formation for up to 1 month compared with the two other groups. The system provided prolonged stability to combat oral adverse challenges and served as an effective surface biobarrier to protect the exposed dentin. CONCLUSION: The establishment of the dentin surface biobarrier consisting of a mesoporous delivery system indicates a promising strategy for the prevention and the management of dentin hypersensitivity and caries after enamel loss.

Polymer conjugation optimizes EDTA as a calcium-chelating agent that exclusively removes extrafibrillar minerals from mineralized collagen.

During development of mineralized collagenous tissues, intrafibrillar mineralization is achieved by preventing mineralization precursor inhibitors that are larger than 40 kDa from entering the collagen fibrils. Such a property is incorporated in the design of a calcium chelator for dentin bonding in the etch-and-rinse technique that selectively demineralizes extrafibrillar apatite while leaving the intrafibrillar minerals intact. This strategy prevents complete demineralization of collagen fibrils, avoids collapse of collagen that blocks resin infiltration after air-drying, and protects the completely demineralized fibrils from bacteria colonization and degradation by endogenous proteases after resin bonding. In the present study, a water-soluble glycol chitosan-EDTA (GCE) conditioner was synthesized by conjugation of EDTA, an effective calcium chelator, to high molecular weight glycol chitosan, which exhibits weak chelation property. The GCE conjugate was purified, characterized by FTIR, 1H NMR, isothermal titration calorimetry and ICP-AES, and subjected to size exclusion dialysis to recover molecules that are >40 kDa. The optimal concentration and application time for etching dentin were determined by bond strength testing to ensure that the dentin bonding results were comparable to phosphoric acid etching, and maintained equivalent bond strength after air-drying of the conditioned collagen matrix. Extrafibrillar demineralization was validated with transmission electron microscopy. Inhibition of endogenous dentin proteases was confirmed using in-situ zymography. The water-soluble GCE dentin conditioner was non-cytotoxic and possessed antibacterial activities against planktonic and single-species biofilms, supporting its ongoing development as a dentin conditioner with air-drying, anti-proteolytic and antibacterial properties to enhance the durability of bonds created using the etch-and-rinse bonding technique. STATEMENT OF SIGNIFICANCE: The current state-of-the-art techniques for filling decayed teeth with plastic tooth-colored materials require conditioning the mineralized, biofilm-covered, decayed dentin with acids or acid resin monomers to create a surface layer of completely- or partially-demineralized collagen matrix for the infiltration of adhesive resin monomers. Nevertheless, fillings prepared using these strategies are not as durable as consumers have anticipated. Conjugation of polymeric glycol chitosan with EDTA produces a new conditioner for dentin bonding that demineralizes only extrafibrillar dentin, reduces endogenous protease activities and kills biofilm bacteria. The high molecular weight glycol chitosan-EDTA is non-cytotoxic to the key regenerative players within the dentin-pulp complex. This advance permits dry bonding and the use of hydrophobic resins.

Influence of naringenin on the biofilm formation of Streptococcus mutans.

OBJECTIVES: To evaluate the effect of naringenin on the biofilm formation of Streptococcus mutans (S. mutans), and to investigate its mechanisms of action and biological toxicity. METHODS: Minimum inhibitory concentrations, growth curves, and biofilm inhibition rates of naringenin were determined to assess its antimicrobial effect on S. mutans. The morphology of S. mutans and the structure of biofilm were observed by FESEM and CLSM. Bacterial aggregation, bacterial surface hydrophobicity, and real-time PCR for gtfB, gtfC, comD, comE, and luxS mRNA expression were assessed to preliminarily investigate the mechanisms of action. MTT test using human dental pulp cells (HDPCs) was also performed to investigate cytotoxicity. RESULTS: The S.mutans growth curves, FESEM, CLSM showed that both 100 and 200 µg/mL of naringenin obviously inhibited S. mutans growth and biofilm formation, increased S. mutans surface hydrophobicity, reduced bacterial aggregation, and downregulated the mRNA expression of gtfB, gtfC, comD, comE, and luxS. However, naringenin at 200 µg/mL slightly decreased the growths of HDPCs compared with 100 µg/mL. CONCLUSION: Naringenin at 100 and 200 µg/mL suppressed the second (bacterial adhesion) and third stages (biofilm maturation) of S. mutans biofilm formation. CLINICAL SIGNIFICANCE: Naringenin is promising for dental clinic promotion to prevent the biofilm formation of S. mutans, serving as a safe anti-caries agent at an appropriate concentration.

Dimethyl Sulfoxide Wet-bonding Technique May Improve the Quality of Dentin Bonding.

PURPOSE: To investigate the effect of the dimethyl-sulfoxide wet-bonding technique on composite-dentin bonds and to explore its potential mechanism. MATERIALS AND METHODS: Thirty human third molars were segmented, ground, etched, and randomly divided into three groups according to the following pretreatments: 1. water; 2. ethanol; 3. 50% (v/v) dimethyl sulfoxide (DMSO). Then, Single Bond 2 was applied and composite buildups were constructed. After 24 h of water storage or 10,000 cycles of thermocycling, the microtensile bond strength (MTBS) and nanoleakage were measured. Contact angle measurement, Masson's trichrome staining, and in situ zymography were used to explore the possible action mechanism of DMSO on adhesive-dentin interfaces. RESULTS: DMSO pretreatment prevented the decline of thermocycled MTBS (p < 0.05) without affecting the immediate MTBS (p > 0.05) compared to the water wet-bonded group. Nanoleakage expression in the thermocycled DMSO wet-bonded group was also less than that in the thermocycled water-wet group (p < 0.05). Moreover, DMSO decreased the contact angle of the dentin surfaces (p < 0.05), reduced the amount of collagen exposure (p < 0.05), and decreased the collagenolytic activity in the hybrid layer (p < 0.05). CONCLUSION: The 50% DMSO pretreatment was effective in increasing the wettability of the etched dentin surface, promoting the penetration of the adhesive monomer, and enhancing the stability of the dentin collagen at the adhesive- dentin interface. All these changes may lead to higher quality dentin bonds, suggesting that DMSO wet bonding is a viable alternative to improve the durability of dentin bonding.

Effect of silane pretreatment on the immediate bonding of universal adhesives to computer-aided design/computer-aided manufacturing lithium disilicate glass ceramics.

The aim of this study was to investigate the effect of silane pretreatment on the universal adhesive bonding between lithium disilicate glass ceramic and composite resin. IPS e.max ceramic blocks etched with hydrofluoric acid were randomly assigned to one of eight groups treated with one of four universal adhesives (two silane-free adhesives and two silane-containing adhesives), each with or without silane pretreatment. Bonded specimens were stored in water for 24 h. The shear bond strength (SBS) of the ceramic-resin interface was measured to evaluate bond strength, and the debonded interface after the SBS test was analysed using field-emission scanning electron microscopy to determine failure mode. Light microscopy was performed to analyse microleakage and marginal sealing ability. Silane pretreatment significantly and positively influenced SBS and marginal sealing ability. For all the universal adhesive groups, SBS increased and the percentage of microleakage decreased after the pretreatment. Without the pretreatment, SBS and the percentage of microleakage were not significantly different between the silane-containing universal adhesive groups and the silane-free groups. Cohesive failure was the main fracture pattern. The results suggest that additional silane pretreatment can effectively improve the bonding strength and marginal sealing of adhesives to lithium disilicate glass ceramics. The bonding performance of silane-containing universal adhesives without pretreatment is similar to that of silane-free adhesives.

Robust and thermoplastic hydrogels with surface micro-patterns for highly oriented growth of osteoblasts.

Biocompatible hydrogels with high strength, high precision patterns, and arbitrary 3D shapes are extremely desired soft platforms in the biomedicine fields. On the basis of the thermal-reversible sol-gel transition of agarose and the formation of nanofibers below 35 °C, a robust and thermoplastic hydrogel (TPG) was fabricated by in situ polymerization of acrylamide in the agarose matrix. The tensile fracture stress/strain values of the TPG were unexpectedly higher than those of both agarose and polyacrylamide hydrogels as a result of the double networks reinforced with nanofibers. The TPG could reversibly soften and harden by heating and cooling treatment, respectively, leading to an excellent mechanical recoverability and reprocessing ability. Thus, arbitrary 3D-shaped hydrogels and micro-patterns embossed on the TPG surface with a high resolution of 1 µm were constructed. The rigid TPG exhibited a remarkable affinity for the adhesion and proliferation of cells. In particular, the TPGs with microgrooves could highly guide the oriented growth of osteoblasts, showing potential applications in the field of tissue engineering.

[The application of universal adhesives in dental bonding].

The bonding restoration has become an important clinical technique for the development of dental bonding technology. Because of its easy operation and the maximum preservation of tooth tissues, bonding repair is widely used in dental restoration. The recent multi-mode universal adhesives have brought new progress in dental bonding restoration. In this article the universal adhesives were reviewed according to its definition, development, improvement, application features and possible problems.

Effect of adjunctive application of epigallocatechin-3-gallate and ethanol-wet bonding on adhesive-dentin bonds.

OBJECTIVES: To determine the effect of the combined use of epigallocatechin-3-gallate (EGCG) and ethanol-wet bonding (EWB) on resin-dentin bonds. METHODS: Sixty molars were sectioned, polished, and randomly divided into six groups (n=10) according to the following pretreatments: group 1, water-wet bonding (WWB); group 2, WWB with 0.02% (w/v) EGCG; group 3, WWB with 0.1% EGCG; group 4, EWB; group 5, EWB with 0.02% EGCG; and group 6, EWB with 0.1% EGCG. An etch-and-rinse adhesive was then used, followed by the resin composites building. The microtensile bond strength (MTBS), failure modes and interfacial nanoleakage were separately determined after 24h water storage or 10,000 runs of thermocycling. RESULTS: Both pretreatment method (P<0.05) and thermocycling (P<0.05) significantly influenced bond strength and nanoleakage. Irrespective of thermocycling, the 0.02% EGCG/ethanol (group 5) pretreated adhesive-dentin interfaces showed higher MTBS than the control group (P<0.05). Nanoleakage expression of all groups increased after thermocycling (P<0.05) except group 5. Adhesive failure was the main fracture pattern in all groups. CONCLUSION: This study showed that pretreatment with 0.02% EGCG/ethanol solutions can effectively improve immediate bond strength and bond stability of etch-and-rinse adhesives on dentin. CLINICAL SIGNIFICANCE: The adjunctive application of EGCG and EWB provides a new strategy for dentists to obtain the desired bond effectiveness during adhesive restoration in clinical practice.

Cyclooxygenase-2-1195G>A Polymorphism and Head and Neck Squamous Cell Carcinoma Susceptibility: A Meta-Analysis of 1564 Cases and 2346 Controls.

BACKGROUND The aim of this study was to investigate the association between cyclooxygenase-2 (COX-2) rs689466 (-1195 G>A) polymorphism and susceptibility to head and neck squamous cell carcinoma (HNSCC) by performing a meta-analysis. MATERIAL AND METHODS PubMed and Embase were searched for relevant cohort and case-control studies up to 13 March 2015. After data extraction and methodological quality assessment for eligible studies, the overall, subgroup, sensitivity, and cumulative meta-analyses were conducted using the Comprehensive Meta-Analysis software (version 2.2). RESULTS Finally, 5 case-control studies involving 1564 HNSCC patients and 2346 healthy controls were included. For overall population, the results of 3 genetic models showed significant association, while the other 2 presented negative association [A vs. G: OR=0.97-1.09, 95%CI=0.97-1.09; AA vs. GG: OR=1.26, 95%CI=1.01-1.57; AA vs. GA: OR=1.21, 95%CI=1.01-1.45); AA vs. (GG+GA): OR=1.20, 95%CI=1.01-1.43; (AA+GA) vs. GG: OR=0.98, 95%CI=0.84-1.15]. Publication bias was not assessed due to the limited number of included studies. CONCLUSIONS This meta-analysis indicated that COX-2 rs689466 polymorphism might be associated with increased susceptibility to HNSCC. We also suggest performing more relevant studies in order to enlarge the sample size and obtain more precise results.

Nanoleakage evaluation at adhesive-dentin interfaces by different observation methods.

The purpose of this study was to evaluate the capability and characteristics of different nanoleakage observation methods, including light microscope (LM), field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and confocal laser scanning microscope (CLSM). Dentin specimens were bonded with either an etch-and-rinse adhesive (SBMP) or a self-etch adhesive (GB), and prepared for nanoleakge evaluation according to different observation methods. LM, FESEM and CLSM results demonstrated that the SBMP group showed more interfacial nanoleakage than the GB group (p<0.05); by contrast, no significant difference was found in TEM results (p>0.05), however, TEM illustrated concrete nanoleakage forms or patterns. The results suggested that different observation methods might exhibit distinct images and a certain degree of variations in nanoleakage statistical results. Researchers should carefully design and calculate the optimum assembly in combination with qualitative and quantitative approaches to obtain objective and accurate nanoleakage evaluation.

Effects of different artificial ageing methods on the degradation of adhesive-dentine interfaces.

OBJECTIVES: To compare the effects of four commonly used artificial ageing methods (water storage, thermocycling, NaOCl storage and pH cycling) on the degradation of adhesive-dentine interfaces. METHODS: Fifty molars were sectioned parallel to the occlusal plane, polished and randomly divided into two adhesive groups: An etch-and-rinse adhesive Adper SingleBond 2 and a self-etch adhesive G-Bond. After the composite built up, the specimens from each adhesive group were sectioned into beams, which were then assigned to one of the following groups: Group 1 (control), 24h of water storage; Group 2, 6 months of water storage; Group 3, 10,000 runs of thermocycling; Group 4, 1h of 10% NaOCl storage; and Group 5, 15 runs of pH cycling. The microtensile bond strengths were then tested. The failure modes were classified with a stereomicroscope and representative interface was analyzed with a field-emission scanning electron microscopy (FESEM). Nanoleakage expression was evaluated through FESEM in the backscattered mode. RESULTS: The four artificial ageing methods decreased the bonding strength to nearly 50% and increased the nanoleakage expression of both adhesive systems compared with the control treatment. Adhesive failures were the predominant fracture modes in all groups. However, differences in detailed morphology were observed among the different groups. CONCLUSIONS: Water storage, thermocycling, NaOCl storage and pH cycling could obtain similar degradation effectiveness through appropriate parameter selection. Each in vitro artificial ageing method had its own mechanisms, characteristics and application scope for degrading the adhesive-dentin interfaces. CLINICAL SIGNIFICANCE: Water storage is simple, low-cost but time-consuming; thermocycling lacks of a standard agreement; NaOCl storage is time-saving but mainly degrades the organic phase; pH cycling can resemble cariogenic condition but needs further studies. Researchers focusing on bonding durability studies should be deliberate in selecting an appropriate ageing model based on the differences of test material, purpose and time.