Implication of ethanol wet-bonding in hybrid layer remineralization

Evaluating the effect of poly (amidoamine) treated bioactive glass nanoparticle incorporated in universal adhesive on bonding to artificially induced caries affected dentin

BACKGROUND

The purpose of this study was to evaluate remineralisation and its effect on microtensile bond-strength of artificially induced caries affected dentin (CAD) when treated with a commercial universal adhesive modified with poly(amidoamine) dendrimer (PAMAM) loaded mesoporous bioactive glass nanoparticles (A-PMBG).

MATERIAL AND METHODS

Mesoporous bioactive glass nanoparticles (MBG) were synthesised using sol-gel process, where PAMAM was loaded (P-MBG) and added to commercial adhesive at different weight percentages (0.2, 0.5, 1 and 2 wt%). First, rheological properties of commercial and modified adhesives were evaluated. The effect of remineralization/hardness and microtensile bond-strength (MTBs) of those samples that mimicked the rheological properties of commercial adhesives were evaluated using Vickers hardness tester and universal testing machine respectively. Scanning-Electron microscope was used to visualize failed samples of MTBs and remineralization samples. Both evaluations were carried out at 1-,3 and 6-month intervals, samples being stored in stimulated salivary fluid during each time interval.

RESULTS

Addition of nanoparticles altered the rheological properties. With increase in the weight percentage of nanoparticles in commercial adhesive, there was significant increase in degree of conversion, viscosity and sedimentation rate (p < 0.05). The 0.2 and 0.5 wgt% groups closely mimicked the properties of commercial adhesive and were evaluated for remineralization and MTBs. After 6 months, 0.2wgt% group showed increased MTBs (p < 0.05) and 0.5wgt% group increased remineralization/hardness (p < 0.05).

CONCLUSION

The complex of PAMAM-MBG-Universal adhesive can remineralize the demineralised CAD thereby improving its bond-strength when evaluated for up to 6-months.

Effect of phytic acid on dentinal collagen solubilization and its binding and debinding potentials to dentin

OBJECTIVES

To study phytic acid (IP6) effect on collagen solubilization by assessing hydroxyproline (HYP) release, evaluate its binding to demineralized (DD) and mineralized dentin (MD) and determine the effect of different media on debinding of IP6.

METHODS

Demineralized dentin beams were incubated in 1%, 2% or 3% IP6 and HYP release was evaluated at 1 or 3 weeks and compared to those obtained in untreated control or phosphoric acid (PA)-treated beams. DD or MD powder was treated with 1%, 2% or 3% IP6 and the decrease in IP6 amount was quantitated by ultraviolet-visible spectroscopy. IP6-treated samples were re-suspended in distilled water, ethanol, urea or sodium chloride and the amount of IP6 displaced was determined.

RESULTS

At 1 week, the control group and IP6 showed lower HYP release when compared to PA (P < 0.05). There was no difference among PA, IP6 and control at 3 weeks (P = 0.22). IP6 binding was concentration dependent. 1% IP6 had higher binding potential with MD compared to DD while 2% IP6 showed the opposite result (P<0.05). 3% IP6 had similar binding values between DD and MD (P = 0.53). The highest debinding in MD occurred with urea for 2%, 3% and 1% IP6 in descending manner. Within each concentration of IP6 in DD, the highest debinding effect was reported with ethanol.

CONCLUSIONS

IP6 bound to DD and MD in a concentration-dependent manner. IP6 was debound from DD mostly by the action of ethanol, while in MD, urea caused the most displacement. Collagen solubilization of IP6-treated DD was comparable to untreated DD.

CLINICAL SIGNIFICANCE

These findings add to the potential use of IP6 as an alternative to PA for dentin etching which possibly results in long-term stability of resin-dentin adhesion.

Comparing Impact of Two Resin Infiltration Systems on Microhardness of Demineralized Human Enamel after Exposure to Acidic Challenge

AIM: This study compared the impact of two resin infiltration systems on microhardness of demineralized enamel before and after an acidic challenge. MATERIALS AND METHODS: A total of forty human maxillary molar teeth were used in this study. Each tooth has 4 groups (four standardized windows onto each tooth). Group A1: Untreated sound enamel surface (positive control), Group A2: Artificially demineralized enamel surface (negative control), Group A3: Icon resin infiltrating to demineralized enamel, while Group A4: Single bond universal adhesive applied to the demineralized enamel surface. All teeth were immersed in a demineralizing solution. The groups (A3 and A4) were further subdivided into two subgroups according to acidic ethanol challenge Subgroup B1: Specimens tested before an acidic challenge and B2: Specimens tested after an acidic challenge. Vickers microhardness test was done for all groups. One-way analysis of variance (ANOVA) was used to study the difference between tested groups on mean microhardness within each group. Tukey’s post-hoc test was used for pair-wise comparison between the means when ANOVA test was performed, and the significance level was set at p ≤ 0.05. RESULTS: Icon resin infiltration and single bond universal adhesive showed significantly higher mean microhardness than negative control, but significantly lower mean microhardness than positive control. However, insignificant difference was found between icon and single bond universal adhesive. After the acidic challenge, icon resin infiltration showed significantly higher mean microhardness than negative control. However, single bond universal adhesive showed insignificant difference as compared to the negative control. CONCLUSION: After an acidic challenge, icon resin infiltration was more successful than single bond universal total-etch adhesive system in microhardness. RECOMMENDATION: Icon resin infiltration technique is a promising, noninvasive approach that prevents the progress of the carious lesion.

Bonding to dentin using an experimental zirconium oxynitrate etchant

OBJECTIVE

To investigate, by means of microtensile bond strength test (μTBS), nanoleakage expression analysis (NL), gelatin zymography and in situ zymography, the effects of an experimental metal salt-based zirconium oxynitrate etchant [ZrO(NO₃)₂,] - ZON with two simplified adhesives on long-term bond strength and endogenous enzymatic activities.

METHODS

Middle/deep coronal dentin surfaces (N = 32) were conditioned either with a traditional 37 % H₃PO₄ etchant (TE) or with ZON. Further, a single-component etch-and-rinse adhesive (EF) or a universal adhesive (AU) were applied and μTBS and NL tests were performed. Additional freshly extracted teeth were processed for gelatin zymography and in situ zymography evaluation. The tests were performed at baseline and (T0) and after 1-year-aging (T12). Bond strength and in situ zymography results were analyzed using analysis of variance (ANOVA) (three-way and one-way, respectively), while Chi-squared test was used for the NL results. Statistical significance was preset at α = 0.05.

RESULTS

All the investigated factors (adhesive system, dentin conditioner and aging) significantly influenced μTBS, with the AU and ZON performing better compared to EF and TE, respectively, and with lower bond strength values after aging (p < 0.05). Incremented silver nitrate deposits were observed at the adhesive interfaces after aging, especially for the TE groups (p < 0.05). Further, the experimental groups treated with ZON had significantly lower levels of enzymatic activity compared to TE, as shown by gelatin and in situ zymography (p < 0.05).

CONCLUSIONS

The experimental etchant demonstrated promising results in hybrid-layer preservation over time when used with simplified bonding systems, and could therefore be recommended in the clinical practice.

Effects of Bioactive Agents on Dentin Mineralization Kinetics After Dentin Bleaching

Objectives:

This study evaluated effects of Bioglass 45S5 (BG) and Biosilicate (BS) remineralization on the chemical composition and bond strength of control dentin (CD) and bleached dentin (BD) surfaces.

Methods and Materials:

Dentin bleaching treatment was performed using the walking bleaching technique with 0.01 g of sodium perborate and 0.5 mL of 3% hydrogen peroxide for 14 days. Remineralization treatment was carried out by rubbing a remineralization solution (0.015 g of BG or BS diluted in 1.35 mL of distilled water) on the etched dentin surface for 30 seconds. Micro-Raman spectroscopy (MRS) was used to quantitatively analyze the mineral matrix ratios of CD and BD (n=5) after remineralization treatment with BG and BS over 15 days of incubation in artificial saliva. The CD and BD discs (n=10) with and without remineralization treatment with BG and BS were restored using a two-step etch-and-rinse adhesive system (Optibond S, Kerr) and five layers of 1-mm-thick composite resin (Filtek Z250, 3M ESPE). The restored dentin discs were sectioned into nine bonded beams with cross-sectional areas of approximately 0.9 mm2 and tested for microtensile bond strength (μTBS). The dentin surface of one fractured beam per tooth was submitted to MRS to characterize the physicochemical composition (n=10) at the interface. The data were analyzed using one-way analysis of variance and the Tukey-Kramer post hoc test (p&lt;0.005).

Results:

MRS bioactive analyses revealed that both BG and BS promoted increased mineral matrix ratios in the CD and BD. Significantly higher μTBS values were found after CD treatment with BG (CD: 57 MPa±11; CD-BG: 78 MPa±15) and when BG and BS were applied to the BD (BD: 42 MPa±5; BD-BG: 71 MPa±14; BD-BS: 64 MPa±11) (p&lt;0.005). The MRS analysis of the fractured dentin beam showed that the remineralization treatment significantly increased the dentin relative mineral concentration and promoted the appearance of new interface peaks, indicating a chemical interaction (p&lt;0.005).

Conclusion:

Remineralization of BD is an effective therapy to restore damage caused by dentin bleaching and acid conditioning. This approach not only increases dentin mineral compounds but also improves dentin's ability to interact chemically with the adhesive system.

Effect of 2% Chlorhexidine Following Acid Etching on Microtensile Bond Strength of Resin Restorations: A Meta-Analysis

Background and Objectives: The aim of this systematic review was to examine the effect of 2% chlorhexidine following acid etching on the microtensile bond strength of resin restorations for different follow-up times. Materials and Methods: A thorough search of PubMed, Scopus, and Embase databases were conducted. In vitro experimental studies or in vivo studies published up to December 2018 with an experimental group treated with a 2% chlorhexidine solution following acid etching and a control group were included, wherein the final restoration used a resin composite in both the groups. Results: Twenty-one articles were identified for qualitative analysis and 18 for meta-analysis. The difference in the means of microtensile bond strength between the two groups was calculated for the different follow-up times. The differences were significant for 6 months (4.30 MPa; 95% CI 2.72–5.89), 12 months (8.41 MPa; 95% CI 4.93–11.88), and 2–5 years including aged and thermocycling samples (9.08 MPa; 95% CI 5.36–12.81). There were no significant differences for the type of adhesive used. A meta-regression model showed a significant effect of time on the microtensile bond strength. Conclusions: The application of a 2% chlorhexidine solution after acid etching increased the microtensile bond strength significantly for follow-up times of 6 months or more. The adhesive type had no influence.

Six-month performance of restorations produced with the ethanol-wet-bonding technique: a randomized trial

This double-blind randomized controlled clinical trial evaluated the effectiveness of dentin pretreatment with 100% ethanol (EWBT - ethanol wet bonding technique) and different adhesive protocols in noncarious cervical lesions (NCCL) after 6 months. Patients presenting at least one NCCL were included. NCCLs (n=148) were randomly assigned to 4 groups: NE (Non-EWBT + three-step etch-and-rinse (Scotchbond Multi Purpose, 3M ESPE [MP]), E (EWBT + MP); EB (EWBT + [Bond - third step of MP]), and EU (EWBT + universal adhesive (Single Bond Universal, 3M ESPE). Conventional acid-etching (Condac 37%, FGM) and nanohybrid resin composite (Z350, 3M ESPE) were used. Trained and calibrated examiners (Kappa = 0.61) evaluated the restorations at baseline (7 days) and 6-month recall using the USPHS modified criteria. Data were subjected to Chi square (α = 0.05). Differences in the success rate were found for the treatments (p = 0.003). EB presented the lowest success rate compared with the other groups (p < 0.02). No significant differences were detected among NE, E, and EU (p > 0.49). The survival rates were 97.23%, 97.30%, 78.95%, and 97.30% for NE, E, EB, and EU, respectively. Regarding postoperative sensitivity, a significant reduction was found for groups E (p = 0.027) and EU (p < 0.01) after 6 months. After 6 months, EWBT associated to the hydrophobic adhesive system had the highest failure rate.

Biological properties of modified bioactive glass on dental pulp cells

Dental caries is a bacteria-caused condition classified among the most common chronic diseases worldwide. Treatment of dental caries implies the use of materials having regenerative and anti-bacterial properties, and controlling inflammation is critical for successful endodontic regeneration.

OBJECTIVES

The aim of this study was to fabricate and characterize a novel composite incorporating sol-gel derived silver-doped bioactive glass (BG) in a chitosan (CS) hydrogel at a 1:1 wt ratio(Ag-BG/CS).

METHODS

The effect of Ag-BG/CS on dental pulp cells (DPCs) proliferation was analyzed by CCK-8 assay, whereas the adhesion of DPCs was evaluated by confocal microscopy. The physical morphology of Ag-BG/CS was analyzed by scanning electron microscope. The anti-inflammatory effect of Ag-BG/CS was investigated by quantitative polymerase chain reaction (qPCR). Moreover, the effect of Ag-BG/CS on odontogenic differentiation of DPCs was studied by immunochemical staining, tissue-nonspecific alkaline phosphatase staining, qPCR, and western blot analyses. The antibacterial activity against dental caries key pathogenic bacteria was also evaluated.

RESULTS

The results of this study showed that Ag-BG/CS did not affect the proliferation of DPCs, it down-regulated the inflammatory-associated markers (IL-1β, IL-6, IL-8, TNF-α) of DPCs treated with Escherichia coli lipopolysaccharide (LPS) by inhibiting NF-κB pathway, and enhanced the in vitro odontogenic differentiation potential of DPCs. Furthermore, Ag-BG/CS strongly inhibited Streptococcus mutans and Lactobacillus casei growth.

CONCLUSIONS

This novel biomaterial possessed antibacterial and anti-inflammatory activity, also enhanced the odontogenic differentiation potential of LPS-induced inflammatory-reacted dental pulp cells. The material introduced in this study may thus represent a suitable dental pulp-capping material for future clinical applications.

Influence of ethanol-wet dentin, adhesive mode of application, and aging on bond strength of universal adhesive

The aim of this study was to evaluate the effect of ethanol on the bond longevity of a universal adhesive system to bovine dentin, under different modes of adhesive application and artificial aging. Bovine dentin was exposed, and the smear layer was standardized by sandpaper polishing. Specimens were randomly divided into 2 groups: ethanol (E) and non-ethanol (N). Groups were subdivided according to adhesive mode of application into etch-and-rinse (Er) and self-etching (S). Resin blocks were built onto the treated surface, and the specimens were stored in deionized water at 37°C for 48 h. Half of the specimens (n = 10) were subjected to thermomechanical aging (A for aged and Na for non-aged). Resin/dentin beams were obtained and subjected to microtensile test in a universal testing machine. Data were analyzed using a three-way ANOVA and Tukey's tests (α = 5%). There was interaction among the three factors (p=0.0003). The use of ethanol resulted in higher values, except for the Er and Na groups (E_Er_Na = N_Er_Na). The mode of application was similar, except for the N and A groups (N_S_A > N_Er_A). For the A groups, the values were lower, except in the cases using ethanol, in which the results were not affected. The study concluded that the use of ethanol resulted in higher microtensile bond strength values, even after aging. The mode of adhesive application did not influence the results.

Biomimetic Mineralizing Agents Recover the Micro Tensile Bond Strength of Demineralized Dentin

Biomimetic remineralization is an approach that mimics natural biomineralization, and improves adhesive procedures. The aim of this paper was to investigate the influence of Dentin Caries-like Lesions (DCLL)-Producing Model on microtensile bond strength (μTBS) of etch and rinse adhesive systems and investigate the effect of remineralizing agents such as Sodium Fluoride (NaF), MI Paste™ (MP) and Curodont™ Repair (CR) on caries-affected dentin (n = 6). Nine groups were established: (1) Sound dentin; (2) Demineralized dentin/Chemical DCLL: (3) Demineralized dentin/Biological DCLL; (4) Chemical/DCLL + NaF; (5) Chemical/DCLL + MP; (6) Chemical/DCLL + CR; (7) Biological/DCLL + NaF; (8) Biological/DCLL + MP; (9) Biological/DCLL + CR. Then all dentin blocks were subjected to a bonding procedure with Adper™ Single Bond 2 adhesive system/Filtek Z350XT 4 mm high block, following this they were immersed in deionized water/24 h and then sectioned with ≅1 mm² beams. The μTBS test was conducted at 1 mm/min/500 N loading. Failure sites were evaluated by SEM (scanning electron microscopy (150×). μTBS data were submitted to factorial ANOVA and Tukey’s test (p < 0.05). The highest values were found when demineralized dentin was treated with MP and CR, regardless caries lesion depth (p < 0.05). There was a predominance of adhesive/mixed in the present study. It was concluded that the use of the artificial dentin caries production models produces differences in the μTBS. Additionally MP and CR remineralizing agents could enhance adhesive procedures even at different models of caries lesion.

The innovative applications of therapeutic nanostructures in dentistry

Nanotechnology has paved multiple ways in preventing, reversing or restoring dental caries which is one of the major health care problems. Nanotechnology aided in processing variety of nanomaterials with innovative dental applications. Some showed antimicrobial effect helping in the preventive stage. Others have remineralizing potential intercepting early lesion progression as nanosized calcium phosphate, carbonate hydroxyapatite nanocrystals, nanoamorphous calcium phosphate and nanoparticulate bioactive glass particularly with provision of self-assembles protein that furnish essential role in biomimetic repair. The unique size of nanomaterials makes them fascinating carriers for dental products. Thus, it is recentlyclaimedthat fortifying the adhesives with nanomaterials that possess biological meritsdoes not only enhance the mechanical and physical properties of the adhesives, but also help to attain and maintain a durable adhesive joint and enhanced longevity. Accordingly, this review will focus on the current status and the future implications of nanotechnology in preventive and adhesive dentistry.

Effect of Chlorhexidine and Ethanol Application on Long-term Push-out Bond Strength of Fiber Posts to Dentin

AIM

The aim of this study was to evaluate the effect of chlorhexidine and ethanol application on the push-out bond strength and bond durability of fiber posts cemented with an etch-and-rinse adhesive system/resin cement to intraradicular dentin.

MATERIALS AND METHODS

Fifty-four bovine roots were shaped for the cementation of a fiberglass post and received the application of 37% phosphoric acid. They were then randomly divided into three groups, according to the type of dentin treatment (n = 18) performed: no treatment (control group), 100% ethanol, or 2% chlorhexidine. Next, the adhesive system (Adper Scotch Bond Multipurpose Plus, 3M ESPE) was applied to the dentin, according to the manufacturer's instructions. Glass fiber posts were cemented with dual resin cement (Rely X ARC, 3M ESPE). After 48 hours, the specimens were serially sectioned for push-out test analysis, providing two slices from each root third (cervical, medium and apical), one of which was tested immediately and the other stored in distilled water for 180 days. The data were analyzed with three-way analysis of variance (ANOVA) for repeated measures and Tukey's test at a 5% significance level.

RESULTS

Intraradicular treatment with chlorhexidine yielded the highest bond strength means, followed by ethanol treatment. The control group presented the lowest bond strength means. Water storage exerted no effect on bond strength values.

CONCLUSION

Both chlorhexidine and ethanol improved push-out bond strength to intraradicular dentin, with the former providing the best results, regardless of the storage time.

CLINICAL SIGNIFICANCE

The application of 2% chlorhexidine or 100% ethanol may be an important step that can be taken to enhance bond strength of fiber posts to intraradicular dentin, when dual resin cements are used.

Immediate human pulp response to ethanol-wet bonding technique

OBJECTIVES

To evaluate the short-term response of human pulps to ethanol-wet bonding technique.

METHODS

Deep class V cavities were prepared on 17 sound premolars and divided into three groups. After acid-etching, the cavities from groups 1 (G1) and 2 (G2) were filled with 100% ethanol or distilled water, respectively, for 60 s before the application of Single Bond 2. In group 3 (G3, control), the cavity floor was lined with calcium hydroxide before etching and bonding. All cavities were restored with resin composite. Two teeth were used as intact control. The teeth were extracted 48h after the clinical procedures. From each tooth serial sections were obtained and stained with haematoxylin and eosin (H/E) and Masson's trichrome. Bacteria microleakage was assessed using Brown & Brenn. All sections were blindly evaluated for five histological features.

RESULTS

Mean remaining dentine thickness was 463±65μm (G1); 425±184μm (G2); and 348±194μm (G3). Similar pulp reactions followed ethanol- or water-wet bonding techniques. Slight inflammatory responses and disruption of the odontoblast layer related to the cavity floor were seen in all groups. Stained bacteria were not detected in any cavities. Normal pulp tissue was observed in G3 except for one case.

CONCLUSIONS

After 48h, ethanol-wet bonding does not increase pulpal damage compared to water-wet bonding technique.

CLINICAL SIGNIFICANCE

Ethanol-wet bonding may increase resin-dentine bond durability. This study reported the in vivo response of human pulp tissue when 100% ethanol was applied previously to an etch-and-rinse simplified adhesive system.

Biomimetic remineralization of dentin

OBJECTIVES

Remineralization of demineralized dentin is important for improving dentin bonding stability and controlling primary and secondary caries. Nevertheless, conventional dentin remineralization strategy is not suitable for remineralizing completely demineralized dentin within hybrid layers created by etch-and-rinse and moderately aggressive self-etch adhesive systems, or the superficial part of a caries-affected dentin lesion left behind after minimally invasive caries removal. Biomimetic remineralization represents a different approach to this problem by attempting to backfill the demineralized dentin collagen with liquid-like amorphous calcium phosphate nanoprecursor particles that are stabilized by biomimetic analogs of noncollagenous proteins.

METHODS

This paper reviewed the changing concepts in calcium phosphate mineralization of fibrillar collagen, including the recently discovered, non-classical particle-based crystallization concept, formation of polymer-induced liquid-precursors (PILP), experimental collagen models for mineralization, and the need for using phosphate-containing biomimetic analogs for biomimetic mineralization of collagen. Published work on the remineralization of resin-dentin bonds and artificial caries-like lesions by various research groups was then reviewed. Finally, the problems and progress associated with the translation of a scientifically sound concept into a clinically applicable approach are discussed.

RESULTS AND SIGNIFICANCE

The particle-based biomimetic remineralization strategy based on the PILP process demonstrates great potential in remineralizing faulty hybrid layers or caries-like dentin. Based on this concept, research in the development of more clinically feasible dentin remineralization strategy, such as incorporating poly(anionic) acid-stabilized amorphous calcium phosphate nanoprecursor-containing mesoporous silica nanofillers in dentin adhesives, may provide a promising strategy for increasing of the durability of resin-dentin bonding and remineralizing caries-affected dentin.

Influence of chlorhexidine and/or ethanol treatment on bond strength of an etch-and-rinse adhesive to dentin: an in vitro and in situ study

The aim of this study was to evaluate the effect of a chlorhexidine and/or ethanol application on the bond strength of an etch-and-rinse, hydrophobic adhesive system either under in vitro aging or in situ cariogenic challenge. The dentin surface of 36 human third molars were flattened and allocated into four groups to be treated with chlorhexidine, ethanol, or chlorhexidine + ethanol or left unexposed to any solution (control) (n=9). Then, a resin composite restoration was made on the dentin surface and longitudinal sticks were obtained. Sticks from each tooth were assigned to three test conditions: stored in water in vitro for 24 hours, stored in water in vitro for 6 months, or worn in situ for 14 days. During in situ wear time, a high-cariogenic challenge condition was simulated. Specimens were tested for microtensile bond strength (μTBS). Multivariate analysis of variance and Tukey's test showed that chlorhexidine, ethanol, or chlorhexidine + ethanol did not affect the μTBS. The in vitro μTBS values were significantly lower for the specimens stored for 6 months than for those stored for 24 hours. Intermediate μTBS values were shown by the specimens worn in situ. Thus, use of chlorhexidine and/or ethanol was incapable of containing the degradation at the bond interface in the in vitro model. The in situ model was capable of reducing bond strength similarly to the in vitro/6 months model. Despite this, the in situ bond strength was still similar to that of the in vitro/24-hour model.

Dentin adhesion and MMPs: a comprehensive review

This review examines the fundamental processes responsible for the aging mechanisms involved in the degradation of resin-bonded interfaces, as well as some potential approaches to prevent and counteract this degradation. Current research in several research centers aims at increasing the resin-dentin bond durability. The hydrophilic and acidic characteristics of current dentin adhesives have made hybrid layers highly prone to water sorption. This, in turn, causes polymer degradation and results in decreased resin-dentin bond strength over time. These unstable polymers inside the hybrid layer may result in denuded collagen fibers, which become vulnerable to mechanical and hydrolytical fatigue, as well as degradation by host-derived proteases with collagenolytic activity. These enzymes, such as matrix metalloproteinases and cysteine cathepsins, have a crucial role in the degradation of type I collagen, the organic component of the hybrid layer. This review will also describe several methods that have been recently advocated to silent the activity of these endogenous proteases.

Bond durability of self-etch adhesive to ethanol-based chlorhexidine pretreated dentin after storage in artificial saliva and under intrapulpal pressure simulation

OBJECTIVE

To evaluate the bond strength durability of a single-step self-etch adhesive to dentin pretreated with either ethanol-based chlorhexidine (ECHX) or water-based chlorhexidine (WCHX) after storage in artificial saliva and under intrapulpal pressure simulation (IPPS).

METHODS

The occlusal enamel of 30 freshly extracted premolars was trimmed to expose midcoronal dentin. Roots were sectioned to expose the pulp chamber. Specimens were distributed over three groups (n=10) according to the dentin pretreatment used. In the first group, Adper Easy One (3M ESPE) was applied to the dentin surfaces according to the manufacturer's instructions (control group). In the second group, dentin was pretreated before bonding with 1 mL of 2% CHX diacetate dissolved in 100% ethanol (ECHX). The third group received the same pretreatment; however, CHX was dissolved in distilled water (WCHX). Pretreatment and bonding were carried out while the specimens were subjected to IPPS. Resin composite (Valux Plus, 3MESPE) buildups were made. After curing, specimens were stored in artificial saliva and under IPPS at 37°C in a specially constructed incubator (n=5/group) either for 24 hours or six months prior to testing. Thereafter, bonded specimens were sectioned into sticks with a cross section of 0.9 ± 0.01 mm(2) and subjected to microtensile bond strength (μTBS) testing (n=25/subgroup) using a universal testing machine. Data were statistically analyzed using two-way analysis of variance (ANOVA) with repeated measures, one-way ANOVA , and Bonferroni post hoc tests (p≤0.05). Failure modes were determined using a scanning electron microscope.

RESULTS

After 24 hours of storage, control and WCHX groups revealed significantly higher μTBS than the ECHX group. After six-month storage in artificial saliva and IPPS, only the WCHX group maintained its μTBS value. The predominant mode of failure was the mixed type, except for the ECHX group, which was mostly adhesive.

CONCLUSION

Pretreatment of the dentin with ECHX had a negative effect on bonding of the tested single-step self-etch adhesive; however, WCHX showed bond stability under IPPS.

Therapeutic effects of novel resin bonding systems containing bioactive glasses on mineral-depleted areas within the bonded-dentine interface

This study aimed in evaluating the effects of two experimental resin bonding systems containing conventional Bioglass 45S5 (BAG) or Zinc-polycarboxylated bioactive glass (BAG-Zn) micro-fillers on the resin-bonded dentine interface after storage in a simulated body fluid solution (SBFS). Three resin bonding systems were formulated: Resin-A: (BAG containing); Resin-B; (BAG-Zn containing); Resin-C (no filler). The ability of the experimental resins to evoke apatite formation was evaluated using confocal Raman spectroscopy. Acid-etched dentine specimens were bonded, and prepared for AFM/nano-indentation analysis in a fully-hydrated status to evaluate the modulus of elasticity (Ei) and hardness (Hi) across the interface at different SBFS storage periods. Further resin-dentine specimens were tested for microtensile bond strength after 24 h or 3 months of SBFS storage. SEM examination was performed after de-bonding and confocal laser microscopy was used to evaluate the ultramorphology of the interfaces and micropermeability. The resin A and B showed a consistent presence of apatite (967 cm(-1)), reduced micropermeability within the resin-dentine interface and a significant increase of the Ei and Hi along the bonded-dentine interface after prolonged SBFS storage. Bond strength values were affected by the resin system (P < 0.0001) and by storage time (P < 0.0001) both after 24 h and 3 months of SBFS storage. In conclusion, resin bonding systems containing bioactive fillers may a have therapeutic effect on the nano-mechanical properties and sealing ability of mineral-depleted resin-dentine interface.

Limitations in bonding to dentin and experimental strategies to prevent bond degradation

The limited durability of resin-dentin bonds severely compromises the lifetime of tooth-colored restorations. Bond degradation occurs via hydrolysis of suboptimally polymerized hydrophilic resin components and degradation of water-rich, resin-sparse collagen matrices by matrix metalloproteinases (MMPs) and cysteine cathepsins. This review examined data generated over the past three years on five experimental strategies developed by different research groups for extending the longevity of resin-dentin bonds. They include: (1) increasing the degree of conversion and esterase resistance of hydrophilic adhesives; (2) the use of broad-spectrum inhibitors of collagenolytic enzymes, including novel inhibitor functional groups grafted to methacrylate resins monomers to produce anti-MMP adhesives; (3) the use of cross-linking agents for silencing the activities of MMP and cathepsins that irreversibly alter the 3-D structures of their catalytic/allosteric domains; (4) ethanol wet-bonding with hydrophobic resins to completely replace water from the extrafibrillar and intrafibrillar collagen compartments and immobilize the collagenolytic enzymes; and (5) biomimetic remineralization of the water-filled collagen matrix using analogs of matrix proteins to progressively replace water with intrafibrillar and extrafibrillar apatites to exclude exogenous collagenolytic enzymes and fossilize endogenous collagenolytic enzymes. A combination of several of these strategies should result in overcoming the critical barriers to progress currently encountered in dentin bonding.

The critical barrier to progress in dentine bonding with the etch-and-rinse technique

OBJECTIVES

The lack of durability in resin-dentine bonds led to the use of chlorhexidine as MMP-inhibitor to prevent the degradation of hybrid layers. Biomimetic remineralisation is a concept-proven approach in preventing the degradation of resin-dentine bonds. The purpose of this study is to examine the integrity of aged resin-dentine interfaces created with a nanofiller-containing etch-and-rinse adhesive after the application of these two approaches.

METHODS

The more established MMP-inhibition approach was examined using a parallel in vivo and in vitro ageing design to facilitate comparison with the biomimetic remineralisation approach using an in vitro ageing design. Specimens bonded without chlorhexidine exhibited extensive degradation of the hybrid layer after 12 months of in vivo ageing.

RESULTS

Dissolution of nanofillers could be seen within a water-rich zone within the adhesive layer. Although specimens bonded with chlorhexidine exhibited intact hybrid layers, water-rich regions remained in those hybrid layers and degradation of nanofillers occurred within the adhesive layer. Specimens subjected to in vitro biomimetic remineralisation followed by in vitro ageing demonstrated intrafibrillar collagen remineralisation within hybrid layers and deposition of mineral nanocrystals in nanovoids within the adhesive.

CONCLUSIONS

The impact was realized by understanding the lack of an inherent mechanism to remove water from resin-dentine interfaces as the critical barrier to progress in bonding with the etch-and-rinse technique. The experimental biomimetic remineralisation strategy offers a creative solution for incorporating a progressive hydration mechanism to achieve this goal, which warrants its translation into a clinically applicable technique.

Ethanol wet-bonding challenges current anti-degradation strategy

The long-term effectiveness of chlorhexidine as a matrix metalloproteinase (MMP) inhibitor may be compromised when water is incompletely removed during dentin bonding. This study challenged this anti-bond degradation strategy by testing the null hypothesis that wet-bonding with water or ethanol has no effect on the effectiveness of chlorhexidine in preventing hybrid layer degradation over an 18-month period. Acid-etched dentin was bonded under pulpal pressure simulation with Scotchbond MP and Single Bond 2, with water wet-bonding or with a hydrophobic adhesive with ethanol wet-bonding, with or without pre-treatment with chlorhexidine diacetate (CHD). Resin-dentin beams were prepared for bond strength and TEM evaluation after 24 hrs and after aging in artificial saliva for 9 and 18 mos. Bonds made to ethanol-saturated dentin did not change over time with preservation of hybrid layer integrity. Bonds made to CHD pre-treated acid-etched dentin with commercial adhesives with water wet-bonding were preserved after 9 mos but not after 18 mos, with severe hybrid layer degradation. The results led to rejection of the null hypothesis and highlight the concept of biomimetic water replacement from the collagen intrafibrillar compartments as the ultimate goal in extending the longevity of resin-dentin bonds.

Biomimetic remineralization as a progressive dehydration mechanism of collagen matrices--implications in the aging of resin-dentin bonds

Biomineralization is a dehydration process in which water from the intrafibrillar compartments of collagen fibrils are progressively replaced by apatites. As water is an important element that induces a lack of durability of resin-dentin bonds, this study has examined the use of a biomimetic remineralization strategy as a progressive dehydration mechanism to preserve joint integrity and maintain adhesive strength after ageing. Human dentin surfaces were bonded with dentin adhesives, restored with resin composites and sectioned into sticks containing the adhesive joint. Experimental specimens were aged in a biomimetic analog-containing remineralizing medium and control specimens in simulated body fluid for up to 12 months. Specimens retrieved after the designated periods were examined by transmission electron microscopy for the presence of water-rich regions using a silver tracer and for collagen degradation within the adhesive joints. Tensile testing was performed to determine the potential loss of bond integrity after ageing. Control specimens exhibited severe collagen degradation within the adhesive joint after ageing. Remineralized specimens exhibited progressive dehydration, as manifested by silver tracer reduction and partial remineralization of water-filled microchannels within the adhesive joint, as well as intrafibrillar remineralization of collagen fibrils that were demineralized initially as part of the bonding procedure. Biomimetic remineralization as a progressive dehydration mechanism of water-rich, resin-sparse collagen matrices enables these adhesive joints to resist degradation over a 12-month ageing period, as verified by the conservation of their tensile bond strength. The ability of the proof of concept biomimetic remineralization strategy to prevent bond degradation warrants further development of clinically relevant delivery systems.

Ethanol wet-bonding technique sensitivity assessed by AFM

In ethanol wet bonding, water is replaced by ethanol to maintain dehydrated collagen matrices in an extended state to facilitate resin infiltration. Since short ethanol dehydration protocols may be ineffective, this study tested the null hypothesis that there are no differences in ethanol dehydration protocols for maintaining the surface roughness, fibril diameter, and interfibrillar spaces of acid-etched dentin. Polished human dentin surfaces were etched with phosphoric acid and water-rinsed. Tested protocols were: (1) water-rinse (control); (2) 100% ethanol-rinse (1-min); (3) 100% ethanol-rinse (5-min); and (4) progressive ethanol replacement (50-100%). Surface roughness, fibril diameter, and interfibrillar spaces were determined with atomic force microscopy and analyzed by one-way analysis of variance and the Student-Newman-Keuls test (α = 0.05). Dentin roughness and fibril diameter significantly decreased when 100% ethanol (1-5 min) was used for rinsing (p < 0.001). Absolute ethanol produced collapse and shrinkage of collagen fibrils. Ascending ethanol concentrations did not collapse the matrix and shrank the fibrils less than absolute ethanol-rinses.