Dry bonding to dentin: Broadening the moisture spectrum and increasing wettability of etch-and-rinse adhesives

ObjectiveTo determine whether the effect of dentin moisture on the etch-and-rinse bonding may be minimized by dry-bonding protocols utilizing aqueous or ethanolic dimethyl sulfoxide (DMSO) pretreatments.MethodsH₃PO₄-etched mid-coronal dentin surfaces from human molars were randomly blot- or air-dried for 30 s and pretreated with DMSO/H₂O or DMSO/EtOH solutions. Untreated samples served as control. Moisture control was performed by either blot- or air-drying. Samples were bonded with a multistep etch-and-rinse adhesive. Restored crown segments (n = 8/group) were stored in distilled water for 24 h and sectioned for microtensile bond strength testing. Resin-dentin beams (0.8 mm²) were tested under tension until fracture (0.5 mm/min) after 24 h and two years of storage in artificial saliva at 37 °C.SEM nanoleakage evaluation was performed on aged samples. Collagen wettability was also measured by sessile drops of the hydrophilic and hydrophobic bonding resins (n = 8/group). Data were examined by factorial ANOVA followed by the Tukey test (α = 0.05).ResultsDry bonding to untreated collagen produced inferior immediate and long-term bond strengths than wet bonding (p < 0.05). Regardless of initial hydration and moisture control, DMSO-dry bonding produced initially higher and stable bond strengths after aging (p < 0.05). DMSO-pretreated groups presented improved collagen wettability with lower silver uptake (p < 0.05).SignificanceDespite the common belief that etch-and-rinse adhesives must be applied onto moist collagen, DMSO-dry bonding protocols not only improved bonding performance and hybrid layer integrity, but also brought more versatility to collagen hybridization by reducing overdrying-related issues.     

To etch or not to etch,Part I: On the fatigue strength and dentin bonding performance of universal adhesives

ObjectiveTo characterize whether the bonding performance and fatigue strength of resin-dentin interfaces created by a universal adhesive would be affected by different H₃PO₄-application times to more accurately assess long-term durability.MethodsMid-coronal flat dentin surfaces with standardized smear-layers were produced on sound third molars, etched with 32% H₃PO₄ for 0, 3 and 15 s, bonded with a mild universal adhesive (3M-ESPE) and restored with a nanofilled composite. Bonded specimens (0.9 × 0.9 mm) were stored in deionized water for 24 h and sectioned into beams for microtensile testing (n = 10). Resin-dentin beams were tested under tension until failure (0.5 mm/min) after 24 h or 6 month storage in artificial saliva at 37 ?C. Bar-shaped resin-dentin beams (0.9 × 0.9 × 12 mm) were tested under 4-point-flexure initially at quasi-static loads (n = 22) and then under cyclic loads (n > 50). The stress-life fatigue behavior was evaluated using the twin-bonded interface approach by the staircase method at 4 Hz. Fractured interfaces and the tension side of unfractured beams were evaluated under SEM, along with the micro-morphology of the etched dentin surfaces and hybrid layers. Data were analyzed by ANOVA and Tukey test and Wilcoxon Rank Sum Test (α = 0.05).ResultsQuasi-static loads were limited to discriminate the bonding performance of resin-dentin interfaces. Application modes significantly affected etching patterns, fatigue strength, endurance limits and hybrid layer morphology (p < 0.001).SignificanceReductions in fatigue strength of self-etched bonded interfaces raise concerns about the true ability of universal adhesives to properly bond to dentin.     

Optimization of the etch-and-rinse technique: New perspectives to improve resin–dentin bonding and hybrid layer integrity by reducing residual water using dimethyl sulfoxide pretreatments

Objective

To determine whether bonding effectiveness and hybrid layer integrity on acid-etched dehydrated dentin would be comparable to the conventional wet-bonding technique through new dentin biomodification approaches using dimethyl sulfoxide (DMSO).

Evaluation of a novel primer containing isocyanate group on dentin bonding durability

ObjectivesTo evaluate the benefits of a novel dentin-bonding primer, namely, isocyanate-terminated urethane methacrylate precursor (UMP), which can form covalent bonds with demineralized dentin collagen.MethodsThe synthesized and purified UMP monomer was characterized and tested its effects on the degree of conversion (DC) and wettability of an acetone-based dental adhesive. Then UMP primers of different concentrations were formulated and used to prepare adhesive specimens, which were compared with solvent-treated groups. Primer-treated specimens with and without aging were also compared. To evaluate the bonding interface, microtensile strength tests, nano-indentation tests and nanoleakage- eavaluation were performed using a field-emission scanning electron microscope and nano-indenter. Data were analyzed using SPSS 20.0 software with significance set at α = 0.05 using one-way analysis of variance (ANOVA) and two-way ANOVA to characterize the effects of the primer.ResultsTreatment with the UMP primer promoted the DC and wettability of the adhesive on the demineralized dentin surface (P < 0.05); it also increased the bond strength of the aged dentin bonding interface (P < 0.05). Nanoleakage was reduced; the bonding interface became more stable, and the continuity and strength of the hybrid layer improved (P < 0.05) following UMP treatment. The application of 5 mM UMP as a primer for dentin bonding could lead to a stable bonding interface and long-lasting bonding effects.SignificanceThe use of 5 mM UMP primer developed in this study could improve dentin bonding durability and has excellent clinical application prospects.     

The roles of 10-methacryloyloxydecyl dihydrogen phosphate and its calcium salt in preserving the adhesive–dentin hybrid layer

Objectives10-Methacryloyloxydecyl dihydrogen phosphate (MDP) has been regarded as the most effective dentin-bonding monomer for more than 20 years. Although the dentin-bonding promoting effect of MDP has been well demonstrated, the mechanisms by which it benefits the stably of collagen within the adhesive–dentin hybrid layer are not currently fully understood. The objective of this study was to investigate the roles of MDP and its calcium salt in preserving the adhesive–dentin hybrid layer.MethodsMDP-conditioned collagen was investigated by Fourier-transform infrared spectroscopy, Ultraviolet–visible spectroscopy, and molecular docking. The structural changes to the dentin surface upon acid-etching and MDP-conditioning were observed by SEM. X-ray diffraction and nuclear magnetic resonance were used to investigate the chemical interactions between MDP and HAp. The collagen-protecting effects of MDP and its Ca salt were investigated using in-situ zymography, rhMMP-9 colorimetric assay, hydroxyproline assay, and molecular docking.ResultsMDP forms a stable collagen-phosphate complex through hydrogen bonding with the collagen in dentin. Furthermore, it generates MDP-Ca salts that are deposited on the dentin collagen scaffold, protecting it from degradation. Moreover, both free MDP and the MDP-Ca salt inhibit matrix metallopeptidase and exogenous proteases, with the inhibitory effect of the calcium salt being significantly stronger than that of the free form.SignificanceMDP-based adhesives preserve the collagen within the hybrid layer by simultaneously improving collagen’s resistance to exogenous enzymes and inhibiting MMP activity, both of which contribute to the longevity of dentin–resin bonding.     

Solvation role of dimethyl sulfoxide on the interaction with dentin bonding systems after 30 months

ObjectivesTo determine whether DMSO could serve as an effective pretreatment to improve the mechanical properties and minimize the degradation of the adhesive interface, through the degree of conversion (DC) and bond strength to dentin of different categories of dentin bonding systems (DBSs) after 30 months.MethodsDMSO (0, 0.5, 1, 2, 5, 10 vol%) were incorporated into four categories of DBSs: Adper Scotchbond Multipurpose (MP), Adper Single Bond 2 (SB), Clearfil SE Bond (CSE) and Adper Scotchbond Universal (SU). DC was evaluated by Fourier transform infrared spectroscopy (FTIR). For microtensile bond strength test (µTBS), 1 % DMSO were applied on dentin as pretreatment before DBSs. For SU, both strategies were tested. Specimens for µTBS were tested after 24 h, 6 and 30 months. DC and µTBS data were subjected to two-way ANOVA and Tukey test (α < 0.05).ResultsIncorporating 5 %/10 % DMSO increased the DC of CSE. Controversially, when combined with SU, 2 % and 10 % DMSO jeopardized the DC. Regarding µTBS, 1 % DMSO pre-treatment increased the bond strength for MP, SB, SU-ER and SU-SE. After 30 months, MP, SU-ER and SU-SE showed a decrease compared to baseline but remained higher than the control.Clinical significanceDMSO pretreatment may be a useful strategy to improve the bond interface over time. Its incorporation seems to favor the non-solvated systems regarding DC while it seems to show long-term benefits for bond strength using 1 % DMSO for MP and SU systems.     

Influence of chairside surface treatments on the shear bond strength of PEKK polymer to veneering resin materials: An in vitro study

Statement of problemHigh-performance thermoplastics have been adopted as an alternative restorative material to metal or ceramics. However, a straightforward surface modification process to provide a durable bond strength between the polymer and the veneering material is lacking.PurposeThe purpose of this in vitro study was to evaluate the shear bond strength (SBS) of different veneering resin materials to polyetherketoneketone (PEKK) after different surface treatments.Material and methodsRectangular (7×7×2 mm) PEKK specimens (N=120) were randomly allocated to the following 6 groups (n=20): untreated (Cnt); nonthermal plasma (NTP) treated; tribochemical silica airborne-particle abrasion with 30-μm silica-modified Al₂O₃ (Tbc); abraded with a coarse-grit diamond rotary instrument (Ab); tribochemical silica airborne-particle abrasion + plasma treated (Tbc_NTP); abraded + plasma treated (Ab_NTP). After a bonding agent (PEKK Bond) was applied to the specimens, each group was divided into 2 subgroups according to the applied veneering resin materials: polymethylmethacrylate (PMMA) and nanohybrid composite resin (NHC, n=10). The specimens were stored in water for 24 hours at 37 °C and subjected to the SBS test by using a universal testing machine, and failure modes were evaluated using a stereomicroscope. Two-way analysis of variance (ANOVA) was performed followed by the Tukey honestly significant difference (HSD) test to statistically analyze the data (α=.05).ResultsThe 2-way ANOVA showed that surface treatment methods, veneering material, and their interactions were significantly different on the SBS values (P<.001). The highest SBS values were determined for the Tbc and Tbc_NTP treatment groups not only for PMMA (10.71 to 11.63 MPa) but also for NHC (19.80 to 20.60 MPa) veneering resin materials (P<.05).ConclusionsThe bonding capacity of PEKK to the PMMA and NHC veneering resin materials can be significantly improved by using tribochemical silica airborne-particle abrasion alone or with nonthermal plasma surface treatment techniques. Furthermore, using NHC veneering resin material is recommended over PMMA.     

Effect of calcium fluoride on the activity of dentin matrix-bound enzymes

ObjectiveMatrix metalloproteinases (MMPs) and cysteine cathepsins (CCs) are two distinct enzymatic pathways responsible for the degradation of collagen fibrils in demineralized dentin. NaF and KF have been shown to inhibit salivary MMP-2, -9 and CCs. This study investigated the inhibitory effect of calcium fluoride (CaF₂) on the dentin matrix-bound MMPs and CCs.DesignPhosphoric acid (10%)-demineralized dentin beams (1 × 2×6 mm) were incubated at 37 °C in an 1 ml of artificial saliva (AS, control), or AS with 6, 12, 24, 48, 120. 179 and 238 mM F containing CaF₂ (n = 10/group) for 1, 7 and 21 days. All groups were further incubated in AS only for 6 months. Total MMP activity, dry mass loss, CTX and hydroxyproline (HYP) analyses were performed after each incubation. The beams were examined under scanning electron microscopy (SEM). MMP-2 and MMP-9 activities were screened with gelatin zymography. Data were analyzed by using ANOVA and Tukey HSD tests (p = .05).ResultsThe total MMP activity was similar for all groups after 21 days and 6 months. After 21 days, the cumulative mass loss and CTX levels were lower compared to control for the CaF₂ ≥48 and CaF₂≥120 mM, respectively (p < .05). After 6 months, no significant difference was detected in the dry mass loss and CTX compared to the control (p > .05), whereas HYP level was higher with F 24 and 238 mM groups. CaF₂-like minerals were observed on the beams under SEM. There was no gelatinase inhibition in zymography.ConclusionCaF₂ does not prevent the degradation of demineralized dentin matrices due to the catalytic activity of MMPs and CCs.     

Novel bioactive adhesive containing dimethylaminohexadecyl methacrylate and calcium phosphate nanoparticles to inhibit metalloproteinases and nanoleakage with three months of aging in artificial saliva

ObjectivesThe objectives of this study were to: (1) develop a multifunctional adhesive via dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP); and (2) investigate its ability to provide metalloproteinases (MMPs) deactivation and remineralization for long-term dentin bonding durability.MethodsDMAHDM and NACP were incorporated into Adper? Single Bond 2 Adhesive (SB2) at mass fractions of 5% and 20%, respectively. Degree of conversion and contact angle were measured. Endogenous MMP activity of the demineralized dentin beams, Masson’s trichrome staining, nano-indentation, microtensile bond strength and interfacial nanoleakage analyses were investigated after 24 h and 3 months of storage aging in artificial saliva.ResultsAdding DMAHDM and NACP did not compromise the degree of conversion and contact angle of SB2 (p > 0.05). DMAHDM and NACP incorporation reduced the endogenous MMP activity by 53 %, facilitated remineralization, and increased the Young’s modulus of hybrid layer by 49 % after 3 months of aging in artificial saliva, compared to control. For SB2 Control, the dentin bond strength decreased by 38 %, with greater nanoleakage expression, after 3 months of aging (p < 0.05). However, DMAHDM+NACP group showed no loss in bond strength, with much less nanoleakage, after 3 months of aging (p > 0.05).SignificanceDMAHDM+NACP adhesive greatly reduced MMP-degradation activity in demineralized dentin, induced remineralization at adhesive-dentin interface, and maintained the dentin bond strength after aging, without adversely affecting polymerization and dentin wettability. This new adhesive has great potential to help eliminate secondary caries, prevent hybrid layer degradation, and increase the resin-dentin bond longevity.     

A multi-functional dentine bonding system combining a phosphate monomer with eugenyl methacrylate

ObjectiveThe tooth-resin composite interface is frequently associated with failure because of microbial contamination, hydrolytic and collagenolytic degradation. Thus, designing a dentine bonding system (DBS) with an intrinsically antimicrobial polymerisable monomer is of significance especially if it can be used with self-etching primers enabling resistance to degradation of the interface.MethodsExperimental adhesives were developed incorporating eugenyl methacrylate (EgMA) at concentrations of 0,10 or 20 wt%, designated as EgMA0, EgMA10 and EgMA20, respectively, for use as a two-step self-etch DBS with the functional monomer bis[2-(methacryloyloxy) ethyl] phosphate (BMEP) in the primer. The curing, thermal and wettability properties of the adhesives were determined, and hybrid layer formation was characterised by confocal laser scanning microscopy, microtensile bond strengths (µTBS) and nanoleakage by back-scattered SEM. In situ zymography was used to assess MMP inhibitory activity of the BMEP-EgMA DBS.ResultsEgMA in the adhesives lowered the polymerisation exotherm and resulted in higher Tg, without negatively affecting degree of conversion. Water sorption and solubility were significantly lower with higher concentrations of EgMA in the adhesive. The formation of a distinct hybrid layer was evident from confocal images with the different adhesives, whilst EgMA20 yielded the highest µTBS post water storage challenges and lowest nanoleakage after 6 months. The experimental DBS exhibited minimal to no MMP activity at 3 months.SignificanceThe hydrophobic nature of EgMA and high cross-link density exerts considerable benefits in lowering water uptake and polymerisation exotherm. The application of EgMA, adhesives in conjunction with BMEP in a multi-functional self-etching DBS can resist MMP activity, hence, enhance longevity of the dentine-resin composite interface.     

Dentin conditioned with a metal salt-based conditioner

ObjectivesUniversal adhesives (UAs) can optionally be applied in either an etch-and-rinse (E&R) or self-etch (SE) bonding mode. As the preferred bonding mode differs for enamel versus dentin, a universal conditioner for both enamel and dentin in replacement of the relatively aggressive phosphoric-acid etchant remains desirable. This study aimed to test if a metal salt-based etchant (ZrO(NO₃)₂) provides as durable bonding to dentin as a classic E&R or SE bonding modeMethodsBefore applying the UA Adhese Universal (‘AdU’; Ivoclar Vivadent) to bur-cut dentin of 24 teeth (n = 8), dentin was conditioned with either (1) an experimental metal salt-based conditioner (‘ZON’; Ivoclar Vivadent) or (2) 37% phosphoric acid (Total Etch gel, Ivoclar Vivadent), representing a classic ‘E&R′ mode; (3) a third experimental group involved AdU applied in SE mode. Bonding effectiveness was determined in terms of immediate (‘1w’) and aged (‘50k’ TC) micro-tensile bond strength (μTBS) to bur-cut dentin. Adhesive-conditioned dentin interfacial interactions were characterized by S/TEM.ResultsLinear mixed-effects modeling revealed significantly higher immediate μTBS to dentin of ZON_AdU than E&R_AdU, while ZON_AdU performed not significantly different from SE_AdU. No significant differences were found between the three experimental groups after 50k TC (aged μTBS). S/TEM disclosed less exposure of dentinal collagen fibrils when AdU was bonded upon ZON etching than when applied in E&R mode. Moreover, ZON resulted in more hydroxyapatite (HAp) crystals remaining at the bottom of the hybrid layer, while dentinal tubule orifices remained nearly fully closed, by which hardly any resin tags were formed.SignificanceThe alternative metal salt-based conditioner revealed at dentin a more HAp-protected hybrid layer with less exposure of collagen fibrils, while a comparable bond strength was obtained to that with a phosphoric-acid E&R as well as with an SE (no conditioner) bonding mode. These findings confirm that the metal salt-based conditioner can be considered as a suitable alternative (enamel/)dentin conditioner to classic phosphoric acid employed in an E&R bonding mode.     

New perspective to improve dentin–adhesive interface stability by using dimethyl sulfoxide wet-bonding and epigallocatechin-3-gallate

ObjectivesTo determine whether dentin–adhesive interface stability would be improved by dimethyl sulfoxide (DMSO) wet-bonding and epigallocatechin-3-gallate (EGCG).MethodsEtched dentin surfaces from sound third molars were randomly assigned to five groups according to different pretreatments: group 1, water wet-bonding (WWB); group 2, 50% (v/v) DMSO wet-bonding (DWB); groups 3–5, 0.01, 0.1, and 1 wt% EGCG-incorporated 50% (v/v) DMSO wet-bonding (0.01%, 0.1%, and 1%EGCG/DWB). Singlebond universal adhesive was applied to the pretreated dentin surfaces, and composite buildups were constructed. Microtensile bond strength (μTBS) and interfacial nanoleakage were respectively examined after 24 h water storage or 1-month collagenase ageing. In situ zymography andStreptococcus mutans (S. mutans) biofilm formation were also investigated.ResultsAfter collagenase ageing, μTBS of groups 4 (0.1%EGCG/DWB) and 5 (1%EGCG/DWB) did not decrease (p > 0.05) and was higher than that of the other three groups (p < 0.05). Nanoleakage expression of groups 4 and 5 was less than that of the other three groups (p < 0.05), regardless of collagenase ageing. Metalloproteinase activities within the hybrid layer in groups 4 and 5 were suppressed. Furthermore, pretreatment with 1%EGCG/DWB (group 5) efficiently inhibited S. mutans biofilm formation along the dentin–adhesive interface.SignificanceThis study suggested that the synergistic action of DMSO wet-bonding and EGCG can effectively improve dentin–adhesive interface stability. This strategy provides clinicians with promising benefits to achieve desirable dentin bonding performance and to prevent secondary caries, thereby extending the longevity of adhesive restorations.     

Bond strength of three chairside crown reline materials to milled polymethyl methacrylate resin

Statement of problemInformation on the bond strength of milled polymethyl methacrylate interim restorations when relined with chairside reline materials is lacking.PurposeThe purpose of this in vitro study was to measure the shear bond strength of various combinations of 3 different chairside reline materials bonded to milled polymethyl methacrylate blocks with 3 different types of surface treatments.Materials and methodsUniform blocks (10×10×22 mm) were milled from tooth-colored polymethyl methacrylate disks (Vivid PMMA; Pearson Dental Supply Co). The surface treatments tested were airborne-particle abrasion with 50-μm particle size aluminosilicate, application of acrylic resin monomer (Jet Liquid; Lang Dental Manufacturing Co) for 180 seconds, and airborne-particle abrasion with monomer application. The control groups were blocks with no surface treatment. The chairside reline materials tested were Jet acrylic resin (Jet Powder; Lang Dental Manufacturing Co), bis-acryl resin (Integrity; Dentsply Sirona), and flowable composite resin (Reveal; Bisco). All materials were applied through a Ø1.5×3-mm bonding ring. Ten specimens for each of the 12 groups were tested in a universal testing machine. Load was applied at a crosshead speed of 1 mm/min. Fracture surfaces were then analyzed for cohesive versus adhesive or mixed failure. Data were analyzed using 2-way ANOVA and Tukey-Kramer post hoc analysis (α=.05).ResultsThe mean shear bond strength values ranged from 1.77 ±0.79 MPa to 28.49 ±5.75 MPa. ANOVA revealed that reline material (P<.05), surface treatment (P<.05), and their interactions (P<.05) significantly affected the shear bond strength among the experimental groups. The strongest combination was Jet acrylic resin applied on specimens treated with airborne-particle abrasion and monomer. All 3 failure modalities (adhesive, cohesive, and mixed modes) were observed.ConclusionsOf the materials tested, the most reliable material to bond to milled polymethyl methacrylate was Jet acrylic resin, and the bond strength values were increased substantially when the milled polymethyl methacrylate surface was airborne-particle abraded and monomer was applied.     

Proanthocyanidin-functionalized hydroxyapatite nanoparticles as dentin biomodifier

ObjectiveThis study evaluated the potential combined effects of nanohydroxyapatite and proanthocyanidin on the remineralization and collagen stabilization of demineralized dentin.MethodsSeventy-five coronal dentin beams (6 × 1 × 1 mm³) were randomly allocated into five experimental groups (n = 15): Sound (no treatment), Control (pH-cycling), nHAp (nanohydroxyapatite), nHAp_PA (Proanthocyanidin-functionalized nanohydroxyapatite), and PA (proanthocyanidin) treatments. The sound group (negative control) were immersed in distilled water over the experimental period. The remaining groups were submitted to a pH-cycling process for 14 days. Following the de-re mineralization process, specimens corresponding to the control group (positive control) were immersed in distilled water whereas the test groups were immersed in 1 mL of respective solution treatment (nHAp, nHAp_PA, or PA) for 1 min. The dentin samples were analyzed to determine their chemical composition (ATR-FTIR and Thermogravimetric) and mineralogical (XRD) characteristics as well as their mechanical response, obtained by three-point bending test.ResultsHigher phosphate content (v₄ PO₄: ATR-FTIR) and amount of mineral (XRD) was observed in the nHAp_PA group. Furthermore, a larger induction of collagen cross-links (ATR-FTIR) and %Organic Matter (TGA) would indicate the PA incorporation and the achievement of dentin matrix stability. These effects on dentin properties were related to increasing flexural strength (MPa), demonstrating that 15% w/v nHAp_PA treatment improved the mechanical properties of the samples.SignificancenHAp_PA shows significant potential for promoting remineralization while improving collagen stability into demineralized dentin in a clinically feasible period of 1 min.     

Biomimetic remineralization of artificial caries dentin lesion using Ca/P-PILP

ObjectiveTo assess the ultrastructural change of demineralized dentin collagen during calcium phosphate polymer-induced liquid precursor (Ca/P-PILP) mediated remineralization process and to evaluate the biomimetic remineralization potential of high concentration Ca/P-PILP at demineralized artificial caries dentin lesion, additionally to investigate the bond interfacial integrity as well as the bonding strength of the biomimetic remineralized artificial caries dentin lesion.MethodsDemineralized dentin collagen of 5 μm thick was biomimetically remineralized with low, medium concentration Ca/P-PILP for 10 days and high concentration Ca/P-PILP for 10, 15, 20 days. Artificial caries dentin lesion at a thickness of 150 ± 50 μm was biomimetically remineralized with high concentration Ca/P-PILP for 20 days. The biomimetic remineralization of demineralized dentin collagen was observed by scanning electron microscopy (SEM). The biomimetic remineralization intensity and depth of artificial caries dentin lesion was assessed by Electron Probe Micro Analyzer (EPMA). The bonding interfacial integrity between remineralized artificial caries dentin and composite resin was observed by Swept-source optical coherence tomography (SS-OCT) and the bonding strength of remineralized artificial caries dentin was evaluated by micro-tensile bond strength analysis (μTBS).ResultsSolely PAA-PASP solution and solely saturated Ca/P solution can’t achieve dentin collagen remineralization. Increased concentration of Ca/P-PILP and prolonged remineralization time can enhance the biomimetic remineralization intensity of demineralized dentin collagen. After treating with high concentration Ca/P-PILP, a 150 ± 50 μm thick layer of demineralized artificial caries dentin lesion was not fully remineralized, and the biomimetic remineralization intensity reached up to 88.0%. Furthermore, a better bonding interfacial integrity with less microgap and increased bond strength at both baseline level and aging level were observed when artificial caries dentin lesion was biomimetically remineralized with high concentration Ca/P-PILP.SignificanceBiomimetic remineralization of demineralized caries dentin lesion promotes its clinical properties for resin composited adhesive restoration.     

A ZnO-doped adhesive reduced collagen degradation favouring dentine remineralization

Objectives

The objective of the study was to determine the efficacy of a ZnO-doped etch and rinse adhesive in decreasing MMPs-mediated collagen degradation at the resin–dentine hybrid layer, and increasing bonding stability.

Methods

C-terminal telopeptide concentrations (ICTP) were determined after 24 h, 1 wk and 4 wk in human dentine beams. Dentine was treated: (1) 37% phosphoric acid for 15 s (PA), (2) PA-etched dentine infiltrated with Single Bond (SB), (3) PA-etched dentine infiltrated with ZnO doped SB (ZnO particles – 10 wt% – were added to the bonding resin) (ZnO–SB), and (4) Clearfil SE Bond primed-dentine was infiltrated with Clearfil SE bonding resin (CSE). Microtensile bond strength (MTBS) was assessed for the different groups at 24 h and after 3 months. Debonded dentine surfaces were studied by scanning electron microscopy.

Results

MMPs-mediated collagen degradation occurred in demineralized dentine (PA). Resin infiltration decreased collagen degradation. The lowest collagen degradation was found for Zn-doped SB, followed by CSE. When these adhesives were applied, ICTP values did not change throughout the study period. At 24 h, similar MTBS was attained for all adhesives. Only SB decreased MTBS after three months.

Conclusions

Addition of ZnO particles to SB produced a reduction in dentine collagen degradation and increased resin–dentine bonds durability. In Zn-doped adhesive interfaces, a calcium phosphate layer and tubular occlusion was encountered at the debonded interface.

Clinical significance

ZnO particles addition into the bonding resin of SB makes a breakthrough to prevent the hybrid layer degradation and to preserve its bonding efficacy overtime.     

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.     

The Efficacy of Different Sealer Removal Protocols on Bonding of Self-etching Adhesives to AH Plus–contaminated Dentin

IntroductionSmearing of unset root canal sealers over the pulp chamber dentin may adversely affect bonding of self-etching adhesives and jeopardize their coronal sealing potential. This study examined the influence of different sealer removal protocols on the microtensile bond strengths of two self-etching adhesives to AH Plus-contaminated dentin.MethodsCoronal dentin surfaces were prepared from extracted human third molars. In the positive control groups, these surfaces were not contaminated with sealer and were bonded with Clearfil SE Bond or Clearfil Tri-S Bond. For the experimental groups, dentin surfaces were contaminated with AH Plus and wiped with either dry cotton pellets, cotton pellets saturated with ethanol, or cotton pellets saturated with Endosolv R followed by rinsing the dissolved sealer with water prior to bonding with the two adhesives. Bonded specimens were sectioned into resin-dentin beams for microtensile bond strength evaluation. Additional specimens were prepared for transmission electron microscopy to examine the ultrastructure and nanoleakage within the hybrid layers.ResultsFor both adhesives, microtensile bond strengths significantly declined when the sealer was removed with dry cotton pellets or cotton pellets saturated with ethanol. Only the Endosolv R/water sealer removal protocol restored tensile bond strengths to those of the uncontaminated positive controls without adversely affecting hybrid layer formation in intact dentin or increasing nanoleakage within the resin-dentin interfaces.ConclusionThe Endosolv R sealer removal protocol appears to be effective in preventing the deterioration of bond strengths of the two self-etching adhesives to AH Plus–contaminated dentin and warrants further clinical investigation.     

Natural saliva as an adjuvant in a secondary caries model based on Streptococcus mutans

ObjectiveTwo factors for secondary caries formation were evaluated using an artificial biofilm model, saliva as additive in culture medium and bonding procedures of composite materials for artificial gap creation.DesignStandardized cavities were prepared in bovine tooth samples (n = 44), treated with two different bonding pretreatments, restored and after artificial ageing incubated with Streptococcus mutans in a Mueller-Hinton-Broth-Sugar medium with or without human saliva for seven days. Secondary caries formation was analyzed using confocal laser scanning microscopy and transversal microradiography.ResultsLesions were significantly pronounced in groups using saliva, but were not influenced by the bonding pretreatments.ConclusionsThe results indicate that the addition of saliva, but not the type of bonding procedure influences the outcome in the present biofilm-based secondary caries model.     

Influence of intermediate resin on the bond strength of light-curing composite resin to polymer substrate

Objectives. The aim of this study was to examine the effect of intermediate resin (IMR) of different monomer compositions and viscosities on the shear bond strength between polymer substrate and light-curing composite. Methods. The substrate used in the study was an autopolymerizing polymethyl methacrylate (PMMA) based polymer. The substrate was treated with the IMR for 3 min before application of light polymerizable particulate filler composite resin. The monomers of the IMR were either bisphenol-A-glycidyl dimethacrylate (BisGMA) and triethyleneglycol dimethacrylate (TEGDMA) or BisGMA and methyl methacrylate (MMA). The shear bond strength of the IMR treated substrate to the particulate filler composite was evaluated after storing the specimens dry and after thermocycling the specimens in water. Light microscope examination was accomplished to determine the swelled layer of the substrate. Results. Significant differences were found between the shear bond strength values of the IMRs (p < 0.001). The bond strengths were generally higher in the BisGMA-MMA groups than in the BisGMA-TEGDMA groups. Two-way ANOVA revealed significant effects of type of IMR (p < 0.001) and thermocycling (p = 0.017) on the shear bond strength. No interaction was found between these variables (p > 0.05). Conclusions. The results suggest that the monomer composition and ratio of the IMRs used in the study influence the shear bond strength of the polymer substrate to the new resin.