Microtensile bond strength to phosphoric acid-etched dentin treated with NaF, KF and CaF2

Purpose: Fluoride compounds have been reported to play a protective role in the host-derived enzymatic degradation of demineralized dentin matrices. The objective of this study was to evaluate the effect of fluoride pretreatment on the immediate and long-term microtensile bond strength (mu TBS) of resin-dentin interfaces. Materials and methods: Mid-coronal dentin surfaces of ninety-nine teeth were etched with 32%wt phosphoric acid and randomly assigned to pretreatment with NaF, KF or CaF2 solutions (6, 24 and 179 mM F content) for 30 s before the application of bonding agent (Scothbond Multi-Purpose, 3 M ESPE). No fluoride pretreatment and a commercially available bonding agent with KF (Excite F, Ivoclar Vivadent) were used as controls. After composite built-up, the specimens were sectioned into TBS test beams, stored in artificial saliva at 37 degrees C for 24 h, 6 or 12 months and tested. Fracture types were evaluated under scanning electron microscope. The data were analyzed with ANOVA and Scheffe post-hoc tests (alpha = 0.05). Pearson Chi-Square test was used to compare the distribution of failure types. Results: Fluoride compound, fluoride concentration and storage time showed significant effect on TBS (p 0.05), except CaF2 179 mM (p <0.05). According to Chi-square test, fracture types were also significantly influenced from the test factors (p <0.05). Conclusions: NaF and KF treatment after acid-etching step of adhesive bonding procedures do not adversely influence the initial or long-term bond strength to dentin, and can improve the maintenance of bond strength durability.Peer reviewe

Influence of polar solvents on permeability, stiffness and collagen dissociation of demineralized dentin

The purpose of this in vitro study was to evaluate and compare the effect of dimethyl sulfoxide (DMSO) or ethanol on the permeability, stiffness and collagen dissociation of demineralized dentin. Dentin cubes (2 x 2 x 2 mm) were demineralized in EDTA and incubated in DMSO or ethanol (0.01, 0.1, 1, 5, 10, 20, 50 and 100%) (n = 10/group) for 30s, followed by 100% HEMA incubation. Extracted HEMA was quantified. For elastic modulus (E), demineralized dentin beams (6 x 2 x 1 mm) were incubated in DMSO or ethanol (1, 10, 20, 50 and 100%) for 10, 30 or 60 min at 3-point bending. Additional demineralized dentin discs (1 mm) were incubated in DMSO (1, 10, 50 and 100%) for 10, 30 and 60 min and the optical clearing effect was observed. The data were analyzed using ANOVA and Tukey's test (alpha = 0.05) using SigmaPlot (Systat Software Inc., San Jose, CA). Compared to controls, HEMA uptake was significantly higher with all DMSO concentrations, and with 0.1% or higher ethanol concentrations (p <0.05). HEMA uptake in DMSO-incubated specimens (0.01, 5 and 10%) was significantly higher than with the ethanol incubation. Significant increase in elastic moduli was observed with 50-100% DMSO- and only with 100% ethanol after 10 min incubation. The optical clearing effect of 50-100% DMSO-incubated dentin disks was observed starting from 10 min. The pretreatment of dentin surfaces with low concentrations of DMSO resulted in significant improvement of the penetration of monomers to demineralized dentin matrices. Increase in penetration of monomers combined with a reversible stiffening of dentin collagenous matrix may explain the previously shown increase in durability of wet- or dry-bonded adhesive interfaces with DMSO treatment.Peer reviewe

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

Objective: Matrix 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. Design: Phosphoric acid (10%)-demineralized dentin beams (1 x 2 x 6 mm) were incubated at 37 degrees 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). Results: The 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), 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. Conclusion: CaF2 does not prevent the degradation of demineralized dentin matrices due to the catalytic activity of MMPs and CCs.Peer reviewe

The pursuit of resin-dentin bond durability : Simultaneous enhancement of collagen structure and polymer network formation in hybrid layers

Objective. Imperfect polymer formation as well as collagen's susceptibility to enzymatic-degradation increase the vulnerability of hybrid layers over time. This study investigated the effect of new dimethyl sulfoxide (DMSO)-containing pretreatments on long-term bond strength, hybrid layer quality, monomer conversion and collagen structure. Methods. H3PO4-etched mid-coronal dentin surfaces from extracted human molars (n = 8) were randomly treated with aqueous and ethanolic DMSO solutions or following the ethanol-wet bonding technique. Dentin bonding was performed with a three-step etch-and-rinse adhesive. Resin-dentin beams (0.8 mm(2)) were stored in artificial saliva at 37 degrees C for 24 h and 2.5 years, submitted to microtensile bond strength testing at 0.5 mm/min and semi-quantitative SEM nanoleakage analysis (n = 8). Micro-Raman spectroscopy was used to determine the degree of conversion at different depths in the hybrid layer (n = 6). Changes in the apparent modulus of elasticity of demineralized collagen beams measuring 0.5 x 1.7 x 7 mm (n = 10) and loss of dry mass (n = 10) after 30 days were calculated via three-point bending and precision weighing, respectively. Results. DMSO-containing pretreatments produced higher bond strengths, which did not change significantly over time presenting lower incidence of water-filled zones. Higher uniformity in monomer conversion across the hybrid layer occurred for all pretreatments. DMSO-induced collagen stiffening was reversible in water, but with lower peptide solubilization. Significance. Improved polymer formation and higher stability of the collagen-structure can be attributed to DMSO's unique ability to simultaneously modify both biological and resin components within the hybrid layer. Pretreatments composed of DMSO/ethanol may be a viable-effective alternative to extend the longevity of resin-dentin bonds. (C) 2021 The Author(s). Published by Elsevier Inc. on behalf of The Academy of Dental Materials.Peer reviewe

Incorporation of dimethyl sulfoxide to model adhesive resins with different hydrophilicities : Physico/mechanical properties

Objective: To understand dimethyl sulfoxide (DMSO) interaction with distinct methacrylate monomer blends and the impact on polymer formation by investigating the combined relationship among degree of resin hydrophilicity, presence of DMSO and specific physico/mechanical properties. Methods: One hydrophobic (R2) and one hydrophilic (R5) methacrylate-based resins with different monomer compositions were solvated in ascending DMSO concentrations (0, 0.01, 0.1, 1, 5, and 10 w/w %). Neat resins (0 w/w % DMSO) were used as controls. The degree of conversion was determined by Fourier-transform infrared spectroscopy. Polymer crosslinking density was indirectly measured by a modified ethanol-water two-stage solvation technique and the biaxial flexural strength was measured after 24 h and 30 days of water storage at 37 degrees C. Water sorption and solubility were gravimetrically assisted during 28 days of water storage to determine the kinetics of water-polymer interactions. Data were analyzed by ANOVA and Tukey test (alpha = 0.05). Results: Incorporation of high DMSO-concentrations significantly increased the degree of conversion of all tested formulations, specifically for the hydrophobic resin (p <0.05). Despite the increase in degree of monomer conversion, higher water sorption/solubility values and lower biaxial flexure strengths were detected as a result of reductions in polymer crosslink density (p <0.05). In general, low DMSO-concentrations had no impact on the biaxial flexural strength, crosslinking density and water sorption/solubility (p <0.05). Conclusion: DMSO-monomer ratio and monomer composition are critical for new dental methacrylate-based adhesive formulations. High DMSO incorporation hampers physico/mechanical properties of methacrylate bonding resins, albeit to a lesser extend when hydrophilic resins are employed. Nonetheless, DMSO-solvated hydrophobic adhesives extensively outperform their hydrophilic correspondents. DMSO incorporation of 1 w/w % may constitute a secure threshold regardless of monomer composition.Peer reviewe

The effect of phytic acid on enzymatic degradation of dentin

We evaluated the effect of phytic acid on matrix metalloproteinase (MMP)- or cysteine cathepsin (CC)-mediated dentin degradation. Demineralized dentin beams were divided into five groups (n = 12) and treated with 1%, 2%, or 3% phytic acid or with 37% phosphoric acid. Untreated demineralized beams served as controls. After incubation for 1 or 3 wk, dry mass loss was determined and aliquots of incubation media were analysed for cross-linked telopeptide of type I collagen (ICTP) fragments for MMP-mediated and c-terminal telopeptide of type I collagen (CTX) for cathepsin-k-mediated degradation. The direct effect of phytic acid was evaluated using MMP activity assay. Data were analysed using repeated-measures anova. ICTP releases with 1% and 2% phytic acid treatment were statistically significantly lower than those following phosphoric acid treatment at 3 wk. The CTX release for phytic acid-treated beams at 3 wk was not significantly different from that of untreated control beams, but it was significantly lower than that of phosphoric acid-treated beams. Their MMP activities at 3 wk were not significantly different from those of the controls but they were significantly lower than those seen for phosphoric acid-treated beams. Compared to phosphoric acid, phytic acid treatment resulted in a reduced dentinal host-derived endogenous enzymatic activity and collagen degradation

Composite repair: On the fatigue strength of universal adhesives

Objectives: To determine whether the composition of universal adhesives and the use of silane coupling agents could affect the fatigue strength of composite repair.Methods: Composite samples were aged in water at 37 degrees C for 90 days and bonded to fresh composite to produce twin-bonded bar-shaped composite specimens (2 x 2 x 12 mm). Five universal adhesives, a multistep composite repair system and a hydrophobic solvent-free resin associated to a separate silane coupling agent application were used for bonding. Composite samples were tested under 4-pointflexure initially at quasi-static loading (n = 12) followed by cyclic loading (n = 25). The stress-life fatigue behavior was evaluated following the staircase method at 4 Hz. The unfractured side of cyclic loaded beams were evaluated under SEM to determine crack initiation sites. Fatigue data was analyzed by ANOVA and Tukey test and Wilcoxon Rank Sum Test (alpha = 0.05).Results: Bonding protocols were unable to restore the cohesive strength of the nanofilled composite (p Significance: Although a trend for simplification invariably overruns current adhesive dentistry, composite repair using solely universal adhesives may result in inferior repair potential. The additonal use of silane coupling agents remains as an important procedure in composite repairs.(c) 2021 The Author(s). Published by Elsevier Inc. on behalf of The Academy of Dental Materials. CC_BY_NC_ND_4.0</p

To etch or not to etch, Part II: On the hydrophobic-rich content and fatigue strength of universal adhesives

Objective: To determine whether smear layer management, via conservative etching pro-tocols, and the hydrophobic-rich content of hybrid layers would affect the fatigue strength of resin-dentin interfaces.Methods: Bar-shaped dentin beams obtained from sound third molars were wet-polished for 30 s. Dentin was etched with 32 % ortho-phosphoric acid for 3 or 15 s, 10 % meta -phosphoric acid for 15 s or by a prime-and-rinse application using a mild universal ad-hesive (Scotchbond Universal, 3M ESPE). Self-etch application served as control. Coating was performed with a solvent-free bisGMA-based resin. Composite buildups were made with a nanofilled composite. Resin-dentin beams with twin-bonded interfaces were sec-tioned and stored in deionized water for 24 h at 37 celcius before 4-point flexural quasi-static monotonic testing (n = 16). Stress-life fatigue behavior was evaluated under cyclic loading (n = 35) by the staircase method at 4 Hz. The tension side of cyclic-loaded unfractured beams were evaluated under SEM, along with the micro-morphology of etched dentin surfaces. Monotonic data was analyzed by two-way ANOVA followed by the Tukey Test and cyclic-loaded data by Kruskal-Wallis on Ranks (alpha = 0.05).Results: Etching protocols and higher hydrophobic-rich content produced significantly higher fatigue life distributions (p MPA 15 s > OPA 3 s > P + R > SE. Less aggressive etching and coating reduced crack formation at hybrid layers.Significance: Current oversimplification trends in resin-dentin bonding constitute a trade-off between hybridization quality and easier adhesive handling. Controlled dentin etching and increasing the hydrophobic-rich content of hybrid layers may be necessary to extend the longevity of mild universal adhesives. (c) 2022 Published by Elsevier Inc. on behalf of The Academy of Dental Materials. CC_BY_NC_ND_4.0</p