Dry bonding: New perspectives for collagen hybridization

Advancements in dental adhesive technology have revolutionized dental treatments, invariably increasing the number and indications of restorative treatment options. Considering current techniques to bond to tooth tissue, dentin can be characterized as the most challenging mineralized dental substrate for successful long-lasting bonding. Resin-dentin bonding relies, partly or totally, on collagen hybridization to couple methacrylate-based resins to the underlying mineralized dentin. The aim of this study series was to revisit the dry-bonding approach by modifying the application protocol to effectively enable resin bonding to air-dried-etched dentin. Dentin pretreatments containing dimethyl sulfoxide (DMSO) in either ethanolic or aqueous solutions (50 % v/v) were tested to determine whether novel DMSO-dry bonding approaches could improve resin-dentin bonding. Mechanical and physical properties of DMSO-containing resins such as degree of conversion, elastic modulus, flexural strength, water sorption and solubility were evaluated. Resin-dentin interfaces were submitted to long-term microtensile testing, nanoleakage and micropermeability evaluation, in situ zymography and degree of conversion. Indirect assessment of enzymatic activity on DMSO-treated collagen was determined by dry mass loss, hydroxyproline quantification and elastic modulus. Gel zymography was used to determine the effect of DMSO pretreatments on MMP-2 and -9 activity. The wettability of air-dried DMSO-treated collagen by hydrophilic and hydrophobic resins was evaluated by contact angle measurements. This study series produced compelling evidence that DMSO-dry bonding constitutes a feasible alternative to reduce residual water from resin-dentin interfaces by broadening the moisture spectrum of demineralized dentin to substantially drier levels. Bonding methacrylate-based resins to extensively air-dried collagen greatly improved resindentinbonding following the DMSO-dry bonding approaches. Higher resin-dentin bond strength was accompanied by better hybrid layer formation with higher monomer conversion and reduced porosities, lower collagenolytic activity, enhanced dentin wettability and lower technique sensitivity. Altogether, such benefits contributed to more efficient collagen hybridization, addressing important issues in resin-dentin bonding with a single bonding protocol.Kuivasidostus: uusia näkökulmia kollageenin hybridisaatioon Sidostusteknologian kehitys on johtanut suuriin muutoksiin hammashoidossa, ja lisännyt merkittävästi korjaavan hoidon indikaatioita ja hoitotoimenpiteiden määrää. Nykyisillä sidostekniikoilla dentiini asettaa suuria haasteita sidoksen pitkäaikaiskestolle. Sidosaineen ja dentiinin liitos perustuu sidosaineen tunkeutumiseen dentiinin kollageeniverkoston sisään (ns. hybridisaatio), jonka kautta metakrylaattipohjaiset sidosaineet kiinnittyvät dentiiniin. Hybridisaatio on monimutkainen prosessi. Toimenpide täytyy suorittaa nopeasti kosteassa kudoksessa, ja sen tulisi kestää jopa vuosikymmeniä. Tämän tutkimussarjan tavoitteena oli tutkia sidostamista kuivaan kudokseen muokkaamalla protokollaa siten, että se onnistuisi ilmakuivattuun happokäsiteltyyn dentiiniin. Tutkimuksissa testattiin dentiinin esikäsittelyä dimetyylisulfoksidin (DMSO) etanoli- ja vesiseosten (50 til.-%) mahdollisia etuja, ja selvitettiin täysin uudenlaisen DMSO-kuivasidostuksen käyttöä sidoksen parantamisessa. Lisäksi selvitettiin DMSO:ta sisältävien sidosaineiden fyysisiä ja mekaanisia ominaisuuksia, kuten konversioastetta, kimmomoduulia, taivutuslujuutta, veden adsorptiota ja liukenemista. Vanhennettuja sidosrajapintoja tutkittiin mikrosidoslujuustestauksella, nanovuotoanalyysillä, mikropermeabiliteettitestauksella, in situ-zymografialla ja konversioasteanalyysillä. Entsyymien vaikutusta DMSO-käsiteltyyn dentiinikollageeniin tutkittiin epäsuorasti kuivapainomenetystä, hydroksiproliinin vapautumista ja kollageenin kimmomoduulia mittaamalla. Geelizymografialla määritettiin DMSO-esikäsittelyn vaikutusta MMP-2:n ja MMP-9:n aktiivisuuteen. Kuivatun DMSO-käsitellyn dentiinin kostutettavuutta tutkittiin kosketuskulmamittauksilla. Tutkimukset osoittivat DMSO-kuivasidostuksen olevan toteuttamiskelpoinen keino vähentää jäännösvettä sidosrajapinnassa mahdollistamalla sidostaminen kuivaan dentiiniin, ja se paransi sidosta merkittävästi. DMSO-kuivasidostaminen paransi dentiinin kostutettavuutta, hybridikerroksen laatua ja monomeerien konversiota, vähensi kollagenolyyttistä aktiivisuutta ja hybridikerroksen huokoisuutta, paransi välitöntä sidoslujuutta ja sen pysyvyyttä, ja vähensi käsittelyvirheiden riskiä. Kaiken kaikkiaan menetelmällä saavutettiin tehokkaampi dentiinikollageenin hybridisaatio vaikuttamalla useisiin sidostamisen kannalta merkittäviin tekijöihin

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

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 p p 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.</p

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). Methods. Etched dentin surfaces from extracted sound molars were randomly bonded in wet or dry conditions (30 s air drying) with DMSO/ethanol or DMSO/H2O as pretreatments using a simplified (Scotchbond Universal Adhesive, 3M ESPE: SU) and a multi-step (Adper Scotchbond Multi-Purpose, 3M ESPE: SBMP) etch-and-rinse adhesives. Untreated dentin surfaces served as control. Bonded teeth (n=8) were stored in distilled water for 24 h and sectioned into resin-dentin beams (0.8 mm(2)) for microtensile bond strength test and quantitative interfacial nanoleakage analysis (n = 8) under SEM. Additional teeth (n = 2) were prepared for micropermeability assessment by CFLSM under simulated pulp ar pressure (20 cm H2O) using 5 mM fluorescein as a tracer. Microtensile data was analyzed by 3-way ANOVA followed by Tukey Test and nanoleakage by Kruskal-Wallis and Dunn-Bonferroni multiple comparison test (alpha = 0.05). Results. While dry-bonding of SBMP produced significantly lower bond strengths than wet-bonding (p Conclusion. DMSO pretreatments may be used as a new suitable strategy to improve bonding of water-based adhesives to demineralized air-dried dentin beyond conventional wetbonding. Less porous resin-dentin interfaces with higher bond strengths on air-dried etched dentin were achieved; nonetheless, overall efficiency varied according to DMSO's co-solvent and adhesive type. Clinical significance. DMSO pretreatments permit etched dentin to be air-dried before hybridization facilitating residual water removal and thus improving bonding effectiveness. This challenges the current paradigm of wet-bonding requirement for the etch-and-rinse approach creating new possibilities to enhance the clinical longevity of resin-dentin interfaces. (C) 2018 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.Peer reviewe

Dentin bond optimization using the dimethyl sulfoxide-wet bonding strategy : A 2-year in vitro study

Objective. This study evaluated a new approach, named dimethyl sulfoxide (DMSO)-wet bonding, to produce more desirable long-term prospects for the ultrafine interactions between synthetic polymeric biomaterials and the inherently hydrated dentin substrate. Methods. Sound third molars were randomly restored with/without DMSO pretreatment using a total-etch (Scocthbond Multipurpose: SBMP) and a self-etch (Clearfil SE Bond: CF) adhesive systems. Restored teeth (n = 10)/group were sectioned into sticks and submitted to different analyses: micro-Raman determined the degree of conversion inside the hybrid layer (DC); resin dentin microtensile bond strength and fracture pattern analysis at 24 h, 1 year and 2 years of aging; and nanoleakage evaluation at 24h and 2 years. Results. DMSO-wet bonding produced significantly higher 24 h bond strengths for SBMP that were sustained over the two-year period, with significantly less adhesive failures. Similarly, DMSO-treated CF samples presented significantly higher bond strength than untreated samples at two years. Both adhesives had significant less adhesive failures at 2 years with DMSO. DMSO had no effect on DC of SBMP, but significantly increased the DC of CE DMSO-treated SBMP samples presented reduced silver uptake compared to untreated samples after aging. Significance. Biomodification of the dentin substrate by the proposed strategy using DMSO is a suitable approach to produce more durable hybrid layers with superior ability to withstand hydrolytic degradation over time. Although the active role of DMSO on dentin bond improvement may vary according to monomer composition, its use seems to be effective on both self-etch and etch-and-rinse bonding mechanisms. (C) 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.Peer reviewe

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

Influence of dimethyl sulfoxide used as a solvent on the physical properties and long-term dentin bonding of hydrophilic resins

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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

In situ analysis of gelatinolytic activity in human dentin

Matrix metalloproteinases (MMPs) such as gelatinases are differentially expressed in human tissues. These enzymes cleave specific substrates involved in cell signaling, tissue development and remodeling and tissue breakdown. Recent evidences show that gelatinases are crucial for normal dentin development and their activity is maintained throughout the entire tooth function in the oral cavity. Due to the lack of information about the exact location and activity of gelatinases in mature human dentin, the present study was designed to examine gelatinolytic levels In sound dentin. In situ zymography using confocal microscopy was performed on both mineralized and demineralized dentin samples. Sites presenting gelatinase activity were identified throughout the entire biological tissue pursuing different gelatinolytic levels for distinct areas: predentin and dentinal tubule regions presented higher gelatinolytic activity compared to intertubular dentin. Dentin regions with higher gelatinolytic activity immunohistochemically were partially correlated with MMP-2 expression. The maintenance of gelatinolytic activity in mature dentin may have biological implications related to biomineralization of predentin and tubular/peritubular dentinal regions, as well as regulation of defensive mechanisms of the dentin-pulp complex.Peer reviewe