Use of marine occurrent extracts to enhance the stability of dentin extracellular matrix.

Chitosan (CS) and phloroglucinol (PhG), two extracts abundantly found in marine life, were investigated for their ability to biomodify demineralized dentin by enhancing collagen crosslinks and improving dentin extracellular matrix (ECM) mechanical and biochemical stability. Dentin obtained from non-carious extracted human molars were demineralized with phosphoric acid. Baseline Fourier-transform infrared (FTIR) spectra, apparent flexural elastic modulus (AE) and dry mass (DM) of each specimen were independently acquired. Specimens were randomly incubated for 5 min into either ultrapure water (no-treatment), 1% glutaraldehyde (GA), 1% CS or 1% PhG. Water and GA were used, respectively, as a negative and positive control for collagen crosslinks. Specimens' post-treatment FTIR spectra, AE, and DM were obtained and compared with correspondent baseline measurements. Additionally, the host-derived proteolytic activity of dentin ECM was assessed using hydroxyproline assay (HYP) and spectrofluorometric analysis of a fluorescent-quenched substrate specific for matrix metalloproteinases (MMPs). Finally, the bond strength of an etch-and-rinse adhesive was evaluated after application of marine compounds as non-rinsing dentin primers. Dentin specimens FTIR spectral profile changed remarkably, and their AE increased significantly after treatment with marine compounds. DM variation, HYP assay and fluorogenic substrate analysis concurrently indicated the biodegradation of CS- and PhG-treated specimens was significantly lesser in comparison with untreated specimens. CS and PhG treatments enhanced biomechanical/biochemical stability of demineralized dentin. These novel results show that PhG is a primer with the capacity to biomodify demineralized dentin, hence rendering it less susceptible to biodegradation by host-proteases.

Dentin Degradation: From Tissue Breakdown to Possibilities for Therapeutic Intervention.

Purpose of the Review: Presently, dental materials science is driven by the search for new and improved materials that can trigger specific reactions from the affected tissue to stimulate repair or regeneration while interacting with the oral environment to promote or maintain oral health. In parallel, evidence from the past decades has challenged the exclusive role of bacteria in dentin tissue degradation in caries, questioning our understanding of caries etiopathogenesis. The goal of this review is to recapitulate the current evidence on the host and bacterial contributions to degradation, inflammation, and repair of the dentin-pulp complex in caries. Recent Findings: Contrasting findings attribute dentin breakdown to the activity of endogenous enzymes, such as matrix metalloproteinases (MMPs) and cathepsins, while the role of bacteria and their by-products in the destruction of dentin organic matrix and pulp inflammation has been for decades supported as an incontestable paradigm. Aiming to better understand the mechanisms involved in collagen degradation by host enzymes in caries, studies have showed that these proteinases are expressed in the mature dentin (i.e., after dentin formation) and become activated by the low pH in the acidic environment resulted by bacterial metabolism in caries. However, different host sources other than dentin-bound proteinases seem to also contribute to caries progression, such as saliva and pulp. Interestingly, studies evaluating pulp responses to bacteria invasion and inflammation in caries report higher levels of MMPs and cathepsins in inflamed tissue, but also showed MMP potential to resolve inflammation and stimulate wound healing. Notably, as reported for other tissues, MMPs exert dual roles in the dentin-pulp complex in caries, participating or regulating both degradative and reparative mechanisms. Summary: The specific roles of host and bacteria and their by-products in caries progression have yet to be clarified. The complex interactions between inflammation and repair in caries pose challenges to a clear understanding of the dentin-pulp complex responses and changes to bacteria invasion. However, it opens new venues for the development of novel therapies and dental biomaterials based on the modulation of specific mechanisms to favor tissue repair and healing.

In vitro assessment of antimicrobial potential of low molecular weight chitosan and its ability to mechanically reinforce and control endogenous proteolytic activity of dentine.

AIMS: Chitosan-based biomaterials exhibit several properties of biological interest for endodontic treatment. Herein, a low molecular weight chitosan (CH) solution was tested for its antimicrobial activity against Enterococcus faecalis (E. faecalis) and effects on dentine structure. METHODOLOGY: The root canal of 27 extracted uniradicular teeth were biomechanically prepared, inoculated with a suspension of E. faecalis and randomly assigned to be irrigated with either 5.25% sodium hypochlorite (NaClO), 0.2% CH or sterile ultrapure water (W). Bacteriologic samples were collected from root canals and quantified for of E. faecalis colony-forming units (CFUs). The effectiveness of CH over E. faecalis biofilms was further measured using the MBEC Assay®. Additionally, dentine beams and dentine powder were obtained, respectively, from crowns and roots of 20 extracted third molars. Dentine samples were treated or not with 17% EDTA and immersed in either CH or W for 1 min. The effects of CH on dentine structure were evaluated by assessment of the modulus of elasticity, endogenous proteolytic activity and biochemical modifications. RESULTS: The number of E. faecalis CFUs was significantly lower for samples irrigated with CH and NaClO. No significant differences were found between CH and NaClO treatments. Higher modulus of elasticity and lower proteolytic activity were reported for dentine CH-treated specimens. Chemical interaction between CH and dentine was observed for samples treated or not with EDTA. CONCLUSIONS: Present findings suggest that CH could be used as an irrigant during root canal treatment with the triple benefit of reducing bacterial activity, mechanically reinforcing dentine and inhibiting dentine proteolytic activity.

Differential analysis of the dentin soluble proteomic.

OBJECTIVES: To perform a differential analysis of the dentin soluble proteomic and assess the effects of tissue health state and protocol for protein extraction. We hypothesized the dentin soluble proteomic varies according to the tissue physiopathological state (intact vs. caries-affected) and protocol used to extract its proteins. METHODS: Dentin from freshly extracted non-carious and carious teeth were randomly assigned for protein extraction using either guanidine-HCl/ethylenediaminetetraacetic acid (EDTA) or acetic acid. Protein extracts from intact and caries-affected dentin were processed and digested with trypsin for shotgun label-free proteomic analysis (nLC-ESI-MS/MS). Peptides identification was performed on a nanoACQUITY UPLC-Xevo Q-Tof MS system. Peptides identified with scores of confidence greater than 95% were included in the quantitative statistical analysis embedded in the PLGS software. Differences between experimental conditions were calculated using Student test-t with significance pre-set at α=0.05. RESULTS: A total of 158 human proteins were identified. Approximately one-sixth of proteins (24/158) were present in at least two different extracts. Conversely, the greatest number of proteins (134/158) was identified uniquely in only one of the extracts. Overall, a larger number of soluble proteins was retrieved from caries-affected than intact dentin (86/158). Likewise, a greater number of proteins was extracted by the guanidine-HCl/EDTA (106/158) in comparison to acetic acid protocol. Several proteins detected in dentin extracts, mainly those from caries-affected teeth, are biological and/or metabolically involved with tissue turnover/remodeling. CONCLUSION: The identity/abundance of soluble proteins retrieved from and remained in dentin noticeably depend on this tissue physiopathological state and protocol used to remove its minerals. CLINICAL SIGNIFICANCE: The present findings brought new insight into the proteomic phenotype of human dentin and may provide targets for the development of novel caries disease-prevention therapies.

Dentin primer based on a highly functionalized gelatin-methacryloyl hydrogel.

Gelatin-methacryloyl hydrogels (GelMA) have demonstrated their utility as scaffolds in a variety of tissue engineering applications. OBJECTIVES: In this study, a highly functionalized GelMA hydrogel was synthesized and assessed for degree of functionalization. As the proposed GelMA hydrogel was coupled to a visible-light photoinitiator, we hypothesized it might serve as base to formulate a model dentin primer for application in restorative dentistry. METHODS: GelMA was mixed with photoinitiator lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), photopolymerized for 0-40 s using a dental light-curing device and tested for extrudability, degree of photo-crosslinking (DPxlink), water sorption/solubility/swelling (WS/SL/SW) and apparent modulus of elasticity (AE). Model dentin primer was prepared by mixing GelMA+LAP with a primer of a commercial three-step etch-and-rinse adhesive. After application of GelMA-based primer to acid-etched dentin, samples were bonded with correspondent adhesive agent, photopolymerized and had their immediate bond strength compared to control samples primed and bonded with the same commercial material. RESULTS: Extrudability of hydrogel was confirmed using a microsyringe to write the acronym "CDMI". DPxlink of GelMA+LAP changed significantly as a function of photopolymerization time (20 s < 30 s ≤ 40 s). WS, SL and SW were significantly reduced in hydrogels polymerized for 30 and 40 s. AE of hydrogels varied significantly as a function of photopolymerization time (20 s < 30 s ≤ 40 s; 20 s ‡ 40 s). Bond strength of dentin primed with GelMA-based primer was lower (∼29.3 MPa) but not significantly of that of control (∼34.6 MPa). CONCLUSIONS: Optimization of a GelMA-based dentin primers can lead to the development of promising biomimetic adhesives for dentin rehabilitation.

Changes to dentin extracellular matrix following treatment with plant-based polyphenols.

This study investigated whether treatment with plant-based polyphenols (PB-P) affected the biochemical and/or biomechanical properties of dentin extracellular matrix (ECM). Three PB-Ps were evaluated: luteolin (LT), galangin (GL), and proanthocyanidin (PAC). Because dentin ECM requires demineralization before treatment, this study also assessed the effect of these PB-Ps on dentin demineralized by two different chemicals. Dentin samples from extracted third molars were obtained, sectioned, and randomly assigned for demineralization with either phosphoric acid (PA) or ethylenediaminetetraacetic acid (EDTA). Following demineralization, baseline infrared (IR) spectra and apparent elastic modulus (AE) of each specimen were independently acquired. Based upon these initial tests, samples were randomly assigned to one of the PB-P treatments to ensure that distribution of baseline AE was similar across treatment groups. IR and AE specimens were individually immersed in either 0.2% LT, 0.4% GL or 1% PAC for 2 min. IR spectra of treated samples were compared to baseline IR spectra, looking for any interaction of PB-Ps with the demineralized dentin. The IR spectrum and AE of each PB-P-treated specimen were compared with their own correspondent baseline measurement. The ability of PB-Ps to inhibit proteolytic activity of dentin ECM was assessed by the hydroxyproline assay. Finally, the effect of PB-Ps on immediate bond strength of a dental adhesive to PA- or EDTA-etched dentin was also evaluated. PB-Ps exhibited distinctively binding affinity to dentin ECM and promoted significant increase in AE. PB-P treatment reduced the degradation rate of dentin ECM without causing detrimental effect on immediate bond strength to dentin. Our work represents the first-time that LT and GL have been assessed as dentin ECM biomodifiers.

Insights into cathepsin-B activity in mature dentin matrix.

OBJECTIVE: Cysteine proteases are lysosomal enzymes that, under specific circumstances, may be secreted into the extracellular space and participate in protein turnover. This study investigated the involvement of cathepsin B in the gelatinolytic activity of mature dentin matrices at neutral pH. DESIGN: Human dentin fragments were made into powder and enzymes were extracted using guanidine-HCl/EDTA. Host-derived dentin proteases (cathepsin B, MMP-2 and MMP-9) were identified by immunoblotting, and their activities were evaluated spectrofluorimetrically using fluorogenic substrates. Proteases activities were monitored by measuring the rate of hydrolysis of substrates in the presence/absence of MMP- or cysteine cathepsin inhibitors, at neutral pH (7.4). Mass spectroscopy was used to determine the substrates' cleavage points. Reverse zymography was performed to examine the gelatinolytic activity of cathepsin B. RESULTS: Western-blots of dentin extracts yielded strong bands at 95, 72 and 30 kDa, corresponding respectively to MMP-9, MMP-2 and Cathepsin B. Greater fluorogenic substrates hydrolysis occurred in the absence of MMP and cysteine cathepsin inhibitors than in their presence. Cathepsin B exhibited significant gelatinolytic activity. CONCLUSIONS: Together with MMP-2 and MMP-9, cathepsin B also account for the host-derived gelatinolytic activity and matrix turnover of mature dentin at physiological, neutral pH.

The effect of dimethyl sulfoxide (DMSO) on dentin bonding and nanoleakage of etch-and-rinse adhesives.

OBJECTIVE: The objective was to examine the effect of a solvent dimethyl sulfoxide (DMSO) on resin-dentin bond durability, as well as potential functional mechanisms behind the effect. METHODS: Microtensile bond strength (µTBS) was evaluated in extracted human teeth in two separate experiments. Dentin specimens were acid-etched and assigned to pre-treatment with 0.5mM (0.004%) DMSO as additional primer for 30s and to controls with water pre-treatment. Two-step etch-and-rinse adhesive (Scotchbond 1XT, 3M ESPE) was applied and resin composite build-ups were created. Specimens were immediately tested for µTBS or stored in artificial saliva for 6 and 12 months prior to testing. Additional immediate and 6-month specimens were examined for interfacial nanoleakage analysis under SEM. Matrix metalloproteinase (MMP) inhibition by DMSO was examined with gelatin zymography. Demineralized dentin disks were incubated in 100% DMSO to observe the optical clearing effect. RESULTS: The use of 0.5mM DMSO had no effect on immediate bond strength or nanoleakage. In controls, µTBS decreased significantly after storage, but increased significantly in DMSO-treated group. The control group had significantly lower µTBS than DMSO-group after 6 and 12 months. DMSO also eliminated the increase in nanoleakage seen in controls. 5% and higher DMSO concentrations significantly inhibited the gelatinases. DMSO induced optical clearing effect demonstrating collagen dissociation. SIGNIFICANCE: DMSO as a solvent may be useful in improving the preservation of long-term dentin-adhesive bond strength. The effect may relate to dentinal enzyme inhibition or improved wetting of collagen by adhesives. The collagen dissociation required much higher DMSO concentrations than the 0.5mM DMSO used for bonding.

Optimizing dentin bond durability: control of collagen degradation by matrix metalloproteinases and cysteine cathepsins.

OBJECTIVES: Contemporary adhesives lose their bond strength to dentin regardless of the bonding system used. This loss relates to the hydrolysis of collagen matrix of the hybrid layers. The preservation of the collagen matrix integrity is a key issue in the attempts to improve the dentin bonding durability. METHODS: Dentin contains collagenolytic enzymes, matrix metalloproteinases (MMPs) and cysteine cathepsins, which are responsible for the hydrolytic degradation of collagen matrix in the bonded interface. RESULTS: The identities, roles and function of collagenolytic enzymes in mineralized dentin has been gathered only within last 15 years, but they have already been demonstrated to have an important role in dental hard tissue pathologies, including the degradation of the hybrid layer. Identifying responsible enzymes facilitates the development of new, more efficient methods to improve the stability of dentin-adhesive bond and durability of bond strength. SIGNIFICANCE: Understanding the nature and role of proteolytic degradation of dentin-adhesive interfaces has improved immensely and has practically grown to a scientific field of its own within only 10 years, holding excellent promise that stable resin-dentin bonds will be routinely available in a daily clinical setting already in a near future.

Intrafibrillar silicification of collagen scaffolds for sustained release of stem cell homing chemokine in hard tissue regeneration.

Traditional bone regeneration strategies relied on supplementation of biomaterials constructs with stem or progenitor cells or growth factors. By contrast, cell homing strategies employ chemokines to mobilize stem or progenitor cells from host bone marrow and tissue niches to injured sites. Although silica-based biomaterials exhibit osteogenic and angiogenic potentials, they lack cell homing capability. Stromal cell-derived factor-1 (SDF-1) plays a pivotal role in mobilization and homing of stem cells to injured tissues. In this work, we demonstrated that 3-dimensional collagen scaffolds infiltrated with intrafibrillar silica are biodegradable and highly biocompatible. They exhibit improved compressive stress-strain responses and toughness over nonsilicified collagen scaffolds. They are osteoconductive and up-regulate expressions of osteogenesis- and angiogenesis-related genes more significantly than nonsilicified collagen scaffolds. In addition, these scaffolds reversibly bind SDF-1α for sustained release of this chemokine, which exhibits in vitro cell homing characteristics. When implanted subcutaneously in an in vivo mouse model, SDF-1α-loaded silicified collagen scaffolds stimulate the formation of ectopic bone and blood capillaries within the scaffold and abrogate the need for cell seeding or supplementation of osteogenic and angiogenic growth factors. Intrafibrillar-silicified collagen scaffolds with sustained SDF-1α release represent a less costly and complex alternative to contemporary cell seeding approaches and provide new therapeutic options for in situ hard tissue regeneration.

Effects of water-storage on the physical and ultramorphological features of adhesives and primer/adhesive mixtures.

The aims of this study were to evaluate the ultimate tensile strength (UTS) and elastic modulus (E) of adhesives, and primer/adhesive mixtures after aging for 6 months in water or oil; and to compare silver uptake patterns under the TEM. A one-step self-etching adhesive (One-up Bond F: OB), two two-step self-etching primers (SE Bond: SE and Protect Bond: CP), and two etch-and-rinse systems (Single Bond: SB and Prime&Bond NT: PB) were used. Bonding and primer solutions of self-etching systems were also mixed (SE+P and CP+P). Most adhesives presented decreased UTS after water-storage. Similar or increased UTS was observed after oil storage. Except for SB, E values did not change after water-storage, but they increased after storage in oil. OB, CP+P and SE+P presented more silver uptake. The effects of water-storage were material-dependent, and significantly affected the mechanical properties and silver uptake patterns of adhesives.

Permeability of Dental Adhesives - A SEM Assessment.

OBJECTIVES: To morphologically evaluate the permeability of different commercial dental adhesives using scanning electron microscopy. METHODS: SEVEN ADHESIVE SYSTEMS WERE EVALUATED: one three-step system (Scotchbond Multi-Purpose - MP); one two-step self-etching primer system (Clearfil SE Bond - SE); three two-step etch-and-rinse systems (Single Bond 2 - SB; Excite - EX; One-Step - OS); and two single-step self-etching adhesives (Adper Prompt - AP; One-Up Bond F - OU). The mixture of primer and bond agents of the Clearfil SE Bond system (SE-PB) was also tested. The adhesives were poured into a brass mold (5.8 mm x 0.8 mm) and light-cured for 80 s at 650 mW/cm2. After a 24 h desiccation process, the specimens were immersed in a 50% ammoniac silver nitrate solution for tracer permeation. Afterwards, they were sectioned in ultra-fine slices, carbon-coated, and analyzed under backscattered electrons in a scanning electron microscopy. RESULTS: MP and SE showed slight and superficial tracer permeation. In EX, SB, and OS, permeation extended beyond the inner superficies of the specimens. SE-PB did not mix well, and most of the tracer was precipitated into the primer agent. In AP and OU, "water-trees" were observed all over the specimens. CONCLUSIONS: Different materials showed distinct permeability in aqueous solution. The extent of tracer permeation varied according to the composition of each material and it was more evident in the more hydrophilic and solvated ones.

The effect of ageing on the elastic modulus and degree of conversion of two multistep adhesive systems.

During the curing reaction, the monomers of dentine bonding systems should cross-link sufficiently to strengthen an adhesive so that it is clinically reliable. This study evaluated how different storage conditions (air vs. water storage) affect the elastic modulus (E-modulus) and degree of conversion (DC) of a three-step etch-and-rinse adhesive and a two-step self-etch adhesive. The biaxial flexural test and Raman microscopy were performed on resin disks made from the bonding agents Adper Scotchbond Multi-Purpose (SBMP; 3M ESPE) and Clearfil Protect Bond (CPB; Kuraray). The measurements were repeated after storage in either air or water for 15 and 30 min and for 1, 24, and 72 h. At time 0, the E-modulus was not affected by the adhesive system, whilst the degree of cure of CPB was higher than that of SBMP. Air storage increased the E-modulus at each ageing interval. Storage in water increased the E-modulus until it reached a maximum at 24 h, after which it decreased significantly at 72 h. No linear correlation between the percentage DC and E-modulus of the two adhesives was found when stored in water. The results of this study indicate that the mechanical properties and polymerization kinetics of SBMP and CPB are affected by storage time and medium.

Substantivity of chlorhexidine to human dentin.

OBJECTIVES: To better comprehend the role of CHX in the preservation of resin-dentin bonds, this study investigated the substantivity of CHX to human dentin. MATERIAL AND METHODS: Dentin disks (n=45) were obtained from the mid-coronal portion of human third molars. One-third of dentin disks were kept mineralized (MD), while the other two-thirds had one of the surfaces partially demineralized with 37% phosphoric acid for 15 s (PDD) or they were totally demineralized with 10% phosphoric acid (TDD). Disks of hydroxyapatite (HA) were also prepared. Specimens were treated with: (1) 10 microL of distilled water (controls), (2) 10 microL of 0.2% chlorhexidine diacetate (0.2% CHX) or (3) 10 microL of 2% chlorhexidine diacetate (2% CHX). Then, they were incubated in 1 mL of PBS (pH 7.4, 37 degrees C). Substantivity was evaluated as a function of the CHX-applied dose after: 0.5 h, 1 h, 3 h, 6 h, 24 h, 168 h (1 week), 672 h (4 weeks) and 1344 h (8 weeks) of incubation. CHX concentration in eluates was spectrophotometrically analyzed at 260 nm. RESULTS: Significant amounts of CHX remained retained in dentin substrates (MD, PPD or TDD), independent on the CHX-applied dose or time of incubation (p<0.05). High amounts of retained CHX onto HA were observed only for specimens treated with the highest concentration of CHX (2%) (p<0.05). CONCLUSION: The outstanding substantivity of CHX to dentin and its reported effect on the inhibition of dentinal proteases may explain why CHX can prolong the durability of resin-dentin bonds.

Cysteine cathepsins in human dentin-pulp complex.

INTRODUCTION: Collagen-degrading matrix metalloproteinases (MMPs) are expressed by odontoblasts and present in dentin. We hypothesized that odontoblasts express other collagen-degrading enzymes such as cysteine cathepsins, and their activity would be present in dentin, because odontoblasts are known to express at least cathepsin D. Effect of transforming growth factor beta (TGF-beta) on cathepsin expression was also analyzed. METHODS: Human odontoblasts and pulp tissue were cultured with and without TGF-beta, and cathepsin gene expression was analyzed with DNA microarrays. Dentin cathepsin and MMP activities were analyzed by degradation of respective specific fluorogenic substrates. RESULTS: Both odontoblasts and pulp tissue demonstrated a wide range of cysteine cathepsin expression that gave minor responses to TGF-beta. Cathepsin and MMP activities were observed in all dentin samples, with significant negative correlations in their activities with tooth age. CONCLUSIONS: These results demonstrate for the first time the presence of cysteine cathepsins in dentin and suggest their role, along with MMPs, in dentin modification with aging.

Effects of ethanol addition on the water sorption/solubility and percent conversion of comonomers in model dental adhesives.

OBJECTIVES: This study evaluated the kinetics of water uptake and percent conversion in neat versus ethanol-solvated resins that were formulated to be used as dental bonding agents. METHODS: Five methacrylate-based resins of known and increasing hydrophilicities (R1, R2, R3, R4 and R5) were used as reference materials. Resins were evaluated as neat bonding agents (100% resin) or they were solvated with absolute ethanol (95% resin/5% ethanol or 85% resin/15% ethanol). Specimens were prepared by dispensing the uncured resin into a circular mold (5.8 mm x 0.8 mm). Photo-activation was performed for 80s. The water sorption/diffusion/solubility was gravimetrically evaluated, while the degree of conversion (DC) was calculated by Fourier-transform infrared spectroscopy. RESULTS: Water sorption increased with the hydrophilicity of the resin blends. In general, the solvated resins exhibited significantly higher water sorption, solubility and water diffusion coefficients when compared to their corresponding neat versions (p<0.05). The only exception was resin R1, the least hydrophilic resin, in which neat and solvated versions exhibited similar water sorption (p>0.05). Addition of ethanol increased the DC of all resins tested, especially of the least hydrophilic, R1 and R2 (p<0.05). Despite the increased DC of ethanol-solvated methacrylate-based resins, it occurs at the expense of an increase in their water sorption/diffusion and solubility values. SIGNIFICANCE: Negative effects of residual ethanol on water sorption/solubility appeared to be greater as the hydrophilicity of the resin blends increased. That is, the use of less hydrophilic resins in dental adhesives may create more reliable and durable bonds to dentin.

Effect of 2% chlorhexidine digluconate on the bond strength to normal versus caries-affected dentin.

This study evaluated the effect of 2% chlorhexidine digluconate (CHX) used as a therapeutic primer on the long-term bond strengths of two etch-and-rinse adhesives to normal (ND) and caries-affected (CAD) dentin. Forty extracted human molars with coronal carious lesions, surrounded by normal dentin, were selected for this study. The flat surfaces of two types of dentin (ND and CAD) were prepared with a water-cooled high-speed diamond disc, then acid-etched, rinsed and air-dried. In the control groups, the dentin was re-hydrated with distilled water, blot-dried and bonded with a three-step (Scotchbond Multi-Purpose-MP) or two-step (Single Bond 2-SB) etch-and-rinse adhesive. In the experimental groups, the dentin was rehydrated with 2% CHX (60 seconds), blot-dried and bonded with the same adhesives. Resin composite build-ups were made. The specimens were prepared for microtensile bond testing in accordance with the non-trimming technique, then tested either immediately or after six-months storage in artificial saliva. The data were analyzed by ANOVA/Bonferroni tests (alpha = 0.05). CHX did not affect the immediate bond strength to ND or CAD (p > 0.05). CHX treatment significantly lowered the loss of bond strength after six months as seen in the control bonds for ND (p < 0.05), but it did not alter the bond strength of CAD (p > 0.05). The application of MP on CHX-treated ND or CAD produced bonds that did not change over six months of storage.

Membrane permeability properties of dental adhesive films.

This study evaluated the permeability properties of five experimental resin membranes that ranged from relatively hydrophobic to relatively hydrophilic to seal acid-etched dentin saturated with water or ethanol. The experimental resins (R1, R2, R3, R4, and R5) were evaluated as neat bonding agents or as solutions solvated with ethanol (70% resin/30% ethanol). The quality of dentin sealing by these experimental resins was expressed in terms of reflection coefficients calculated as the ratio of the effective osmotic pressure to the theoretical osmotic pressure of test solutions. The effective osmotic pressure produced across resin-bonded dentin was induced in hypertonic solutions (CaCl(2) or albumin) at zero hydrostatic pressure. The outward fluid flow induced by these solutions was brought to zero by applying an opposing negative hydrostatic pressure. The least hydrophilic resins blends, R1 and R2, exhibited significantly (p < 0.05) higher reflection coefficients than the most hydrophilic resins (R4 and R5) in both conditions of dentin saturation (water and ethanol). The reflection coefficients of neat resins were, in general, significantly higher when compared with their corresponding solvated versions in both conditions of dentin saturation. In dentin saturated with ethanol, bonding with neat or solvated resins, resulted in reflection coefficients that were significantly higher when compared with the results obtained in dentin saturated with water. Reflection coefficients of CaCl(2) (ca. 1 x 10(-4)) were significantly lower (p < 0.05) than for albumin (ca. 3 x 10(-2)). Application of hydrophobic resins may provide better sealing of acid-etched dentin if the substrate is saturated with ethanol, instead of water.

Host-derived loss of dentin matrix stiffness associated with solubilization of collagen.

Matrix metalloproteinases (MMPs) bound to dentin matrices are activated during adhesive bonding procedures and are thought to contribute to the progressive degradation of resin-dentin bonds over time. The purpose of this study was to evaluate the changes in mechanical, biochemical, and structural properties of demineralized dentin treated with or without chlorhexidine (CHX), a known MMP-inhibitor. After demineralizing dentin beams in EDTA or phosphoric acid (PA), the baseline modulus of elasticity (E) of each beam was measured by three-point flexure. Specimens were pretreated with water (control) or with 2% CHX (experimental) and then incubated in artificial saliva (AS) at 37 degrees C for 4 weeks. The E of each specimen was remeasured weekly and, the media was analyzed for solubilized dentin collagen at first and fourth week of incubation. Some specimens were processed for electron microscopy (TEM) immediately after demineralization and after 4 weeks of incubation. In EDTA and PA-demineralized specimens, the E of the control specimens fell (p < 0.05) after incubation in AS, whereas there were no changes in E of the CHX-pretreated specimens over time. More collagen was solubilized from PA-demineralized controls (p < 0.05) than from EDTA-demineralized matrices after 1 or 4 weeks. Less collagen (p < 0.05) was solubilized from CHX-pretreated specimens demineralized in EDTA compared with PA. TEM examination of control beams revealed that prolonged demineralization of dentin in 10% PA (12 h) did not denature the collagen fibrils.