The effects of ethanol on the size-exclusion characteristics of type I dentin collagen to adhesive resin monomers.

During dentin bonding with etch-and-rinse adhesive systems, phosphoric acid etching of mineralized dentin solubilizes the mineral crystallites and replaces them with bound and unbound water. During the infiltration phase of dentin bonding, solvated adhesive resin comonomers are supposed to replace all of the unbound collagen water and polymerize into copolymers. A recently published review suggested that dental monomers are too large to enter and displace water from tightly-packed collagen molecules. Conversely, recent work from the authors' laboratory demonstrated that HEMA and TEGDMA freely equilibrate with water-saturated dentin matrices. However, because adhesive blends are solvated in organic solvents, those solvents may remove enough free water to allow collagen molecules to come close enough to exclude adhesive monomer permeation. The present study analyzed the size-exclusion characteristics of dentin collagen, using a gel permeation-like column chromatography technique, filled with dentin powder instead of Sephadex beads as the stationary phase. The elution volumes of different sized test molecules, including adhesive resin monomers, studied in both water-saturated dentin, and again in ethanol-dehydrated dentin powder, showed that adhesive resin monomers can freely diffuse into both hydrated and dehydrated collagen molecules. Under these in vitro conditions, all free and some of the loosely-bound water seems to have been removed by ethanol. These results validate the concept that adhesive resin monomers can permeate tightly-bound water in ethanol-saturated collagen molecules during infiltration by etch-and-rinse adhesives. STATEMENT OF SIGNIFICANCE: It has been reported that collagen molecules in dentin matrices are packed too close together to allow permeation of adhesive monomers between them. Resin infiltration, in this view, would be limited to extrafibrillar spaces. Our work suggests that monomers equilibrate with collagen water in both water and ethanol-saturated dentin matrices.

Increased Durability of Resin-Dentin Bonds Following Cross-Linking Treatment.

OBJECTIVES: This study evaluated the long-term effect of carbodiimide treatments of acid-etched dentin on resin-dentin bond strength of a simplified etch-and-rinse adhesive system. METHODS: Forty-eight sound third molars were divided into three groups (n=16) according to the dentin treatment: G1: deionized water; G2: 0.5 mol/L 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) applied for 30 seconds; and G3: 0.5 mol/L EDC applied for 60 seconds. Flat dentin surfaces were produced, etched with 37% phosphoric acid for 15 seconds, and then treated with deionized water for 60 seconds or with 0.5 mol/L EDC for 30 or 60 seconds prior to the application of Single Bond 2. Crowns were restored with resin composite, and beam specimens were prepared for microtensile testing. The beams from each group were tested 24 hours or 6 or 12 months after the adhesive procedures. One slab from each tooth was prepared and analyzed for nanoleakage. Bond strength (MPa) data were submitted to analysis of variance and Tukey test (α=0.05). RESULTS: The treatment of dentin with 0.5 mol/L EDC for 30 seconds (24.1±6.2 MPa) and 60 seconds (25.5±5.1 MPa) did not negatively affect the immediate bond strength of Single Bond 2 when compared to the control group (24.6±7.3 MPa). Additionally, EDC prevented resin-dentin bond degradation after 12 months in artificial saliva for both periods of treatment. An increased accumulation of silver ions was seen for the control group over time, while a much lower amount of silver grains was observed for the EDC-treated groups. CONCLUSIONS: 0.5 mol/L EDC was able to prevent resin-dentin bond degradation after 12 months, especially when applied for 60 seconds.

Transdentinal cytotoxicity of carbodiimide (EDC) and glutaraldehyde on odontoblast-like cells.

OBJECTIVE: To evaluate the transdentinal cytotoxicity of three different concentrations of carbodiimide (EDC) or 5% glutaraldehyde (GA) on MDPC-23 cells. METHODS: Seventy 0.4-mm-thick dentin disks obtained from human molars were adapted to artificial pulp chambers. MDPC-23 cells were seeded on the pulpal surface of the disks. After 48 hours, the occlusal dentin was acid-etched and treated for 60 seconds with one of the following solutions (n=10): no treatment (negative control); 0.1 M, 0.3 M, or 0.5 M EDC; 5% GA; Sorensen buffer; or 29% hydrogen peroxide (positive control). Cell viability and morphology were assessed by methyltetrazolium assay and scanning electron microscopy (SEM), respectively. The eluates were collected after the treatments and applied on MDPC-23 seeded in a 24-well plate to analyze cell death, total protein (TP), and collagen production. The last two tests were performed 24 hours and seven days after the challenge. Data were analyzed by Kruskal-Wallis and Mann-Whitney tests (p<0.05). RESULTS: EDC at all test concentrations did not reduce cell viability, while 5% GA did increase cell metabolism. Cell death by necrosis was not elicited by EDC or 5% GA. At the 24-hour period, 0.3 M and 0.5 M EDC reduced TP production by 18% and 36.8%, respectively. At seven days, increased TP production was observed in all groups. Collagen production at the 24-hour period was reduced when 0.5 M EDC was used. After seven days, no difference was observed among the groups. SEM showed no alteration in cell morphology or number, except in the hydrogen peroxide group. CONCLUSIONS: Treatment of acid-etched dentin with EDC or GA did not cause transdentinal cytotoxic effects on odontoblast-like cells.

Wettability of chlorhexidine treated non-carious and caries-affected dentine.

BACKGROUND: The wettability of a surface is a prerequisite for adhesion and the type of dentine plays an important role in this property. This study evaluated the effect of different excipients of chlorhexidine (CHX) on sound and caries-affected dentine wettability. METHODS: Flat dentine surfaces were prepared (n = 100) and artificial caries was induced in half of the sample. For each substrate, sound and caries-affected dentine, surfaces were assigned to five groups: (1) smear-covered dentine; (2) smear-free dentine saturated with water; (3) ethanol; (4) 1% CHX in water; or (5) 1% chlorhexidine in ethanol. The infected dentine was ground with 320-grit silicon carbide paper to the level of affected dentine. The smear layer was removed with acid, followed by rinsing, blot drying and the application of each solution (60 seconds). Single Bond 2 was applied to each surface and contact angles were measured using a goniometer. Data were analysed by ANOVA and Student­Newman­Keuls (a = 0.05). RESULTS: Contact angles were higher on sound dentine, regardless of the treatment. For sound and caries-affected dentine significantly higher angles were obtained on smear-covered dentine. Acid-etched dentine saturated with ethanol and ethanol/CHX resulted in significantly lower angles but only for sound dentine. Neither water and water/CHX nor ethanol and ethanol/CHX solutions differ with respect to dentine wettability. CONCLUSIONS: Caries-affected dentine wettability is higher than sound dentine, and chlorhexidine does not influence this property.

Inactivation of matrix-bound matrix metalloproteinases by cross-linking agents in acid-etched dentin.

OBJECTIVES: Published transmission electron microscopy analysis of in vitro resin-dentin bonds shows that, after 44 months, almost 70% of collagen fibrils from the hybrid layer disappear. Matrix metalloproteinases (MMPs) play an important role in that process and are thought to be the main factor responsible for the solubilization of dentin collagen. Therefore, this study aimed to evaluate the inactivation of matrix-bound MMPs by two different cross-linking agents, carbodiimide (EDC) or proanthocyanidin (PA), or the MMP-inhibitor, chlorhexidine (CHX), on acid-etched dentin using a simplified MMP assay method. MATERIALS AND METHODS: Dentin beams (2×1×6 mm) were obtained from mid-coronal dentin of sound third molars and randomly divided into six groups (G) according to the dentin treatment: G1: Deionized water (control); G2: 0.1 M EDC; G3: 0.5 M EDC; G4: 0.5 M EDC + 35% hydroxyethyl methacrylate (HEMA); G5: 5% PA; and G6: 2% CHX. The beams were etched for 15 seconds with 37% phosphoric acid, rinsed, and then immersed for 60 seconds in one of the treatment solutions. The data were expressed both in absorbance values at 412 nm and in MMP-9 activity equivalents. The total MMP activity of dentin was analyzed for one hour by colorimetric assay (Sensolyte). Data were submitted to Wilcoxon nonparametric test and Mann-Whitney tests (p>0.05). RESULTS: All experimental cross-linking solutions significantly reduced MMP activity from 79.8% to 95.2% when compared to the control group. No difference was observed among 0.1 M EDC (84.8%), 5% PA (87.6%), and 2% CHX (79.8%). Addition of 35% HEMA to 0.5 M EDC produced inactivation (95.2%) that was similar to that of 0.5 M EDC alone (92.7%). CONCLUSION: Dentin treatment with cross-linking agents is effective to significantly reduce MMP activity. Mixing 0.5 M EDC and 35% HEMA did not influence EDC inhibitor potential.

The importance of size-exclusion characteristics of type I collagen in bonding to dentin matrices.

The mineral phase of dentin is located primarily within collagen fibrils. During development, bone or dentin collagen fibrils are formed first and then water within the fibril is replaced with apatite crystallites. Mineralized collagen contains very little water. During dentin bonding, acid-etching of mineralized dentin solubilizes the mineral crystallites and replaces them with water. During the infiltration phase of dentin bonding, adhesive comonomers are supposed to replace all of the collagen water with adhesive monomers that are then polymerized into copolymers. The authors of a recently published review suggested that dental monomers were too large to enter and displace water from collagen fibrils. If that were true, the endogenous proteases bound to dentin collagen could be responsible for unimpeded collagen degradation that is responsible for the poor durability of resin-dentin bonds. The current work studied the size-exclusion characteristics of dentin collagen, using a gel-filtration-like column chromatography technique, using dentin powder instead of Sephadex. The elution volumes of test molecules, including adhesive monomers, revealed that adhesive monomers smaller than ∼1000 Da can freely diffuse into collagen water, while molecules of 10,000 Da begin to be excluded, and bovine serum albumin (66,000 Da) was fully excluded. These results validate the concept that dental monomers can permeate between collagen molecules during infiltration by etch-and-rinse adhesives in water-saturated matrices.

Effect of phosphoric acid on the degradation of human dentin matrix.

This study determined if dentin proteases are denatured by phosphoric acid (PA) used in etch-and-rinse dentin adhesives. Dentin beams were completely demineralized with EDTA for 30 days. We "acid-etched" experimental groups by exposing the demineralized dentin beams to 1, 10, or 37 mass% PA for 15 sec or 15 min. Control beams were not exposed to PA but were incubated in simulated body fluid for 3 days to assay their total endogenous telopeptidase activity, by their ability to solubilize C-terminal crosslinked telopeptides ICTP and CTX from insoluble dentin collagen. Control beams released 6.1 ± 0.8 ng ICTP and 0.6 ± 0.1 ng CTX/mg dry-wt/3 days. Positive control beams pre-incubated in p-aminophenylmercuric acetate, a compound known to activate proMMPs, released about the same amount of ICTP peptides, but released significantly less CTX. Beams immersed in 1, 10, or 37 mass% PA for 15 sec or 15 min released amounts of ICTP and CTX similar to that released by the controls (p > 0.05). Beams incubated in galardin, an MMP inhibitor, or E-64, a cathepsin inhibitor, blocked most of the release of ICTP and CTX, respectively. It is concluded that PA does not denature endogenous MMP and cathepsin activities of dentin matrices.