Geneviève Grégoire

X-ray photoelectron spectroscopy study of the dentin-glass ionomer cement interface.

OBJECTIVES The work was carried out with a view to identifying the elements composing the glass ionomer under study, and then to characterising the interactions occurring between this particular glass ionomer and the dentin substrate on which it was placed and with which it interacted. METHODS The samples studied were sections of healthy human dentin on which a very thin film of auto-polymerisable cement, composed of a powder and a liquid, was deposited under para-clinical conditions. After separation, the interfaces on the dentin side and on the glass ionomer side were studied using X-ray Photoelectron Spectroscopy (XPS). RESULTS This study showed that the dentin and glass ionomer cement exchanged mineral and organic elements. The acid contained in the liquid showed a certain degree of aggressivity, despite the presence of the glass ionomer. The dentin protein was, in fact, rapidly denuded from the very first minute. Migration of the mineral elements from one substrate to the other led to the formation of an intermediate layer on the surface of the materials. SIGNIFICANCE This layer, which forms an interphase, enables the material to adhere to the dentin.

Dentin permeability: Self-etching and one-bottle dentin bonding systems

STATEMENT OF PROBLEM There are many bonding systems available, with or without a prior acid etch. The mechanisms differ from system to system. Therefore it is important that the clinician know which are the most effective and which provide the best seal. PURPOSE This study measured the infiltration of physiological saline solution across dentin after application of self-etching or 1-bottle dentin bonding systems. MATERIALS AND METHODS Thirty-six extracted noncarious human third molars from patients 18 to 25 years old were used for this study. Dentin disks were cut from crown segments parallel to the occlusal surface at the incisal portion of the pulp cavity. The 36 disks, each 1 mm thick, were divided into 6 groups (n=6 per group), each of which received one of the following dentin bonding systems: Optibond Solo Plus and Excite, which have ethanol as the solvent; Prime & Bond NT, which has acetone as the solvent; Single Bond, which has a mixed solvent; and Clearfil SE Bond or Prompt L-Pop, both self-etching systems The hydraulic conductance, the volume of fluid transported across a known area of surface (0.28 cm(2)) per unit time under a unit pressure gradient (200 cm H(2)O), was analyzed for the self-etching and 1-bottle dentin bonding systems with the Flodec apparatus. Both sides of each specimen were etched with 36% phosphoric acid for 30 seconds. Measurements were made every 30 seconds for 15 minutes. The initial measurement served as the reference value for each specimen. The measurements were repeated when a smear layer had been formed and, finally, after one of the 6 bonding systems had been applied. The data were analyzed by use of analysis of variance and a posteriori tests (Fischers PLSD, Duncans new multiple range) with alpha=.05. RESULTS The greatest mean reduction (40%, P<.05) in penetration was observed with the 4 products with conventional etching: Optibond Solo Plus, Single Bond, Excite, and Prime & Bond NT. The self-etching products were associated with reductions of 36% (Clearfil SE Bond) and 16% (Prompt L Pop). Standard deviations were high, 50% of the mean value, except for the Single Bond group (-42 +/- 13) and Prime & Bond NT (-41 +/- 14). CONCLUSION Within the limitations of this study, the 4 bonding systems tested with a phosphoric acid before etching provided a greater decrease in dentin permeability than the 2 self-etching systems. The difference in permeability decrease was significant for Prompt L-Pop but not for Clearfil SE Bond.

Water distribution in dentin matrices: bound vs. unbound water.

OBJECTIVE This work measured the amount of bound versus unbound water in completely-demineralized dentin. METHODS Dentin beams prepared from extracted human teeth were completely demineralized, rinsed and dried to constant mass. They were rehydrated in 41% relative humidity (RH), while gravimetrically measuring their mass increase until the first plateau was reached at 0.064 (vacuum) or 0.116 gH2O/g dry mass (Drierite). The specimens were then exposed to 60% RH until attaining the second plateau at 0.220 (vacuum) or 0.191 gH2O/g dry mass (Drierite), and subsequently exposed to 99% RH until attaining the third plateau at 0.493 (vacuum) or 0.401 gH2O/g dry mass (Drierite). RESULTS Exposure of the first layer of bound water to 0% RH for 5 min produced a -0.3% loss of bound water; in the second layer of bound water it caused a -3.3% loss of bound water; in the third layer it caused a -6% loss of bound water. Immersion in 100% ethanol or acetone for 5 min produced a 2.8 and 1.9% loss of bound water from the first layer, respectively; it caused a -4 and -7% loss of bound water in the second layer, respectively; and a -17 and -23% loss of bound water in the third layer. Bound water represented 21-25% of total dentin water. Chemical dehydration of water-saturated dentin with ethanol/acetone for 1 min only removed between 25 and 35% of unbound water, respectively. SIGNIFICANCE Attempts to remove bound water by evaporation were not very successful. Chemical dehydration with 100% acetone was more successful than 100% ethanol especially the third layer of bound water. Since unbound water represents between 75 and 79% of total matrix water, the more such water can be removed, the more resin can be infiltrated.

Solvent composition of one-step self-etch adhesives and dentine wettability

OBJECTIVES Our aim was to determine the wettability of dentine by four commercial self-etch adhesives and evaluate their spreading rate on the dentine surface. Any correlation with chemical composition was sought, particularly with the amount of solvent or HEMA present in the adhesive. The adhesives used were AdheSE One, Optibond All.In.One, Adper Easy Bond and XenoV. METHODS Chemical compositions were determined by proton nuclear magnetic resonance (NMR) spectroscopy of the adhesives dissolved in dimethylsulfoxide. Apparent contact angles for sessile drops of adhesives were measured on dentine slices as a function of time for up to 180s. The water contact angles were determined for fully polymerised adhesives. RESULTS All adhesives were water-based with total solvent contents ranging from 27% to 73% for HEMA-free adhesives, and averaging 45% for HEMA containing adhesives. The contents in hydrophobic groups decreased as water contents increased. No differences were found in the adhesive contact angles after 180s even though the spreading rates were different for the products tested. CONCLUSION Water contact angles differed significantly but were not correlated with HEMA or solvent presence. Manufacturers use different approaches to stabilise acid co-monomer ingredients in self-etch adhesives. Co-solvents, HEMA, or acrylamides without co-solvents are used to simultaneously etch and infiltrate dentine. A large proportion of water is necessary for decalcification action.

Does strontium play a role in the cariostatic activity of glass ionomer? Strontium diffusion and antibacterial activity

OBJECTIVES The aim of this work was to evaluate the activity of strontium ions on the main pathogens of the oral flora. The leaching of strontium from resin modified glass ionomer cements (RMGIC) was evaluated together with its uptake by superficial dental enamel. METHODS The antibacterial activity was measured by the growth inhibition method following exposure of supra- and sub-gingival bacteria to a range of strontium concentrations (0.19 moll(-1), 0.37 moll(-1), 0.74 moll(-1) and 1.11 moll(-1)). Strontium concentrations were analyzed chemically and migration at 5 microm and 15 microm depths was quantified by microprobe following Fuji Ortho LC application on the vestibular enamel of extracted teeth. RESULTS Strontium was found in appreciable amounts (0.8 wt.%) in superficial enamel, but in insignificant concentrations deeper in. At the same time, 8% fluoroapatite was formed in the enamel. Under our experimental conditions, strontium had no significant antibacterial activity; only one log reduction of activity was observed at the highest concentrations tested. CONCLUSIONS RMGIC releases strontium ions which are rapidly exchanged for calcium ions in the superficial enamel. No significant antibacterial activity was observed for strontium ions alone at the concentrations considered. However synergistic effects with fluoride could promote antibacterial activity.

Water permeability, hybrid layer long-term integrity and reaction mechanism of a two-step adhesive system

OBJECTIVES Our aim was to investigate the reaction mechanism of formation of the hybrid layer by a HEMA-containing self-etch adhesive and to study fluid filtration, contact angle and interfacial ultrastructure by SEM following a 1 year ageing period. METHODS Acidic behaviour and chemical interactions between Silorane System Adhesive and dentine were studied by potentiometric titrations, atomic absorption spectroscopy and infrared spectroscopy. The hydrophilicity of the adhesive was evaluated using the sessile drop method and dentine permeability by hydraulic conductance. The morphological study of the dentine/adhesive system interface was conducted using SEM. RESULTS The Silorane System Adhesive behaved as a multi-acid with several different pK(a) values. When the adhesive was in contact with dentine, the acid was progressively consumed and calcium ions were released. The acrylate substituted phosphonate bound strongly to apatite crystals. The polyacrylic acid copolymer reacted with calcium ions and formed an interpenetrating polymer network (IPN). Water contact angle measurements showed rapid spreading on primer (angles reached 15 degrees at 30s) and larger contact angles when the Silorane bonding layer was added (from over 60 degrees to 44 degrees ). A thick, homogeneous hybrid layer was observed both initially and after 1 year of ageing, with a corresponding hydraulic conductance of -48.50% initially and -52.07% at 12 months. CONCLUSION The Silorane System Adhesive is capable of both dissolving calcium ions and binding to apatite surfaces. The results showed the hydrophilicity of the adhesive, which formed an IPN-like hybrid layer that conserved adequate impermeability over a 1-year period.

Modifications of the organic and mineral fractions of dental tissues following conditioning by self-etching adhesives

OBJECTIVES Our objective was to analyse the acid strengths and concentrations in contemporary self-etch adhesives and test whether the adhesion/decalcification concept functions the same way for all products. METHODS The self-etching adhesives were dissolved in a 50% water-ethanol solvent, these were reacted with biological apatite (HA) in the form of powder of human dentine in order to quantify calcium release and study the reaction products as a function of acid strengths and concentrations. The four self-etching adhesives investigated were AdheSE One (Ivoclar Vivadent, Schaan, Liechtenstein), Adper Easy Bond (3M ESPE, St Paul, MN, USA), Optibond All-In-One (KERR, Orange, CA, USA), Xeno V (Dentsply De Trey, Konstanz, Germany). RESULTS Acid concentrations were found to span the range from 1 to 2 mmol/l, and the acid dissociation constants varied between apparent pKa values of 3.4 and 4.2. The pH values changed with time from values near 2.8 to 3.6, confirming the buffering action of HA. The stronger acids dissolved more calcium ions but left less organic matter attached to the tissue particles. Thermogravimetric and infrared analysis demonstrated that the weaker acids tended to bind to HA surfaces and increased significantly the organic to mineral ratios of the powders. CONCLUSION Self-etching adhesives can be differentiated and classified in two types: weak acids attach to the mineral phase and leach little calcium; strong acids bind to the calcium ions, demineralize more and tend to debond from the dentinal hard tissues by forming more soluble calcium salts.

Effects of dentine moisture on the permeability of total-etch and one-step self-etch adhesives.

OBJECTIVES The aim of this study was to compare the technique sensitivity of a one-bottle total-etch adhesive and a self-etch primer adhesive to the moisture condition of the dentine substrate. METHODS The methods used were hydraulic conductance, light microscopy and scanning electron microscopy. RESULTS When the moisture conditions of the dentine surface are modified with respect to the standard, the bonded interfaces obtained with the one-bottle total-etch Adper Scotch Bond 1 XT (SB) and the all-in-one self-etch Adper Prompt L-Pop (AP) are morphologically highly perturbed. But, although this study also showed a significant (p<0.01) relationship between increases in permeability of resin-bonded dentine and variations of dentine moisture conditions with SB, a significant relationship was found only for the influence of the over-wet condition with AP. CONCLUSION Within the limitations of this study, the self-etch primer tested gave a greater reduction in dentine permeability than the one-bottle adhesive, while being more tolerant to handling. Although excess water should be avoided with both these systems, air-drying can be an alternative to wet-bonding with the self-etch primers, thus reducing the sensitivity to technique.

Morphological study of fiber-reinforced post–bonding system–root dentin interface by evaluation of two bonding systems

UNLABELLED Morphological study of fiber post/bonding system/root dentin interface by evaluation of two bonding systems. OBJECTIVES The aim of the study was to analyze the interfaces, and thus the seal, between root dentin and bonded fiber-reinforced posts. The interfaces were obtained by applying two enamel-dentin adhesive systems, a one-bottle system used after application of phosphoric acid and a self-etch system, both used with an adhesive cement. The interface was evaluated by SEM observation of the continuity of the hybrid layer and the morphology of the resin tags, in terms of length, density and presence of side branches, at the interface between the fiber-reinforced post, the bonding system and the root dentin. METHODS Twenty-six anterior single-rooted teeth extracted for periodontal reasons were treated endodontically and then randomly separated into two groups of 13 teeth each: group 1: Excite DSC (Ivoclar Vivadent, Liechtenstein); group 2: AdheSE DC (Ivoclar Vivadent, Schaan, Liechtenstein). After preparation of the root canal and application of the adhesive, each specimen received a Postec translucent FRC post (Ivoclar Vivadent, Schaan, Liechtenstein) that was cemented in with Variolink II dual-curing luting composite (Ivoclar Vivadent, Schaan, Liechtenstein). The specimens were then prepared for SEM observation of the continuity of the hybrid layer and scoring of the morphology of the resin tags in each third of the root (at 1, 4.5 and 8mm from the coronal surface). RESULTS There was no significant difference (at p<0.05) between the two groups in terms of continuity of the hybrid layer or morphology of the resin tags. The hybrid layer was present, unbroken and uniform in both the group where adhesive was used with a phosphoric acid total etch and the self-etch system group. Whatever the bonding system, the resin tags had side branches, and greater length and density in the cervical third than in the middle or apical thirds. Bubbles were found in the cement layer in most of the specimens. CONCLUSIONS The one-bottle and self-etch bonding systems gave similar results in terms of interface morphology when a translucent fiber-reinforced post was cemented into the endodontically prepared roots.

HEMA reactivity with demineralized dentin

OBJECTIVES 2-Hydroxyethylmethacrylate (HEMA) was compared to its epoxy analogue, glycidoxypropylmethacrylate (GMA), for reactivity with 2,6-diaminohexanoic acid (Lysine), an amino acid present in collagen possessing a reactive amino side chain. The aim was to verify whether HEMA could chemically react with collagen fibers. METHODS Capillary electrophoresis was used to analyse reaction products together with computer aided chemistry. Retention of HEMA in demineralized dentine particles was investigated by infrared spectroscopy. RESULTS It was found by that HEMA does not form any new molecular species when contacted with lysine whereas GMA completely reacts to form the expected addition product. Computer aided chemistry confirmed this finding. Infrared spectroscopy showed that demineralized dentin has strong affinity for HEMA and retains this monomer despite extensive water washing. CONCLUSIONS We interpret this behavior as demonstrating solvation of HEMA in the collagen polymer network.