3D optical detection in radiodosimetry: EasyDosit hydrogel characterization.

In this study the spectrophotometric behaviour of gelatin-based hydrogels, in the presence and absence of dyes, was studied. The aim was to formulate equivalent-tissue phantoms to be used as 3D-dosimeter, suitable for Optical Computed Tomography (OCT). The hydrogels show good transparency and good stability of baseline optical density and, in the presence of dye, the response of optical density as a function of concentration was higher than in aqueous solution. The hydrogels were formulated in order to reduce the diffusion of the image of the irradiated field over time and to have stable fantoms as a function of time. To this purpose, the diffusion coefficients of two dyes, Bromophenol Blue (BPB) and Bromocresol Green (BCG), were determined as a function of the hydrogel chemical composition. As comparison, in some experiments Xylenol Orange (XO) was used. In particular, the presence of sucrose, as thickener, can reduce to almost half BPB mobility. In conclusion, it was shown that optical properties and controlled dye diffusion in gelatin-based hydrogels could allow using them as 3D-dosimeter for optical detection.

Hydroxyapatite-based sorbents: elaboration, characterization and application for the removal of catechol from the aqueous phase.

Hydroxyapatite (HAP) is highly considered as good sorbent for the removal of metals from the aqueous phase. However, soluble metals co-exist with organic pollutants in wastewaters. But little work has been devoted to investigate the reactivity of HAP for the removal of organic compounds. The main objective of this work is to study the reactivity of HAP-based sorbents for the removal of catechol as a model organic pollutant from an aqueous solution. Thus, HAP sorbents were firstly synthesized using calcium carbonate and potassium dihydrogen phosphate under moderate conditions (25-80°C, atmospheric pressure). A zinc-doped HAP was also used as sorbent, which was obtained from the contact of HAP with an aqueous solution of zinc nitrate. All the sorbents were characterized by different standard physico-chemical techniques. The sorption of catechol was carried out in a batch reactor under stirring at room temperature and pressure. Zinc-doped HAP sorbent was found to be more reactive than non-doped HAP sorbents for the fixation of catechol. The highest sorption capacity was of 15 mg of C per gram of zinc-doped HAP sorbent. The results obtained suggest the reaction scheme of HAP sorbents with metals and organic pollutants when HAP sorbents were used for the treatment of complex wastewaters.

Hydroxyapatite precipitation with Hydron Blue dye.

Calcium phosphate, in the form of amorphous hydroxyapatite, precipitates out of neutral water solutions containing calcium and phosphate ions in the form of small agglomerates of 18 µm average size. When Hydron Blue dye (HB) is added, the insoluble particles gradually agglomerate further to 50 µm sizes. However, the removal capacity of hydroxyapatite for the dye is increased when the calcium phosphate nucleates and forms in the presence of dye. When coprecipitates form, the particules average 20 µm size and contain up to 60% organic matter. Nascent calcium phosphate particles have strong capacity for Hydron Blue dye removal. Thus smaller calcium phosphate particles increase the amount of dye molecules in water pollution control.

Fluid flow through dentin-self-etch resin interface during long term in vitro aging.

This work aimed at characterizing the interface between dentin and the resin-infiltrated dentin made following the etching procedure that prepares for the bonding of tooth-colored restorations. The non-destructive measurement of fluid flow through the dentin-self-etch resin interface was followed repeatedly during a two year aging period. Two self-etch adhesive systems were selected for experiments on the evolution of permeability and evaluation of infrared spectral changes following the 24 month aging period. The adhesives contained water and a co-solvent, namely acetone for iBond, and t-butanol for Xeno V. For both adhesive systems, the permeability decreased during the first 3 months after etching, reaching values of -66.9 and -70.5% for iBond and Xeno V, respectively. Afterwards, the fluid flow slowly increased but still remained below 50% of the initial value following the 2-year aging period. The slow degradation of the resin-dentin interface, attributed to water impregnated collagen hydrolysis, is evidenced by these variations in fluid flow, and is also noted by the increase in water-related infrared absorption bands at 3300 cm(-1) and at 1600 cm(-1). The results are discussed in terms of co-solvent hydrophobicity, evaporation rate and viscosity together with resin infiltration depth and affinity for water.

Carbonate-containing apatite (CAP) synthesis under moderate conditions starting from calcium carbonate and orthophosphoric acid.

The synthesis of carbonate-containing apatite (CAP) from calcium carbonate and orthophosphoric acid under moderate conditions was investigated. In all cases, complete precipitation of orthophosphate species was observed. The reaction temperature influenced strongly the decomposition of calcium carbonate and therefore the composition of formed products. The reaction temperature of 80 °C was found to be effective for the complete decomposition of calcium carbonate particles after 48 h of reaction. Infra-red spectroscopy (IR), nuclear magnetic resonance (NMR), thermogravimetry/mass spectroscopy (TG-MS) coupling, and X-ray diffraction (XRD) characterizations allowed the identification of the composition of formed products. By increasing the reaction temperature from 20 °C to 80 °C, the content of A-type CAP increased and that of B-type CAP decreased, according to the favorable effect of temperature on the formation of A-type CAP. The total amount of carbonate content incorporated in CAP's structure, which was determined by TG-MS analysis, increased with the reaction temperature and reached up to 4.1% at 80 °C. At this temperature, the solid product was mainly composed of apatitic components and showed the typical flat-needle-like structure of CAP particles obtained in hydrothermal conditions. These results show an interesting one-step synthesis of CAP from calcium carbonate and orthophosphoric acid as low cost but high purity starting materials.

Depletion of water molecules during ethanol wet-bonding with etch and rinse dental adhesives.

The treatment of demineralized dentin with ethanol has been proposed as a way to improve hydrophobic monomer penetration into otherwise water saturated collagen fibrils. The ethanol rinse is expected to preserve the fibrils from collapsing while optimizing resin constituent infiltration for better long term adhesion. The physico-chemical investigations of demineralized dentin confirmed objectively these working hypotheses. Namely, Differential Scanning Calorimetry (DSC) measurements of the melting point of water molecules pointed to the presence of free and bound water states. Unfreezable water was the main type of water remaining following a rinsing step with absolute ethanol. Two different liquid water phases were also observed by Magic Angle Spinning (MAS) solid state Nuclear magnetic Resonance (NMR) spectroscopy. Infrared spectra of ethanol treated specimens illustrated differences with the fully hydrated specimens concerning the polar carbonyl vibrations. Optical microscopy observations as well as scanning electron microscopy showed an improved dentin-adhesive interface with ethanol wet bonding. The results indicate that water can be confined to strongly bound structural molecules when excess water is removed with ethanol prior to adhesive application. This should preserve collagen from hydrolysis upon aging of the hybrid layer.

Critical surface energy of composite cement containing MDP (10-methacryloyloxydecyl dihydrogen phosphate) and chemical bonding to hydroxyapatite.

Self-adhesive composite cements are increasingly used for cementing inlays/onlays, intraradicular posts, crowns and laminate veneers. Wider clinical acceptance is driven by simpler and faster handling procedures, much like observed for self-etching adhesives. 10-Methacryloyloxydecyl dihydrogen phosphate (MDP) is a bi-functional monomer incorporated as the reactive ingredient in a contemporary self-adhesive cement. We have examined the surface free energy parameters of this cement and studied the mode of action of the cement on dentine substrate by contact angle measurements to determine the critical surface energy of the cement. Retention of the infrared absorption bands characteristic of the acrylate moieties on the surface of hydroxyapatite particles suggests that MDP contributes to the overall bonding to dentine by forming ionic chemical bonds with surface calcium ions in dentine crystalites.

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.

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.

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.

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.

Mechanical properties of glass fiber-reinforced endodontic posts.

Five types of posts from three different manufacturers (RTD, France, Carbotech, France and Ivoclar-Vivadent, Liechenstein) were subjected to three-point bending tests in order to obtain fatigue results, flexural strength and modulus. Transverse and longitudinal polished sections were examined by scanning electron microscopy and evaluated by computer-assisted image analysis. Physical parameters, including volume % of fibers, their dispersion index and coordination number, were calculated and correlated with mechanical properties. The weaker posts showed more fiber dispersion, higher resin contents, larger numbers of visible defects and reduced fatigue resistance. The flexural strength was inversely correlated with fiber diameter and the flexural modulus was weakly related to coordination number, volume % of fibers and dispersion index. The interfacial adhesion between the silica fibers and the resin matrix was observed to be of paramount importance.

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.

Hazardous animal waste carcasses transformation into slow release fertilizers.

Because of the need to address disposal of materials infected with pathogens new regulations have come into effect for the transport and disposal of dead farm animals or carcasses. For precautionary reasons, disposal to landfill, composting, biogas generation or fertilizer use are banned recycling paths because of incomplete knowledge about contamination transmission paths. Thermal treatment is recognized as a safe elimination process. Animal wastes have a high calorific value (above 16 MJ/kg). However, combustion of the organics leaves mineral residues (near 30%). The ashes contain mostly calcium and phosphate with some sodium, potassium and magnesium. We have examined the transformation of the ashes into a slow release fertilizer. We used a mixture of acids to partly dissolve the combustion residues and form slurry. In a second step, base was added to neutralize and solidify the reaction mixture. The final product was a whitish polycrystalline solid. Leaching tests were made to evaluate the nutrient release rate in laboratory columns. Water leachates were analyzed for up to ten pore-bed volumes and showed, as expected, large differences in release rates. Nitrate release was slowed and phosphate did not level even after ten pore-bed volumes. This demonstrates that insoluble precipitates (gypsum) contribute to control soluble ion release.

Adhesion of a quartz fibre post to a composite resin core: influence of bonding agents and their curing mode.

Fibre-reinforced composite posts are currently used to restore endodontically-treated teeth. Push-out tests were carried out to evaluate the performance of several bonding agents on the retention of an endodontic quartz fibre post to a composite resin core. Five bonding agents were investigated in both self-cure and light-cure modes. Ten experimental groups of 10 posts each were constituted as a function of curing mode and bonding agent. Specimens were mounted in a dedicated Teflon mould. This experimental set-up allowed the determination of true shear strength. One-way ANOVA and Student-Newman-Keuls tests were used for statistical analysis. The bonding strengths ranged from 23.4 MPa to 35.3 MPa. The best results were obtained with a light-cure self-etch bonding agent; in all cases photo-polymerisation led to statistically higher bonding strengths compared to chemical auto-polymerisation. Shear bond strength at the post-adhesive interface was also found to be significantly dependent on the nature of the bonding agent. AdheSe self-etch bonding agent was more effective than etch-and-rinse single-component bonding agents.

Acrylophosphonic acid reactivity with calcium ions and biological apatite.

OBJECTIVES: Acrylophosphonic acid (H(2)L) was reacted with biological apatite originating from dental enamel powder in order to identify and study the reaction products formed during the use of self-etch monomers. Nuclear magnetic resonance spectroscopy (NMR) showed the formation of brushite and a calcium salt of acrylophosphonic acid. This Ca salt was further synthesized and characterized by NMR, Fourier transform-infrared (FT-IR) and chromatography coupled with potentiometric analysis. The results reveal that calcium ions form a compound with two mono-deprotonated acrylophosphonate anions at physiological pH values. Thus, dissolution of the biological apatite by the acid-etch releases phosphate and calcium ions that combine to form brushite. The remaining dissolved Ca neutralize the acrylophosphonic acid to form an ionic salt of formula Ca(HL)(2). SIGNIFICANCE: The stoichiometry of this calcium salt allows us to conclude that, following a self-etch procedure, dissolved Ca ions participate in the formation of crosslinks in the complex photopolymerized copolymer composite network of the hybrid layer.

The role of acrylophosphonic acid monomers in the formation of hybrid layers based on self-etch adhesives.

UNLABELLED: The role of acrylophosphonic acid monomers in the formation of hybrid layers based on self-etch adhesives. OBJECTIVES: Our plan was to define the reaction products formed when an acrylophosphonic acid reacts with tooth hard tissue. Our aim was to describe the incorporation of the reaction products in the hybrid layer formed. METHODS: Potentiometric methods were used to measure acid dissociation constants and investigate calcium complex formation. Infrared spectroscopy and NMR were used to follow water contents and show transformation of phosphorous containing compounds. RESULTS: The acrylophosphonic acid contained in AdheSE (Ivoclar Vivadent, Schaan, Liechtenstein) is characterized by two acidities with pK(a1)=2.4 and pK(a2)=7.0, and interacts with calcium ions in a purely ionic fashion. When hydroxyapatite crystals are dissociated by the presence of AdheSE, brushite is formed together with a calcium cross-linked network of the phosphonate containing copolymer. CONCLUSION: The results give a new image of the hybrid layer where the adhesive behaves like an ionomer resin incorporating collagen but also minerals and salt bridges.

Surface treatments on quartz fiber post: influence on adhesion and flexural properties.

PURPOSE: To evaluate (1) the effect of various surface treatments to optimize post adhesion, and (2) if these surface treatments had any adverse effect on the overall mechanical and chemical properties of the posts. METHODS: Six experimental batches were set according to the nature of the surface treatments which were followed or not by post silanization. Post surface treatments were: control, chloroform (CHCl3) and sandblasting (sand) with Al2O3 50 microm. The silane (sil) used was Silane Coupling Agent Calibra. In all cases, a dual-cure bonding agent was applied Prime&Bond NT + Self Cure Activator. The Groups were: 1 (control), 2 (sil), 3 (CHCl3), 4 (CHCl3 + sil), 5 (sand), 6 (sand + sil). Following surface treatments, the posts were embedded in resin composite and the composite-post interfacial strength was investigated with a push-out test. Flexural and fatigue tests were performed to control the mechanical performances of the treated posts. Push-out data were analyzed using two-way ANOVA and Scheffé's multiple means comparisons test (alpha = 0.05). SEM observations revealed the topographical modifications induced by sandblasting and the solvent. RESULTS: Sandblasting or surface treatment with chloroform increased the bond strength (P < 0.001). The best values were obtained with the combination of sandblasting followed by post silanization. The flexural properties were not modified by the surface treatments (P = 0.072) and all the posts reached 3,000,000 cycles without breaking.

Release of aqueous calcium and phosphate from human dental enamel following administration of self-etching adhesives.

Seven self-etching adhesives were studied on an experimental reconstituted human enamel model. The objective was to evaluate the acid dissociation step of the enamel minerals. The self-etching products were applied to the enamel specimens according to the manufacturers' instructions and then rinsed with distilled water. The aqueous calcium and phosphate released were analysed chemically by atomic absorption and ion chromatography, respectively. Results show widely varying concentrations related to pH, acid concentration and calcium binding capacity. All concentrations are less than reference values obtained with orthophosphoric acid. The effectiveness of self-etchants is discussed in terms of their ability to demineralise human enamel and incorporate the released ions in the subsequent HEMA co-polymer composing the hybrid layer.