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Chemical characterization of the dentin/adhesive interface by Fourier transform infrared photoacoustic spectroscopy.

Irreversible bonding of composite materials to tooth structure depends on chemical as well as mechanical adhesion. The proposed bonding mechanism for several commercial dental adhesives is chemical adhesion to the dentin surface. The purpose of this in vitro investigation was to characterize the chemical nature of the surface interaction between dentin and two commercial adhesives by use of Fourier transform infrared photoacoustic spectroscopy (FTIR/PAS). The occlusal thirds of the crowns of freshly extracted, non-carious, unerupted human molars were sectioned perpendicular to the long axis. Dentin disks, 6 mm x 2 mm, were prepared from these sectioned teeth. The exposed dentin surface was treated with either Scotchbond 2, a BIS-GMA resin, or Dentin-Adhesit, a polyurethane resin. All spectra were recorded from 4000 to 400 cm-1 by use of an Analect RFX-65 FTIR spectrometer equipped with an MTEC Photoacoustics Model 200 photoacoustic cell. An initial spectrum of the dentin surface was collected. This surface was primed according to manufacturers instructions and spectra recorded of the primed surface plus one to three layers of adhesive. By comparison of these spectra, it was possible for us to record changes in the phosphate and amide I and II bands due to surface interactions between the adhesive and the dentin. Although early results do not indicate covalent bonding between the dentin and these adhesives, this technique presents several advantages for spectroscopic evaluation of the dentin/adhesive interface.

Properties of expanding SOC/epoxy copolymers for dental use in dental composites

The objective of this work was to develop copolymers of alicyclic spiroorthocarbonates (SOCs) and epoxies that would yield hard non-shrinking matrix resins suitable for formulating dental composites. Several reactant ratio combinations of a four-component SOC/epoxy comonomer system were developed that demonstrated a copolymer expansion of between 0.1 and 0.8% on polymerization. The physical properties of tensile strength (29-48 MPa), water solubility of less than 5 microgram/mm(3), and water sorption of less than 50 microgram/mm(3) for the copolymer containing 5% SOC suggest that these materials have potential as matrix resins for dental composites.

In vitro cytotoxicity of solid epoxy-based dental resins and their components

OBJECTIVEnThe objective of this study was to evaluate the effect of adding a spiroorthocarbonate (SOC) or a polyol on the cytotoxicity of epoxy-based dental resins.nnnMETHODSnResins contained one of the epoxies: diglycidyl ether Bisphenol A (GY-6004); 3,4-epoxycyclohexanemethyl-3,4-epoxycyclohexane carboxylate (UVR-6105); vinyl cyclohexane dioxide (ERL-4206) or the three-epoxy mixture (Epoxy-M). The SOC was t/t-2,3,8,9-di(tetramethylene)-1,5,7,11-tetraoxaspiro[5.5]undecane (SOC). The polyols were polytetrahydrofuran (p-THF-250) and polycaprolactone triol (TONE-301). The photoinitiator (4-octylphenyl)phenyliodonium hexafluoroantimonate and camphorquinone were used for light curing the resins. Four types of resins (epoxy, SOC/epoxy, polyol/epoxy and SOC/polyol/epoxy) were evaluated for cytotoxicity as solids in the agar diffusion assay and as aqueous extracts in the MTT assay using L929 cells.nnnRESULTSnIn agar diffusion analysis, ERL-4206 and UVR-6105 resins were severely cytotoxic (+3), but the addition of SOC changed them to non-cytotoxic (-). Addition of 1-3% SOC changed Epoxy-M from mild (+) to non-cytotoxic. Adding SOC changed GY-6004 from moderate (+2) to mild (-) cytotoxicity. Generally, addition of SOC did not change cytotoxicity when added to polyol/epoxy combinations. Either polyol produced resins with reduced cytotoxicity when added to UVR-6105, but the opposite occurred when added to Epoxy-M resins. In MTT analysis, percent cell survival from 100 microliters resin extracts were statistically compared (ANOVA, p < 0.05). Epoxy-M and GY-6004 resin extracts were significantly less cytotoxic than UVR-6105 and ERL-4206 resin extracts were. Overall, the SOC component reduced the cytotoxicity of all SOC/epoxy combinations, except SOC/ERL-4206, which was significantly more cytotoxic than ERL-4206 resin extract. This may be the result of cell fixative effects observed for SOC/ERL-4206 in agar diffusion analysis. Addition of SOC produced significantly less cytotoxic SOC/polyol/Epoxy-M resins when compared to its non-SOC counterpart. The contrary result was obtained with SOC/polyol/UVR-6105 resin combinations. Consistent with agar diffusion results, adding polyol significantly decreased cytotoxicity of UVR-6105 resins. The cytotoxicity of these resins may be related to the 50% cytotoxicity (TC50) of their components as leachates. The TC50 values of the individual components were compared to BISGMA. Polyols, epoxy monomers, SOC monomer and camphorquinone were significantly (p < 0.05) less cytotoxic than BISGMA.nnnSIGNIFICANCEnAddition of SOCs and polyols in the formulation of epoxy-based resins may contribute to development of biocompatible dental composites.

Synthesis and polymerization of new expanding dental monomers.

The objective of this work was to develop polymeric materials that expand slightly upon polymerization and that could potentially be used as matrix resins for dental composites. A series of stereoisomeric alicyclic spiroorthocarbonates (SOCs) that expand when polymerized were synthesized. Three of these SOC racemates were analyzed: cis/cis-, cis/trans- and trans/trans-2,3,8,9-di(tetramethylene)-1,5,7,11-tetraoxaspiro[5.5] undecane. The degrees of expansion, approximately 3.9% and 3.5%, for the cis/cis and trans/trans, were determined by measuring the specific volume of the monomers and polymers in dilute solutions. This method of determining densities and subsequent calculated expansion or shrinkage was validated by duplicating the reported shrinkage of 4-tert-butylphenyl glycidyl ether, styrene, and methyl methacrylate. Based on these data and spectral data obtained using other analytical techniques, these stereoisomeric alicyclic SOCs appear to have potential as nonshrinking polymer or copolymer matrices for dental composites.

Comparison of two-surface and multiple-surface scoring methodologies for in vitro microleakage studies.

Investigators differ on the use of a two-surface or multiple-surface scoring methodology in sectional microleakage studies. This study compared microleakage scores using both two-surface and multiple-surface scoring methods for two preparation types and two different dentin bonding agents. Twenty freshly extracted molars each received one box-shaped and one V-shaped restoration on the mesial or distal surface. Each restoration was cut occlusogingivally into four sections, yielding eight surfaces for scoring. Surfaces were marked to identify central (I), lateral (II), and end (III) locations, then scored by two calibrated raters. The Wilcoxon Matched-Pairs Signed-Rank Test showed a statistically significant difference (p less than or equal to 0.05) in median microleakage scores obtained by an end two- surface and multiple-surface evaluation for V-shaped preparations restored with Scotchbond 2, P-50. No other statistically significant comparisons were detected. Results suggest that microleakage may be more extreme at end surfaces and that these end surfaces should be scored so that an accurate microleakage value could be assigned to composite restorations.

Auger electron spectroscopy of dentin: elemental quantification and the effects of electron and ion bombardment

Auger electron spectroscopy was used in this investigation to quantify the elemental composition of various dentin surfaces. The surfaces included the smeared layer, produced by abrasion, as well as surfaces prepared by fracturing in vacuum and in air. Quantification was aided by spectra obtained from standard samples of the two main components of dentin, hydroxyapatite, and collagen. Experimental conditions were found whereby the samples could be analyzed without conductive coatings. Ion sputter etch rates were measured for dentin, hydroxyapatite, and collagen. Under the conditions used here, it was observed that collagen etched at a rate approximately five times greater than hydroxyapatite. Auger spectra of the sputtered surfaces indicated significant ion beam-induced sample changes in collagen and dentin; no significant changes were found with hydroxyapatite. The results of this investigation demonstrate that Auger electron spectroscopy can be used to characterize dentinal surfaces and that ion sputtering can cause changes in the surface composition of dentin.