Assessment of cytotoxicity and DNA damage exhibited by siloranes and oxiranes in cultured mammalian cells.

The potential reactivity and structural properties of oxiranes (epoxides) are advantageous when considering polymers for medical devices. However, epoxy compounds are widely known to have genotoxic properties. The objective of the study was to evaluate the cytotoxicity and primary DNA damage effects induced by oxiranes and siloranes, silicon containing oxiranes. The siloranes, Ph-Sil, Tet-Sil, and Sil-Mix and the oxiranes Cyracure UVR-6105 and 1,3-bis[2-(2-oxiranylmethyl) phenoxy]pentane (OMP-5) were dissolved in organic solvents and dilutions containing less than 0.5% solvent were used in biological assays. The concentration that reduced the viability of 50% (TC(50)) of L929 cells was measured using the MTT assay and guided the selection of subtoxic doses for evaluation of DNA damage. Ph-Sil was more cytotoxic than OMP-5, Cyracure UVR-6105 and Sil-Mix. However, the TC(50) value of Tet-Sil could not be determined due to its poor solubility. DNA damage was evaluated in the sister chromatid exchange (SCE) assay with CHO cells, and the alkaline comet assay with L929 cells. In contrast to the siloranes, the oxiranes exhibited significant increases (p>0.05) in SCE frequencies and DNA migration relative to their solvent controls. Our findings support previous reports that siloranes have low genotoxic potential and can be suitable components for development of biomaterials.

Assessment of the relative skin sensitization potency of siloranes and bis-GMA using the local lymph node assay and QSAR predicted potency.

Siloranes are silicon and oxirane (epoxy) containing monomers used for new dental composite development. The siloranes 3,4-epoxycyclohexylethyl-cyclopolymethylsiloxane (Tet-Sil) and bis-3,4-epoxycyclohexylethyl-phenyl-methylsilane (Ph-Sil) have in common cycloaliphatic epoxy moieties. The epoxy group is of concern in their biocompatibility since most epoxy compounds are known skin sensitizers. The objective of this study was to determine the in vivo skin sensitization potency of the siloranes in the local lymph node assay. A comparison was made with well-known chemical allergens, bis-GMA and DNCB. Female mice (CBA/CaJ) were exposed topically (dorsum of both ears) to several doses of acetone:olive oil in the ratio of 4:1 v/v. Doses were defined by a predictive structure-activity model (QSAR) for contact sensitization. Lymph node cell (LNC) proliferation was measured on the sixth day by incorporation of radioactive thymidine into DNA of lymph node cells. The effective concentration (EC3) that produced a 3-fold stimulation in LNC proliferation relative to controls was extrapolated from dose-response curves. DNCB was a strong sensitizer (EC3 = 0.06%). The EC3 values of Ph-Sil and bis-GMA were 19% and 45%, respectively, making these weak contact sensitizers. Tet-Sil did not increase lymph node proliferation when compared with controls. In contrast to Tet-Sil, the unpolymerized monomers Ph-Sil and bis-GMA have the capacity to induce LNC proliferation, characteristic of a T-cell mediated skin contact sensitization.

Correlation of apoptotic potential of simple oxiranes with cytotoxicity.

The measurement of primary DNA damage caused by oxirane chemicals can be confounded by apoptotic-generated DNA autolysis. The apoptogenic potential of oxiranes requires knowledge of the relationship between the apoptotic threshold dose and cytotoxic dose for interpretation of DNA damage assays. This research determined the relationship between cytotoxic and apoptotic doses for seven simple oxiranes of varying structure. This relationship between cytotoxic and apoptotic thresholds was determined simultaneously in in vitro cell culture. L929 cells in log-phase growth were exposed to the oxiranes for 24 h in 25 cm(2) and then assayed fluorometrically in 96-well plates for Caspase 3. Viability was assessed using Trypan Blue exclusion and loss of Caspase 3 activity. Ranked apoptotic potency was: diepoxybutane (DEB)>styrene oxide (SO)>phenyl glycidyl ether (PGE)>epichlorhydrin (EPI)>glycidol (GLY)>epoxybutane (EB)>epoxycyclohexane (ECH). Relative cytotoxicity was significantly correlated (r(s)=0.86, p=0.02) with potencies: DEB>EPI>PGE>SO>GLY>EB>ECH. These structurally-diverse, simple oxiranes were all capable of inducing apoptosis at doses several-fold below their cytotoxic concentrations. Difunctionality and aromaticity were key predictors of potency for both. Caspase 3 activity was an accurate indicator of necrosis which correlated with Trypan Blue results.

Aromatic dental monomers affect the activity of cholesterol esterase.

The dental restorative monomer, BISGMA (2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane), and bisphenol A diglycidyl ether (BADGE) increase the velocity of the reaction catalyzed by pancreatic cholesterol esterase (CEase, bovine). The metabolite of these monomers, bisphenol A bis(2,3-dihydroxypropyl) ether, and a common plasticizer, di-2-ethylhexyl phthalate (DEHP), also increase the velocity of CEase-catalyzed ester hydrolysis. BISGMA at concentrations of 1.5-8.0 microM increases the velocity to 126-169% of its value in the absence of BISGMA. Increasing BISGMA above 8 microM caused no further increase in velocity. BADGE at 7-25 microM increases the velocity to 112-205% of its value without BADGE. The metabolite of BISGMA and BADGE at concentrations of 2.0-7.1 microM increases the velocity to 103-113% of its value without metabolite. DEHP at concentrations of 0.52-4.3 microM increases the velocity to 108-187% of its value without DEHP. On the other hand, bisphenol A dimethacrylate is a competitive inhibitor of CEase, with a K(i) of 3.1 microM.

Shear strength of the physis varies with anatomic location and is a function of modulus, inclination, and thickness.

Slipped capital femoral epiphysis involves the gradual displacement of the femoral head relative to the neck. Many theories have arisen to explain this slip. Frequently cited etiological factors include increases in physeal thickness and inclination. Slipped epiphysis has been postulated to result from shear overload that causes separation through the hypertrophic cellular zone. We sought to answer the following questions: (a) Do significant regional differences in strength and stiffness exist within a given physis? (b) Are regional differences in resistance to shear related to thickness and inclination of the physis? (c) Does physeal compression cause mammillary interdigitation to begin sooner and increase the resistance to shear before, during, and after failure? (d) Does shear failure occur at displacements detectable by radiography? and (e) Does cleavage occur throughout the entire columnar zone, and do the chondrocyte columns remain intact on both sides of the cleavage plane? We prepared beam-shaped microstructural samples from different sites of the bovine proximal tibial physis. We determined thickness, inclination, ultimate stress and strain, modulus, and strain energy density at ultimate stress as a function of location. Using scanning electron microscopy, we also examined the entire failed surface of several samples. Forty-eight samples were tested by displacing the epiphysis end anteriorly, without axial (across the thickness) constraint; 41 were sheared while an average axial compressive stress of 0.3 MPa was applied to the physis. The posterior region had the greatest strength and stiffness, lowest physeal thickness, and steepest inclination. Compressing the plate did not increase the shear strength or tangent modulus. Ultimate strength varied inversely with thickness and increased when shearing up steeper inclinations; however, it was more strongly associated with the modulus, implying that additional factors control both strength and modulus. Scanning electron microscopy revealed that the plane of fracture differed widely between and within samples, involving all zones of the growth plate. On either side of the fracture, individual chondrocyte columns remained intact, although separated from neighboring columns.

Tensile properties of the physis vary with anatomic location, thickness, strain rate and age.

The variable outcome of physeal distraction has raised questions as to the mechanism by which bone lengthening is achieved. Is it by stretching of the matrix or does it stimulate growth? In order to explore the contribution of matrix stretching, we sought to answer the following questions in an animal model: (a) Are the tensile properties of the lateral side of the proximal tibial physis different from the medial? (b) Are the tensile properties strain-rate dependent? (c) Does the growth plate fracture through any preferred zone in tension? (d) Are the tensile properties of the bovine growth plate a function of age? (e) Are thicker growth plates weaker in tension? (f) Are the tensile properties of the bovine growth plate comparable to those of a child's? We compared bone-cartilage-bone specimens (0.5 x 2.5 mm2 in cross-section) from the lateral, central and medial regions of the proximal tibial growth plates of 12- to 18-month heifers. 70 specimens were tested to failure in tension at 0.0004, 0.004 and 0.04 mm/s. Tensile strength and tangent modulus were 33% and 25% greater, respectively, on the lateral side compared with the medial, and both were increased at the higher strain rates. We found no difference in the ultimate strains by region or strain rate. Thicker growth plates were weaker. Scanning electron microscopy revealed a three-dimensional fracture pattern extending from the upper columnar into the reserve zone. Bundles of intact chondrons remained intact, but only on the metaphyseal side, having been torn from an interterritorial matrix which remained mostly on the epiphyseal side of the fracture. We compared 21 specimens of 12- to 18-month and 19 specimens of 5-month calves from similar regions of the proximal tibia. These were tested to failure in tension at 0.004 mm/s. The older bovine growth plate was 25% thinner, 34% stronger and failed at 65% greater strain. For comparison, we tested eight samples from the femoral capital growth plate of two cerebral palsy patients. These were twice as thick as our bovine samples and about half as strong, but with similar ultimate strain values.

The effects of ion sputtering on dentin and its relation to depth profiling.

Characterization of the dentin surface and the dentin/adhesive interface is fundamental to investigations concerning adhesive bonding to dentin. It has been shown that good adhesive bonding depends on both the structure and composition of the dentin surface. A combination of ion sputter etching and Auger electron spectroscopy can be used to obtain surface composition and elemental depth profiles at interfaces. This investigation was conducted to examine the changes induced in human dentin by ion sputtering under conditions commonly encountered during depth profiling. The sputtering was conducted with argon ions at 7.5 keV and an ion flux ranging from 10(18)-10(19) ions/m2s. The amount of material sputtered was calculated from profilometer measurements of the sample surface. The surface composition was monitored by Auger electron spectroscopy. The results indicate that, under these conditions, collagen was removed at a much faster rate than hydroxyapatite, causing the surface composition of dentin to change during the sputtering process. The sputter yields for hydroxyapatite and collagen were found to be 5 and 28 atoms/ion, respectively, at a sputter angle of 45 degrees. At a sputter angle of 29 degrees, the yields were 2 and 25 atoms/ion, respectively. Both the changes in composition of dentin and the measured sputter rates are in agreement with the behavior predicted by a theoretical model for two phase materials (Blaise, 1978; Blaise et al., 1978).

Design and development of isocyanatoacrylates as dental adhesives.

During the last 12 years, significant progress has been made in the development of dental adhesive systems. Some of the more promising systems are based on multifunctional structures that contain polymerizable vinyl double bonds and reactive isocyanate groups. The utility of compounds with such structures as adhesives arises in part because their isocyanate functionality is available for reaction independently, without compromising the reactivity of the vinyl groups. The hypotheses tested in this investigation were: (1) that the monomer reactivity ratios (r1, r2) for the free-radical-initiated copolymerization of ethyl alpha-isocyanatoacrylate (alpha-EIA) and 2-isocyanatoethyl methacrylate (IEM) with selected vinyl monomers can be determined; (2) that these reactivity ratios can be used to establish Q (reactivity) and e (polarity) values for alpha-EIA and IEM; and (3) that these reactivity parameters can be useful in designing copolymers with controlled compositions for dental adhesive applications. The free-radical copolymerization characteristics of alpha-EIA and IEM were studied. The isocyanate monomers were copolymerized at seven comonomer ratios with n-butyl acrylate (NBA), methyl methacrylate (MMA), and styrene (STY). Reactivity ratios, r1 and r2, were calculated for each of the copolymer systems, giving:IEM (r1) = 0.38 and STY (r2) = 0.44; IEM (r1) = 1.19 and MMA (r2) = 0.84; IEM (r1) = 2.50 and NBA (r2) = 0.40; alpha-EIA (r1) = 2.20 and STY (r2) = 0.06; alpha-EIA (r1) = 7.00 and MMA (r2) = 0.10; and alpha-EIA (r1) = 23.50 and NBA (r2) = 0.04. The Q (reactivity) and e (polarity) values for IEM and alpha-EIA were calculated from r1 and r2 with use of the Alfrey-Price equations, giving, for IEM, Q = 0.89 and e = 0.60, and, for alpha-EIA, Q = 7.64 and e = 0.74. These reactivity parameters are useful for tailoring copolymers with controlled compositions and properties. Based on these calculated reactivity parameters, several copolymers of IEM [for example, IEM/2-hydroxyethyl methacrylate (HEMA)] are currently being prepared and evaluated as adhesives.

Elements of light-cured epoxy-based dental polymer systems.

The greatest problem with current dental composite systems is their polymerization shrinkage. Extensive work is being done by many investigators to alleviate this problem. Our approach has been to examine epoxy- and spiro-orthocarbonate (SOC)-based resins. The hypothesis to be tested in this study was that the cure characteristics of experimental visible-light-cured epoxy resin systems are governed by the types and concentrations of co-reactants and activators. Resin samples containing onium salt initiators and a thiozanthone sensitizer were successfully cured by means of either an experimental visible-light irradiation system or a commercially available dental lamp. Test resins consisted of di-epoxies alone or in combination, epoxy mixtures in combination with an SOC, or an epoxy in combination with a caprolactone-derived polyol. Significant findings were as follows: (a) Resins containing the SOC had longer cure times than their counterparts; (b) the optimum ratios of epoxy to polyol for most rapid cure were 50:50 or 60:40 under conditions tested; (c) resins containing TONE 305 polyol generally were faster to cure than those containing no polyol, or TONES 201 or 310; and (d) a resin mixture was found that had a cure time of 1 to 3 min when irradiated with a commercial dental lamp. Based on this exploratory study, it should be possible for clinically relevant cure times to be achieved for visible-light-cured epoxy-based resins by careful manipulation and optimization of key elements.

Scanning transmission electron microscopy/energy-dispersive spectroscopy analysis of the dentin adhesive interface using a labeled 2-hydroxyethylmethacrylate analogue.

In an attempt to compare the morphology of the dentin adhesive interface and the wetting and penetration of the adhesive in relation to the dentin surface, we studied four dentin adhesive systems using scanning transmission electron microscopy (STEM) and energy-dispersive spectroscopy (EDS). 2-Hydroxyethylmethacrylate (HEMA), a monomer common to many commercial dentin adhesive systems, was altered to produce a thiolated analogue (HETMA). Sulfur, traceable by EDS and STEM, was substituted for the oxygen atom in the backbone of the HEMA molecule. The resulting analogue, with solubility parameters and other wetting and physical properties very similar to those of HEMA, was applied to four sets of tooth specimens, each pre-treated with a different primer or etchant. Three separate pre-treatments--nitric acid, maleic acid, and citric acid/ferric chloride--created a demineralized zone approximately 1 to 3 microns thick at the dentin surface. The HETMA was found to permeate freely into this zone when either of the latter two pre-treatments was used. However, the band of dentin that was demineralized by the nitric acid pre-treatment appeared impermeable to the HETMA. The fourth pre-treatment, an alcohol-based solution including the phosphorus acid ester PENTA and HEMA, modified the smear layer of the tooth slightly and did not appear to demineralize the dentin. HETMA applied to the specimens pre-treated with PENTA and HEMA was clearly in intimate contact with the dentin or modified smear layer; however, it did not penetrate or diffuse into these areas. It did flow into the dentinal tubules, as was also evident with each of the other systems. It was concluded that the acid pre-treatment of the dentin greatly influenced the wetting behavior of the dentin adhesive and thus could substantially affect the resultant bond strength of the dentin adhesive systems.

Effects of dental resins on TNF-alpha-induced ICAM-1 expression in endothelial cells.

Many reports have demonstrated inflammation after the placement of dental restorations. To explain this side-effect, we studied a biomarker in the inflammatory response. The intercellular adhesion molecule-1 (ICAM-1) is a key mediator for recruitment of leukocytes to the site of inflammation. Therefore, we investigated whether methacrylates (a BISGMA-based dental resin, BISGMA, and MAA) and Cyracure UVR 6105, an epoxy monomer, could alter ICAM-1 expression in unstimulated and TNF-alpha-stimulated endothelial cells. Six-well plates with monolayers of human umbilical vein cells, ECV 304 (ATCC CRL 1998), were exposed to TNF-alpha (1 ng/mL) in the presence and absence of subtoxic and TC50 doses of chemicals for 24 hrs at 37 degrees C/5% CO2. Several doses of TNF-alpha (0.5-2 ng/mL) were coincubated with 100 microL of undiluted aqueous dental resin extracts. Cells were harvested and stained with mAB FITC-conjugated anti-human ICAM-1 (CD54). ICAM-1 expression was measured by flow cytometry. Cells expressed basal levels of ICAM-1, which was up-regulated by TNF-alpha but was not changed by all samples studied. Except for UVR 6105, the methacrylates significantly decreased ICAM-1 expression in TNF-alpha-stimulated cells. These findings suggest that methacrylates may decrease the recruitment of leukocytes to sites of inflammation.

Biocompatibility of hydroxylated metabolites of BISGMA and BFDGE.

Unpolymerized dental monomers can leach out into the oral biophase and are bioavailable for metabolism. We hypothesize that metabolites would be less toxic than parent monomers. We first identified the formation of metabolites from bisphenol F diglycidyl ether (BFDGE) and Bisphenol A glycidyl methacrylate (BISGMA) after their exposure to liver S9 fractions. Then, the metabolites and parent compounds were subjected to in vitro cytotoxicity, mutagenicity, and estrogenicity studies. Bisphenol A bis(2,3-dihydroxypropyl) ether and bisphenol F bis(2,3-dihydroxypropyl) ether were the hydroxylated metabolites of BISGMA and BFDGE, respectively. Cytotoxicity against L929 cells showed that the metabolites were significantly (p < 0.05) less cytotoxic than the parent monomers. Only BFDGE was mutagenic in the Ames assay with strain TA100 of Salmonella typhimurium. Parent and metabolite compounds did not stimulate estrogen-dependent MCF-7 cell proliferation above solvent controls. These results indicated that the hydroxylated metabolites were non-mutagenic, non-estrogenic, and less cytotoxic than their parent monomers.

A TEM study of two water-based adhesive systems bonded to dry and wet dentin.

To keep the exposed collagen scaffold penetrable to resin, it has been recommended that the conditioned dentin surface be maintained in a visibly moist condition, a clinical technique commonly referred to as wet bonding. In this study, resin-dentin interfaces produced with two water-based adhesive systems--OptiBond (OPTI, Kerr) and Scotchbond Multi-Purpose (SBMP, 3M)--were compared by transmission electron microscopy, following the application of either a dry- or a wet-bonding technique. The hypothesis advanced was that the ultramorphology of the hybrid layer would differ depending on which bonding method was applied. A morphologically well-organized hybrid layer of collagen fibrils intermingled with resin in tiny interfibrillar channels was consistently formed by the OPTI system. The SBMP system was found to produce a hybrid layer with a more variable ultrastructure, less distinctly outlined collagen fibrils, and a characteristic electron-dense phase located at its surface. No major differences in hybrid layer ultrastructure were observed when the two adhesive systems investigated were bonded to either dry or wet dentin. When the adhesives were dry-bonded, no ultrastructural evidence of collapsed demineralized collagen, incompletely or not at all infiltrated by resin, could be detected. In addition, when the two adhesives were bonded to wet dentin, no signs of overwetting phenomena, that would have indicated that water was ineffectively removed, were apparent. It has been hypothesized that the amount of water provided with the hydrophilic primer solution of either of the two adhesive systems investigated suffices to re-hydrate and re-expand the gently air-dried and collapsed collagen network. Further research should be directed to determine whether this hypothesized self-rewetting effect can be extrapolated to other adhesive systems that provide water-based primers.

Correlative transmission electron microscopy examination of nondemineralized and demineralized resin-dentin interfaces formed by two dentin adhesive systems.

The resin-dentin interface formed by two dentin adhesives, Optibond (OPTI, Kerr) and Scotchbond Multi-Purpose (SBMP, 3M), was ultramorphologically examined by transmission electron microscopy (TEM). Ultrastructural information from nondemineralized and demineralized sections was correlated. It was hypothesized that the different chemical formulations of the two adhesives would result in a different morphological appearance of the hybrid layer. Ultrastructural TEM examination proved that each of the two dentin adhesive systems was able to establish a micromechanical bond between dentin and resin with the formation of a hybrid layer. However, the interfacial hybridization process that took place to produce this resin-dentin bond appeared to be specifically related to the chemical composition and application modes of both systems. OPTI consistently presented with a hybrid layer with a relatively uniform ultrastructure, electron density, and acid resistance. These three parameters were found to be more variable for the hybrid layer formed by SBMP. Characteristic of SBMP was the identification of an amorphous phase deposited at the outer surface of the hybrid layer. Although both adhesive systems investigated follow a total-etch concept, their specific chemical formulations result in different interfacial ultrastructures that are probably related to different underlying bonding mechanisms. The clinical significance of these morphological findings, however, is still unknown.

Quantitative analysis of the dentin adhesive interface by Auger spectroscopy.

The ultimate success of a dentin adhesive bond is dependent in large part on specific conditions at the interface between the tooth and the adhesive. Most current dentin adhesive systems use some sort of pre-treatment to demineralize the first few microns of the dentin surface, leaving a meshwork of collagen into which the adhesive resin can penetrate, infiltrate, and polymerize. The general hypothesis tested in this experiment was that the penetration and distribution of adhesive resin into the demineralized zone are a function of the conditioner used as a pre-treatment for the adhesive application. Four commercially available adhesive systems were modified to incorporate hydroxyethylthiomethacrylate (HETMA), a sulfur-substituted, traceable analogue of 2-hydroxyethylmethacrylate (HEMA), thereby allowing for a qualitative measurement of the amount and distribution of monomer in the treated dentin substrate by energy-dispersive x-ray spectroscopy (EDS) and a quantitative measurement by Auger electron spectroscopy (AES). The dentin pre-treatments investigated were: (1) 10% citric acid/3% ferric chloride, (2) 10% maleic acid, (3) 2.5% nitric acid, and (4) an alcoholic solution of HEMA with a phosphorus acid ester. These pre-treatments were applied to freshly extracted teeth that had been sectioned to expose the dentin and ground to simulate the smeared layer. After the appropriate pre-treatment was applied, a 10% (v/v) solution of HETMA in acetone was applied to the surface, followed by the corresponding adhesive resin, which was then polymerized. The samples were then processed for observation by scanning transmission electron microscopy (STEM), AES, and STEM/EDS analysis. The results indicated significant differences in the ability of HETMA to penetrate the dentin surface conditioned by the four pretreatments investigated here. This study also demonstrated that AES and STEM/EDS could be used in a correlative fashion to determine the distribution of HETMA within or adjacent to the treated dentin surface.

Semiempirical and ab initio conformational analysis of 2-methylene-8,8-dimethyl-1,4,6,10-tetraoxaspiro[4.5] decane with application of GIAO-SCF methods to NMR spectrum interpretation.

The GIAO-SCF method for calculating isotropic nuclear magnetic shielding values has been utilized to explain certain features in the 1H-NMR spectrum of 2-methylene-8,8-dimethyl-1,4,6,10-tetraoxaspiro[4.5] decane. Population distributions of the low-energy conformers based on their ab initio energies were used to produce weighting factors for the individual calculated shielding values to calculate the weighted average of the shielding values for a complete set of conformers. The differences in 1H chemical shifts between the hydrogens of the two methyl groups and between the axial and equatorial hydrogens in 2-methylene-8,8-dimethyl-1,4,6,10-tetraoxaspiro[4.5] decane were shown to be due to energy differences between the chair and boat orientations of the six-membered ring and contribution from a twist-boat conformation. Results suggest a hypothesis that intramolecular differences in chemical shift might be calculated to a greater degree of accuracy than chemical shifts calculated relative to a standard.

The effectiveness of two sonic and two ultrasonic scaler tips in furcations.

This study compared the effectiveness of two sonic and two ultrasonic scaler tips on artificial calculus removal from the furcations of mandibular first and second molars. Twenty-four extracted mandibular molars were cleaned and randomly assigned to one of four treatment groups. Teeth were split buccal lingually, artificial calculus was placed in the furcation areas, and the teeth were photographed with a stereo camera. Teeth were reconnected with bonding material and mounted in a typodont with simulated gingiva and attached to a dental chair. Teeth were instrumented with either a Cavitron TFI10 tip, Cavitron EWPP tip, Titan-S Universal tip, or Titan-S Sickle tip by a licensed dental hygienist until each tooth was judged calculus free to the touch with a CH3 explorer. Time for each instrumentation period was recorded. Following instrumentation, the teeth were again split and photographed. Stereophotogrammetry was used to produce tracings of the teeth with initial calculus and remaining calculus. Pre-instrumentation and post-instrumentation amounts of calculus on the surface area were computed using the Bioquant system. A two factor analysis of variance was conducted followed with a Newman-Keuls Multiple Comparison Technique to test for within and between differences. Significant differences (P less than or equal to 0.01) were found between pre- and post-amounts of calculus for all tips. No significant differences (P less than or equal to 0.05) were found between the four instrument tips with respect to percentage of furcation surface with calculus remaining. No differences were found between tips with regard to the time required to clean the test surfaces.

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 manufacturer's 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.

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.

Microtensile testing of dentin adhesives.

OBJECTIVES: This study was conducted in order to compare the microtensile and shear bond strengths of five commercial dentin adhesive systems. Scotchbond Multipurpose with maleic acid (SM), Scotchbond Multipurpose with phosphoric acid (SP), Scotchbond Multipurpose Plus (SBP), Clearfil Liner Bond System (CL), and Prime and Bond (PB) were tested. METHODS: Thirty extracted unerupted third molars, in groups of six teeth per adhesive system, were prepared for microtensile testing. The specimens were tested following a 24 h incubation at 37 degrees C in normal saline. Shear bond testing was performed on 35 additional teeth, using seven teeth per adhesive system. After testing, the fracture sites were observed using light microscopy and a scanning electron microscope to determine the type of failure involved. RESULTS: The microtensile test results (mean +/- SD) were SM, 24.6 +/- 7.2 MPa; SP, 28.8 +/- 11.8 MPa; SBP, 22.7 +/- 6.5 MPa; PB, 25.5 +/- 9.4 MPa; and CL, 36.8 +/- 10.0 MPa. A Bonferroni post-hoc test showed significantly (p < 0.05) greater strength for CL compared to SM, SP, SBP, and PB. The shear bond strength test results were SM, 19.4 +/- 4.4 MPa; SP, 24.5 +/- 8.4 MPa; SBP, 15.3 +/- 4.9 MPa; PB, 23.2 +/- 7.1 MPa; and CL, 24.8 +/- 3.5 MPa. No statistically significant differences were found among the shear bond strength test results. The shear bond test produced significantly more failures within dentin and composite than the microtensile method. SIGNIFICANCE: It is concluded that the microtensile test produced a more definitive assessment of adhesive bond strength than the shear bond test. Microtensile testing showed CL to be significantly stronger than SM, SP, SBP, and PB (p < 0.05).