Effect of bioactive borate glass microstructure on bone regeneration, angiogenesis, and hydroxyapatite conversion in a rat calvarial defect model.

Borate bioactive glasses are biocompatible and enhance new bone formation, but the effect of their microstructure on bone regeneration has received little attention. In this study scaffolds of borate bioactive glass (1393B3) with three different microstructures (trabecular, fibrous, and oriented) were compared for their capacity to regenerate bone in a rat calvarial defect model. 12weeks post-implantation the amount of new bone, mineralization, and blood vessel area in the scaffolds were evaluated using histomorphometric analysis and scanning electron microscopy. The amount of new bone formed was 33%, 23%, and 15%, respectively, of the total defect area for the trabecular, oriented, and fibrous microstructures. In comparison, the percent new bone formed in implants composed of silicate 45S5 bioactive glass particles (250-300µm) was 19%. Doping the borate glass with copper (0.4 wt.% CuO) had little effect on bone regeneration in the trabecular and oriented scaffolds, but significantly enhanced bone regeneration in the fibrous scaffolds (from 15 to 33%). The scaffolds were completely converted to hydroxyapatite within the 12week implantation. The amount of hydroxyapatite formed, 22%, 35%, and 48%, respectively, for the trabecular, oriented, and fibrous scaffolds, increased with increasing volume fraction of glass in the as-fabricated scaffold. Blood vessels infiltrated into all the scaffolds, but the trabecular scaffolds had a higher average blood vessel area compared with the oriented and fibrous scaffolds. While all three scaffold microstructures were effective in supporting bone regeneration, the trabecular scaffolds supported more bone formation and may be more promising in bone repair.

Silorane resin supports proliferation, differentiation, and mineralization of MLO-A5 bone cells in vitro and bone formation in vivo.

Methyl methacrylate used in bone cements has drawbacks of toxicity, high exotherm, and considerable shrinkage. A new resin, based on silorane/oxirane chemistry, has been shown to have little toxicity, low exotherm, and low shrinkage. We hypothesized that silorane-based resins may also be useful as components of bone cements as well as other bone applications and began testing on bone cell function in vitro and in vivo. MLO-A5, late osteoblast cells, were exposed to polymerized silorane (SilMix) resin (and a standard polymerized bisGMA/TEGDMA methacrylate (BT) resin and compared to culture wells without resins as control. A significant cytotoxic effect was observed with the BT resin resulting in no cell growth, whereas in contrast, SilMix resin had no toxic effects on MLO-A5 cell proliferation, differentiation, nor mineralization. The cells cultured with SilMix produced increasing amounts of alkaline phosphatase (1.8-fold) compared to control cultures. Compared to control cultures, an actual enhancement of mineralization was observed in the silorane resin-containing cultures at days 10 and 11 as determined by von Kossa (1.8-2.0 fold increase) and Alizarin red staining (1.8-fold increase). A normal bone calcium/phosphate atomic ratio was observed by elemental analysis along with normal collagen formation. When used in vivo to stabilize osteotomies, no inflammatory response was observed, and the bone continued to heal. In conclusion, the silorane resin, SilMix, was shown to not only be non cytototoxic, but actually supported bone cell function. Therefore, this resin has significant potential for the development of a nontoxic bone cement or bone stabilizer.

Estimation of properties of a photoinitiated silorane-based composite with potential for orthopaedic applications.

We have synthesized a filler-reinforced silorane composite that has potential applications in orthopaedic surgery, such as for a bone stabilizer. The purpose of the present work was to develop a method for estimating four properties of this material; namely, maximum exotherm temperature, flexural strength, flexural modulus, and fracture toughness. The method involved the use of mixture design-of-experiments and regression analysis of results obtained using 23 formulations of the composite. We validated the estimation method by showing that, for each of four composite formulations that were not included in the method development, the value of each of the aforementioned properties was not significantly different from that obtained experimentally. Our estimation method has the potential for use in the development of a wide range of orthopaedic materials.

Effects of simulated functional loading conditions on dentin, composite, and laminate structures.

Use of composite restorations continues to increase, tempered by more potential problems when placed in posterior dentition. Thus, it is essential to understand how these materials function under stress-bearing clinical conditions. Because mastication is difficult to replicate in the laboratory, cyclic loading is frequently used within in vitro evaluations but often employs traditional fatigue testing, which typically does not simulate occlusal loading because higher stresses and loading frequencies are used, so failure mechanisms may be different. This investigation utilized relevant parameters (specimen size, loading frequency) to assess the effects of cyclic loading on flexural mechanical properties and fracture morphology of (coronal) dentin, composite, and dentin-adhesive-composite "laminate" structures. Incremental monitoring of flexural modulus on individual beams over 60,000 loading cycles revealed a gradual increase across materials; post hoc comparisons indicated statistical significance only for 1 versus 60k cycles. Paired specimens were tested (one exposed to 60k loading cycles, one to static loading only), and comparisons of flexural modulus and strength showed statistically significantly higher values for cyclically loaded specimens across materials, with no observable differences in fracture morphology. Localized reorganization of dentin collagen and polymer chains could have increased flexural modulus and strength during cyclic loading, which may have implications toward the life and failure mechanisms of clinical restorations and underlying tooth structure.

Fluoride prophylactic agents effect on ceramic bracket tie-wing fracture strength.

OBJECTIVE: To test the hypothesis that fluoride prophylactic agents do not affect the fracture strength and fracture morphology of the tie-wing complex of ceramic brackets. MATERIALS AND METHODS: The fracture strength of the distal incisal tie-wing of two polycrystalline brackets, Clarity and Mystique, and a monocrystalline bracket, Inspire, was measured after the brackets were exposed to either Prevident, Phos-flur gel, or distilled water (control). Scanning electron microscopy was used to qualitatively evaluate the tie-wing intact and fractured surfaces. RESULTS: A two-way analysis of variance and Fisher-Hayter post hoc test, alpha = .05, indicated a significant decrease in tie-wing fracture strength following both fluoride treatments when compared with the distilled water control only with the monocrystalline bracket. None of the bracket brands exhibited any qualitative differences in the tie-wing intact or fracture surfaces as a function of fluoride treatment. CONCLUSIONS: The hypothesis is rejected. Based on the results, using topical fluoride agents with monocrystalline brackets might be contraindicated because of increased tie-wing fracture susceptibility.

Subgingival microbiologic effects of one-time irradiation by CO2 laser: a pilot study.

BACKGROUND: Third-generation carbon dioxide (3-CO(2)) lasers have handpieces that accommodate a periodontal insert that permits irradiation directly into the periodontal pocket/sulcus. The purpose of this pilot study was to evaluate, by scanning electron microscopy (SEM), the surface effects of 3-CO(2) laser treatment on the root surfaces and soft tissues and to investigate the effects of 3-CO(2) laser on periodontal pathogenic bacteria compared to negative controls. METHODS: Five patients with chronic periodontitis and treatment planned for a maxillary immediate denture were included in the study. Periodontal pockets with a mean probing depth of 5.5 +/- 0.8 mm were irradiated one time by CO(2) laser (wavelength of 10,600 nm) at a power of 2.2 W, 50 Hz, an 80-millisecond pulse length, and an exposure rate of 1 mm per 5 seconds. DNA analysis of eight periodontal bacteria was performed on samples collected from laser-treated and control sites prior to and immediately following treatment and was compared between groups. In addition, block biopsies, including soft tissue, were harvested for SEM examination. RESULTS: SEM examination of test group specimens showed heat damage on the soft tissues in three of 17 specimens (17.6%). In addition, 11.7% (two of 17) of the 3-CO(2)-treated teeth exhibited localized slight damage to root surfaces. Microbiologic results of the control sites indicated that 90.6% of the bacterial counts remained the same, 6% increased, and 3% decreased. In the test group, 71.25% of the bacterial count analyses for the eight different periodontal microbes remained the same, 12.50% increased, and 16.25% decreased. CONCLUSION: A one-time use of the 3-CO(2) laser in periodontal pockets did not sterilize or substantially reduce subgingival bacterial populations compared to negative controls.

Rescue of odontogenesis in Dmp1-deficient mice by targeted re-expression of DMP1 reveals roles for DMP1 in early odontogenesis and dentin apposition in vivo.

Dentin matrix protein 1 (DMP1) is expressed in both pulp and odontoblast cells and deletion of the Dmp1 gene leads to defects in odontogenesis and mineralization. The goals of this study were to examine how DMP1 controls dentin mineralization and odontogenesis in vivo. Fluorochrome labeling of dentin in Dmp1-null mice showed a diffuse labeling pattern with a 3-fold reduction in dentin appositional rate compared to controls. Deletion of DMP1 was also associated with abnormalities in the dentinal tubule system and delayed formation of the third molar. Unlike the mineralization defect in Vitamin D receptor-null mice, the mineralization defect in Dmp1-null mice was not rescued by a high calcium and phosphate diet, suggesting a different effect of DMP1 on mineralization. Re-expression of Dmp1 in early and late odontoblasts under control of the Col1a1 promoter rescued the defects in mineralization as well as the defects in the dentinal tubules and third molar development. In contrast, re-expression of Dmp1 in mature odontoblasts, using the Dspp promoter, produced only a partial rescue of the mineralization defects. These data suggest that DMP1 is a key regulator of odontoblast differentiation, formation of the dentin tubular system and mineralization and its expression is required in both early and late odontoblasts for normal odontogenesis to proceed.

Adhesive analysis of voids in Class II composite resin restorations at the axial and gingival cavity walls restored under in vivo versus in vitro conditions.

OBJECTIVES: Adhesive analysis, under the scanning electron microscope of microtensile specimens that failed through the adhesive interface, was conducted to evaluate the amount of voids present at the axial versus gingival cavity walls of class II composite restorations restored under in vivo and in vitro conditions. METHODS: Five patients received class II resin composite restorations, under in vivo and in vitro conditions. A total of 14 premolar teeth yielded 59 (n=59) microtensile adhesive specimens that fractured through the adhesive interface. The fractured surfaces of all specimens were examined and the % area of voids was measured. RESULTS: Voids at the adhesive joint were highly predictive of bond strengths. An increase in the number of voids resulted in a decrease in the microtensile bond strength. The area of voids at the adhesive interface was as follows: in vivo axial 13.6+/-25.6% (n=12); in vivo gingival 48.8+/-29.2% (n=12); in vitro axial 0.0+/-0.0% (n=19) and in vitro gingival 11.7+/-17.6% (n=16). SIGNIFICANCE: Composite resin may bond differently to dentin depending upon the amount of voids and the cavity wall involved. The bond to the gingival wall was not as reliable as the bond to the axial wall. An increase in the amount of surface voids was a major factor for reducing microtensile bond strengths of adhesive to dentin.

Properties of silorane-based dental resins and composites containing a stress-reducing monomer.

OBJECTIVE: To evaluate properties of silorane-based resins and composites containing a stress reducing monomer. METHODS: Resin mixtures and composites were formulated containing (a) a developmental stress reducing monomer [TOSU; Midwest Research Institute]; (b) Sil-Mix (3M-ESPE); (c) photo cationic initiator system. Standard BISGMA/TEGDMA resin (B/T) and composite (Filtek Z250) were used as controls. Polymerization volume change was measured using a NIST mercury dilatometer and polymerization stress using an Enduratec mechanical testing machine. Three point bend tests determined flexural elastic modulus, work of fracture, and ultimate strength (ADA 27; ISO 4049). Fracture toughness was measured using ASTM E399-90. Four groups of resins and composites were tested: Sil-Mix, methacrylate standard, and Sil-Mix with two addition levels of TOSU. An ANOVA was used and significant differences ranked using Student-Newman-Keuls test (alpha=0.05). RESULTS: Polymerization stress values for resins containing TOSU were significantly less than the other materials. Polymerization shrinkage values for Sil-Mix formulations were significantly less than for B/T, but were not different from each other. TOSU-containing formulations generally had somewhat lower mechanical properties values than Sil-Mix or B/T. Polymerization stress values for Sil-Mix-based composites were significantly less as compared to Z250. The 1wt.% TOSU composite had the lowest stress. No difference between composite groups was noted for fracture toughness or work of fracture. For ultimate strength, the 5wt.% TOSU formulation differed significantly from Z250. All Sil-Mix formulations had elastic modulus values significantly different from Z250. SIGNIFICANCE: The ability of TOSU to reduce polymerization stress without a proportional reduction in mechanical properties provides a basis for improvement of silorane-based composites.

In vitro microtensile bond strength of four adhesives tested at the gingival and pulpal walls of Class II restorations.

BACKGROUND: The authors compared the microtensile bond strength of teeth restored with four adhesives at the gingival and pulpal cavity walls of Class II resin-based composite restorations. METHODS: Five pairs of extracted third molars received two Class II preparations/restorations in each tooth. The authors randomly assigned each preparation to one of four adhesive groups: Adper Scotchbond Multipurpose Dental Adhesive (SBMP) (3M ESPE, St. Paul, Minn.), Clearfil SE Bond (CFSE) (Kuraray America, New York City), Prime & Bond NT (PBNT) (Dentsply Caulk, Milford, Del.) and PQ1 (Ultradent, South Jordan, Utah). They restored the teeth and obtained microtensile specimens from each cavity wall. Specimens were tested on a testing machine until they failed. RESULTS: The mean (+/- standard deviation) bond strengths (in megapascals) were as follows: SBMP (pulpal), 36.4 (17.2); SBMP (gingival), 29.7 (15.3); CFSE (pulpal), 50.8 (13.6); CFSE (gingival), 50.2 (14.0); PBNT (pulpal), 38.3 (19.2); PBNT (gingival), 38.9 (17.7); PQ1 (pulpal), 58.7 (8.7); and PQ1 (gingival), 54.5 (18.5). A two-way analysis of variance found an adhesive effect (P < .001) but no location effect (P >.05). CONCLUSIONS: PQ1 and CFSE performed the best. The results showed no significant difference in microtensile bond strength at the gingival wall versus the pulpal wall. CLINICAL IMPLICATIONS: Under in vitro conditions, a total-etch ethanol-based adhesive (PQ1) failed cohesively more often than did the other adhesives tested.

Marginal adaptation of Cerec 3 CAD/CAM composite crowns using two different finish line preparation designs.

PURPOSE: The purpose of this study was to compare marginal discrepancies of Cerec 3 CAD/CAM composite crowns, fabricated on human prepared teeth with two different finish line designs, chamfer and shoulder. MATERIALS AND METHODS: Sixteen human molar teeth were used to prepare full crowns. Eight teeth were prepared with a 1-mm-wide chamfer finish line and the other eight with a 1.2- to 1.5-mm circumferential shoulder. Cerec 3 crowns were fabricated from optical impressions using Paradigm MZ100 composite polymer. Marginal adaptation was evaluated in two ways: (1) using modified United States Public Health Service (USPHS) criteria to evaluate eight preselected sites on each crown margin, and (2) using scanning electron microscopy (SEM) to measure marginal gaps on all four axial walls with 15 measurements on each wall (60 measurements per crown). An evaluation of the number of acceptable crowns, determined by having all measured sites per tooth with margin gap size less than 100 microm, as a function of finish line design was also conducted. RESULTS: In both chamfer and shoulder groups, there were only two crowns (out of eight) with clinically acceptable ratings for all eight measurement sites according to USPHS criteria. Fisher's chi-square analysis showed that there was no statistically significant difference in marginal adaptability as a function of finish line design ( p>0.05). With SEM imaging, overall mean marginal gaps for the chamfer group were 65.9+/-38.7 microm (range 35.0 to 130.0 microm), and for the shoulder group were 46.0+/-9.2 microm (range 26.3 to 55.6 microm); this difference was not found to be statistically significant ( p>0.05). While crown assessment based on mean marginal discrepancy measurements indicated that both the chamfer and shoulder groups were considered clinically acceptable (<100 microm); crown acceptability based on all measurement sites being less than 100 mum indicated that in the chamfer and shoulder groups there were four and three acceptable crowns out of eight, respectively. The Fisher's chi-square test indicated no statistically significant difference between the groups ( p>0.05). An agreement rate of 81.2% was calculated between the two evaluation methods, modified USPHS criteria and SEM measurements. CONCLUSIONS: Based on mean marginal discrepancy measurements, the typical marginal assessment technique, Cerec 3 Paradigm MZ100 crown restorations appear to have acceptable marginal adaptability (mean discrepancies <100 microm). Thus, the evidence from this investigation would suggest that the finish line preparation design had no effect on marginal adaptation for Cerec 3 composite crowns.

Stability of silorane dental monomers in aqueous systems.

UNLABELLED: Siloranes (silicon-based monomers with oxirane functionality) are investigated as matrix resins for new low shrinkage/stress dental composites. Compounds containing oxirane groups are known to be reactive with water, which could impart instability to the composite. OBJECTIVE: To test the stability of siloranes by measuring changes in the chemical structure of the oxirane group in aqueous environments. METHODS: Two siloranes (PH-SIL and TET-SIL) and their 1:1 mixture (SIL-MIX) were evaluated (n=2-3). Siloranes were mixed in aqueous solutions with and without 1% tetrahydrofuran (THF) containing either liver esterase or epoxide hydrolase at pH 7.4, or dilute HCl at pH 1.4. The stability of conventional dioxiranes 3,4-epoxycyclohexyl-methyl-3,4-epoxycyclohexane carboxylate (ECHM-ECHC), and bisphenol A diglycidyl ether (BADGE) were also monitored under similar conditions. NMR was used to estimate the extent of reaction and give structural information about reaction products. RESULTS: Siloranes were found to be stable for 24h in all aqueous environments tested. In contrast, ECHM-ECHC reacted at pH 1.4 to form species containing oxirane, ester, hydroxyl and carboxylic acid groups. Water hydrolyzed the ester group of ECHM-ECHC in the presence of liver esterase. In the presence of epoxide hydrolase, BADGE oxirane groups were hydrolyzed to diols, hydrolysis ranged from 0 to 34% depending on the aqueous environment. CONCLUSION: The stability and insolubility of siloranes in biological fluid simulants suggests that these may be more suitable for use in the oral environment than conventional oxirane-functional monomers.

Quantum-Mechanical QSPR Models for Polymerization Volume Change of Epoxides and Methacrylates Based on Mercury Dilatometry Results.

Polymerization volume change (PVC) was measured systematically using mercury dilatometry for 41 epoxide and methacrylate monomers with quartz filler. Quantitative structure property relationship (QSPR) models were developed based on this previously unreported data to gain insight in the data collection method for future models. Successful models included only data from those samples which polymerized to hardness. The most significant descriptors in these models related to monomer reactivity. In contrast, PVC data collected under experimental conditions which maximized monomer conversion resulted in descriptors describing size and branching, indicating conversion must be considered for future PVC measurements. A Rule of Mixtures (ROM) correction term improved correlations of the dilatometer data with varying quartz content, and an adjustment for conversion may similarly enable inclusion of data which had not polymerize to hardness.

Quantum mechanical structure-activity relationship analyses for skin sensitization.

Allergic contact dermatitis (ACD) results in inflammation of the skin due to sensitization of the immunologic system to a particular substance. The sensitization process is limited by the compound's ability to both permeate and react with proteins in the integumentary system. Currently, only in vivo animal tests such as the local lymph node assay (LLNA) are recognized by regulatory authorities for risk assessment of ACD. A quantitative structure-activity relationship has been developed to predict relative potency, which allows for the prediction of relative sensitization potentials. The experimental values used in this study include EC3 values (the concentration at which the stimulation index equals 3) from LLNA tests. The predictions in this model enable categorization of the compounds into three groups on the basis of risk of sensitization and enable screening of candidate molecules using rapid SAM1 semiempirical calculations prior to animal testing. The model may also be used to reduce the number of animals subjected to testing by providing estimated concentrations required for useful data of risk assessment. The effect of averaging available literature values on predictive ability is also investigated. The model includes halogenated compounds, aromatic compounds, alcohols, aldehydes, and ketones. The computational investigation resulted in a two-descriptor model that is consistent with the assumed mechanism for sensitization.

An application of the QM-QSAR method to predict and rationalize lipophilicity of simple monomers.

OBJECTIVES: The goal of this study is to develop a model used to predict octanol/water partition coefficients (log P(o/w)) values for a variety of potential dental materials. In this way, a primary consideration for potential toxicity and a rough estimate of solubility in various environments can be obtained. METHOD: The AM1 semiempirical quantum mechanical method (in AMPAC) was used to compute chemical data for all compounds in the study. CODESSA then imported the chemical information from AMPAC and computed a large set of informational descriptors. A quantitative structure activity relationship (QSAR) model was derived correlating experimental results from a training set of molecules with certain of the descriptors computed above. RESULTS: A training set of 92 molecules was used to derive the QSAR model and three descriptors were obtained: the molecular surface area, the total dipole moment of the molecule, and FPSA-3 (fractional atom charge weighted partial positive surface area). Various quality indicators were also computed and all fell within acceptable ranges: R(2)=0.945; adjusted R(2)=0.943; R(cv)(2)=0.940; variance inflation factors (VIF) for the descriptors above are 1.116, 1.044, and 1.162, respectively. SIGNIFICANCE: This QSAR model can be used to accurately and rapidly predict log P(o/w) values for a wide variety of small organic molecules, including potential dental monomers.

Photopolymerization of developmental monomers for dental cationically initiated matrix resins.

OBJECTIVES: The objectives were to investigate the structure and selected physical properties of products resulting from the photopolymerization of a binary mixture containing an aliphatic dioxirane, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (ECHM-ECHC) and a potential expanding monomer, 3,9-bis(oxiranylcyclohexylmethyl)-1,5,7,11-tetraoxaspiro[5.5]undecane (BOCHM-TOSU). METHODS: Reaction mixtures were irradiated with a dental curing lamp at room temperature. Some reactions were quenched prior to gel point. Oligomeric products were separated from unreacted monomers by column chromatography, and analyzed by NMR. Physical properties of polymeric solids were measured using accepted standard methods. Protonation energies for monomers were calculated using semi-empirical quantum mechanical methods. RESULTS: Types of oligomers found included poly(ether)s and poly(carbonate)s. Quantum mechanical calculations indicated preferential attack at the more nucleophilic oxaspirocyclic ring sites. For cured solid polymer samples, the elastic modulus was 2.39 +/- 0.24 GPa and the fracture toughness was 0.73 +/- 0.10 MPa m(1/2). These values were similar to those measured for a cured conventional BISGMA/TEGDMA matrix resin. SIGNIFICANCE: The room-temperature photopolymerization of an aliphatic dioxirane and a potential expanding monomer demonstrates the possibility of making cross-linked copolymer resins with improved polymerization shrinkage characteristics for use in dental composites.

In vitro mutagenicity and metabolism of the cycloaliphatic epoxy Cyracure UVR 6105.

Cyracure UVR 6105 is a cycloaliphatic epoxy monomer and has both carboxylate and epoxy groups, with the potential for rapid polymerization. It is widely used in industry for the preparation of inks, resins, coatings, and was proposed for incorporation into dental composites. The objective of this study was to determine the mutagenic potential of this chemical related to its metabolite products. Several doses of Cyracure UVR 6105 were dissolved in DMSO and subjected to the Ames Salmonella mutagenicity assay. A metabolic activation system (S9-mix) was used consisting of Arochlor-induced liver S9 homogenate enriched with NADP and glucose-6-phosphate cofactors. In contrast to studies without S9-mix, Cyracure UVR 6105 exhibited enhanced genotoxic activities with strains TA100 and TA1535 in the presence of liver S9-mix. From in vitro metabolism of Cyracure UVR 6105 with S9-mix, as used in the Ames assay, several metabolites were identified. The alcohol metabolite, 3,4-epoxycyclohexylmethanol, containing intact epoxy group was identified in the organic solvent extract. This metabolite was synthesized and proved to be mutagenic against TA100 when assayed in the presence and absence of S9-mix. Results showed that the increased mutagenicity of Cyracure UVR-6105 in the presence of liver enzymes is due to the formation of the mutagenic metabolite 3,4-epoxycyclohexylmethanol.

In vivo versus in vitro microtensile bond strength of axial versus gingival cavity preparation walls in Class II resin-based composite restorations.

BACKGROUND: Gingival margins in Class II composite restorations are a site of frequent failure. The purpose of the authors' study was to compare the microtensile dentin bond strength of gingival and axial restored cavity preparation walls of Class II composite restorations under in vivo and in vitro conditions. METHODS: After obtaining informed consent, the authors placed Class II resin-based composite restorations in 14 premolar teeth from five patients, under in vivo or in vitro conditions. The teeth were sectioned to obtain rectangular specimens from axial and gingival walls with a surface area of approximately 0.5 square millimeter. The authors tested 85 microtensile adhesive samples from the 14 teeth on a testing instrument (Universal Instron, Model 125, Instron, Canton, Mass.) until failure. RESULTS: The mean (+/- standard deviation) mircotensile dentin bond strengths in mega-pascals were as follows: in vivo axial, 36.5 (14.9); in vivo gingival, 17.6 (11.6); in vitro axial, 49.5 (13.9); in vitro gingival, 34.0 (13.1). A two-way analysis of variance found a statistically significant difference between in vitro and in vivo conditions and between the axial and gingival walls (P < or = .001). Eighty-eight percent of the fractured samples involved the adhesive layer as observed under scanning electron microscopy up to x2,500. Seventeen of the gingival samples and two of the axial samples debonded during the preparation phase and could not be tested. CONCLUSION: The dentinal microtensile strength of adhesive/resin-based composite bonded to the gingival wall was significantly weaker than the bond to the axial wall, and in vivo conditions produced significantly weaker bond strengths than did in vitro conditions. CLINICAL IMPLICATIONS: The dentinal adhesive bond of resin-based composite to gingival walls is significantly weaker and thus more subject to failure than the bond to axial walls. In vitro bond strength studies may overestimate the bond strength of adhesives in in vivo applications.

Genotoxicity assessment of oxirane-based dental monomers in mammalian cells.

The potential use of oxirane (epoxy) monomers in dental composite development raises the concern to test their genetic safety. Oxiranes can interact with DNA resulting in DNA damage, mutations, and possibly carcinogenesis. Our objective was to evaluate DNA damage and cell-cycle disruption in mammalian cells after exposure to epoxy monomers. The experimental oxiranes were Araldite trade mark GY 281, Cyracure trade mark UVR 6105 and 1,3-dioxane-2,2'-1,3-dioxane-5',4'-bicyclo[4.1.0] heptane (DECHE-TOSU). L929 fibroblast cells were incubated with the monomer for 7 and 24 h at 37 degrees C/5% CO(2). After incubation, cells were subjected to DNA damage alkaline unwinding assay and flow cytometry cell-cycle analysis. Lack of DNA damage and cell-cycle effects were observed with DECHE-TOSU. Exposure to subtoxic doses of Araldite trade mark GY 281 or Cyracure trade mark UVR 6105 caused DNA damage and cell cycle disruption. A significant (p < 0.01) effect for Araldite trade mark GY 281 was observed with cell populations in G1 and G2/M when compared to DMSO solvent control. Similar comparisons revealed significant differences in G2/M cell cycle population after 24-h exposure to 100 microM Cyracure trade mark UVR 6105. For comparison, BISGMA was evaluated to produce DNA damage but without cell-cycle effects suggesting DNA repair mechanisms were effective. Our findings with DECHE-TOSU, Araldite trade mark GY 281 and Cyracure trade mark UVR 6105 indicated cell-cycle disruption followed DNA damage.

An in-vitro microtensile test of Scotchbond Multi-Purpose adhesive applied at different priming times.

Adhesive bonding to dentin can fail if the dentin is too wet during application of the bonding resin. This study compared the in vitro 24-hour microtensile bond strength of teeth restored at four different priming times at the gingival cavity wall of Class II resin composite restorations. After IRB approval, six pairs of extracted third molars (yielding 12 teeth) received a proximal Class II prep/restoration in each tooth. Each pair was from the same patient. Four treatment groups were randomly assigned for each pair. The treatment groups were: TM-primer applied and dried according to manufacturer's directions; T30-primer allowed to dry for an additional 30 seconds; T60-primer dried for an additional 60 seconds; T120-primer dried for an additional 120 seconds. The teeth were restored with 3M ESPE Scotchbond Multi-Purpose Dental Adhesive and 3M ESPE Z100 Restorative. Manufacturers' directions were followed except for the additional primer dwelling times. The teeth were sectioned to obtain rectangular specimens with a surface area of approximately 0.5 mm2. Samples were tested on the Instron at 1.0 mm/minute until failure. The results in megapaschals were TM (n=15) 25.5+/-12.2; T30 (n=14) 22.7+/-13.6; T60 (n=15) 28.1+/-14.7; T120 (n=20) 27.7+/-15.2. Samples that debonded during the preparation phase and could not be tested from each group were TM=5, T30=6, T60=5, T120=1. A one-way ANOVA found no statistically significant difference between groups. Ninety percent of the samples broke through the adhesive layer as observed under the scanning electron microscope at 2000x. A chi square analysis found no difference in the number of debonds between groups. Increasing the primer drying time did not increase the microtensile bond strength of adhesive bonded to the dentin gingival wall.