Unrestricted linear dimensional changes of two hard chairside reline resins and one heat-curing acrylic resin

The selection and use of hard chairside reline resins must be made with regard to dimensional stability, which will influence the accuracy of fit of the denture base. This study compared the dimensional change of two hard chairside reline resins (Duraliner II and Kooliner) and one heat-curing denture base resin (Lucitone 550). A stainless steel mold with reference dimensions (AB, CD) was used to obtain the samples. The materials were processed according to the manufacturer's recommendations. Measurements of the dimensions were made after processing and after the samples had been stored in distilled water at 37° C for eight different periods of time. The data were recorded and then analyzed with analysis of variance. All materials showed shrinkage immediately after processing (p < 0.05). The only resin that exhibited shrinkage after 60 days of storage in water was Duraliner II; these changes could be clinically significant in regard of tissue fit.

Water sorption, solubility, and bond strength of two autopolymerizing acrylic resins and one heat-polymerizing acrylic resin.

STATEMENT OF PROBLEM: Because water sorption of autopolymerizing acrylic reline resins is accompanied by volumetric change, it is a physical property of importance. As residual monomer leaches into the oral fluids and causes tissue irritation, low solubility of these resins is desired. Another requirement is a satisfactory bond between the autopolymerizing acrylic resins and the denture base acrylic resin. PURPOSE: This study compared the water sorption, solubility, and the transverse bond strength of 2 autopolymerizing acrylic resins (Duraliner II and Kooliner) and 1 heat-polymerizing acrylic resin (Lucitone 550). MATERIAL AND METHODS: The water sorption and solubility test was performed as per International Standards Organization Specification No. 1567 for denture base polymers. Bond strengths between the autopolymerizing acrylic resins and the heat-polymerizing acrylic resin were determine with a 3-point loading test made on specimens immersed in distilled water at 37 degrees C for 50 hours and for 30 days. Visual inspection determined whether failures were adhesive or cohesive. RESULTS: Duraliner II acrylic resin showed significantly lower water sorption than Kooliner and Lucitone 550 acrylic resins. No difference was noted in the solubility of all materials. Kooliner acrylic resin demonstrated significantly lower transverse bond strength to denture base acrylic resin and failed adhesively. The failures seen with Duraliner II acrylic resin were primarily cohesive in nature. CONCLUSIONS: Autopolymerizing acrylic reline resins met water sorption and solubility requirements. However, Kooliner acrylic resin demonstrated significantly lower bond strength to denture base acrylic resin.

Phase behavior of synthetic amphiphile vesicles investigated by calorimetry and fluorescence methods

The understanding of biological membranes may be improved by investigating physical properties of vesicles from natural or synthetic amphiphiles. The application of vesicles as mimetic agents depends on the knowledgment of their structure and properties. Vesicles having different curvature and size may be obtained using different preparation protocols. We have used differential scanning calorimetry (DSC) and steady-state fluorescence to investigate the gel to liquid-crystal phase transition of vesicles prepared by sonication (SUV) and non-sonication (GUV) of the synthetic dioctadecyldimethylammonium bromide (DODAB) in aqueous solution. DSC thermograms for a non-sonicated dispersion show a well-defined pre- and main transition corresponding to two narrow peaks at 36 and 45°C in the first upscan, while in a second upscan, only the main peak was observed. The sharpness of the peaks indicate a cooperative phase behavior for GUV. For a sonicated DODAB dispersion, the first upscan shows a third peak at 40.3°C, whereas for the second upscan the peaks are not well-defined, indicating a less cooperative phase behavior. Alternatively, the fluorescence quantum yield (Φ f) and the anisotropy (r) of trans, trans, trans-1-[4-(3-carboxypropyl)-phenyl]-6-[4-butylphenyl]-1,3,5-hexatriene (4H4A) and the ratio I 1/I 3 of the first to the third vibronic peaks of the pyrene emission spectrum as function of temperature are used as well to describe the phase behavior of DODAB sonicated and non-sonicated dispersions. It is in good agreement with the DSC results that the cooperativity of the thermotropic process is diminished under sonication of the DODAB dispersion, meaning that sonication changes from homogeneous to heterogeneous populations of the amphiphile aggregates. The pre- and main transitions obtained from these techniques are in fairly good accord with results from the literature.

Tensile bond strengths of hard chairside reline resins as influenced by water storage

Due to gradual resorption of the edentulous ridge bone, removable prostheses often require denture base relines to improve fit and stability. This research evaluated the bond strength between one heat-cured acrylic resin (Lucitone 550®) and two hard chairside reline resins, after two different periods of storage in water (50 h and 30 days). The bond strength was evaluated using a tensile test. The mode of failure, adhesive or cohesive, was also recorded. The results submitted to the Kruskal-Wallis test indicated that the highest tensile strengths were achieved with intact Lucitone 550® denture base resin in both periods of storage in water. After 50 h of storage in water, Duraliner II® reline material exhibited the highest bond strength to the denture base resin. After 30 days of storage in water, Duraliner II® reline resin demonstrated a significant reduction in adhesion, showing lower tensile bond strength than Kooliner® material. Both hard chairside reline materials failed adhesively across Lucitone 550® denture base resin, in both periods of time. © 1999 Blackwell Science Ltd.

Biocompatibility of two current adhesive resins

The purpose of the study was to evaluate the biocompatibility of two current adhesive resins and a calcium hydroxide cement. Fifty-four polyethylene tubes were filled with these dental materials, which were hand-mixed or light-cured according to the manufacturer's directions: group 1-Clearfill Liner Bond 2 (Kuraray); group 2-Single Bond (3M); and group 3-calcium hydroxide cement (Dycal-Dentsply). The materials were implanted into dorsal connective tissue of rats, which were killed 7, 30, and 60 days after the implantation procedure. The implant sites were excised, immersed in buffered Karnovsky's fixative, and processed using routine histological techniques. Sections of 6 μm thickness were stained with hematoxylin and eosin and assessed under light microscopy. Both adhesive resins at 7 days elicited a moderate/intense inflammatory reaction that decreased over time. Fibrous capsules surrounding the tubes were observed at 30 days. Half of the samples in groups 1 and 2 showed thin fibrous capsule formation containing macrophages, capillaries, lymphocytes, fibroblasts, and collagen fibers. Connective tissue healing was observed even though many specimens exhibited a persistent inflammatory reaction mediated by macrophages and giant cells at the 60-day evaluation. Dycal allowed complete healing at 30 days with only a thin fibrous capsule. In conclusion, all experimental materials were successfully walled off by the connective tissue of the rat. However the adhesive resins may release particulates that may, in turn, induce a persistent local inflammatory reaction. Consequently, in this specific condition, these materials cannot be regarded as biocompatible. Dycal was less irritating than the adhesive resins and was better tolerated by the connective tissue. Copyright © 2000 by The American Association of Endodontists.

Toxicity of synthetic piperonyl compounds to leaf-cutting ants and their symbiotic fungus

The development of Leucoagaricus gongylophorus, the fungus cultured by the leaf-cutting ant Atta sexdens was inhibited in vitro by synthetic compounds containing the piperonyl group. In addition, worker ants that were fed daily on an artificial diet to which these compounds were added had a higher mortality rate than the controls. The inhibition of the fungal growth increased with the size of the carbon side chain ranging from C1 through C8 and decreasing thereafter. 1-(3,4-Methylenedioxybenzyloxy)octane (compound 5) was the most active compound and inhibited the fungal development by 80% at a concentration of 15 μg m1-1. With worker ants the toxic effects started with compound 5 and increased with the number of carbons in the side chain. Thus, for the same concentration (100 μg m1-1) the mortality rates observed after 8 days of diet ingestion were 82%, 66% and 42%, for 1-(3,4-methylenedioxybenzyloxy)decane, 1-(3,4-methylenedioxybenzyloxy)dodecane and compound 5, respectively, whereas with commercial piperonyl butoxide the mortality was 68%. The latter compound, which is known as a synergist insecticide, was as inhibitory to the symbiotic fungus as the synthetic compound 5. The possibility of controlling these insects in the future using compounds that can target simultaneously both organisms is discussed. © 2001 Society of Chemical Industry.

In vitro cytotoxicity of some natural and semi-synthetic isocoumarins from Paepalanthus bromelioides

Numerous natural compounds have a potential for therapeutic applications, but may have to be chemically modified to alter toxic side effects. We investigated structural parameters that could affect the cytotoxicity of isocoumarins similar to 9,10-dihydroxy-5,7-dimethoxy-1H-naphtho(2,3c)pyran-1-one (paepalantine 1). Paepalantine 1 has antimicrobial activity, as well as significant in vitro cytotoxic effects in the McCoy cell line. Two other natural and two semi-synthetic isocoumarins with similar structures obtained from the capitula of Paepalanthus bromelioides were tested on the same cell line by the neutral red assay. Substitution of the 9 and/or 10-OH group made these compounds less cytotoxic.

Light-induced electric dipole relaxation in synthetic and natural alexandrite

We present results of thermally stimulated depolarization current (TSDC) measurements in synthetic and natural alexandrite, which show TSDC bands related to the presence of electric dipoles in both types of samples. Synthetic material shows a wide TSDC band with a peak at 179 K, which can be fitted by two distinct relaxing dipole distributions. For natural alexandrite the TSDC band has a maximum around 195 K and can be fitted by three different distributions. Both samples present one of the calculated curves with a peak about 179 K, with activation energy of 0.57 eV and constant relaxation time of 1 × 10-14 sec. Photo-induced TSDC shows that TSDC bands can also be generated by simultaneous application of light and an electric field at 77 K.

Evaluation of marginal microleakage in Class II cavities: Effect of microhybrid, flowable, and compactable resins

Objective: The goal of the present study was to evaluate the microleakage on the cementum/dentin and enamel surfaces in Class II restorations, using different kinds of resin composite (microhybrid, flowable, and compactable). Method and materials: Forty human caries-free molars were extracted and selected. Eighty Class II standardized cavities were made in the cervical wall at the cementoenamel junction (CEJ) and at the mesial and distal surfaces. The teeth were divided into four groups: G1 - adhesive system + microhybrid resin composite Z100; G2 - adhesive system + compactable resin composite Prodigy Condensable; G3 - adhesive system + flowable resin composite Revolution + Z100 resin composite; G4 - adhesive system + Revolution fluid resin + compactable resin composite Prodigy Condensable. The adhesive system used in this study was Scotchbond Multi-Purpose Plus. The specimens were thermocycled in baths of 5°C and 55°C for 1,000 cycles and immersed in 50% silver nitrate solution. The specimens then were sectioned and evaluated on degree of dye penetration. Results: The results were evaluated using the nonparametric Kruskall-Wallis test, which showed a statistically significant difference between groups G1 and G4, G2 and G4, and G3 and G4. Conclusions: None of the materials was able to eliminate the marginal microleakage at the cervical wall; the application of a low-viscosity resin composite combined with a compactable resin composite significantly decreased the microleakage.

Polymerization shrinkage evaluation of three packable composite resins using a gas pycnometer.

Modern restorative dentistry has been playing an outstanding role lately since composite resins, allied to adhesive systems, have been widely applied on anterior and posterior teeth restorations. The evolution of composite resins has mostly been verified due to the improvement of their aesthetic behavior and the increase in their compressive and abrasive strengths. In spite of these developments, the polymerization shrinkage inherent to the material has been a major deficiency that, so far, has been impossible to avoid. Using a gas pycnometry, this research investigated the polymerization shrinkage of three packable composite resins: Filtek P60 (3M), Prodigy Condensable (Kerr), and SureFil (Dentsply/Caulk), varying the distance from the light source to the surface of the resins (2 mm or 10 mm). The pycnometer Accupyc 1330 (Micromeritics, USA) precisely records helium displacement, allowing fast and reliable measurements of the volume of composite resin immediately before and after polymerization, without interference of temperature or humidity. Results were not found to be statistically different for the three tested resins, either for 2 mm or 10 mm-distance from the light source to the composite surface.

Effectiveness of Microwave Sterilization on Three Hard Chairside Reline Resins

Purpose: The aim of this study was to evaluate the effectiveness of microwave irradiation sterilization on hard chairside reline resins. Materials and Methods: Specimens of three reline resins (Kooliner, Tokuso Rebase, and Ufi Gel Hard) were fabricated and subjected to ethylene oxide sterilization. The specimens were then individually inoculated (107 cfu/mL) with Tryptic Soy Broth media containing one of the tested microorganisms (C albicans, S aureus, B subtilis, and P aeruginosa). After 48 hours at 37°C, the samples were vortexed for 1 minute and allowed to stand for 9 minutes, followed by a short vortex to resuspend any organisms present. After inoculation, 40 specimens of each material were immersed in 200 mL of water and subjected to microwave irradiation at 650 W for 6 minutes. Forty non-irradiated specimens were used as positive controls. Replicate specimens (25 μL) of suspension were plated at dilutions of 10-3 to 10-6 on plates of selective media appropriate for each organism. All plates were incubated at 37°C for 48 hours. After incubation, colonies were counted, and the data were statistically analyzed by the Kruskal-Wallis test. Twelve specimens of each material were prepared for SEM. Results: All immersed specimens showed consistent sterilization of all the individual organisms after microwave irradiation. SEM examination indicated an alteration in cell morphology after microwave irradiation. Conclusion: Microwave sterilization for 6 minutes at 650 W proved to be effective for the sterilization of hard chairside reline resins.

Cytotoxicity of denture base resins: Effect of water bath and microwave postpolymerization heat treatments

Purpose: This study compared the effect of two postpolymerization heat treatments on the cytotoxicity of three denture base resins on L929 cells using 3H-thymidine incorporation and MTT assays. Materials and Methods: Sample disks of Lucitone 550, QC 20, and Acron MC resins were fabricated under aseptic conditions and stored in distilled water at 37°C for 48 hours. Specimens were then divided into three groups: (1) heat treated in microwave oven for 3 minutes at 500 W; (2) heat treated in water bath at 55°C for 60 minutes; and (3) no heat treatment. Eluates were prepared by placing three disks into a sterile glass vial with 9 mL of Eagle's medium and incubating at 37°C for 24 hours. The cytotoxic effect from the eluates was evaluated using the 3H-thymidine incorporation and MTT assays, which reflect DNA synthesis levels and cell metabolism, respectively. Results: The components leached from the resins were cytotoxic to L929 cells when 3H- thymidine incorporation assay was employed. In contrast, eluates from all resins revealed noncytotoxic effects as measured by MTT assay. For both MTT assay and 3H-thymidine incorporation, the heat treatments did not decrease the cytotoxicity of the materials tested. Conclusion: Resins were graded by 3H-thymidine incorporation assay as slightly cytotoxic and by MTT assay as noncytotoxic. Cytotoxicity of the denture base materials was not influenced by microwave or water bath heat treatment.

Surface roughness of packable composite resins polished with various systems

Purpose: The aim of this study was to evaluate the surface roughness of four packable composite resins, SureFil™ (Dentsply, Petrópolis, Rio de Janeiro, Brazil), Prodigy Condensable™ (Kerr Co., Orange, CA, USA), Filtek P60™ (3M do Brasil, São Paulo, Brazil), and ALERT® (Jeneric/Pentron, Inc., Wallingford, CT, USA) and one microhybrid composite resin (Filtek Z250™, 3M do Brasil) after polishing with four finishing systems. Materials and Methods: Twenty specimens were made of each material (5 mm in diameter and 4 mm high) and were analyzed with a profilometer (Perthometer® S8P, Perthen, Mahr, Germany) to measure the mean surface roughness (Ra). The specimens were then divided into four groups according to the polishing system: group 1 - Sof-Lex™ (3M do Brasil), group 2 - Enhance™ (Dentsply), group 3 - Composite Finishing Kit (KG Sorensen, Barueri, São Paulo, Brazil), and group 4 - Jiffy Polisher Cups® (Ultradent Products, Inc., South Jordan, UT, USA). The specimens were polished and then evaluated for Ra, and the data were subjected to analysis of variance, analysis of covariance, and Tukey's test (p = .05). Results: The mean Ra of SureFil polished with Sof-Lex was significantly lower than that of KG points. Prodigy Condensable polished with Enhance showed a significantly less rough surface than when polished with Sof-Lex. Filtek P60 did not exhibit a significant difference with the various polishing systems. For ALERT the lowest mean Ra was obtained with Sof-Lex and the highest mean Ra with KG points. Regarding Filtek Z250, polishing with KG and Jiffy points resulted in a significantly lower mean Ra than when polished with Enhance. Conclusions: Packable composite resins display variable roughness depending on the polishing system used; the Sof-Lex disks and Jiffy points resulted in the best Ra values for the majority of the materials tested.

Electroantennographic responses of Heterotermes tenuis (Isoptera: Rhinotermitidae) to synthetic (3Z,6Z,8E)-Dodecatrien-1-ol

The subterranean termite Heterotermes tenuis (Isoptera: Rhinotermitidae) is a pest of great importance for the Brazilian economy as it causes serious damages in commercial reforestations of Eucalyptus spp. and sugarcane cultures. (3Z,6Z,8E)-Dodecatrien-1-ol has been identified as a pheromone of some species of subterranean termites. The objective of this research was to synthesize (3Z,6Z,8E)-dodecatrien-1-ol and determine by electroantennographic (EAG) bioassays the selectivity and sensitivity of H. tenius antennae to its whole worker extract and to the synthetic triene alcohol.

Influence of light curing source on microhardness of composite resins of different shades

Introduction: The evolution of light curing units can be noticed by the different systems recently introduced. The technology of LED units promises longer lifetime, without heating and with production of specific light for activation of camphorquinone. However, further studies are still required to check the real curing effectiveness of these units. Purpose: This study evaluated the microhardness of 4 shades (B-0.5, B-1, B-2 and B-3) of composite resin Filtek Z-250 (3M ESPE) after light curing with 4 light sources, being one halogen (Ultralux - Dabi Atlante) and three LED (Ultraled - Dabi Atlante, Ultrablue - DMC and Elipar Freelight - 3M ESPE). Methods: 192 specimens were distributed into 16 groups, and materials were inserted in a single increment in cylindrical templates measuring 4mm x 4mm and light cured as recommended by the manufacturer. Then, they were submitted to microhardness test on the top and bottom aspects of the cylinders. Results: The hardness values achieved were submitted to analysis of variance and to Tukey test at 5% confidence level. It was observed that microhardness of specimens varied according to the shade of the material and light sources employed. The LED appliance emitting greater light intensity provided the highest hardness values with shade B-0.5, allowing the best curing. On the other hand, appliances with low light intensity were the least effective. It was also observed that the bottom of specimens was more sensitive to changes in shade. Conclusion: Light intensity of LED light curing units is fundamental for their good functioning, especially when applied in resins with darker shades.