Bonding durability of silorane and methacrylate-based resins to enamel.

AIM: Few studies compared the silorane and mechacrylate based resins bonded to enamel. The aim of this study was to evaluate the bonding durability of silorane and methacrylate-based resins to enamel. METHODS: Twenty seven molars were divided into G1 Clearfil SE Bond/Filtek Z350; G2 Adper Easy One/Filtek Z350; and G3 P90 Adhesive System/Filtek P90 groups. Following application of adhesive systems, blocks of composites were built, samples were stored in water (24 hours/37 ºC), sectioned (0.8 mm²) and tested in tensile (24 hours and 6 months). Fractures were observed (40×). Bond strength (in MPa) was analysed by MANOVA General Linear Model and Tukey's post-hoc test at 5%. The power test was calculated. The etching pattern was observed. RESULTS: There were differences for material (P=0.029), storage time (P=0.012) and their interaction (P=0.000). Similar bond strengths were found at 24 h for all. The bond strength of G1 decreased after 6 months. At 6 months, G2 showed higher bond strength than G1 and G3, that were similar. The power-test value was 0.87. Mixed fractures and enamel rods were observed. CONCLUSION: Bond strength varied over time depending on the restorative system.

Influence of different photo-activation distances on cytotoxicity of a dental adhesive model resin.

AIM: This study evaluated the cytotoxicity of a dental bonding model resin (DBMR) submitted to different photo-activation distances. METHODS: A monomer mixture based on Bis-GMA and HEMA was used to assess the cytotoxicity in a mouse fibroblast-cell line. To promote different photo-activation distances glass slides were interposed between DBMR surface and halogen light curing unit (LCU) tip. Afterwards, the specimens were immersed in RPMI culture medium for 24 h to obtain extracts. The extracts were incubated in contact with the cells for 24 h. Finally, an MTT colorimetric assay was used to assess the cytotoxicity. The cell viability data (absorbance) were analyzed by one way ANOVA followed by Tukey's test (P<0.05). RESULTS: The light output decreased according to the increase in the number of glass slides between the halogen LCU tip and DBMR surface. Yet, the distance between the tip of the curing light system and the specimens had significant influence on the cytotoxicity. All extracts produced by groups submitted to different photo-activation distances showed cytotoxic effect after 24h of incubation. CONCLUSION: The photo-activation distance and the interposition of glass slides between LCU tip and DBMR was shown to play an important role in the cytotoxic effect.

Influence of the volume of composite and photoactivation method on push-out bond strength and Knoop hardness of a resin composite.

AIM: The aim of this paper was to evaluate the influence of modulated photoactivation methods and volume of composite on Knoop hardness (KHN) and push-out bond strength (PBS) of Filtek Z350 to root dentin. METHODS: Three volumes (small, medium and large) of composite were bulk inserted in cavities prepared in 90 premolars. The specimens were photoactivated with continuous light, pulse-delay, or soft-start methods and submitted to PBS and KHN tests. The failure pattern was evaluated in stereomicroscope after the bond strength test. The data were submitted to two-way ANOVA and Tukey's test (P<0.05). RESULTS: Modulated photoactivation methods showed a higher PBS than continuous method (P<0.05). Medium volume of composite showed higher PBS than small and large volumes when photoactivated with continuous method (P<0.05). Pulse-delay significantly increased KHN for medium and large volumes in comparison to continuous method (P<0.05). Medium volume of composite showed KHN significantly higher than small and large volumes (P<0.05). CONCLUSION: The volume of composite influenced the PBS and KHN of resin composites. Pulse-delay showed the highest bond strength to dentin, as well KHN similar to the conventional method. The analysis of the failure pattern showed predominance of adhesive failure.

Effect of polymerization cycles on the linear dimensional change, hardness and impact strength of denture base acrylic resins.

AIM: This study verified the effect of polymerizing cycles on the linear dimensional change, hardness and impact strength of denture acrylic resins. METHODS: One hundred and twenty samples (N.=10) each for the Classico and Vipi acrylic resins were made according to the manufacturers' instructions. The polymerization cycles were: 1- water bath at 74 ºC for 9 hr; 2- water bath at 74ºC for 8 hr and temperature increased to 100 ºC for 1 hr; 3- water bath at 74 ºC for 2 hr and temperature increased to 100 ºC for 1 hr; and 4- water bath at 120ºC and 60 pounds pressure for 1 hr. Samples were deflasked after flask cooling and submitted to finishing. Linear distances between referential points in the samples were measured at deflasking and after water storage for 7 and 30 days with a comparator microscope with an accuracy of 0.0005 mm. Knoop hardness test was accomplished in a durometer with a load of 25 gf for 10 sec and an average of three indentations was considered for the sample hardness. Impact strength (kgf/cm²) was measured by the Charpy system with load of 40 kpcm. Data were submitted to ANOVA and Tukey's test (5%). RESULTS: Dimensional changes in the A-B and A-C distances, hardness values and impact strength for Classico and Vipi resins were differently influenced by the polymerization cycles, when deflasking and water storage for 7 and 30 days were considered. CONCLUSION: Linear dimensional change, hardness and impact strength of denture acrylic resins were differently affected by the polymerization cycles.

Comparison between two methods to evaluate temperature changes produced by composite light curing units and polymerization techniques.

AIM: This study evaluated the temperature change into the pulp chamber during the light curing of composite resin by direct (bovine tooth) and indirect (matrix) methods. METHODS: Direct method: fifty standardized cavities (2x2x2 mm) were prepared in bovine incisors, which were randomly assigned to evaluation of the temperature changes in the pulp chamber. Indirect method: temperature changes were evaluated through a dentine slice of 1.0 mm thickness in a elastomer cubic mold (2x2x2 mm). Filtek Z250 composite resin (3M/ESPE) was photo-activated using three light curing units: quartz-tungsten-halogen (QTH) by continuous, soft-start or intermittent light modulations; light emitting diode (LED); and plasma arc-curing (PAC). Ten groups (N.=10) were established according to technique evaluation and photo-activation methods. All experiments were carried out in a controlled environment (37 °C and 50 ± 10% relative humidity). The temperature changes were recorded using a digital thermometer attached to a type-K thermocouple in contact with the dentin slice (indirect method) or in contact with the axial wall (dentin) of pulp chamber (direct method). The results were submitted to ANOVA and Tukey's test (α=0.05). RESULTS: Temperature changes were statistically higher for the matrix indirect method (2.56 ºC) than bovine teeth direct method (1.17ºC). The change temperature was statistically higher for the PAC (1.77 ºC) when compared to other photo-activation modes in bovine teeth direct method. CONCLUSION: The two methods of temperature evaluation were different, however indirect method detected the higher temperature increase. Higher energy density arising from the light curing units and polymerization techniques promoted higher temperature increase.