Contraction stress and physical properties development of a resin-based composite irradiated using modulated curing methods at two C-factor levels

OBJECTIVES

The objective of this study was to verify the influence of curing methods on contraction stress, stress rate and degree of conversion (DC) of a restorative composite at two C-factor levels.

METHODS

For the stress test, composite was applied between two for 15 min from diameter glass rods mounted in a servohydraulic machine, and stress was monitored for 10 min from the beginning of light curing. Stress rates were calculated as the change in stress versus time at each second. DC was measured by micro-FTIR. Four curing methods were tested at two C-factor levels (1.5 and 3.0): continuous light (CL), soft-start (SS) and two pulse delay methods using different initial irradiances--150 mW/cm(2) (PD150) and 80 mW/cm(2) (PD80). Results were analyzed by ANOVA and Tukey's test (alpha=0.05).

RESULTS

For the stress test, at CF 1.5, PD80 presented the lowest mean value, statistically different from the others. PD150 also showed a mean value statistically inferior to CL. At CF 3.0, no statistical difference was observed among CL, SS and PD150. PD80 presented statistically lower stress values compared to CL and SS. Stress values at CF 3.0 were statistically higher than those at CF 1.5 for all curing methods. CL presented the highest maximum stress rate, followed by SS, PD150 and PD80, for both C-factors. In the DC test, no difference was observed among the methods and between the C-factor levels.

SIGNIFICANCE

Modulated curing methods were shown to be effective in reducing contraction stress rate, without compromising the DC of the restorative composite. C-factor was shown to influence negatively the stress rate and the amount of stress generated.

Modulated photoactivation methods—Effect on marginal and internal gap formation of restorations using different restorative composites

This study evaluated the effect of modulated photoactivation methods on gap formation of restorations using different composites.

METHODS

Sixty human third molars were selected, sectioned (two fragments), and ground to expose a flat enamel area. A cavity (5 mm long x 2 mm wide x 2 mm deep--outer margins in enamel and inner margins in dentin) was prepared on the central area of flattened surface. Single bond adhesive system was applied according to manufacturer's instructions. The specimens were assigned into 12 groups (n = 10), according to the restorative composite (Filtek Z250, Herculite XRV, and Heliomolar) and the photoactivation method [continuous light (CL); soft-start (SS); pulse delay (PD); and intermittent light (IL)]. Outer margins were stained using Caries Detector, observed under stereomicroscope, and images were transferred to a computer measurement program. Then, the specimens were sectioned in slices and the internal gaps were assigned using the same method. The length of gaps was expressed as a percentage of total length of the margins. Data (internal adaptation) were submitted to ANOVA and Tukey's test.

RESULTS

All restorations showed perfect seal of the enamel outer margins. Modulated photoactivation methods (SS, PD, and IL) showed a significant reduction on internal gap formation when compared with CL, regardless of the composite. Filtek Z250 showed the best internal adaptation, regardless of the photoactivation method.

CONCLUSION

Modulated photoactivation methods decrease the internal gap formation of composite restorations, and should be encouraged on clinical practice.

ExoU-induced procoagulant activity in Pseudomonas aeruginosa-infected airway cells

The present study addressed the question whether ExoU, a Pseudomonas aeruginosa toxin with phospholipase A2 (PLA2) activity, may induce airway epithelial cells to overexpress tissue factor (TF) and exhibit a procoagulant phenotype. Cells from the human bronchial epithelial BEAS-2B line were infected with an ExoU-producing P. aeruginosa strain, pre-treated or not with the cytosolic PLA2 inhibitor methylarachidonyl fluorophosphate (MAFP), or with two ExoU-deficient mutants. Control noninfected and infected cells were assessed for the expression of: 1) TF mRNA by RT-PCR; 2) cell-associated TF by enzyme immunoassay and flow cytometry; 3) procoagulant activity by a colorimetric assay; and 4) microparticle-associated TF by flow cytometry. An enzyme immunoassay was also used to assess cell-associated TF in lung extracts from mice infected intratracheally with ExoU-producing and -deficient bacteria. Cells infected with the wild-type bacteria had higher levels of TF mRNA, cell-associated TF expression, procoagulant activity and released microparticle-associated TF than cells infected with the mutants. Bacterial treatment with MAFP significantly reduced the expression of TF by infected cells. Lung samples from mice infected with the wild-type bacteria exhibited higher levels of cell-associated TF and procoagulant activity. The present results demonstrate that ExoU may contribute to the pathogenesis of lung injury by inducing a tissue factor-dependent procoagulant activity in airway epithelial cells.

Comparative evaluation of Knoop hardness and depth of cure of ORMOCER based resin composites

The purpose of this study was to evaluate the Knoop hardness and the depth of cure of Ormocer based composites and to compare them with traditional Bis-GMA or derivatives based composites. Four composite were selected: Two Ormocer based (Definite and Admira), a hybrid (Z250) and a microfilled (A110). Cylindrical specimens with 3mm in diameter for 5mm in height were prepared in a metallic mould and photoactived according the manufacturer’s instructions with the curing light unit XL2500 (3M/ESPE). After, they were stored for 24 hours at 37ºC. Knoop hardness measures were obtained with Micro hardness tester HMV (Shimadzu-Japan), with a load of 50g for 15s. Five specimens were made for each resin composite and three Knoop hardness measurements were obtained on surface, 1mm, 2mm, 3mm and 4mm depths. The results were submitted to ANOVA and Tukey’s test at 5% level. According to the results, at all depths, Z250 was harder than the others composites. The composites Definite, Admira and A110 had no statistical differences in KHN until the depth of 2mm, after A110 showed decrease in hardness values. Generally, for all tested materials the deeper layers showed lower Knoop hardness values than those of the surface. Compared with hardness surface, statistically significant reductions in KHN occurred at depths of 2mm for Z250 and A110 and 3mm for Definite and Admira. It could be concluded that ORMOCER based materials showed intermediated hardness values and satisfactory depth of cure, when compared to the conventional composites.

Influence of different flasking and polymerizing methods on the occlusal vertical dimension of complete dentures

The flasking and polymerization technique for resins can introduce stresses during processing which may lead to denture base distortions, artificial teeth displacement and increases in the occlusal vertical dimension (OVD). This study investigated whether the association of microwave heat-activation (MH) and bimaxillary flasking (BF) minimizes the possible increases in OVD after prostheses processing. Forty pairs of complete dentures were waxed with the artificial teeth in closed occlusion and divided into four groups according to investing and heating methods: G1 (control) = monomaxillary/water bath; G2 = monomaxillary/microwave; G3 = bimaxillary/water bath and G4 = bimaxillary/microwave. OVD was measured using a digital caliper before and after prostheses processing. Results were submitted to statistical analysis (Student's t-test for multiple comparisons and post hoc ANOVA, alpha = 0.05). Comparison of values before and after processing showed that OVD increased in all groups after polymerization (p < 0.001), regardless of flasking and polymerization methods. Statistically, G2 had the greatest difference in OVD when compared to G1 (p = 0.014), G3 (p = 0.019) and G4 (p = 0.024). G3 and G4 showed similar results statistically when compared to G1 (control). Both investing and heating methods resulted in an increase in OVD after processing. However, the prostheses invested in bimaxillary flasks showed the lowest changes in OVD, regardless of the polymerization method.