Effects of Polymerization Mode and Interaction with Hydroxyapatite on the Rate of pH Neutralization, Mechanical Properties, and Depth of Cure in Self-Adhesive Cements.

OBJECTIVE: The aim of the study was to evaluate the physicochemical properties of self-adhesive resin cements associated with hydroxyapatite (HAp) according to the polymerization activation. MATERIALS AND METHODS: Specimens of cements (PermaCem 2.0 [DMG]; MaxCem Elite [Kerr], and RelyX U200 [3M ESPE]) were distributed into three groups: activation mode; self-cured and dual-cured modes; and association or not with HAp powder mode. The pH neutralization was evaluated as a function of time. Flexural strength and elastic modulus were also tested (0.5 mm/min.). The depth of cure was also analyzed using the scraping test (ISO 4049). Infrared spectroscopy was also used to collect the spectra of specimens to evaluate the chemical bonds. Statistical comparisons were conducted at 5% of significance. RESULTS: The aggressiveness of the self-adhesive resin cements evaluated varied among the materials with a tendency for neutralization. Self-cure groups exhibited lower pH throughout the entire evaluation when compared with that of the dual-cure ones, irrespective of the addition of HAp. MaxCem Elite when photoactivated was the only cement influenced by the addition of the HAp in terms of mechanical properties. The self-adhesive cements tested presented equivalent depth of cure based on the ISO 4049 requirements, regardless of the evaluated factors. CONCLUSIONS: Based on the parameters evaluated, the results demonstrated that most of the self-adhesive cements remained unaltered or improved when mixed with HAp, regardless of the activation mode.

Surface morphological and physical characterizations of glass ionomer cements after sterilization processes.

The aim of this study was to investigate if sterilization methods would promote changes in the selected adhesion-related surface properties of glass ionomer cements (GICs). Riva self-cure (RSC) and Riva light-cure (RLC) GICs were tested. Thirty samples were prepared according to the type of material (RSC and RLC) and sterilization method: hydrogen peroxide gas plasma (HPGP), steam sterilization (SS), and no sterilization (n = 5 per group). A Teflon matrix (5 × 2 mm) was filled with one of the GICs to produce the samples. For the groups with the RLC material, the samples were light cured using a light curing unit for 20 s. After 24 hr, finishing and polishing were performed in all samples and then they were sterilized. Surface roughness, wettability, and micromorphology were accessed using a profilometer, a goniometer, and a scanning electron microscopy, respectively. Data were statistically analyzed through a two-way ANOVA and Tukey post-hoc test (p < .05). Both sterilization methods promoted similar roughness values to the nonsterilized samples (p > .05). HPGP decreased contact angle for RSC (p < .01), and SS increased contact angle for RLC (p < .01). Samples subjected to HPGP presented similar surface micromorphology to nonsterilized ones, regardless of the material. SS promoted exposition of smaller filler particles in both materials. Although sterilization methods did not alter surface roughness and wettability, the sterilization methods selectively altered the micromorphology of the materials tested. RESEARCH HIGHLIGHTS: This study's main finding suggests that each sterilization method altered the surface of glass ionomers in different ways. Thus, the choice of sterilization methods prior to bacterial adhesion can lead to a bias in antimicrobial studies.

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.

UNLABELLED: 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.

Minimally invasive dentistry: bond strength of different sealant and filling materials to enamel.

PURPOSE: The purpose of this study was to evaluate the shear bond strength of different sealant and filling materials, used in minimally invasive dentistry, to human enamel. MATERIALS AND METHODS: Thirty-five sound extracted third molars were selected. The crowns were longitudinally sectioned, embedded in polystyrene resin, and grounded until a flat enamel surface was reached. The samples were assigned into seven groups (n = 10), according to the materials: G1-Fluoroshield; G2-Clinpro; G3-Dyract AP; G4-F2000; G5-Vitremer; G6-Fuji IX; G7-Vidrion F. All materials were applied according to the manufacturer's instructions. The samples were stored in distilled water at 37 degrees C for 24 h and submitted to a shear bonding strength test in a universal testing machine with a crosshead speed of 0.5 mm/min. The failure sites were observed in Scanning Electron Microscopy (SEM). The data were submitted to ANOVA and Tukey's tests (p < 0.05). RESULTS: The mean values (MPa) of shear bond strength were for Fluroshield (25.92 +/- 8.83), Vitremer (20.41 +/- 13.34), Dyract AP (17.08 +/- 6.38), Clinpro (12.82 +/- 8.38), F2000 (8.71 +/- 3.74), Fuji IX (7.64 +/- 2.57), and Vidrion F (4.54 +/- 2.11). Fluroshield resin sealant and Vitremer resin modified glass-ionomer showed statistically higher shear bond strength values than the conventional glass ionomer (GIC) cements. Clinpro and F2000 showed bond strength values with statistical difference only from Fluroshield. The failure mode varied among the groups. The majority of samples presented mixed failure. CONCLUSION: FluroShield and Vitremer showed better performance of shear bond strength to enamel than conventional GIC.