Effect of food-simulating solvents on flexural properties of bulk-fill resin composites.

PURPOSE: This study evaluated the flexural strength of bulk-fills after immersion in food-simulating solvents. METHODS: Four overlapping segments along both sides of bar-shaped specimens (25 × 2 × 2 mm) made from bulk-fill composite were irradiated with an Elipar LED light-curing (1,200 mW/cm2 for 20 s) device. The specimens were then divided into four groups (n = 20), according to storage media-namely, distilled water, 99% ethanol, heptane, and methyl ethyl ketone-at 37oC for 4 weeks. Flexural testing was done with a universal testing machine at a crosshead speed of 1 mm/min. RESULTS: Data were analyzed with the two-way and one-way ANOVA and post-hoc Tukey (HSD) tests (P < 0.05), along with the Weibull statistic. Flexural properties significantly differed in relation to the bulk-fill and solvent used. The flexural properties of bulk-fills decreased in solvents. SonicFill in distilled water had the highest values for flexural properties (σf = 165.77 MPa; Ef = 10.3 GPa), followed by the values for SonicFill in ethanol and those for X-tra base and everX Posterior in water. Venus Bulk Fill in methyl ethyl ketone yielded the lowest values (σf = 74.11 MPa; Ef = 3.06 GPa). CONCLUSION: The flexural properties of bulk-fills are affected by the food-simulating solvent used and by the filler content, type, and resin component.

The effect of a bioglass paste on enamel exposed to erosive challenge.

OBJECTIVES: The current study is evaluating the effect of using a 45S5 bioglass paste and topical fluoride application on the cross sectional micro-hardness and the chemical surface changes of eroded enamel. METHODS: Enamel discs were obtained from the buccal surface of one hundred extracted human non-carious third molars. The enamel surfaces were ground flat and each disc was coated with two layers of acid resistant nail varnish except for an exposed treatment window (3mm×2mm) on the buccal surface of the tooth. All specimens were challenged for 60 min by orange juice (Tropicana, Chicago, USA) pH 3.85+0.5. The specimens were divided into four groups: the 45S5 bioglass paste group, fluoride gel group (5 min application), fluoride gel group (24h application) while the rest of specimens served as control. The cross-sectional micro-hardness of 20 specimens from each group was measured. Five specimens from each group had their top eroded enamel surfaces examined by SEM-EDS. One-way ANOVA was used to compare the cross-sectional micro-hardness of the three groups p<0.05. RESULTS: 45S5 bioglass paste application significantly improved the sub-surface eroded enamel when compared to fluoride and control specimens (p<0.05). CONCLUSION: 45S5 bioglass paste can efficiently improve the micro-hardness of the sub-surface eroded enamel surface. CLINICAL SIGNIFICANCE: The use of the 45S5 Bioglass paste can be used efficiently as a potent remineralizing agent for the sub-surface enamel lesions resulting from erosive challenges.

Viscoelastic stability of resin-composites aged in food-simulating solvents.

OBJECTIVE: To study time-dependent viscoelastic deformation (creep and recovery) of resin-composites, after conditioning in food-simulating solvents, under a compressive stress at 37°C. METHODS: Five dimethacrylate-based composites: (Spectrum TPH, Premise Body, Tetric Ceram HB, Filtek P60, X-tra fil), and two Ormocers (Experimental Ormocer V 28407, Admira) were studied. Three groups of cylindrical specimens (4mm×6mm) were prepared and then conditioned in 3 solvents: methyl ethyl ketone (MEK), ethanol, and water for 1 month at 37°C. The compressive creep-strain under 35MPa in 37°C water was recorded continuously for 2h and then the unloaded recovery-strain was monitored for another 2h. The data were analyzed by one-way ANOVA and Bonferroni's test. RESULTS: The materials all exhibited classic creep and recovery curves, with most parameters being significantly different (p<0.0001) for each solvent condition. All materials showed lower creep-strain in water than in ethanol or MEK solvents. Maximum creep-strain and permanent-set gave negative linear-regression (r(2)>0.98) with logarithm of the solvent solubility-parameter. The % mean (SD) creep-strain ranged from a minimum of 0.82 (0.01) for the Exp. Ormocer in water to the maximum of 4.19 (0.30) for Admira in MEK. Similar trends were found for permanent-set. The dimethacrylate-based composites behaved as an intermediate group, apart from X-tra fil that had similar stability to the Exp. Ormocer. SIGNIFICANCE: The viscoelastic stability (low creep and permanent-set) of the Exp. Ormocer, compared to many dimethacrylate-based composites, in food-simulating solvents may be due to its diluent-free formulation. This was closely matched by a highly-filled dimethacrylate material (X-tra fil).

Sorption and solubility characteristics of self-adhesive resin cements.

OBJECTIVE: The aim of this in vitro study was to evaluate some sorption characteristics [sorption (S), solubility (SL) and the percentages of mass change (M(g)%), solubility (SL%) as well as sorbed liquid (S%)] of self-adhesive resin cements when immersed in distilled water and lactic acid. METHODS: A disc-shaped specimen of each self-adhesive resin cements [G-Cem (GC), SmartCem™ 2 (SC2), RelyX™ U100 (R1), RelyX™ Unicem 2 (RU2)] were prepared in a split-Teflon mold and irradiated by an Optilux 501 light cure at 580mW/cm(2) for 40s in eight overlapping sections each side. The volume of each specimen was calculated and placed inside a desiccator containing anhydrous calcium chloride, then weighed on an analytical electronic balance. Two independent groups were established according to the immersion media or liquids (distilled water and 0.01M lactic acid) maintained at 37°C for the time intervals: 1, 6, 12, 24, 48 and 168h, where the sorption (S) property (µg/mm(3)) was calculated. However, the SL, M(g)%, SL% and S% were measured after 168h of immersion. The data were statistically analyzed by repeated measures ANOVA, one-way ANOVA and post hoc Tukey's test (p<0.05). RESULTS: Analysis of variance revealed highly significant differences between the materials for the sorption and solubility values examined with some exceptions (p<0.05). However, independent samples T-test expressed significant differences of all the sorption values between both water and lactic acid media for the resin cements with some border significances (p>0.05). The highest liquid's sorption was exhibited by GC material after immersion in lactic acid for 168h period followed by SC2 (37.83 and 34.15µg/mm(3), respectively), while the lowest sorption was presented by RU2 cement after 1h immersion period in water (3.89µg/mm(3)). Stereomicroscope showed homogenous surface topography in RU2 and R1 samples, while some striated cracks and microvoids were observed in GC and SC2 materials, respectively. The SL values followed this order: RU2

Effect of finishing/polishing systems on the surface roughness of novel posterior composites.

PURPOSE: The aim of this in vitro study was to evaluate and compare the surface finish of some direct posterior resin composites with new novel ones, which are based on a resin matrix other than the ordinary dimethacrylate, after fine finishing and polishing with eight different systems. MATERIALS AND METHODS: Forty-eight disk-shaped specimens of the posterior composites were prepared in a split Teflon mold and irradiated by an Astralis 10 light cure (560 mW/cm(2) for 10 seconds) at four quadrants on each sample's side. The specimens were divided into eight groups according to the designed finishing and/or polishing protocols. The surface roughness in the form of surface finish (Ra) was recorded using a contact profilometer. The surface of the specimens was observed under the scanning electron microscope. RESULTS: Analysis of variance revealed highly significant differences between the materials for the Ra roughness parameter at each finishing and polishing system used (p < 0.05). On the one hand, Filtek P90 (3M ESPE Dental Products, Seefeld, Germany) and Definite (Degussa, Dental Centrum, Hanau, Germany) provided the smoothest surface finish (Ra) when they were finished and polished with a series of Sof-Lex pop-on disks (3M ESPE Dental Products) and Astropol (Ivoclar Vivadent, Schaan, Liechtenstein), respectively. On the other hand, Filtek P60 (3M ESPE Dental Products) presented the roughest surface when it was finished with Fini disks (Jeneric/Pentron Clinical Technologies, Wallingford, CT, USA). Scanning electron microscope images indicated a uniform surface topography for Filtek P90 with most finishing/polishing systems. Contrary to CompoSite polishers (Shofu Inc., Kyoto, Japan), Astropol showed the smoothest surface finish with most of the investigated composites. CLINICAL SIGNIFICANCE The smoothest surface finish was achieved by most of the finishing/polishing systems investigated specifically on cationic (Filtek P90) and organically modified ceramics (Definite) composites compared with dimethacrylate-based composites, suggesting their successful clinical use.