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Etching enamel significantly increased the SBS of composite to enamel. Clearfil SE had significantly greater bond strength to enamel than either universal adhesive, which were not significantly different from each other.

The incorporation of prepolymerized-filler particles in hybrid resin composite systems may result in a reduction of mechanical properties. SUMMARYThis study compared the properties of newer hybrid resin composites with prepolymerizedfiller particles to traditional hybrids and a microfill composite. The following properties were examined per composite: diametral tensile strength, flexural strength/modulus, Knoop microhardness and polymerization shrinkage. Physical properties were determined for each composite group (n=8), showing significant differences between groups per property (p<0.001). In general, the traditional hybrid composites (Z250, Esthet-X) had higher strength, composites containing pre-polymerized fillers (Gradia Direct Posterior, Premise) performed more moderately and the microfill composite (Durafill VS) had lower strength. Premise and Durafill VS had the lowest polymerization shrinkage.

Purpose: The aim of this study was to examine the influence of light guide type on the distribution of irradiant emission from a light-emitting diode (LED) curing light and to measure the effect of light dispersion on surface microhardness across the top and bottom surfaces of two types of composite resins. Materials and Methods:A laser beam analyzer (LBA-700, Spiricon) was used to evaluate light distribution (Top Hat factor [THF]) across the distal surface of a standard and turbo light guide from an LED curing light (Bluephase, Ivoclar Vivadent). Composites (Z100 [hybrid], A110 [microfill]; 3M ESPE) were placed in blackened rings (2 ¥ 11 mm) and exposed at 0 mm for 5 seconds (Z100) or 15 seconds (A110) using the light guides at similar irradiance, energy density, and exit diameters (N = 5). Similar irradiance values were produced by using the turbo light guide on the "low power" setting of the curing light and the "high power" setting when using the standard light guide. THF values were analyzed with an unpaired t-test. Knoop hardness (KHN) was determined on the top and bottom surfaces (Leco) in 1-mm lateral increments from the specimen center and proceeding 4 mm in both east-west and north-south directions. The effects of the major factors (light guide type and lateral distance) on the hardness of each composite were analyzed using multiple analysis of variance (ANOVA), and a two-tailed, unpaired Dunnett's t-test determined when lateral hardness values significantly differed from that at the specimen center. The percentage difference between maximum and minimum (maxmin) hardness values for each specimen, with respect to distance from specimen center, and the percentage decrease for the standard and turbo light guides, with respect to both composite resin types, were compared using ANOVA and the Tukey's post-hoc test. Results:The standard guide had a significantly higher (i.e., more uniform light distribution) THF than did the turbo tip (p < 0.001). For the microfill, significant differences in hardness were found based on the distance from the specimen center (p < 0.0001), and with respect to the top or bottom surfaces (p < 0.0001). However, no difference was found between the two types of light guides (p = 0.939). For the hybrid, significant differences in hardness were found based on lateral distance (p < 0.001), surface (p < 0.001), and light guide type (p = 0.045).

The latest generation of LED curing lights provides DC ratios similar to or better than the halogen curing light at a curing distance of 5 mm. Dispersion of light plays a significant role in the DC of resin composite. To maximize curing effectiveness, light guides should be maintained in close proximity to the surface of the light-activated restorative material.