The purpose of this study was to assess the background color-interceptive ability and opacity of opaque shade composites (Universal composite, Filtek Z350, Charisma, Clearfil ST, Palpaque Estelite, Esthet-X, and Metafil Flo).

Twenty four background specimens (diameter 5.5 mm, thickness 3.0 mm) with Root dentin Mustard (Bisco, Schaumburg, IL, USA) were made. The CIE L^*a^*b^* value of background specimens was measured by a spectrophotometer (Spectrolino, GretagMacbeth, Regensdorf, Switzerland). Three specimens in every group were filled on the background specimens. The surface color of samples was measured by a spectrophotometer in 3.0 mm and every thickness to 0.5 mm while grinding. The color difference in the background color along with 3.0 mm specimen gauged the masking effect in each thickness while grinding and polishing. The opacity was calculated in 1 mm thick specimens.

The opacity was in the decreasing order of Clearfil ST, Metafil Flo, Filtek Z350, Palpaque Estelite, Universal composite, Charisma, and Esthet-X (p < 0.05). As the thickness get reduced, L^* value showed decreasing, a^* increasing tendency. The surface color difference between pair of the 3.0 mm thick specimen and after grinding in same opaque resin was above 3.3 except Clearfil ST and Metafil Flo. The color difference (ΔE^*) between pair of background specimen and opaque resin builtup specimen showed more than 10.0 regardless kinds and thickness.

The variance in opacity characteristics and color of the opaque composites is dependent upon manufacturer. When using the opaque resin, the optical properties of each material must be considered as well as cavity.

The purpose of this study was to evaluate the effect of increasing application time of single bottle adhesives (SBA) to microtensile bond strength (MTBS) of dried dentin. To expose the superficial dentin surfaces, human molars were sectioned perpendicular to the long axis of tooth. 32% phosphoric acid gels were applied for 15s and rinsed. The teeth were randomly assigned to 3 groups ; S group (Single Bond), O group (One-Step), P group (Prime & Bond NT). Each group was divided to 3 subgroups (W: dentin wipe with wet gauge and light cured immediately, D: dentin dried for 30s and light cured immediately, 30: dentin dried for 30s and light cured after applying SBA for 30s). Composite resin was built up on the dentin surface and sectioned to obtain 20 specimens with 1 mm² cross sectional area and the MTBS was measured.

For Single Bond, the mean MTBS of S-W and S-30 group were higher than that of S-D group statistically (P < 0.05). For One-Step, the mean MTBS of O-D group was statistically lower than that of O-W group (P < 0.05). For Prime & Bond NT, the mean MTBS of P-30 group was statistically lower than that of P-D group (P < 0.05).