Objectives: To evaluate surface characteristics of seven flowable (f) or condensable (c) conventional (cv) and polyacid-modified (pm) composite resins after a 196-day-storage in four artificial saliva solutions. Methods: Each 75 specimens were made from the following composite resins: Flowline (f, cv)=I, Tetric Flow (f, cv)=II, Revolcin Flow (f, cv)=III, Dyract flow (f, pm)=IV, Dyract AP (c, pm)=V, Tetric Ceram (c, cv)=VI, Revolcin Fil (c, cv)=VII according to the manufacturersx instructions. 24h after polymerization, each 3 randomly selected samples were stored in 5 mL of one of the following media: distilled water, acidic buffer/pH 4.2, neutral buffer/pH 7.0, and neutral buffer supplemented with 1.6 u/mL porcine liver esterase. Each assay was repeated five times. Dry-stored specimens of each material served as controls. Surface microhardness (Vickers) and surface roughness (Ra) of 5 randomly selected samples per medium and composite were determined prior to wet storage (baseline), and then after 24, 96, and 144h, 8, 14, 28, 56, 112, and 196 days. Results were statistically evaluated by an ANOVA using Scheffe-tests (p < 0.05). Results: Vickers hardness of all materials except for product I was significantly reduced due to storage in artificial salivas in comparison to baseline and to dry-stored controls (p < 0.05). Surface hardness of flowable materials was significantly lower in comparison to condensable composites (p < 0.05). In addition, all flowable cv-composites revealed a significantly higher Vickers hardness compared to the flowable pm-material. No significant changes of surface roughness dependent on storage condition or time were observed (p < 0.05). Conclusions: From our results we conclude that the surface microhardness of flowable composite resins, specifically of the tested poly-acid modified material, is significantly lower in comparison to condensable composites.

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