The mixed d Do patients and dentists differ in accuracy of shade selection ? d To what extent do the instruments match the color perception of the human eye ?

One of the most challenging tasks in dentistry is selecting a shade for a restoration in a single maxillary central incisor. From a functional aspect, the correct shade of a crown has little importance in the success of the restoration, but it often is the foremost factor in patient acceptance. More than 80 percent of patients with an anterior metal ceramic restoration were aware of a shade mismatch relative to the adjacent natural tooth. Restoration remakes owing to shade mismatches can be a financial burden to all involved. Shade selection normally is accomplished by means of visual comparison of the selected tooth with shade tabs from commercially available shade guides. This process usually is quick and cost effective. Also, the clinician’s ability to discriminate tooth color can be improved with training and experience. However, shade selection is limited in part to the clinician’s understanding of color science and is more subjective than objective. Color perception varies between people and within a person over time. Approximately 8 percent of men and 0.5 percent of women have a color-vision defect or difficulty differentiating reds and greens. Our purpose in this study was to evaluate the accuracy of four commercially available dental clinical spectrophotometers in comparison with the accuracy of human evaluators. Additionally, we investigated the influence of ambient lighting and the evaluator’s color acuity in shade selection. We addressed four investigative questions in this study: formance on a relative scale. For example, to reduce the risk of marginal gaps, shrinkage and shrinkage stress should be kept to a minimum. VOCO’s x-tra fill, which is a bulk-fill composite, showed the lowest volumetric shrinkage value, and the high-viscosity SonicFill and flowable SureFil SDR flow (both bulk fills) had the lowest value for polymerization shrinkage stress as compared with the other resin-based composites. In contrast with the lower values preferred for polymerization shrinkage and shrinkage stress, higher values are preferred for fracture toughness (the ability to resist fracture) and fracture work (the ability to resist growth of a crack), both of which give an idea of the product’s durability. VOCO’s x-tra fill had a high fracture toughness. That product rated similarly to the others in terms of fracture work. Venus Bulk Fill had the highest fracture work measurement. Color stability is an important feature for resin-based composites. We tested these restoratives to ensure that they maintained their color in wet and dry environments. Two products—Tetric EvoCeram Bulk Fill and x-tra fill—showed variation in color after 30 days’ storage in water. All other products maintained color according to visual inspection by three independent observers (A.T., G.G.Z., A.H.). In addition to the previously described properties, we measured radiopacity as part of our laboratory evaluation. The average radiopacity of dentin is equivalent to 1.11 mm of aluminum (Al) and of enamel is equivalent to 2.05 mm Al. All tested products exhibited a radiopacity value greater than 1 mm Al, which is required by the standard. Conclusions. In this evaluation, we compared several properties of bulk-fill versus multiincrement–fill resin-based composites and found performance of restoratives in both categories to be acceptable according to an international standard, with the exception of depth of cure and hardness. Three of the bulk-fill resin-based composites (SonicFill, Tetric EvoCeram Bulk Fill and Alert Condensable Composite) did not achieve adequate depth of cure when tested according to the standard. All products but one (Alert Condensable Composite) demonstrated adequate hardness after curing in a subsequent test (Knoop hardness test). With the exception of depth of cure and Knoop hardness, we found the laboratory performance of bulk-fill resin-based composites to be comparable to that of traditional multi-increment–fill resinbased composites. n