| Objective:The porcelain laminate veneer(PLV) has became a better prosthodontic treatment method in the anterior region for it’s minimal preparation volume, natural appearance, color stability and excellent property in esthetics and biocompatibility. While the cha llenge with veneer restorations is difficult to achieve ideal color for there have a variety of factors. The final color of a ceramic restoration could be influenced by the color and thickness of PLV, the color of inherent tooth and the color of masking porcelain. When the color of PLV restoration cannot match with adjacent tooth, clinicians use resin cements frequently to mask the underlying color and modify the color the final restoration. In this study, we investigated the effects of different thicknesses and several resin luting cements on the final color of PLV restorations, to provide theoretical basis for tooth preparation and resin luting cements selection.Content and Methods:1. Specimens Preparation 1.1 The lost wax casting method was used to make IPS e.max Press LTA1 casting porcelain pieces into circular cast ceramic slices(with a diameter of 10 mm, thickness of 1.2 mm). Substantly, the surfaces of circular cast ceramic slices were flattened. All specimens were blasted with sand and cleaned by distilled water, t hen dried and spared. The slices were glazed by itself according to the instructions of manufacturer. After been fired, all specimens were polished with the same speed by grit paper in one polishing machine. To make sure the thickness of porcelain specime ns were 0.3 mm, 0.5 mm, 0.7 mm, 0.9 mm and 1.0 mm, respectively. The thickness of the specimens was controlled by an electronic sliding caliper. And the errors were controlled at ±0.02 mm. According to the thickness, specimens were divided into five groups. 1.2. Eight resin background disks(ND5 shade) were fabricated using a silicone rubber mold with diameter of 10 mm and thick of 4.5 mm. For the each side of resin background disks were cured for 40 s by light polymerization.The surfaces of disks were adjusted by grit paper into 4.0 mm thickness. The thickness of the disks was controlled by an electronic sliding caliper. Errors were controlled at ±0.02 mm. All the specimens were cleaned for ten minutes by distilled water, and then dried and spared. 2. Measurement of the color and statistic analysis: A1-color porcelain disc specimens(diameter: 10 mm; thickness: 0.3 mm, 0.5 mm, 0.7 mm, 0.9 mm and 1.0 mm) were seated on ND5 shade of resin specimens to mimic PLV laying on tooth substrates. The specimens was divided into control group(samples on the correct position with water) and resin luting cement group(samples on the correct position with luting cement). The luting cement(Shades of +3, +2, +1, 0,-1,-2,-3)were applied into the inter-layer of porcelain laminate veneer and resin speci mens, respectively. The color of all specimens were measured by the Olympus Crystaleye spectrophotometer and subsequently converted to CIE L*a*b* values. The center of the specimen was the measuring point. And each specimen was measured for three times in average. The lightness differences(ΔL*) and color differences(ΔE) were calculated from the value of L*, a*and b*. The results were statistically analyzed by SPSS11.5.Results:1. In the same thickness groups, there are significant statistical differences between resin luting cement group and control group(P<0.05). The color difference(ΔE) was more than 1.5 NBS. And the color of the porcelain samples performed a higher lightness differences(ΔL*) value, as well as a higher color differences(ΔE), using luting cement with +3、-3 shade. 2. The results of the same resin luting cement groups in which the thickness of the porcelain sample was different had significant difference(P<0.05). With the increasing of the thickness of the porcelain samples, the degree of lightness differences(ΔL*) and the color difference(ΔE) were decreased. And when the thickness of porcelain samples reached to l.0 mm, the lightness differences(ΔL*) and the color difference(ΔE) were lowest. 3. The color difference(ΔE) between luting agent group and control group was influenced by the thickness of porcelain sample and the shade of resin luting cement(P<0.05).Conclusion:The thickness of the PLV and the shade of resin luting cement all influenced the resultant color of laminate restorations. The opaque capacity of porcelain veneers became strong when the thickness was thicker. The influence to the color of resin luting cement decreased when the thickness of PLV became thicker. In addition, when the thickness of PLV reached to l.0 mm, the resin luting cemen had lest effect on the final color of it. And the color of the porcelain samples tried in with +3、-3 shade performed a higher ΔL* value and a higher ΔE, which implied +3、-3 paste ’s opaque capacity was stronger. It could be concluded that the appropriate thickness of PLV and the proper resin luting cement could adjust the final color of PLV restorations. |
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