Assessment of resin cement residue removal technique impact on cementation quality and discoloration using micro-CT and stereomicroscopy

The objective of this study was to compare the size of marginal defects in micro-CT images and evaluate discoloration for adhesively cemented veneers when using two cement removal techniques. Twenty premolars were included and all were prepared similarly: 0.5 mm deep with rounded corners, chamfer finish line, borders in enamel.Ceramic (IPS e.max CAD) veneers were made using a scanner Ceramill Map 600 and milling device Ceramill Motion 2. The cement gap was set to 0.02 mm and PANAVIA V5 (Kuraray, Noritake) cement system was used. The specimens were divided in 2 groups. For first group (n = 10) cement excess was removed with a probe after 3 – 5 second polymerization continuing to complete polymerization. For second group (n = 10) cement excess was removed with a brush, then completely polymerized. All teeth were stored in alginate gel until micro-CT examination (Scanco medical µCT50). Scanning was done twice: directly after cementation and after thermocycling (Thermocycler 1100/1200, SD Mechatronik, Germany) in distilled water for 10’000 cycles between 5oC and 55oC. For each tooth 413 micro-CT slices (starting 2 mm from the tip of the cusp) were obtained. To analyze discolouration, teeth were coloured using 0,5% basic fuchsine and examined under stereomicroscope. Depth of dye infiltration was scored with score 0 (no discolouration) to 5 (discolouration along the entire margin). All specimens exhibited cementation defects most common of them being structural defects inside cement layer and irrelevant overfill (cement covers the veneer surface). Some teeth showed extensive cement overfill or underfill (concave cement contour). Removal with a probe showed more contour defects (p<0.0000001). Differences in defect types between groups were not found. According to our preliminary results cement removal with a brush shows less contour defects and could be more stable against discoloration.