| Purpose:The purpose of this in vitro study was to evaluate the marginal and internal adaption of cobalt-chromium metal copings fabricated with different impression methods(direct scanning, silicone impression scanning and stone die scanning)and different techniques(selective laser melting, CAD/CAM milling and casting).Methods:Five extracted maxillary second premolars with no caries or anatomical defects which were for orthodontic treatment were chosen for this study. The teeth were prepared to receive a single metal-ceramic crown, which were fixed on the acrylic resin model. After the preparation, a polyvinyl silicone impression of the teeth was taken using the double impression technique, and poured with Type Ⅳ dental stone. The prepared teeth, silicone impression and stone die were scanned to obtain three digital models for designing the copings. Fifteen metal copings were fabricated using selective laser melting(SLM) and fifteen metal copings were fabricated using CAD/CAM milling(CM) based on the three digital models, five for each digital models, respectively. In addition, five resin copings were made using 3D printing. Then ten metal copings were fabricated with casting: five for lost-wax casting(LW) and five for lost-resin casting(LR). Silicone replica technique was used to obtain the space between copings and teeth. An micro-computed tomography(Micro-CT) device was used to evaluate marginal and internal adaption. For each coping, marginal adaption was measured at 40 points, 20 points for absolute marginal discrepancy(AMD) and 20 points for marginal gap(MG), and internal adaption was measured at 80 points for four region, chamfer area(CA), axial wall(AW), axial-occlusal transition area(AOT) and occlusal area(OA), 20 points for each region. For each group, 600 measurements were made. Data were statistically analyzed by 1-way ANOVA at the 5% significance using SPSS 16.0 software.Results:The mean values of AMD for SLM, CM and LW were 88.21±23.16μm, 90.60±26.14μm and 147.77±43.88μm, respectively. The mean values of MG for SLM, CM and LW were 60.72±22.27μm, 62.52±23.74μm and 108.04±36.44μm, respectively. The internal gap of SLM, CM and LW were 128.35±67.67μm, 90.71±42.26μm and 128.94±49.32μm, respectively. The AMD, MG and internal gap for LR were 155.13±47.27μm, 117.23±39.63μm and 112.10±36.59μm.Conclusion:The marginal adaption of metal copings fabricated with SLM and CM were within clinically acceptable range and were significantly lower than LW. Copings fabricated with CM have the best internal adaption, and there was no difference between the internal adaption of SLM and LW. Different digital impression methods did not influence the marginal adaption of SLM copings or CM copings, but the silicone impression scanning method was better than the other two impression scanning methods for internal adaption. There was no difference between the marginal adaption of LW and LR, but the internal adaption of LR was better than LW, and 3D printing resin coping can replace the wax pattern for fabricating copings. Micro-CT is a reliable tool to evaluate marginal and internal adaption. |
PDF Full Text Request