Fit of 4-unit FDPs made of zirconia and CoCr-alloy after chairside and labside digitalization – A laboratory study

ObjectivesTo analyse the marginal fit of 4-unit fixed dental prostheses (FDPs) and the accuracy of three-dimensional cast-datasets using both approaches to Computer Aided Design (CAD)/Computer Aided Manufacturing (CAM): direct and indirect digitalization.MethodsA titanium model of a 4-unit FDP was digitized by an intraoral scanning device (iTero, Align Technology, Carlstadt, US; DD, n = 12). Additionally 12 conventional impressions were taken and referring master casts were digitized by a laboratory scanner (CS2, Straumann, Basel, Switzerland; ID, n = 12). Frameworks were fabricated (CARES CADCAM GmbH, Straumann, Markkleeberg, Germany) from base metal alloy (coron, Straumann; DD-C: n = 12; ID-C: n = 12) and zirconia (zerion, Straumann; DD-Z: n = 12; ID-Z: n = 12) from the same datasets. The marginal fit of the resulting frameworks and the accuracy of the underlying datasets from DD and ID were evaluated. Data were analyzed by unpaired two sample Student's t-test with Levene-test (p < 0.05).ResultsFrameworks from group DD-C showed significantly better marginal fit than ID-C (DD-C: 56.90 ± 27.37 μm, ID-C: 90.64 ± 90.81 μm). For zirconia frameworks no differences between both digitalization methods (DD-Z: 127.23 ± 66.87 μm, ID-Z: 141.08 ± 193.17 μm) could be observed. Base metal alloy frameworks exhibited significantly better marginal fit than zirconia frameworks (DD: p < 0.001; ID: p = 0.022). Regarding the accuracy group DD showed significantly higher “trueness” than ID.SignificanceDirect and indirect digitalization lead to clinically acceptable marginal fit of 4-unit FDPs from base metal alloy and zirconia. Higher accuracy of datasets from DD leads to better marginal fit of frameworks from base metal alloy but not for ones from zirconia.