Accuracy of implant-supported crowns fabricated by additive and subtractive manufacturing technologies using ceramic-filled resins: An in vitro study

Statement of problem: Although resin materials and additive manufacturing (AM) technologies have been evolving rapidly, they still present limitations compared with subtractive manufacturing (SM). These limitations become particularly relevant in prefabricated abutments with detailed retentive geometries, where minor deviations can compromise the fit and retention of the restoration. Purpose: The aim of this in vitro study was to compare the accuracy (trueness and precision) of the SM and 2 AM methods, both overall and of the buccal, proximal, cusp, fossa, intaglio, and margin regions, to produce single implant-supported crowns. Material and methods: Implant-supported crowns with prefabricated abutments (RC Variobase for Crown; Institute Straumann AG) simulating a mandibular first molar were manufactured using 3 manufacturing methods: digital light projection (DLP), stereolithography (SLA), and SM, with 15 specimens per group. The accuracy was evaluated using an intraoral scanner to generate a standard tessellation language (STL) file and a metrology software program to compare both STL files: the original design with the manufactured crown. The following 6 regions were assessed: buccal, proximal, cusp, fossa, intaglio, and margin. Root mean square (RMS) deviations and color maps were generated to quantify deviations. Kruskal-Wallis with Bonferroni-adjusted Mann-Whitney and Friedman with Bonferroni-adjusted Wilcoxon tests were used to analyze the data (α=.05). Results: The SM group demonstrated higher trueness and precision than SLA (P<.001 and P<.001 respectively) and higher trueness and precision than DLP (P<.001 and P<.001 respectively). The DLP group showed lower trueness at the margin region than SLA (P<.001) and SM (P<.001). The DLP also had lower precision at the margin region than SLA (P<.001) and SM (P<.001). Conclusions: The SM group showed the highest accuracy, DLP the lowest, especially at the margin region. All methods demonstrated intaglio accuracy values within ranges previously associated with clinically acceptable internal fit.