Additive vs. Subtractive CAD/CAM Procedures in Manufacturing of the PMMA Interim Dental Crowns. A Comparative in vitro Study of Internal Fit

Abstract

CAD/CAM procedures are increasingly used to the manufacturing of 3D-designed PMMA interim dental crowns. The aim of this in vitro study was to compare the internal fit of interim PMMA crowns fabricated by subtractive versus additive CAD/CAM procedures. Starting from a Co-Cr CAD/CAM master abutment model, 20 standardized dental models of dental stone were done by double impression technique. Subsequently two groups of interim PMMA interim crowns, each of them having 10 specimens, were CAM obtained either by milling or 3D printing, using Exocad software package, milling machine Rolland DWX-50, and the 3D printer MoonRay S 100 respectively. An electronic digital caliper Powerfix Profi+ was used for measurements of the chrome cobalt abutment and crowns inner diameter in 4 directions (mesial-distal gingival, buccal-lingual gingival, mesial-distal occlusal, and buccal-lingual occlusal). The null hypothesis that the internal dimensional accuracy of interim PMMA crowns fabricated by DLP additive method would not be different compared to those obtained by milling procedure was rejected since the printed PMMA interim crowns were more accurate. This study concluded that the milled PMMA interim crowns show larger internal dimensional variations than the 3D printed ones. However, the fit variation among interim crowns fabricated by both procedures was statistically non significant, so that both CAM technologies may be equally used in manufacturing process.