Purpose: To evaluate how model resin and shaft taper affect the trueness and fit of additively manufactured removable dies in narrow ridge casts. Materials and Methods: A typodont model with a prepared mandibular molar was scanned to design virtual dies with different shaft tapers (0-degree [straight], 5-degree tapered, and 10-degree tapered). In total, 15 dies and one hollowed cast per taper were additively manufactured from two resins (G PRINT 3D Model [GP] and DentaMODEL [DM]). Dies and casts were digitized to evaluate their trueness (root mean square [RMS]). The fit of the dies was evaluated with crown portion’s RMS when seated in the cast and with distance deviations. Kruskal-Wallis and Mann-Whitney U tests were used to analyze data (α =.05). Results: GP dies had lower overall, root, and base RMS, while DM dies had lower crown RMS (P ≤ .016). Straight dies had the highest overall, root, and base RMS within GP (P ≤ .030). The 10-degree dies had the lowest overall and base RMS, lower crown RMS than straight dies, and lower root RMS than 5-degree dies within DM (P ≤ .047). When the dies were seated, GP had lower crown portion RMS within 5- and 10 degree dies, and 5-degree dies had the highest RMS within DM (P ≤ .003). GP had smaller distance deviations within 5- and 10-degree dies. The 5-degree dies had the largest deviations within DM (P ≤ .049). Conclusions: GP dies mostly had higher trueness and better fit. Straight dies mostly had lower trueness within GP, and 10-degree taper mostly led to higher trueness within DM. The shaft taper affected the fit of DM dies.
