Marginal and Internal Gaps, Surface Roughness and Fracture Resistance of Provisional Crowns Fabricated With 3D Printing and Milling Systems.

Abstract

To compare the marginal and internal gap, surface roughness, fracture resistance and mode of failure of provisional crowns fabricated with 3D printing and CAD/CAM manufacturing techniques. A maxillary first premolar was prepared for an all-ceramic crown and reproduced in cobalt-chromium metal dies (n=30) following CAD/CAM technology. The die was digitally scanned and exocad software was used to design the missing crown, which was manufactured using a CAM milling machine and two types of 3D printing machines (SLA and DLP) to produce 10 provisional crowns per group. The crowns were cemented to their respective dies and stored in water (24 hours; 37°C) followed by 600 thermal cycles (5°C/55°C) and 100,000 mechanical cycles (at 50N). Marginal and internal gap measurements were carried out using a 3D superimposition technique. Surface roughness (Ra) was determined using a profilometer at 0.5 mm/second cross-head speed. The crowns were loaded to fracture at 0.5 mm/minute cross-head speed. Fracture forces and mode of failure were recorded, and data were analyzed using one-way analysis of variance (ANOVA) and multiple comparisons post hoc tests (p<0.05). The SLA group exhibited higher marginal and internal gaps than both the CAD/CAM and DLP groups (p<0.05). The DLP group showed higher surface roughness than the CAD/CAM and SLA groups (p<0.01). The CAD/CAM and SLA groups showed higher resistance to fracture than the DLP (p<0.05) group. Mode of failure I: Minimal crown fracture or crack, was predominate among DLP and SLA crowns (60%), while the Mode II: Less than half of the crown lost, was predominant among CAD/CAM crowns (60%). Crowns manufactured following CAD/CAM technique have better marginal and internal fit, surface roughness than SLA and DLP crowns. The CAD/CAM and SLA crowns showed higher resistance to fracture than the DLP crowns.