Effect of half-digital workflows on the adaptation of custom CAD-CAM composite post-and-cores

Even without the use of an intraoral scanner, post-and-cores can be obtained by using a part-digital fabrication workflow that requires pattern modeling (direct, indirect, or impression); however, studies on the adaptation of computer-aided design and computer-aided manufacturing (CAD-CAM) composite resin post-and-cores in comparison with metal cast post-and-cores are sparse.

The purpose of this in vitro study was to analyze the adaptation of CAD-CAM composite resin post-and-cores fabricated through a part-digital fabrication workflow and to compare it with that of metal cast post-and-cores fabricated through conventional methods.

Eight extracted human premolars were endodontically treated and prepared for custom post-and-cores. Metal cast post-and-cores were fabricated with Ni-Cr alloy (Fit Cast-Sb Plus; Talmax) and conventional resin pattern modeling methods directly in the root canal (conventional direct modeling) or indirectly in a stone cast (conventional indirect modeling). Composite resin post-and-cores were milled from nanohybrid glass-ceramic composite resin CAD-CAM blocks (Brava Block; FGM) by using the part-digital workflow. A laboratory scanner was used to digitalize polyvinyl siloxane impressions (part-digital scanned impression direct CAD-CAM [PSC]) of the root canals and resin patterns fabricated directly (part-digital direct CAD-CAM [PDC]) or indirectly (part-digital indirect CAD-CAM [PIC]). All post-and-cores were placed in the respectively prepared root canals, scanned with microcomputed tomography, and measured in terms of volume of the cementation space, the luting cement film thickness in each root third, and the apical gap between the apical end of the post-and-cores and remaining gutta percha (apical gap). The groups were compared for each adaptation parameter by using 2-way (volume of the cementation space and apical gap) and 3-way (film thickness) ANOVA, and the Games-Howell multicomparison post hoc test (α=.05).

The conventional direct modeling group had lower mean volume of the cementation space than all CAD-CAM composite resin post-and-cores (P<.041). The conventional indirect modeling group had a lower volume of the cementation space mean than PDC (P<.024) but was not significantly different from PIC (P=.577) or PSC (P=.221). Regardless of the fabrication workflow, no differences were observed among the CAD-CAM composite resin post-and-cores (P>.05). At the apical root third, conventional direct modeling and conventional indirect modeling had lower film thickness means than PSC or PDC (P<.05). In the middle third, conventional direct modeling and conventional indirect modeling had lower film thickness means than PDC (P≤.001). At the cervical third, no differences in film thickness means were observed among the groups (P>.05). PDC had a lower apical gap mean than PSC (P=.013), while no significant differences were found for other pair comparisons (P>.05).

Metal post-and-cores had slightly better adaptation than the CAD-CAM composite resin post-and-cores; however, the part-digital fabrication workflow of CAD-CAM composite resin post-and-cores provided adaptation parameters within a clinically acceptable range and is less time consuming.