Adaptation of maxillary removable partial denture frameworks fabricated with a direct digital workflow: A randomized crossover clinical trial.

Objectives: To compare the adaptation of maxillary removable partial denture (RPD) frameworks fabricated through direct digital workflows with that of traditional cast frameworks and indirect digital frameworks.

Methods: The workflow for fabricating the digital cobalt-chromium framework encompassed intraoral scanning (IOS) using Trios 3, computer-aided survey and design, and subsequently either the lost-wax technique from a printed resin framework pattern (Framework B) or direct selective laser melting (SLM) (Framework C). The traditional cast framework (Framework A) was selected as a control. All three frameworks were tested in the designed sequence, and the scores of the frameworks were recorded based on the specialists' evaluations. The adaptation of the frameworks was measured via the silicone lining method. The average thickness of the light-body silicone was determined using Geomagic software for three-dimensional (3D) analysis. Chromatograms were used for the qualitative visualization of the deviations.

Results: Fifty-eight patients were enrolled. The evaluation scores of the specialists indicated that Framework C had superior framework seating (P = 0.02) and posterior strap fitting of major connectors (P = 0.034) compared with Framework A. Regarding the 3D analysis of the overall adaptation of the major connectors, Framework A demonstrated significantly better adaptation than Framework B (P = 0.012), while there was no significant difference between Frameworks A and C (P = 0.305) or between Frameworks B and C (P = 0.133). Moreover, the classification of dentition defects had no significant effect on the adaptation of the three frameworks (P > 0.05). The type of major connectors had no significant effect on the adaptation of Frameworks A and C (P > 0.05), but a significant difference was observed in the adaptation among different major connectors in Framework B (P < 0.05).

Conclusions: The maxillary RPD frameworks fabricated through the direct digital technique (a combination of IOS and SLM) presented overall adaptation consistent with those of the conventional method, but had better framework seating and posterior strap fitting.

Clinical Significance: A direct digital workflow in the manufacturing of maxillary RPD framework is a valid alternative to conventional methods and will be a promising approach in the future. (The clinical trial registration number: ChiCTR-ONC-16009899).