Influence of fabrication method on the manufacturing accuracy and internal discrepancy of removable partial dentures: A systematic review and meta-analysis

Statement of problem: Removable partial dentures (RPDs) can be fabricated with conventional casting procedures or computer-aided design and computer-aided manufacturing (CAD-CAM) technologies; however, the manufacturing accuracy and internal discrepancy differences among these manufacturing methods remain uncertain. Purpose: The purpose of this systematic review and meta-analysis was to assess the influence of the fabricating method (casting, milling, or additive manufacturing) on the accuracy and internal discrepancy of RPDs. Material and methods: An electronic search of the literature was performed in 6 databases: PubMed/Medline, Embase, Web of Science, Scopus, Cochrane, and Google Scholar. The studies that assessed the accuracy and internal discrepancy of RPDs fabricated from casting, milling, and additive manufacturing were included. Studies reporting gaps (mean) and standard deviations were included in the meta-analysis. Publication bias was identified using funnel plot asymmetry and the Egger test. Results: A total of 25 articles were included. The internal discrepancy of the additively manufactured RPDs ranged from 14.4 to 511 mu m and from 7 to 419 mu m in conventionally fabricated RPDs. For the milling method, 20 to 66 mu m horizontal and 17 to 59 mu m vertical discrepancies were reported. The Egger tests indicated no publication bias among the studies that were included in the meta-analysis. Four included studies resulted in more than the acceptable clinical gap (311 mu m) for the CAD-CAM method. Independently of the manufacturing method, the greatest internal discrepancies reported were observed under the major connectors. RPDs fabricated by using CAD-CAM techniques required fewer clinical appointments, the RPD design was easier to reproduce, and laboratory time was less than with conventional procedures. However, the reviewed studies described several disadvantages, including limited RPD design programs, difficulties in defining the occlusal plane, expensive materials, and increased laboratory cost. Conclusions: Additive and subtractive technologies provide accurate methods for RPD fabrication; however, all challenges, including limited design software programs have not yet been overcome, and casting is still needed when the framework pattern is milled or printed.