Accuracy of Mandibular Removable Partial Denture Frameworks Fabricated by 3D Printing and Conventional Techniques

Abstract

Herein, we used digital superimposition to evaluate the accuracy of metal frameworks for mandibular removable partial dentures fabricated using three techniques. Thirty master casts of a mandibular dentiform were categorized into three groups (n = 10) based on the framework manufacturing method: selective laser melting-based metal three-dimensional (3D) printing (SLM), digital light projection-based resin 3D printing and subsequent casting (RPC), and conventional casting (CON). The master casts were scanned twice, initially after preparation and subsequently after attaching silicone using the frameworks. These scan files were digitally superimposed to measure the silicone thickness. Statistical analysis was conducted using SPSS Statistics (Version 23.0, IBM Corp., Somers, NY, USA). One-way ANOVA and a post hoc Tukey's multiple comparison tests were performed to determine differences among the three groups (α = 0.05). The RPC group exhibited significantly higher overall and mean internal discrepancies at rest and tissue stops than the SLM and CON groups, which exhibited statistically insignificant differences. Thus, SLM fabrication resulted in comparable accuracy to that achieved by CON, whereas sequentially performing resin 3D printing and casting induced inferior accuracy. However, all frameworks across the three groups were clinically acceptable.

Keywords: 3D printing; accuracy; removable partial denture framework; selective laser melting; superimposition.

Figure 1

Three manufacturing methods for mandibular RPD metal frameworks: (A) SLM-based metal 3D printing (SLM group), (B) combined method of DLP-based resin 3D printing and casting (RPC group), and (C) conventional lost-wax casting (CON group).

Figure 2

Three kinds of mandibular RPD metal frameworks prior to finishing and 3D-printed resin pattern: (A) metal 3D-printed framework, (B) 3D-printed resin pattern for RPC group, (C) 3D-printed resin-cast framework, and (D) conventional cast framework. Note that the shape of (C) is identical to (A); however, the color of (C) is identical to (D) due to the use of the same casting alloy.

Figure 3

Screenshots of the measurement steps with the 3D metrology software. The thickness of the imprinted silicone material representing the internal discrepancies was measured by superimposing two STL files: the cast only and the silicone-attached cast. (A) Superimposition of the two STL files by local best-fit alignment function of the metrology software, (B) manual selection of each measurement area, and (C) selected border lines at eight measurement areas (three rests, four tissue stops, and one lingual bar area) and color mapping of the areas (green represents good fit, yellow to red represents positive error, blue represents negative error).

Figure 4

Comparisons of the overall internal discrepancies (IDOs) and internal discrepancies at rests, tissue stops, and lingual bars (IDR, IDT, and IDL, respectively) of mandibular RPD metal frameworks fabricated using three methods (SLM: selective laser melting-based metal 3D printing, RPC: DLP-based resin 3D printing and subsequent casting, CON: conventional lost-wax casting). The asterisks indicate statistically significant differences among the three groups (p < 0.05).