Flexural strength of 3D printing-manufactured three-unit resin prostheses

Abstract

FlashForge Co., Zhejiang, China). All three groups had a effective building direction of 30°, were made of different materials, and were printed using AM techniques. Each group was consisted of 15 specimens. Two control groups having 15 specimens each, also used: CV group with PMMA–resin specimens fabricated using the CV method, and SM group with PMMA-resin specimens fabricated using the SM method. A flexural strength test was applied to all three experimental groups and the two control groups. To determine the dependent and independent variables, building direction, type of material used, and flexural strength of the specimens, statistical analyses were performed with a significance level of p < 0.05. Results: For the DLP specimens, in the flexural strength test conducted for the five different building directions of 0˚, 30˚, 45˚, 60˚, and 90˚, the mean flexural strengths were 1053 ± 168 N, 1183 ± 141 N, 1178 ± 81 N, 1166 ± 134 N, and 949 ± 170 N respectively. The group with a building direction of 90˚ showed significantly lower flexural strength than the groups with building directions of 30˚ (p < 0.001), 45˚ (p < 0.001), and 60˚ (p = 0.001). No significant differences were observed among the groups with building directions of 0˚, 30˚, 45˚, and 60˚ (p > 0.05). The CV, SM, DLP, and SLA experimental groups showed a flexural strength of 565 ± 180 N, 1218 ± 59 N, 1189 ± 174 N, and 1318 ± 69 N, respectively. The FDM group showed no fracture but only dents

hence, the flexural strength could not determined in this case. With respect to the statistical significance, the DLP and SLA groups showed higher flexural strength than the control group CV (p < 0.001), and no significant difference was observed between DLP and SM (p = 0.930), and between SLA and SM (p = 0.181). Conclusion: In the case of the DLP group, the flexural strength was significantly lower when the building direction was 90˚ than when it was 30˚, 45˚, or 60˚. The CV group showed significantly lower flexural strength than the DLP, SLA, and SM groups. No significant difference was observed in the flexural strength of the DLP and SLA groups compared to the SM group. The flexural strength of the FDM group could not be measured as the specimens of this group were not fractured but dented during the flexural strength test.

-Abstract-

Flexural strength of 3D printing-manufactured three-unit resin prostheses

Sang-Mo Park, DDS, MSD Department of Prosthodontics, Graduate School, Seoul National University (Supervised by Professor Seong-Kyun Kim, DDS, MSD, PhD)

Purpose: Additive manufacturing (AM) has many advantages in the fabrication of a dental prosthesis, in comparison with the conventional method (CV) and subtractive manufacturing (SM). However, few studies have reported on the physical properties of AM in dentistry. In this study, I investigated the flexural strength of three-unit resin prostheses made using the AM method. A three-unit resin prosthesis was fabricated using digital light processing (DLP), and the building direction with the maximum flexural strength was determined. In addition, the flexural strengths of three-unit resin prostheses fabricated using various AM methods were compared with those fabricated using the CV and SM techniques. Materials and Methods: A metal jig for a three-unit resin prosthesis with a pontic in the middle and an indenter, which applied force to the midpoint of the pontic, were fabricated. Following this, specimens made of poly methyl methacrylate (PMMA). a three-dimensional (3D) printing resin (C&B

Nextdent Co., Seosterberg, Netherlands), were fabricated with a DLP printer (DP-150

Veltz 3D Co., Incheon, Korea). These specimens were made in such a way that they could be adopted to the metal jig from five different building directions: 0°, 30°, 45°, 60°, and 90°, those were denoted as groups DLP 0˚, DLP 30˚, DLP 45˚, DLP 60˚, and DLP 90˚. In all, 15 specimens for each building direction were fabricated, and the specimen group with the highest flexural strength was determined through a flexural strength test and statistical analysis. The building direction of the group that exhibited the highest flexural strength was set as the effective direction. However, in the absence of such a value, the building direction of the group that showed the highest mean value of flexural strength was set as the effective direction. Thus, the building direction of 30° was set as the effective building direction. The following three experimental groups of specimens were considered in this study: (1) DLP group-samples prepared from a PMMA-based resin and printed with a DLP printer, (2) stereolithography (SLA) group-specimens prepared from a PMMA-based resin (GPGR04

Formlabs Co., Somervile, MA, USA) and printed with a SLA printer (Form2

Formlabs Co., Somervile, MA, USA), and (3) fused deposition manufacturing (FDM) group-specimens prepared from a poly-lactic acid (PLA)-based resin (PLA

ColorFabb Co., Belfeld, Netherlands) and printed with a FDM printer (Creatorpro