In vitro study on the influence of postpolymerization and aging on the Martens parameters of 3D-printed occlusal devices

Statement of problem. Additive manufacturing has been proposed for the fabrication of occlusal devices. However, information about the mechanical properties of additively manufactured devices is lacking. Purpose. The purpose of this in vitro study was to evaluate the influence of the postpolymerization unit and artificial aging on the Martens hardness (HM) and indentation modulus (E-IT) of different 3D-printed materials in comparison with a conventionally milled material. Material and methods. Thirty disks (20 mm in diameter and 5 mm in thickness) were additively manufactured (D20 II, Rapidshape & Form 2) for each 3D-printed material (NextDent Splint, Formlabs Dental LT Clear, and Freeprint Splint). As a control, 10 disks of the same thickness were cut from a conventionally milled material (Temp Premium). Each specimen was measured for HM and E-IT (ZHU 0,2) after fabrication. The specimens were stored in water at 37 degrees C and measured again after 2 and 4 weeks. The data were analyzed statistically by using the Kruskal-Wallis, Mann-Whitney U, and Wilcoxon tests (adjusted by Bonferroni correction alpha=.05/27=.002). Results. The highest influence on HM parameters was shown by artificial aging (partial eta squared: HM: eta(2)(P)=0.840, E-IT: eta(2)(P)=0.855, P<.001), followed by the material (HM: eta(2)(P)=0.690 E-IT: eta(2)(P)=0.845, P<.001) and the postpolymerization unit (HM: eta(2)(P)=0.649, E-IT: eta(2)(P)=0.778, P<.001). Initial HM values ranged from 147 +/- 8.11 N/mm(2) for Formlabs postpolymerized in Otoflash to 89.5 +/- 8.55 N/mm(2) for Detax postpolymerized in the Labolight unit. E-IT values ranged from 3.92 +/- 0.061 kN/mm(2) for Formlabs postpolymerized in Otoflash to 2.48 +/- 0.212 kN/mm(2) for Detax postpolymerized in the Labolight unit. In general, HM and E-IT values decreased after water storage, whereas the values remained unchanged for the control group. Conclusions. HM parameters of additively manufactured occlusal devices depend on postpolymerization strategy. Otoflash and Printbox result in higher HM and E-IT values. The 3Dprinted materials are more prone to artificial aging than the control group, which brings into question their long-term service.