Mechanical and physical properties of splint materials for oral appliances produced by additive, subtractive and conventional manufacturing.

OBJECTIVES

To investigate the flexural strength (FS), elastic modulus (E), Martens hardness (HM), water sorption (w), water solubility (w) and degree of conversion (DC) of 3D-printed, milled and injection molded splint materials.

METHODS

Specimens (N = 1140) were fabricated from five 3D-printed (GR-22 flex, GR-10 guide, ProArt Print Splint clear, V-Print Splint, V-Print Splint comfort), five milled (BioniCut, EldyPlus, ProArt CAD Splint clear, Temp Premium Flexible, Thermeo) and two injection molded (PalaXPress clear, Pro Base Cold) materials. FS, E, HM, w, w and DC were tested initially (24 h, 37 °C, HO), after water storage (90 d, 37 °C, HO) as well as after thermal cycling (5000 thermal cycles, 5/55 °C). Data were analyzed with Kolmogorov-Smirnov, Kruskal- Wallis, Mann-Whitney U test and Spearman's correlation (p < 0.05).

RESULTS

Initially, the mean flexural strength values ranged from 1.9 to 90.7 MPa for printed, 3.8 to 107 MPa for milled and 99.7 to 102 MPa for injection molded materials. The initial mean elastic modulus values were 0.0 to 2.4 GPa for printed, 0.1 to 2.7 GPa for milled and 2.8 GPa for injection molded materials. The initial mean Martens hardness values were 14.5 to 126 N/mm for printed, 50.2 to 171 N/mm for milled and 143 to 151 N/mm for injection molded materials. Initially, the mean water sorption values ranged from 23.1 to 41.2 μg/mm for printed, 4.5 to 23.5 μg/mm for milled and from 22.5 to 23.3 μg/ mm for injection molded materials. The initial mean water solubility values ranged from 2.2 to 7.1 μg/mm for printed, 0.0 to 0.5 μg/mm for milled and 0.1 to 0.3 μg/mm for injection molded materials. After water storage and thermal cycling most of the values decreased and some increased. The mean DC values ranged initially from 72.3 to 94.5 %, after water storage from 74.2 to 96.8 % and after thermal cycling from 75.6 to 95.4 % for the printed materials.

SIGNIFICANCE

The mechanical and physical properties of printed, milled and injection molded materials for occlusal devices vary and are influenced by aging processes. For clinical applications, materials need to be chosen according to the specific indications.