Fracture Toughness and Impact Strength of 3D-Printed Splints

Objectives: To compare fracture toughness and impact strength of 3D-printed splint materials to milled and heat cured materials.
Methods: Bars (4mm×8mm×39mm for toughness and 50mm×6mm×2mm for impact) of 3D-printed splint resins, KeySplint Soft and Hard (KSS and KSH, Keystone) and Nightguard Flex and Firm (NFX and NFM, SprintRay) were printed using a DLP 3D Printer (Pro 95, SprintRay), and post-processed. Milled specimens (MILL, ProArt CAD, Ivoclar) were fabricated in a milling unit and heat-cured specimens (HC, Excel Formula, St. George Technology) were produced using a wax pattern and heat-curing technique. Specimens were polished to 600grit SiC paper. Fracture toughness bars had a 3mm cut placed in their center with a saw blade and a 100-400µm notch with a razor blade. Impact specimens had a 1.2mm notch in their center with a 45degree router bit. Specimens (n=14/group) were stored for 48hrs at 37C in water (wet) and half were removed from water for (dry) storage. For fracture toughness, specimens were placed with their pre-crack downwards and loaded to failure at 1mm/min in a universal testing machine. For impact strength, specimens were tested with an Izod impact machine (Model Impact 104, Tinius Olsen) with the notch facing towards the pendulum hammer. A 7.5J pendulum hammer was released from an angle of 150 and the energy absorbed was recorded. Data were analyzed with 2-way ANOVA and Tukey post-hoc tests (alpha=.05).
Results: Data for fracture toughness and impact strength are presented in the Table. 2-way ANOVA determined that there were significant differences between materials and testing condition (wet/dry) and their interaction for fracture toughness and impact strength (p<0.001). Tukey post-hoc analyses found significant differences between groups as indicated by different letters in the same column in the Table.
Conclusions: Soft/flexible 3D-printed splint materials have greater fracture toughness and impact strength than hard/firm materials.