In vitro investigation of the influence of printing direction on the flexural strength, flexural modulus and fractographic analysis of 3D-printed temporary materials.

The aim of this in vitro study was to evaluate the effect of printing direction and aging on the mechanical strength of 3D-printed temporary resin-based composites. Three hundred and sixty specimens (2×2×25 mm³) out of three materials were DLP printed. Specimens were either stored in distilled water for 24 h at 37°C or additionally subjected to thermocycling. Flexural strength (FS) and flexural modulus (FM) were evaluated in a three-point bending test considering three printing directions. Fractography was carried out by light microscopy, surfaces were categorized according to fracture origin. FS ranged from 93.2 to 159.9 MPa and 76.8 to 135.1 MPa in nonaged and aged specimens in the material sequence: Freeprint temp<Nextdentc&b<3Delta temp. Printing direction exerted a strong influence on 3Delta temp (ηp2=0.407) and had an influence on fracture origin in Freeprint temp aged (p=0.009) and 3Delta temp (p=0.042) nonaged specimens. The effects of printing direction on FS were material dependent and lower than the effects of aging.