Fracture resistance and surface roughness assessment of digitally fabricated interim bridges

Abstract

The aim of this study was to evaluate the fracture resistance and surface roughness of interim bridges with different span lengths fabricated using two additive manufacturing techniques: stereolithography (SLA) and digital light processing (DLP), and to compare them with conventionally milled restorations. Specimens were allocated into 3 groups according to fabrication technique (SLA, DLP, and milling; n=24 per group) and further subdivided based on span length (3-unit, 4-unit, and 6-unit; n=8 per group). The interim bridges were cemented onto their corresponding models, mounted in a universal testing machine, and progressively loaded until fracture. For surface roughness evaluation, 30 specimens were produced and divided into 3 groups according to fabrication technique (n=10). Mean surface roughness (Ra) was measured using a non-contact optical profilometer before and after polishing. The SLA bridges demonstrated fracture resistance values of 367±52 N for 3-unit, 124±22 N for 4-unit, and 91±31 N for 6-unit restorations. The DLP group exhibited lower fracture resistance values, with 283±28 N for 3-unit, 85±8 N for 4-unit, and 106±33 N for 6-unit bridges. Prior to polishing, milled specimens showed the highest mean surface roughness (32±3 μm), followed by DLP (14±1 μm), whereas SLA specimens exhibited the lowest Ra values (4±2 μm). Fracture resistance of milled bridges surpassed 3D printed bridges across different span lengths. Long span three-dimensional (3D) printed bridges did not meet the clinical requirements for initial fracture resistance of interim bridges. Digitally fabricated bridges have clinically acceptable surface roughness following standard polishing techniques . • Span length is a key factor in selecting interim bridge manufacturing techniques. • A 3D-customized fracture base can reduce time and material consumption while enhancing standardization. • All digital manufacturing techniques for interim bridges can produce a clinically acceptable surface finish.