Edge strength of definitive 3D-printed restorative resin materials

Statement of the problem
With the advent of digital technology in dentistry, manual methods for creating dental restorations are being replaced by digital CAD/CAM processes involving three-dimensional (3D) printing and milling. Marginal degradation and chipping are common issues, yet the literature on the edge strength of 3D-printed restorative materials remains limited. Uncertainties remain regarding the impact of print orientation on edge strength, necessitating further investigation to ensure clinical efficacy.
Purpose
The purpose of this study was to evaluate the influence of print orientation on the edge strength of 3D-printed dental restorative resins indicated for definitive and interim use and compare them with milled materials.
Materials and methods
Specimens (14 ×14 ×2 mm) were additively manufactured in three orientations (0, 45, and 90 degrees) using five 3D printed resins: VarseoSmile Crownplus (VCP), Crowntec (CT), Nextdent C&B MFH (ND), Dima C&B temp (DT), and GC temp print (GC). A DLP 3D printer (ASIGA MAX UV) was used, with post-processing parameters set according to manufacturer recommendations. Edge strength was measured at 0.5 mm and 1 mm distance from the edge using a CK 10 testing machine. Specimens were tested in dry conditions (0.5 mm) and after 48 hours of storage in artificial saliva at 37°C (0.5 mm and 1 mm). Failure modes were analysed visually and using optical and scanning electron microscopy. Filler content was assessed using the Ash method, and statistical analysis was conducted using ANOVA. Pearson correlation was used to assess the relationship between filler weight and edge strength.
Results
Due to severe deformation before chipping under load at both distances, data for the 3D-printed and milled interim materials were excluded. The 90-degree printing orientation of definitive materials demonstrated significantly higher edge strength after 48 hours in artificial saliva compared to the 0- and 45-degree orientations (P < 0.001). Significant differences were observed between the 3D printed and milled materials at 0.5 (P < 0.001) mm but not at 1 mm (P ≥ 0.804). Failure modes were predominantly surface indentation without visible cracking (58 %), followed by surface indentation with visible cracking (17 %), edge chipping (0.2 %), and specimen fracture (13 %). A non-significant negative correlation was observed between filler weight and edge strength (r = 0.161, P < 0.680).
Conclusions
Based on the current findings, 3D printing definitive resin materials at a 90-degree orientation provided increased edge strength. 3D-printed materials can better resist crack propagation compared to milled composites.
Clinical implications
Optimizing the print orientation to 90-degree can improve the edge strength of definitive 3D printed materials.