Comparative Strength Study of Indirect Permanent Restorations: 3D-Printed, Milled, and Conventional Dental Composites

<b>Background/Objectives</b>: Limited research has been performed to assess the strength of resin-bonded 3D-printed restorations. Based on that, this study investigates the impact of different manufacturing methods on the fracture load of indirect composite restorations (ICRs) following an aging process. <b>Methods</b>: Three manufacturing techniques-conventional (CRC), milled (MRC), and printed (PRC)-were evaluated using 60 specimens, each with a diameter of 10 mm and a thickness of 1.0 mm. Sandblasting with Al₂O₃ particles was employed to optimize the bonding process, significantly influencing surface roughness parameters (Ra, Rz, RSm). All specimens were bonded to the dentin analog using composite resin cement and subjected to either 10,000 thermocycles (TC) or storage (ST) at 37 °C in distilled water. Fracture load assessments were performed using a universal testing machine. A finite element analysis was conducted to assess stress distribution. <b>Results</b>: Two-way ANOVA results indicated that the manufacturing method significantly affected mean fracture load values (<i>p</i> < 0.001), with PRC showing the highest mean fracture load (4185 ± 914 N), followed by MRC (2495 ± 941 N) and CRC (599 ± 292 N). The aging protocol did not have a significant impact on fracture load. <b>Conclusions</b>: This study revealed that 3D-printed resin composite exhibited comparable strength to milled resin composite when adhesively cemented, suggesting it is a promising option for indirect composite restorations based on its mechanical performance. However, further research is needed to evaluate its bond strength and optimal surface treatment methods to prevent early debonding.