Evaluation of mechanical properties of CAD-CAM composite resins for milled versus 3D printed definitive restorations: A systematic review and meta-analysis

STATEMENT OF PROBLEM: Three-dimensionally (3D) printed composite resin materials for definitive restorations have recently been introduced but doubts still exist regarding their mechanical properties. PURPOSE: The purpose of this systematic review and meta-analysis was to compare the mechanical properties of computer-aided design and computer-aided manufacturing (CAD-CAM) composite resins used in the fabrication of definitive restorations using 3D printing and milling methods. MATERIAL AND METHODS: This systematic review followed the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines and was registered on the Open Science Framework (https://osf.io/gps2f/) platform for in vitro studies. A population, intervention, comparison, and outcome (PICO) question was formulated: "Do the CAD-CAM composite resins for definitive restorations used in the 3D printing method have mechanical properties similar to those used in the milling method?" A literature search was carried out in the PubMed/MEDLINE, Web of Science, Scopus, Embase, and Lilacs databases until November 2024. The risk of bias was assessed using the RoBDEMAT tool. The meta-analysis was performed by using the RevMan 5.4 program (α=.05). RESULTS: A total of 6 in vitro studies published until November 2024 were included after the search, and a total of 440 specimens were evaluated. Milled composite resins demonstrated higher values for flexural strength in the 3-point bend test (P<.001; SMD: -1.76; 95% CI: -2.51 to -1.02), microhardness (P<.001; SMD: -2.32; 95% CI: -2.66 to -2.05), and elastic modulus (P<.001; SMD: -4.28; 95% CI: -6.51 to -2.05). In the biaxial flexural strength test, no significant differences were observed (P=.29; SMD: -0.74; 95% CI: -2.11 to -0.62). All meta-analyses exhibited high heterogeneity (I²>84%), except for microhardness (I²=5%). CONCLUSIONS: When the flexural strength, elastic modulus, and Vickers microhardness for CAD-CAM composite resins (3D printed and milled) were evaluated, the milled resins exhibited better mechanical properties.