The effect of cyclic loading on the fracture resistance of 3D-printed and CAD/CAM milled zirconia crowns—an in vitro study

Abstract

Objectives The aim of this study was to evaluate the effect of cyclic mechanical loading on the fracture resistance of 3D-printed zirconia crowns in comparison to milled zirconia crowns. Materials and methods Monolithic zirconia crowns (n = 30) were manufactured using subtractive milling (group M) and 3D additive printing (group P). Nine samples of each group were fractured under one-time loading while the other 6 samples were subjected to cyclic loading for 1.2 million cycles before being subjected to one-time loading until fracture. Scanning electron microscope (SEM) fractographic analysis was carried out on fractured fragments of representative samples. Results The mean for fracture resistance of group M was 1890 N without cyclic loading and 1642 N after being subjected to cyclic loading, and they were significantly higher than that of group P (1658 N and 1224 N respectively). Conclusions The fabrication technique and cyclic loading affect the fracture resistance of zirconia crowns. Although the fracture resistance values for the 3D-printed crowns were lower than those of the milled, still they are higher than the masticatory forces and thus could be considered being clinically acceptable. Clinical relevance Concerning fracture resistance, 3D-printed crowns can withstand the masticatory forces for the long term without any cracks or failure.

3D Printed Materials for Permanent Restorations in Indirect Restorative and Prosthetic Dentistry: A Critical Review of the Literature

“…In line with Ucar et al [35], Refaie et al [58] stated that zirconia manufacturing via 3D printing still needs improvements, especially in terms of porosity. Milled zirconia crowns showed significantly higher fracture resistance compared to the 3D printed crowns.…”

“…In addition to 3D printed resin composites, ceramics and zirconia have also been tested [ 28 , 34 , 35 , 36 , 38 , 47 , 53 , 54 , 55 , 58 ].…”

“…The crowns were intact in all groups at the end of the experimental procedure. Refaie et al [ 58 ] evaluated the fracture resistance of 3D printed and milled zirconia crowns and found that the immediate fracture resistance of all crowns exceeded 790 N, which is higher than the physiological biting force, reported in the literature to be 450–520 N, and of the forces reported in bruxism, reported to be 790 N [ 66 , 67 ]. The fracture resistance was reported to be reduced after cyclic loading, thus remaining higher than 790N.…”

Flexural strength, flexural modulus and microhardness of milled vs. fused deposition modeling printed Zirconia; effect of conventional vs. speed sintering

“…According to the results obtained from this study, the first null hypothesis was rejected because the milled groups had significantly higher flexural strength (P < 0.0001), flexural modulus (P < 0.0001), and Vickers microhardness values (P < 0.0001). The second null hypothesis, which stated that the sintering speed cycle (conventional vs. speed sintering) has no significant effect on flexural strength, flexural modulus, and Vickers microhardness, was also rejected due to the milled speed group having significantly higher microhardness values than the rest of the groups [21,[34][35][36]36]. Thermocycling is a method used to quickly simulate intraoral variations in thermal and fatigue resistances that cause mechanical stresses and cracks in restorations that can affect their longevity [33,36].…”