Flexural Strength and Stress Analysis of CAD-CAM Milled Glass Fiber Post and Core

Intraradicular posts have the potential to induce mechanical stresses within the root structure during masticatory activities, hence contributing to fatigue and ultimately resulting in the fracture of the remaining dental structure. The objective of this work was to compare the stress pattern generated on the root by a computer-aided design and computer-aided manufacturing (CAD-CAM) milled fiberglass post under occlusal load in a photoelastic simulation and to compare its flexural strength (FS) to other types of posts. A total of 15 simulated roots, produced from photoelastic resins, were created using human canine teeth. These specimens were then separated into three distinct groups: Fiber post conventional, which consisted of fiberglass posts; fiber post customizable, which involved prefabricated fiberglass posts anatomized with composite resin; and fiber post CAD-CAM, which utilized CAD-CAM milled fiberglass posts. Following the application of Relyx ARC cement, the posts underwent photoelastic testing using a polariscope and FS testing using a universal testing machine. The data were submitted to analysis of variance (ANOVA) and Tukey's test at 5% significance level. It was found that the stress was significantly greater (p < 0.05) for the customizable post (246.5 MPa ± 218.7) in comparison to both the conventional (135.8 MPa ± 99.3) and CAD-CAM (136.5 MPa ± 68.4) posts; the latter group exhibited the lowest flexural values (50.8 MPa ± 7.9), which were significantly different from both the conventional group (123.0 MPa ± 26.9) and the customized group (230.3 MPa ± 18.9), which also differed from each other. The modulus of elasticity showed statistical differences (p  < 0.05) among the three different methods: CAD-CAM (0.50 GPa ± 0.06), conventional (1.75 GPa ± 0.13), and custom (3.46 GPa ± 0.19). The FS and elasticity modulus of customized posts were significantly higher than those of CAD-CAM, that exhibited the lowest values. Intermediate values were demonstrated by conventional posts. In comparison, to the customized post, the stress study revealed that conventional and CAD-CAM posts had a lower stress in the apical area and a lower general root stress value; but the cervical stress from CAD-CAM posts were practically twice of conventional and customized posts.