Ludovichetti, Francesco Saverio (2019) CAD/CAM monolithic materials: wear resistance and abrasiveness, and the effect of grinding and polishing on their roughness and fracture resistance. [Ph.D. thesis]
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Abstract (italian or english)
This thesis consists of two studies, both investigating the computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic materials.
First study. Aim. The wear resistance and abrasiveness of Lava Ultimate, Vita Enamic, Vita Suprinity, IPS e.max CAD, and Lava Plus, as well as some properties that might be related to, were analyzed. Methods. Specimens from these materials had their roughness, hardness, and coefficient of friction evaluated, respectively in confocal microscope, microdurometer, and tribometer. The 2-body wear test, wherein the materials acted as abraders and, together with bovine enamel, also as antagonists, was also carried out. The wear rate was determined with surface profilometer and the worn surfaces were observed by scanning electron microscopy (SEM). Results. Vita Enamic and Lava Ultimate showed the highest roughness, whereas IPS e.max CAD and Vita Suprinity, the lowest. The hardness result was Lava Plus > (Vita Suprinity=IPS e.max CAD) > Vita Enamic >Lava Ultimate. Lava Ultimate exhibited a higher coefficient of friction than IPS e.max CAD and Lava Plus. Lava Plus and IPS e.max CAD showed significantly higher potential to wear Lava Ultimate. These two materials, together with Vita Suprinity, provided the highest wear of enamel and Vita Enamic. Vita Suprinity and IPS e.max CAD exhibited the highest wear against Lava Plus, and the inverse also occurred. Vita Enamic and Lava Ultimate were among the materials that caused the lowest wear of enamel and all other evaluated materials. Conclusion. The nanofilled composite resin and polymer-infiltrated ceramic were more antagonist-friendly (whether enamel or CAD-CAM material) than glass-ceramics and zirconia. Care should be taken when selecting the material that will contact mainly with glass-ceramics. Hardness should also be considered when selecting a material.
Second study. Aim. To evaluate the effect of grinding and polishing on the roughness and fracture resistance of Lava Ultimate, Vita Enamic, Vita Suprinity, and IPS e.max CAD, submitted to mechanical aging. Methods. Disks from these materials were analyzed for roughness: 1) after polishing with silicon carbide papers (Lava Ultimate and Vita Enamic) or glazing (IPS e.max CAD and Vita Suprinity) (control); 2) after grinding with 30-μm grit diamond rotary instruments; 3) and after grinding and polishing with the polishing kit Ceramiste Polishers. For fracture resistance, a simplified tri-layer model consisting of restorative disk, epoxy resin disk, and a steel ring was used. The bonded tri-layer disks received the same conditions described for the roughness analysis. Half of the specimens underwent mechanical aging for 1×106 cycles. All specimens were loaded until failure. The Weibull modulus was calculated. Results. Among the control groups, no significant difference was found between the IPS e.max CAD and Vita Suprinity and between the Lava Ultimate and Vita Enamic, which were rougher than the glass-ceramic materials. After grinding, this behavior was maintained, except for the Vita Enamic, whose roughness was similar to that of the IPS e.max CAD. After polishing, the Vita Enamic showed the highest roughness, whereas the other materials were not statistically different. IPS e.max CAD and Vita Suprinity showed the lowest roughness in the control groups. For Lava Ultimate and Vita Enamic, polishing provided the lowest roughness. Grinding followed or not by polishing, and mechanical aging, did not adversely affect fracture resistance or the reliability of the materials. Conclusions. Polishing did not recover the initial roughness of the glass-ceramic materials. Fracture resistance was not affected by grinding, followed or not by polishing, even after mechanical aging.
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