The Effect of Thermocycling and Surface Treatments on the Surface Roughness and Microhardness of Three Heat-Pressed Ceramics Systems

Abstract

Dental ceramic restorations are widely used in restorative dentistry. However, these restorations can be affected once cemented in the oral cavity by several factors. How can conventional surface treatments, such as glazing and mechanical polishing, diminish the effects of aging? The purpose of this in vitro study was to evaluate the effect of thermocycling and conventional surface treatments on the surface roughness and microhardness of three types of glass-ceramics by using a profilometer, scanning electron microscopy (SEM), atomic force microscopy (AFM), and a microhardness tester. Three types of ceramic systems (zirconia reinforced lithium silicate glass-ceramic, lithium disilicate glass-ceramic, and feldspathic glass-ceramic) (n = 48) were prepared. The samples were subjected to thermocycling for 10,000 cycles. Surface roughness was evaluated numerically using a profilometer and visually by using SEM and AFM. Microhardness was performed using a microhardness tester. The data were interpreted using the ANOVA test, and the results were correlated using Pearson’s correlation formula (r). Significant differences were found before and after thermocycling for the Ra (p < 0.01) and Rz (p < 0.05) parameters. As well, differences between glazed and polished surfaces were significant before and after thermocycling for surface roughness and microhardness (p < 0.05). A correlation was made between average surface roughness and microhardness (r = −460) and for the maximum surface roughness and microhardness (r = −606). Aging increases the roughness and decreases in time the microhardness. The tested ceramic systems behaved differently to the aging and surface treatments. Surface treatments had a significant impact on the microhardness and surface characteristics. The glazed groups were reported with higher surface roughness and lower microhardness when compared to the polished groups before and after thermocycling. The measuring roughness techniques determine the scale-dependent values for the Ra (Sa) and Rz (Sq) parameters. Thermocycling almost doubled the surface roughness for all the tested samples. Microhardness decreased only for the Celtra glazed samples. Nano-roughness increased the values for Vita and slightly for Emax. Thermocycling had little effect on Emax ceramic and a more significant impact on Celtra Press ceramic.

Surface Characterization and Optical Properties of Reinforced Dental Glass-Ceramics Related to Artificial Aging

“…Ra values above 0.2 µm have been reported to lead to increased plaque accumulation and periodontal inflammation, as well as a higher risk of dental caries [47,48]. Recorded values for Ra during this study are below this value.…”

“…AFM analysis possess an essential advantage in studying ceramic materials because it provides high-resolution and three-dimensional visualization of the studied surface. It showed results that demonstrated that polished surfaces presented significantly higher values when compared to the glazed ones [46,47]. Topographic analyses using AFM bring information at the nano level, and nano roughness is not positively correlated with microroughness.…”

Wear, Microhardness and Fracture Toughness of Different CAD/CAM Ceramics

“…The current study results came in partial agreement with Vasiliu et al (2020) (42) , who recorded no significant effect of thermocycling on microhardness of lithium disilicate and zirconia reinforcedlithium silicate ceramics, while they found no significant difference in microhardness of both ceramics.…”

Wear resistance and surface roughness of two types of monolithic glass ceramics: An in vitro study

“…These results were agreed with Vasiliu et al findings which revealed that lithium disilicate glass-ceramic was rarely affected by thermocycling. Furthermore, its surface polishing resulted in lower roughness compared to the glazed Celtra groups (34) . The roughness mean value of E-max CAD group was decreased significantly after wear simulation with enamel antagonist, which may be due to the polished surface together with the high hardness of E-max CAD.…”