The Influence of Thermal Tempering on the Fracture Resistance of Four Heat Pressed Lithia-based glass ceramic Crowns

Abstract

<title>Abstract</title> <bold>Background</bold> This in-vitro study aimed to evaluate the impact of thermal tempering and ceramic type on the fracture resistance of four heat-pressed glass ceramics. <bold>Methods</bold> A total of 84 glass-ceramic crowns were pressed and randomly allocated into four equal groups (n=21) according to the ceramic type: Group (E): IPS e.max Press, Group (L): GC initial LiSi Press, Group (C): Celtra Press and Group (A): VITA Ambria. The crowns of each group were equally allocated into three subgroups (n = 7) regarding the subsequent thermal tempering temperature. Subgroup (T0): No tempering. Subgroup (T1): Tempering at 9% below pressing temperature. Subgroup (T2): Tempering at 5% below pressing temperature. Samples were tested for fracture resistance using a universal testing machine. A scanning electron microscope, X-ray diffraction and Energy Dispersive x-ray analysis were utilized to disclose the microstructural features. <bold>Results</bold> When there is no tempering, IPS e.max press showed a significant elevated fracture resistance. There was an insignificant difference between other ceramics. While with tempering (T2) as well as (T1), Lisi press (L) showed a significant elevated fracture resistance. There was an insignificant difference between other ceramics. <bold>Conclusions</bold> Incorporation of zirconia oxide into the lithium disilicate glass matrix did not show improvement in the fracture resistance. Thermal tempering procedure had significant effect on fracture resistance.