Effect of Heat Tempering on the Biaxial Flexural Strength of four Heat Pressed glass ceramics (an in vitro study)

Abstract

Objectives: the aim of this study was to evaluate the effect of thermal tempering on the biaxial flexural strength of four types of heat pressed Lithium disilicates glass ceramics. Methods: Sixty heat-pressed glass ceramic discs were fabricated (diameter = 15 mm; thickness = 1mm) and allocated among four groups (n = 15): IPS e.max Press (E), GC initial LiSi Press (L), Celtra Press (C) and VITA Ambria (A). Each group was subdivided into three subgroups (n=5) according to suggested thermal tempering temperature: NO thermal tempering (T0), thermal tempering at a temperature 9% below the recommended pressing temperature (T1) and thermal tempering at a temperature 5% below the recommended pressing temperature (T2). Biaxial flexural strength was measured. Scanning electron microscope (SEM) was performed for microstructural characterization. To determine the crystalline phases of Lithium disilicates glass-ceramics, X-ray diffraction (XRD) was used. Statistical analysis was then performed. Results: IPS e.max Press showed the highest mean strength. There was no difference in strength between Celtra Press and VITA Ambria; both showed the lowest mean strength values. Regardless of ceramic type 5% below pressing temperature showed the highest mean strength and No thermal tempering showed the lowest mean strength. Conclusion: Regarding flexural strength; heat tempering at 5% below the pressing temperature of IPS Emax press showed the highest values. Vita Ambria without heat tempering showed the lowest values.