Effect of multiple firing on flexural strength and color stability of pressable all ceramic material: An In-vitro study

Introduction: Pressable all-ceramic materials are widely used in dentistry. Determining the effect of multiple firing on color stability and flexural strength will help to improve these materials so that they can remain resistant to fracture in restorative work. Aim: The aim of this study was to evaluate the change in flexural strength and color stability of pressable all ceramic material after repeated firing, which may be unavoidable when color and shape corrections are necessary for use in dental restorations. Materials and Methods: Thirty standardized bar specimens measuring 25-mm length, 10-mm width, and 2-mm thickness were fabricated from VITA PM 9 pressable all ceramic material according to the manufacturer's instructions. Each group of specimen was tested for color change using the spectrophotometer and flexural strength (three-point flexural strength test) using the universal testing machine after third (n = 10), fourth (n = 10), and fifth (n = 10) firings. The data were analyzed using a one-way analysis of variance. The Tukey honestly significant difference test was used to perform multiple comparisons. Results: L*a*b* values of the ceramic specimens were affected by the number of firings (3, 4, and 5 firings) (P 0.05). There were statistically significant differences (P < 0.05) in the mean flexural strength values of the three groups. Conclusion: Repeated firing of leucite-based heat-pressed ceramic exhibited color changes that are clinically acceptable, but the strength of the ceramic decreases significantly. Thus, repeated firing is an important factor with respect to color and strength of definitive restoration and should be considered during shade selection and fabrication.