Influência da quantidade e do posicionamento de espécimes de cerâmica feldspática no forno de sinterização sobre a sua resistência biaxial e opacidade

Abstract

Introduction: Aesthetics and longevity of dental ceramics are two of the most common requirements of patients and dentists today. Various factors are related to obtaining these properties during manufacture of prosthetic crown, but the influence of firing conditions in relation to arrangement of the ceramic in the furnace has not yet been clarified in the literature. Objective: To evaluate the effect of the number and position specimens during firing in a furnace of feldspathic ceramic discs on the flexural strength and opacity. Methods: Ninety VM9 feldspathic ceramic discs were made in metallic molds divided into two groups according to follow: G1- 15 specimens sintered one at a time, placed in the center of the furnace; and G5 - 75 specimens sintered 5 at a time, where 1 disc was positioned in the center of the furnace and the others 4 on the periphery, a total of 15 firings with 5 specimens each time. After that, all discs were ground and polished to present regular surface and final dimensions of 1.2 mm (thickness) and 13.5 mm (diameter). Then, all specimens were evaluated in relation to opacity using a spectrophotometer and subjected to biaxial flexural strength test. Four ANOVA 1-way were carried out, two for biaxial strength and two for opacity. Results: There was no statistical difference between specimens positioned in the center and the mean of the four specimens positioned in the periphery of the furnace (comparison center x periphery) for flexural strength (p=0.08), only for opacity (p=0.009). However, statistical difference was found between group 1 and specimen positioned in the center of the G5 (comparison number of specimens by firing) to both flexural strength (p=0.025) and opacity (p=0.0001). Conclusion: Number of specimens by firing in the furnace seems influence the biaxial flexural strength and opacity of feldspathic ceramic discs, furthermore, also the positioning of the specimens in the furnace (center x periphery) influence the opacity.