Influence of Additive Firing on the Surface Characteristics, Streptococcus mutans Viability and Optical Properties of Zirconia

Abstract

The purpose of this study was to observe whether the repetitive firing of dental zirconia caused changes in surface characteristics, S. mutans viability, and optical properties of zirconia. Dental zirconia blocks were sintered and randomly distributed into seven experimental groups: F0-F6. Except for F0, which only went through sintering, the additive firing was performed in order for F1-F6. Surface roughness, contact angle, S. mutans viability by fluorescence, and translucency parameter were measured. They were all highest after sintering (F0) and decreased after additive firings (F1–F6). The additive firing of zirconia after sintering decreased surface roughness, contact angle, S. mutans viability, and translucency. The number of firings after the first firing was not found to be critical in surface characteristics, S. mutans viability, and optical property. Changes in surface characteristics might have led to a decrease in S. mutans viability, while the change of translucency was not clinically significant. This implies that additive firing may prevent secondary caries under zirconia restorations, not compromising esthetic appearance.

Effect of Repeated Firings and Thickness on Optical Properties of Variable Preshaded and Shaded Novel Translucent Zirconia Blocks

“…The repeated firings changed the translucency 0.5 mm thick specimens but had no significant effect on 1 and 1.5 mm thick specimens. TP values are decreased from 1 to 3 firings, while translucency is increased from 3 to 5 firings for all thickness specimens which is consistent with conducted by Moon et al [14] and Fathi et al [18].…”

“…O'Brien et al [ 13 ] reported the perceivable color differences of specimens between 3rd and 5th firings. Firing processes can cause changes on optic and mechanical properties of the zirconia [ 14 ]. After repetitive firing procedures, differences in flexural strength, microhardness, and marginal fit can be seen in zirconia [ 15 ].…”

Effects of multiple firings on the translucency, crystalline phase, and mechanical strength of highly translucent zirconia

“…Altan and Cinar 27) reported that multiple firing cycles decrease the translucency of zirconia. Several previous scholars have reported a significant decrease in translucency from the first to the third firing [27][28][29] . These results suggest that multiple firing cycles may decrease the translucency of highly translucent zirconia.…”