Effect of Distance to the Heat Source During Firing on the Final Color of Metal-Ceramic Restorations: An In Vitro Study

Background This study aimed to evaluate the influence of furnace positioning and sequential firing procedures on the final color of metal-ceramic restorations. Methods Forty-two disc-shaped metal-ceramic specimens were fabricated and veneered with dentin, enamel, transparent, and glaze porcelain layers. Specimens were positioned at three different zones within the porcelain furnace (inner, middle, and outer) and subjected to standardized firing cycles. Color measurements were performed using a spectrophotometer after each firing phase. Color differences (ΔE*) were calculated between the control (center) and each group, and the clinical relevance was interpreted according to perceptibility (ΔE*=1.74) and acceptability (ΔE*=3.48) thresholds. Statistical analysis was conducted using two-way ANOVA and post hoc Tukey's HSD tests (α = 0.05). Results Both furnace position (p < 0.05) and firing procedure (p 0 < 0.05) significantly affected color differences. The greatest color changes were observed in specimens placed in the outer zone (ΔE = 6.90), whereas specimens in the inner zone exhibited minimal color differences (ΔE = 1.80). Outer and middle specimens exceeded the clinical acceptability threshold, while inner specimens remained within clinically acceptable limits. Conclusions The position of metal-ceramic restorations within the furnace during firing procedures significantly affects the final color outcome. Careful placement of restorations during porcelain firing is essential to ensure optimal color stability.