Background <p>Additional firing to repair a lost proximal contact or porcelain chipping might affect the fracture strength of a metal-ceramic crown. This study aimed to evaluate the effect of glazing and hydrothermal aging on the fracture strength of metal-ceramic crowns after additional firing.</p> Methods <p>A total of 40 metal-ceramic crowns were fabricated and divided evenly into five groups: not aged/glazed (G0), 3-month-old/glazed (G3), 24-month-old/glazed (G24), 3-month-old/unglazed (nG3), and 24-month-old/unglazed (nG24). Autoclaving was used as the aging protocol. All groups underwent an additional firing cycle, and fracture strength was measured. Data were analyzed using ANOVA and independent t-tests.</p> Results <p>G0 demonstrated the highest fracture strength (4405.00 ± 1528.20&#xa0;N), followed by G3, nG3, G24, and nG24, respectively. There was a significant difference between G0 and G24 (<i>P</i> =.01), G0 and nG3 (<i>P</i> =.00), and G0 and nG24 (<i>P</i> =.00).</p> Conclusion <p>Glazing does not significantly affect the fracture strength of a metal-ceramic crown undergoing additional firing; however, aging has a significant adverse effect on fracture strength. This negative effect is not significant until after 3 months.</p>