Description:
<jats:p> <jats:italic>
<jats:styled-content>Purpose:</jats:styled-content>
</jats:italic> The purpose of this study was to test the hypothesis that the increase in fracture toughness of a fluorcanasite‐based glass‐ceramic is a linear function of crystal volume fraction.</jats:p><jats:p> <jats:italic>
<jats:styled-content>Materials and Methods:</jats:styled-content>
</jats:italic> A total of 60 specimen bars (20 × 5 × 2 mm<jats:sup>3</jats:sup>) were cut from parent glass blocks, polished, annealed, randomly divided into six groups, nucleated at 680°C/4 hr, and crystallized at the following temperatures and times: (1) 850°C/0.5 hr, (2) 850°C/1 hr, (3) 850°C/3 hr, (4) 750°C/6 hr, (5) 800°C/6 hr, or (6) 850°C/6 hr. Indentation flaws were produced by a microhardness indenter at the center of one surface, and the prepared specimens were subjected to three‐point flexure loading with the severely flawed surface under tension at a crosshead speed of 0.5 mm/min. Flexural strength and fracture toughness (<jats:italic>K</jats:italic><jats:sub>IC</jats:sub>) were calculated based on the indentation‐strength technique. Crystal volume fraction (<jats:italic>V</jats:italic><jats:sub>c</jats:sub>) was determined by quantitative stereology of scanning electron images of each group of ceramic specimens. Statistical analysis was performed using ANOVA and Duncan's multiple comparison test (α= 0.05).</jats:p><jats:p> <jats:italic>
<jats:styled-content>Results:</jats:styled-content>
</jats:italic> The mean <jats:italic>K</jats:italic><jats:sub>IC</jats:sub> and <jats:italic>V</jats:italic><jats:sub>c</jats:sub> values ranged from 2.7 to 3.9 MPa m<jats:sup>1/2</jats:sup> and 37% to 71% within the crystallization temperature range of 750 to 850°C. Five statistical subsets of groups 1, 2/4, 3, 5, and 6 were determined as a function of crystallization temperature and holding time (Duncan's multiple comparison analysis; α= 0.05). The lowest and highest <jats:italic>K</jats:italic><jats:sub>IC</jats:sub> and <jats:italic>V</jats:italic><jats:sub>c</jats:sub> values were associated with Groups 1 (850°C/0.5 hr) and 6 (850°C/6 hr), respectively. Fracture toughness increased linearly as a function of crystal volume fraction (correlation coefficient <jats:italic>R</jats:italic><jats:sup>2</jats:sup>= 0.67). The fracture toughness increased by 45% when the crystal volume fraction increased by 92%.</jats:p><jats:p> <jats:italic>
<jats:styled-content>Conclusions:</jats:styled-content>
</jats:italic> Mean <jats:italic>K</jats:italic><jats:sub>IC</jats:sub> values increased as a linear function of crystal volume fraction in a fluorcanasite‐based glass‐ceramic within the crystallization temperature range of 750 to 850°C and at isothermal crystallization time range of 0.5 to 6 hours. The control of crystallization temperature and isothermal holding time should be optimized to generate tougher, more reliable ceramic prostheses in the shortest period of time.</jats:p>