Residual stresses in Y-TZP crowns due to changes in the thermal contraction coefficient of veneers

AbstractObjective t the hypothesis that the difference in the coefficient of thermal contraction of the veneering porcelain above (αliquid) and below (αsolid) its Tg plays an important role in stress development during a fast cooling protocol of Y-TZP crowns. s dimensional finite element models of veneered Y-TZP crowns were developed. Heat transfer analyses were conducted with two cooling protocols: slow (group A) and fast (groups B–F). Calculated temperatures as a function of time were used to determine the thermal stresses. Porcelain αsolid was kept constant while its αliquid was varied, creating different Δα/αsolid conditions: 0, 1, 1.5, 2 and 3 (groups B–F, respectively). Maximum (σ1) and minimum (σ3) residual principal stress distributions in the porcelain layer were compared. s e slowly cooled crown, positive σ1 were observed in the porcelain, orientated perpendicular to the core–veneer interface (“radial” orientation). Simultaneously, negative σ3 were observed within the porcelain, mostly in a hoop orientation (“hoop–arch”). For rapidly cooled crowns, stress patterns varied depending on Δα/αsolid ratios. For groups B and C, the patterns were similar to those found in group A for σ1 (“radial”) and σ3 (“hoop–arch”). For groups D–F, stress distribution changed significantly, with σ1 forming a “hoop-arch” pattern while σ3 developed a “radial” pattern. icance ensile stresses generated in the veneering layer during fast cooling protocols due to porcelain high Δα/αsolid ratio will facilitate flaw propagation from the surface toward the core, which negatively affects the potential clinical longevity of a crown.