OBJECTIVE: To test 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. METHODS: Three-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. RESULTS: For the 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. SIGNIFICANCE: Hoop tensile 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.
OBJECTIVE: To test 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. METHODS: Three-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. RESULTS: For the 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. SIGNIFICANCE: Hoop tensile 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.
Authors: Carina B Tanaka; Hossam Harisha; Marta Baldassarri; Mark S Wolff; Hui Tong; Josete B C Meira; Yu Zhang Journal: Ceram Int Date: 2016-05-15 Impact factor: 4.527
Authors: Camila da Silva Rodrigues; Iana Lamadrid Aurélio; Marina da Rosa Kaizer; Yu Zhang; Liliana Gressler May Journal: Dent Mater Date: 2019-03-04 Impact factor: 5.304
Authors: Vinicius Pavesi Fardin; Gerson Bonfante; Paulo G Coelho; Edmara T P Bergamo; Dimorvan Bordin; Malvin N Janal; Nick Tovar; Lukasz Witek; Estevam A Bonfante Journal: J Appl Oral Sci Date: 2022-04-22 Impact factor: 3.144