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

Author(s)

Meira, Josete B. C. ^[1] ; Reis, Bruno R. ^[1] ; Tanaka, Carina B. ^[1] ; Ballester, Rafael Y. ^[1] ; Cesar, Paulo F. ^[1] ; Versluis, Antheunis ^[2] ; Swain, Michael V. ^[3]

Affiliation

^[1] Univ Sao Paulo, Sch Dent, Biomat & Oral Biol Dept, Sao Paulo - Brazil

^[2] Univ Tennessee, Ctr Hlth Sci, Coll Dent, Memphis, TN 38163 - USA

^[3] Univ Sydney, Sydney Dent Hosp, Biomat Unit, Sydney, NSW 2006 - Australia

• Document type: Journal article
• Source: Dental Materials; v. 29, n. 5, p. 594-601, MAY 2013.
• Web of Science Citations: 23

Abstract

Objective. To test the hypothesis that the difference in the coefficient of thermal contraction of the veneering porcelain above (alpha(liquid)) and below (alpha(solid)) its T-g 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 alpha(solid) was kept constant while its alpha(liquid) was varied, creating different Delta alpha/alpha(solid) conditions: 0, 1, 1.5, 2 and 3 (groups B-F, respectively). Maximum (sigma(1)) and minimum (sigma(3)) residual principal stress distributions in the porcelain layer were compared. Results. For the slowly cooled crown, positive sigma(1) were observed in the porcelain, orientated perpendicular to the core-veneer interface ({''}radial{''} orientation). Simultaneously, negative sigma(3) were observed within the porcelain, mostly in a hoop orientation ({''}hoop-arch{''}). For rapidly cooled crowns, stress patterns varied depending on Delta alpha/alpha(solid) ratios. For groups B and C, the patterns were similar to those found in group A for sigma(1) ({''}radial{''}) and sigma(3) ({''}hoop-arch{''}). For groups D-F, stress distribution changed significantly, with sigma(1) forming a ``hoop-arch{''} pattern while sigma(3) developed a ``radial{''} pattern. Significance. Hoop tensile stresses generated in the veneering layer during fast cooling protocols due to porcelain high Delta alpha/alpha(solid) ratio will facilitate flaw propagation from the surface toward the core, which negatively affects the potential clinical longevity of a crown. (C) 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. (AU)

• FAPESP's process: 09/06266-7 - Finite element analysis of the failure mechanism of porcelain applied on zirconia (Y-TZP) frameworks
• Grantee: Josete Barbosa Cruz Meira
• Support type: Scholarships abroad - New Frontiers