title: Spatial distribution of residual stresses in glass-ZrO2 sphero-cylindrical bilayers.
abstract: Residual stresses arising from inhomogeneous cooling after sintering have shown to play a preponderant role in the higher incidence of chippings observed for glass-zirconia dental prostheses. Still, current descriptions of their nature and distribution have failed to reconcile with clinical findings. Therefore, an axisymmetric sphero-cylindrical bilayer model was used in this study to determine the effect of the cooling rate on the final spatial distribution of residual stresses. Zirconia frameworks with two different radii (1.6 and 3.2mm) were CAD/CAM fabricated. Subsequent glass overlays with two different thickness ratios (1:1 and 2:1) were generated and heat pressed onto the zirconia substrates. The obtained structures were submitted to a last firing process and fast- (45°C/s) or slow-cooled (0.5°C/s) to room temperature. Unbonded bilayers were produced by firing glass overlays onto boron nitride coated zirconia. Thin sagittal and transversal sections were obtained from the specimens to assess residual stress distribution by means of light birefringence. The applied cooling rates did not affect distribution or magnitude of radial residual stresses (sagittal sections), whereas increased hoop stress magnitudes were measured (transversal sections) in fast-cooled specimens. A distinct stress nature was observed for the hoop stress component of unbonded overlays after fast cooling. Interaction between stress components seems to govern the final stress distribution, highlighting the importance of a multiaxial assessment of this problem in three-dimensional structures.
authors.affiliation: Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), Dental Clinic 1-Operative Dentistry and Periodontology, Research Laboratory for Dental Biomaterials, Glueckstrasse 11, 91054 Erlangen, Germany; Department of Restorative Dentistry, Faculty of Dentistry, University of Concepción, Concepción, Chile.
authors.forename: Michael
authors.initials: M
authors.lastname: Wendler
authors.affiliation: Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), Dental Clinic 1-Operative Dentistry and Periodontology, Research Laboratory for Dental Biomaterials, Glueckstrasse 11, 91054 Erlangen, Germany.
authors.forename: Renan
authors.initials: R
authors.lastname: Belli
authors.affiliation: Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), Dental Clinic 1-Operative Dentistry and Periodontology, Research Laboratory for Dental Biomaterials, Glueckstrasse 11, 91054 Erlangen, Germany.
authors.forename: Anselm
authors.initials: A
authors.lastname: Petschelt
authors.affiliation: Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), Dental Clinic 1-Operative Dentistry and Periodontology, Research Laboratory for Dental Biomaterials, Glueckstrasse 11, 91054 Erlangen, Germany. Electronic address: ulrich.lohbauer@fau.de.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Lohbauer
mesh_terms: D003799:Dental Stress Analysis; D003801:Dental Veneers; D005898:Glass; D008422:Materials Testing; D013314:Stress, Mechanical; D015040:Zirconium
chemical_list: D015040:Zirconium
keywords: Cooling rate; Glass-zirconia bilayer; Light birefringence; Residual stress; Thermal mismatch