Abstract
Objectives: Stresses produced during the fabrication of copings and by chewing activity can induce a tetragonal-to-monoclinic (t–m) transformation of zirconia. As a consequence, in the m-phase, the material is not able to hinder possible cracks by the favorable mechanism known as “transformation toughening”. This study aimed at evaluating if different marginal preparations of zirconia copings can cause a premature phase transformation immediately after manufacturing milling and after chewing simulation. Methods: Ninety copings using three commercial zirconia ceramics (Nobel Procera Zirconia, Nobel Biocare Management AG; Lava Classic, 3M ESPE; Lava Plus, 3M ESPE) were prepared with deep-chamfer, slight-chamfer, or feather-edge finish lines (n = 10). Specimens were tested in a chewing simulator (CS-4.4, SD Mechatronik) under cyclic occlusal loads simulating one year of clinical service. Raman spectra were acquired and analyzed for each specimen along the finish lines and at the top of each coping before and after chewing simulation, respectively. Results: Raman analysis did not show any t–m transformation both before and after chewing simulation, as the typical monoclinic bands at 181 cm−1 and 192 cm−1 were not detected in any of the tested specimens. Conclusions: After a one-year simulation of chewing activity, irrespective of preparation geometry, zirconia copings did not show any sign of t–m transformation, either in the load application areas or at the margins. Consequently, manufacturing milling even in thin thickness did not cause any structural modification of zirconia ceramics “as received by manufacturers” both before and after chewing simulation.
Highlights
Due to patients increasing demand for aesthetics, as well as the introduction of the latest innovative dental technologies, the use of high-strength polycrystalline ceramics has become fairly widespread in the last decade [1,2,3,4,5,6]
After a one-year simulation of chewing activity, irrespective of preparation geometry, zirconia copings did not show any sign of t–m transformation, either in the load application areas or at the margins
Manufacturing milling even in thin thickness did not cause any structural modification of zirconia ceramics “as received by manufacturers” both before and after chewing simulation
Summary
Due to patients increasing demand for aesthetics, as well as the introduction of the latest innovative dental technologies, the use of high-strength polycrystalline ceramics has become fairly widespread in the last decade [1,2,3,4,5,6]. Besides offering a more natural appearance of restorations, the biocompatibility and physical properties of zirconia frameworks are widely appreciated by clinicians for their enhanced 11, x fracture. Chemical stability, high toughness (KIC = 9–10 MN/m3/2 ), and flexural strength 2(>1. Zirconia is an allotropic metastable material, which can be present in different crystallographic physical properties of zirconia frameworks are widely appreciated by clinicians for their enhanced structures chemical with the samehigh chemical composition [9,10]. GPa) by [2,4].increasing
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