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Effects of Finish Line Design and Fatigue Cyclic Loading on Phase Transformation of Zirconia Dental Ceramics: A Qualitative Micro-Raman Spectroscopic Analysis

1
Department of Neurosciences, Reproductive and Odontostomatological Sciences, Division of Prosthodontics and Digital Dentistry, University of Naples “Federico II”, via S. Pansini 5, 80131 Naples, Italy
2
Department of Medical Sciences, University of Trieste, Piazza dell’Ospitale 1, 34129 Trieste, Italy
3
Department of Biomedical Science and Neuromotor Sciences, DIBINEM, University of Bologna, Via San Vitale 59, 40123 Bologna, Italy
*
Author to whom correspondence should be addressed.
Materials 2019, 12(6), 863; https://doi.org/10.3390/ma12060863
Received: 27 January 2019 / Revised: 28 February 2019 / Accepted: 12 March 2019 / Published: 14 March 2019
(This article belongs to the Special Issue Current and Future Trends in Dental Materials)
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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. View Full-Text
Keywords: finish line; zirconia coping; Raman spectroscopy; transformation toughening; chewing simulation finish line; zirconia coping; Raman spectroscopy; transformation toughening; chewing simulation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Sorrentino, R.; Navarra, C.O.; Di Lenarda, R.; Breschi, L.; Zarone, F.; Cadenaro, M.; Spagnuolo, G. Effects of Finish Line Design and Fatigue Cyclic Loading on Phase Transformation of Zirconia Dental Ceramics: A Qualitative Micro-Raman Spectroscopic Analysis. Materials 2019, 12, 863.

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