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The Journal of Adhesive Dentistry
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J Adhes Dent 16 (2014), No. 5     21. Nov. 2014
J Adhes Dent 16 (2014), No. 5  (21.11.2014)

Page 407-413, doi:10.3290/j.jad.a32664, PubMed:25191668


Effect of Non-ionizing Radio Frequency Signals of Magnetic Resonance Imaging on Physical Properties of Dental Alloys and Metal-Ceramic Adhesion
El-Bediwi, Abu Bakr / El-Fallal, Abeer / Saker, Samah / Özcan, Mutlu
Purpose: To assess the influence of non-ionizing radio frequency signals of magnetic resonance imaging (MRI) on physical properties of dental alloys and metal-ceramic adhesion.
Materials and Methods: A total of 120 disk-shaped wax patterns (10 mm x 10 mm x 1 mm) were cast in a base metal alloy (Ni-Cr alloy) and commercially pure titanium (Ti) following the manufacturing recommendation. After casting, air abrasion and ultrasonic cleaning, feldspathic ceramic was applied and fired according to manufacturer's instructions using a standard mold. The specimens were subjected to 3000 thermocycles in distilled water between 5°C and 55°C, then veneered alloy specimens were randomly assigned to three groups according to MRI exposure time: a) 15 min of MRI exposure, b) 30 min of MRI exposure and c) no MRI exposure (control group). The specimens were subjected to shear loading until failure. A separate set of Ni-Cr and Ti specimens were prepared, and after exposure to MRI for 15 and 30 min, x-ray diffraction (XRD) analysis, surface roughness, and Vicker's hardness were measured.
Results: Both the alloy type (p < 0.005) and exposure duration (p < 0.005) had a significant effect on the bond results. While the control group presented the highest bond strength for Ni-Cr and Ti (36.9 ± 1.4 and 21.5 ± 1.6 MPa, respectively), 30 min MRI exposure significantly decreased the bond strength for both alloys (29.4 ± 1.5 and 12.8 ± 1.5 MPa, respectively) (p < 0.05). XRD analysis indicated formation of the crystalline phase as well as change in crystal size and position for Ni-Cr and Ti after MRI. Compared to the control group where alloys were not exposed to MRI (Ni-Cr: 0.40 μm; Ti: 0.17 μm), surface roughness increased (Ni-Cr: 0.54 μm; Ti: 1.1 μm). Vicker's hardness of both alloys decreased after 30 min MRI (Ni-Cr: 329.5; Ti: 216.1) compared to the control group c (Ni-Cr: 356.1; Ti: 662.1), being more significant for Ti (p < 0.005).
Conclusion: Ni-Cr alloy is recommended over Ti for the fabrication of metal-ceramic restorations for patients with a history of frequent exposure to MRI.

Keywords: adhesion, base alloy, chipping, magnetic resonance imaging, metal-ceramic, roughness, titanium