title: Effect of non-ionizing radio frequency signals of magnetic resonance imaging on physical properties of dental alloys and metal-ceramic adhesion.
abstract: OBJECTIVE
  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.
  
  
  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).
  
  
  CONCLUSIONS
  Ni-Cr alloy is recommended over Ti for the fabrication of metal-ceramic restorations for patients with a history of frequent exposure to MRI.
authors.forename: Abu Bakr
authors.initials: AB
authors.lastname: El-Bediwi
authors.forename: Abeer
authors.initials: A
authors.lastname: El-Fallal
authors.forename: Samah
authors.initials: S
authors.lastname: Saker
authors.forename: Mutlu
authors.initials: M
authors.lastname: Ozcan
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D000538:Aluminum Silicates / Q000737:chemistry; D002858:Chromium Alloys / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry*; D001840:Dental Bonding; D045662:Dental Etching / Q000379:methods; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D003801:Dental Veneers; D006244:Hardness; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000379:methods*; D055585:Physical Phenomena; D017680:Potassium Compounds / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014025:Titanium / Q000737:chemistry; D014465:Ultrasonics; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D000538:Aluminum Silicates; D002858:Chromium Alloys; D003722:Dental Alloys; D017680:Potassium Compounds; D014867:Water; D003776:Dental Porcelain; C016447:feldspar; D014025:Titanium; D000537:Aluminum Oxide