Influence of common fixed retainers on the diagnostic quality of cranial magnetic resonance images.
BACKGROUND
Orthodontists are often asked to remove fixed retainers before magnetic resonance imaging (MRI). This study was undertaken to assess the effects of 2 commonly used fixed retainers on MRI distortion and whether they should be removed.


METHODS
MRI scans were performed on a dry skull with Twistflex (Dentaurum, Ispringen, Germany) and Ortho Flex Tech (Reliance Orthodontic Products, Itasca, Ill) retainers. Two neuroradiologists independently ranked the distortions. The influence of the fixed retainers' alloys, their distance to the area of diagnosis, location, strength of the magnetic field, and the spin-echo sequence were examined. Statistical analysis included kappa and Pearson chi-square tests.


RESULTS
Ortho Flex Tech retainers caused no distortion. Twistflex retainers caused distortion in 46% of the tests in areas close to the retainer (tongue and jaws). Maxillary fixed retainers and the combination of maxillary and mandibular fixed retainers further increased the distortion. Greater distortion was observed with 3-T magnetic fields and T1-weighted spin-echo sequences.


CONCLUSIONS
Removal of the Ortho Flex Tech retainer is unnecessary before MRI. Removal of the Twistflex should be considered if the MRI scans are performed to diagnose areas close to the fixed retainers, when 3-T magnetic fields and T1-weighted sequences are used, and when both maxillary and mandibular fixed retainers are present.
Clinical lecturer and director, Postgraduate Program, Department of Orthodontics, Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Israel. Electronic address: mshalish@hadassah.org.il.
Miriam
M
Shalish
Clinical instructor, Department of Orthodontics, Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Israel.
Nimrod
N
Dykstein
Head, Oral & Maxillofacial Radiology Unit, Oral Medicine Department, Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Israel.
Silvina
S
Friedlander-Barenboim
Clinical instructor, Department of Radiology, Hadassah Medical Center, Jerusalem, Israel.
Eliel
E
Ben-David
Professor and head, Neuroradiology Unit, Department of Radiology, Hadassah Medical Center, Jerusalem, Israel.
John Moshe
JM
Gomori
Associate professor and chair, Department of Orthodontics, Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Israel.
Stella
S
Chaushu
D016477:Artifacts; D003287:Contrast Media; D003722:Dental Alloys / Q000737:chemistry; D005260:Female; D005682:Gadolinium; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008334:Mandible / Q000473:pathology; D008437:Maxilla / Q000473:pathology; D008536:Meglumine; D009942:Organometallic Compounds; D016382:Orthodontic Appliance Design; D018704:Orthodontic Retainers; D012886:Skull / Q000473:pathology; D013193:Stainless Steel / Q000737:chemistry; D014059:Tongue / Q000473:pathology
D003287:Contrast Media; D003722:Dental Alloys; D006047:Gold Alloys; D009942:Organometallic Compounds; D013193:Stainless Steel; D008536:Meglumine; D005682:Gadolinium; C072417:gadoterate meglumine