Effect of Magnetic Resonance Imaging at 1.5 T and 3 T on Temperature and Bond Strength of Orthodontic Bands with Welded Tubes: An In Vitro Study.

Magnetic resonance imaging (MRI) is a widely used diagnostic technique. Patients wearing orthodontic devices are often requested to remove their appliances before an MRI exam, even when the exam involves anatomical areas far from the head, in order to prevent the heating and detachment of the appliances. The present report aims to evaluate changes in temperature and adhesive forces of molar bands after MRI at two different strength outputs. Sixty stainless steel molar bands were bonded on permanent human upper molars using two different cements: Unitek Multi-Cure Glass Ionomer Band Cement (3M Unitek, Monrovia, CA, USA) and Transbond Plus Light Cure Band Adhesive (3M Unitek). Appliances were subjected to MRI with two different strengths (1.5 Tesla and 3 Tesla). Tubes and band temperature was measured before and after MRI. Subsequently, the shear bond strength (SBS) test was calculated. Data underwent statistical analysis (p < 0.05). After MRI, molar bands exhibited significant heating, even though not clinically relevant, with a temperature increase ranging between 0.48 °C and 1.25 °C (p < 0.05). SBS did not show significant differences (p > 0.05). The present study suggests that, under MRI, the molar bands tested are safe; therefore, their removal could be not recommended for non-head and neck MRI exams. Removal would be necessary just in artifact risk areas.

Orthodontic Fixed Retainer and Unwanted Movements of Lower Anterior Teeth: A Case Report.

The use of fixed retainers at the end of an orthodontic treatment has become a standard practice. Nonetheless, orthodontic relapse can still occur, requiring retreatment in the most severe cases. This case report describes a patient with a mandibular canine to canine fixed retainer presenting uncontrolled torque on all lower anterior teeth, probably due to tongue thrust and/or activation of the wire. Multibracket orthodontic treatment was performed, and an orthodontic lingual sectional was used to control (reposition) the root movement of the lower right cuspid. This case highlights the need for clinicians and patients to be aware of the potential problems associated with bonded retainers. In addition, patients with an orthodontic fixed retainer need regular short-term observation by an orthodontist in order to detect any adverse movements and long-term control by a general dentist.