Accuracy of fit of 3-to-3 retainers after adhesive fixation using a neodymium-iron-boron magnet chain

Abstract

Six-base retainers are often used to prevent tertiary crowding. To minimize shear stress on the retainer, these should be fitted as precisely as possible. The aim of this study was to compare the accuracy of fit of 6-base retainers after adhesive fixation using a neodymium-iron-boron (NdFeB) magnet chain or a resin positioning aid. A 6-base retainer was prepared for 40 pseudo-anonymous lower jaw models (2 x 20). Temporary fixation was performed with a resin positioning aid or a NdFeB magnet chain. The adhesive fixation of the retainers was randomized. The area and vertical distance between wire and teeth were determined by histomorphometry. The results were evaluated by ANOVA. The probability of error was specified as 5%. With the magnetic chain method, the area was significantly smaller than with the positioning aid (p = 0.0125). The difference between the two methods was ca. 1.3 mm(2). Moreover, the measured distance was affected significantly by the method used (p < 0.0002). With the magnet chain, the distance between the tooth and retainer was reduced by a mean of 0.05 mm. The fit of the retainer wire improves somewhat when the NdFeB magnet chain is used even though the wire is not as precisely positioned as it would be with a custom-made positioning aid.