722 - Unintended tooth movement during retention due to deterioration of flexible spiral wire retainers

To evaluate the effects of high-intensity light curing units (light-emitting diode [LED] and plasma arc curing [PAC]) on the microleakage of flexible spiral wire retainers (FSWRs) at the composite/enamel and composite/wire interfaces. Forty-five human mandibular incisor teeth were separated into three groups of 15 teeth. Multistranded PentaOne wire of .0215 inch diameter was bonded to enamel and was cured with three different light curing units: a quartz-tungsten-halogen (QTH) unit and two high-intensity units (ie, LED and PAC). A conventional halogen light served as the control. Samples were sealed with nail varnish, stained with 0.5% basic fuchsine, and sectioned. Transverse sections were evaluated under a stereomicroscope and were scored for microleakage for the composite/enamel and composite/wire interfaces. Statistical analysis was performed by Kruskal-Wallis and Mann-Whitney U-tests with Bonferroni correction. Little or no microleakage was detected at the composite/enamel interface of the FSWR cured with three different light sources. However, at the composite/wire interface, statistically significant differences were found between the QTH (mean, 1.10 +/- 1.05 mm) and high-intensity curing units. The PAC resulted in the greatest amount of microleakage (mean, 2.63 +/- 1.49 mm), whereas no statistically significant difference was noted between the PAC and the LED (mean, 2.35 +/- 1.28 mm). High-intensity light curing units show statistically significant microleakage at the composite/wire interface and therefore may not be safe for use in bonding FSWRs.

Objectives:The aim of this study was to evaluate the cytotoxic effects of fiber reinforced composite bonded retainers in comparison with flexible spiral wires (FSWs) under high and low cariogenic-simulated environments using human oral fibroblasts.Materials and Methods:Four types of bonded retainers were evaluated: (1) reinforced with glass fibers: Interlig (Angelus), (2) reinforced with polyethylene fibers: Connect (Kerr), (3) reinforced with quartz fibers: Quartz Splint UD (RTD), and (4) FSW. Twenty specimens of each sample group were prepared with the same surface area and halved. Next, half of them were placed in a high cariogenic environment 60 min in 10% lactic acid 3 times a day and remained in Fusayama Meyer artificial saliva for the rest of the day) and the other half were placed in a low cariogenic environment 20 min in 10% lactic acid 3 times a day and remained in Fusayama Meyer artificial saliva for the rest of the day) for 1, 7 and 30 days. Cell viability was assessed by MTT assay. Data were analyzed using SPSS software (α =0.05).Results:During the 1st month, cytotoxicity reduced gradually. In the low cariogenic-simulated environment, the cytotoxicity of all of the groups were reported to be mild at day 30 and the difference between them was significant (P = 0.016). In the same period in the high cariogenic-simulated environment, the cytotoxicity of Connect and Quartz Splint was mild, and they had lower cytotoxicity than the other groups. Meanwhile, Interlig had moderate (52%) and FSW had severe cytotoxicity (22%) and the difference between the groups was also significant (P = 0.000).Conclusions:FSW retainers are not recommended in those at high-risk for dental caries. However, in those at low-risk, there is no difference from the standpoint of cytotoxicity.