Force decay and dimensional changes of thermoplastic and novel thermoset elastomeric ligatures.

OBJECTIVES To compare over a period of 8 weeks (1) the force decay and (2) the dimensional changes between thermoplastic (TP) and thermoset (TS) elastomeric ligatures. MATERIALS AND METHODS TP and TS elastomeric ligatures were obtained from Rocky Mountain Orthodontics™. The TS ligatures were custom made specifically for this study. The sample included 72 clear TP and 72 clear TS elastomeric ligatures. The experiment was performed in a simulated oral environment (pH of 6.75) at 37°C. The remaining forces and the dimensional changes were measured at different time points over a period of 8 weeks. RESULTS Student's t-tests revealed significant differences in percent force loss, percent change in outer diameter, percent change in inner diameter, and percent change in wall thickness between TP and TS elastomeric ligatures across all time points (P < .001). The difference in percent change in width between TP and TS elastomeric ligatures was not significant at all time points (P > .05). The mean difference in force loss between TP and TS across all time points was 22.91%. The TP and TS specimens exhibited 93.04% and 77.41% force loss, respectively, at the 28th day. CONCLUSIONS This novel TS elastomeric ligature showed significantly less force decay and dimensional changes over time; therefore, it might be superior during initial leveling and aligning and during finishing stages. Using a transfer jig to prevent relaxation of the specimens before force measurement showed that force decay of commercially available elastomeric ligatures was greater than that described in previous publications.

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