Invivo and invitro tensile properties of orthodontic elastomeric chains – A comparative study

Aim: This study was to evaluate the permanent elongation and tensile strength of elastomeric chains in vivo and in vitro of three commonly available brands. Materials and Method: Two types (open & closed chains) of three brands of elastomeric modules producing six groups were included in the study. Specimens were measured by digital caliper and classified into four groups based on their ageing state: (a) as received; (b) subjected to a 24 hours steady strain in air determined as 50% of original length; (c) exposed intraorally for 24 hours; and (d) retrieved following 3 weeks of intraoral exposure. The final lengths of all the specimens were measured and mean percentage elongation was calculated for each group and was analysed with two-way ANOVA. For tensile strength, the specimens were subjected to the above said conditions and were subjected to tensile stress and their behavior was analysed with three-way ANOVA and Tukey's multiple comparison test. Results: The results showed that open E-chains show more percentage elongation compared to closed types. The tensile strengths of the E-chains in all the groups decreased after being subjected to intraoral conditions. The decrease in the tensile strength was proportional to the time in the oral cavity. Conclusion: Open E-chains have higher percentage elongation compared to closed E- chains in vitro but closed E-chains have higher percentage elongation compared to open E-chains in vivo. Among the different test conditions, the maximum percentage elongation was seen after 3 weeks intraoral stretching and least by the E-chains stretched 24 hours in air. The tensile strength was most in the in vitro conditions and least after three weeks stretching intraorally. Clinical Significance: The most important problem of the E-chains is their force decay during the time so being aware of the various factors that can affect their characteristic and force decay pattern is essential. This can help practitioners to use chains in a better way.