Creep, Hardness, and Elastic Modulus of Lingual Fixed Retainers Adhesives

The aims of this study were twofold: a) to characterize a wide array of time-independent and -dependent properties and b) to find possible correlations among the properties tested. Seven commercially available orthodontic adhesives were included in this study and ten cylindrical specimens were prepared from each material. Five specimens from each material were used for the characterization of Martens Hardness (HM), indentation modulus (E_IT), and elastic index (η_IT), and the remaining five for the determination of indentation creep (C_IT). Al the aforementioned properties were identified by employing an Instrumented Indentations Testing (IIT) device with a Vickers indenter. The results of HM, E_IT, η_IT, and C_IT were statistically analyzed by one way ANOVA and Tukey post hoc test, while the possible correlations among the aforementioned properties were determined by Spearman correlation test. Statistical significant differences were identified for all properties among the materials tested. Spearman correlation reveals that HM has a positive correlation with E_IT. Both properties demonstrated a negative correlation with η_IT and C_IT, while no correlation was identified between η_IT and C_IT. Significant differences in the mechanical properties tested may also imply differences in their clinical behavior and efficacy.