Influence of storage conditions on the mechanical properties of intermaxillary elastics

Latex intermaxillary elastics (IE) are common orthodontic auxiliaries, but their generated force degrades over time. This study investigated the impact of light and heat exposure during storage on the IE force.

From 500 3/16" Medium IE ten test groups were formed. For one month, four groups were exposed to natural daylight and four to a temperature of 50° C in three different packaging types (original semi-opaque, transparent, and closed orthodontic box) or stored loosely. The control groups were stored in the dark at 23° C. The initial extension force (F₀), the residual force after 2 h of tensile loading (F_2h) at three times original diameter and maximal force at break (F_max) were measured. Visual evaluation using a stereomicroscope and light microscope was conducted, and shape, visible damage or defects, and colour changes were documented.

After light exposure, IE stored loosely showed the lowest mean forces (F₀, F₂_h, F_max), all lower than those of the control, while IE stored in a box maintained values closest to the control. Significant differences in force magnitudes were observed between different packaging types, especially in F_2h and F_max. Heat exposure had minimal effect on F₀ values, and reductions were limited mainly to F₂_h for IE stored in transparent packaging and in the box, and F_max in the loosely stored group. Shape variability was observed in 21% of IE, with major defects in 6% and minor defects in 31%. Light exposure resulted in visible discoloration.

One month of light exposure reduced IE force even when stored in original packaging. Heat was less harmful, though residual force still declined. Storage in a box yielded the best results. Structural defects or shape irregularities may contribute to the differences in force degradation. Patient guidelines should advise keeping IE in a light-proof container at a stable room temperature.