The mechanical strength of orthodontic elastomeric memory chains and plastic chains: An in vitro study.

Background. The loss of physical properties of orthodontic chains has been a topic of discussion among scientists and clinicians, motivating efforts to improve elastic materials and minimize the decrease of force. Orthodontic companies have introduced memory elastomers, which, according to the manufacturers, have improved mechanical properties. Objectives. The aim of the study was to evaluate the effects of stretching elastomeric chains submerged in 37 degrees C artificial saliva. Material and methods. The study assessed 2 types of chains. The first phase of the study evaluated 1) the tensile strength of the chains; and 2) elongation at the time of tearing in an environment outside of the oral cavity (without exposition). The second phase of the study evaluated 1) permanent deformation after stretching; 2) elongation at the time of tearing; and 3) the tensile strength of the chain in conditions similar to those present in the oral cavity. Results. In the experiments using artificial saliva, pronounced force decay was observed in the plastic chain, in which, after just 7 days, force decreased almost by half compared to the initial value, with a continuous downward trend. The memory chain, however, showed increased elasticity, and after the first week of exposition the force decay at the time of tearing was around 20% of the initial value. Force decay at the time of tearing remained at a steady level between 14.4 and 25.4% throughout the whole period of exposition. In the plastic chain this value oscillated between 50.3 and 55.9%. In the experiments assessing permanent deformation of the chains performed after each week of exposition, the specimens prepared from the memory chain stretched from 8 cm to approximately 9.5 cm after exposition, while the specimens prepared from the plastic chain stretched to approximately 13 cm. Conclusions. Memory chains are more effective in orthodontic treatment due to diminished loss of mechanical and elastic capabilities, when compared to plastic chains.