Structural conformation of in vitro and in vivo aged orthodontic elastomeric modules

The objectives of this study were to investigate the structural characteristics of open and closed elastomeric modules in the as-received condition, and following (a) 24-hour in vitro loading determined as a 50 per cent extension relative to their original length; (b) 24-hour intra-oral exposure; (c) 3-week intra-oral exposure. Ten specimens of each type (open and closed) of the three brands of elastic chains were included in the study (total of 60). All specimens were subjected to (a) optical transmission microscopy utilizing phase contrast and polarized light modes, (b) micro MIR FT-IR spectroscopy, and (c) scanning electron microscopy and electron probe X-ray microanalysis. Stretched elastomers demonstrated a honeycomb pattern of filament detachment corresponding to strained areas. The chains possessing a well-differentiated inter-modular link presented higher strain concentration gradients located in the link. Phase contrast imaging revealed that the stress adsorption mechanism of these materials involved macromolecular chain orientation and elongation co-axially to the applied load. The specimens retrieved after 24 hours had acquired a proteinaceous film rich in alcohol groups with minimal evidence of phosphate mineralization, while the 3-week retrieved specimens presented precipitation of Ca- and P-forming calcium phosphates. The high protein content of the biofilm organized on the surface of these materials, as well as the calcification pattern found, were similar to a non-specific mechanism of film adsorption of biomaterials exposed to body fluids. The results have clinical implications for aspects of retraction control through sliding mechanics with the use of elastomeric ligatures, and the potential detrimental effects on dental and periodontal tissues such as decalcification and gingival inflammation, respectively. In addition, the experimental protocols adopted for the in vitro study of the force decay of elastomerics should be modified to include parameters pertinent to adsorption phenomena and calcification processes documented to occur in vivo.