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

The objectives of this study were to investigate the structural characteris tics of open and closed elastomeric modules in the as-received condition, a nd following (a) 24-hour in vitro loading determined as a 50 per cent exten sion 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 ut ilizing phase contrast and polarized light modes, (b) micro MIR FT-IR spect roscopy, and (c) scanning electron microscopy and electron probe X-ray micr oanalysis. Stretched elastomers demonstrated a honeycomb pattern of filament detachmen t corresponding to strained areas. The chains possessing a well-differentia ted inter-modular link presented higher strain concentration gradients loca ted 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 2 4 hours had acquired a proteinaceous film rich in alcohol groups with minim al evidence of phosphate mineralization, while the 3-week retrieved specime ns presented precipitation of Ca- and P-forming calcium phosphates. The hig h protein content of the biofilm organized on the surface of these material s, as well as the calcification pattern found, were similar to a non-specif ic mechanism of film adsorption of biomaterials exposed to body fluids. The results have clinical implications for aspects of retraction control th rough sliding mechanics with the use of elastomeric ligatures, and the pote ntial detrimental effects on dental and periodontal tissues such as decalci fication and gingival inflammation, respectively. In addition, the experime ntal protocols adopted for the in vitro study of the force decay of elastom erics should be modified to include parameters pertinent to adsorption phen omena and calcification processes documented to occur in vivo.