Intraoral aging of the inner headgear component: a potential biocompatibility concern?

The effect of intraoral aging of biomaterials on the modification of their surface properties has mostly been unknown. The purpose of this study was to investigate and characterize surface alterations of retrieved inner face-bow headgear components. Specimens were prepared from 3 areas of retrieved headgear wires: inner-outer face-bow soldered junction, buccal segment, and projection entering the buccal tube. Specimens from as-received headgear wires that matched the brand and size of the retrieved wires were also fabricated; all specimens were then subjected to multitechnique characterization. Optical microscopy revealed extensive biofilm islands of amorphous precipitants and accumulated microcrystalline particles. Micro-multiple internal reflectance Fourier transform infrared spectroscopy investigation of the retrieved wire samples demonstrated the presence of a proteinaceous biofilm, the organic constituents of which were mainly amide, alcohol, and carbonate. Scanning electron microscopy and radiographic microanalysis showed that the elemental species precipitated on the material surface were mainly calcium and phosphorus, forming calcium-phosphorus precipitates with thicknesses reaching 300 microm, whereas radiograph fluorescence spectrometry provided evidence of integument calcification through identification of calcium and phosphorus peaks. The clinical implication of the aging pattern that was identified relates to the potential protective role or induction of disintegration by the biofilm adsorbed on the wire that affected the biocompatibility of the alloy. Whereas further investigation is suggested for the clarification of the effect of intraoral aging on ionic release, the results of this study emphasize the necessity for the incorporation of in vivo approaches, including retrieval analyses, in the study of the biologic performance of orthodontic materials.