Retrieval analysis of lingual fixed retainer adhesives

Introduction: Our objective was to analyze the surface and bulk properties alterations of clinically aged composites used for fixed retention. Methods: Twenty-six lingual retainers bonded for different time periods (2.2-17.4 years) were retrieved from postorthodontic patients. Fifteen lingual retainers had been cemented by a chemically cured adhesive (Maximum Cure, Reliance Orthodontic Products, Itasca, Ill), and 11 were treated with a photo-cured adhesive (Flow-Tain, Reliance Orthodontic Products). The first group was in service for 2.8 to 17.4 years and the second for 2.2 to 5.4 years. Five specimens from each material were prepared and used as the control (or reference) group. The debonded surfaces from enamel were studied by attenuated total reflectance Fourier transform infrared spectroscopy (n = 3 per material per group), low-vacuum scanning electron microscopy, and energy dispersive x-ray microanalysis (n = 3 per material per group). All specimens were used for the assessment of Vickers hardness, indentation modulus, and elastic index with the instrumented indentation testing method. The values of Vickers hardness, indentation modulus, and elastic index were compared between the retrieved and the reference groups with 1-way analysis of variance and the Student-Newman-Keuls multiple comparison test (alpha = 0.05). Results: The attenuated total reflectance Fourier transform infrared spectroscopy analysis showed that both retrieved composites demonstrated reduced unsaturation in comparison with the corresponding reference specimens. Some bonded surfaces showed development of organic integuments. All retrieved specimens showed reduced silicon content. Barium was identified only in the photo-cured group. No significant differences were found between the reference and retrieved groups in Vickers hardness, indentation modulus, and elastic index. Conclusions: Despite the changes in composition, the mechanical properties of the materials tested remained unaffected by intraoral aging.