Retention Systems in Surgical Obturator Prostheses for Patients Subjected to Maxillary Resections

Objective: To evaluate clasp retention systems in surgical obturator prostheses after different maxillary resections. Method: Different chemically activated acrylic resin maxillary models received surgical obturator prostheses, in a sample constituted by the following groups: Group 1 - circumferential clasp (C clasp) in the first and second maxillary molars contralateral to the resection and Hawley labial bow (G1a - Aramany Class II, G1b - Aramany Class II without maxillary canine and G1c - Aramany Class I); Group 2 - C clasp in the first and second premolar and in the first and second molar (G2 Aramany Class I). Mechanical cycling was performed at intervals of 0, 28, 120 and 360 insertion/removal cycles, considering four daily removals during a 3-month period. Tensile strength tests were performed in the beginning and at each interval of the mechanical cycling. Results: All groups presented a decrease of retention along the cycling period. The group G2 was superior to the others at all evaluated moments, followed by the groups G1a, G1b and G1c in a decreasing order. The decrease of the retention in the groups G1a, G1b and G1c was not statistically significant up to cycle 120. Group G2 presented a significant reduction of retention at cycle 28, non-significant at cycle 120 and significant again at cycle 360. Conclusion: The substitution of Hawley labial bow by circumferential clasps in the premolars provided greater retention. The retention provided by the system with Hawley labial bow depends on the amplitude of loss, in such a way that the greater the loss, the lower the retention; the significant retention loss after 1 month suggests the need of periodic activation of the retention systems.