Adjustments and Complications of Mandibular Overdentures Retained by Four Implants. A Comparison Between Superstructures With and Without Cantilever Extensions

Purpose: The aims of the study were to evaluate the postinsertion care needed by patients treated with four implants to retain mandibular overdentures and to compare two types of superstructures. Materials and Methods: The study consisted of 54 patients who had been treated with conventional maxillary dentures and mandibular overdentures retained by four implants and a triple-bar superstructure with cantilever extensions (28 patients) or without cantilever extensions (26 patients). Differences between both groups with regard to age, gender, length, and diameter of the implants and preoperative mandibular bone height were tested by means of Student's t and chi-square tests with a probability level of 0.05. No significant differences were found. Both groups were retrospectively compared on adjustments and complications. The follow-up period after insertion of the dentures was 2 years. Results: During the 2-year follow-up, 17 patients of the cantilever-extension group and 20 patients of the group without cantilever extensions needed adjustments, and 17 patients of the cantilever group and 12 patients of the group without cantilever extensions had to be treated because of complications. Significantly more (P 0.05, chi-square test) superstructure fractures were present in the cantilever group (14 occasions in 7 patients) than in the group without cantilever extensions (1 occasion). All superstructure fractures in the cantilever group involved the cantilever extensions. Conclusion: This study demonstrated a considerable need for postinsertion care, confirming the necessity of routine follow-up services for patients restored with implant-retained overdentures. Furthermore, the results of this study suggest restriction of the use of cantilever extensions.