Purpose: To compare the retention of clasps made from cast cobalt-chromium (Co-Cr) and acetal resin in maxillary obturator prostheses for Aramany class 1 and class 2 defects with two different undercut depths (0.010 and 0.015 inch) on anterior and molar abutment teeth before and after cyclic testing. Materials and methods: Maxillary obturator prostheses for Aramany class 1 and class 2 defects were fabricated with clasps of Co-Cr and acetal resin. The study comprised four groups: group A (Co-Cr clasps, class 1 defects), group B (Co-Cr clasps, class 2 defects), group C (acetal resin clasps, class 1 defects), and group D (acetal resin clasps, class 2 defects). Each group was subdivided based on undercut depth (0.010 and 0.015 inch). The obturator prostheses were tested for retention using pull-out tests before and after 1,095 mechanical stress cycles. Statistical analysis was done using the Mann–Whitney U test. Results: For class 1 defects, cobalt-chromium clasps with 0.010 inch undercuts showed an initial retention force of 13.42 N (anterior) and 14.17 N (molar), which decreased postcycling. Clasps with a 0.015 inch undercut started with slightly higher retention, which also reduced after cycling. Acetal resin clasps, on the other hand, demonstrated lower initial retention values (e.g., 6.70 N and 7.25 N) and a significant drop postcycling. For class 2 defects, cobalt-chromium clasps performed similarly with higher initial forces than acetal resin, which again showed lower initial retention and greater reduction over time. Across both defect classes, cobalt-chromium clasps maintained superior retention compared to acetal resin. Conclusion: The study shows that both acetal resin and Co-Cr clasps provide good retention in maxillary obturator prostheses. Acetal resin is beneficial for esthetics and comfort, while Co-Cr offers superior strength and durability, making both materials valuable in different clinical scenarios.