Abstract:

This study aimed to evaluate stress distribution around two and four implants supporting maxillary implant overdentures retained by locator attachments, comparing full and partial palatal coverage designs. Four identical acrylic models representing completely edentulous maxillary arches were fabricated and covered with polyvinyl siloxane impression material to simulate the oral mucosa overlying the residual ridge. The models were divided into two main groups according to the number of installed implants (two or four), and each group was further subdivided based on palatal design (full or partial palatal coverage). Locator abutments (female components) were secured to the implants using an abutment driver, after which the prosthetic frameworks were constructed. Four strain gauges were bonded to each implant fixture using strain gauge cement to record strain values. A LLOYD digital loading device was employed to apply controlled compressive loads, and the resulting stresses around the implants were measured for each configuration.

Statistical analysis revealed a significant difference in stress values between two-implant overdentures with full palatal coverage (30.64 ± 17.47 N/m × 10²) and those with partial palatal coverage (49.72 ± 23.17 N/m × 10²), with higher stresses observed in the partial coverage design. In contrast, although four-implant overdentures with partial palatal coverage (8.77 ± 4.54 N/m × 10²) demonstrated higher mean stress values than those with full palatal coverage (5.51 ± 3.83 N/m × 10²), this difference was not statistically significant.

Within the limitations of this in vitro study, full palatal coverage design resulted in lower stress values compared to partial palatal coverage in two-implant-supported maxillary overdentures. For four-implant-supported overdentures, full palatal coverage also showed lower stress values; however, the difference was not statistically significant.

Abstract:

This study aimed to compare the amount of stress generated on two versus four implants with equator attachments in maxillary implant overdentures with palatal coverage and palateless designs. Four standardized educational edentulous maxillary models simulating bone type II were used. The models were divided into two main groups according to palatal design (palatal coverage and palateless), and each group was further subdivided based on the number of implants (two or four implants). In the two-implant subgroup, implants were placed bilaterally in the canine regions perpendicular to the residual ridge using a surgical stent, whereas in the four-implant subgroup, implants were installed bilaterally in the canine and second premolar regions. Equator attachments with appropriate cuff heights were selected, and framework patterns were constructed. Four strain gauges were cemented to each fixture using strain gauge cement. A LLOYD digital loading device was used to apply compressive loads to measure the resulting stresses around the implants for each attachment configuration. The results demonstrated a statistically significant difference between stresses on two implants with equator attachments (74.53 ± 35.9 N/m × 10²) and four implants with equator attachments (10.85 ± 10.81 N/m × 10²) within the same palatal coverage design. Similarly, a statistically significant difference was found between stresses on two implants with equator attachments (123.75 ± 44.60 N/m × 10²) and four implants with equator attachments (14.51 ± 14.60 N/m × 10²) within the same palateless design. It was concluded that stress on two implants with equator attachments was markedly greater in the palateless design compared with the palatal coverage design, whereas stress on four implants with equator attachments was slightly greater in the palateless design than in the palatal coverage design, with no statistically significant difference.

This study compared the retention of polyamide clasps engaging porcelain-fused-to-metal and zirconia retainers with identical 0.50 mm undercuts in posterior free-end saddle maxillary removable partial dentures. Four standardized acrylic resin models simulating maxillary bilateral posterior edentulous with first premolar abutments were prepared to receive either porcelain-fused-to-metal or zirconia crowns incorporating mesial occlusal rest seats. Polyamide RPA clasps were fabricated using an injection molding technique and tested for retention using a universal testing machine at a crosshead speed of 5 mm/min. The mean retention force of polyamide clasps was 6.68 ± 2.59 N for zirconia crowns and 5.47 ± 2.27 N for porcelain-fused-to-metal crowns. The results demonstrated minimal loss of retention for polyamide clasps against both ceramic materials, with no significant difference in retention related to the type of ceramic retainer.