Load bearing capacity of 3-unit screw-retained implant-supported fixed dental prostheses with a mesial and distal cantilever on a single implant: A comparative in vitro study

Objectives: To assess the mechanical durability of monolithic zirconia implant-supported fixed dental prostheses (iFDP) design on one implant, with a distal and a mesial extension cantilever bonded to a titanium base compared to established designs on two implants. Materials and methods: Roxolid Tissue level (TL), and tissue level x (TLX) implants were used to manufacture screw-retained 3-unit iFDPs (n = 60, n = 10 per group), with following configurations (X: Cantilever; I: Implant, T: Test group, C: Control group): T1: X-I-X (TL); T2: X-I-X (TLX); T3: I-I-X (TL); T4: I-I-X (TLX); C1: I-X-I (TL); C2: I-X-I (TLX). The iFDPs were thermomechanically aged and subsequently loaded until fracture using a universal testing machine. The failure load at first crack (F-initial) and at catastrophic fracture (F-max) were measured and statistical evaluation was performed using two-way ANOVA and Tukey's post-hoc tests. Results: The mean values ranged between 190 +/- 73 and 510 +/- 459 N for F-initial groups, and between 468 +/- 76 and 1579 +/- 249 N for F-max, respectively. Regarding F-initial, neither the implant type, nor the iFDP configuration significantly influenced measured failure loads (all p > 0.05). The choice of implant type did not show any significant effect (p > 0.05), while reconstruction design significantly affected F-max data (I-I-X-a < X-I-X-b < I-X-I (c)) (p < 0.05). The mesial and distal extension groups (X-I-X) showed fractures only at the cantilever extension site, while the distal extension group (I-I-X) showed one abutment and one connector fracture at the implant/reconstruction interface. Conclusion: Results suggest that iFDPs with I-X-I design can be recommended regardless of tested implant type followed by the mesial and distal extension design on one implant abutment (X-I-X).