Effect of prosthetic framework material, cantilever length and opposing arch on peri-implant strain in an all-on-four implant prostheses.

Aim: To evaluate the effect of prosthetic framework material and cantilever length on peri-implant strain in mandibular all-on-four implant-supported prostheses with different types of arch antagonist forces.

Materials and Methods: Models simulating a completely edentulous mandibular arch fabricated in heat-cured acrylic resin were used. On the acrylic models, four implants were placed at regions 34, 32, 42, and 44 simulating all-on-four implant placements. Implant-supported screw-retained fixed prosthesis frameworks were fabricated using three different materials (cobalt-chromium, zirconia, and polyetheretherketone) and with three different cantilever lengths (zero mm, 15 mm, and 25 mm). Strain gauges were attached on the model at the buccal and lingual positions of each implant. Forces simulating opposing natural dentition, conventional complete denture, and the parafunctional habit were applied to the models. The peri-implant strain in each strain gauge was recorded.

Results: Least peri-implant strains (67 microstrains) were observed when forces simulating conventional complete dentures were applied on the models and the highest peri-implant strains (9091 microstrains) were observed when forces simulating parafunctional habit were applied. One-way ANOVA test followed by Tukey's post hoc analysis was performed to compare the mean deformation scores between different materials at 50 N load. The level of significance [P-value] was set at P < 0.05. Tests showed significant differences between zero mm and the other types in all the different materials, and also between 1.5 x AP and 2.5 x AP for Zirconia and Peek material at P = 0.02 & P = .008, respectively. The results showed that the type of framework material, cantilever length, and occlusal forces from the opposing arch influence the peri-implant strain in the bone in all-on-four implant-supported prostheses.

Conclusion: Rehabilitation of a single, completely edentulous arch with implant-supported prostheses should consider the situation of the opposing arch. The choice of framework material, as well as the cantilever length, should be altered based on the forces from the opposing arch.