Biomechanical in vitro evaluation of two full-arch rehabilitations supported by four or five implants

The aim of this in vitro study was to evaluate the stress pattern on the abutments in two different full-arch implant-supported clinically equivalent prosthetic rehabilitations.

Two steel master casts were created and titanium implants were inserted in two different configurations. One configuration used four implants, with the distal implants tilted 30 degrees (4IMP configuration), and the other used five axially inclined implants (5IMP configuration). A straight multiunit abutment (MUA) was connected to every axial implant and a 30-degree angulated MUA was connected to each tilted implant. One titanium framework was fabricated for each configuration, with a 5-mm (4IMP configuration) or a 15-mm (5IMP configuration) distal cantilever length. Six cycles of vertical loading between 20 and 200 N were applied unilaterally at the most distal point of the frameworks on both sides. Readings of the deformations at the abutment level were obtained with the use of linear strain gauges.

A similar pattern of deformation was seen in both configurations. The greatest compressive stress was measured by the strain gauge on the abutment closest to load application and was similar for the 4IMP and 5IMP configurations. The tensile stress measured on the same abutment was higher in the 5IMP configuration than in the 4IMP configuration. In terms of the distribution of stresses, the deformation measured on the central abutment in the 5IMP configuration was less than 10% of the overall stress in all the tested conditions.

There was no difference in strain between the two different designs, so the use of tilted implants with angulated abutments to reduce cantilever length could be considered a viable clinical option.