Biomechanical response of maxillary all-on-4 systems under different lateral occlusal guidance patterns: a three-dimensional finite element study

The All-on-4 concept is widely used for the rehabilitation of edentulous patients; however, the optimal design of lateral occlusal guidance for maxillary All-on-4 prostheses remains unclear. Currently, there is a lack of biomechanical evidence regarding different lateral guidance patterns under varying bone quality conditions. A three-dimensional finite element model was created using cone-beam computed tomography and intraoral scanning data from a single healthy volunteer with intact natural dentition and bilateral canine-protected occlusion. Four NobelActive implants (4.3 × 13 mm) were placed in the maxilla according to the All-on-4 protocol. Four lateral occlusal schemes were simulated: canine-protected occlusion, two-tooth group function, three-tooth group function, and posterior group function. Displacement-controlled quasi-static loading was applied to simulate lateral mandibular movements under three bone quality types (D2, D3, and D4, based on Misch classification). Stress was mainly concentrated at the implant cervical regions and the abutment–implant interfaces. Under D2 bone quality, the abutment at position 12 exhibited a maximum stress of 230.09 MPa in canine-protected occlusion, rising to 259.88 MPa in three-tooth group function. Compared with canine-protected occlusion (113.65 MPa), the maximum implant stress at position 15 under three-tooth group function (165.47 MPa) increased by 45.6%; at position 25, the increase was 75.6% (from 115.14 MPa to 202.23 MPa). Maximum framework deformation ranged from 0.0569 mm (D2, three-tooth group function) to 0.0672 mm (D4, canine-protected occlusion). Posterior group function produced lower stresses than canine-protected occlusion for some components. Canine-protected occlusion reduces stress concentration in implants and multi-unit abutments of the maxillary All-on-4 system compared with two-tooth and three-tooth group function, with exceptions in comparisons involving posterior group function. Decreased stress at the implant-abutment interface with lower cancellous stiffness is accompanied by increased framework deformation. These biomechanical findings suggest that canine-protected occlusion may offer mechanical advantages for maxillary All-on-4 rehabilitation, though clinical implementation should consider individual patient factors.