Evaluation of biomechanical effects of different implant thread designs and diameters on all-on-four concept

Aim All-on-four concept involves the use of four anterior dental implants in the edentulous jaw to overcome anatomic limitations of residual alveolar bone. The impact of implant thread design and diameter on the biomechanical performance of all-on-four concept is not yet fully understood. The purpose of this study was to investigate the biomechanical behavior of all-on-four concept with different combinations of thread designs and diameters through a three dimensional Finite Element Analysis. Materials and methods Six three-dimensional finite element models of edentulous mandible were developed. The models included the combinations of 3.5 and 4.3 mm diameter implants with active and passive thread designs. Vertical, oblique and horizontal loads were applied anterior to the end of the cantilever. Von Mises, maximum principal and minimum principal stresses were analysed. Results The results indicated a tendency towards stress reduction in Von Mises stress values of dental implants with the increase in diameter for both mesial and distal implants. In narrow implants active thread design  resulted in lower Von Mises stress values than passive thread design. Active thread design demonstrated higher bone stress when compared to passive thread design. The analysis also revealed the importance of mesial implant for diminishing stresses on the distal implant and their surrounding bone under horizontal and oblique loading. Conclusion The comparison of the models suggest that use of wide implant is advantageous in the all-on-four concept. There is a biomechanical advantage in using narrow implants with active thread design in horizontally inadequate bone. The thread design was more significant in terms of increasing bone stress than  implant diameter. The mesial implant influences the biomechanical behavior of the whole design, contributing to a more favorable stress distribution under horizontal and oblique loading conditions.