# Finite Element Analysis of Peri-Implant Stress in Maxillary All-on-Four Rehabilitation: Effects of Posterior Implant Angulation and Loading Protocol

## TL;DR

This study uses computer modeling to show how implant angle and timing of loading affect stress around dental implants in maxillary rehabilitations.

## Contribution

The study introduces a novel biomechanical analysis of posterior implant angulation and loading protocols in All-on-Four dental rehabilitation.

## Key findings

- Posterior implant tilt significantly reduces peri-implant stress, with 59% reduction at 45° inclination under immediate loading.
- Immediate loading increases stress at lower angulations, while delayed loading reduces stress at extreme tilts.
- Anterior implants consistently experience lower stress levels across all configurations.

## Abstract

Objective: To evaluate the biomechanical effects of varying posterior implant inclinations and loading protocols on peri-implant stress distribution in full-arch maxillary rehabilitations using the All-on-Four concept. Methodology: A three-dimensional finite element model of an edentulous atrophic maxilla was developed from a digital point cloud. Four implants were placed according to the All-on-Four protocol: two anterior vertical implants and two posterior implants with inclinations of 0°, 15°, 30°, or 45°. Mini-abutments and a titanium bar prosthesis were included. Material properties were assumed as homogeneous, isotropic, and linearly elastic. Immediate loading was simulated using frictional contacts (µ = 0.3), whereas delayed loading assumed complete osseointegration (bonded contacts). The models were meshed using 10-node quadratic tetrahedral elements (SOLID187) in ANSYS®. Maximum von Mises stress in cortical bone, cancellous bone, implants, abutments, and the prosthetic bar was assessed. Results: Posterior implant tilt significantly reduced peri-implant stress. Under immediate loading, the highest stress occurred at 0° inclination in the posterior left implant (82.36 MPa) and decreased progressively with increasing tilt, reaching 33.63 MPa at 45° (≈59% reduction). Delayed loading generally produces lower stress magnitudes, particularly at extreme tilts. Anterior implants experienced lower stress levels across all configurations. Comparative analysis demonstrated that immediate loading increased stress at lower angulations, while differences between loading protocols were minimal at higher inclinations. Conclusions: Posterior implant angulation and loading protocol critically influence peri-implant stress distribution. Increased posterior tilt combined with appropriate loading reduces peak cortical bone stresses, supporting biomechanical optimization in All-on-Four maxillary rehabilitations.