Stress patterns around distal angled implants in the all-on-four concept configuration

Area of Science:

• Dental Implantology
• Biomaterials Science
• Biomechanics

Background:

• The All-on-Four (Ao4) concept is a prosthodontic technique utilizing four implants to support a full-arch prosthesis.
• Immediate loading protocols are often employed with the Ao4 concept.
• Distal implants in the Ao4 configuration are frequently placed at an angle to optimize prosthetic support.

Purpose of the Study:

• To qualitatively analyze stress distribution around the angled distal implant in the All-on-Four concept.
• To investigate the influence of distal implant angulation on peri-implant stress patterns.

Main Methods:

• Four photoelastic acrylic resin models simulating the Ao4 configuration were fabricated.
• Distal implants were placed at increasing angles (0, 15, 30, 45 degrees) in each model.
• Photoelastic analysis using a circular polariscope quantified stress patterns under varying loads (5, 10, 15 kg).

Main Results:

• Minimal stress differences were noted between straight and angled (15, 30 degrees) distal implants.
• The central implant region consistently showed the lowest stress (fringe order).
• The apical region exhibited higher stress concentrations than the coronal region for all angulations.
• Significant stress increases were observed around implants angled at 45 degrees.

Conclusions:

• Peri-implant bone adjacent to 45-degree angled distal abutments may experience excessive occlusal forces.
• Higher implant angulation in the Ao4 concept can lead to increased stress on surrounding bone.
• Careful consideration of distal implant angulation is crucial to avoid peri-implant bone overload.