Comparison of stress distributions of zygomatic implant, trans-sinus implant and pterygoid implant concepts in atrophic maxilla: A finite element analysis

Objective: Extramaxillary anchorage areas can be used in the rehabilitation of severely atrophic maxilla without grafting procedures in cases that there is not sufficient bone for convensional implant placement. The zygomatic buttress, pterygoid plates, and lateral nasal bone areas are frequently used as anchorage regions. The concepts of zigomatic implants, trans-sinus implants, and pterygoid implants are based on the principle of obtaining anchorage using these regions. The aim of this study is to evaluate the stress values generated by zigomatic implant, trans-sinus implant, and pterygoid implant concepts in implants and the surrounding alveolar bone in atrophic maxilla using the finite element stress analysis method. Methods: In this study, 3D finite element analysis (FEA) method was used. Conventional implants, 10 mm in length, was placed in the lateral tooth region in all models. In the posterior region, trans-sinus implants (30°) or zygomatic implants (45°) were placed in second premolar region. Zygomatic implant were placed with extrasinus technique. Pterygoid implants (45°) were placed in second molar region. A titanium bar supported polymethylmethacrylate (PMMA) prosthesis was designed for prosthetic restoration. A force of 300 N was applied vertically and obliquely (20°) to all created models (Model 1: zygomatic implant, Model 2: zygomatic and pterygoid implant, Model 3: transsinus implant, Model 4: transsinus and pterygoid implant). Results: Oblique forces caused more stress than vertical forces. When comparing zygomatic implant and trans-sinus implant models; lower stress values were observed in the zygomatic implant model in all conditions in vertical loading (except Von Mises stress values in implants number 5 and tension-type stresses in the trabecular bone) and oblique loading (except tension-type stresses in the trabecular bone around the anterior implant). Compared to the All-on-4 concept, lower stress values were generally found in models that converted to the All-on-6 concept by adding a pterygoid implant. It was observed that the Von Mises stress values decreased by more than 50% in the number 5 implant area, especially in the models with pterygoid implants. Conclusions: The stress values on the bone and implants of the zygomatic implant and additionally placed pterygoid implants are lower. Keywords: Atrophic maxilla, zygomatic implant, trans-sinus implant, pterygoid implant, finite element stress analysis