An Evaluation of the Stress Distribution in Screw Retained Implants of Different Crown Implant Ratios in Different Bone Densities Under Various Loads-A FEM Study.

INTRODUCTION: Studies on stress distribution around screw retained implants in different bone densities are limited. In clinical situations crowns of different heights are placed on the implants and the effect of varying crown implant ratio on the bone is not understood properly.

AIM: To evaluate and compare the stress distribution in different screw retained implants for different crown-implant ratios in different bone densities under various occlusal loads using three dimensional finite element analyses.

MATERIALS AND METHODS: In this invitro study the stress distribution was evaluated and compared between two different crown heights (7.5mm, 10mm) retained on implants by using different screw materials (commercially pure titanium, titanium alloy) in two different densities of bone D2, D3 under various load (100N, 200N) applications by using finite element analysis.

RESULTS: For crown height of 7.5mm, in D2 bone density when vertical load of 200N was applied, the maximum stress concentration was 1780N/cm(2), for oblique load of 100N it was 2936N/cm(2) respectively and in D3 bone density when vertical load of 200N was applied, the maximum stress concentration was 1820N/cm(2), for oblique load of 100N it was 3477N/cm(2) respectively. When the crown height is increased to 10mm, the maximum stress concentration in D2 bone was 1875N/cm(2) for vertical load, 4015N/cm(2) for oblique load and in D3 bone the maximum stress concentration was 2123N/cm(2) for vertical load and 4236N/ cm(2) for oblique load. In case of titanium screws for crown height of 7.5 mm, when vertical load was applied, stress concentration was 1603 N/cm(2) where as for titanium alloy screw it was 1820N/cm(2). In case of 10mm crown height stress concentration was 1904N/cm(2) for titanium screw and 2123N/cm(2) for titanium alloy screw. In case of oblique loading for 7.5mm crown height stress concentration was 3155N/cm(2) for titanium screw 3477N/cm(2) for titanium alloy screw. For 10mm crown height stress concentration was 4236N/cm(2) for titanium screw, 4663N/cm(2) for titanium alloy screw.

CONCLUSION: Stress concentration was less and stress distribution was better in D2 bone density than in D3 bone density. Stress concentration was less and stress distribution was better in commercially pure titanium screw than in titanium alloy screw. With the increase in the height of crown (i.e., from 7.5mm to 10mm) stress concentration and stress distribution also increased.