A 3-D Finite Element Study of the Influence of Crown-Implant Ratio on Stress Distribution

Abstract

The purpose of this study was to assess the influence of the crown height of external hexagon implants on the displacement and distribution of stress to the implant/bone system, using the three-dimensional finite element method. The InVesalius and Rhinoceros 4.0 softwares were used to generate the bone model by computed tomography. Each model was composed of a bone block with one implant (3.75x10.0 mm) with external hexagon connections and crowns with 10 mm, 12.5 mm and 15 mm in height. A 200 N axial and a 100 N oblique (45°) load were applied. The models were solved by the NeiNastran 9.0 and Femap 10.0 softwares to obtain the results that were visualized by maps of displacement, von Mises stress (crown/implant) and maximum principal stress (bone). The crown height under axial load did not influence the stress displacement and concentration, while the oblique loading increased these factors. The highest stress was observed in the neck of the implant screw on the side opposite to the loading. This stress was also transferred to the crown/platform/bone interface. The results of this study suggest that the increase in crown height enhanced stress concentration at the implant/bone tissue and increased displacement in the bone tissue, mainly under oblique loading.

Three-Dimensional Finite Element Analysis of Varying Diameter and Connection Type in Implants with High Crown-Implant Ratio

“…These results are consistent with the literature (7)(8)(9)12,21). This fact may be due to oblique loading tends to increase stress concentration on (compression) and against (tensile) the loading direction (8).…”

“…Additionally, the width and/or height of the hexagon can contribute to the increase in stress concentration in the bone tissue region (19). Therefore, the use of external hexagon implants should be avoided, especially in situations where there is an increase in the crown-implant ratio (7,20), or in cases where use implants with a wide diameter is not feasible, since stress concentration in the cortical bone could exceed the physiological limits and consequently accelerate the bone resorption process, which could compromise the rehabilitation.…”

“…Oblique loading should be considered more harmful to bone tissue, which may contribute to higher values of bone resorption over time. Thus, it is important to perform a rigorous occlusal adjustment to transfer the centric contacts allowing a distribution in the long axis of the implant, avoiding an oblique overload in the peri-implant region (7).…”

“…However, there is concern regarding the longevity of these implants from a biomechanical perspective (4). The incidence of oblique loads at short implants can impact longevity (5), mainly owing to the increase in crown-implant ratio (6), which increases stress concentration in the bone tissue around the implant (7).…”

Retention System and Splinting on Morse Taper Implants in the Posterior Maxilla by 3D Finite Element Analysis

“…The 3D finite element analysis (FEA) methodology used here follows that of previous studies (3,9). Each model was composed of a bone block of the maxillary area of the first premolar to first molar, with trabecular bone in the center surrounded by 1 mm of cortical bone.…”