A finite element study of short dental implants in the posterior maxilla.

PURPOSE: Elevated bite forces and reduced bone densities and dimensions associated with posterior regions of the maxilla cause relatively high failure rates when short dental implants are placed to substitute missing teeth. This study uses the finite element method to evaluate four distinctly different short implant designs (Bicon, Neodent, Nobel Biocare, and Straumann) for their influences on the von Mises stress characteristics within the posterior maxilla. MATERIALS AND METHODS: Finite element models of the supporting bone and tooth crowns are developed based on computed tomography data, and implant geometries are obtained from manufacturers' catalogs. The finite element models are meshed using three-dimensional hexahedral and wedge-shaped brick elements. Assumptions made in the analyses are: linear elastic material properties for bone, 50% osseointegration between bone and implant, and crown height-implant length ratio of 2:1. RESULTS: Bicon's neck indentation produced reduced stress in the cortical bone when compared with the Nobel Biocare and Straumann systems. The increased taper of the Neodent design decreased the stress level in cancellous bone. Nobel Biocare's rounded thread crest and reduced thread pitch produced a smoother stress profile. Straumann's increased thread pitch produced elevated stress in the cancellous bone. Generally, stresses were concentrated in the crestal bone region around the implant neck, attributable to the inclined nature of the masticatory force. CONCLUSION: Nobel Biocare and Bicon systems are recommended for use in type 4 cancellous and cortical bone, respectively.

Evaluation of multiple implant-bone parameters on stress characteristics in the mandible under traumatic loading conditions.

PURPOSE: The inter-relationships between various implant and bone parameters were evaluated for their influence on the von Mises stress distribution within the mandible using the finite element procedure. The maximum compressive stresses in cancellous and cortical bone were compared to the published stress-strain data to determine bone fracturing status when the maximum (traumatic) loading is applied. MATERIALS AND METHODS: Parameters considered herein include the implant diameter and length. Also considered are Young's modulus of cancellous bone and that of cortical bone, along with its thickness. The implant-bone system was modeled using two-dimensional plane strain elements, 50% osseointegration between implant and cancellous bone was assumed, and linear relationships were assumed between the stress value and Young's modulus of both cancellous and cortical bone at any specific point within the mandible. RESULTS: Implant length was more influential than implant diameter within cancellous bone, whereas implant diameter was more influential in cortical bone. A ranking of all the parameters indicated that the applied masticatory force had a more significant influence on the stress difference, in both cancellous and cortical bone, than all other parameters. Young's modulus of cortical bone and implant length were least influential in cancellous and cortical bone, respectively. Under traumatic loading, cancellous bone fractured for all parameter combinations. When all parameters were set to their average values, the cortical bone did not fracture under traumatic loading. However, it fractured if all the parameters were all set to the minimum values. CONCLUSION: Quantitative evaluation and ranking of the major implant and bone parameters will help provide practical guidelines that are useful for the design and testing of dental implants. The study may also be of interest to dental professionals in evaluating possible implant placement options under various clinical scenarios.

Influence of bone and dental implant parameters on stress distribution in the mandible: a finite element study.

PURPOSE: The complicated relationships between mandibular bone components and dental implants have attracted the attention of structural mechanics researchers as well as dental practitioners. Using the finite element method, the present study evaluated various bone and implant parameters for their influence on the distribution of von Mises stresses within the mandible. MATERIALS AND METHODS: Various parameters were considered, including Young's modulus of cancellous bone, which varies from 1 to 4 GPa, and that of cortical bone, which is between 7 and 20 GPa. Implant length (7, 9, 11, 13, and 15 mm), implant diameter (3.5, 4.0, 4.5, and 5.5 mm), and cortical bone thickness (0.3 to 2.1 mm) were also considered as parameters. Assumptions made in the analysis were: modeling of the complex material and geometric properties of the bone and implant using two-dimensional triangular and quadrilateral plane strain elements, 50% osseointegration between bone and implant, and linear relationships between the stress value and Young's modulus of both cancellous and cortical bone at any specific point. RESULTS: An increase in Young's modulus and a decrease in the cortical bone thickness resulted in elevated stresses within both cancellous and cortical bone. Increases in the implant length led to greater surface contact between the bone and implant, thereby reducing the magnitude of stress. CONCLUSIONS: The applied masticatory force was demonstrated to be the most influential, in terms of differences between minimum and maximum stress values, versus all other parameters. Therefore loading should be considered of vital importance when planning implant placement.

Step-wise analysis of the dental implant insertion process using the finite element technique.

OBJECTIVES: Using the finite element method (FEM), the insertion process of a dental implant into a section of the human mandible is analysed. The ultimate aim of this article is to advance the use of an innovative engineering approach in dental practices, especially in the process of dental implantation. MATERIAL AND METHODS: The FEM and analysis techniques are used to replicate and evaluate the stress profile created within the mandible during the implantation process. RESULTS: The von Mises stress profiles in both cancellous and cortical bone are examined during implant insertion. The applied torque and the insertion stage are found to strongly influence the resulting stress profile within the surrounding jawbone. CONCLUSIONS: Through the combination of both dental and engineering expertise, a simplified and efficient modelling technique is developed. This improves the understanding of the biomechanical reaction that the jawbone exhibits due to the insertion of implant. The current research is a pilot study using the FEM to model and simulate the dental implantation process. The assumptions made in the modelling and simulation process are: (1) the implantation process is simulated as a step-wise process instead of a continuous process; (2) the implant is parallel threaded and the implant does not rotate during insertion into the jawbone. Although the modelling and simulation techniques had to be simplified, a significant amount of information is gained that helps lay a good foundation for future research. Recommendations for future studies include the variation of the torque applied during the implantation process and upgrading the software capabilities to simulate the full dynamical process of implantation.