The application of engineering knowledge in dentistry has helped the understanding of biomechanics aspects related to osseointegrated implants. Several techniques have been used to evaluate the biomechanical load on implants comprising the use of photoelastic stress analysis, finite element stress analysis, and strain-gauge analysis. The limited quantitative information obtained from photoelasticity studies and the strain-gauge method is one of the underlying reasons for popularity of finite element stress analysis (FEA). The FEA can simulate stress using a computer-created model to calculate stress, strain, and displacement. Such analysis has the advantage of allowing several conditions to be changed easily and allows measurement of stress distribution around implants at optional points that are difficult to examine clinically. However, all the 3 methodologies can be useful to evaluate biomechanical implant behavior close to the clinical condition provided that the researcher has enough knowledge in model fabrication (experimental delineation) and results analysis (Assunção WG, Barão VA, Tabata LF, Gomes EA, Delben JA, dos Santos PH. Biomechanics studies in dentistry: bioengineering applied in oral implantology. J Craniofac Surg. 2009;20:1173–1177).
In FEA studies, bone is generally modeled as a continuum material. However, bone failure and bone adaptation processes are occurring at the discrete level of individual trabeculae, hence the assessment of stresses and strains at this level is relevant. The author in this study aimed to investigate how peri-implant strain distribution and load transfer between implant and bone are affected by the continuum assumption. A computational study in which cancellous screws were inserted in continuum and discrete models of trabecular bone and axial loading was simulated. It had proved strong differences in bone-implant stiffness between the discrete and continuum bone model. They are significantly influenced by bone density and applied boundary conditions. Furthermore, load transfer from the screw to the surrounding bone is of significant difference between the continuum and discrete models, especially for low-density bone. The author concluded that continuum bone models are of limited use for finite element analysis of peri-implant mechanical loading in trabecular bone when a precise quantification of peri-implant stresses and strains is required. Therefore, this study result carried the following message to the researchers; when the bone density is low or in simulating the trabecular bone, finite element models which accurately represent trabecular microarchitecture is highly recommended.
Omar Bayati, BDS, MDS
Literature Review Editor, Journal of Oral Implantology