Redirecting Bone Stress and Stain to Stimulate Bone Remodeling

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Redirecting Bone Stress and Stain to Stimulate Bone Remodeling
April 5, 2003
Brandon Wong
Compton Implants
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Implants have improved the function of long span prosthesis by improving its support, resistance and retention, but the stress and strains produced during function pushes the limits of the supporting bone and prosthesis. Stress is the force placed on an object and strain is the objects reaction to the force, such as deformation. One of the fatal factors of implants is uncontrolled force, which have been blamed for epithelium growth along the implant screw; however, those same forces can be redirected to stimulate the bone and perhaps enhance osteointegration after primary stability has been established. i,ii The study of the internal and external forces within a biological system is called, biomechanics.iii.
Dental implant biomechanics can be studied in different parts, such as the effects of direction and magnitude of load, the occlusal forces produced during implant therapy, implant systems effect on bone quality and the prosthesis ability to redirect force. iv The drive behind dental implant biomechanics is the dream to improve the success rates of implants especially immediate loaded implants because immediate prosthesis allows faster oral rehabilitation of the patient.
The biomechanics of implants is a large field of study and this paper will explore how stress and stain can be controlled in implant-supported prosthesis to enhance bone remodelling by examining the stress and stain within the implant system, the bones reaction to those strains and how those forces could be controlled.
a) Stress and Stain in the Implant system
The forces that could be produced during occlusal function are axial loading and bending moments. v Axial loading is produced when a load is placed on the long axis of the tooth and this force is desirable because the resulting forces are distributed evenly along the implant-bone surface.
The bending moments are produced when a lateral force is place on the occlusal surface and this force is unfavourable because it creates a gradient of force along the implant-bone surface. The bending moment is expressed as lever arm distance times force and the physics of the implant could be understood using a see-saw analogy. (Fig. 1) Using the see saw analogy, if the implant where to fulcrum on the implant-framework edge and the distance from the fulcrum to the gold screw is close to zero, the force could reach close to infinity. Fortunately, this does not happen because there is some stress breaking activity associated with the bending of the gold screw, which redirects the forces. Unfortunately, there is a limit to the flexion, which is called the proportional limit. This is when the material no longer follows a linear relationship between bending and force (HookeǃÙs law) and may begin to deform.
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