Biomechanical factors affecting the bone-dental implant interface.

While it is known that dental implants can 'work'--the success of the Branemark 'osseointegrated' implant is a prime example--implants can also fail. The challenge is to develop a basic science understanding of all aspects which contribute to implant performance. In designing a successful dental implant, the main objective is to ensure that the implant can support biting forces and deliver them safely to interfacial tissues over the long term. Biomechanics are central in this design problem. Key topics include: (1) the nature of the biting forces on the implants; (2) how the biting forces are transferred to the interfacial tissues; (3) how the interfacial tissues react, biologically, to stress transfer conditions. For biting forces on dental implants, the basic problem is to determine the in-vivo loading components on implants in various prosthetic situations, e.g. for implants acting as single tooth replacements or as multiple supports for loaded bridgework. Significant progress has been made; several theoretical models have been presented for determining the partitioning of forces among dental implants supporting bridgework. However, more work will be needed to clarify how well these models match reality. Interfacial stress transfer and interfacial biology represent more difficult, interrelated problems. One problem is that the multitude of different shapes, sizes, materials, surgical sites and animal models for dental implants has precluded any generally accepted rules for biologically 'favorable' vs 'unfavorable' interfacial stress transfer conditions. While many engineering studies have shown that variables such as implant shape, elastic modulus, extent of bonding between implant and bone, etc., can affect the stress transfer conditions, the unresolved question is whether there is any biological significance to such differences. Recent research suggests that, at the very least, our search for a more detailed hypothesis regarding the relationship between interface mechanics and biology should take account of basic bone physiology, e.g. wound healing after implantation plus basic processes of bone modeling and remodeling.