Although the biologic principles underlying successful clinical implants are still not completely understood, it is clear that both physical and chemical attributes of the material may influence the clinical outcome. Knowledge of the stresses and strains in an implant system and superstructure is still incomplete, but micromotion at the interface must be avoided for bone fixation. The composition and topography of the implant surface influence the cellular events at the bone-biomaterial interface. These surface parameters require definition to interpret the tissue response to a particular material. Hydroxyapatite-coated surfaces are an example of a variable implant modality that has resulted in variable clinical performance. The clinician should consider all the available information on material and design before embarking on extensive clinical trial.