Bioactive ceramics are used as bulk, porous bodies, or surface-active layers on dental implants and as morphogenetically active scaffolds inserted into the jawbone. While the former has been popularly applied as artificial dental roots for recovering the function of lost teeth, the latter are increasingly used for regenerating bone tissue. In both cases, the common fundamental basis is to understand how the new bone is formed on the surfaces of introduced foreign bodies, integrated together with the autologous bone through complex biological processes and cell-materials interactions. Efforts are thus made in this chapter to elucidate the biological origins of those phenomenological terms that have often eluded satisfactory scientific definition on this particular topic of practice-motivated science. Bone-growth mechanisms are discussed together with possible characterization and quantification methods. The role of surface morphology and multi-scale structures in promoting bone growth is emphasized. Based on the state-of-the-art understanding all the way down to molecular, cellular, and genetic levels, bioactive ceramics are categorized and presented in relation to their potential applications in dentistry. The design concept of implants for enhancing early healing and for enabling immediate loading is also discussed.