The oral and craniofacial bones are essential for determining individual appearance and enabling mastication, respiration, and phonation. The cranium exhibits a complex architecture composed of multiple small bones. The development of this structured organization is a consequence of the well-coordinated functions of various bone cells, such as chondrocytes, osteoblasts, osteoclasts, and osteocytes. These cells contribute to both the development and maintenance of bone, known as the modeling and remodeling phases, respectively. The differentiation and function of these bone cells can be influenced by intrinsic and extrinsic stimuli, resulting in the adaptation of bone morphology and functions when stimulation occurs within physiological ranges. In contrast, excessive or abnormal stimuli, including genetic mutations, endocrine disorders, abnormal mechanical loading, tumor formation, and aberrant immune responses, can lead to bone malformations and dysfunction. The immune system, originally developed as a defense mechanism against non-self entities, can disrupt the physiological structures and functions of organs when dysregulated. Bone metabolism can be influenced by the immune system, both directly and indirectly via other biological systems, and irregular activation of the immune system can cause inflammatory bone diseases as well as bone diseases of other categories. A precise understanding of these bone diseases requires insights into the involvement of the immune system. This chapter summarizes our knowledge of how the immune system functions during the development and maintenance of oral and craniofacial bones.
