Normal formation and development defects of the human dentition

The development of the human dentition involves a highly orchestrated series of events that are strictly genetically controlled. The developmental timing, location, morphology, structure, and composition of teeth are primarily determined by cascades of molecular events that are regulated by hundreds of genes.(40) Normally, humans have 20 primary (i.e., deciduous, or shedding) teeth, which are lost in childhood, and 32 permanent teeth. Dentition begins to form at approximately 6 weeks in utero and continues through late adolescence, when the development of the permanent third molars is completed. Because the development of dentition is prolonged, it is susceptible to environmental influences for many years. A basic understanding of normal dentition and its development allows clinicians to accurately identify normal and abnormal dental conditions and make recommendations for appropriate therapeutic interventions and patient counseling. Delineating normal from abnormal dental development requires careful evaluation of the patient, including a medical, dental, and family history; clinical examination; and radiographic evaluation and may require special laboratory tests. This article reviews normal dentition and fundamental concepts of tooth development and provides a conceptual framework for diagnosing developmental defects of teeth.