Controlling the eruption and development of dentitions is fundamental for a good oral health. The early diagnosis and adequate treatment of occasional developmental disorders are essential to achieve occlusal, functional and esthetic harmony. Abnormality is the term used for classification of alterations and is the most common developmental anomaly in humans. Even though several factors causing tooth malformations have been identified, many are still partially understood, thus requiring a more thorough study. Anyway, the available knowledge provides bases to attempt the early diagnosis of tooth abnormalities, to allow the adoption of preventive and effective therapeutic approaches.