Dens invaginatus  Dens invaginatus (DI), also known as tooth within a tooth, is a rare dental malformation found in teeth where there is an infolding of enamel into dentine. The prevalence of condition is 0.3 - 10%, affecting more males than females. The condition is presented in two forms, coronal and radicular, with the coronal form being more common. DI is a malformation of teeth most likely resulting from an infolding of the dental papilla during tooth development or invagination of all layers of the enamel organ in dental papillae. Affected teeth show a deep infolding of enamel and dentine starting from the foramen coecum or even the tip of the cusps and which may extend deep into the root. Teeth most affected are maxillary lateral incisors (80%), followed by maxillary canines (20%). Bilateral occurrence is not uncommon (25%). Tooth affected by this condition has a higher risk of developing caries and periradicular pathology. The thin layer of the infolding enamel could be chipped off easily, providing entrance for microorganisms into the tooth canal. This can cause abscess formation, displacement of dental structures (i.e. teeth). Preventive measures should be taken. Cause of DI is unclear. However, there are several theories:  During clinical examination, abnormally shaped tooth can be observed. Tooth with this condition can have a conical shape or deep pit on the lingual side or have an exaggerated talon cusp. Although examination may reveal a fissure on the surface of anterior tooth, radiographic examination is the way. On a periapical radiograph, the invagination lesion will appear as a radiolucent pocket. It is usually seen beneath the cingulum or incisal edge. Larger lesions can appear as fissures. A radio-opaque could be shown. Pulp may be involved and the root canal could have complex anatomy. Two periapical radiographs are often required to make sure that it is not a masked lesion. Cone beam computed tomography (CBCT) is useful in diagnosing DI. It provides clinicians a detailed 3D image and could aid treatment planning. Feasibility of root canal treatment or apical surgery or other procedures could be assessed.