<unk>  is a defect of the teeth in which the<unk>  is deficient in quantity, caused by defective<unk>  matrix formation during<unk>  development, as a result of inherited and acquired systemic condition(s). It can be identified as missing tooth structure and may manifest as pits or grooves in the crown of the affected teeth, and in extreme cases, some portions of the crown of the tooth may have no<unk> , exposing the dentin. It may be generalized across the dentition or localized to a few teeth. Defects are categorized by shape or location. Common categories are pit-form, plane-form, linear-form, and localised<unk> . Hypoplastic lesions are found in areas of the teeth where the<unk>  was being actively formed during a systemic or local disturbance. Since the formation of<unk>  extends over a long period of time, defects may be confined to one well-defined area of the affected teeth. Knowledge of chronological development of deciduous and permanent teeth makes it possible to determine the approximate time at which the developmental disturbance occurred.<unk>  varies substantially among populations and can be used to infer health and behavioural impacts from the past. Defects have also been found in a variety of non-human animals.
Enamel hypoplasia
Cartilage–hair hypoplasia
Maxillary hypoplasia
Spotted lunulae
Hemifacial hypertrophy
Chattering teeth
Blue nails
Enamel pearl