This paper presents an assessment of enamel defects (hypoplasias) in the permanent anterior teeth of three Tupí-Mondé-speaking groups from the Brazilian Amazonia: the Gavião, Suruí, and Zoró. These are native societies that experienced the onset of permanent contact with Brazilian national society in different periods of the 20th century. Tupí-Mondé dentition is highly hypoplastic, which is possibly related to exposure to adverse health and nutritional conditions. Data for the Gavião, Suruí, and Zoró are in agreement with results from other populations that show that certain teeth, the maxillary central incisors and the mandibular canines in particular, tend to be more hypoplastic. Although all types of teeth show hypoplasia concentrations at some enamel zones, there is substantial intertooth variation in the age at which peaks occur. It is argued that hypoplasia concentrations at certain ages are unlikely to be related to postweaning stresses for the Tupí-Mondé. Statistically significant associations between presence of enamel defects and deficits in physical growth (height-for-age) were detected in children 7-11 years of age. Diachronic assessment of enamel defects, which rested upon the potential of enamel as "memory" of past periods of systemic physiological perturbation, allowed us to unravel aspects related to the dynamics of Tupí-Mondé life during the 20th century. Frequencies of enamel zones with defects peaked during the contact years of each of the Tupí-Mondé groups, attesting to the extreme social and biological hardships that characterized the contact experiences of these native societies with Brazilian national society.