Dentition of titanosaurs (Dinosauria, Sauropoda) from the Upper Cretaceous of Río Negro Province, Argentina: morphology, implantation and replacement. A fragment of dentary of a titanosaur sauropod from the Anacleto Formation (Upper Cretaceous of the Río Negro Province) is described. Inside the alveoli, functional and replacement teeth in successive “premature” stages are observed. At least in the preserved portion, an alternate teeth replacement pattern is observed. The histological analysis of this specimen allowed identifying the attachment dental tissues (alveolar bone, cementum and periodontal ligament). Numerous isolated teeth from the same unit and from the overlying Allen Formation are described. Based on these, a classification of the wear facets is proposed: 1) Teeth with only one facet: on the labial side, on the lingual side, or on the lateral side. 2) Teeth with two facets: the bigger on the labial side and the smaller on the lingual side; the bigger on the lingual side and the smaller on the labial side; the bigger on the lingual side and the smaller on the mesial or distal edge. 3) Teeth with three facets: one on the lingual side, the others on the mesial and distal edges; one on the lingual side, the others on the labial and mesial or distal edges; one on the labial side, the others on the mesial and distal edges. 4) Teeth with four facets: the smaller on the labial side, the bigger on the lingual side, and two lateral facets, one on the mesial and the other on the distal edges. Finally, we propose a hypothesis about the origin of the wear facets.