Dense incisors (din) is a new autosomal recessive mutation in the mouse that interferes with complete eruption of the incisors. The initial eruption of incisors through the gingiva does not differ in mutants and normal littermates, but subsequent further eruption of incisors is arrested in mutants. Radiographic examinations show that, because the incisors do not erupt, continued dentin formation gradually occludes the pulp chambers of these teeth creating as dense incisor. The arrested eruption of the incisor results in an anterior open bite. The pleiotropic phenotype of din/din mutant mice also includes small body size, reduced ear pinna size, and coat color dilution. The din mutation was mapped to Chr 16 near the pituitary transcription factor gene Pit1, but din is not a mutation in Pit1.