Comparative morphogenesis of mouse and rat mandibular first molars (M1): a review of developmental timing, structure, and signaling pathways

Rodents have been studied widely to evaluate the cellular and molecular mechanism of tooth development, although significant differences exist between them that impact how the researchers design their experiment. The mandibular first molar M1 is the most studied tooth in both species and provides a model for crown morphogenesis, root initiation, periodontal ligament organization, and the tooth eruption. In mice the M1 development is rapid, the crown complete at birth and the tooth eruption postnatal P20-21, while in rats the tooth development events are delayed, with larger tooth germs and tooth eruption at P17. However, rats provide advantages for microinjection, histology and biochemical assays due to their larger molar compared to mice. In comparison, mice provide an excellent model for genetic related studies. However, systematic side-by-side analysis is limited, leaving a gap in understanding how timing, genetic signaling, and eruption are related among species. This review focuses on current knowledge of rat-mouse M1 development and compares the two models to help the researcher to determine model selection, and experimental design, particularly when translating the finding to human development or pathology.