Both epidermal growth factor (EGF) and colony-stimulating factor-1 (CSF-1) have been shown to accelerate eruption of teeth in rodents. We compared the effects of neonatal injections of EGF (1 micrograms/g body weight) and CSF-1 (10(6) units) alone or together on the eruption of incisors and first molars. EGF accelerated the eruption of incisors with no significant effect on first molars. CSF-1, in contrast, accelerated molar eruption more than incisor eruption. CSF-1, but not EGF, increased the numbers of mononuclear cells in the dental follicle and osteoclasts on adjacent alveolar bone surfaces around the first molar and produced enhanced resorption of crypt surfaces as revealed by scanning electron microscopy. These data suggest that during eruption rodent incisors and molars may preferentially respond to different molecular regulators.