LOCALIZATION OF EPIDERMAL GROWTH-FACTOR AND ITS RECEPTOR IN MANDIBULAR MOLARS OF THE RAT PRIOR TO AND DURING PREFUNCTIONAL TOOTH ERUPTION

Immunoperoxidase localization of epidermal growth factor receptors (EGFR) and epidermal growth factor (EGF) itself was examined in rat first and second mandibular molars postnatally from day 0 to 12. The results showed that the dental follicle stained heavily for EGFR from day 0 to 8, declined in staining at day 9, and was devoid of stain from day 10 onward. Preosteoblasts and osteoblasts of alveolar bone also stained and lesser staining of ameloblasts and odontoblasts was observed. Except for staining of occasional isolated cells, the stellate reticulum did not stain. Light staining of the dental pulp of the first mandibular molar was seen from day 0 onward but the pulp of the second molar did not stain until approximately day 6. With respect to EGF, the dental follicle also stained for it until day 12. The ameloblasts stained more intensely for EGF than for EGFR. Because injections of EGF cause premature eruption of teeth and because the presence of a dental follicle is necessary for eruption, this study suggests that EGF could have its effect on the follicle as seen by the presence of EGFR receptors on the follicle. Moreover, because EGF exerts its effects early (day 0-3) to cause eruption and because the influx of monocytes into the follicle to form osteoclasts for bone resorption for eruption occurs early, the heavy staining for EGFR in the follicle early followed by the absence of staining at day 10 correlates chronologically with the key molecular and cellular events of eruption. Finally, the presence of EGF in the follicle, as well as enamel organ, could provide an endogenous source of EGF to regulate tooth eruption, either by an autocrine or a paracrine effect. Thus, the localization of EGFR and EGF in the dental follicle coupled with the chronology of localization suggests that EGF could play a physiological role in tooth eruption.