Scanning electron microscopy of trypsin-treated enamel from fluorosed rat molars

Fluoride-induced pitting and porosity of teeth have long been observed, but little progress has been made in determining their origin. We have observed, in the trypsin-treated surfaces of enamel, pits that disappear on completion of maturation, following the removal of the protein matrix and full mineralization. Since these pits were considered to be similar to those seen in fluorotic teeth, this scanning electron microscope (SEM) study was undertaken to determine the effect of fluoride on these transient developmental pits during enamel matrix maturation. A group of 20 eight-day-old rats was given daily intraperitoneal injections of NaF (20 mg/kg [9 mg F-/kg] body weight) for five days. Twenty control animals received intraperitoneal injections of isotonic saline. Maxillary and mandibular molars were dissected from the 13-day-old animals, washed in HEPES buffered (Ca2+/Mg2+) free basal medium, Eagle's (BME), incubated in 3% trypsin/BME for 5-10 min at room temperature, then indirectly sonicated in BME for 2-4 min. Clean crowns were fixed in 2.5% glutaraldehyde for three hr, dehydrated, critical-point-dried, and sputter-coated for SEM. Pits in the surfaces of developing enamel were observed in all groups. In control teeth, the pitting was restricted to the cervical margin, whereas in teeth from the fluoride-treated animals, pits were observed on some cuspal surfaces in addition to the cervical margin. These results confirmed that pits in trypsin-treated surfaces of developing enamel are a transient developmental event and showed that, in the presence of a high dose of fluoride, the maturation of enamel is modified with retention of the pits.