Analysis of Odontoblasts Function in Estrogen-deficient Rats

Abstract

 Purpose: Estrogen has long been known as a hormone that affects the remodeling of bone tissue. Recently, its receptors were identified in odontoblasts in addition to osteoblasts and osteoclasts. However, little is known about the receptor functions of odontoblasts. Therefore, in this study, the effect of estrogen on dentinogenesis was examined histochemically using estrogen-deficient rat models.
 Materials and methods: Ninety-six 10-week-old female SD rats were used for this experiment. They were equally divided into three groups (32 each) : the OVX (Ovariectomized rats) group, the Sham group with laparotomy alone, and the OVX+E₂ group, which was administered with 20 μg/kg/day estradiol (E₂) daily from the next day after ovariectomization. All groups were bred for four weeks, and their body weights were measured daily. Thereafter, to induce reparative dentin formation, 1.0 mm-diameter cavity preparation filled with light-cured resin composite was applied to the first molars in the lower jaw on each side. Tooth samples were taken on Days 3, 7, and 14, while blood and femur samples were collected at the same time to measure estradiol levels and bone density by DEXA. Each sample was subjected to H-E staining. On Day 14, Alcian blue staining and immunohistochemical staining were performed for ER-α and ER-β. Meanwhile, in order to compare the formation of secondary dentin, calcein was administered at 3-day intervals to the groups that were not subjected to cavity formation, and the groups were monitored by fluorescence microscopy.
 Results: The OVX group showed weight gain and a decrease of estradiol levels compared to the Sham and OVX+E₂ groups. The results of DEXA and H-E staining revealed decreased bone density, presenting osteoporosis. The results of immunohistochemical staining indicated that ER-α and ER-β localized at the nucleus of odontoblasts. The amounts of reparative dentin formation were the most in the Sham group, followed by the OVX+E₂ and OVX groups. The OVX+E₂ group showed the highest formation of secondary dentin, followed by the Sham and OVX groups.
 Conclusion: The OVX group manifested osteoporosis, and the formation of reparative dentin and secondary dentin was suppressed. The OVX+E₂ group showed no trace of osteoporosis, and recovery in the amount of dentin formation was observed. These results suggest that estrogen is involved in dentinogenesis.