An ultrastructural study of the effect of a diabetogenic dose of alloxan on the secretory ameloblasts of the rat incisor

Hyperglycemia and xerostomia are key determinants of tooth decay in type 1 diabetic mice

Insulin-dependent type 1 diabetes mellitus (DM) and oral diseases are closely interrelated. Poor metabolic control in diabetics is associated with a high risk of gingivitis, periodontitis and tooth loss. Salivary flow declines in diabetics and patients suffer from xerostomia. Reduced saliva predisposes to enamel hypomineralization and caries formation; however, the mechanisms that initiate and lead to progression of tooth decay and periodontitis in type 1 DM have not been explored. To address this issue, we analyzed tooth morphology in Akita ⁻/⁻ mice that harbor a point mutation in the Ins2 insulin gene, which leads to progressive hyperglycemia. Mandibles from Akita ⁻/⁻ and wild-type littermates were analyzed by microCT, scanning EM and histology; teeth were examined for amelogenin (Amel) and ameloblastin (Ambn) expression. Mice were injected with pilocarpine to assess saliva production. As hyperglycemia may alter pulp repair, the effect of high glucose levels on the proliferation/differentiation of cultured MD10-F2 pulp cells was also analyzed. Results showed that Akita ⁻/⁻ mice at 6 weeks of age showed chalky white incisors that correlated with marked hyperglycemia and impaired saliva production. MicroCT of Akita ⁻/⁻ teeth revealed excessive enamel wearing and hypomineralization; immunostaining for Amel and Ambn was decreased. A striking feature was invasion of dentinal tubules with Streptococcus mitis and microabcesses that originated in the coronal pulp and progressed to pulp necrosis and periapical periodontitis. High levels of glucose also inhibited MD10-F2 cell proliferation and differentiation. Our findings provide the first evidence that hyperglycemia in combination with reduced saliva in a model of type1 DM leads to decreased enamel mineralization/matrix proteins and predisposes to excessive wearing and decay. Importantly, hyperglycemia adversely affects enamel matrix proteins and pulp repair. Early detection and treatment of hyperglycemia and hyposalivation may provide a useful strategy for preventing the dental complications of diabetes and promoting oral health in this population.

Enamel hypoplasia in a litter of rats with alloxan-induced diabetes mellitus

Enamel hypoplasia is an important clinical problem commonly seen in children born to diabetic women. We aimed to characterize the enamel hypoplasia in Wistar rats born to alloxan-induced diabetes mellitus rats. Groups consisted of pregnant rats supplemented (ISDR) or not (NISDR) with insulin and controls, in which sterile saline solution was administered instead of alloxan or insulin. The mandibular incisors of one-month-old rats born to these mothers were analyzed. Whitish defective enamel was found macroscopically in both experimental groups (ISDR = 37.5%, NISDR = 33.3%) but not in the control group. Mild to severe enamel hypoplasia was observed by scanning electron microscopy (ISDR = 93.8%; NISDR = 100%, control = 4.2%). The severity of hypoplasia correlated positively with the maternal level of blood glucose. In conclusion, the intensity of enamel hypoplasia in the teeth of the litter born to alloxan-induced diabetic rats was variable and was dependent on the glycemic level of the pregnant rat.

The effect of streptozotocin on the secretory activity of ameloblasts in rat incisor as revealed by radioautography after 3H-proline administration

The effect of a diabetogenic dose of streptozotocin on the secretory activity of ameloblasts was investigated in the rat incisor by radioautography. One group of male Sprague-Dawley rats was injected intravenously with streptozotocin in citrate buffer (pH 4.5). One hour later, this group was again injected intravenously with 3H-proline (2 mCi/kg). A control group of animals was injected with 3H-proline only. All the animals were sacrificed in groups of three at 5 min, 1 h, 2 h, 4 h and 8 h after 3H-proline injection by perfusion with 3% phosphate-buffered formaldehyde followed by an additional perfusion with 2.5% phosphate-buffered glutaraldehyde. The incisors were extracted with the jaws, demineralized, and prepared for radioautographic observations and analysis. The principal effects of streptozotocin were as follows: There was an inhibition of 3H-proline incorporation into the secretory ameloblasts at 5 min after injection. This was followed by a larger uptake and a slower passage of the label out of the cells into the enamel matrix than that seen in the control sample. Finally, there was a slower secretion of labeled proteins out of Tomes' processes between 1 and 4 h after injection. Therefore, streptozotocin had a temporary inhibitory effect on the incorporation and secretion of 3H-proline by the secretory ameloblasts of the rat incisor. This effect was present for about 4 h and was completely reversed 9 h after streptozotocin injection.