Correlation of transversal microradiography and microhardness on in situ-induced demineralization in irradiated and nonirradiated human dental enamel

The objective was to evaluate whether a correlation exists between microhar dness (MH) and transversal microradiographical (TMR) data for in situ-induc ed caries lesions in irradiated and nonirradiated human enamel. Enamel spec imens were prepared from the lingual and buccal surfaces of 20 freshly extr acted, caries-free third molars. The surfaces were polished (4000 grit). Ei ther the lingual or the buccal specimen of each tooth was irradiated with 6 0 Gy; the other sample was not irradiated. Two irradiated and two nonirradi ated specimens were inserted into both buccal aspects of each of five intra oral mandibular appliances. The appliances were worn by five persons for 6 weeks day and night. One side was brushed daily with a fluoride-free toothp aste; on the other side, dental plaque was allowed to grow. Individual oral hygiene was performed without any fluorides. During meals, the appliance w as stored in 10% sucrose solution. Then the enamel specimens were cut perpe ndicular to their oral surface. The cut surface was polished (4000 grit) an d the Knoop hardness number (KHN) was measured across the lesions, at 25, 5 0 and 75 mu m from the oral surface. After MH testing the samples were poli shed again, thereby reducing the surface by about 10 mu m. Subsequently, th e slabs were ground to a thickness of 90 mu m, and studied by means of TMR. Mineral loss was calculated with dedicated software at the locations corre sponding to the MH testing. A total of 120 paired data was submitted to lin ear-regression analysis. Neither MH nor TMR showed significant differences between irradiated and nonirradiated enamel lesions. A linear relation was found between root KHN and the mineral volume percent. In naturally induced caries lesions, MH values can be converted to mineral volume percent using the equation [21.19 + 3.66.root KHN]. This equation fits the data with a r eliable correlation coefficient (r(2) = 0.915). (C) 1999 Elsevier Science L td. All rights reserved.