Higher osteoclastic demineralization and highly mineralized cement lines with osteocalcin deposition in a mandibular cortical bone of autosomal dominant osteopetrosis type II: Ultrastructural and undecalcified histological investigations

In this study we report on histological and ultrastructural investigations of the mandibular cortical bone in a case of autosomal dominant osteopetros is type II complicated by mandibular osteomyelitis. Histologically, there w as a marked increase in the number and size of osteoclasts on the inner bon e surface. An undecalcified preparation showed a pair of deeply stained (hi ghly demineralized) and stain-phobic (highly mineralized) layers on the bon e surface just beneath the osteoclasts. The layers were incorporated into t he bone matrix during the remodeling process as thickened cement lines. A c ontact microradiogram of the cortical bone revealed highly mineralized laye rs at the cement lines, which were closely correlated with immunohistochemi cal evidence of deposition of osteocalcin at the thickened cement lines. Ul trastructural examination showed that the osteoclasts had a typical clear z one, but they were deficient in ruffled border formation and had numerous l ysosomal vacuoles containing dense substances. An electron-dense amorphous material layer was present on the bone surface just beneath the osteoclasts as well as at the cement lines. The layer was partly composed of a short f ibrillar material, and it partially revealed the lamellar structure. Conseq uently, an osteoclastic malfunction might be primarily involved in the proc ess of bone matrix resorption rather than demineralization, resulting in hi gher demineralization and abnormal material deposition on the bone surface and at the cement lines. Furthermore, evidence of active osteoclastic bone resorption with a brush border formation at the bone involved in the inflam matory lesion in this case suggests that the osteoclastic malfunction is in fluenced and recovered by a microenvironment such as inflammatory cytokines , (C) 2000 by Elsevier Science Inc. All rights reserved.