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Cementum and Dentin in Hypophosphatasia

¹ Department of Periodontology, Academic Center for Dentistry Amsterdam (ACTA), Universiteit van Amsterdam, and Vrije Universiteit, Louwesweg 1, 1066 EA Amsterdam, The Netherlands;
² Division of Rheumatology, Department of Medicine, Medical College of Wisconsin, Milwaukee, WI, USA;
³ Department of Chemistry, Indiana University-Purdue University, Fort Wayne, IN, USA; and
⁴ Center for Metabolic Bone Disease and Molecular Research, Shriners Hospitals for Children, St. Louis, MO, USA;

View larger version (21K): [in a new window]   Figure 1. Sampling of dentin. (A) ± 100-µm-thick longitudinal sections were used for LM, EM, and biochemical analyses. (B) Dentin was sampled at 4 zones: crown (C) and root (R1-3). Samples were taken by means of a dental bur (1 mm diameter) running at low speed to prevent overheating. For microradiography, 200-µm-thick transverse sections were prepared (dashed lines). (C) Mineral density was determined at sites 1–4. P = pulp; E = enamel.

View larger version (106K): [in a new window]   Figure 2. Microscopic appearance of dental-periodontal interface in HPP and control specimens (A-E) and dentin mineral content (F). (A,B) Light microscopy of a control (A) and an HPP tooth (B). Note the absence of acellular cementum (c) in HPP. The arrow marks a periodontal ligament cell that has migrated into the orifice of a dentinal tubule. d = dentin; p = periodontal ligament. (C,D) EM showing interface between dentin (d) and periodontal ligament (p) of a HPP tooth. Acellular cementum is absent. Note the presence of a thin, electron-dense, amorphous layer covering the interface. Occasionally, individual collagen fibrils seem to cross the interface (arrow; shown at higher magnification in D). (E) Cellular cementum (cc) around the apex of an HPP tooth. (F) Relationship between HPP tooth age and mineral content in the 4 dentin compartments (C, R1-3; expressed as µg Ca/µg hydroxyproline).

View larger version (18K): [in a new window]   Figure 3. Biochemical analyses of pulp and periodontal ligament specimens (A-C). (A) mRNA expression of NPP1, ANK, TNSALP, collagen I-1, and osteonectin relative to ß2-microglobulin in periodontal ligament (open bars) and pulp (dashed bars) from normal teeth (mean ± SD; n = 14 for all datasets). (B) Activities of NPP1 (substrates: p-nitrophenyl phenylphosphonate and p-nitrophenylthymidine 5-monophosphate, respectively) and TNSALP (substrate: p-nitrophenylphosphate) in periodontal ligament (open bars) and pulp (dashed bars) of normal teeth (n = 20). Activities are given as mU/µg DNA. (C) Concentration of PPi relative to DNA content in periodontal ligament (open bar) and pulp (dashed bar) of normal teeth (n = 20). *p < 0.05; **p < 0.01; ***p < 0.001 according to the Wilcoxon signed-rank test.