title: Kallikrein-related peptidase 4, matrix metalloproteinase 20, and the maturation of murine and porcine enamel.
abstract: The crowns of matrix metalloproteinase 20 (Mmp20) null mice fracture at the dentino-enamel junction (DEJ), whereas the crowns of kallikrein-related peptidase 4 (Klk4) null mice fracture in the deep enamel just above the DEJ. We used backscatter scanning electron microscopy to assess enamel mineralization in incisors from 9-wk-old wild-type, Klk4 null, and Mmp20 null mice, and in developing pig molars. We observed a line of hypermineralization along the DEJ in developing wild-type mouse and pig teeth. This line was discernible from the early secretory stage until the enamel in the maturation stage reached a similar density. The line was apparent in Klk4 null mice, but absent in Mmp20 null mice. Enamel in the Klk4 null mice matured normally at the surface, but was progressively less mineralized with depth. Enamel in the Mmp20 null mice formed as a mineral bilayer, with neither layer looking like true enamel. The most superficial mineral layer expanded during the maturation stage and formed irregular surface nodules. A surprising finding was the observation of electron backscatter from mid-maturation wild-type ameloblasts, which we attributed to the accumulation and release of iron. We conclude that enamel breaks in the deep enamel of Klk4 null mice because of decreasing enamel maturation with depth, and at the DEJ in Mmp20 null mice because of hypomineralization at the DEJ.
authors.affiliation: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, MI 48108, USA.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Hu
authors.forename: Jan C-C
authors.initials: JC
authors.lastname: Hu
authors.forename: Charles E
authors.initials: CE
authors.lastname: Smith
authors.forename: John D
authors.initials: JD
authors.lastname: Bartlett
authors.forename: James P
authors.initials: JP
authors.lastname: Simmer
mesh_terms: D000293:Adolescent; D000565:Ameloblasts / Q000201:enzymology; D000566:Amelogenesis / Q000502:physiology*; D000818:Animals; D002130:Calcium Phosphates / Q000032:analysis; D003743:Dental Enamel / Q000201:enzymology* / Q000254:growth & development* / Q000648:ultrastructure; D003744:Dental Enamel Hypoplasia / Q000235:genetics*; D003746:Dental Enamel Proteins / Q000032:analysis / Q000378:metabolism; D006801:Humans; D007501:Iron / Q000032:analysis; D007610:Kallikreins / Q000235:genetics / Q000502:physiology*; D053519:Matrix Metalloproteinase 20 / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008855:Microscopy, Electron, Scanning; D012542:Scattering, Radiation; D013052:Spectrometry, X-Ray Emission; D034421:Sus scrofa; D014074:Tooth Calcification / Q000502:physiology
chemical_list: D002130:Calcium Phosphates; D003746:Dental Enamel Proteins; D007501:Iron; D007610:Kallikreins; C120801:kallikrein 4; D053519:Matrix Metalloproteinase 20; C507113:Mmp20 protein, mouse