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Decreased Mineral Content in MMP-20 Null Mouse Enamel is Prominent During the Maturation Stage

¹ Department of Cytokine Biology and ² Department of Biomineralization, The Forsyth Institute, 140 The Fenway, Boston, MA 02115, USA; and
³ Laboratory for the Study of Calcified Tissues and Biomaterials, Faculté de médecine dentaire, Université de Montréal, Montreal, QC, Canada H3C 3J7;

View larger version (17K): [in a new window]   Figure 1. Normalized FTIR absorption spectra of enamel from wild-type (solid line) and MMP-20 null mice (dashed line), collected in ATR (A) and reflectance modes (B). Amide I protein band and 3 PO4 band are shown. Enamel from 4 null and 4 control teeth were analyzed.

View larger version (19K): [in a new window]   Figure 2. Means plots ± 95% confidence intervals of enamel mineral (ash) weight (A), protein content (B), mineral-to-protein (M:P) ratios (C), and percent mineral by weight (D) for wild-type (circles) vs. MMP-20 null (squares) incisors as a function of developmental stage (S, secretory; EM, early mature; NM, nearly mature). Differences in mineral content magnify as enamel development proceeds (A, S NM), and more protein appears to be retained in the nearly mature enamel of the MMP-20 null mice (B, NM). Ratio (C) and percent mineral by weight (D) differences are significant only relative to nearly mature enamel (NM; see also Table), when MMP-20 is not normally expressed (N values are provided in the Table).

View larger version (12K): [in a new window]   Figure 3. Box chart representing Knoop microhardness data for enamel from 2 maxillary incisors each from MMP-20 null mice (KO) and wild-type mice (WT). The Y-axis shows Knoop hardness numbers (KHN). The boxes outline the 25–75% data range, whiskers represent the standard deviation, squares in the boxes correspond to the mean hardness value, crosses (X) delimit the 99% data range, and hyphens (-) represent minimum and maximum hardness values. Average hardness for wild-type enamel (WTenamel) is 327 KHN10 (SD ± 70) and 207 KHN10 (SD ± 63) for MMP-20 null enamel (KOenamel). Student’s t test analysis demonstrated that the two means were significantly different (p = 0.005).