Changes in matrix phosphorylation during bovine dentin development

Abstract

Phosphorylation of the organic matrix proteins of dentin is important for the initiation of mineralization, but its relevance in later mineralization stages is controversial. The objective of this study was to analyze changes in the total matrix phosphate content during dentin development and to identify their origin. Amino acid and total matrix phosphate analyses of microdissected developing mantle and circumpulpal fetal bovine dentin specimens were performed. The amino acid composition showed few changes during mantle and circumpulpal dentin maturation. However, the total matrix phosphate content showed a significant, positive correlation with tissue maturation in both mantle and circumpulpal dentin, with a two- and a three-fold increase, respectively, being observed. The data indicate that changes occur in the pattern of phosphorylation of matrix proteins during dentin maturation, which we suggest may play a functional role in later stages of tooth mineralization.

Fig. 1

Microdissection of dentin specimens. (A) Incisor cut longitudinally at 800-μm intervals. Sections were numbered based on the distance from the cervix. (B) Section used for dentin microdissection. Labial and lingual aspects of incisor. D, dentin; E, enamel; P, pulp. (C) Schematic of areas used for microdissection on detail (framed) from the section in (B). C, circumpulpal dentin; DEJ, dentin–enamel junction; M, mantle dentin.

Fig. 2

Relative content of amino acids (mmol per mmol of collagen) in dentin matrix as a function of distance from the cervix. (A) Aspartic acid (Asp), (B) serine (Ser), and (C) threonine (Thr) from mantle dentin specimens. (D) Asp, (E) Ser, and (F) Thr from circumpulpal dentin. Pearson’s coeffcient (R) and statistical significance of relative content correlation with distance from cervix (where correlation is significant) are noted for each amino acid. Linear regression is shown. *Indicates statistical significance.

Fig. 3

Relative matrix phosphate content in dentin as a function of distance from the cervix. (A) Mantle dentin and (B) circumpulpal dentin from incisor specimens I3 and I4. Pearson’s coeffcient (R) and statistical significance of relative content correlation with distance from the cervix are noted. Linear regression is shown. **Indicates statistical significance.

Fig. 4

Relative matrix phosphate content in dentin as a function of distance from the cervix. (A) Mantle dentin and (B) circumpulpal dentin. Incisors I1 and I2.

Fig. 5

Relative amino acid and phosphate content of matrix as a function of distance from the mineralization front. (A) Aspartic acid (Asp), serine (Ser), and threonine (Thr) relative content in dentin matrix. (B) Relative matrix phosphate content. The presence of an asterisk between groups indicates statistical significance (*, P < 0.05, **, P < 0.01). min. front, mineralization front.