Influence of DSS-8 on Dentin Remineralization
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Influence of DSS-8 on Dentin Remineralization
1. Introduction Dentin is a complex composite of organized collagen matrix filled with submicronsized calcium-deficient, carbonate-rich apatite crystallites.1 Together, the collagen and apatites form dentinal tubules that house the odontoblasts.2,3 Unlike enamel, exposed dentin can result in hypersensitivity which is often treated with desensitizing toothpastes which are not always effective, necessitating the placement of artificial restorative materials if the hypersensitivity persists.
A preferred approach is to promote the
deposition of apatite like minerals onto exposed dentin surfaces. Dentin phosphoprotein (DPP) is known to play a critical role in tooth mineralization and is the most abundant non-collagenous extracellular matrix component in dentin.
DPP contains high
concentrations of serine (45-50 %) and aspartic acid (35-38 %),4 and human DPP contains numerous repetitive nucleotide sequences of aspartate-serine-serine (DSS) that promote the formation of hydroxyapatite. Of these, the octuple repeats of aspartateserine-serine, DSS-8 peptides, are the most active in the mediation of biologically directed mineral deposition.5-8
This study investigates the effects of DSS-8 on
microstructures, phase composition, hardness and elastic modulus for human dentin in the remineralization process.
2 Materials and methods 2.1 Materials preparation Human permanent molars were collected from local dental offices and washed in distilled water. The teeth were embedded in epoxy resin (Leco, St. Joseph, MI) and then crosssections along the parallel median plane were cut using a 331-CA diamond blade
(Struers, Cleveland, OH). Subsequently, the surfaces were polished using 800 grit and 1200 grit silicon carbide (SiC) sand papers, followed by 3 µm, 1 µm and 0.5 µm Al2O3 and 0.06 µm colloidal silica in sequence. After polishing, all samples were individually sonicated in deionized (DI) water for 5 minutes.
2.2 Mineral Deposition For the remineralization process, samples were exposed to either 0 mM or 12.5 µM DSS-8 dissolved in HEPES buffer solution (pH 7.0) for 30 minutes prior to immersion in simulated body fluids (SBF)9-11 at 36.8 ℃ for 24 hours (pH 6.8) to promote the nucleation of hydroxyapatite (HA) crystals. The ionic composition of SBF is shown in Table I below.
Table I The compositions of blood plasma and simulated body fluid (SBF) solution Ionic Concentration
+
+
2+
2+
-
-
2-
2-
Ca
Mg
HCO
Blood Plasma
142.0 5.0 2.5
1.5
27.0
103.0 1.0
0.5
SBF
142.0 5.0 2.5
1.5
27.0
103.0 1.0
0.5
( mM )
Na
K
3
Cl
HPO
4
SO
4
2.3 Characterization The surface hardness and modulus of dentin before and after remineralization was characterized by nanoindentation. Surface roughness was evaluated by atomic force microscopy. Surface phase changes was evaluated by grazing incidence x-ray diffraction.
3 Results and Discussion 3.1 Indentation hardness and Young’s modulus of dentin Surface hardness of dentin remains unchanged from 0.80 before to 0.83
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