Effect of Proteoglycans and Poly-l-aspartic Acid on Dentin Remineralization

Objective: To determine the remineralization roles of proteoglycans (PG), a major non-collagenous protein (NCP), and poly-l-aspartic acid (Pasp) on stiffness recovery of artificially induced demineralized dentin. Method: Ten sound human molars crowns were sectioned occlusal-gingival into four rectangular beams with dimensions of 0.3mm x 1.7mm x 6.0mm. Beams were fully demineralized in demineralization buffer (pH = 4.6) at 37°C for 1 week. Half of the samples were treated with 4M GuCl extraction solution for 48 hours to remove proteoglycans from the dentin matrix. A glycosaminoglycans chains detection assay was used to confirm PG removal. A micro-flexural method was used to assess the modulus of elasticity of the beams using a three-point bending setup at 3% strain. Baseline measurements were taken immediately before immersion in CaCl₂ and KH₂PO₄ remineralization solution (pH = 7.4) at 37°C under constant stirring. Half of each group (n=5) were immersed in remineralization buffer containing 50µg/ml Pasp (Alamanda Polymers), while the other half received only remineralization buffer. Solutions were renewed every 48 hours and maintained at pH 7.4. Stiffness recovery was assessed after 24 hrs and weekly thereafter for 6 weeks. Data were calculated in MPa and statistically analyzed using ANOVA and Games-Howell tests (α = 0.05). Result: Significant interactions were depicted between presence of PG vs. Pasp vs. Time (p<0.011) and PG vs. Pasp (p<0.001). Baseline values averaged 6.41 ± 2.75. Efficiency of Pasp to recover the modulus of elasticity of dentin was dependant upon the presence of PG. After 6 weeks, the highest recovery was observed for Pasp treated samples containing proteoglycans (773.14 ± 331.98). Conclusion: The preliminary findings confirm the role of Pasp in enhancing dentin remineralization; and highlights the importance of the composition of the dentin matrix on remineralization potential. Remaining NCP, specifically proteoglycans, can affect the remineralization of dentin matrix.