Enamel remineralization by amelogenin-containing hydrogel with oral simulated biofilm

Enamel remineralization with the assistant of fluoride and recombinant full-length amelogenin has been proven a promising approach via the formation of enamel-like nanocrystals. Objectives: To investigate the effect of amelogenin-containing hydrogels on the enamel hardness at the initial stage of remineralization in the presence oral simulated biofilms. Methods: Amelogenin-containing remineralization hydrogels were prepared and the releasing profile of protein and ions was tested. Artificial caries on tooth slabs were generated by etching in pH=4.5 lactic acid. Thirty tooth slabs were treated for 5 days with three remineralization hydrogels (n=10 each group) in the presence of ten-multispecies oral biofilm in a constant depth film fermentor (CDFF) (pH=7.2 continuous flow 0.5ml/min, at 5%CO₂ and 95%N₂, 37^oC): Gel-1: hydrogel containing amelogenin (100ug/mL) and [Ca]=2.5mM, [PO₄]=1.5mM and [F]=10mg/L. Gel-2 contained no amelogenin; other compositions were the same as Gel-1. Gel-3 contained no amelogenin and fluoride; other compositions were the same as Gel-1. Knoop's hardness numbers (KHN) were tested by a microhardness tester (Buehler) with 25g force. ANOVA with Tukey's post-hoc test was used to compare the five materials' increase in hardness.

Results: Table 1. Knoop hardness before and after remineralization (Mean±SD)

Materials	Gel-1	Gel -2	Gel -3
Baseline	232.43±43.15a	266.61±73.60a	259.73±31.07a
Artificial Caries(AC)	21.25±13.93b	31.09±25.08b	19.56±31.10b
Remineralization Treatment(RT)	147.47±43.98cA	84.26±32.29cB	77.48±20.72bB
Increase (RT-AC)	126.22±48.79A	53.17±47.99B	57.93±27.70B

Lower-case superscripts indicate grouping in each column. Upper-case superscripts indicate grouping in last row. Different letters indicate significant difference (p<0.05).

Treatment with all three remineralization hydrogels increased the surface hardness significantly (p<0.05).  Gel-1 group had significantly greater hardness increase than Gel-2 and Gel 3 (p<0.001). Densely-packed enamel-like nanorods were observed on the tooth in Gel-1. Conclusions: Remineralization hydrogel containing amelogenin and fluoride leads to a significant recovery of the hardness of eroded enamel in CDFF multispecies oral biofilm models. Supported by NIH/NCRR-COBRE grant 5P20RR020160-05.