In-Vitro Bioactivity of Enamel-Based Biomaterials Designed to Assist Enamel Remineralization

Objectives: There is an appreciation that the use of molecule analogs of native tissues can serve as template to recapitulate and promote endogenous regeneration of injured parent tissues. Herein, we developed and characterized biomaterials derived from dental enamel which were envisioned to assist the remineralization of dental caries- and/or erosion-affected lesions. Specifically, we investigated the in-vitro bioactivity of proposed materials after incubation in a simulated-body-fluid (SBF) with optimum ion concentration to elicit apatite formation.
Methods: Enamel fragments were obtained from 18 caries-free extracted teeth. Fragments were pooled, washed, air-dried, weighed, stored in liquid-nitrogen, and reduced into powder using a mechanical ball-mill (Restch). Retrieved powder was separated into 3-equal aliquots (4g/each), treated as follows: 1) control (untreated-enamel); 2) lactic- (treated with 0.78M lactic acid-pH 4.2); or 3) citric- (treated with 0.015M citric acid-pH 3.3). Each sample was added with 0.2g of alginate (Dentsply/Sirona) and hand-mixed with 1mL of water. Resultant paste-like biomaterials were injected into custom made molds to produce disc-like constructs (1x4mm diameter). Constructs were stored either in dry conditions, ultrapure water or SBF for 2, 4 and 8 days (n=3/biomaterial/storage-condition). At incubation-endpoints, specimens were analyzed using an ATR-FTIR instrument (Spectrum-Two, PerkinElmer). Shifts in spectral peaks corresponding to apatite mineral were compared among samples and against pristine materials (enamel, lactic-treated enamel, citric-treated enamel, alginate, and hydroxyapatite).
Results: An increased absorbance of IR-peaks for apatite (~564, 938, 1000cm-¹) were seen on lactic- and citric-treated samples, respectively, at day-2 and -4 of SBF-incubation. Lactic-treated samples showed significant increase of apatite peaks at all SBF-incubation-endpoints (p<0.05), while citric-treated samples demonstrated a significant increase for those corresponding peaks at day-4 and -8 of SBF-incubation (p<0.05). No significant shift/increasing of apatite IR-peaks was observed for dried- or water-stored samples.
Conclusions: Newly developed enamel-alginate biomaterials showed promising in-vitro bioactivity and could be further explored in enamel remineralization schemes.