Physicochemical Evaluation of Bioactive Polymeric Composites Based on Hybrid Amorphous Calcium Phosphates
Joseph M. Antonucci, Drago Skrtic, A W. Hailer, E D. Eanes
Amorphous calcium phosphate (ACP), an important precursor in the biological formation of hydroxyapatite (HAP), has recently been utilized as a bioactive filler in resin-based dental materials. It was found that, if ACP was stabilized against premature internal conversion into HAP by inclusion of pyrophosphate (P2O7) ions, methacrylate-based composites containing the P2O7-stabilized ACP released supersaturating levels of calcium and phosphate ions over extended periods of time to form HAP external to the composite. Such composites were found to also effectively remineralize in vitro caries-like enamel lesions that were induced artificially in extracted bovine incisors. Because these bioactive composites are significantly weaker in mechanical strength than glass-filled composites they are limited in their dental applications.This study was designed to determine the feasibility of introducing glass-forming elements during the synthesis of ACP so that the resulting hybrid fillers would have greater potential for strengthening the composites, e.g., improved interfacial interactions with the polymer phase. Specifically, tetraethoxysilane (TEOS) and zirconyl chloride (ZrOCl2), were used in separate preparations to modify P2O7-stabilized ACP fillers. New composites containing these hybrid ACP fillers were then evaluated to establish whether these silica- or zirconia-ACP fillers improved their mechanical properties without compromising their calcium and phosphate ion release. The synthesis of these hybrid ACP fillers was carried out in the presence mole fraction of 10 % of either TEOS or ZrOCl2 relative to the phosphate reactant. The polymeric phases of the composites were derived from 2,2-bis[p-(2'-hydroxy-3'-methacryloxypropoxy)phenyl]propane (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) (mass fraction, 49.5 % for each component). When 2-hydroxyethyl methacrylate (HEMA; mass fraction, 28.0 %), zirconyl methacrylate (ZrM; mass fraction, 0.8%), camphorquinone (CQ; mass fraction 2 %) and ethyl-4-dimethylaminobenzoate (4EDMAB; mass fraction 0.8 %) were added to BisGMA/TEGDMA the mass fraction of each component of this base resin was 35.1 %. Physicochemical evaluation of the hybridized fillers and of composites derived from the hybridized fillers (mass fraction 40 %) and the resin (mass fraction, 60 %) included Fourier-transform infrared spectroscopic analysis, X-ray diffraction, dissolution/transformation kinetic studies and biaxial flexure testing before and after immersion in buffered saline solutions.Hybrid ACP-filled composites, both uncured and cured, showed no signs of internal conversion of ACP into HAP when kept dry over CaSO4 in a desiccator. Moreover, upon immersion in saline buffer, conversion to HAP occurred more slowly when hybridized ACPs were utilized in the polymerized composites. Consequently, mineral ion release from such composites was not adversely affected by hybridization. Comparison of biaxial flexure strength values of hybridized vs. unhybridized ACP composite disks revealed a uniform increase in the mechanical strength of the hybrid specimens. The relative increases in strength of 28 % and 27 % for ZrOCl2-modified composites and 33 % and 47 % for TEOS-composites before and after immersion, respectively, were found statistically significant (p 2O7-stabilized ACP filled composites, while retaining, if not enhancing their remineralization potential, by introducing hybridizing agents such as TEOS or ZrOCl2 during the synthesis of ACP. Such hybridized ACP fillers are expected to yield bioactive composites for more demanding restorative, sealant and adhesive applications.
June 7-8, 1999
International Symposium on Advanced Materials With Biomedical Applications
, Skrtic, D.
, Hailer, A.
and Eanes, E.
Physicochemical Evaluation of Bioactive Polymeric Composites Based on Hybrid Amorphous Calcium Phosphates, International Symposium on Advanced Materials With Biomedical Applications, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=851595
(Accessed June 4, 2023)