Dental Composites Based on Amorphous Calcium Phosphate — Resin Composition/Physicochemical Properties Study

Abstract

This study explores how the resin composition/structure affects the physicochemical properties of copolymers and their amorphous calcium phosphate (ACP)-filled composites. A series of photo-polymerizable binary and ternary matrices are formulated utilizing 2,2-bis[ p-(2^'-hydroxy-3^'methacryloxypropoxy)phenyl]propane, 2,2-bis[ p-(2^'-methacryloxypropoxy)phenyl]-propane (EBPADMA), or a urethane dimethacrylate as base monomers, and triethylene glycol dimethacrylate or hexamethylene dimethacrylate (HmDMA) with or without 2-hydroxyethyl methacrylate (HEMA) as diluent monomer. Unfilled copolymers and composites filled with 40% by mass zirconia-hybridized ACP are evaluated for biaxial flexure strength (BFS), degree of conversion (DC), mineral ion release, polymerization shrinkage (PS), and water sorption (WS). The average DC values are 82—94% and 74—91% for copolymers and composites, respectively. Unrelated to the resin composition, the PS values of composites are up to 8.4 vol. % and the BFS values of wet composite specimens are on average 51 ± 8 MPa. The maximum WS values attained in copolymers and composites reach 4.8 mass%. Inclusion of hydrophobic HmDMA monomer in the matrices significantly reduces the WS. The levels of Ca and PO₄ released from all types of composites are significantly above the minimum necessary for the re-deposition of apatite to occur. Elevated Ca, and to a lesser extent PO₄ release, is observed in HEMA-containing, ternary EBPADMA formulations. Further resin reformulations may be needed to improve the PS of composite specimens. Poor dispersion of `as-synthesized' ACP within the composite contributes to their inferior mechanical performance.

Keywords

amorphous calcium phosphate biaxial flexure strength composite copolymer degree of vinyl conversion ion release polymerization shrinkage water sorption.

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