Abstract
Our studies of amorphous calcium phosphate (ACP)-based materials over the last decade have yielded bioactive polymeric composites capable of protecting teeth from demineralization or even regenerating lost tooth mineral. The anti-cariogenic/re-mineralizing potential of these ACP composites originates from their propensity, when exposed to the oral environment, to release in a sustained manner sufficient levels of mineral-forming calcium and phosphate ions to promote formation of stable apatitic tooth mineral. However, the less than optimal ACP filler/resin matrix cohesion, excessive polymerization shrinkage and water sorption of these experimental materials can adversely affect their physicochemical and mechanical properties, and, ultimately, limit their lifespan. This study demonstrates the effects of chemical structure and composition of the methacrylate monomers used to form the matrix phase of composites on degree of vinyl conversion (DVC) and water sorption of both copolymers and composites and the release of mineral ions from the composites. Modification of ACP surface via introducing cations and/or polymers ab initio during filler synthesis failed to yield mechanically improved composites. However, moderate improvement in composite’s mechanical stability without compromising its remineralization potential was achieved by silanization and/or milling of ACP filler. Using ethoxylated bisphenol A dimethacrylate or urethane dimethacrylate as base monomers and adding moderate amounts of hydrophilic 2-hydroxyethyl methacrylate or its isomer ethyl-α-hydroxymethacrylate appears to be a promising route to maximize the remineralizing ability of the filler while maintaining high DVC. Exploration of the structure/composition/property relationships of ACP fillers and polymer matrices is complex but essential for achieving a better understanding of the fundamental mechanisms that govern dissolution/re-precipitation of bioactive ACP fillers, and, ultimately, the suitability of the composites for clinical evaluation.
Highlights
Despite significant reduction in the occurrence of dental caries in some segments of population, it remains one of the most prevalent diseases affecting humans
Synthesized pyrophosphate-stabilized amorphous calcium phosphate (ACP) [15], the bioactive filler used to formulate polymeric ACP composites, is typically highly agglomerated with a heterogeneous particle size distribution ranging from submicrometer up to 100 to 200 μm
It has been documented in the literature that metal ions in dental materials may: affect calcium phosphate precipitation and/or transformation [16,17], improve adhesive bonding of composites via chelating and/or multiple interacting with surface-active resin comonomers [18], promote bone regeneration [19, 20], regulate dental calculus formation [21], affect the free-radical polymerization of the resins [22], aid in detecting defects in the subsurface wear layer [23] and control the topical calcium fluoride deposition in bio-glasses [24]
Summary
Despite significant reduction in the occurrence of dental caries in some segments of population, it remains one of the most prevalent diseases affecting humans. Physicochemical data [7,8,9,10,11,12] and the results of in vitro testing [13,14] show that ACP composites in various biostable matrices release calcium and phosphate ions in a manner that effectively buffers free calcium and phosphate ion activities and, in turn, maintains the desired state of supersaturation with respect to tooth mineral As a result, these composites have the capacity to prevent the formation of new carious lesions, and actively repair existing incipient lesions. The comprehensive structure-composition-property relationship studies are expected to improve our understanding of the multifaceted interactions occurring at the filler/polymer interfaces expanding the knowledge base needed for the successful design of improved calcium phosphate-based dental composites
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