Objective: This study explores the efficacy of an experimental orthodontic amorphous calcium phosphate (ACP) composite to remineralize in vitro subsurface enamel lesions microradiographically similar to those seen in early caries. Methods:Lesions were artificially created in extracted human molars. Single tooth sections a minimum of 120 μm thick were cut and individually placed in holders exposing only the carious enamel surface. The exposed surfaces were either left untreated (control) or coated with a 1 mm thick layer of the experimental ACP composite (mass fraction 40 % zirconiahybridized ACP and 60 % photo-activated resin), or a commercial fluoride-releasing orthodontic cement. The composite-coated sections were then photo-cured and microradiographic images were taken of all three groups of specimens before the treatment. Specimens were then cyclically immersed in demineralizing and remineralizing solutions for one month at 37 °C to simulate the pH changes occurring in the oral environment. Microradiographs of all specimens were taken before and after treatment. Results:Quantitative digital image analysis of matched areas from the contact microradiographs taken before and after treatment indicated higher mineral recovery with ACP composites compared to the commercial orthodontic F-releasing cement (14.4 % vs. 4.3 %, respectively), while the control specimens showed an average of 55.4 % further demineralization.Significance: Experimental ACP composite efficiently established mineral ion transfer throughout the body of the lesions and restored the mineral lost due to acid attack. It can be considered a useful adjuvant for the control of caries in orthodontic applications.

This study evaluates the bond strength and related properties of photo-polymerizable, remineralizing amorphous calcium phosphate (ACP) polymeric composite-adhesive systems to dentin after various periods of aqueous aging at 37 °C. An experimental ACP base and lining composite was made from a photo-activated resin comprising 2,2-bis[p-(2’-hydroxy-3’-methacryloxypropoxy)phenyl]propane (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA) and zirconyl dimethacrylate (ZrDMA); designated BTHZ. An experimental orthodontic composite was formulated from a photo-activated resin comprising ethoxylated bisphenol A dimethacrylate (EBPADMA), TEGDMA, HEMA and methacryloxyethyl phthalate (MEP); designated ETHM. In both composite series three fillers were compared: 1) freshly precipitated zirconium-modified ACP freshly precipitated (as-prepared Zr-ACP), 2) milled Zr-ACP and 3) an ion-leachable fluoride glass. In addition to the shear bond strength (SBS), work to fracture and failure modes of the orthodontic composites were determined. The SBS of the base and lining ACP composites appeared unaffected by filler type or immersion time. In the orthodontic ACP composite series, milled ACP composites showed initial mechanical advantages over as-prepared ACP composites, and produced higher incidence of a failure mode consistent with stronger adhesion. After six months of aqueous exposure, 80 % of specimens failed at the dentin-primer interface, with a 42 % overall reduction in bond strength. BTHZ and ETHM based ACP composites are potentially effective anti-demineralizing-remineralizing agents with possible clinical utility as protective base-liners and orthodontic cements, respectively. The analysis of the bond strength and failure modalities suggests that milled ACP composites may offer greater potential in clinical applications.

This study explores degree of vinyl conversion (DVC), polymerization shrinkage (PS) and shrinkage stress (PSS) of the experimental amorphous calcium phosphate (ACP) composites intended for use as an endodontic sealer. Light-cure (LC), chemical cure (CC) or dual-cure (DC; combined light and chemical cure) resins comprised urethane dimethacrylate (UDMA), 2-hydroxyethyl methacrylate (HEMA), methacryloyloxyethyl phthalate (MEP) and a high molecular mass oligomeric co-monomer, poly(ethyleneglycol)-extended UDMA (PEG-U) (designated UPHM resin). To fabricate composites, a mass fraction of 60 % UPHM resin was blended with a mass fraction of 40 % as-made (am-ACP) or ground ACP (g-ACP). DVC values of copolymer (unfilled UPHM resin) and composite specimens were determined by infrared spectroscopy. Glass-filled composites were used as controls. PS and PSS of composites were determined by dilatometry and tensometry, respectively. LC copolymers attained extraordinary high DVC values at 24 h post-cure (95.7 %), compared to CC (52 %) and DC (79.3 %) copolymer specimens. While the DVC values of LC and DC am-ACP composites were reduced between 5 and 10 %, DVC values of DC g-ACP composites increased almost 8 % compared to the corresponding copolymers. High DVC attained in LC composites was, expectedly, accompanied with high PS values (on average 7 vol%). However, PSS developed in LC and especially DC composites did not exceed PSS values seen in other UDMA-based composites. Based on this initial evaluation, it is concluded that, DC, g-ACP filled UPHM composite shows promise as an endodontic sealer. However, further physicochemical evaluations, including water sorption, mechanical stability and ion release as well as a leachability studies need to be performed before this experimental material is tested for cellular responses and, eventually recommended for clinical utility. Keywordsamorphous calcium phosphate; endodontic composite; degree of vinyl conversion; polymerization shrinkage; polymerization stress a justin.odonell@nist.gov b drago.skrtic@nist.gov