The aim of the study was to evaluate the effect of experimental composites containing dicalcium phosphate dihydrate (DCPD) on remineralization of enamel lesions. Five resin‐based composites containing equal parts (in mols) of bisphenol‐A glycidyl dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA), and 60 vol % of fillers were manipulated. Filler phase was constituted by silanized barium glass and 0, 10, or 20 vol % of DPCD particles, either functionalized (F) or nonfunctionalized (NF) with TEGDMA. Artificial subsurface lesions were produced in human enamel fragments and divided according to the resin composite applied on the lesion (no DCPD, 20% NF, 20% F, 10% NF, 10% F) plus a group without composite build‐up (nontreated, NT). Fragments were exposed to 16 days of pH cycling. Specimens were evaluated using transverse microradiography (TMR). Calcium and phosphate concentrations in pH‐cycling solutions were determined by spectrophotometry. TMR and ionic concentrations were analyzed using one‐way ANOVA/Tukey and Kruskal–Wallis/Dunn test, respectively (alpha: 0.05). All composite groups showed enamel remineralization (3%–23%). Higher mineral recovery in the middle (7%–11%) and bottom (2%–7%) thirds of the lesion was observed in groups with DCPD‐containing composites compared to the “no DCPD” group (middle: 1%, bottom: −3%). Lesion depth was significantly reduced in groups using DCPD‐containing composites compared to NT group. No noticeable increase in calcium and phosphate ions was observed in the pH‐cycling solutions due to the presence of DCPD in the composites. In conclusion, composites with DCPD fractions as low as 10%, regardless of functionalization, were able to promote mineral recovery and reduce lesion depth of enamel lesions. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1542–1550, 2019.
This study describes the synthesis of dicalcium phosphate dihydrate (DCPD) particles in the presence of different ethylene glycol dimethacrylates (EGDMA, ethylene glycol/EG units: 1, 2, 3 or 4) at two monomer-to-ammonium phosphate molar ratios (1:1 and 2:1), as a strategy to develop CaP-monomer particles with improved interaction with resin matrices. Particles displaying high surface areas and organic contents were added to a photocurable BisGMA-TEGDMA resin and the resulting materials were tested for degree of conversion (DC), biaxial flexural strength (BFS), flexural modulus, and ion release. Data were subjected to one-way ANOVA or Kruskal-Wallis/Dunn test (alpha: 0.05). Functionalization with EGDMA derivatives was dependent upon the length of the spacer group and monomer concentration in the synthesis. No differences in DC were observed among materials (p > 0.05). A 39% increase in BFS was obtained with the use of particles with the highest functionalization level compared to non-functionalized particles (p < 0.001). The use of functionalized DCPD reduced flexural modulus in comparison to non-functionalized particles (p < 0.001). Calcium release was similar among materials and remained constant during the experiment, while phosphate release was higher at 7 days in comparison to the remaining weeks (p < 0.001). In conclusion, diethylene glycol dimethacrylate resulted in the highest functionalization levels and the highest BFS among DCPD-containing materials. Ion release was not affected by functionalization. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2018.
Calcium orthophosphates (CaP) synthesis involves several chemical equilibria that define the phases present in the final product. From the biomaterials standpoint, it is important to gain knowledge on how synthesis parameters affect phase formation and particle size. This study evaluates the interaction between temperature (24 or 45 °C) and pH conditions (4.5, 6.5, or drifting) on CaP precipitation in terms of yield, phase formation, density, morphology, and size distribution. Calcium and phosphate solutions (Ca/P = 1.0) are mixed and kept under stirring for 3 h. The precipitate is freeze-dried and characterized. Under drifting pH and pH 4.5, dicalcium phosphate dihydrate (DCPD, CaHPO 4 × 2H 2 O) is the predominant phase at both temperatures; however, some samples also present peaks ascribed to dicalcium phosphate anhydrous (DCPA, CaHPO 4 ). At pH 6.5, diffractograms reveal a mixture of low-crystallinity DCPD and DCPA (24 °C) or low crystallinity hydroxyapatite [HAP, Ca 10 (OH) 2 (PO 4 ) 6 ] (45 °C). In spite of the different morphologies (plates or aggregates), particle size remains within a relatively narrow range (D 50 = 12-28 µm). DCPD precipitation is favored under more acidic or drifting pH, while HAP is formed under nearly neutral pH 6.5.
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