In vitro remineralization of artificial enamel caries with resin composites containing calcium phosphate particles.

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.

Development of calcium phosphate/ethylene glycol dimethacrylate particles for dental applications.

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. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 708-715, 2019.

Mechanical characterization and ion release of bioactive dental composites containing calcium phosphate particles.

OBJECTIVE: to verify the effect of the addition of dicalcium phosphate dihydrate (DCPD) particles functionalized with di- or triethylene glycol dimethacrylate (DEGDMA or TEGDMA) on the degree of conversion (DC), post-gel shrinkage (PS), mechanical properties, and ion release of experimental composites. METHODS: Four composites were prepared containing a BisGMA/TEGDMA matrix and 60 vol% of fillers. The positive control contained only barium glass fillers, while in the other composites 15 vol% of the barium was replaced by DCPD. Besides the functionalized particles, non-functionalized DCPD was also tested. DC after 24 h (n = 3) was determined by FTIR spectroscopy. The strain gage method was used to obtain PS 5 min after photoactivation (n = 5). Flexural strength and modulus (n = 10) were calculated based on the biaxial flexural test results, after specimen storage for 24 h or 60 days in water. The same storage times were used for fracture toughness testing (FT, n = 10). Calcium and phosphate release up to 60 days was quantified by ICP-OES (n = 3). Data were analyzed by ANOVA/Tukey test (alpha: 5%). RESULTS: Composites containing functionalized DCPD presented higher DC than the control (p < 0.001). The material containing DEGDMA-functionalized particles showed higher PS than the other composites (p < 0.001). After 60 days, only the composite with DEGDMA-functionalized DCPD presented fracture strength similar to the control, while for flexural modulus only the composite with TEGDMA-functionalized particles was lower than the control (p < 0.001). FT of all composites containing DCPD was higher than the control after 60 days (p < 0.005). Calcium release was higher for the composite with non-functionalized DCPD at 15 days and no significant reductions were observed for composites with functionalized DCPD during the observation period (p < 0.001). For all the tested composites, phosphate release was higher at 15 days than in the subsequent periods, and no difference among them was recorded at 45 and 60 days (p < 0.001). CONCLUSIONS: DCPD functionalization affected all the studied variables. The composite with DEGDMA-functionalized particles was the only material with strength similar to the control after 60 days in water; however, it also presented the highest shrinkage. The presence of DCPD improved FT, regardless of functionalization. DCPD functionalization reduced ion release only during the first 15 days.

Ion-releasing dental restorative composites containing functionalized brushite nanoparticles for improved mechanical strength.

OBJECTIVES: This study describes the synthesis of brushite nanoparticles (CaHPO4·2H2O) functionalized with triethylene glycol dimethacrylate (TEGDMA) and their application in dental restorative composites with remineralizing capabilities. METHODS: Nanoparticles were synthesized, with TEGDMA being added to one of the precursor solutions at three different molar ratios (0:1, 0.5:1 and 1:1, in relation to the ammonium phosphate precursor). Then, they were added (10 vol%) to a photocurable dimethacrylate matrix containing 50 vol% of reinforcing glass particles. The resulting composites were tested for degree of conversion, biaxial flexural strength and elastic modulus (after 24h and 28days in water), and ion release (over a 28-day period). Commercial composites (one microhybrid and one microfilled) were tested as controls. RESULTS: The final TEGDMA content in the functionalizing layer was modulated by the molar ratio added to the precursor solution. Functionalization reduced nanoparticle size, but did not reduce agglomeration. Improved mechanical properties were found for the composite containing nanoparticles with higher TEGDMA level in comparison to the composite containing non-functionalized nanoparticles or those with a low TEGDMA level. All brushite composites presented statistically significant reductions in strength after 28 days in water, but only the material with high-TEGDMA nanoparticles retained strength similar to the microhybrid commercial control. Overall, ion release was not affected by functionalization and presented steady levels for 28 days. SIGNIFICANCE: Though agglomeration was not reduced by functionalization, the improvement in the matrix-nanoparticle interface allowed for a stronger material, without compromising its remineralizing potential.

Synthesis and characterization of silver phosphate/calcium phosphate mixed particles capable of silver nanoparticle formation by photoreduction.

Silver phosphate is a semi-conductor sensitive to UV-Vis radiation (<530nm). Exposure to radiation removes electrons from the oxygen valence shell, which are scavenged by silver cations (Ag+), forming metallic silver (Ag0) nanoparticles. The possibility of silver nanoparticle formation in situ by a photoreduction process was the basis for the application of mixed calcium phosphate/silver phosphate particles as remineralizing and antibacterial fillers in resin-based dental materials. Mixed phosphate particles were synthesized, characterized and added to a dimethacrylate resin in 20% or 30% mass fractions to investigate their efficacy as ion-releasing fillers for dental remineralization and antibacterial activity. The formation of metallic silver nanoparticles after exposure to visible radiation from a dental curing unit (peak emission: 470nm) was demonstrated by particle X-ray diffraction and scanning electron microscopy analysis of the composite fractured surface. Calcium and phosphate release from materials containing the mixed particles were similar to those containing pure CaP particles, whereas Streptococcus mutans colonies were reduced by three orders of magnitude in relation to the control, which can be attributed to silver release. As expected, the optical properties of the materials containing mixed phosphate particles were compromised by the presence of silver. Nevertheless, materials containing mixed phosphate particles presented higher fracture strength and elastic modulus than those with pure CaP particles.

Polymerization stress of experimental composites containing random short glass fibers.

OBJECTIVE: To test the null hypotheses that (1) the replacement of particles by short fibers does not affect polymerization stress (PS), flexural modulus (FM) or volumetric shrinkage (VS) of experimental composites and (2) PS is not affected by specimen thickness. METHODS: Three experimental composites were prepared, each containing similar mass fractions of BisGMA and TEGDMA and 60 vol% of fillers, being 0%, 3% or 6% constituted by 1.6-mm long glass fibers and the remaining by 1µm glass particles. PS (n=5) was tested in a high compliance system, using two specimen heights (1.5mm and 4.0mm). VS and maximum shrinkage rate were obtained in a mercury dilatometer (n=3). FM was tested in three-point bending (n=10). As an additional control, a commercial composite (Filtek Z250, 3M ESPE) was tested. Data were recorded 10min after the onset of photoactivation and analyzed by ANOVA/Tukey test (FM only) and Kruskal-Wallis (alpha: 5%). RESULTS: At both specimen heights, the composite with 3% of fibers presented significantly higher PS than the controls (which showed similar PS values). Replacing 6% of particles by fibers did not increase PS significantly. FM was reduced in the presence of fibers, and 6% of fibers led to a decrease in VS. Shrinkage rate was not affected by the fibers. SIGNIFICANCE: Replacing 3vol% of particles by fibers resulted in significantly higher PS, which was associated to a decrease in FM compared to the control. PS was not affected by specimen height for any of the tested materials.

Calcium and phosphate release from resin-based materials containing different calcium orthophosphate nanoparticles.

The study compared ion release from resin-based materials containing calcium orthophosphates. Amorphous calcium phosphate (ACP), dicalcium phosphate anhydrous (DCPA), dicalcium phosphate dihydrate (DCPD), and tricalcium phosphate (ß-TCP) nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), and surface area (nitrogen adsorption isotherms, BET method). Nanoparticles were added to a dimethacrylate-based resin and materials were tested for degree of conversion (DC) and calcium/phosphate release up to 28 days under pH 5.5 and 7.0. Data were analyzed by ANOVA/Tukey test (alpha: 0.05).The crystallinity of DCPA, DCPD, and ß-TCP were confirmed, as well as the ACP amorphous nature. DCPD and ß-TCP presented larger agglomerates than DCPA and ACP. The surface area of ACP was 5-11 times higher than those of the other nanoparticles. Materials showed similar DC. The material containing ACP released significantly more ions than the others, which released similar amounts of calcium and, in most cases, phosphate. Ion release was not affected by pH. Calcium release decreased between 7 and 21 days, while phosphate levels remained constant after 14 days. In conclusion, ACP higher ion release can be ascribed to its high surface area. DCPA, DCPD, and ß-TCP had similar performances as ion-releasing fillers.