Effect of a calcium silicate cement and experimental glass ionomer cements containing calcium orthophosphate particles on demineralized dentin.

OBJECTIVE: The study aims to evaluate the effect of a glass ionomer cement (GIC; Fuji 9 Gold Label, GC) with added calcium orthophosphate particles and a calcium silicate cement (CSC; Biodentine, Septodont) regarding ion release, degradation in water, mineral content, and mechanical properties of demineralized dentin samples. METHODS: GIC, GIC + 5% DCPD (dicalcium phosphate dihydrate), GIC + 15% DCPD, GIC + 5% ß-TCP (tricalcium phosphate), GIC + 15% ß-TCP (by mass), and CSC were evaluated for Ca2+/Sr2+/F- release in water for 56 days. Cement mass loss was evaluated after 7-day immersion in water. Partially demineralized dentin disks were kept in contact with materials while immersed in simulated body fluid (SBF) at 37 °C for 56 days. The "mineral-to-matrix ratio" (MMR) was determined by ATR-FTIR spectroscopy. Dentin hardness and elastic modulus were obtained by nanoindentation. Samples were observed under scanning and transmission electron microscopy. Data were analyzed by ANOVA/Tukey test (α = 0.05). RESULTS: Ca2+ release from CSC and GIC (µg/cm2) were 4737.0 ± 735.9 and 13.6 ± 1.6, respectively. In relation to the unmodified GIC, the addition of DCPD or ß-TCP increased ion release (p < 0.001). Only the dentin disks in contact with CSC presented higher MMR (p < 0.05) and mechanical properties than those restored with a resin composite used as control (p < 0.05). Mass loss was similar for GIC and CSC; however, the addition of DCPD or ß-TCP increased GIC degradation (p < 0.05). CONCLUSION: Despite the increase in ion release, the additional Ca2+ sources did not impart remineralizing capability to GIC. Both unmodified GIC and CSC showed similar degradation in water. CLINICAL RELEVANCE: CSC was able to promote dentin remineralization.

Glass ionomer cement with calcium-releasing particles: Effect on dentin mineral content and mechanical properties.

OBJECTIVE: to evaluate the effect a glass ionomer cement (GIC) containing hydroxyapatite (HAp) or calcium silicate (CaSi) particles on mineral content and mechanical properties of demineralized dentin. Ion release and compressive strength (CS) of the cements were also evaluated. METHODS: GIC (Fuji 9 Gold Label, GC), GIC+ 5%HAp and GIC+ 5%CaSi (by mass) were evaluated. Ion release was determined by induced coupled plasma optical emission spectroscopy (Ca2+/Sr2+) or ion-specific electrode (F-) (n = 3). A composite (Filtek Z250, 3 M ESPE) was used as control in remineralization tests. Demineralized dentin discs were kept in contact with materials in simulated body fluid (SBF) at 37 °C for eight weeks. Mineral:matrix ratio (MMR) was determined by ATR-FTIR spectroscopy (n = 5). Dentin hardness (H) and elastic modulus (E) were determined by nanoindentation (n = 10). CS was tested after 24 h and 7d in deionized water (n = 12). Data were analyzed by ANOVA/Tukey test (α = 0.05). RESULTS: Ca2+ and Sr2+ release was higher for the modified materials (p < 0.05). Only GIC+ 5%HAp showed higher F- release than the control (p < 0.05). All groups showed statistically significant increases in MMR, with no differences among them after 8 weeks (p > 0.05). No differences in dentin H or E were observed among groups (p > 0.05). HAp-modified GIC showed increased initial CS, while adding CaSi had the opposite effect (p < 0.05). After 7 days, GIC+ 5%CaSi presented lower CS in relation to control and GIC+ 5%HAp (p < 0.05). SIGNIFICANCE: GIC modification with HAp or CaSi affected CS and increased ion release; however, none of the groups showed evidence of dentin remineralization in comparison to the negative control.

Synthesis of Submicrometric Chitosan Particles Loaded with Calcium Phosphate for Biomedical Applications.

Chitosan particles loaded with dibasic calcium phosphate anhydrous (DCPA) is a promising strategy for combining antimicrobial and osteoconduction properties in regenerative medicine. However, mostly micrometer-sized particles have been reported in the literature, limiting their use and reducing their effect in the biomedical field. We have recently overcome this limitation by developing submicrometer-sized particles with electrospray technique. The objective of this study was to understand how the process parameters control the size and properties of submicrometer chitosan particles loaded with DCPA. Solutions of 10 mg/mL chitosan and 2.5 mg/mL DCPA in a 90% acetic acid were electrosprayed under three distinct flow rate conditions: 0.2, 0.5, and 1.0 mL/h. The particles were crosslinked in a glutaraldehyde atmosphere and characterized in terms of their morphology, inorganic content, zeta potential, and minimum inhibitory concentration (MIC) against S. mutans. All conditions showed particles with two similar morphologies: one small-sized with a spherical shape and another larger-sized with a bi-concave shape. All generated a broad particle size distribution, with a similar mean size of ~ 235 nm. The addition of DCPA decreased the zeta potential for all the samples, but it was above 30 mV, indicating a low aggregation potential. The lower flow rate showed the worst efficacy for DCPA incorporation. Antimicrobial activity was greater in chitosan/DCPA particles with flow rate of 0.5 mL/h. It can be concluded that the flow rate of 0.5 mL/h presents the best compromise solution in terms of morphology, zeta potential, MIC, and inorganic content.

Development of brushite particles synthesized in the presence of acidic monomers for dental applications.

OBJECTIVES: To synthesize and characterize brushite particles in the presence of acidic monomers (acrylic acid/AA, citric acid/CA, and methacryloyloxyethyl phosphate/MOEP) and evaluate the effect of these particles on degree of conversion (DC), flexural strength/modulus (FS/FM) and ion release of experimental composites. METHODS: Particles were synthesized by co-precipitation with monomers added to the phosphate precursor solution and characterized for monomer content, size and morphology. Composites containing 20 vol% brushite and 40 vol% reinforcing glass were tested for DC, FS and FM (after 24 h and 60 d in water), and 60-day ion release. Data were subjected to ANOVA/Tukey tests (DC) or Kruskal-Wallis/Dunn tests (FS and FM, alpha: 5%). RESULTS: The presence of acidic monomers affected particle morphology. Monomer content on the particles was low (0.1-1.4% by mass). Composites presented similar DC. For FS/24 h, only the composite containing DCPD_AA was statistically similar to the composite containing 60 vol% of reinforcing glass (without brushite, "control"). After 60 days, all brushite-containing materials showed similar FS, statistically lower than the control composite (p<0.01). Composites containing DCPD_AA, DCPD_MOEP or DCPD_U ("unmodified") showed statistically similar FM/24 h, higher than the control composite. After prolonged immersion, all composites were similar to the control composite, except DCPD_AA. Cumulative ion release ranged from 21 ppm to 28 ppm (calcium) and 9 ppm to 17 ppm (phosphate). Statistically significant reductions in ion release between 15 and 60 days were detected only for the composite containing DCPD_MOEP. SIGNIFICANCE: Acidic monomers added to the synthesis affected brushite particle morphology. After 60-day storage in water, composite strength was similar among all brushite-containing composites. Ion release was sustained for 60 days and it was not affected by particle morphology.

Effect of calcium orthophosphate: Reinforcing glass ratio and prolonged water storage on flexural properties of remineralizing composites.

OBJECTIVES: To compare the effects of replacing reinforcing barium glass particles by DCPD (dicalcium phosphate dihydrate), as opposed to simply reducing glass filler content, on composite flexural properties and degree of conversion (DC). On a second set of experiments, composites with different "DCPD: glass" ratios were exposed to prolonged water immersion to verify if the presence of DCPD particles increased hydrolytic degradation. METHODS: Two series of composites were prepared: 1) composites with total inorganic content of 50 vol% and "DCPD: glass" ratios ranging from zero (glass only) to 1.0 (DCPD only), in 0.25 increments, and 2) composites containing only silanized glass (from zero to 50 vol%). Disk-shaped specimens were fractured under biaxial flexural loading after 24 h in water. Another set of specimens of composites with different "DCPD: glass" ratios was stored in water for 24 h, 30, 60, 90 and 120 days and tested in flexure. DC was determined using FTIR spectroscopy. Data were analyzed using Kruskal-Wallis/Dunn test (flexural properties) or ANOVA/Tukey test (DC, alpha: 0.05). RESULTS: For glass-only composites, reducing inorganic content caused a linear decrease in strength. The presence of DCPD did not affect composite strength up until a "DCPD: glass" ratio of 0.5. On the other hand, materials with 0.75 and 1.0 DCPD showed significantly lower strength than the glass-only composite with 12.5 vol% filler and the unfilled resin, respectively (p < 0.001). Except for the 0.25 DCPD composite, the presence of DCPD did not contribute to increase flexural modulus. After water storage, composites containing DCPD showed higher percent reductions in properties than the control, but only in a few cases the effect was statistically significant (strength: 0.5 DCPD, modulus: 0.25 and 1.0 DCPD). DC was only marginally affected by DCPD fraction. SIGNIFICANCE: For composites with "DCPD: glass" of 0.25 and 0.5, reductions in strength were related to the lower glass content, and not due to the presence of DCPD. Flexural modulus was primarily defined by glass content. Overall, composites containing DCPD particles presented higher reductions in properties after water storage, but it remained within limits reported for commercial materials.

Development of novel dental restorative composites with dibasic calcium phosphate loaded chitosan fillers.

The incorporation of antimicrobial agents in restorative dental composites has the potential to slow the development of carious lesions. OBJECTIVE: The objectives of the present study were to develop experimental composite resins with chitosan or chitosan loaded with dibasic calcium phosphate anhydrous (DCPA) particles and to demonstrate their antimicrobial potential without loss of mechanical properties or biocompatibility. METHODS: Chitosan and chitosan/DCPA particles were synthetized by the electrospray method. Experimental composites were formulated by adding 0, 0.5, or 1.0 wt% particles into a resin matrix along with 60 wt% barium glass. The degree of conversion and mechanical properties were measured after 1 and 90 days of aging in water after photoactivation. Cytotoxicity and genotoxicity were evaluated using fibroblasts from dental pulp in conditioned medium. The antimicrobial activity against Streptococcus mutans was assessed by crystal violet biofilm assay. RESULTS: The experimental restorative composites were not found to be cytotoxic or genotoxic, with cell viability of 93.1 ± 8.0% (p = 0.328) and 3.0 ± 0.8% micronucleus per group (p = 0.1078), respectively. The antimicrobial results showed that all composites with approximately 20% less biofilm (p < 0.001) relative to the control. No chitosan release was detected from the composites, suggesting direct contact of the bacteria with exposed chitosan particles on the surface was responsible for the observed antimicrobial effect. The addition of the chitosan and chitosan/DCPA submicrometer (<250 nm average diameter) particles to restorative composites did not change the degree of conversion, flexural strength, elastic modulus and fracture toughness compared to the control group after 90 days aging in water. SIGNIFICANCE: It can be concluded that the addition of chitosan or chitosan/DCPA particles in the restorative composites induced antimicrobial activity without compromising the mechanical properties or biocompatibility of the composites.

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.

Polymer-based material containing calcium phosphate particles functionalized with a dimethacrylate monomer for use in restorative dentistry.

Dicalcium phosphate dihydrate particles functionalized with triethyleneglycol dimethacrylate were synthesized and added to a photocurable mixture of bisphenol-A glycidyl dimethacrylate and triethyleneglycol dimethacrylate with the purpose of developing a resin composite capable of releasing calcium and phosphate ions to foster dental remineralization. Particle functionalization would minimize the deleterious effect of adding low cohesive strength nano-structured particles with no chemical interaction with the organic matrix on the material's mechanical properties. The results showed that calcium release over 28 days was not impaired by particle functionalization. A statistically significant 32% increase in strength was recorded with the use of functionalized dicalcium phosphate dihydrate in comparison to the material containing non-functionalized particles. However, the strength of the unfilled resin was not matched by the composite with functionalized particles. Elastic modulus increased with particle incorporation, regardless of functionalization. Degree of conversion and optical properties (total transmittance and color change/ΔE) of the resin-based materials were not affected by the addition of dicalcium phosphate dihydrate particles (functionalized or not).

Bioactive composites containing TEGDMA-functionalized calcium phosphate particles: Degree of conversion, fracture strength and ion release evaluation.

OBJECTIVE: To evaluate the strength and ion release of experimental composites containing TEGDMA-functionalized calcium phosphate particles. METHODS: Seven composites containing equal parts (in mols) of BisGMA and TEGDMA and 60vol% of fillers were manipulated. Filler phase was constituted by silanized barium glass and 0% (control), 10% or 20% (volume) of dicalcium phosphate dihydrate (DPCD) particles, either non-functionalized or functionalized with two different TEDGMA contents. DCPD particles were synthesized and characterized by X-ray diffraction (XRD), elemental analysis, surface area and dynamic light scattering. Composites were tested for degree of conversion (DC) by near-FTIR. Biaxial flexural strength (BFS) was determined after 24h and 28days in water. Calcium and phosphate release after 7days was assessed using inductively coupled plasma optical emission spectrometry (ICP-OES). Data were analyzed by ANOVA/Tukey test (alpha:5%). RESULTS: XRD confirmed the crystalline structure corresponding to DCPD. Elemental analysis revealed particles with zero, 14% or 22% TEGDMA, with similar D50 (around 19µm) and surface areas from 3.5 to 11.4m2/g. The presence of DCPD did not reduce DC. After 24h, functionalization (both 14% and 22% TEGDMA) improved composite strength in comparison to non-functionalized DCPD, both at 10% and 20% levels. After 28days, BFS of materials containing 10% functionalized DCPD were statistically similar to the control containing only barium glass. Among composites containing 10% DCPD, particle functionalization with 14% TEGDMA did not jeopardize ion release. SIGNIFICANCE: At 10vol%, the use of TEGDMA-functionalized CaP particles improved composite strength in relation to non-functionalized particles, while maintaining similar ion release levels.

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.

Effect of diphenyliodonium hexafluorophosphate on the physical and chemical properties of ethanolic solvated resins containing camphorquinone and 1-phenyl-1,2-propanedione sensitizers as initiators.

OBJECTIVES: To evaluate the effects of the diphenyliodonium hexafluorophosphate (DPI) on the physical and mechanical properties of solvated dental adhesive resins containing camphorquinone (CQ) and/or 1-phenyl-1,2-propanedione (PPD) as initiators. METHODS: Model solvated resins containing bisphenol glycidyl methacrylate (BisGMA); triethyleneglycol dimethacrylate (TEGDMA); 1,3-glycerol dimethacrylate (GDMA); 2-hydroxyethyl methacrylate (HEMA); dimethylaminoethyl amine benzoate (EDAB) and ethanol were prepared. The resins were divided in 24 test groups according to the incorporated initiator systems (CQ-0.5 or 1mol%; PPD-0.5 or 1mol%; CQ+PPD-0.5 or 1mol%) as well the presence of DPI (0, 0.5 or 1mol%). Degree of conversion (using Fourier-transformed near infra-red spectroscopy), flexural strength and modulus by three point bending, cohesive strength and water sorption and solubility were measured. Data were statistically analyzed by one and two way ANOVA and Tukey's test (α=0.05). RESULTS: DPI increased the degree of conversion of all materials tested. Camphorquinone promoted higher degree of conversion than resins containing only PPD or CQ+PPD. Generally, the resins containing PPD+CQ with DPI presented higher flexural strength and modulus, cohesive strength, as well lower water sorption and solubility. SIGNIFICANCE: The use of PPD combined with CQ can increase the physical properties of the solvated resins. DPI improved the monomer conversion of all experimental materials and can positively modulate most of the physical properties of the solvated resins.

Mechanical properties and ion release from bioactive restorative composites containing glass fillers and calcium phosphate nano-structured particles.

OBJECTIVE: To evaluate the effect of the replacement of barium glass by dicalcium phosphate dihydrate (DCPD) particles on the mechanical properties and degree of conversion (DC) of composites. Additionally, calcium and hydrogen phosphate (HPO4(2-)) release were followed for 28 days. METHODS: Nine composites containing equal parts (in mols) of BisGMA and TEGDMA and 40, 50 or 60 vol% of total filler were manipulated. Filler phase was constituted by silanated barium glass and 0%, 10% or 20% of DCPD particles. DC was determined by near-FTIR. Biaxial flexural strength (BFS) and modulus (E) were tested using the "piston on three balls" method, while fracture toughness (KIc) used the "single edge notched beam" method. Specimens were tested after 24h and 28 days in water. Ion release was determined using inductively coupled plasma optical emission spectrometry (ICP-OES). Data were analyzed by ANOVA/Tukey (DC and ion release) or Kruskal-Wallis/Mann-Whitney (mechanical properties; alpha: 5%). RESULTS: DC was not affected by DCPD. The presence of DCPD reduced BFS for both storage times, while differences in E became evident after 28 days. After 24h, KIc increased with the addition of DCPD; after 28 days, however, KIc decreased only for DCPD-containing composites. Calcium release was similar for both DCPD contents and remained fairly constant during the 28-day period. Overall, HPO4(2-) release was higher at 7 days and did not decrease after 14 days. SIGNIFICANCE: The composite with the highest filler level and 10% DCPD represented the best compromise between mechanical properties after aging in water and ion release.

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.

Fracture toughness and cyclic fatigue resistance of resin composites with different filler size distributions.

OBJECTIVES: To verify the influence of filler size distributions on fracture toughness (KIc), initial fracture strength (IFS) and cyclic fatigue resistance (CFR) of experimental resin composites. METHODS: Four composites were prepared with same inorganic content (78 wt%), in which 67 wt% was constituted by glass particles with d50 of 0.5; 0.9; 1.2; 1.9 µm KIc of the composites was determined by the single-edge notched beam (SENB) method. To evaluate the IFS and the CFR a biaxial bending test configuration was used. The CFR was determined under cyclic loading for 10(5) cycles using the 'staircase' approach. The fracture surfaces of IFS and CFR specimens were analyzed under scanning electron microscope (SEM). RESULTS: There was a positive linear correlation between d50 vs. KIc and statistical difference was found only between C0.5 (1.24±0.10 MPa m0.5) and C1.9 (1.41±0.17 MPa m0.5). There were no statistical differences among IFS means, which ranged from 155.4±18.8 MPa (C0.9) to 170.7±23.1 MPa (C1.2). C0.5 (93.0±18.6a MPa) showed the highest and C0.9 the lowest CFR (82.5±8.0c MPa). There was no correlation between CFR with d50 values or with KIc means. SEM images showed the morphology with brittle fracture patterns for the surfaces of IFS specimens and a more smooth fracture surface for CFR specimens. SIGNIFICANCE: Resin composites showed different failure mechanisms for quasi-static and fatigue loading. For KIc and IFS, composites with larger filler size distributions showed better results due to crack deflection; while under cyclic loading, viscous behavior was predominant and composites with smaller particles showed higher fatigue resistance.

Effect of temperature on composite polymerization stress and degree of conversion.

OBJECTIVE: To test the following hypotheses: (1) degree of conversion (DC) and polymerization stress (PS) increase with composite temperature (2) reduced light-exposure applied to pre-heated composites produces similar conversion as room temperature with decreased PS. METHODS: Composite specimens (diameter: 5mm, height: 2mm) were tested isothermally at 22°C (control), 40°C, and 60°C using light-exposures of 5 or 20s (control). DC was accessed 5min after light initiation by FTIR at the specimen bottom surface. Maximum and final PS were determined, also isothermally, for 5min on a universal testing machine. Non-isothermal stress was also measured with composite maintained at 22°C or 60°C, and irradiated for 20s at 30°C. Data were analyzed using two-way ANOVA/Tukey and Student's t-test (α=5%). RESULTS: Both DC and isothermal maximum stress increased with temperature (p<0.001) and exposure duration (p<0.001). Isothermal maximum/final stress (MPa) were 3.4±2.0b/3.4±2.0A (22°C), 3.7±1.5b/3.6±1.4A (40°C) and 5.1±2.0a/4.0±1.6A (60°C). Conversion values (%) were 39.2±7.1c (22°C), 50.0±5.4b (40°C) and 58.5±5.7a (60°C). The reduction of light exposure duration (from 20s to 5s) with pre-heated composite yielded the same or significantly higher conversion (%) than control (22°C, 20s/control: 45.4±1.8b, 40°C, 5s s: 45.1±0.5b, 60°C, 5s s: 53.7±2.7a, p<0.01). Non-Isothermal conditions showed significantly higher stress for 60°C than 22°C (in MPa, maximum: 4.7±0.5 and 3.7±0.4, final: 4.6±0.6 and 3.6±0.4, respectively). CLINICAL SIGNIFICANCE: Increasing composite temperature allows for reduced exposure duration and lower polymerization stress (both maximum and final) while maintaining or increasing degree of conversion.

Improved polymerization efficiency of methacrylate-based cements containing an iodonium salt.

OBJECTIVE: This study evaluated the effect of adding diphenyliodonium hexafluorphosphate (DPI) as a third component of the free-radical photoinitiator system of model resin cements on their photopolymerization kinetics/stress and fundamental properties. METHODS: A model resin cement containing a 1:1 mass ratio of 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane and triethyleneglycol dimethacrylate was obtained. Camphorquinone (1 mol%) and 2-(dimethylamino)ethyl methacrylate (2 mol%) were added to monomer blend. Six mixtures were obtained by incorporation of 0 (control), 0.25, 0.5, 1, 2, or 4 mol% of DPI. The cements were loaded with a 60% mass fraction of silanated glass fillers. Polymerization kinetics (using Fourier-transform near-infrared spectroscopy), flexural strength and modulus, water uptake/solubility, and polymerization stress were assessed. Data were statistically analyzed using one-way ANOVA and Student-Newman-Keuls' test (P ≤ 0.05). RESULTS: In the DPI-modified materials, the onset of autodeceleration occurred earlier and at higher conversion compared with the control cement. The addition of DPI also led to a more active early-stage polymerization. The flexural modulus was generally higher for DPI-containing materials. Water uptake and solubility were generally lower for materials with DPI fractions ≥ 0.5%. Significant increase of polymerization stress was observed only in the group with 1 mol% of DPI compared with the control cement. SIGNIFICANCE: The effect of DPI on the photopolymerization reactivity of the cement is concentration-dependent; the use of DPI could result in better polymerization efficiency of resin-based cements.