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

Composite Containing Calcium Phosphate Particles Functionalized with 10-MDP

The phosphate ester monomer 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) is capable of bonding to hydroxyapatite and, for this reason, is a key component of several self-etch adhesives. In this study, dicalcium phosphate dihydrate particles (DCPD; CaHPO4.2H2O) were functionalized with 10-MDP and used to formulate an experimental composite with 50 vol% inorganic content (3:1 DCPD:silanated barium glass ratio) dispersed in a BisGMA/TEGDMA matrix. The tested hypothesis was that DCPD functionalization would improve the composite's mechanical performance without compromising Ca2+ release. Composites containing nonfunctionalized DCPD or only reinforcing glass (in both cases, with or without 10-MDP mixed in the resin phase) were used as controls. Materials were tested for degree of conversion (DC; by Fourier transform infrared spectroscopy), water sorption (WS) and solubility (SL; according to ISO 4049), biaxial flexural strength (BFS)/modulus (FM) after 24 h and 5 mo in water, and 28-d Ca2+ release in water (by plasma-coupled optical emission spectroscopy). Data were analyzed using analysis of variance/Tukey test (alpha: 5%). DCPD functionalization did not interfere with DC. The composite containing functionalized DCPD showed significantly lower WS and SL in comparison with the material formulated with nonfunctionalized particles. The presence of 10-MDP (as a functionalizing agent or dispersed in the resin phase) reduced the composite's initial BFS and FM. After 5 mo in water, the composite with functionalized DCPD and both glass-only composites were able to maintain their mechanical properties at levels statistically similar to what was observed after 24 h. Ca2+ release was significantly reduced in both formulations containing 10-MDP. In conclusion, DCPD functionalization with 10-MDP increased the composite's resistance to hydrolytic degradation, improving its mechanical stability after prolonged water storage. However, the impaired water transit at the particle-matrix interface led to a reduction in Ca2+ release.

POSS hybrid bioactive glass dental composite resin materials: Synthesis and analysis

INTRODUCTION

This study create a dental composite by hybirding polyhedral oligo-sesquioxide nano monomers and bioactive glass BG 45S5.

METHODS

Make an experimental composite resin material with a 60 % filler content overall by substituting 20 % of the filler with BG 45S5. The experimental resins are grouped and named P0, P2, P4, P6 and P8 based on the reactive nanomonomer methacrylic acid-based multifaceted oligomeric sesquisiloxane (POSS) added by 2 %-8 % in the resin matrix portion of each group. Utilize a universal testing machine to analyze and compare the mechanical properties of these, then perform Fourier infrared spectrum analysis, double bond conversion analysis, and scanning electron microscope analysis. Based on this, after soaking the experimental materials artificial saliva solution or lactic acid solution for a while, the pH changes of the solution, the release of Ca2+ and PO43- ions, and the precipitation of apatite on the resin material's surface were tested and analyzed. Cell viability tests were used to assess sample cell viability and quantify the cytotoxicity of biological cells. The independent sample t-test was used to examine the group comparisons, and a difference was considered statistically significant at P<0.05.

RESULTS

Outstanding mechanical and the double bond conversion are demonstrated by the nanocomposites when the POSS concentration hits 4 wt%. Agglomeration will cause the performance to deteriorate if the concentration beyond this threshold. In the P4 group, the double bond conversion, CS, and FS rose by a large margin, respectively, in comparison to the blank control group P0. Thankfully, the data demonstrate that adding POSS increases adhesive ability when compared to the blank group P0, however, there is no discernible difference between the other experimental groups. The acid neutralization capacity of the P4 group is essentially the same as that of the control group (P0). Ca2+ and PO43- ions are released in significant amounts following treatment with lactic acid solution, although this tendency is clearly less pronounced in artificial saliva. SEM and EDX data indicate that when the experimental resin is soaked in lactic acid solution and artificial saliva, apatite precipitation will happen on its surface. The results of the cell viability test indicated that there was no statistically significant difference between the experimental groups, and the viability of the cells increased after 24hours and 48 hours.

CONCLUSIONS

POSS was included into the composite resin along with 20% bioactive glass as a filler. When the proportion of POSS is less than 4%, the indices of composite resin materials rise in a dose-dependent way. When this value is surpassed, performance begins to deteriorate. The inclusion of POSS has no influence on the biological activity of the composites, which means that the hybrid composite resin is capable of acid neutralization, ion release, and apatite precipitation.

CLINICAL SIGNIFICANCE

The experimental composite resin can be used as an intelligent material in clinical treatment. It has the clinical application potential of preventing demineralization of tooth hard tissue, promoting remineralization, and improving edge sealing through apatite precipitation.

Evaluation of flexural strength, degree of conversion, and demineralization-prevention properties in adjacent tooth structures of an experimental fissure sealant containing nano-calcium-phosphate compounds

BACKGROUND

The present study aimed to evaluate the flexural strength, degree of conversion, and demineralization-prevention ability of an experimental fissure sealant containing nano-calcium-phosphate compounds.

METHODS

An experimental sealant was formulated using silica and nano hydroxyapatite filler particles. The control group consisted of the DENU Seal (n = 10, each group). The flexural bond strength was evaluated by UTM. DC was evaluated by FTIR. To evaluate the demineralization-prevention ability, Cl V cavities in 10 third molar teeth restored with two sealant products, followed by an acid challenge then the Vickers microhardness test was carried out.

RESULTS

The mean flexural strength in the commercial group was higher than the experimental group. However, the mean flexural modulus was not significantly different between the two groups. In the experimental group, DC was significantly higher than the commercial group. Adjacent to the interface, the decrease in microhardness in the experimental group was significantly less than the commercial group. However, on the tooth surface, there were no significant differences between the two groups. In the experimental group, the decrease in microhardness at the interface was less than at the tooth surface, however the situation was opposite in the commercial group.

CONCLUSIONS

Incorporating hydroxyapatite into the sealant structure might prevent demineralization, without adverse effects on flexural modulus and degree of conversion.

Compositional boundaries for functional dental composites containing calcium orthophosphate particles

OBJECTIVES

To investigate the interrelationships among handling, degree of conversion (DC), mechanical behavior and Ca2+ release of composites containing dicalcium phosphate dihydrate (DCPD, CaHPO4.2H2O), as a function of total inorganic content and DCPD: glass ratio.

METHODS

Twenty-one formulations (1 BisGMA: 1 TEGDMA, in mols) with inorganic fractions ranging from zero to 50 vol% and different DCPD: glass ratios were evaluated for viscosity (parallel plate rheometer, n = 3), DC (near-FTIR spectroscopy, n = 3), fracture toughness/K1C (single-edge notched beam, n = 7-11) and 14-day Ca2+ release (inductively coupled plasma optical emission spectroscopy, n = 3). Data were analyzed by ANOVA/Tukey test (except viscosity, where Kruskal-Wallis/Dunn tests were used, α: 0.05).

RESULTS

Viscosity and DC increased with DCPD: glass ratio among composites with the same inorganic content (p < 0.001). At inorganic fractions of 40 vol% and 50 vol%, keeping DCPD content at a maximum of 30 vol% did not compromise K1C. Ca2+ release showed an exponential relationship with DCPD mass fraction in the formulation (R2 = 0.986). After 14 days, a maximum of 3.8% of the Ca2+ mass in the specimen was released.

CONCLUSION

Formulations containing 30 vol% DCPD and 10-20 vol% glass represent the best compromise between viscosity, K1C and Ca2+ release. Materials with 40 vol% DCPD should not be disregarded, bearing in mind that Ca2+ release will be maximized at the expense of K1C.

TEGDMA-Functionalized Dicalcium Phosphate Dihydrate Resin-Based Composites Prevent Secondary Caries in an In Vitro Biofilm Model

This study evaluated the efficacy of experimental TEGDMA-functionalized dicalcium phosphate dihydrate (T-DCPD) filler-based resin-based composites (RBC) in preventing caries lesions around the restoration margins (secondary caries, SC). Standardized Class-II cavities were made in sound molars with the cervical margin in dentin. Cavities were filled with a commercial resin-modified glass-ionomer cement (RMGIC) or experimental RBCs containing a bisGMA-TEGDMA resin blend and one of the following inorganic fractions: 60 wt.% Ba glass (RBC-0); 40 wt.% Ba glass and 20 wt.% T-DCPD (RBC-20); or 20 wt.% Ba glass and 40 wt.% T-DCPD (RBC-40). An open-system bioreactor produced Streptococcus mutans biofilm-driven SC. Specimens were scanned using micro-CT to evaluate demineralization depths. Scanning electron microscopy and energy-dispersive X-ray spectroscopy characterized the specimen surfaces, and antimicrobial activity, buffering effect, and ion uptake by the biofilms were also evaluated. ANOVA and Tukey’s tests were applied at p < 0.05. RBC-0 and RBC-20 showed SC development in dentin, while RBC-40 and RMGIC significantly reduced the lesion depth at the restoration margin (p < 0.0001). Initial enamel demineralization could be observed only around the RBC-0 and RBC-20 restorations. Direct antibiofilm activity can explain SC reduction by RMGIC, whereas a buffering effect on the acidogenicity of biofilm can explain the behavior of RBC-40. Experimental RBC with CaP-releasing functionalized T-DCPD filler could prevent SC with the same efficacy as F-releasing materials.

Ion release and hydroxyapatite precipitation of resin composites functionalized with two types of bioactive glass

OBJECTIVES

To prepare experimental composites with bioactive glass (BG) and investigate their release of calcium (Ca), phosphate (PO₄), and fluoride (F), as well as pH changes and apatite precipitation after immersion.

METHODS

Experimental composites were prepared with 0, 10, or 20 wt% of either BG 45S5 or a customized low-Na F-containing BG. Three commercial ion-releasing materials were used for reference. Material specimens were immersed in lactic acid (pH = 4.0) and artificial saliva (pH = 6.4). Ion concentrations (atomic absorption spectrometry for Ca, UV-vis spectrometry for PO₄, and ion-selective electrode for F) and pH were measured after 4, 8, 12, 16, 20, 24, 28, and 32 days. After immersion, composite specimens were analyzed using scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy.

RESULTS

Material-dependent concentrations of Ca, PO₄, and F were measured in the lactic acid solution, while a decrease of Ca and PO₄ concentrations was observed in artificial saliva. The uptake of ions from artificial saliva indicates their precipitation on specimen surfaces, which was supported by the results of SEM and FTIR investigations. In experimental composites functionalized with both bioactive glass types and a commercial "alkasite" material, apatite was precipitated not only in artificial saliva but also in the lactic acid solution.

CONCLUSIONS

Experimental BG-containing composites and selected commercial restorative materials demonstrated the potential for releasing multiple ion types and increasing pH.

CLINICAL SIGNIFICANCE

The observed effects can be beneficial for preventing demineralization and promoting remineralization of dental hard tissues, while apatite precipitation can additionally help in sealing marginal discontinuities.

Development and characterization of experimental ZnO cement containing niobophosphate bioactive glass as filling temporary material

Aims

The aim of this study was to develop and characterize a temporary restorative material based on a zinc oxide matrix containing niobophosphate bioactive glass (NbG) for the caries-affected dentin treatment.

Material and methods

NbG was added to a ZnO₂ matrix in different concentrations (wt%). EDS-SEM, ATR-FTIR and XRD analyses were performed to characterize the cement. Calcium release was evaluated in TRIS solution after 1, 7 and 14 days by colorimetric method (A₆₅₀). Compressive strengths and setting times were performed to analyze mechanical properties.

Results

EDS spectra confirmed the presence of Ca, P and Nb in the groups containing NbG. EDS mapping exhibit the ZnO₂ homogeneous distribution, and NbG immersed in this matrix. Peaks suggesting interaction between matrix and NbG were not detected in Ftir spectra. Calcium releasing showed to be time-dependent for experimental groups containing 10, 20, 30 and 40%. The NbG incorporation progressively increased the compressive strength values in the experimental groups. NbG incorporation seemed to influence the ZnO₂ matrix early setting reaction. No statistical difference was observed in the final setting time.

Conclusion

The addition of NbG particles into zinc oxide matrix could work as a mechanical reinforcement. It is suggested that the calcium released by the cement containing at least 10% NbG could induce apatite formation.

Fabrication and characterization of remineralizing dental composites containing calcium type pre-reacted glass-ionomer (PRG-Ca) fillers

OBJECTIVE

To fabricate and characterize dental composites with calcium type pre-reacted glass-ionomer (PRG-Ca) fillers.

METHODS

PRG-Ca fillers were prepared by the reaction of calcium fluoroaluminosilicate glass with polyacrylic acid. Seven dental composites were produced from the same organic matrix (70/30wt% Bis-GMA/TEGDMA), with partial replacement of barium borosilicate (BaBSi) fillers (60wt%) by PRG-Ca fillers (wt%): E0 (0) - control, E1 (10), E2 (20), E3 (30), E4 (40), E5 (50) and E6 (60). Enamel remineralization was evaluated in caries-like enamel lesions induced by S. mutans biofilm using micro-CT. The following properties were characterized: degree of conversion (DC%), roughness (Ra), Knoop hardness (KHN), flexural strength (FS), flexural modulus (FM), water sorption (W_sp), water solubility (W_sl), and translucency (TP). Data were analyzed to one-way ANOVA and Tukey's HSD test (α=0.05).

RESULTS

All composites with PRG-Ca induced enamel remineralization. E0 and E1 presented similar and highest DC% than E2=E3=E4=E5=E6. Ra and KHN were not influenced by PRG-Ca fillers (p<0.05). The higher the content of PRG-Ca, the lower FS, FM and TP (p<0.05). W_sp increased linearly with the content of PRG-Ca fillers (p<0.05). E6 presented the highest W_sl (p<0.05), while the W_sl of the other composites were not different from each other (p>0.05).

SIGNIFICANCE

Incorporation of 10-40wt.% of PRG-Ca fillers endowed remineralizing potential to dental composites without jeopardizing the overall behavior of their physicochemical properties. Dental composites with PRG-Ca fillers seems to be a good alternative for reinforcing the enamel against caries development.

Development of a Bioactive Flowable Resin Composite Containing a Zinc-Doped Phosphate-Based Glass

Flowable resins used for dental restoration are subject to biofilm formation. Zinc has antibacterial properties. Thus, we prepared a zinc-doped phosphate-based glass (Zn-PBG) to dope a flowable resin and evaluated the antibacterial activity of the composite against Streptococcus mutans (S. mutans) to extrapolate the preventative effect toward secondary caries. The composites were prepared having 0 (control), 1.9, 3.8, and 5.4 wt.% Zn-PBG. The flexural strength, elastic modulus, microhardness, depth of cure, ion release, inhibition zone size, and number of colony-forming units were evaluated and analyzed using ANOVA. The flexural strength of the control was significantly higher than those of Zn-PBG samples (p < 0.05). However, all samples meet the International Standard, ISO 4049. The microhardness was not significantly different for the control group and 1.9 and 3.8 wt.% groups, but the 5.4 wt.% Zn-PBG group had a significantly lower microhardness (p < 0.05). Further, the composite resins increasingly released P, Ca, Na, and Zn ions with an increase in Zn-PBG content (p < 0.05). The colony-forming unit count revealed a significant reduction in S. mutans viability (p < 0.05) with increase in Zn-PBG content. Therefore, the addition of Zn-PBG to flowable composite resins enhances antibacterial activity and could aid the prevention of secondary caries.

Mechanical properties and surface roughness of polymer-based materials containing DCPD particles

The purpose of this study was to synthesize dicalcium phosphate dihydrate (DCPD) particles functionalized with triethylene glycol dimethacrylate (TEGDMA) through different routes by varying the receptor solution: ammonium phosphate (AP groups) or calcium nitrate (CN groups) and the moment in which TEGDMA was incorporated: ab initio (ab) or at the end of dripping the solution (ap). Two syntheses were performed without adding TEGDMA (nf). The particles were characterized by X-ray diffractometry, true density (using a helium pycnometer), surface area, and scanning electron microscopy. A 20 vol% of DCPD particles from the D, E, and F groups was added to the resin matrix to determine the degree of conversion (DC), biaxial flexural strength (BFS), the flexural modulus (FM), and surface roughness after an abrasive challenge (RA). A group with silanized barium glass particles was tested as a control. The data were submitted to ANOVA/Tukey's test (DC, BFS, and RA), and the Kruskal-Wallis test (FM) (alpha = 0.05). BFS values varied between 83 and 142 MPa, and the CN_ab group presented a similar value (123 MPa) to the control group. FM values varied between 3.6 and 8.7 GPa (CN_ab and CN_nf groups, respectively), with a significant difference found only between these groups. RA did not result in significant differences. The use of calcium nitrate solution as a receptor, together with ab initio functionalization formed particles with larger surface areas. Higher BFS values were observed for the material containing DCPD particles with a higher surface area. In general, the DC, FM, and RA values were not affected by the variables studied.

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.

Fabrication and characterization of remineralizing dental composites containing hydroxyapatite nanoparticles

The aim of this study was to fabricate and characterize dental composites containing hydroxyapatite nanoparticles (HApNPs). Four dental composites were produced from the same organic matrix (70 wt% Bis-GMA and 30 wt% TEGDMA), with partial replacement of BaBSi particles (65 wt%) by HApNPs in the following concentrations (wt%): E0 (0) - control, E10 (10), E20 (20) and E30 (30). Ca²⁺ and PO₄^3- release was evaluated in solutions with different pHs (4, 5.5, and 7) using atomic emission spectroscopy with microwave-induced nitrogen plasma while the enamel remineralization potential was evaluated in caries-like enamel lesions induced by S. mutans biofilm using micro-CT. The following properties were characterized: degree of conversion (DC%), microhardness (KHN), flexural strength (FS), elastic modulus (EM) and translucency (TP). The higher the HApNPs content, the higher the Ca²⁺ and PO₄^3- release. The ions release was influenced by pH (4 > 5.5 > 7) (p < 0.05). All composites loaded with HApNPs were able to remineralize the enamel (E30 = E20 > E10) (p < 0.05). Contrarily, E0 was not able of recovering the enamel mineral loss. E0 and E10 presented highest DC%, while E20 and E30 showed similar and lowest DC%. KHN and FS were decreased with the addition of HApNPs, while EM was not influenced by the incorporation of HApNPs. E10 presented statistically similar TP to E0, while this property decreased for E20 and E30 (p < 0.05). Incorporation of HApNPs into dental composites promoted enamel remineralization, mainly at potentially cariogenic pH (= 4), while maintained their overall performance in terms of physicomechanical properties.

Bioactive Materials Subjected to Erosion/Abrasion and Their Influence on Dental Tissues

OBJECTIVE

The objective of this study was to evaluate the effect of erosion or erosion-abrasion on bioactive materials and adjacent enamel/dentin areas.

METHODS AND MATERIALS

Enamel and dentin blocks (4×4×2 mm) were embedded side by side in acrylic resin, and a standardized cavity (1.2×4×1.5 mm) was prepared between them. Preparations were restored with the following materials: composite resin (Filtek Z350, control); experimental composite containing di-calcium phosphate dihydrate particles (DCPD); Giomer (Beautifil II), high viscosity glass ionomer cement (GIC, Fuji IX); and a resin-modified GIC (Fuji II LC). The specimens were submitted to two cycling models (n=10): erosion or erosion-abrasion. The challenges consisted of five-minute immersion in 0.3% citric acid solution, followed by 60-minute exposure to artificial saliva. Toothbrushing was carried out twice daily, 30 minutes after the first and last exposures to acid. Dental and material surface loss (SL, in μm) were determined by optical profilometry. Data were analyzed with Kruskal-Wallis and Dunn tests (α=0.05).

RESULTS

Under erosion, for enamel, only the GIC groups presented lower SL values than Z350 (p<0.001 for Fuji IX and p=0.018 for Fuji II LC). For dentin, none of the materials showed significantly lower SL values than Z350 (p>0.05). For material, the GICs had significantly higher SL values than those of Z350 (p<0.001 for Fuji IX and p=0.002 for Fuji II LC). Under erosion-abrasion, the enamel SL value was significantly lower around Fuji II LC compared with the other materials (p<0.05). No significant differences were observed among groups for dentin SL (p=0.063). The GICs and Giomer showed higher SL values than Z350 (p<0.001 for the GICs and p=0.041 for Giomer).

CONCLUSION

Both GIC-based materials were susceptible to erosive wear; however, they promoted the lowest erosive loss of adjacent enamel. Against erosion-abrasion, only Fuji II LC was able to reduce enamel loss. For dentin, none of the materials exhibited a significant protective effect.

Preparation and in vitro evaluation of strontium-doped calcium silicate/gypsum bioactive bone cement

The combination of two or more bioactive components with different biodegradability could cooperatively improve the physicochemical and biological performances of the biomaterials. Here we explore the use of α-calcium sulfate hemihydrate (α-CSH) and calcium silicate with and without strontium doping (Sr-CSi, CSi) to fabricate new bioactive cements with appropriate biodegradability as bone implants. The cements were fabricated by adding different amounts (0-35 wt%) of Sr-CSi (or CSi) into the α-CSH-based pastes at a liquid-to-solid ratio of 0.4. The addition of Sr-CSi into α-CSH cements not only led to a pH rise in the immersion medium, but also changed the surface reactivity of cements, making them more bioactive and therefore promoting apatite mineralization in simulated body fluid (SBF). The impact of additives on long-term in vitro degradation was evaluated by soaking the cements in Tris buffer, SBF, and α-minimal essential medium (α-MEM) for a period of five weeks. An addition of 20% Sr-CSi to α-CSH cement retarded the weight loss of the samples to 36% (in Tris buffer), 43% (in SBF) and 54% (in α-MEM) as compared with the pure α-CSH cement. However, the addition of CSi resulted in a slightly faster degradation in comparison with Sr-CSi in these media. Finally, the in vitro cell-ion dissolution products interaction study using human fetal osteoblast cells demonstrated that the addition of Sr-CSi improved cell viability and proliferation. These results indicate that tailorable bioactivity and biodegradation behavior can be achieved in gypsum cement by adding Sr-CSi, and such biocements will be of benefit for enhancing bone defect repair.