Synthesis of chemically modified BisGMA analog with low viscosity and potential physical and biological properties for dental resin composite

Synthesis and Characterization of a Chemico-structurally Modified Bis-GMA Analog for Dental Applications

AIM

This study aimed to synthesize and characterize a novel Bis-GMA analog, termed P-Bis-GMA, through structural modification by replacing hydroxyl (-OH) groups with phosphonooxy [-O-P(=O)(OH)2] groups and to evaluate and compare its viscosity with Bis-GMA.

MATERIALS AND METHODS

Bis-GMA, triethylamine, dichloromethane, and phosphoryl chloride were utilized for the synthesis of P-Bis-GMA through phosphorylation. Fourier discerned the chemical structure of the synthesized P-Bis-GMA transform infrared spectroscopy (FTIR), and its viscosity was assessed by rheometry in oscillatory shear mode over a frequency sweep range of 0.1-100 (ω, rad/s) at 25°C with a 25 mm parallel plate design and a 0.5 mm gap. The data was recorded and statistically analyzed.

RESULTS

The FTIR analysis confirmed the successful synthesis of P-Bis-GMA, evidenced by the disappearance of hydroxyl (-OH) peaks and the emergence of phosphonooxy [-O-P(=O)(OH)2] peaks in the P-Bis-GMA. Rheological testing demonstrated a notable reduction in viscosity for P-Bis-GMA (436.62 Pa.s) when compared to conventional Bis-GMA (1089.02 Pa.s), indicating improved handling characteristics.

CONCLUSION

P-Bis-GMA was successfully synthesized by phosphorylation reaction where the -OH groups responsible for the high viscosity in the Bis-GMA were replaced with the [-O-P(=O)(OH)2] groups with significantly reduced viscosity.

CLINICAL SIGNIFICANCE

The development of P-Bis-GMA holds promise for simplifying dental procedures by reducing chairside time with uncooperative children. The P-Bis-GMA-based composites possess self-adhering properties thereby eschewing the etching and bonding procedures with reduced moisture contamination of the restoration during bonding. This ultimately leads to better clinical outcomes and improved patient experiences by reducing technical vulnerabilities. How to cite this article: Ajay R, Selvabalaji A, Muthamilselvi M, et al. Synthesis and Characterization of a Chemico-structurally Modified Bis-GMA Analog for Dental Applications. J Contemp Dent Pract 2024;25(6):588-592.

Synthesis of polymerizable betulin maleic diester derivative for dental restorative resins with antibacterial activity

OBJECTIVE

Bisphenol A glycidyl methacrylate (Bis-GMA) is of great importance for dental materials as the preferred monomer. However, the presence of bisphenol-A (BPA) core in Bis-GMA structure causes potential concerns since it is associated with endocrine diseases, developmental abnormalities, and cancer lesions. Therefore, it is desirable to develop an alternative replacement for Bis-GMA and explore the intrinsic relationship between monomer structure and resin properties.

METHODS

Here, the betulin maleic diester derivative (MABet) was synthesized by a facile esterification reaction using plant-derived betulin and maleic anhydride as raw materials. Its chemical structure was confirmed by 1H and 13C NMR spectra, FT-IR spectra, and HR-MS, respectively. The as-synthesized MABet was then used as polymerizable comonomer to partially or completely substitute Bis-GMA in a 50:50 Bis-GMA: TEGDMA resin (5B5T) to formulate dental restorative resins. These were then determined for the viscosity behavior, light transmittance, real-time degree of conversion, residual monomers, mechanical performance, cytotoxicity, and antibacterial activity against Streptococcus mutans (S. mutans) in detail.

RESULTS

Among all experimental resins, increasing the MABet concentration to 50 wt% made the resultant 5MABet5T resin have a maximum in viscosity and appear dark yellowish after polymerization. In contrast, the 1MABet4B5T resin with 10 wt% MABet possessed comparable shear viscosity and polymerization conversion (46.6 ± 1.0% in 60 s), higher flexural and compressive strength (89.7 ± 7.8 MPa; 345.5 ± 14.4 MPa) to those of the 5B5T control (48.5 ± 0.6%; 65.7 ± 6.7 MPa; 223.8 ± 57.1 MPa). This optimal resin also had significantly lower S. mutans colony counts (0.35 ×108 CFU/mL) than 5B5T (7.6 ×108 CFU/mL) without affecting cytocompatibility.

SIGNIFICANCE

Introducing plant-derived polymerizable MABet monomer into dental restorative resins is an effective strategy for producing antibacterial dental materials with superior physicochemical property.

Selective optical sensing of iron(III) ions in an aqueous medium by benzochromone-based Schiff base and its application on test strips

In this work, we designed and synthesized a novel, simple, low-cost, and effective chromone-based Schiff base ligand (HL) and its application as a chemosensor for Fe3+ detection. The structure of the synthesized sensor bears carboxylic, azomethine, and carbonyl groups which act as chelating sites for the detection of Fe3+ ions. The chemosensor HL exhibited highly selective detection of Fe3+ via a significant colour change from yellow to brown. The colour change is due to the ligand-to-metal charge-transfer (LMCT) mechanism. The sensor (HL) was characterized using UV-Vis, FTIR, NMR (1H- and 13C), and mass spectroscopy. The ligand solubility, detection condition, and sensitivity assessment suggested optimal use of DMF-water (9:1 v/v) as a working solvent at pH 7.0. Among a list of 15 metal ions screened, HL was highly selective, with instant response, towards Fe3+ ions without significant interferences with the other metal ions. The complexation ratio and association constants of HL to Fe3+ was determined by Job's plot and Benesi-Hildebrand methods, and were 2:1 and 2.24 × 103 M-1, respectively, with a detection limit of 2.86 μM. The HL probe was also applied to detect Fe3+ in real samples with acceptable performance. The simple test strips have been successfully developed and applied to the visual monitoring of Fe3+ ions with a detection limit of 68 µM. The DFT was used to examine the best interaction mode of HL with Fe metal to be Fe(III)-L or Fe(III)-2L. The chemical-reactivity and molecular electrostatic optional were figured to predict the interaction behaviour of the tested compounds.

A low-shrinkage-stress and anti-bacterial adherent dental resin composite: physicochemical properties and biocompatibility

Polymerisation shrinkage and biofilm accumulation are the two main problems associated with dental resin composites (DRCs) that induce secondary caries, which can cause restoration failure. Polymerisation shrinkage can lead to microleakage gaps between the tooth and the DRCs, causing the aggregation of bacteria and development of secondary caries. Reducing the shrinkage stress (SS) and improving the resistance to bacterial adhesion have always been the focus of this field in modifying DRCs. A thiol-ene resin system can effectively reduce the polymerisation SS via its step-growth mechanism for delaying the gel point. Fluorinated compounds can reduce the surface free energies, thereby reducing bacterial adhesion. Thus, in this study, a range of mass fractions (0, 10, 20, 30, and 40 wt%) of a fluorinated thiol-ene resin system were added to a fluorinated dimethacrylate resin system/tricyclo decanedimethanol diacrylate to create a fluorinated methacrylate-thiol-ene ternary resin matrix. DRCs were prepared using the obtained ternary resin matrix, and their physical and chemical properties, effect on bacterial adhesion, and biocompatibility were investigated. The results demonstrated that the volumetric shrinkage and SS of the DRCs were reduced with no reduction in conversion degree even after the thiol-ene resin system was added. All DRC-based fluorinated resin systems exhibited an excellent anti-bacterial adhesion effect, as evidenced by the colony-forming unit counts, live/dead bacterial staining, and crystal violet staining tests against Streptococcus mutans (S. mutans). The genetic expressions associated with the bacterial adhesion of S. mutans were substantially affected after being cultured with fluorinated DRCs. All fluorinated DRCs demonstrated good biocompatibility through the in vitro cytotoxicity test and live/dead staining images of the L-929 cells. The above results illustrate that the DRCs based on the fluorinated methacrylate-thiol-ene resin matrix can be potentially applied in clinical practice due to their low SS and anti-bacterial adhesion effect.

Advancing Dimethacrylate Dental Composites by Synergy of Pre-Polymerized TEGDMA Co-Filler: A Physio-Mechanical Evaluation

Dental resin composites (DRCs) have gained immense popularity as filling material in direct dental restorations. They are highly valued for their ability to closely resemble natural teeth and withstand harsh oral conditions. To increase the clinical performance of dental restorations, various fillers are incorporated into DRCs. Herein, the effect of incorporating pre-polymerized triethylene glycol dimethacrylate (P-TEGDMA) as a co-filler in varying proportions (0%, 2.5%, 5%, and 10% by weight) into bisphenol A-glycidyl methacrylate (BisGMA)/TEGDMA/SiO2 resin composite was investigated. The obtained DRCs were examined for morphology, rheological properties, degree of crosslinking (DC), Vickers microhardness (VMH), thermal stability, and flexural strength (FS). The results revealed that SiO2 and P-TEGDMA particles were uniformly dispersed. The introduction of P-TEGDMA particles (2.5 wt.%) into the resin composite had a remarkable effect, leading to a significant reduction (p ≤ 0.05) in complex viscosity, decreasing from 393.84 ± 21.65 Pa.s to 152.84 ± 23.94 Pa.s. As a result, the DC was significantly (p ≤ 0.05) improved from 61.76 ± 3.80% to 68.77 ± 2.31%. In addition, the composite mixture demonstrated a higher storage modulus (G') than loss modulus (G″), indicative of its predominantly elastic nature. Moreover, the thermal stability of the DRCs was improved with the addition of P-TEGDMA particles by increasing the degradation temperature from 410 °C to 440 °C. However, the VMH was negatively affected. The study suggests that P-TEGDMA particles have the potential to be used as co-fillers alongside other inorganic fillers, offering a means to fine-tune the properties of DRCs and optimize their clinical performance.

Physical-Chemical and Microhardness Properties of Model Dental Composites Containing 1,2-Bismethacrylate-3-eugenyl Propane Monomer

A new eugenyl dimethacrylated monomer (symbolled BisMEP) has recently been synthesized. It showed promising viscosity and polymerizability as resin for dental composite. As a new monomer, BisMEP must be assessed further; thus, various physical, chemical, and mechanical properties have to be investigated. In this work, the aim was to investigate the potential use of BisMEP in place of the BisGMA matrix of resin-based composites (RBCs), totally or partially. Therefore, a list of model composites (CEa0, CEa25, CEa50, and CEa100) were prepared, which made up of 66 wt% synthesized silica fillers and 34 wt% organic matrices (BisGMA and TEGDMA; 1:1 wt/wt), while the novel BisMEP monomer has replaced the BisGMA content as 0.0, 25, 50, and 100 wt%, respectively. The RBCs were analyzed for their degree of conversion (DC)-based depth of cure at 1 and 2 mm thickness (DC1 and DC2), Vickers hardness (HV), water uptake (WSP), and water solubility (WSL) properties. Data were statistically analyzed using IBM SPSS v21, and the significance level was taken as p < 0.05. The results revealed no significant differences (p > 0.05) in the DC at 1 and 2 mm depth for the same composite. No significant differences in the DC between CEa0, CEa25, and CEa50; however, the difference becomes substantial (p < 0.05) with CEa100, suggesting possible incorporation of BisMEP at low dosage. Furthermore, DC1 for CEa0-CEa50 and DC2 for CEa0-CEa25 were found to be above the proposed minimum limit DC of 55%. Statistical analysis of the HV data showed no significant difference between CEa0, CEa25, and CEa50, while the difference became statistically significant after totally replacing BisGMA with BisMEP (CEa100). Notably, no significant differences in the WSP of various composites were detected. Likewise, WSL tests revealed no significant differences between such composites. These results suggest the possible usage of BisMEP in a mixture with BisGMA with no significant adverse effect on the DC, HV, WSP, and degradation (WSL).

Fabrication of Novel Pre-Polymerized BisGMA/Silica Nanocomposites: Physio-Mechanical Considerations

Resin composite mimics tooth tissues both in structure and properties, and thus, they can withstand high biting force and the harsh environmental conditions of the mouth. Various inorganic nano- and micro-fillers are commonly used to enhance these composites' properties. In this study, we adopted a novel approach by using pre-polymerized bisphenol A-glycidyl methacrylate (BisGMA) ground particles (XL-BisGMA) as fillers in a BisGMA/triethylene glycol dimethacrylate (TEGDMA) resin system in combination with SiO₂ nanoparticles. The BisGMA/TEGDMA/SiO₂ mixture was filled with various concentrations of XL-BisGMA (0, 2.5, 5, and 10 wt.%). The XL-BisGMA added composites were evaluated for viscosity, degree of conversion (DC), microhardness, and thermal properties. The results demonstrated that the addition of a lower concentration of XL-BisGMA particles (2.5 wt.%) significantly reduced (p ≤ 0.05) the complex viscosity from 374.6 (Pa·s) to 170.84. (Pa·s). Similarly, DC was also increased significantly (p ≤ 0.05) by the addition of 2.5 wt.% XL-BisGMA, with the pristine composite showing a DC of (62.19 ± 3.2%) increased to (69.10 ± 3.4%). Moreover, the decomposition temperature has been increased from 410 °C for the pristine composite (BT-SB0) to 450 °C for the composite with 10 wt.% of XL-BisGMA (BT-SB10). The microhardness has also been significantly reduced (p ≤ 0.05) from 47.44 HV for the pristine composite (BT-SB0) to 29.91 HV for the composite with 2.5 wt.% of XL-BisGMA (BT-SB2.5). These results suggest that a XL-BisGMA could be used to a certain percentage as a promising filler in combination with inorganic fillers to enhance the DC and flow properties of the corresponding resin-based dental composites.

Formulation, Configuration, and Physical Properties of Dental Composite Resin Containing a Novel 2π + 2π Photodimerized Crosslinker - Cinnamyl Methacrylate: An In Vitro Research

AIM

To formulate and characterize the chemical structure of a new dental composite with photodimerized cinnamyl methacrylate (PD-CMA) photo-crosslinking comonomer and to evaluate the monomer-to-polymer conversion (MPC) and glass transition temperature (Tg) of the new composite copolymers.

MATERIALS AND METHODS

CMA was PD by ultraviolet C-type (UVC) irradiation. The research groups were a control group C0 without PD-CMA and two trial groups: E10 (10 wt. % PD-CMA substituted in the base comonomers (B) and diluent (D) mixture); E20 (20 wt.% PD-CMA completely replacing the diluent (D) monomer). Infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies were employed for ascertaining copolymerization (CP). The surface features and composition of the copolymers were explained by field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) spectroscopy, respectively. The MPC and Tg of the copolymers were assessed using FTIR and differential scanning calorimetry, respectively. Statistical tests were used to compare the groups.

RESULTS

The configuration of the new copolymers P (BD-Co-CMA) and P(B-Co-CMA) was confirmed. The MPC% and T g of the copolymers were better than the control. PD-CMA at 20 wt. % in the P (B-Co-CMA) copolymer exhibited the highest MPC% and Tg.

CONCLUSION

The incorporation of PD-CMA in the composite resin resulted in new P (BD-Co-CMA) and P (B-Co-CMA) copolymers with improved MPC% and Tg.

CLINICAL SIGNIFICANCE

The substitution with PD-CMA offset the shortcomings of the conventional BD comonomers concerning the mechanical properties and biocompatibility of the restorative composite resin. This might ameliorate the restorations in vivo longevity and serviceability.

Novel 1,2-Bismethacrylate-3-Eugenyl Propane for Resin Composites: Synthesis, Characterization, Rheological, and Degree of Conversion

This work aimed to synthesize a novel dimethacrylated-derivative of eugenol (Eg) (termed EgGAA) as potential biomaterial for certain applications such as dental fillings and adhesives. EgGAA was synthesized through a two-step reaction: (i) a mono methacrylated-eugenol (EgGMA) was produced via a ring-opening etherification of glycidyl methacrylate (GMA) with Eg; (ii) EgGMA was condensed with methacryloyl chloride into EgGAA. EgGAA was further incorporated in matrices containing BisGMA and TEGDMA (50:50 wt%) (TBEa), in which EgGAA replaced BisGMA as 0–100 wt% to get a series of unfilled resin composites (TBEa0–TBEa100), and by addition of reinforcing silica (66 wt%), a series of filled resins were also obtained (F-TBEa0–F-TBEa100). Synthesized monomers were analyzed for their structural, spectral, and thermal properties using FTIR, 1H- and 13C-NMR, mass spectrometry, TGA, and DSC. Composites rheological and DC were analyzed. The viscosity (η, Pa·s) of EgGAA (0.379) was 1533 times lower than BisGMA (581.0) and 125 times higher than TEGDMA (0.003). Rheology of unfilled resins (TBEa) indicated Newtonian fluids, with viscosity decreased from 0.164 Pa·s (TBEa0) to 0.010 Pa·s (TBEa100) when EgGAA totally replaced BisGMA. However, composites showed non-Newtonian and shear-thinning behavior, with complex viscosity (η*) being shear-independent at high angular frequencies (10–100 rad/s). The loss factor crossover points were at 45.6, 20.3, 20.4, and 25.6 rad/s, indicating a higher elastic portion for EgGAA-free composite. The DC was insignificantly decreased from 61.22% for the control to 59.85% and 59.50% for F-TBEa25 and F-TBEa50, respectively, while the difference became significant when EgGAA totally replaced BisGMA (F-TBEa100, DC = 52.54%). Accordingly, these properties could encourage further investigation of Eg-containing resin-based composite as filling materials in terms of their physicochemical, mechanical, and biological potentiality as dental material.

Influence of Eugenol and Its Novel Methacrylated Derivative on the Polymerization Degree of Resin-Based Composites

The aim of this work was to assess the limiting rate of eugenol (Eg) and eugenyl-glycidyl methacrylate (EgGMA) at which the ideal degree of conversion (DC) of resin composites is achieved. For this, two series of experimental composites, containing, besides reinforcing silica and a photo-initiator system, either EgGMA or Eg molecules at 0-6.8 wt% per resin matrix, principally consisting of urethane dimethacrylate (50 wt% per composite), were prepared and denoted as UGx and UEx, where x refers to the EgGMA or Eg wt% in the composite, respectively. Disc-shaped specimens (5 × 1 mm) were fabricated, photocured for 60 s, and analyzed for their Fourier transform infrared spectra before and after curing. The results revealed concentration-dependent DC, increased from 56.70% (control; UG0 = UE0) to 63.87% and 65.06% for UG3.4 and UE0.4, respectively, then dramatically decreased with the concentration increase. The insufficiency in DC due to EgGMA and Eg incorporation, i.e., DC below the suggested clinical limit (>55%), was observed beyond UG3.4 and UE0.8. The mechanism behind such inhibition is still not fully determined; however, radicals generated by Eg may drive its free radical polymerization inhibitory activity, while the steric hindrance and reactivity of EgGMA express its traced effect at high percentages. Therefore, while Eg is a severe inhibitor for radical polymerization, EgGMA is safer and can be used to benefit resin-based composites when used at a low percentage per resin.

The Biological Activity of Fragmented Computer-Aided Design/Manufacturing Dental Materials before and after Exposure to Acidic Environment

Three ceramic and composite computer-aided design/computer-aided manufacturing (CAD/CAM) materials from different manufacturers (Cerasmart (CS)-nanoceramic resin; Straumann Nice (SN)-glass ceramic and Tetric CAD (TC)-composite resin) were tested to investigate the biocompatibility and sustainability on human fibroblasts and keratinocytes cells. Each type of CAD/CAM blocks restorative materials with fine and rough surfaces was exposed to an acidic environment for one month. After that, various powders were obtained by milling. In parallel, powders were also prepared from each restorative material, which were not exposed to the acidic environment. The cytotoxic effects were investigated by means of MTT and LDH assays, as well as nitric oxide production on two human normal cell lines, namely, fibroblasts (BJ) and keratinocytes (HaCaT). In addition, the degree of adhesion of fibroblast cells to each CAD/CAM material was evaluated by scanning electron microscopy (SEM). The results showed that the two samples that were exposed to an acidic environment (CS and SN) induced a reduction of mitochondrial activity and plasma membrane damage as regards the fibroblast cells. A similar effect was observed in TC_fine-exposed material, which seemed to induce necrosis at the tested concentration of 1 mg/mL. No oxidative stress was observed in fibroblasts and keratinocytes treated with the CAD/CAM materials. Regarding the adhesion degree, it was found that the fibroblasts adhere to all the occlusal veneers tested, with the mention that the CS and SN materials have a weaker adhesion with fewer cytoplasmic extensions than TC material. With all of this considered, the CAD/CAM restorative materials tested are biocompatible and represent support for the attachment and dispersion of cells.

Influence of Air-Barrier and Curing Light Distance on Conversion and Micro-Hardness of Dental Polymeric Materials

This study aims to assess the conversion degree and hardness behavior of two new commercial dental restorative composites that have been submitted to light curing in different environments (air and glycerin, respectively) at various distances from the light source (1 to 5 mm) and to better understand the influence of the preparation conditions of the restorative materials. Through FT-IR spectrometry, the crosslinking degree of the commercial restorative materials have been investigated and different conversion values were obtained (from ~17% to ~90%) but more importantly, it was shown that the polymerization environment exhibits a significant influence on the crosslinking degree of the resin-based composites especially for obtaining degrees of higher polymerization. Additionally, the mechanical properties of the restorative materials were studied using the nanoindentation technique showing that the nano-hardness behavior is strongly influenced not only by the polymerization lamp position, but also by the chemical structure of the materials and polymerization conditions. Thus, the nanoindentation results showed that the highest nano-hardness values (~0.86 GPa) were obtained in the case of the flowable C3 composite that contains BisEMA and UDMA as a polymerizable organic matrix when crosslinked at 1 mm distance from the curing lamp using glycerin as an oxygen-inhibitor layer.

A Study on the Photopolymerization Kinetics of Selected Dental Resins Using Fourier Infrared Spectroscopy (FTIR)

The aim of the presented study was a comparative analysis of the polymerization kinetics of dental resin-based composites currently used in dentistry in different environmental conditions (irradiance, activation time, layer thickness). The photopolymerization kinetics of eleven dental resins were investigated using a Woodpecker LED source. The DC was measured by FTIR in transmission mode and attenuated total reflection (ATR) from 5 s to 7 days. In the transmission mode, the spectra from parallel optical layers (about 0.2 mm thick) of samples placed between the KBr crystals were recorded. In the reflection mode, an ATR attachment with a diamond window was used. The DC calculation method was applied based on the application of a monomer absorption band at 1638 cm^-1 (stretching vibration double bond C=C of the vinyl group) without using a reference band. The data were analyzed by performing an ANOVA test comparison between sample groups at the significance level α = 0.05. For all tested materials, the polymerization kinetics consist of three stages. The fastest stage occurs during the irradiation, and the achieved DC value is 70-75% of the maximum value 5 s after the irradiation. Another 15-20% DC increase at a moderate speed takes about 15-20 min. There is also a very slow further increase in DC of 5-10% within 5 days after irradiation. For 8 out of the 11 tested fillings, the optimal photopolymerization conditions are as follows: a power density of 400 or 1000 mW/cm²; an exposure time of 10 s; and a thickness of the irradiated resin layer of up to 2 mm. The influence of various conditions and factors on the reaction kinetics is dominant only in the early, rapid phase of the conversion. After longer times, the DC values gradually level out under different light conditions. The DC of the dental resins are dependent on the irradiance, light source, filler type, time after irradiance, and monomer thickness.

Investigation of antimicrobial and mechanical effects of functional nanoparticles in novel dental resin composites

OBJECTIVES

Imidazole and benzimidazole derivatives have recently attracted attention as remarkable materials due to their advantages in chemistry, pharmacology, and biomaterials. This article focuses on dental composites with azole functional groups incorporated to affect their physicochemical and mechanical properties and antibacterial activity.

METHODS

Dental composites were fabricated by embedding the functionalized imidazole and benzimidazole nanoparticles into a Bis-GMA/TEGDMA matrix to form the imidazole and benzimidazole dental composites series (I and B). The material was produced through hand blending of the monomer (50:50, wt%), filler (0-30, wt%), and initiator combination (CQ/EDMAB:0.8:1.6, wt%), and LED light-curing unit for 60 s.

RESULTS

Using various characterization techniques, I and B series were validated. The dental composites' approximate solubility and sorption significances were evaluated by conducting experiments on specific dental composite formulations. Fenton reaction test was performed to determine the chemical stability of the dental composites. The mechanical properties of the dental composites were investigated. Finally, by testing cell growth in the presence of composites, their antibacterial activities were determined.

CONCLUSIONS

In this study, it was observed that the mechanical, physiochemical, and antibacterial properties of the functional azole-containing nanoparticles were positively improved by adding them to the structure of dental composites. These experimental results paved the way for the synthesized materials to be used in industrial applications.

CLINICAL SIGNIFICANCE

Since the chemical, mechanical, and antimicrobial properties of dental composites containing 10% imidazole and benzimidazole functional nanoparticles are far superior, they constitute an excellent alternative for preventing dental caries and long-term use of dental composites.

Water Sorption, Water Solubility, and Rheological Properties of Resin-Based Dental Composites Incorporating Immobilizable Eugenol-Derivative Monomer

The present study aimed to evaluate the properties of new dental formulations incorporating a new polymerizable-derivative of eugenol (EgGMA). The experimental composites were prepared (by weight) with 35% resin-based matrix (1:1, bisphenol A-glycidyl methacrylate/triethylene glycol dimethacrylate) and 65% reinforcing materials (4:3, hydroxyapatite/zirconium oxide). A portion of 0.0, 2.5, and 5.0% of the resins with respect to the total composite was replaced by EgGMA monomer to obtain TBEg0, TBEg2.5, and TBEg5, respectively. The complex viscosity (at 25 and 37 °C), degree of conversion (DC), and water sorption (W_SP) and water solubility (W_SL) (3 cycles of sorption-desorption process) were investigated. Data were statistically analyzed using one-way and Tukey post-hoc tests. The results revealed a viscosity reduction with shear-thinning behavior as the EgGMA amount and temperature increased. The average complex viscosities at a lower frequency (ω = 1.0 rad/s) and at 25 °C were 234.7 ± 13.4, 86.4 ± 16.5, and 57.3 ± 17.1 (kPa·s) for TBEg0, TBEg2.5, and TBEg5, respectively. The inclusion of EgGMA led to a lower DC and W_SP but higher W_SL, compared to those of the reference (TBEg0). However, no significant differences between TBEg2.5 and control were detected (p > 0.05). Therefore, the incorporation of EgGMA in a low quantity, e.g., up to 8.45 mol% of resins, within the matrix may enhance the composite’s performance, including handling and solubility properties without any apparent effect on DC and water sorption, making it a promising monomeric biomaterial for various applications including restorative dentistry.

Eugenyl-2-Hydroxypropyl Methacrylate-Incorporated Experimental Dental Composite: Degree of Polymerization and In Vitro Cytotoxicity Evaluation

The aim of this study was to evaluate the properties of new dental formulations containing eugenyl-2-hydroxypropyl methacrylate (EgGMA) monomer, as restorative dental material, in terms of their degree of photopolymerization and cytotoxicity. The target model composites (TBEg0, TBEg2.5, and TBEg5) were prepared by mixing 35% organic matrix (TEGDMA/BisGMA (50/50 wt%) of which 0, 2.5, and 5 wt%, respectively, were replaced with EgGMA monomer) with 65% filler (silanized hydroxyapatite (HA)/zinc oxide (ZnO₂), 4:3 by weight). The vinylic double-bond conversion (DC) after light-curing was studied using Fourier transform infrared technique whereas cell viability was in vitro tested using primary human gingival fibroblasts cells over 7 days by means of AlamarBlue colorimetric assay. The obtained data were statistically analyzed using ANOVA and Tukey post-hoc tests. The results revealed no significant difference in DC between TBEg2.5 (66.49%) and control (TBEg0; 68.74%), whereas both differ significantly with TBEg5, likely due to the inhibitory effect of eugenol moiety at high concentration. The cell viability test indicated that all the composites are biocompatible. No significant difference was counted between TBEg2.5 and TBEg5, however, both differed significantly from the control (TBEg0). Thus, even though its apparent negative effect on polymerization, EgGMA is potentially safer than bisphenol-derived monomers. Such potential properties may encourage further investigations on term of EgGMA amount optimization, compatibility with other dental resins, and antimicrobial activity.

Molecular dynamics investigation of structural and mechanical properties of silica nanorod reinforced dental resin composites

In this work, molecular dynamics simulations are conducted to investigate the structural and mechanical properties of dental materials, i.e., the silica nanorod reinforced Bis-GMA/TEGDMA resin composite. The effects of loading content and size of the silica nanorods on the composite stiffness were performed by examining resin chain conformation, hydrogen bonds and matrix/filler binding energy. It is revealed that the presence of the silica nanorod causes polymer chain expansion, endowing the resins with higher stiffness. Moreover, the volumetric hydrogen bonds and binding energy increase considerably with the loading content, but decrease gradually with the diameter or show almost independence of the length. Furthermore, the composite moduli were quantified by the micromechanics models and the transverse moduli were well predicted by the Counto model, signifying a perfect bonding between the matrix and nanorod. The chain expansion and energetic matrix/filler interactions are believed to contribute to the significant mechanical reinforcement of the composites with the loading content. However, the length of the nanorod has a little effect on the composite moduli due to the unaltered interfacial interaction. In contrast, a smaller diameter is supposed to give a larger modulus, and this is not observed in this work due to the synergic effects of improved matrix/filler interaction and actual reduced filler volume fraction. The mechanical enhancement by the rod-like structures is more influenced by the loading content, but less so by the size of the nanorod, and it also exhibits superior mechanical performance as compared to nanoparticles. The findings thus extend the current understanding of the nanostructure and mechanical properties of silica nanorod reinforced dental resin composites from an atomic/molecular perspective.

A Review on Current Trends of Polymers in Orthodontics: BPA-Free and Smart Materials

Polymeric materials have always established an edge over other classes of materials due to their potential applications in various fields of biomedical engineering. Orthodontics is an emerging field in which polymers have attracted the enormous attention of researchers. In particular, thermoplastic materials have a great future utility in orthodontics, both as aligners and as retainer appliances. In recent years, the use of polycarbonate brackets and base monomers bisphenol A glycerolate dimethacrylate (bis-GMA) has been associated with the potential release of bisphenol A (BPA) in the oral environment. BPA is a toxic compound that acts as an endocrine disruptor that can affect human health. Therefore, there is a continuous search for non-BPA materials with satisfactory mechanical properties and an esthetic appearance as an alternative to polycarbonate brackets and conventional bis-GMA compounds. This study aims to review the recent developments of BPA-free monomers in the application of resin dental composites and adhesives. The most promising polymeric smart materials are also discussed for their relevance to future orthodontic applications.

Synthesis, Characterization, Single-Crystal X-ray Structure and Biological Activities of [(Z)-N′-(4-Methoxybenzylidene)benzohydrazide–Nickel(II)] Complex

(Z)-N′-(4-methoxybenzylidene)benzohydrazide (HL) and its Ni(II) complex (Ni(II)-2L) were synthesized using eco-friendly protocols. The single X-ray crystal structure of Ni(II)-2L was solved. Moreover, the structural properties were evaluated using Fourier transform infrared, proton nuclear magnetic resonance, mass, and Ultraviolet/Visible spectroscopy. The diamagnetic and thermal stability were assessed using magnetic susceptibility and thermogravimetric analysis, respectively. The biological activities of both HL and Ni(II)-2L (62.5–1000 μg/mL) against Gram-positive (Staphylococcus aureus and Streptococcus pyogenes) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacterial and fungal (Candida albicans, Aspergillus niger, and Aspergillus clavatus) species were studied using the minimum inhibitory concentration (MIC) tests method in reference to Gentamycin and Nystatin standard drugs, respectively. The results revealed an affordable, environmentally friendly, and efficient synthetic method of HL using water as a green solvent. The Ni(II)-2L complex crystallized in a distorted square planar, P21/n space group, and one Ni(II) to two bidentate negatively charged ligand ratio. The analysis of biological activity revealed higher activity of the complex against S. aureus and S. pyogenes (bacteria) and A. niger and A. clavatus (fungi) compared to the ligand. However, the highest activity was at a MIC of 62.5 μg/mL for the complex against S. pyogenes and for the ligand against E. coli. Therefore, both HL and Ni(II)-2L could be promising potential antimicrobials and their selective activity could be an additional benefit of these bioactive materials.

A Low-Viscosity BisGMA Derivative for Resin Composites: Synthesis, Characterization, and Evaluation of Its Rheological Properties

This study aimed to synthesize new bisphenol A-glycidyl methacrylate (BisGMA) derivatives, targeting a reduction in its viscosity by substituting one of its OH groups, the leading cause of its high viscosity, with a chlorine atom. Hence, this monochloro-BisGMA (mCl-BisGMA) monomer was synthesized by Appel reaction procedure, and its structure was confirmed using Fourier transform infrared spectroscopy, ¹H and ¹³C-nuclear magnetic resonance spectroscopy, and mass spectroscopy. The viscosity of mCl-BisGMA (8.3 Pa·s) was measured under rheometry conditions, and it was found to be more than 65-fold lower than that of BisGMA (566.1 Pa·s) at 25 °C. For the assessment of the viscosity changes of model resins in the presence of mCl-BisGMA, a series of resin matrices, in which, besides BisGMA, 50 wt % was triethylene glycol dimethacrylate, were prepared and evaluated at 20, 25, and 35 °C. Thus, BisGMA was incrementally replaced by 25% mCl-BisGMA to obtain TBC0, TBC25, TBC50, TBC75, and TBC100 blends. The viscosity decreased with temperature, and the mCl-BisGMA content in the resin mixture increased. The substantial reduction in the viscosity value of mCl-BisGMA compared with that of BisGMA may imply its potential use as a dental resin matrix, either alone or in combination with traditional monomers. However, the various properties of mCl-BisGMA-containing matrices should be evaluated.

Evaluation of Synergic Potential of rGO/SiO2 as Hybrid Filler for BisGMA/TEGDMA Dental Composites

Graphene and graphene oxide based nanomaterials have attained immense significance in research because of their matchless physiochemical characteristics. Although potential biomedical applications of graphene have been extensively studied, however, dentistry related applications were rarely explored. This study aimed to investigate the effect of various percentages of surface modified reduce graphene oxide (S-rGO) in combination with SiO₂ nanoparticles (bulk filler) on numerous physio-mechanical characteristics of acrylate-based (BisGMA/TEGDMA: 1:1 by wt.) composites. BisGMA/TEGDMA reinforced with 30 wt.% surface modified fumed-silica (S-A200) was considered as control group (base composite). Various concentrations (0, 0.5, 1, 2, 4 wt.%) of S-rGO were incorporated into the base composite via solution casting and high-speed mixing. The obtained composites were characterized for rheological properties before curing by using Rheometer (Anton Paar, USA) in the oscillatory mode under a frequency sweep over a range of angular frequency of 0.1–100 rad/s at 25 °C. The degree of conversion (DC) was measured by using Fourier transform infrared spectroscopy (FTIR). A Nano-indentation test was carried out to obtain nano-hardness and elastic modulus. The surface roughness was measured by optical microscope (Bruker^®), 3D non-contact surface profilometer. The structural and morphological properties were studied by using Scanning Electron Microscopy (SEM). The mean and standard deviation were calculated and a simple mean comparisons test was performed for comparison using SPSS. The results revealed that the addition of a tiny proportion of S-rGO considerably increased the nano-indentation hardness, elastic modulus and DC. Conversely, a gradual reduction in viscosity was observed with increasing S-rGO concentration. The study demonstrates that a small fraction of S-rGO in combination with SiO₂ could enhance physical, mechanical and rheological properties of acrylate based composites. Thus S-rGO/SiO₂ combination could be used as a potential hybrid filler for dental nanocomposites.

Novel Metformin-Based Schiff Bases: Synthesis, Characterization, and Antibacterial Evaluation

Novel Schiff bases of metformin hydrochloride and (ortho)para-nitrobenzaldehyde were synthesized by employing two efficient environmentally friendly methods, namely, stirring and microwave-assisted methods using water as the solvent. The advantage of microwave irradiation over the other methods was represented in the reduction of reaction time and wastes, and good yields; however, water in both methods plays the role of eco-friendly solvent. The structural properties of the (ortho)para-isomer products were analyzed by elemental analysis, Fourier transform infrared (FTIR) spectroscopy, UV-Visible (UV-Vis) spectroscopy, ¹H nuclear magnetic resonance (NMR) spectroscopy, ¹³C NMR spectroscopy, mass spectroscopy, and differential scanning calorimetry (DSC). The newly synthesized compounds were screened for their antibacterial activity against selected Gram-positive (ATCC 25923, ATCC 43300, and ATCC 29212) and Gram-negative (ATCC 25922, ATCC 27853, and ATCC 700603) bacteria using the agar well diffusion method. Compared with the standard drug streptomycin, both Schiff bases exhibited moderate bactericidal activity against the tested bacteria with higher values of ortho-nitro compared with the para-nitro isomer; however, no effect on ATCC 43300 and ATCC 27853 was observed under the experimental conditions employed.

A Guide through the Dental Dimethacrylate Polymer Network Structural Characterization and Interpretation of Physico-Mechanical Properties

Material characterization by the determination of relationships between structure and properties at different scales is essential for contemporary material engineering. This review article provides a summary of such studies on dimethacrylate polymer networks. These polymers serve as photocuring organic matrices in the composite dental restorative materials. The polymer network structure was discussed from the perspective of the following three aspects: the chemical structure, molecular structure (characterized by the degree of conversion and crosslink density (chemical as well as physical)), and supramolecular structure (characterized by the microgel agglomerate dimensions). Instrumental techniques and methodologies currently used for the determination of particular structural parameters were summarized. The influence of those parameters as well as the role of hydrogen bonding on basic mechanical properties of dimethacrylate polymer networks were finally demonstrated. Mechanical strength, modulus of elasticity, hardness, and impact resistance were discussed. The issue of the relationship between chemical structure and water sorption was also addressed.