A comparative study on the mechanical and antibacterial properties of BPA-free dental resin composites

OBJECTIVE

The commonly used base monomer utilized in resinous commercial dental restorative products is bis-GMA which is derived from bisphenol-A (BPA) - a well-known compound which may disrupt endocrine functions. To address concerns about its leaching into the oral environment and to optimize the quality of dental composites, a BPA-free alternative base monomer, fluorinated urethane dimethacrylate (FUDMA), was designed by modifying a UDMA monomer system.

METHODS

Nine groups of composites were prepared by mixing the base monomers and TEGDMA in a ratio of 70/30 wt% to which were added silanized glass particles (mean diameter: 0.7 µm) in 3 different volume fractions (40, 45, and 50 vol%). Bis-GMA and UDMA base monomers were used as control groups in the same ratios. Various properties including degree of conversion (DC), flexural strength (FS) and flexural modulus (FM), water sorption (WS), solubility (SL), surface hardness and roughness, and initial adhesion property against S.mutans were investigated. One-way analysis of variance followed by Bonferroni test at α = 0.05 was used to analyze the results.

RESULTS

A significant difference in FS between FUDMA-based composite with 40 vol% filler (120.3 ± 10.4 MPa) and Bis-GMA-based composite with the same filler fraction (105.8 ± 10.0 MPa) was observed but there was no significant difference among other groups. The UDMA based group exhibited the highest WS (1.3 ± 0.3 %). Bis-GMA showed greater initial bacterial adhesion but was not statistically different from the other groups (p = 0.082).

SIGNIFICANCE

FUDMA-based resin composites exhibit comparable mechanical and bacterial adhesion properties compared with Bis-GMA and UDMA-based composites. The FUDMA composites show positive outcomes indicating they could be used as substitute composites to Bis-GMA-based composites.

Tailoring the monomers to overcome the shortcomings of current dental resin composites - review

Dental resin composites (DRCs) have become the first choice among different restorative materials for direct anterior and posterior restorations in the clinic. Though the properties of DRCs have been improved greatly in recent years, they still have several shortcomings, such as volumetric shrinkage and shrinkage stress, biofilm development, lack of radio-opacity for some specific DRCs, and estrogenicity, which need to be overcome. The resin matrix, composed of different monomers, constitutes the continuous phase and determine the performance of DRCs. Thus, the chemical structure of the monomers plays an important role in modifying the properties of DRCs. Numerous researchers have taken to design and develop novel monomers with specific functions for the purpose of fulfilling the needs in dentistry. In this review, the development of monomers in DRCs were highlighted, especially focusing on strategies aimed at reducing volumetric shrinkage and shrinkage stress, endowing bacteriocidal and antibacterial adhesion activities as well as protein-repelling activity, increasing radio-opacity, and replacing Bis-GMA. The influences of these novel monomers on the properties of DRCs were also discussed.

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.

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.

Volumetric additive manufacturing via tomographic reconstruction

Additive manufacturing promises enormous geometrical freedom and the potential to combine materials for complex functions. The speed, geometry, and surface quality limitations of additive processes are linked to their reliance on material layering. We demonstrated concurrent printing of all points within a three-dimensional object by illuminating a rotating volume of photosensitive material with a dynamically evolving light pattern. We printed features as small as 0.3 millimeters in engineering acrylate polymers and printed soft structures with exceptionally smooth surfaces into a gelatin methacrylate hydrogel. Our process enables us to construct components that encase other preexisting solid objects, allowing for multimaterial fabrication. We developed models to describe speed and spatial resolution capabilities and demonstrated printing times of 30 to 120 seconds for diverse centimeter-scale objects.

Preparation of a Bis-GMA-Free Dental Resin System with Synthesized Fluorinated Dimethacrylate Monomers

With the aim of reducing human exposure to Bisphenol A (BPA) derivatives in dentistry, a fluorinated dimethacrylate monomer was synthesized to replace 2,2-bis[4-(2-hydroxy-3-methacryloy-loxypropyl)-phenyl]propane (Bis-GMA) as the base monomer of dental resin. After mixing with reactive diluent triethyleneglycol dimethacrylate (TEGDMA), fluorinated dimethacrylate (FDMA)/TEGDMA was prepared and compared with Bis-GMA/TEGDMA in physicochemical properties, such as double bond conversion (DC), volumetric shrinkage (VS), water sorption (WS) and solubility (WSL), flexural strength (FS) and modulus (FM). The results showed that, when compared with Bis-GMA based resin, FDMA-based resin had several advantages, such as higher DC, lower VS, lower WS, and higher FS after water immersion. All of these revealed that FDMA had potential to be used as a substitute for Bis-GMA. Of course, many more studies, such as biocompatibility testing, should be undertaken to prove whether FDMA could be applied in clinic.

Preparation and characterization of Bis-GMA free dental resin system with synthesized dimethacrylate monomer TDDMMA derived from tricyclo[5.2.1.0(2,6)]-decanedimethanol

As a substitute for 2,2-bis[4-(2-hydroxy-3- methacryloxypropoxy)phenyl] propane (Bis-GMA) in dental materials, a new dimethacrylate monomer TDDMMA without bisphenol-A structure was synthesized through the reaction between tricyclo[5.2.1.0(2,6)]- decanedimethanol and 2-isocyanatoethyl methacrylate. The TDDMMA was mixed with triethylene glycol dimethacrylate (TEGDMA) to prepare Bis-GMA free dental resin. Physicochemical properties, such as double bond conversion (DC), polymerization shrinkage (VS), water sorption (WS) and solubility (SL), flexural strength (FS) and modulus (FM) and fracture energy of TDDMMA/TEGDMA resin system were investigated. Bis-GMA/TEGDMA resin system was used as a control. The results showed that, compared with Bis-GMA/TEGDMA resin system, TDDMMA/TEGDMA resin system had comparable VS and several advantages like higher DC, lower SL and better mechanical properties after water immersion.