Development of highly reactive mono-(meth)acrylates as reactive diluents for dimethacrylate-based dental resin systems

Epigallocatechin gallate-immobilized antimicrobial resin with rechargeable fluorinated synergistic composite for enhanced caries control

OBJECTIVES

Given the global prevalence of dental caries, impacting 2.5 billion individuals, the development of sophisticated prevention filling materials is crucial. Streptococcus mutans, the principal caries-causing strain, produces acids that demineralize teeth and initiate dental caries. To address this issue, we aimed to develop a synergistic resin-based composite for enhancing caries control.

METHODS

The synergistic resin composite incorporates fluorinated kaolinite and silanized Al2O3 nanoparticle fillers into an epigallocatechin gallate (EGCG) immobilized urethane-modified epoxy acrylate (U-EA) resin matrix, referred to the as-prepared resin composite. The EGCG-modified TPGDA/U-EA network was synthesized by preparing methacrylate-functionalized isocyanate (HI), reacting it with EGCG to form HI-EGCG, and then incorporating HI-EGCG into the TPGDA/U-EA matrix. The lamellar space within the kaolinite layer was expanded through the intercalation of acrylamide into kaolinite, enhancing its capability to adsorb and release fluoride ions (F-). The layered structure of acrylamide/ kaolinite in the U-EA resin composite acts as a F- reservoir.

RESULTS

The physico-mechanical properties of the as-prepared resin composites are comparable to those of commercial products, exhibiting lower polymerization shrinkage, substantial F- release and recharge and favorable diametral tensile strength. The immobilized EGCG in the composite exhibits potent antimicrobial properties, effectively reducing the biofilm biomass. Furthermore, the synergistic effect of EGCG and fluorinated kaolinite efficiently counteracts acid-induced hydroxyapatite dissolution, thereby suppressing demineralization and promoting enamel remineralization.

SIGNIFICANCE

Our innovative EGCG and fluoride synergistic composite provides enhanced antimicrobial properties, durable anti-demineralization, and tooth remineralization effects, positioning it as a promising solution for effective caries control and long-term dental maintenance.

Enhanced anti-bacterial adhesion effect of FDMA/SR833s based dental resin composites by using 1H,1H-heptafluorobutyl methacrylate as partial diluent

With the purpose of further reducing surface free energy to achieve better anti-bacterial adhesion effect of fluorinated dimethacrylate (FDMA)/tricyclo (5.2.1.0) decanedimethanol diacrylate (SR833s) based dental resin composites (DS), 1H,1H-heptafluorobutyl methacrylate (FBMA) was used to partially replace SR933s as reactive diluent. According to the degree of substitution, the obtained resin composites were marked as DSF-1 (20 wt.% of SR833s was replaced by FBMA), DSF-2 (40 wt.% of SR833s was replaced by FBMA), and DSF-3 (60 wt.% of SR833s was replaced by FBMA). Bisphenol A glycidyl dimethacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) based resin composite (BT) was used as control. The influence of FBMA concentration on double bond conversion (DC), contact angle, surface free energy, anti-bacterial adhesion effect against Streptococcus mutans (S. mutans), volumetric shrinkage (VS) and shrinkage stress (SS), flexural strength (FS) and modulus (FM), water sorption (WS) and solubility (SL) were investigated. The results showed that FBMA addition could reduce surface free energy from 44.6 mN/m for DS to 32.9 mN/m for DSF-3, and lead to better anti-bacterial adhesion effect (the amounts of adherent bacteria decreased from 2.03 × 105 CFU/mm2 for DS to 6.44 × 104 CFU/mm2 for DSF-3). The FBMA had no negative effects on DC, VS, SS, WS, and SL. Too high a concentration of FBMA reduced FS and FM before water immersion, but the values were still higher than those of BT.

Evaluation of the effects of whitening toothpaste containing nanohydroxyapatite on surface roughness and color change in restorative materials

Background

The effects of whitening toothpastes containing nanohydroxyapatite on the surfaces of restorative materials are not well known. This study evaluated the changes in surface roughness and color of coffee-stained restorative materials after brushing with nanohydroxyapatite and other whitening toothpastes.

Methods

Disc-shaped specimens were formed using microhybrid, nanohybrid, and supra-nano-filled composite (n = 30) and stained with a coffee solution. A brushing simulation was applied with toothpastes containing nanohydroxyapatite (Dentiste Plus White), perlite (Signal White System) and hydrogen peroxide (Colgate Optic White) for 7, 15, and 30 days. Color and surface roughness measurements were taken before and after brushing. Color change (∆E₀₀) was calculated using the CIEDE2000 system.

Results

Supra-nano-filled composite-Dentiste Plus White, supra-nano-filled composite-Colgate Optic White, and nanohybrid composite-Signal White System were the groups with the greatest color change observed on the 7th, 15th, and 30th days, respectively. The smallest color change was seen in the microhybrid composite-Signal White System, microhybrid composite-Dentiste Plus White, and nanohybrid composite-Dentiste Plus White groups on the 7th, 15th, and 30th days, respectively. No significant surface roughness changes were observed in the nanohybrid composite-Dentiste Plus White, supra-nano-filled composite-Colgate Optic White, supra-nano-filled composite-Dentiste Plus White, or supra-nano-filled composite-Signal White System groups.

Conclusions

Whitening toothpaste containing nanohydroxyapatite provided a high degree of color change in the short term and did not create significant surface roughness in nanohybrid or supra-nano-filled composites.

Quantifying the Release of Titanium From the Titanium Dioxide-Impregnated Composites Used in Orthodontic Bonding

BACKGROUND

Previous literature data has extensively assessed the biocompatibility of various orthodontic adhesives and their components, where the results of most of the studies showed cytotoxic effects of different degrees owing to the unbound molecules released structurally from the cured components.

AIM

The present in-vitro study was aimed to assess the release of titanium dioxide nanoparticles in the artificial saliva from the orthodontic composites impregnated with titanium dioxide nanoparticles of 5% w/w (weight/weight) and 1% w/w used for metal brackets bonding.

METHODS

The study assessed 160 teeth extracted freshly during orthodontic treatment and divided into two groups of 80 samples, each that bonded to orthodontic brackets having 5% w/w and 1% w/w composites with titanium dioxide nanoparticles kept in the artificial saliva. Quantification was done for 5% w/w and 1% w/w composites having titanium nanoparticles with inductively coupled plasma mass spectroscopy at 24 hours, two, four, and six months.

RESULTS

It was seen that in teeth with 1% titanium dioxide, the greatest titanium release was seen at two months, with non-significant release after two months. In teeth with 5% w/w titanium dioxide nanoparticles showed significant titanium release all the time. A significantly greater titanium dioxide release on increasing concentration from 1% to 5% was seen for the 5% w/w group at all the assessment times.

CONCLUSION

The present study concludes that a higher release of titanium is seen in 5% w/w composite containing titanium dioxide nanoparticles, and the concentrations of 1% and 5% can be safely used and are considered to be within permissible limits.

Preparation of a fluorinated dental resin system and its anti-adhesive properties against S. mutans

OBJECTIVES

The purpose of this study was to characterize physicochemical properties and investigate anti-bacterial adhesion effect of dental resins containing fluorinated monomers.

METHOD

Fluorinated dimethacrylate FDMA was mixed with commonly used reactive diluent triethylene- glycol dimethacrylate (TEGDMA) and fluorinated diluent 1 H,1 H-heptafluorobutyl methacrylate (FBMA) separately at a mass ratio of 60 wt./40 wt. to prepare fluorinated resin systems. Double bond conversion (DC), flexural strength (FS) and modulus (FM), water sorption (WS) and solubility (SL), contact angle and surface free energy, surface element concentration, and anti-adhesion effect against Streptococcus mutans (S. mutans) were investigated according to standard or referenced methods. 2,2-bis[4-(2-hydroxy-3-methacryloy-loxypropyl)-phenyl]propane (Bis-GMA)/TEGDMA (60/40, wt./wt.) was used as control.

RESULTS

Both fluorinated resin systems had higher DC than Bis-GMA based resin (p < 0.05); compared with Bis-GMA based resin (FS, FDMA/TEGDMA resin system had higher FS (p < 0.05) and comparable FM (p > 0.05), while FDMA/FBMA resins system had lower FS and FM (p < 0.05). Both fluorinated resin systems had lower WS and SL than Bis-GMA based resin (p < 0.05), and FDMA/TEGDMA resin system had the lowest WS (p < 0.05) in all experimental resin systems. Only FDMA/FBMA resin system showed lower surface free energy than Bis-GMA based resin (p < 0.05). When the surface was smooth, FDMA/FBMA resin system had lower amount of adherent S. mutans than Bis-GMA based resin (p < 0.05), while after the surface became roughness, FDMA/FBMA resin system had comparable amount of adherent S. mutans as Bis-GMA based resin (p > 0.05).

SIGNIFICANCE

Resin system prepared exclusively with fluorinated methacrylate monomers reduced the S. mutans adhesion due to their increased hydrophobicity and decreased surface energy., while flexural properties of it should be improved.

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.

Quantification of Titanium Release From Titanium Dioxide Impregnated Composites in Orthodontic Bonding—An In Vitro Study

Objective

To evaluate the quantity of titanium dioxide nanoparticles released into the artificial salivary medium from orthodontic composite impregnated with 1% weight/weight (w/w) and 5% w/w titanium dioxide nanoparticles (TiO2 NPs) used for bonding metal brackets, thereby eventually comprehending the permissible levels.

Materials and Method

Eighty freshly extracted teeth for orthodontic treatment were divided into 2 groups of 40 teeth each and were bonded with brackets containing 1% w/w and 5% w/w composite containing titanium dioxide nanoparticles and placed in an artificial salivary medium. Quantification of 1% w/w and 5% w/w composite containing titanium nanoparticles was done using inductively coupled plasma mass spectroscopy for 4 timely periods 24 h, 2 months, 4 months, and 6 months.

Results

In the teeth that received 1% TiO2, the amount of titanium released was greatest in 2 months with no significant release at later intervals. In the second group that received 5%, there was a significant release of titanium at all intervals, with highest release at second month. On comparing the 2 concentrations at 4 different time intervals, the quantities were significantly greater in the 5% group at all time frames, thus implying a significant increase in titanium released with an increase in concentration from 1% to 5%.

Conclusion

Titanium release was higher in 5% w/w composite containing nanoparticles than 1% w/w composite containing nanoparticles, and 1% and 5% concentrations can be used safely and are within the permissible limits.

Development of new diacrylate monomers as substitutes for Bis-GMA and UDMA

OBJECTIVE

Bisphenol A-glycidyl methacrylate (Bis-GMA) and urethane dimethacrylate (UDMA) are widely used as the primary components of (meth)acrylic monomers. However, the use of Bis-GMA, which is a bisphenol A derivative, in dentistry is being questioned after bisphenol A was found to exhibit estrogenic activity. Although UDMA is being considered as a substitute for bis-GMA, the mechanical properties of cured resin composites containing UDMA are less than desirable. Therefore, in this study, we developed new alternative (meth)acrylic monomers to enhance the mechanical strength of cured composite resins.

METHODS

Five urethane acrylic monomers were synthesized in this study as (meth)acrylic monomer substituents to replace Bis-GMA and UDMA. The elastic modulus, strength, and breaking energy values of cured resins consisting of mixtures of the urethane acrylates and diluting monomers were determined using the three-point flexural test. The data obtained were analyzed using one-way ANOVA and the post-hoc Tukey HSD tests (p < 0.05). Viscosities of the urethane acrylic monomers were measured with a cone-plate viscometer. Refractive indices of the urethane acrylic monomers were determined with an Abbe refractometer.

RESULTS

The results of the three-point flexural tests revealed that the cured urethane acrylic monomer-based resin exhibited higher elastic modulus (up to 40%) and strength (up to 21%) compared to the cured UDMA-based resin. Viscosity and refractive index of the urethane acrylic monomers were between those of UDMA and Bis-GMA.

SIGNIFICANCE

The developed urethane diacrylates prepared from diisocyanates which have an aromatic or aliphatic ring, 1,3-bis(1-isocyanato-1-methylethyl)benzene (TMXDI), 1,3-bis(isocyanatomethyl)benzene (XDI), or norbornane diisocyanate (NBDI) are worth considering as alternative options of Bis-GMA and UDMA for restorative resin composites.

Mechanical properties enhancement of self-cured PMMA reinforced with zirconia and boron nitride nanopowders for high-performance dental materials

We report on the mechanical properties regarding self-cured acrylic polymethyl methacrylate (PMMA) reinforced with hexagonal boron nitride (h-BN) and stabilized zirconia (8Y ZrO₂) nanopowders. The nanocomposites were prepared by using both manual and ultrasonic mixing techniques. The fabricated specimens were subjected to micro indentation, bending strength, and modulus of elasticity measurements. A fully complete polymerization process under liquid monomer was provided by ultrasonic mixing as evidenced by Fourier transform infrared (FTIR) measurement. Independently of the nanopowder used, the hardness, bending strength, and modulus of elasticity of the formed nanocomposites highly increase in values with the increase of the filler concentrations. Higher bending strengths and modulus of elasticity of the nanocomposite were recorded when using h-BN nanopowder fillers whereas hardness increases when using 8Y ZrO₂ nanopowder. Results showed that with respect to the unloaded specimens made by manual mixing, ultrasonic mixing of PMMA with a 5 wt% h-BN increased the flexural strength (FS) and the modulus of elasticity or Young's modulus (YM) values to about 550% and 240%, respectively. However, a similar concentration of 8Y ZrO₂ increased the Vickers Hardness numbers (VH) to about 400%. This may suggest that PMMA loaded with a combination of h-BN and 8Y ZrO₂ nanopowders may lead to nanocomposites with outstanding mechanical performance.

Effect of Hexagonal Boron nitride Nanopowder Reinforcement and Mixing Methods on Physical and Mechanical Properties of Self-Cured PMMA for Dental Applications

We report for the first time on the effect of biocompatible hexagonal boron nitride (h-BN) nanopowder reinforcement with different concentrations on the structural and mechanical properties of fabricated self-cured polymethyl methacrylate (PMMA) based dental materials (GC UNIFAST III). A comparison among the structural and mechanical properties between hand and ultrasonic mixing is also presented. Fabricated specimens were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), micro indentation, and flexural strength techniques. The ultrasonic mixing method provides better sample textures of the composite as compared to hand mixing. It is found that XRD and IR intensity of the peaks increases with the increase of h-BN concentration due to nanocomposite formation. The additions of h-BN nanoparticles to the acrylic resin enhanced the hardness and the flexibility values of the composites. Independently of the mixing method used, adding h-BN nanopowder relatively increases the Vickers Hardness numbers (VH) and Flexural Strength (FS) of the unmodified materials. However, using ultrasonic mixing method combined with h-BN nanopowder increases VH numbers to 300% and FS values to 550% with respect to the unmodified sample made by hand mixing. The results obtained are very encouraging and will support future research in vivo, to confirm whether PMMA loaded with h-BN nanoparticles is an improvement compared to current dental restorative materials.

Effects of deformation rate variation on biaxial flexural properties of dental resin composites

Objectives

This study aimed to determine the biaxial flexural strength (BFS) of resin composite materials at distinct deformation rates.

Methods

Two micro-hybrid [Filtek Z100™ Restorative (Z100), Filtek™ Z250 (Z250)] and two nano-filled [Filtek™ Supreme XT Body (FSB), Filtek™ Supreme Translucent (FST)] composite resins were selected. Disc-shaped (12 × 1 mm) specimens were fabricated using nylon split moulds. Bar-shaped specimens (25 × 2 × 2 mm) were fabricated from each material to determine the flexural modulus. The specimens were tested for BFS and flexural modulus under dry and wet conditions after 1, 13, and 52 weeks.

Results

The highest BFS was recorded for Z250 (162 ± 19 MPa), followed by FST (154 ± 16 MPa), Z100 (150 ± 18 MPa), and FSB (136 ± 18 MPa). The materials exhibited a clear trend of increase in BFS with deformation rate. Following immersion for 1 week, the BFS was 126 ± 18 MPa for Z100, and 124 ± 17 MPa for Z250, which were higher than those of FSB (99 ± 16 MPa) and FST (115 ± 19 MPa) under comparable conditions. There was a remarkable reduction in the flexural moduli of the specimens immersed for 1 week compared to those of the dry specimens: Z100 (from 18.3 ± 1.2 GPa for dry specimen to 15.7 ± 0.8 GPa after immersion for 1 week), Z250 (from 16.7 ± 0.8 GPa to 13.3 ± 1.4 GPa), FSB (from 13.7 ± 0.6 GPa to 11.0 ± 2.1 GPa) and FST (from 12.7 ± 2.3 GPa to 10.4 ± 1.0 GPa).

Conclusion

This study concludes that the BFS and flexural moduli of resin-based dental restoratives decline when they are immersed in an aqueous medium until saturation with water. However, after equilibrium is established, the immersion medium does not affect the restorative materials further. Variations in deformation rate did not have a significant effect on the BFS of resin-based dental restoratives.

Effect of low-shrinkage monomers on the physicochemical properties of experimental composite resin

This study was conducted to determine whether novel experimental low-shrinkage dimethacrylate co-monomers could provide low polymerization shrinkage composites without sacrifice to degree of conversion, and mechanical properties of the composites. Experimental composites were prepared by mixing 28.6 wt% of bisphenol-A-glycidyl dimethacrylate based resin matrix (bis-GMA) with various weight-fractions of co-monomers; tricyclo decanedimethanol dacrylate (SR833s) and isobornyl acrylate (IBOA) to 71.4 wt% of particulate-fillers. A composite based on bis-GMA/TEGDMA (triethylene glycol dimethacrylate) was used as a control. Fracture toughness and flexural strength were determined for each experimental material following international standards. Degree of monomer-conversion (DC%) was determined by FTIR spectrometry. The volumetric shrinkage in percent was calculated as a buoyancy change in distilled water by means of the Archimedes’ principle. Polymerization shrinkage-strain and -stress of the specimens were measured using the strain-gage technique and tensilometer, respectively with respect to time. Statistical analysis revealed that control group had the highest double-bond conversion (p < .05) among the experimental resins tested. All of the experimental composite resins had comparable flexural strength, modulus, and fracture toughness (p > .05). Volumetric shrinkage and shrinkage stress decreased with increasing IBOA concentration. Replacing TEGDMA with SR833s and IBOA can decrease the volumetric shrinkage, shrinkage strain, and shrinkage stress of composite resins without affecting the mechanical properties. However, the degree of conversion was also decreased.

The influence of adding modified zirconium oxide-titanium dioxide nano-particles on mechanical properties of orthodontic adhesive: an in vitro study

BACKGROUND

The purpose of this in-vitro study was to examine the effect of incorporating different concentrations of Zirconium oxide-Titanium dioxide (ZrO2-TiO2) nanoparticles, which can have antibacterial properties, on the mechanical properties of an orthodontic adhesive.

METHODS

ZrO2-TiO2 (Zirconium oxide, HWNANO, Hongwu International Group Ltd, China) -Titanium dioxide, Nanoshell, USA) nanopowder were incorporated into orthodontic adhesive (Transbond XT, 3 M Unitek, Monrovia, USA) with different concentrations (0.5% weight nonofiller and 1% weight nanofiller). The size of nanoparticle was 70-80 nm for ZrO2 and less than 50 nm for TiO2. For measuring the shear bond strength of the three groups of orthodontic adhesives [Transbond (control), Transbond mixed with 0.5% weight ZrO2-TiO2, and Transbond mixed with 1% weight ZrO2-TiO2], 30 freshly extracted human first premolars were used and bonded with stainless steel metal brackets (Dentaurum®, Discovery®, Deutschland), using the 3 orthodontic adhesives and 3 M Unitek; Transbond TM Plus Self-Etching Primer (10 samples in each group). The recorded values of compressive strength and tensile strength (measured separately on 10 samples of orthodontic adhesives (add the 3 D size of sample, light cured for 40 s on both sides) of each orthodontic adhesives), as well as the shear bond strength in Mega Pascal unit (MPa) were collected and exposed to one-way analysis of variance (ANOVA) and Tukey's post-hoc tests.

RESULTS

orthodontic adhesive with 1% weight ZrO2-TiO2 showed the highest mean compressive (73.42 ± 1.55 MPa, p: 0.003, F: 12.74), tensile strength (8.65 ± 0.74 MPa, p: 0.001, F: 68.20), and shear bond strength (20.05 ± 0.2 MPa, p: 0.001, F: 0.17).

CONCLUSIONS

Adding ZrO2-TiO2 nanoparticle to orthodontic adhesive increased compressive strength, tensile strength, and shear bond strength in vitro, but in vivo studies and randomized clinical trials are needed to validate the present findings.

Bonding BisGMA to Dentin—a Proof of Concept for Hydrophobic Dentin Bonding

The use of TEGDMA as a diluent comonomer in the formulation of hydrophobic adhesives for ethanol wet-bonding is a concern, due to its leaching potential, higher water sorption, and bio-incompatibility. This study tested the hypothesis that hydrophobic bonding to acid-etched dentin may be accomplished with the use of ethanol-solvated BisGMA only. Phosphoric-acid-etched, oxalate-occluded, deep coronal dentin bonded under 20 cm water pressure with experimental BisGMA adhesives by ethanol wet-bonding exhibited tensile strengths that were not significantly different from that achieved with OptiBond FL bonded according to the manufacturer-recommended protocol, with similar acid-/base-resistant hybrid layers, resin tags, and nanoleakage distribution. Ethanol replacement of water-saturated dentin produced wider interfibrillar spaces, more extensive shrinkage of the collagen fibrils, and narrower hybrid layers. Experimental BisGMA adhesives provide the proof of concept that relatively hydrophobic resins may be coupled to acid-etched dentin by increasing its hydrophobic characteristics via ethanol replacement. They should be further optimized before clinical application.

Synthesis of antibacterial methacrylate monomer derived from thiazole and its application in dental resin

A non-quaternary ammonium antibacterial methacrylate monomer MEMT derived from thiazole was synthesized and applied into UDMA/TEGDMA dental resin with a series of mass fraction (10 wt%, 20 wt%, and 30 wt%). Double bond conversion, polymerization shrinkage, water sorption, solubility, flexural strength and modulus, and antibacterial activity of MEMT containing resin formulations were investigated with UDMA/TEGDMA as control resin. The results showed that MEMT containing dental resin had higher double bond conversion than control resin. Compared with control polymer, all MEMT containing polymer had comparable or lower polymerization shrinkage, water sorption and solubility, except for the polymer with 30 wt% of MEMT which had higher water sorption and solubility than control polymer. The MEMT had no influence on flexural strength and modulus before water immersion, but all MEMT containing polymers had lower flexural strength and modulus than control polymer after water immersion. The MEMT could endow dental polymer with obvious antibacterial activity by immobilizing MEMT into the polymeric network.

Synthesis of antibacterial and radio-opaque dimethacrylate monomers and their potential application in dental resin

OBJECTIVE

In this study, three dimethacrylate quaternary ammonium compounds N,N-bis[2-(3-(methacryloyloxy)propanamido)ethyl]-N-methyldodecyl ammonium iodide (QADMAI-12), N,N-bis[2-(3-(methacryloyloxy)propanamido)ethyl]-N-methylhexadecyl-ammonium iodide (QADMAI-16), and N,N-bis[2-(3-(methacryloyloxy)propanamido)ethyl]-N-methyloctadectyl ammonium iodide (QADMAI-18) were synthesized and proposed to be used as antibacterial and radio-opaque agents in dental resin.

METHODS

All QADMAIs were synthesized through a 2-steps reaction route, and their structures were confirmed by FT-IR and 1H NMR spectra. Antibacterial activities against Streptococcus mutans (S. mutans) of QADMAIs were measured by agar diffusion test. Each QADMAI was mixed with TEGDMA (50/50, w/w) and photoinitiation system (0.7 wt% of CQ and 0.7 wt% of DMAEMA) to form resin system. Degree of monomer conversion (DC) was determined by FT-IR analysis. The flexural strength (FS) and modulus (FM) of the polymer were measured using a three-point bending set up. Radiograph was taken to determine the radio-opacity of the polymer, and aluminum step-wedge (0.5-4 mm) was used as calibration standard. Surface charge density was measured using fluorescein binding. A single-species biofilm model with S. mutans as the tests organism was used to evaluate the antibacterial property of the polymer. Bis-GMA/TEGDMA resin system was used as control material in all of the tests.

RESULTS

FT-IR and 1H NMR spectra showed that the structures of QADMAIs were the same as designed. ANOVA analysis revealed that antibacterial activity of QADMAI decreased with the increasing of alkyl chain length (p<0.05). QADMAI containing polymers had higher DC (p<0.05) but lower FS and FM (p<0.05) than control polymer. Alkyl chain length had no influence on DC (p>0.05), but FS and FM of QADMAI-12 containing polymer were better than those of QADMAI-16 and QADMAI-18 containing polymers (p<0.05). QADMAI containing polymers had much better radio-opacity than control polymer (p<0.05), and the radio-opacity of polymer decreased with the increasing of alkyl chain length (p<0.05). All of QADMAIs containing polymers had higher surface charge density than control polymer (p<0.05), and surface charge densities of QADMAI-12 and QADMAI-16 containing polymers were nearly the same (p>0.05) which were higher than that of QADMAI-18 containing polymer (p<0.05). All of QADMAI containing polymers had good inhibitory effect on biofilm formation.

SIGNIFICANCE

QADMAIs had no miscibility problem with TEGDMA, and QADMAIs could endow dental resin with both antibacterial activity and radio-opacity. Formulation of QADMAI containing resin should be optimized in terms of mechanical stregth to satisfy the requirements of dental resin for clinical application.

Preparation and evaluation of dental resin with antibacterial and radio-opaque functions

In order to prepare antibacterial and radio-opaque dental resin, a methacrylate monomer named 2-Dimethyl-2-dodecyl-1-methacryloxyethyl ammonium iodine (DDMAI) with both antibacterial and radio-opaque activities was added into a 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropyl)-phenyl]propane (Bis-GMA)/methyl methacrylate (MMA) dental resin system. Degree of conversion (DC), flexural strength (FS) and modulus (FM), water sorption (WS) and solubility (WSL), antibacterial activity, and radio-opacity (ROX) of the obtained dental resin system were investigated. Bis-GMA/MMA resin system without DDMAI was used as a control. The results showed that DDMAI could endow BIS-GMA/MMA resin system with good antibacterial (p < 0.05) and radio-opaque function without influencing the DC (p > 0.05). However, incorporating DDMAI into Bis-GMA/MMA resin could reduce mechanical properties (p < 0.05) and increase WS and WSL (p < 0.05), thus further work is needed in order to optimize the resin formulation.

Wear model simulating clinical abrasion on composite filling materials

The aim of this study was to establish a wear model for testing composite filling materials with abrasion properties closer to a clinical situation. In addition, the model was used to evaluate the effect of filler volume and particle size on surface roughness and wear resistance. Each incisor tooth was prepared with nine identical standardized cavities with respect to depth, diameter, and angle. Generic composite of 3 different filler volumes and 3 different particle sizes held together with the same resin were randomly filled in respective cavities. A multidirectional wet-grinder with molar cusps as antagonist wore the surface of the incisors containing the composite fillings in a bath of human saliva at a constant temperature of 37°C. The present study suggests that the most wear resistant filling materials should consist of medium filling content (75%) and that particles size is not as critical as earlier reported.

Recent advances and developments in composite dental restorative materials

Composite dental restorations represent a unique class of biomaterials with severe restrictions on biocompatibility, curing behavior, esthetics, and ultimate material properties. These materials are presently limited by shrinkage and polymerization-induced shrinkage stress, limited toughness, the presence of unreacted monomer that remains following the polymerization, and several other factors. Fortunately, these materials have been the focus of a great deal of research in recent years with the goal of improving restoration performance by changing the initiation system, monomers, and fillers and their coupling agents, and by developing novel polymerization strategies. Here, we review the general characteristics of the polymerization reaction and recent approaches that have been taken to improve composite restorative performance.

Evaluation of new tri-methacrylates as a reactive diluent in root canal sealant

In this work, a novel tri-methacrylate oligomer, GPTEMA, with three long-branched chain structures was synthesized through the reaction of glycerol propoxylate triglycidyl ether (GPTE) and methacrylic acid. The structure of GPTEMA was confirmed by FT-IR, (1)H-NMR, gel-permeation chromatography (GPC) and element analysis. The GPTEMA was used to partially or completely replace TEGDMA as reactive diluent and applied in a root canal sealant system containing Bis-GMA. The effects of GPTEMA on the polymerization behavior of Bis-GMA/TEGDMA/GPTEMA co-polymer and properties of its polymerizing product were investigated. Polymerization shrinkage, double bond conversion, glass transition temperature, flexural strength, flexural modulus, water sorption and diffusion coefficient of the Bis-GMA/TEGDMA/GPTEMA co-polymer were measured. The results illustrated that the Bis-GMA/TEGDMA/GPTEMA co-polymer attained lower polymerization shrinkage and higher double bond conversion. However, its T g, flexural strength and flexural modulus decreased with increasing content of GPTEMA, water sorption and diffusion coefficient increased with increasing content of GPTEMA.