NMR characterization of the formation kinetics and structure of di-O-benzylidene sorbitol gels self-assembled in organic solvents.

The molecule 1,3:2,4-di-O-benzylidene sorbitol (DBS) is a common "gelator" that forms thermally reversible gels in diverse organic solvents. Solid-state (13)C and (1)H NMR techniques, along with electron microscopy, are utilized in an exploratory study of DBS in the gelled state where we consider both in situ and dried gels. The gels were formed in either acetone or benzene, with the former being a better solvent for DBS. We find the in situ or dried DBS gels to be composed of rigid twisted nanofibrils (∼15 to 21 nm in diameter). The fibrils show local molecular ordering, but not crystalline order, and they contain no trapped solvent. The molecular mobility at the fibril surface is modestly enhanced, and all the free hydroxyl groups of the sorbitol moiety are involved in strong hydrogen bonding. We also attempted to find a truly crystalline form of DBS whose structure, as judged by the similarity of (13)C spectra, is close to that of the fibrils. We partially succeeded in this quest, employing melt crystallization followed by slow cooling. However, this sample was a mixed crystal having small domains, where only one type of domain was structurally similar to the fibrils. We also investigated the long-time evolution of the in situ DBS gel network. Specifically, high-resolution NMR kinetic studies were performed over periods of days where the residual concentration of DBS in acetone solution was monitored during and after gel formation. The DBS concentration on these long timescales evolved slowly, and we introduce a simple mathematical model and equation to describe this phenomenon.

Interphase effects in dental nanocomposites investigated by small-angle neutron scattering.

Small-angle and ultrasmall-angle neutron scattering (SANS and USANS) were used to characterize silica nanoparticle dispersion morphologies and the interphase in thermoset dimethacrylate polymer nanocomposites. Silica nanoparticle fillers were silanized with varying mass ratios of 3-methacryloxypropyltrimethoxysilane (MPTMS), a silane that interacts with the matrix through covalent and H-bonding, and n-octyltrimethoxysilane (OTMS), a silane that interacts through weak dispersion forces. Interphases with high OTMS mass fractions were found to be fractally rough with fractal dimensions, D(s), between 2.19 and 2.49. This roughness was associated with poor interfacial adhesion and inferior mechanical properties. Mean interparticle distances calculated for composites containing 10 mass % and 25 mass % silica suggest that the nanoparticles treated with more MPTMS than OTMS may be better dispersed than OTMS-rich nanoparticles. The results indicate that the covalent bonding and H-bonding of MPTMS-rich nanoparticles with the matrix are necessary for preparing well-dispersed nanocomposites. In addition, interphases containing equal masses of MPTMS and OTMS may yield composites with overall optimal properties. Finally, the combined SANS/USANS data could distinguish the differences, as a function of silane chemistry, in the nanoparticle/silane and silane/matrix interfaces that affect the overall mechanical properties of the composites.

The use of amorphous calcium phosphate composites as bioactive basing materials: their effect on the strength of the composite/adhesive/dentin bond.

BACKGROUND: Amorphous calcium phosphate (ACP) composites release calcium and phosphate ions in aqueous environments, which may lead to deposition of apatitic mineral in tooth structure. The authors evaluate the strength of the composite/adhesive/dentin bond shear bond strength (SBS) for ACP basing-composites after various periods of water aging. METHODS: The authors made the experimental composites by using two resin matrices with various ACPs or a commercial strontium ion-leachable glass. They applied successive coats of a dentin adhesive and basing composite to an acid-etched dentin surface and photopolymerized them. They added a commercial resin-based composite and light cured it. They determined the specimens' SBS after they were aged in water for various periods at 37 degrees C. RESULTS: The SBS of the ACP composites was 18.3 +/- 3.5 megapascals, independent of filler type, resin composition and water-aging interval. After 24 hours of water aging, 92.6 percent of surfaces showed the adhesive failure. After two weeks of water aging, adhesive/cohesive failures were predominant in unmilled and milled ACP composites. CONCLUSIONS: The SBS of ACP composites appears to be unaffected by filler type or immersion time for up to six months. The type of adhesive failure occurring with prolonged aqueous exposure is affected by filler type. CLINICAL IMPLICATIONS: These materials may be effective remineralizing/antidemineralizing agents and may be clinically applicable as adhesives, protective liners and bases, orthodontic cements and pit-and-fissure sealants.

The effects of two monofunctional diluent monomers and two photoinitiator systems on the properties of UDMA-based composites.

PURPOSE: To compare the effects of two types of monofunctional co-monomers and two types of photoinitiator systems on the properties of urethane dimethacrylate (UDMA) based dental restorative composites. METHODS: The resin blends consisted of UDMA and a diluent co-monomer at a molar ratio of 9:1. The diluent comonomers were neo-decyl vinyl ester (Neo 10) or n-hexyl methacrylate (HMA). The photoinitiator system consisted of a bis-acyl phosphine oxide (BAPO) or camphorquinone plus ethyl 4-(dimethylamino)benzoate (CQ/4E). Each initiator system was utilized at 1% or 2% by mass of the resin blend. These resin blends were mixed by hand with silanized zirconia glass (85.7% by mass) to make the various composites. Flexural strength (FS) specimens, made from these pastes by visible light photopolymerization, were tested to failure after 24 hours water storage. Mercury dilatometry was used to evaluate the shrinkage, and the degree of double bond conversion was evaluated using near infrared spectroscopy (NIR). The first hypothesis tested was that use of Neo 10 in a UDMA composite would not have an effect on properties compared to the methacrylate HMA. The second hypothesis tested was that the BAPO initiator would not have an effect on the properties of a UDMA-based composite compared to the CQ/4E initiator. RESULTS: The hypotheses were tested at alpha = 0.05 and beta = 0.20. The major finding was that the lower level (1% by mass) of BAPO resulted in lower FS, lower conversion and lower shrinkage (rejecting the hypothesis that there was no difference due to initiator used) than composites formulated with the higher level of this initiator or either level of the CQ/4E initiator system, regardless of the comonomer used. The effects of two comonomers used were not differentiated in this study with respect to the properties examined (accepting the hypothesis that there was no difference due to diluent monomer).

Surface treatment with N,N'-dimethacryloylcystine for enhanced bonding of resin to dental alloys.

The aim of this study was to develop an effective primer to improve the adhesive property between all kinds of dental metal alloy and resin cement. To this end, we synthesized N,N'-dimethacryloylcystine (NDMCC) which had both disulfide functional group (to improve adhesion between precious metal alloy and resin) and carboxyl group (to improve adhesion between non-precious metal alloy and resin). With the presence of SuperBond C&B, the adhesion between precious, semi-precious, and non-precious dental metal alloys and resin cement was improved when compared to the untreated controls. However, the adhesive property between all types of dental metal alloy and resin cement was not improved with Panavia 21EX. In particular, reduced bond strength in the case of non-precious metal alloy was speculated to arise from the acid-base neutralization reaction between the carboxyl group of NDMCC and the amine present in the polymerization initiator system of Panavia 21EX.

Ethoxylated bisphenol dimethacrylate-based amorphous calcium phosphate composites.

Improving the anti-demineralizing/remineralizing and mechanical properties of amorphous calcium phosphate (ACP) composites has been the focus of our recent research. In this study, an ethoxylated bisphenol A dimethacrylate (EBPADMA) was blended with triethylene glycol dimethacrylate (TEGDMA), 2-hydroxyethyl methacrylate (HEMA) and methacryloxyethyl phthalate (MEP) to form experimental resins with different EBPADMA/TEGDMA molar ratios (0.50, 0.85 and 1.35) and a constant HEMA/MEP molar ratio (8.26). Composites were prepared by admixture of either unmilled or milled zirconia-ACP filler (40% by mass) and photo-activated resin (60% by mass). One aim was to test if improved ion release can be achieved by elevating the EBPADMA/TEGDMA ratio while lowering the level of surface active methacryloxyethyl phthalate in the resin without adversely affecting the biaxial flexure strength (BFS), degree of vinyl conversion (DC) and water sorption (WS) of composites. A second aim was to assess the effect of using milled vs. unmilled ACP on these properties. Ion release of all composites was significantly above the theoretical minimum necessary for remineralization. Calcium ion release was not impeded by binding with the carboxylic acid groups of MEP. Increased supersaturation was attained with increasing EBPADMA/TEGDMA ratio in the resin. Variations in resin composition had no effect on BFS or DC of composites. The BFS of the milled ACP composites was higher than the BFS of unmilled ACP composites (56% and 79%, respectively for dry and wet specimens). DC of composites was only moderately reduced (13.6% and 7.3%, for unmilled and milled ACP, respectively) compared to unfilled resins. WS decreased in the following order: unmilled ACP composites>milled ACP composites>copolymers. Fine-tuning of the resin and utilizing milled ACP filler improved the remineralizing potential of ACP composites without impeding their DC, BFS or WS.

Interphase structure-property relationships in thermoset dimethacrylate nanocomposites.

OBJECTIVES: The aim of this research was to better understand the relationships between interphase composition and the resultant mechanical properties of thermoset methacrylate nanocomposites, ultimately for the purpose of improving the properties of dental restorative materials through manipulation of the interphase. METHODS: Silica nanoparticles were silanized with three different silanes and blends of those silanes to generate six different interphase compositions. The silanes varied in their relative polarity, flexibility, and reactivity towards photo-polymerization. Composites containing 60% by mass of the silanized fillers were prepared and analyzed for uncured paste handling characteristics, vinyl conversion, biaxial flexure strength (BFS), modulus, and Knoop hardness. RESULTS: Dual silanization of the fillers improved the handling characteristics of the uncured composite pastes compared to those containing fillers silanized with 3-methacryloxypropyltrimethoxysilane. To obtain high BFS, functional groups reactive in free radical polymerization were needed in the composite interphase, but a high concentration of those groups was not necessary. Moduli were highest for composites with interphases that contained styrylethyltrimethoxysilane, a reactive aromatic silane. The hardness values of the composites with reactive interphases were all comparable. Methacrylate conversion was only modestly influenced by silane interphase composition. SIGNIFICANCE: This study suggests that dual silanization is a practical method for improving the handling characteristics of uncured dental restorative nanocomposites while maintaining or improving the mechanical properties of the cured composites.

Polymeric dental composites based on remineralizing amorphous calcium phosphate fillers.

For over two decades we have systematically explored structure-composition-property relationships of amorphous calcium phosphate (ACP)-based polymeric dental composites. The appeal of these bioactive materials stems from their intrinsic ability to prevent demineralization and/or restore defective tooth structures via sustained release of remineralizing calcium and phosphate ions. Due to the compositional similarity of the ACP to biological tooth mineral, ACP-based composites should exhibit excellent biocompatibility. Research described in this article has already yielded remineralizing sealants and orthodontic adhesives as well as a prototype root canal sealer. Our work has also contributed to a better understanding on how polymer matrix structure and filler/matrix interactions affect the critical properties of these polymeric composites and their overall performance. The addition of antimicrobial compounds to the formulation of ACP composites could increase their medical and dental regenerative treatment applications, thereby benefiting an even greater number of patients.

Novel rechargeable calcium phosphate dental nanocomposite.

OBJECTIVES: Calcium phosphate (CaP) composites with Ca and P ion release can remineralize tooth lesions and inhibit caries. But the ion release lasts only a few months. The objectives of this study were to develop rechargeable CaP dental composite for the first time, and investigate the Ca and P recharge and re-release of composites with nanoparticles of amorphous calcium phosphate (NACP) to achieve long-term inhibition of caries. METHODS: Three NACP nanocomposites were fabricated with resin matrix of: (1) bisphenol A glycidyl dimethacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) at 1:1 mass ratio (referred to as BT group); (2) pyromellitic glycerol dimethacrylate (PMGDM) and ethoxylated bisphenol A dimethacrylate (EBPADMA) at 1:1 ratio (PE group); (3) BisGMA, TEGDMA, and Bis[2-(methacryloyloxy)ethyl] phosphate (BisMEP) at 2:1:1 ratio (BTM group). Each resin was filled with 20% NACP and 50% glass particles, and the composite was photo-cured. Specimens were tested for flexural strength and elastic modulus, Ca and P ion release, and Ca and P ion recharge and re-release. RESULTS: NACP nanocomposites had strengths 3-fold of, and elastic moduli similar to, commercial resin-modified glass ionomer controls. CaP ion recharge capability was the greatest for PE group, followed by BTM group, with BT group being the lowest (p<0.05). For each recharge cycle, CaP re-release reached similarly high levels, showing that CaP re-release did not decrease with more recharge cycles. After six recharge/re-release cycles, NACP nanocomposites without further recharge had continuous CaP ion release for 42 d. SIGNIFICANCE: Novel rechargeable CaP composites achieved long-term and sustained Ca and P ion release. Rechargeable NACP nanocomposite is promising for caries-inhibiting restorations, and the Ca and P ion recharge and re-release method has wide applicability to dental composites, adhesives, cements and sealants to achieve long-term caries-inhibition.

Novel Dental Cement to Combat Biofilms and Reduce Acids for Orthodontic Applications to Avoid Enamel Demineralization.

Orthodontic treatments often lead to biofilm buildup and white spot lesions due to enamel demineralization. The objectives of this study were to develop a novel bioactive orthodontic cement to prevent white spot lesions, and to determine the effects of cement compositions on biofilm growth and acid production. 2-methacryloyloxyethyl phosphorylcholine (MPC), nanoparticles of silver (NAg), and dimethylaminohexadecyl methacrylate (DMAHDM) were incorporated into a resin-modified glass ionomer cement (RMGI). Enamel shear bond strength (SBS) was determined. Protein adsorption was determined using a micro bicinchoninic acid method. A dental plaque microcosm biofilm model with human saliva as inoculum was used to investigate metabolic activity, colony-forming units (CFU) and lactic acid production. Incorporating 3% of MPC, 1.5% of DMAHDM, and 0.1% of NAg into RMGI, and immersing in distilled water at 37 °C for 30 days, did not decrease the SBS, compared to control (p > 0.1). RMGI with 3% MPC + 1.5% DMAHDM + 0.1% NAg had protein amount that was 1/10 that of control. RMGI with triple agents (MPC + DMAHDM + NAg) had much stronger antibacterial property than using a single agent or double agents (p < 0.05). Biofilm CFU on RMGI with triple agents was reduced by more than 3 orders of magnitude, compared to commercial control. Biofilm metabolic activity and acid production were also greatly reduced. In conclusion, adding MPC + DMAHDM + NAg in RMGI substantially inhibited biofilm viability and acid production, without compromising the orthodontic bracket bond strength to enamel. The novel bioactive cement is promising for orthodontic applications to hinder biofilms and plaque buildup and enamel demineralization.

Systematic variation of interfacial phase reactivity in dental nanocomposites.

This study was designed to determine the effect of varying the chemistry of the interfacial phase on critical composite properties in dental nanocomposite materials. Silica nanoparticles were silanized with varying ratios of 3-methacryloxypropyltrimethoxysilane (MPTMS) and octyltrimethoxysilane (OTMS) while keeping the total amount of silane constant at 10% by mass fraction relative to the mass of filler. The silanized nanoparticles were mixed into a dimethacrylate resin (60% filler by mass fraction). The mechanical properties of the uncured pastes were assessed by compression testing between parallel plates. The composites were photo-cured and tested by biaxial flexure and three-point bend flexure testing. Fracture surfaces were analyzed by field-emission scanning electron microscopy (FE-SEM). At maximized filler mass fractions, the workabilities of the uncured pastes were better maintained as the fraction of OTMS in the interphase increased relative to MPTMS. The flexure strengths and moduli of the MPTMS silanized and dual silanized composites were similar but decreased as OTMS mass fractions in the silane mixture increased to 7.5% and 10%. FE-SEM images revealed evidence for phase separation in the composites containing silica silanized with high fractions of OTMS. Among the potential practical benefits of dual silanized nanoparticles are the improved workability of composite pastes with higher filler loadings that should lead to higher modulus composites with lower polymerization shrinkage.

Chemistry of Silanes: Interfaces in Dental Polymers and Composites.

The performance and service life of glass-or ceramic-filled polymeric composites depend on the nature of their resin, filler and interfacial phases as well as the efficacy of the polymerization process. The synergy that exists between the organic polymer matrix and the usually inorganic reinforcing filler phase is principally mediated by the interfacial/interphasial phase. This latter phase develops as a result of the dual reactivity of a silane coupling agent, (YRSiX3), a bifunctional molecule capable of reacting with the silanol groups of glass or ceramic fillers via its silane functional group (-SiX3) to form Si-O-Si- bonds to filler surfaces, and also with the resin phase by graft copolymerization via its Y functional group, usually a methacrylic vinyl group. In this paper, we explore some of the chemistry of organosilanes, especially that of functional organosilanes (or silane coupling agents as they are commonly known) that are used to mediate interfacial bonding in mineral reinforced polymeric composites. The chemistry of organosilanes can be quite complex involving hydrolytically initiated self-condensation reactions in solvents (including monomers) that can culminate in polymeric silsesquioxane structures, exchange reactions with hydroxylated or carboxylated monomers to form silyl ethers and esters, as well as the formation of silane derived interfaces by adhesive coupling with siliceous mineral surfaces.

Effect of bifunctional comonomers on mechanical strength and water sorption of amorphous calcium phosphate- and silanized glass-filled Bis-GMA-based composites.

This study seeks to elucidate structure-property relationships in a series of unfilled dental copolymers and their composites. The copolymers/composites were derived from photo-activated binary monomer systems based on 2,2-bis[p-2'-hydroxy-3'-methacryloxypropoxy)phenyl] propane (Bis-GMA) and equimolar amounts of a bifunctional, surface-active comonomer, i.e., 2-hydroxyethyl methacrylate (HEMA), glycerol dimethacrylate (GDMA) or ethylene glycol methacrylate phosphate (PHEMA). Triethyleneglycol dimethacrylate, a widely used comonomer for Bis-GMA, was used as a control. Two types of fillers were investigated: (1) a hydrophilic, silica-modified amorphous calcium phosphate (Si-ACP) and (2) a more hydrophobic, silanized nanosized silica (n-SiO(2)). Both the unfilled copolymers and their composites were evaluated for biaxial flexure strength (BFS), both dry and wet after 30 days immersion in buffered saline, and for water sorption (WS) and their WS kinetic profiles. The Bis-GMA copolymers and composites derived from HEMA and GDMA had BFS and WS values, as well as WS kinetic profiles, similar to the controls. Copolymers and composites based on Bis-GMA/PHEMA had lower BFS and higher WS values. Si-ACP composites had significantly lower BFS values (that were further diminished on soaking) than their copolymers. WS increased as the level of this filler was increased except for Bis-GMA/PHEMA composites. With n-SiO(2) as the filler, a more moderate reduction in BFS occurred compared to the unfilled copolymers. By contrast to Si-ACP composites, the WS of all the n-SiO(2) composites decreased with increasing filler level. From this study it is evident that both the chemical structure of the polymer matrix and the type of filler system can have significant effects on the strength and water-related properties of dental composites.

Dental resin composites containing silica-fused whiskers--effects of whisker-to-silica ratio on fracture toughness and indentation properties.

Dental resin composites need to be strengthened in order to improve their performance in large stress-bearing applications such as crowns and multiple-unit restorations. Recently, silica-fused ceramic whiskers were used to reinforce dental composites, and the whisker-to-silica ratio was found to be a key microstructural parameter that determined the composite strength. The aim of this study was to further investigate the effects of whisker-to-silica ratio on the fracture toughness, elastic modulus, hardness and brittleness of the composite. Silica particles and silicon carbide whiskers were mixed at whisker:silica mass ratios of 0:1, 1:5. 1:2, 1:1, 2:1, 5:1, and 1:0. Each mixture was thermally fused, silanized and combined with a dental resin at a filler mass percentage of 60%. Fracture toughness was measured with a single-edge notched beam method. Elastic modulus and hardness were measured with a nano-indentation system. Whisker:silica ratio had significant effects on composite properties. The composite toughness (mean+/-SD; n = 9) at whisker:silica = 2:1 was (2.47+/-0.28) MPa m(1/2), significantly higher than (1.02+/-0.23) at whisker:silica = 0:1, (1.13+/-0.19) of a prosthetic composite control, and (0.95+/-0.11) of an inlay/onlay composite control (Tukey's at family confidence coefficient = 0.95). Elastic modulus increased monotonically and hardness plateaued with increasing the whisker:silica ratio. Increasing the whisker:silica ratio also decreased the composite brittleness, which became about 1/3 of that of the inlay:onlay control. Electron microscopy revealed relatively flat fracture surfaces for the controls, but much rougher ones for the whisker composites, with fracture steps and whisker pullout contributing to toughness. The whiskers appeared to be well-bonded with the matrix, probably due to the fused silica producing rough whisker surfaces. Reinforcement with silica-fused whiskers resulted in novel dental composites that possessed fracture toughness two times higher than, and brittleness less than half of current dental composites.

A microshear test to measure bond strengths of dentin-polymer interfaces.

The microbond test. a single fiber shear test, has been adapted to be a microshear test for the measurement of the adhesion of resin-based dental materials to dentin and enamel. The objective of this study is to improve the design of this microshear test so that it can provide accurate and reliable shear bond strength data. In the current design of the microshear test apparatus, the bonding diameters of the specimens have been as small as 0.70 mm. The smaller diameters give researchers the ability to test several bonded specimens on one flat dentin or enamel surface, thus allowing both for the regional mapping of the mineralized surface and the conservation of extracted teeth needed to provide the necessary substrates. The test corfiguration used in earlier studies has been modified through finite element analysis to address concerns in the test methodology. The results of this study show that the microshear bond test can be a useful tool in helping to understand the complex interactions that occur at the interface between dental composites and dentin and/or enamel surfaces, especially at interfacial sites not amenable to macroshear testing.

Synthesis, characterization and evaluation of urethane derivatives of Bis-GMA.

OBJECTIVES: The aims of the study were to synthesize derivatives of Bis-GMA having pendant n-alkyl urethane substituents and to characterize and evaluate their physicochemical properties. METHODS: Stoichiometric amounts of Bis-GMA and n-alkyl isocyanates were reacted in dichloromethane with dibutyltin dilaurate as a catalyst. Volumetric shrinkage, water uptake, degree of vinyl conversion, refractive index and viscosity of resulting urethane monomers and those of Bis-GMA were measured. The flexural strengths of their corresponding homopolymers and that of Bis-GMA were also measured. RESULTS: These types of urethane derivatives of Bis-GMA exhibited lower viscosities and were more hydrophobic than Bis-GMA. Generally, the viscosity of these experimental monomers decreased with increasing chain length of the alkyl urethane substituent. Photopolymerization of the new monomers gave high degrees of vinyl conversion compared to Bis-GMA. The experimental monomers also yielded polymers with lower polymerization shrinkages at equivalent degrees of vinyl conversion, than Bis-GMA. The refractive indices of these urethane derivatives were similar to Bis-GMA, but the flexural strengths of their polymers were lower than that of the Bis-GMA homopolymer, decreasing with increasing chain length of the alkyl urethane substituent. SIGNIFICANCE: Because of their excellent overall properties, these new derivatives of Bis-GMA have potential as dental monomers that can improve many properties of resin based dental materials that utilize methacrylate monomer systems.

Structural and dynamical studies of acid-mediated conversion in amorphous-calcium-phosphate based dental composites.

OBJECTIVE: To investigate the complex structural and dynamical conversion process of the amorphous-calcium-phosphate (ACP)-to-apatite transition in ACP based dental composite materials. METHODS: Composite disks were prepared using zirconia hybridized ACP fillers (0.4 mass fraction) and photo-activated Bis-GMA/TEGDMA resin (0.6 mass fraction). We performed an investigation of the solution-mediated ACP-to-apatite conversion mechanism in controlled acidic aqueous environment with in situ ultra-small angle X-ray scattering based coherent X-ray photon correlation spectroscopy and ex situ X-ray diffraction, as well as other complementary techniques. RESULTS: We established that the ACP-to-apatite conversion in ACP composites is a two-step process, owing to the sensitivity to local structural changes provided by coherent X-rays. Initially, ACP undergoes a local microstructural rearrangement without losing its amorphous character. We established the catalytic role of the acid and found the time scale of this rearrangement strongly depends on the pH of the solution, which agrees with previous findings about ACP without the polymer matrix being present. In the second step, ACP is converted to an apatitic form with the crystallinity of the formed crystallites being poor. Separately, we also confirmed that in the regular Zr-modified ACP the rate of ACP conversion to hydroxyapatite is slowed significantly compared to unmodified ACP, which is beneficial for targeted slow release of functional calcium and phosphate ions from dental composite materials. SIGNIFICANCE: For the first time, we were able to follow the complete solution-mediated transition process from ACP to apatite in this class of dental composites in a controlled aqueous environment. A two-step process, suggested previously, was conclusively identified.

Evaluation of three-dimensional biofilms on antibacterial bonding agents containing novel quaternary ammonium methacrylates.

Antibacterial adhesives are promising to inhibit biofilms and secondary caries. The objectives of this study were to synthesize and incorporate quaternary ammonium methacrylates into adhesives, and investigate the alkyl chain length effects on three-dimensional biofilms adherent on adhesives for the first time. Six quaternary ammonium methacrylates with chain lengths of 3, 6, 9, 12, 16 and 18 were synthesized and incorporated into Scotchbond Multi-Purpose. Streptococcus mutans bacteria were cultured on resin to form biofilms. Confocal laser scanning microscopy was used to measure biofilm thickness, live/dead volumes and live-bacteria percentage vs. distance from resin surface. Biofilm thickness was the greatest for Scotchbond control; it decreased with increasing chain length, reaching a minimum at chain length 16. Live-biofilm volume had a similar trend. Dead-biofilm volume increased with increasing chain length. The adhesive with chain length 9 had 37% live bacteria near resin surface, but close to 100% live bacteria in the biofilm top section. For chain length 16, there were nearly 0% live bacteria throughout the three-dimensional biofilm. In conclusion, strong antibacterial activity was achieved by adding quaternary ammonium into adhesive, with biofilm thickness and live-biofilm volume decreasing as chain length was increased from 3 to 16. Antibacterial adhesives typically only inhibited bacteria close to its surface; however, adhesive with chain length 16 had mostly dead bacteria in the entire three-dimensional biofilm. Antibacterial adhesive with chain length 16 is promising to inhibit biofilms at the margins and combat secondary caries.

Effects of dual antibacterial agents MDPB and nano-silver in primer on microcosm biofilm, cytotoxicity and dentine bond properties.

OBJECTIVES: The objective of this study was to investigate the effects of dentine primer containing dual antibacterial agents, namely, 12-methacryloyloxydodecylpyridinium bromide (MDPB) and nanoparticles of silver (NAg), on dentine bond strength, dental plaque microcosm biofilm response, and fibroblast cytotoxicity for the first time. METHODS: Scotchbond Multi-Purpose (SBMP) was used as the parent bonding agent. Four primers were tested: SBMP primer control (referred to as "P"), P+5% MDPB, P+0.05% NAg, and P+5% MDPB+0.05% NAg. Dentine shear bond strengths were measured using extracted human teeth. Biofilms from the mixed saliva of 10 donors were cultured to investigate metabolic activity, colony-forming units (CFU), and lactic acid production. Human fibroblast cytotoxicity of the four primers was tested in vitro. RESULTS: Incorporating MDPB and NAg into primer did not reduce dentine bond strength compared to control (p>0.1). SEM revealed well-bonded adhesive-dentine interfaces with numerous resin tags. MDPB or NAg each greatly reduced biofilm viability and acid production, compared to control. Dual agents MDPB+NAg had a much stronger effect than either agent alone (p<0.05), increasing inhibition zone size and reducing metabolic activity, CFU and lactic acid by an order of magnitude, compared to control. There was no difference in cytotoxicity between commercial control and antibacterial primers (p>0.1). CONCLUSIONS: The method of using dual agents MDPB+NAg in the primer yielded potent antibacterial properties. Hence, this method may be promising to combat residual bacteria in tooth cavity and invading bacteria at the margins. The dual agents MDPB+NAg may have wide applicability to other adhesives, composites, sealants and cements to inhibit biofilms and caries.

Ultra-small-angle X-ray scattering-X-ray photon correlation spectroscopy studies of incipient structural changes in amorphous calcium phosphate-based dental composites.

The local structural changes in amorphous calcium phosphate (ACP)-based dental composites were studied under isothermal conditions using both static, bulk measurement techniques and a recently developed methodology based on combined ultra-small angle X-ray scattering-X-ray photon correlation spectroscopy (USAXS-XPCS), which permits a dynamic approach. While results from conventional bulk measurements do not show clear signs of structural change, USAXS-XPCS results reveal unambiguous evidence for local structural variations on a similar time scale to that of water loss in the ACP fillers. A thermal-expansion-based simulation indicates that thermal behavior alone does not account for the observed dynamics. Together, these results suggest that changes in the water content of ACP affect the composite morphology due to changes in ACP structure that occur without an amorphous-to-crystalline conversion. It is also noted that biomedical materials research could benefit greatly from USAXS-XPCS, a dynamic approach.