Characterization of the bioactivity of two commercial composites

The aim of this study was to characterize the ion release, pH changes and apatite formation ability of two potentially bioactive composites Cention N (CN) and Activa (ACT). Ion release and apatite formation was investigated in three different immersion media: Tris buffer pH 7.3 (TB), Artificial Saliva pH 4 (AS4) and Artificial Saliva pH 7 (AS7) in order to mimic the conditions present in the mouth. Fluoride release was followed using an ion selective electrode, whilst all other ions were determined by inductively coupled plasma optical emission spectroscopy. Apatite formation was followed by FTIR and XRD. SEM was used to follow glass degradation and apatite formation on both polished cross-sections and surfaces of the composites.ACT released very few ions including fluoride upon immersion in TB and AS7, but released more ions including significant quantities of Al in AS4. This would suggest the glasses in ACT are acid degradable fluoro-alumino-silicate glasses similar to the glasses used in glass ionomer cements. There was no evidence of any apatite formation with ACT.CN released more ions in TB and AS7 than ACT and formed an apatite like phase in AS7. The calcium fluoro-silicate glass in CN was observed to degrade significantly in AS4. CN has bioactive properties that may explain the low incidence of secondary caries found clinically with this composite.     

Remineralising fluorine containing bioactive glass composites

ObjectivesThe objective was to investigate the mechanical properties, fluoride release and apatite formation of resin based dental composites based on a fluoride containing Bioactive Glass (BG) with and without a silylating agent.MethodsA SiO₂–P₂O₅–CaO–SrO–Na₂O–CaF₂ BG was synthesized by the melt quench route. This glass and a commercially available inert glass (IG) were incorporated into a light cured BisGMA-TEGMA resin. The composite resins were then evaluated in terms of their ability to form apatite by Fourier Transform Infrared spectroscopy (FTIR) and by scanning electron microscopy (SEM) following immersion in artificial saliva at pH 4 (AS4) and pH 7 (AS7). The experiments were performed with and without silylation of the BG. The compressive strength and flexural strength were determined after 1, 28 and 84 days of immersion in the AS4 and AS7 immersion media.ResultsThe FTIR spectra of the BG composites exhibited split bands at approximately 560 and 600 cm^?1 corresponding to a apatite formation in the surface or on the surface under all immersion conditions. SEM showed the presence of a reacted layer of glass particles in the composite surface and the presence of a surface layer of apatite in AS7.The compressive strength and flexural strength were significantly higher for the silylated BG composites. The strengths of both silylated and non silylated BG composites and IG composites decreased upon immersion.SignificanceBG composites exhibit reduced strengths upon immersion but still exhibit strengths comparable to existing composites after 84 days of immersion.     

A comparative evaluation of ion release characteristics of three different dental varnishes containing fluoride either with CPP-ACP or bioactive glass

ObjectiveTo compare ion release characteristics of three different dental varnishes either containing CPP-ACP and fluoride (CPP-ACPF, MI Varnish GC, Japan), bioactive glass and fluoride (BGAF, Dentsply Sirona USA) or fluoride alone (NUPRO White, Dentsply Sirona USA) using fluoride-Ion Selective Electrode (F-ISE), Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), ¹⁹F and ³¹P Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR).MethodsA thin layer (0.0674 ± 0.0005 g) of each varnish (20 × 25 mm in area) was spread on a roughened glass slide (n = 7). They were separately immersed in 10 ml Tris buffer (0.06 M, pH = 7.30), and changed after 1, 2, 4, 6, 24 and 48 h. Fluoride-ion concentration at each time using the F-ISE, whilst calcium and phosphate release were investigated using ICP-OES. XRD, FTIR. MAS-NMR analyses were also performed before and after immersion.ResultsThe cumulative F-ion release was significantly higher in CPP-ACPF (1.113 mmol/g) > BGAF(0.638) > F(0.112) (p < 0.001). The cumulative calcium and phosphorus were higher in the CPP-ACPF (0.137 mmol/g, 0.119) than BGAF (0.067, 0.015) (p < 0.001) respectively. The XRD and ¹⁹F MAS-NMR confirmed the presence of NaF peaks in all cases before immersion. There were less prominent signal and appearance of fluorapatite crystals after immersion. ¹⁹F MAS-NMR revealed CaF₂ formation after immersion in both CPP-ACPF and BGAF. ³¹P MAS-NMR showed phosphate signals in both CPP-ACPF and BGAF before immersion. FTIR failed to show any signs of apatite formation.SignificanceBoth CPP-ACP and bioactive glass enhanced ion release without compromising the bioavailability of fluoride. The CPP-ACPF varnish had the most promising ion release.     

Dual-functional adhesive containing amorphous calcium phosphate nanoparticles and dimethylaminohexadecyl methacrylate promoted enamel remineralization in a biofilm-challenged environment

ObjectiveThe cariogenic biofilm on enamel, restoration, and bonding interface is closely related to dental caries and composite restoration failure. Enamel remineralization at adhesive interface is conducive to protecting bonding interface and inhibiting secondary caries. This study intended to assess the remineralization efficiency of adhesive with dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP) on initial caries lesion of biofilm-coated enamel.MethodsArtificial initial carious lesion was created via 72-hour immersion in demineralization solution and cariogenic biofilm was formed after 24-hour culture of Streptococcus mutans (S. mutans). Specimens were then divided into 4 groups: enamel control, enamel treated with NACP, DMAHDM and NACP+DMAHDM respectively. Samples next underwent 7-day cycling, 4 h in BHIS (brain heart infusion broth containing 1 % sucrose) and 20 h in AS (artificial saliva) per day. The pH of BHIS was tested daily. So did the concentration of calcium and phosphate in BHIS and AS. Live/dead staining, colony-forming unit (CFU) count, and lactic acid production of biofilms were measured 7 days later. The enamel remineralization efficiency was evaluated by microhardness testing and transverse microradiography (TMR) quantitatively.ResultsEnamel of NACP+DMAHDM group demonstrated excellent remineralization effectiveness. And the NACP+DMAHDM adhesive released a great number of Ca²⁺ and PO₄^3- ions, increased pH to 5.81 via acid neutralization, decreased production of lactic acid, and reduced CFU count of S. mutans (P < 0.05).SignificanceThe NACP+DMAHDM adhesive would be applicable to preventing secondary caries, strengthening enamel-adhesive interface, and extending the lifespan of composite restoration.     

Effect of co-precipitation plus spray-drying of nano-CaF2 on mechanical and fluoride properties of nanocomposite

ObjectiveFluoride (F)-releasing restoratives typically are either weak mechanically or release only low levels of F ions. The objectives of this study were to: (1) develop a novel photo-cured nanocomposite with strong mechanical properties and high levels of sustained F ion release via a two-step “co-precipitation + spray-drying” technique to synthesize CaF₂ nanoparticles (nCaF₂); and (2) investigate the effect of spray-drying treatment after co-precipitation of nCaF₂ on mechanical properties and F ion release of composite.MethodsTwo types of CaF₂ particles were synthesized: A co-precipitation method yielded CaF₂cp; “co-precipitation + spray-drying” yielded nCaF₂cpsd. Composites were fabricated with fillers of: (1) 0% CaF₂ + 70% glass; (2) 10% CaF₂cp + 60% glass; (3) 15% CaF₂cp + 55% glass; (4) 20% CaF₂cp + 50% glass; (5) 10% nCaF₂cpsd + 60% glass; (6) 15% nCaF₂cpsd + 55% glass; and (7) 20% nCaF₂cpsd + 50% glass. A commercial F-releasing nanocomposite served as control.ResultsThe nCaF₂cpsd had much smaller particle size (median = 32 nm) and narrower distribution (22–57 nm) than CaF₂cp (median = 5.25 μm, 162 nm–67 μm). The composite containing nCaF₂cpsd had greater flowability, flexural strength, elastic modulus and hardness than CaF₂cp composite and commercial control composite. At 84-day immersion in water, the nanocomposites containing 20% nCaF₂cpsd had 65 times higher cumulative F release, and 77 times greater long-term F-release rate, than commercial control.ConclusionsA novel two-step “co-precipitation + spray-drying” technique of synthesizing nCaF₂ was developed. The photo-cured nanocomposite containing 20% nCaF₂cpsd possessed strong mechanical properties and excellent long-term F-release ability, and hence is promising for dental restoration applications to inhibit secondary caries.     

Novel pit and fissure sealant containing nano-CaF2 and dimethylaminohexadecyl methacrylate with double benefits of fluoride release and antibacterial function

ObjectivePit and fissure sealants with antibacterial and remineralization properties have broad application prospects in caries prevention. The objectives of this study were to: (1) develop a novel pit and fissure sealant containing CaF₂ nanoparticles (nCaF₂) and dimethylaminohexadecyl methacrylate (DMAHDM); and (2) investigate the effects of nCaF₂ and DMAHDM on biofilm response and fluoride (F) ion release for the first time.MethodsHelioseal F was used as a control. Bioactive sealants were formulated with DMAHDM and nCaF₂. Flow properties, enamel shear bond strength, hardness and F ion releases were measured. Streptococcus mutans (S. mutans) biofilms were grown on sealants. Biofilm metabolic activity, lactic acid production, colony-forming units (CFU), and pH of biofilm culture medium were measured.ResultsAdding 5% DMAHDM and 20% nCaF₂ did not reduce the paste flow and enamel bond strength, compared to control (p < 0.05). Hardness of sealants with 20% nCaF₂ and DMAHDM was higher than control (p < 0.05). The F ion release from 20% nCaF₂ was much higher than that of commercial control (p < 0.05). The sealant with DMAHDM reduced the S. mutans biofilm CFU by 4 logs. The pH in biofilm medium of the new bioactive sealant was much higher (pH 6.8) than that of commercial sealant (pH 4.66) (p < 0.05).SignificanceThe new bioactive pit and fissure sealant with nCaF₂ and DMAHDM achieved high fluoride release and strong antibacterial performance. This novel fluoride-releasing and antibacterial sealant is promising to inhibit caries and promote the remineralizaton of enamel and dentin.     

Nanocomposite containing amorphous calcium phosphate nanoparticles for caries inhibition

Objectives

The main challenges facing composite restorations are secondary caries and bulk fracture. The objectives of this study were to synthesize novel nanoparticles of amorphous calcium phosphate (NACP), develop NACP nanocomposite with calcium (Ca) and phosphate (PO₄) ion release to combat caries, and investigate the effects of NACP filler level and glass co-filler reinforcement on composite properties.

Methods

NACP (diameter = 116 nm) were synthesized via a spray-drying technique for the first time. Since the local plaque pH in the oral cavity can decrease to 5 or 4, photo-activated composites were tested with immersion in solutions of pH 7, 5.5, and 4. Composite mechanical properties as well as Ca and PO₄ ion release were measured vs. pH and filler level.

Results

Increasing the NACP filler level increased the ion release. At 28 d and pH 4, the Ca release was (4.66 ± 0.05) mmol/L at 20% NACP, much higher than (0.33 ± 0.08) at 10% NACP (p < 0.05). Decreasing the pH increased the ion release. At 20% NACP, the PO₄ release at 28 d was (1.84 ± 0.12) mmol/L at pH 4, higher than (0.59 ± 0.08) at pH 5.5, and (0.12 ± 0.01) at pH 7 (p < 0.05). However, pH had little effect on composite mechanical properties. Flexural strength at 15% NACP was (96 ± 13) MPa at pH 4, similar to (89 ± 13) MPa at pH 5.5, and (89 ± 19) MPa at pH 7 (p > 0.1). The new NACP nanocomposites had strengths that were 2-fold those of previous calcium phosphate composites and resin-modified glass ionomer control.

Significance

NACP composites were developed for the first time. Their strengths matched or exceeded a commercial composite with little ion release, and were 2-fold those of previous Ca-PO₄ composites. The nanocomposite was “smart” as it greatly increased the ion release at a cariogenic pH 4, when these ions would be most needed to inhibit caries. Hence, the new NACP composite may be promising for stress-bearing and caries-inhibiting restorations.     

Are inert glasses really inert?

ObjectivesThe aim of this study was to investigate the degradation of inert glass fillers which are commonly used in conventional resin-based composites to provide radiopacity, reduce the polymerization shrinkage and improve the mechanical properties.Methods75 mg of five different glass powders (1 µm) was immersed separately into 50 mL of acetic acid (pH 4) and tris buffer (pH 7.4) for up to 4 weeks. At each time point the glass powder was filtered and dried for characterization using ATR-FTIR and XRD to assess the degradation behavior and crystallization. ICP-OES, ISE and pH measurements were performed on the supernatant solutions to monitor the pH and ion release.ResultsAlthough FTIR and XRD analysis showed no significant glass degradation or crystallization upon immersion, there was a substantial release of ions from the inert fillers, especially from BABFG and CDL. Barium release for these fillers were 270 and 165 ppm respectively. G018–373 glass presented the lowest ion release followed by GM27884 and BABG. The ion release was more pronounced in acidic conditions compared to neutral conditions apart from the fluoride release.SignificanceInert glasses are not as inert as previously thought. This may result in leaching of ions, potentially causing toxicity, reduction in mechanical properties, increased wear and subsequent failure of the composite material. The ions released from the inert glass may interfere with other glass fillers such as bioactive glass fillers, inhibiting degradation of the bioactive glass, beneficial ion release from the bioactive glass, pH neutralization and apatite formation.     

Calcium and phosphate ion releasing composite: Effect of pH on release and mechanical properties

ObjectivesSecondary caries and restoration fracture are the two main challenges facing tooth cavity restorations. The objective of this study was to develop a composite using tetracalcium phosphate (TTCP) fillers and whiskers to be stress-bearing, and to be “smart” to increase the calcium (Ca) and phosphate (PO₄) ion release at cariogenic pH.MethodsTTCP was ball-milled to obtain four different particle sizes: 16.2, 2.4, 1.3, and 0.97 μm. Whiskers fused with nano-sized silica were combined with TTCP as fillers in a resin. Filler level mass fractions varied from 0 to 75%. Ca and PO₄ ion releases were measured vs. time at pH of 7.4, 6, and 4. Composite mechanical properties were measured via three-point flexure before and after immersion in solutions at the three pH.ResultsTTCP composite without whiskers had flexural strength similar to a resin-modified glass ionomer (Vitremer) and previous Ca–PO₄ composites. With whiskers, the TTCP composite had a flexural strength (mean ± S.D.; n = 5) of (116 ± 9) MPa, similar to (112 ± 14) MPa of a stress-bearing, non-releasing hybrid composite (TPH) (p > 0.1). The Ca release was (1.22 ± 0.16) mmol/L at pH of 4, higher than (0.54 ± 0.09) at pH of 6, and (0.22 ± 0.06) at pH of 7.4 (p < 0.05). PO₄ release was also dramatically increased at acidic pH. After immersion, the TTCP–whisker composite matched the strength of TPH at all three pH (p > 0.1); both TTCP–whisker composite and TPH had strengths about threefold that of a releasing control.SignificanceThe new TTCP–whisker composite was “smart” and increased the Ca and PO₄ release dramatically when the pH was reduced from neutral to a cariogenic pH of 4, when these ions are most needed to inhibit caries. Its strength was two- to threefold higher than previously known Ca–PO₄ composites and resin-modified glass ionomer. This composite may have the potential to provide the necessary combination of load-bearing and caries-inhibiting capabilities.     

Ion release and physical properties of CPP–ACP modified GIC in acid solutions

A new glass-ionomer cement (GIC) (Fuji VII? EP) includes 3% (w/w) casein phosphopeptide–amorphous calcium phosphate (CPP–ACP) to enhance ion release.ObjectivesTo assess this new GIC compared with a GIC without CPP–ACP (Fuji VII?) with respect to ion release, changes in surface hardness and in mass under a variety of acidic and neutral conditions.MethodsEighty blocks of Fuji VII? (F7) and Fuji VII? EP (F7EP) were subjected to three acidic solutions (lactic and citric acids pH 5.0, hydrochloric acid pH 2.0) and water (pH 6.9) over a three-day period. Ion release, surface hardness and weight measurements were carried out every 24 h.ResultsHigher calcium ion release from F7EP was observed under all acidic conditions. Increased inorganic phosphate ion release was observed for F7EP in hydrochloric and citric acids. Fluoride ion release was similar between F7 and F7EP under all conditions but was significantly higher in acids compared with water. After three days there was no significant difference in surface hardness (p > 0.05) between the two materials under all conditions except hydrochloric acid. Minimal change in mass was observed for F7 and F7EP in water, lactic and hydrochloric acids, however citric acid caused significantly more mass loss compared with water (p < 0.001).ConclusionIncorporation of 3% (w/w) CPP–ACP into F7 enhanced calcium and phosphate ion release, with no significant change in fluoride ion release and no adverse effects on surface hardness or change in mass.Clinical significance statementGICs have the potential to release fluoride ions particularly under acidic conditions associated with dental caries and erosion. A new GIC containing CPP–ACP and fluoride releases not only fluoride ions but also calcium and phosphate ions under acidic conditions which should help to inhibit demineralisation associated with caries and erosion.     

Bioactivity and fluoride release of strontium and fluoride modified Biodentine

Biodentine? is a novel tricalcium silicate based material used both as a coronal dentine replacement and in pulp therapy. Its multiple use in sealing perforations, pulp capping and as a temporary restoration arises from its ability to promote dentine formation and to confer an excellent marginal seal. However, there is still room for improvement of this cement as it lacks the anticariogenic effect typically conferred by fluoride ion release as seen in glass ionomer cement based dental materials. Therefore, this study was conducted to investigate the impact of bioactive glass addition to Biodentine?.

Bioactive glass composite for orthodontic adhesives — Formation and characterisation of apatites using MAS-NMR and SEM

Objectives

To study the dissolution and fluoroapatite (FAP) formation of a new bioactive glass (BAG)-resin adhesive in an acidic solution in reference to neutral solutions, using the magic angle spinning-nuclear magnetic resonance (MAS-NMR) and the scanning electron microscopy (SEM).

Effect of fluoride-releasing restorative materials on bacteria-induced pH fall at the bacteria–material interface: An in vitro model study

Objectives

Inhibition of bacterial acid production by dental restorative materials is one of the strategies for secondary caries prevention. This study aimed to evaluate the effect of fluoride-releasing restorative materials on bacteria-induced pH fall at the bacteria–material interface.

Methods

Four fluoride-releasing restorative materials, glass-ionomer cement (GIC), resin-modified glass-ionomer cement (RMGIC), resin composite (RC) and flowable resin composite (FRC) were used. Each specimen was immersed in potassium phosphate buffer at pH 7.0 for 10 min and 4 weeks, and in potassium acetate buffer at pH 5.5 for 4 weeks. An experimental apparatus was made of polymethyl methacrylate and had a well with restorative materials or polymethyl methacrylate (control) at the bottom. The well was packed with cells of Streptococcus mutans, and the pH at the interface between cells and materials was monitored using a miniature pH electrode after the addition of 1% glucose for 90 min, and the fluoride released into the well was quantified using a fluoride ion electrode.

Results

The pH of GIC (4.98–5.18), RMGIC (4.77–4.99), RC (4.62–4.75) and FRC (4.54–4.84) at 90 min were higher than that of control (4.31–4.49). The fluoride amounts released from GIC were the highest, followed by RMGIC, RC and FRC, irrespective of immersion conditions. Saliva coating on materials had no significant effect.

Conclusions

The fluoride-releasing restorative materials inhibited pH fall at the bacteria–material interface. The degree of inhibition of pH fall seemed to correspond to the amount of fluoride detected, suggesting that the inhibition was due to the fluoride released from these materials.

Clinical significance

A little amount of fluoride actually released from the fluoride-releasing materials may have caries preventive potential for oral bacteria.     

Fluoride and calcium release from peppermint-flavored fluoride varnish containing dicalcium-phosphate-dihydrate coated with xylitol

Bakground: Fluoride varnish with high initial fluoride and calcium release can help patients with high-risk caries. Ample quantities of free fluoride and calcium ions in the oral cavity can enhance enamel remineralization. This study aimed to investigate the effect of dicalcium phosphate dihydrate coated with xylitol (DCPD-xylitol), in fluoride varnish, on the release of fluoride and calcium ions in the oral cavity.Materials and methodsDCPD powder with xylitol was synthesized by preparing a 60% xylitol solution and mixed it with DCPD solution. The mixture was stirred for 1 h at room temperature and dried at 80 °C for 18 h to reduce the water content. Then, the powder was used in the formulation of peppermint-flavored fluoride varnish as an active agent. The amounts of fluoride and calcium ion released in deionized water at 37 °C for 6 h were assessed with an ion-selective electrode. The cumulative fluoride and calcium ion release data were analyzed using one-way analysis of variance (ANOVA) and the post hoc Tukey test with α = 0.05.ResultsThe results showed that the addition of DCPD coated with xylitol provided better bioavailability of the ions than DCPD without coating. Peppermint-flavored fluoride varnish (PFFV) with DCPD-xylitol 1% gave the highest fluoride ion release (296.90 mg/L) compared to the varnishes with other xylitol concentrations and the positive control. In contrast, PFFV DCPD-xylitol 5% afforded the highest calcium ion release at 111.20 mg/L.ConclusionsThis study concluded that xylitol affects the bioavailability of free fluoride and calcium ions in varnishes. However, the efficacy of fluoride and calcium uptake in enamel and under different in vitro media conditions requires further investigation.     

Novel rechargeable calcium fluoride dental nanocomposites

ObjectivesComposite restorations with calcium fluoride nanoparticles (nCaF₂) can remineralize tooth structure through F and Ca ion release. However, the persistence of ion release is limited. The objectives for this study were to achieve long-term remineralization by developing a rechargeable nCaF₂ nanocomposite and investigating the F and Ca recharge and re-release capabilities.MethodsThree nCaF₂ nanocomposites were formulated: (1) BT-nCaF₂:Bisphenol A glycidyl dimethacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA); (2) PE-nCaF₂:Pyromellitic glycerol dimethacrylate (PMGDM) and ethoxylated bisphenol A dimethacrylate (EBPADMA); (3) BTM-nCaF₂:BisGMA, TEGDMA, and Bis[2-(methacryloyloxy)ethyl] phosphate (Bis-MEP). All formulations contained 15% nCaF₂ and 55% glass particles. Initial flexural strength and elastic modulus, F and Ca ion release, recharge and re-release were tested and compared to three commercial fluoride-containing materials.ResultsBT and BTM nCaF₂ composites were 3–4 times stronger and had elastic modulus 2 times that of resin-modified glass ionomer controls. PE-nCaF₂ had comparable strength to RMGIs. All nCaF₂ composites had significant F and Ca ion release and ion rechargeability. In F and Ca recharging cycles, PE-nCaF₂ had the highest ion recharging capability among nCaF₂ groups, followed by BT-nCaF₂ and BTM-nCaF₂ (p < 0.05). For all recharge cycles, ion release maintained similar levels, demonstrating long-term ion release was possible. Furthermore, after the final recharge cycle, nCaF₂ nanocomposites provided continuous ion release for 42 days without further recharge.SignificanceNovel nCaF₂ rechargeable nanocomposites exhibited significant F and Ca ion release over multiple recharge cycles, demonstrating continuous long-term ion release. These nanocomposites are promising restorations with lasting remineralization potential.     

The impact of glass ionomer cement and composite resin on microscale pH in cariogenic biofilms and demineralization of dental tissues

ObjectiveSecondary caries is among the most frequent reasons for the failure of dental restorations. Glass ionomer cement (GIC) restorations have been proposed to protect the surrounding dental tissues from demineralization through the release of fluoride and by buffering the acid attack from dental biofilms. In contrast, the lack of buffering by composite resin (CR) restorations has been suggested as a promoting factor for the development of secondary caries.MethodsThe present study employed transversal microradiography and confocal microscopy based pH ratiometry to quantify mineral loss and map microscale pH gradients inside Streptococcus mutans biofilms grown on compound specimens consisting of enamel, dentin and either GIC or CR.ResultsMineral loss in dentin was significantly lower next to GIC than next to CR, but no significant differences in local biofilm pH were observed between the two restorative materials.SignificanceThe cariostatic effect of GIC relies predominantly on the provision of fluoride and not on a direct buffering action. The lack of buffering by CR did not affect local biofilm pH and may therefore be of minor importance for secondary caries development.     

Chitosan microparticles for the controlled delivery of fluoride

ObjectivesTo manufacture and characterise chitosan/fluoride microparticles prepared by spray drying and assess their utility as controlled release vehicles for fluoride.MethodsMicroparticles were manufactured from dispersions containing 1.0% and 2.0% (w/v) chitosan and 0.20% or 0.40% (w/v) NaF in the absence/presence of glutaraldehyde. Particle size distributions were determined using laser diffraction; fluoride loading and release were determined by ion-selective electrode. Release profiles were studied in isotonic media (pH 5.5) over 360 min; microparticles exhibiting greatest cumulative fluoride release were further evaluated at pH 4.0 and 7.0. Particle morphology was investigated using environmental scanning electron microscopy. Bioadhesion parameters were determined with a texture-probe analyser.ResultsMicroparticles exhibited low polydispersity and volume mean diameters (VMDs) <6 μm. VMDs increased on doubling the chitosan/fluoride concentrations but were largely independent of glutaraldehyde concentration. Recovered yields were inversely proportional to dispersion viscosity due to compromised fluid atomisation; adding NaF reduced viscosity and improved yields. Best-case entrapment efficiency and NaF loading were 84.1% and 14%, respectively. Release profiles were biphasic, releasing 40–60% of the total fluoride during the first 600 s, followed by a prolonged release phase extending out to 6 h. Incorporation of 0.40% NaF to the 2.0% chitosan dispersion yielded microparticles with reduced bioadhesive parameters (F_max and WOA) versus the chitosan-only control whilst retaining significant bioadhesive potential.ConclusionsBioadhesive chitosan/fluoride microparticles manufactured using a spray-drying protocol have been extensively characterised and further opportunity for optimisation identified. These microparticles may provide a means of increasing fluoride uptake from oral care products to provide increased protection against caries, however further work is required to demonstrate this principle in vivo.Clinical significanceSpray-drying is a low-cost route for the manufacture of bioadhesive chitosan/fluoride microparticles which can be exploited as controlled fluoride release agents to aid fluoride retention in the oral cavity. The potential exists to optimise release profiles to suit the delivery format thereby maximising the cariostatic benefits.     

Electrochemical evaluation of the hydrogen peroxide- and fluoride-induced corrosive property and its recovery on the titanium surface

PurposeThis study aimed to elucidate the effects of hydrogen peroxide (H₂O₂) and sodium fluoride (NaF) on titanium surfaces under conditions mimicking those encountered during dental treatment.MethodsTitanium samples were immersed in artificial saliva (AS), 1 M H₂O₂, 1 M H₂O₂ with catalase, 1000 ppmF NaF, 1 M H₂O₂ with 1000 ppmF NaF, or 9000 ppmF NaF (9000 ppmF NaF: pH 5.3, other solutions: pH 6.5) for 3 min. The electrochemical properties of the titanium samples were analyzed before and after the immersion procedures using a potentiostat. The amounts of titanium eluted into each solution were measured using inductively coupled plasma mass spectrometry. The post-immersion color changes (ΔE*ab) and gloss values of the titanium samples were determined using spectrophotometry. Moreover, the solution-treated titanium samples were subsequently immersed in AS and analyzed electrochemically at 1, 2, 3, 4, 6, 8, and 24 h.ResultsThe immersion of titanium in any of the solutions except 1000 ppmF NaF caused significant increases in corrosive and passive currents and significant reductions in polarization resistance. No titanium elution or color changes were observed, except when 9000 ppmF NaF was used. After immersion in AS, the electrochemical properties of all of the titanium samples, except the 9000 ppmF NaF-treated samples, recovered within 24 h.ConclusionsOne M H₂O₂ and 1000 ppmF NaF can be used alone or in combination in the clinical setting without causing significant titanium corrosion because the corrosive properties they induce is reversible. However, highly concentrated acidic fluorides can cause irreversible corrosion.     

In vitro evaluation of composite containing DMAHDM and calcium phosphate nanoparticles on recurrent caries inhibition at bovine enamel-restoration margins

ObjectiveRecurrent caries is a primary reason for restoration failure caused by biofilm acids. The objectives of this study were to: (1) develop a novel multifunctional composite with antibacterial function and calcium (Ca) and phosphate (P) ion release, and (2) investigate the effects on enamel demineralization and hardness at the margins under biofilms.MethodsDimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP) were incorporated into composite. Four groups were tested: (1) Commercial control (Heliomolar), (2) Experimental control (0% DMAHDM + 0% NACP), (3) antibacterial group (3% DMAHDM + 0% NACP), (D) antibacterial and remineralizing group (3% DMAHDM + 30% NACP). Mechanical properties and Ca and P ion release were measured. Colony-forming units (CFU), lactic acid and polysaccharide of Streptococcus mutans (S. mutans) biofilms were evaluated. Demineralization of bovine enamel with restorations was induced via S. mutans, and enamel hardness was measured. Data were analyzed via one-way and two-way analyses of variance and Tukey’s multiple comparison tests.ResultsAdding DMAHDM and NACP into composite did not compromise the mechanical properties (P > 0.05). Ca and P ion release of 3% DMAHDM + 30% NACP was increased at cariogenic low pH. Biofilm lactic acid and polysaccharides were greatly decreased via DMAHDM, and CFU was reduced by 4 logs (P < 0.05). Under biofilm acids, enamel hardness at the margins was decreased to about 0.5 GPa for control; it was about 1 GPa for antibacterial group, and 1.3 GPa for antibacterial and remineralizing group (P < 0.05).ConclusionsThe novel 3% DMAHDM + 30% NACP composite had strong antibacterial effects. It substantially reduced enamel demineralization adjacent to restorations under biofilm acid attacks, yielding enamel hardness that was 2-fold greater than that of control composites. The novel multifunctional composite is promising to inhibit recurrent caries.     

3种玻璃离子水门汀氟释放能力的体外研究

目的：对比研究3种玻璃离子水门汀在人工唾液中的氟释放能力。方法：选择FujiCem、FujiPlus和FujiI水门汀，分别制备10个直径4mm，高8mm的试样，每个试样浸入1ml人工唾液中，恒温37℃。采用离子选择电极分别于第1d、2d、3d、7d、14d、30d、90d测定3种材料的氟释放量。采用SPSS13．0软件进行统计分析。结果：3种材料均在第1d的氟释放量最高。第2d急剧下降，随后氟离子释放趋于平稳。在各个测量时间点，FujiCem的氟释放累积量最高，除了第1d外，FujiPlus释放量最低，且3种材料在90d测定的氟累积释放量总体均数间、组间两两比较均存在显著差异，P〈0．05，有统计学意义。结论：3种材料均能在一定时间内持续缓慢地向周围环境中释放氟离子，而FujiCem显示出更好的氟离子释放能力，在预防继发龋的发生方面具有一定的优势。