Short- and Long-Term Dentin Bond Strength of Bioactive Glass-Modified Dental Adhesives.

This study investigated the short- and long-term effects of dental adhesives doped with nano-sized bioactive glass 45S5 (BAG) on the resin-dentin interfacial bond strength. Two etch-and-rinse adhesives (Adper Scotchbond Multi-Purpose (ASB) and Solobond Plus (SB)) and one self-etch adhesive (Clearfil SE Bond (CF)) were doped with different concentrations of BAG (5, 10, and 20 wt%). The unmodified (0 wt% BAG) commercial adhesives served as control groups. Dentin of 120 molars (n = 10 per group) was treated with the different adhesives, followed by buildups with a conventional composite restorative material. From each tooth, 14 sticks were prepared for micro-tensile bond strength (µTBS) testing. The sticks were stored in simulated body fluid at 37 °C and tested after 24 h or six months for µTBS and failure mode. Data were analyzed using Kruskal-Wallis tests in combination with post-hoc Conover-tests and Wilcoxon signed-rank tests at a level of significance of α = 0.05. After 24 h and six months, both etch-and-rinse adhesives with a low BAG content (up to 10 wt% for ASB and 5 wt% for SB) showed similar µTBSs as their respective control groups (0 wt% BAG). CF showed a significant decrease in µTBS even after addition of 5 wt% BAG. At a high concentration of added BAG (20 wt%), all three adhesives showed a significant decrease in µTBS compared to the unmodified controls. The CF control group showed significantly lower µTBS after 6 months of storage than after 24 h. In contrast, the µTBS of all CF groups modified with BAG was unaffected by aging. In conclusion, the tested etch-and-rinse adhesives can be modified with up to 5 wt% (SB), or 10 wt% (ASB) of BAG without reducing their short- and long-term dentin bond strength. Moreover, the addition of nano-sized BAG may prevent long-term bond strength deterioration of a self-etch adhesive.

Polymerization and shrinkage stress formation of experimental resin composites doped with nano- vs. micron-sized bioactive glasses.

This study investigated the effect of adding bioactive glass 45S5 (BG) of different particle sizes to dental composite on resin polymerization and shrinkage stress formation. Commercial flowable composite was mixed with either 15 wt% BG fillers (nanometric, micrometric, or hybrid BG) or inert barium glass. Real-time linear polymerization shrinkage and shrinkage stress were recorded, and the degree of conversion was measured using FTIR spectroscopy. The commercial (unmodified) composite developed significantly higher linear shrinkage and shrinkage stress than the groups with 15 wt% added inert or BG fillers. After adding inert barium glass, the composite showed significantly higher linear shrinkage than when micrometric BG was added. The addition of bioactive or inert glass fillers did not affect the degree of conversion. Shrinkage stress can be reduced by adding inert or bioactive fillers (nano- and/or microparticulate BG) without affecting monomer conversion.

Hydrogen Peroxide Versus Sodium Hypochlorite: All a Matter of pH?

INTRODUCTION: Hydrogen peroxide (H2O2) and sodium hypochlorite (NaOCl) solutions are similar in that they contain oxidizing agents with a bleaching effect. NaOCl solutions are stable at a high pH, at which they also exert increased cleansing/proteolysis. On the other hand, H2O2 solutions are natively acidic, yet gain bleaching power on organic stains when alkalized. It was investigated whether alkalizing a H2O2 solution would also let it dissolve soft tissue or increase its bleaching power on blood-stained dentin. METHODS: The stability of alkalized H2O2 solutions was assessed by iodometric titration. Soft tissue dissolution was investigated on porcine palatal mucosa. The bleaching effect (ΔL∗) after 60 minutes of exposure was monitored in blood-stained human dentin using a calibrated spectrophotometer. To compare similar molarities, 2.5% H2O2 solutions were used here, and 5.0% NaOCl was used as the positive control, whereas nonbuffered saline solution served as the negative control. RESULTS: Adding alkali (NaOH) to the H2O2 solutions rendered them unstable in a dose-dependent manner. A H2O2 solution of pH 11.1 was chosen for the main experiments (tissue dissolution and bleaching effect) and compared with a native counterpart (pH = 4.7). Alkalizing the H2O2 solution had no discernible effect on its soft tissue dissolution or bleaching power (P = .75 compared with the native H2O2 solution). The NaOCl solution of similar molar concentration had a considerably (P < .001) higher tissue dissolving and bleaching effect under current conditions. CONCLUSIONS: The proteolytic/bleaching effects of NaOCl solutions are unique and cannot be achieved by altering the pH of peroxide solutions.

Polymerization shrinkage behaviour of resin composites functionalized with unsilanized bioactive glass fillers.

Previous work has shown that partial replacement of reinforcing fillers with unsilanized silica particles can diminish polymerization shrinkage stress of dental resin composites. The aim of the present study was to investigate whether such an effect can be attained by using unsilanized bioactive glass (BG). Incorporating BG fillers into resin composites is interesting due to their potential for exerting caries-preventive effects. Experimental light-curable composites with a total filler load of 77 wt% were prepared. Reinforcing fillers were partially replaced with 0-60 wt% of BG 45S5 and an experimental low-sodium fluoride-containing BG. The following properties were investigated: linear shrinkage, degree of conversion, shrinkage stress, maximum shrinkage stress rate, and time to achieve maximum shrinkage stress rate. The diminishing effect of BG 45S5 on shrinkage stress was mediated by a decrease in degree of conversion caused by this BG type. In contrast, as the degree of conversion remained unaffected by the experimental BG, the resulting shrinkage behaviour was governed by the effect of varying amounts of silanized and unsilanized fillers on material's viscoelastic properties. The replacement of silanized reinforcing fillers with unsilanized BG did not reduce polymerization shrinkage stress unless the reduction was attained indirectly through a diminished degree of conversion.

Curing potential of experimental resin composites filled with bioactive glass: A comparison between Bis-EMA and UDMA based resin systems.

OBJECTIVES: To evaluate the degree of conversion, light transmittance, and depth of cure of two experimental light-curable bioactive glass (BG)-containing composite series based on different resin systems. METHODS: Experimental composite series based on either Bis-EMA or UDMA resin were prepared. Each series contained 0, 5, 10, 20, and 40wt% of BG 45S5. Reinforcing fillers were added up to a total filler load of 70wt%. The degree of conversion was evaluated using Raman spectroscopy, while light transmittance was measured using visible light spectroscopy. The depth of cure was estimated from the degree of conversion data and using the ISO 4049 scraping test. RESULTS: Replacement of reinforcing fillers with BG can diminish the degree of conversion, light transmittance, and depth of cure. The effect of BG on the aforementioned properties was highly variable between the experimental series. While in the Bis-EMA series, the degree of conversion was significantly impaired by BG, all of the composites in the UDMA series attained clinically acceptable degree of conversion values. The reduction of the degree of conversion in the Bis-EMA series occurred independently of the changes in light transmittance. The UDMA series showed better light transmittance and consequently higher depth of cure than the Bis-EMA series. The depth of cure for all composites in the UDMA series was above 2mm. SIGNIFICANCE: While the Bis-EMA series demonstrated clinically acceptable curing potential only for 0-10wt% of BG loading, an excellent curing potential in the UDMA series was observed for a wide range (0-40wt%) of BG loadings.

Directing Stem Cell Commitment by Amorphous Calcium Phosphate Nanoparticles Incorporated in PLGA: Relevance of the Free Calcium Ion Concentration.

The microenvironment of mesenchymal stem cells (MSCs) is responsible for the modulation in MSC commitment. Nanocomposites with an inorganic and an organic component have been investigated, and osteogenesis of MSCs has been attributed to inorganic phases such as calcium phosphate under several conditions. Here, electrospun meshes and two-dimensional films of poly(lactic-co-glycolic acid) (PLGA) or nanocomposites of PLGA and amorphous calcium phosphate nanoparticles (PLGA/aCaP) seeded with human adipose-derived stem cells (ASCs) were analyzed for the expression of selected marker genes. In a two-week in vitro experiment, osteogenic commitment was not found to be favored on PLGA/aCaP compared to pure PLGA. Analysis of the medium revealed a significant reduction of the Ca2+ concentration when incubated with PLGA/aCaP, caused by chemical precipitation of hydroxyapatite (HAp) on aCaP seeds of PLGA/aCaP. Upon offering a constant Ca2+ concentration, however, the previously observed anti-osteogenic effect was reversed: alkaline phosphatase, an early osteogenic marker gene, was upregulated on PLGA/aCaP compared to pristine PLGA. Hence, in addition to the cell-material interaction, the material-medium interaction was also important for the stem cell commitment here, affecting the cell-medium interaction. Complex in vitro models should therefore consider all factors, as coupled impacts might emerge.

Bioactivity and Physico-Chemical Properties of Dental Composites Functionalized with Nano- vs. Micro-Sized Bioactive Glass.

Bioactive resin composites can contribute to the prevention of secondary caries, which is one of the main reasons for failure of contemporary dental restorations. This study investigated the effect of particle size of bioactive glass 45S5 on chemical and physical composite properties. Four experimental composites were prepared by admixing the following fillers into a commercial flowable composite: (1) 15 wt% of micro-sized bioactive glass, (2) 15 wt% of nano-sized bioactive glass, (3) a combination of micro- (7.5 wt%) and nano-sized (7.5 wt%) bioactive glass, and (4) 15 wt% of micro-sized inert barium glass. Hydroxyapatite precipitation and pH rise in phosphate-buffered saline were evaluated during 28 days. Degree of conversion and Knoop microhardness were measured 24 h after specimen preparation and after 28 days of phosphate-buffered saline immersion. Data were analyzed using non-parametric statistics (Kruskal-Wallis and Wilcoxon tests) at an overall level of significance of 5%. Downsizing the bioactive glass particles from micro- to nano-size considerably improved their capability to increase pH. The effect of nano-sized bioactive glass on degree of conversion and Knoop microhardness was similar to that of micro-sized bioactive glass. Composites containing nano-sized bioactive glass formed a more uniform hydroxyapatite layer after phosphate-buffered saline immersion than composites containing exclusively micro-sized particles. Partial replacement of nano- by micro-sized bioactive glass in the hybrid composite did not impair its reactivity, degree of conversion (p > 0.05), and Knoop microhardness (p > 0.05). It is concluded that downsizing bioactive glass particles to nano-size improves the alkalizing potential of experimental composites with no negative effects on their fundamental properties.

Light Transmittance and Polymerization of Bulk-Fill Composite Materials Doped with Bioactive Micro-Fillers.

This study investigated the effect of bioactive micro-fillers on the light transmittance and polymerization of three commercially available bulk-fill resin composites. These were mixed with 20 wt% bioactive glass 45S5, Portland cement, inert dental barium glass, or nothing (controls). Composites were photo-activated and light transmittance through 4 mm thick specimens was measured in real time. Moreover, degree of conversion (DC) and Knoop hardness (KHN) were assessed. Light transmittance of all bulk-fill composites significantly decreased (p < 0.05) with addition of 20 wt% bioactive glass 45S5 but not when inert barium glass was added. For bulk-fill composites modified with Portland cement, light irradiance dropped below the detection limit at 4 mm depth. The DC at the top surface of the specimens was not affected by addition of bioactive or inert micro-fillers. The bottom-to-top ratio of both DC and KHN surpassed 80% for bulk-fill composites modified with 20 wt% bioactive or inert glass fillers but fell below 20% when the composites were modified with Portland cement. In contrast to Portland cement, the addition of 20 wt% bioactive glass maintains adequate polymerization of bulk-fill composites placed at 4 mm thickness, despite a decrease in light transmittance compared to the unmodified materials.

Effects of endodontic irrigants on blood and blood-stained dentin.

OBJECTIVES: This study aimed to investigate bleaching effects of common endodontic irrigants on human whole blood and blood-stained dentin. Specifically, it was assessed whether sodium hypochlorite at a clinically recommended concentration (2.5% NaOCl) would bleach with similar efficacy as a peroxide-based irrigant at higher molarity (5% H2O2). Furthermore, the effects of a NaOCl-compatible chelator with a high affinity to iron (Dual Rinse HEDP) were investigated. METHODS: Human whole blood was mixed at a 1:20 ratio with either phosphate-buffered saline, 9% HEDP, 2.5% NaOCl, 2.5% NaOCl containing 9% HEDP, or 5% H2O2. Effects were assessed spectrometrically and photographically. Human dentin specimens were prepared with a methacrylate reservoir for liquids and a polished assessment side over 1 mm dentin thickness. Dentin was stained using human whole blood for 3 weeks and subsequently exposed to the irrigants for 60 min. Measurements were performed in the CIELAB color space. Results were compared using parametric tests with the alpha-type error set to 5%. RESULTS: When directly exposed, the solutions containing NaOCl completely discolored the blood, while the 5% H2O2 exerted a bleaching effect without complete dissolution of dissolved matter, and the pure 9% HEDP had no effect at all. The NaOCl solutions bleached blood-stained dentin more efficiently than H2O2 (p < 0.05). CONCLUSIONS: Under the current conditions, the 2.5% NaOCl solution had a stronger bleaching effect on blood and blood-stained dentin than 5% H2O2. HEDP did not have any direct impact on blood color or NaOCl-derived bleaching.

Modification of silicone elastomers with Bioglass 45S5® increases in ovo tissue biointegration.

Silicone is an important material family used for various medical implants. It is biocompatible, but its bioinertness prevents cell attachment, and thus tissue biointegration of silicone implants. This often results in constrictive fibrosis and implant failure. Bioglass 45S5® (BG) could be a suitable material to alter the properties of silicone, render it bioactive and improve tissue integration. Therefore, BG micro- or nanoparticles were blended into medical-grade silicone and 2D as well as 3D structures of the resulting composites were analyzed in ovo by a chick chorioallantoic membrane (CAM) assay. The biomechanical properties of the composites were measured and the bioactivity of the composites was verified in simulated body fluid. The bioactivity of BG-containing composites was confirmed visually by the formation of hydroxyapatite through scanning electron microscopy as well as by infrared spectroscopy. BG stiffens as prepared non-porous composites by 13% and 36% for micro- and nanocomposites respectively. In particular, after implantation for 7 days, the Young's modulus had increased significantly from 1.20 ± 0.01 to 1.57 ± 0.03 MPa for microcomposites and 1.44 ± 0.03 to 1.69 ± 0.29 MPa to for nanocpmosites. Still, the materials remain highly elastic and are comparably soft. The incorporation of BG into silicone overcame the bioinertness of the pure polymer. Although the overall tissue integration was weak, it was significantly improved for BG-containing porous silicones (+72% for microcomposites) and even further enhanced for composites containing nanoparticles (+94%). These findings make BG a suitable material to improve silicone implant properties. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1180-1188, 2019.

Bioactivity and properties of a dental adhesive functionalized with polyhedral oligomeric silsesquioxanes (POSS) and bioactive glass.

OBJECTIVES: This study aimed to analyze the effect of infiltrating a commercial adhesive with nanosized bioactive glass (BG-Bi) particles or methacryl-functionalized polyhedral oligomeric silsesquioxanes (POSS) on material properties and bioactivity. METHODS: An acetone-based dental adhesive (Solobond Plus adhesive, VOCO GmbH, Cuxhaven, Germany) was infiltrated with nanosized bioactive glass particles (0.1 or 1wt%), or with monofunctional or multifunctional POSS particles (10 or 20wt%). Unfilled adhesive served as control. Dispersion and hydrodynamic radius of the nanoparticles were studied by dynamic light scattering. Set specimens were immersed for 28days in artificial saliva at 37°C, and surfaces were mapped for the formation of calcium phospate (Ca/P) precipitates (scanning electron microscopy/energy-dispersive X-ray spectroscopy). Viscosity (rheometry) and the structural characteristic of the networks were studied, such as degree of conversion (FTIR spectroscopy), sol fraction and water sorption. RESULTS: POSS particles showed a good dispersion of the particles for both types of particles being smaller than 3nm, while the bioactive glass particles had a strong tendency to agglomerate. All nanoparticles induced the formation of Ca/P precipitates. The viscosity of the adhesive was not or only slightly increased by POSS particle addition but strongly increased by the bioactive glass particles. The degree of conversion, water sorption and sol fraction showed a maintained or improved network structure and properties when filled with BG-Bi and multifunctional POSS, however, less polymerization was found when loading a monofunctional POSS. SIGNIFICANCE: Multifunctional POSS may be incorporated into dental adhesives to provide a bioactive potential without changing material properties adversely.

Interactions between the Tetrasodium Salts of EDTA and 1-Hydroxyethane 1,1-Diphosphonic Acid with Sodium Hypochlorite Irrigants.

INTRODUCTION: A clinically useful all-in-one endodontic irrigant with combined proteolytic and decalcifying properties is still elusive. In this study, the chemical effects of dissolving the tetrasodium salts of 1-hydroxyethane 1,1-diphosphonic acid (Na4HEDP) or Na4EDTA directly in sodium hypochlorite (NaOCl) irrigants in polypropylene syringes were assessed during the course of 1 hour. METHODS: The solubility of the salts in water was determined. Their compatibility with 1% and 5% NaOCl was measured by iodometric titration and in a calcium complexation experiment by using a Ca2+-selective electrode. RESULTS: The salts dissolved within 1 minute. The dissolution maximum of Na4HEDP in water (wt/total wt) was 44.6% ± 1.6%. The corresponding dissolution maximum of Na4EDTA was 38.2% ± 0.8%. Na4HEDP at 18% in 5% NaOCl caused a mere loss of 16% of the initially available chlorine during 1 hour. In contrast, a corresponding mixture between NaOCl and the Na4EDTA salt caused 95% reduction in available chlorine after 1 minute. Mixtures of 3% Na4EDTA with 1% NaOCl were more stable, but only for 30 minutes. Na4HEDP lost 24% of its calcium complexation capacity after 60 minutes. The corresponding loss for Na4EDTA was 34%. CONCLUSIONS: The compatibility and solubility of particulate Na4HEDP with/in NaOCl solutions are such that these components can be mixed and used for up to 1 hour. In contrast, short-term compatibility of the Na4EDTA salt with NaOCl solutions was considerably lower, decreasing at higher concentrations of either compound. Especially for Na4HEDP but also for Na4EDTA, the NaOCl had little effect on calcium complexation.

Nanoscale bioactive glass activates osteoclastic differentiation of RAW 264.7 cells.

BACKGROUND: There is limited knowledge regarding differentiation of osteoclasts in the presence of nanoscale bioactive glass (nBG). This investigation examined increasing concentrations of 45S5 nBG and their influence on osteoclast differentiation. MATERIALS & METHODS: Different concentrations of 45S5 nBG were cultured up to 14 days with the murine RAW264.7 cell line and human primary monocytes cultured with M-CSF and RANKL. RESULTS: Culturing cells for 14 days with 500 µg/ml nBG showed a viability of 100%; however DNA synthesis was reduced, supporting differentiation into osteoclast-like cells. Using RAW cells, activation of nine genes, including cell fusion genes, occurred in an nBG concentration dependent manner. Low concentrations of nBG increased expression of genes involved in commitment to cell fusion, whereas high concentrations increased gene expression supporting osteoclast-like differentiation. CONCLUSION: nBG enhances both RAW264.7 and human osteoclast differentiation. nBG controlled gene expression in a concentration dependent manner could reflect normal regulation during bone growth.

Oral biofilm and caries-infiltrant interactions on enamel.

OBJECTIVES: This study aimed to analyze interactions between oral biofilms and a dental triethylene glycol dimethacrylate (TEGDMA)-based resin infiltration material on enamel. METHODS: Demineralized enamel specimens (14 days, acidic buffer, pH 5.0) were either infiltrated with a commercial TEGDMA resin and subjected to a three-species biofilm (Streptococcus mutans UAB 159, Streptococcus oralis OMZ 607 and Actinomyces oris OMZ 745) (group 1), applied to the biofilm (group 2), or merely resin infiltrated (group 3). A control group received no treatment (4). Biofilm formation and metabolic activity of biofilms were measured for group (1) and (2) after 24h CFU and a resazurin assay. Resin biodegradation was measured for group (1) and (3) by high performance liquid chromatography (HPLC) coupled with mass spectrometry after 6 and 24h incubation. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) images were taken to study the biofilm and material's autofluorescence in groups (1-4) after 24h. RESULTS: SEM and CLSM images showed reduced biofilm formation on resin-infiltrated specimens (group 1) compared to group 2, while no biofilm was detectable on groups 3 and 4. CFU data (log10 CFU per mL) of group 1 showed significantly reduced bacterial numbers (p<0.05) compared to group 2. However, HPLC analysis of TEGDMA leakage after 6h and 24h revealed no differences between group 1 and group 3. CONCLUSIONS: The results of the current study indicate that freshly resin-infiltrated enamel surfaces show a biofilm reducing effect, while monomer leakage was not affected by bacterial presence. CLINICAL SIGNIFICANCE: Resin infiltrated enamel surfaces are constantly exposed to the oral microflora. Yet, it is not known how biofilms interact with enamel-penetrated resins and if and to which extent accessory alignments in oral hygiene are needed.

Preclinical in vivo Performance of Novel Biodegradable, Electrospun Poly(lactic acid) and Poly(lactic-co-glycolic acid) Nanocomposites: A Review.

Bone substitute materials have witnessed tremendous development over the past decades and autogenous bone may still be considered the gold standard for many clinicians and clinical approaches in order to rebuild and restore bone defects. However, a plethora of novel xenogenic and synthetic bone substitute materials have been introduced in recent years in the field of bone regeneration. As the development of bone is actually a calcification process within a collagen fiber arrangement, the use of scaffolds in the formation of fibers may offer some advantages, along with additional handling characteristics. This review focuses on material characteristics and degradation behavior of electrospun biodegradable polyester scaffolds. Furthermore, we concentrated on the preclinical in vivo performance with regard to bone regeneration in preclinical studies. The major findings are as follows: Scaffold composition and architecture determine its biological behavior and degradation characteristics; The incorporation of inorganic substances and/or organic substances within composite scaffolds enhances new bone formation; L-poly(lactic acid) and poly(lactic-co-glycolic acid) composite scaffolds, especially when combined with basic substances like hydroxyapatite, tricalcium phosphate or demineralized bone powder, seem not to induce inflammatory tissue reactions in vivo.

Functionalizing a dentin bonding resin to become bioactive.

OBJECTIVES: To investigate chemo-mechanical effects of incorporating alkaline bioactive glass nanoparticles into a light-curable dental resin matrix. METHODS: An unfilled Bis-GMA/TEGDMA material was infiltrated with up to 20 wt% of ultrafine SiO2-Na2O-CaO-P2O5-Bi2O3 particles. The unfilled and filled resins were investigated regarding their viscosity before setting and compared to commercially available materials. Set specimens were immersed for 21 days in phosphate buffered saline at 37°C. Water uptake, pH, Knoop hardness, and degree of conversion of freshly polymerized and stored samples were investigated. Resin surfaces were viewed and mapped in a scanning electron microscope for the formation of calcium phosphate (Ca/P) precipitates. In addition, Raman spectroscopy was performed. Numeric values were statistically compared (p<0.01). RESULTS: Viscosity increased with particle loading, but remained below that of a flowable dental composite material. Water uptake into and pH induction from the polymerized samples also increased with particle loading (p<0.01). The addition of 20 wt% nanoparticles had no significant influence on microhardness, yet it slightly (p<0.01) increased the degree of conversion after 21 days. Ca/P precipitates formed on specimens filled with 20 wt% of the particles, while they were scarce on counterparts loaded with 10 wt%, and absent on unfilled resin surfaces. SIGNIFICANCE: The results of the current study show that a Bis-GMA-based resin can be functionalized using alkaline nanoparticles. A material with bioactive properties and similar hardness as the unfilled resin was obtained by incorporating 20wt% of ultrafine SiO2-Na2O-CaO-P2O5-Bi2O3 particles into the resin matrix.

Effect of direct current on surface structure and cytocompatibility of titanium dental implants.

PURPOSE: A low direct current can be used to disinfect dental titanium implants in simulated physiologic environments. The aim of this study was to determine whether this treatment affects implant surface structure and cytocompatibility. MATERIALS AND METHODS: Titanium test disks with a sandblasted, acid-etched, large-grit (SLA) surface were placed as anodes in an electrolytic bath with physiologic saline and treated with 15 mA of current for 15 minutes. Surfaces were analyzed by light and electron microscopy and contact angle measurement. Depth profile analyses of SLA disks were run at subsurface levels from 0 to 1,000 nm. The proliferation and viability of preosteoblastic cells and human foreskin fibroblasts on implant surfaces were assessed. Alkaline phosphatase (ALP) activity was determined with and without exposure to bone morphogenetic protein-2 (BMP-2). Mineralization was determined after 4 weeks. RESULTS: A blue discoloration was observed after treating the SLA disks, but no damage was recognized microscopically. An oxidation layer formed on the surface and the wettability of the disks increased significantly. Cell proliferation and initial maturation were not affected by the treatment. Mineralization and ALP activity of BMP-exposed cells, however, were slightly but significantly reduced on test disks. CONCLUSIONS: The current study showed that the alterations in implant color after electrochemical treatment did not reflect significant surface changes, which would preclude cell adhesion and growth or have a major impact on osteoblastic differentiation or maturation.

A new method to assess available chlorine in small volumes of liquid.

INTRODUCTION: There is no robust and simple way to quantify available chlorine from small volumes such as human root canals. Therefore, a new method was developed and assessed. METHODS: Standardized size-40 paper points were soaked in a 15% (w/v) potassium iodide solution for 1 minute. Subsequently, the paper points were placed in an incubator and dried at 110°C for 4 hours. The paper points (n = 5 per measurement) were then dipped in different concentrations of NaOCl and photographed under standardized conditions in RAW format. The pictures were imported to image processing software and adjusted to the standardized background. The red, green, and blue levels of the paper points were assessed at a predefined area. Inverse regression was used to determine NaOCl concentration from red, green, and blue values, with both explanatory and outcome variables log-transformed to base 10. RESULTS: The red value measurements were chosen for further analysis based on a comparison of the coefficient of determination (R(2)) and a residual analysis. The method was applied to concentrations of NaOCl between 0.0001% and 1% (R(2) = 0.92). In this range, NaOCI concentrations could be assessed with an error not larger than 3-fold the determined concentration. CONCLUSIONS: The present method proved to be robust to determine the order of magnitude of available chlorine that is present in a small volume. This should be useful for endodontic research.

Effect of low direct current on anaerobic multispecies biofilm adhering to a titanium implant surface.

PURPOSE: Peri-implantitis is caused by biofilm adhering to the implant. It has been shown that bactericidal electrolysis products are generated when a low direct current is applied to a titanium implant used as the anode. The hypothesis of this study was that low-current electrolysis would eradicate viable bacteria in a simulated subgingival multispecies biofilm adhering to a titanium implant surface. MATERIAL AND METHODS: Biofilms consisting of eight anaerobic species were grown on pellicle-coated titanium discs with sand-blasted, acid-etched, large-grit (SLA; Straumann, Basel, Switzerland) surface. After 40.5 hours of growth, discs were treated with 10 mA for 10 minutes in an electrolytical setup with physiological saline and gelatin. RESULTS: Low direct current at discs used as the cathode caused a reduction of three to four orders of magnitude in viable counts, while no viable bacteria were recovered from anode discs (Mann-Whitney U-test, p < .01). Confocal laser scanning microscopy in combination with a live/dead stain showed biofilm detachment at the cathode and reduced viability at the anode. CONCLUSION: Electrochemical treatment of diseased implants appears to be promising and well worth investigating further.

pH-dependent antibacterial effects on oral microorganisms through pure PLGA implants and composites with nanosized bioactive glass.

Biomaterials made of biodegradable poly(α-hydroxyesters) such as poly(lactide-co-glycolide) (PLGA) are known to decrease the pH in the vicinity of the implants. Bioactive glass (BG) is being investigated as a counteracting agent buffering the acidic degradation products. However, in dentistry the question arises whether an antibacterial effect is rather obtained from pure PLGA or from BG/PLGA composites, as BG has been proved to be antimicrobial. In the present study the antimicrobial properties of electrospun PLGA and BG45S5/PLGA fibres were investigated using human oral bacteria (specified with mass spectrometry) incubated for up to 24 h. BG45S5 nanoparticles were prepared by flame spray synthesis. The change in colony-forming units (CFU) of the bacteria was correlated with the pH of the medium during incubation. The morphology and structure of the scaffolds as well as the appearance of the bacteria were followed bymicroscopy. Additionally, we studied if the presence of BG45S5 had an influence on the degradation speed of the polymer. Finally, it turned out that the pH increase induced by the presence of BG45S5 in the scaffold did not last long enough to show a reduction in CFU. On the contrary, pure PLGA demonstrated antibacterial properties that should be taken into consideration when designing biomaterials for dental applications.