Influence of Layer Thickness and Shade on the Transmission of Light through Contemporary Resin Composites.

BACKGROUND: Material-dependent parameters have an important impact on the efficiency of light polymerization. The present in vitro study aimed to investigate the influence of the increment thickness and shade of nano- and nanohybrid resin composites on the transmission of curing light. METHODS: Three contemporary resin composites were evaluated: Tetric EvoCeram® (TEC); Venus Diamond® (VD); and Filtek Supreme XTE® (FS XTE). Light transmission (LT) was recorded in accordance with the sample thickness (0.5 to 2.7 mm) and the shade. Polymerized samples were irradiated for 10 s each using the high-power LED curing light Celalux 2 (1900 mW/cm2). LT was simultaneously recorded using the MARC Patient Simulator (MARC-PS). RESULTS: LT was strongly influenced by the composite layer thickness. For 0.5 mm-thick samples, a mean power density of 735 mW/cm2 was recorded at the bottom side. For the 2.7 mm samples, a mean power density of 107 mW/cm2 was measured. Only LT was markedly reduced in the case of darker shades. From A1 to A4, LT decreased by 39.3% for FS XTE and 50.8% for TEC. Dentin shades of FS XTE and TEC (A2, A4) showed the lowest LT. CONCLUSIONS: The thickness and shade of resin composite increments strongly influences the transmission of curing light. More precise information about these parameters should be included in the manufacture manual.

Coaxial electrospun nanofibers as drug delivery system for local treatment of periodontitis.

OBJECTIVES: The aim of the present study was to prepare resorbable polylactide fibers for periodontitis treatment using coaxial electrospinning to optimize the release of metronidazole (MNA) by reducing the initial burst effect. METHODS: Poly(L-lactide-co-D,L-lactide) (PLA) fibers mats with different distributions of metronidazole (MNA) were manufactured by coaxial electrospinning (COAX). By COAX spinning the central core of the fiber was enriched with 40% MNA (m/m), while the sheath of the fiber consisted of PLA only (test group). In contrast, fibers of the control group were prepared by conventional electrospinning with the same amount of MNA but with a homogenous drug distribution (HDD - homogenously distributed drug). The release of MNA was determined by analyzing aliquots from the fiber mats using UV-VIS spectroscopy. Agar diffusion tests were carried out to determine the antibacterial effect on periodontopathogenic bacteria. Biocompatibility was tested in direct contact to human gingival fibroblasts (HGF) for two days. RESULTS: The COAX mats showed a retarded drug release compared to the conventional HDD fibers. After 24 h, 64% of total MNA was released cumulatively from the COAX fibers while 90% of the MNA was released from the HDD fibers (controls). The antibacterial effect of COAX fibers was significantly higher after 24 h compared to the HDD fibers. Cell cultivation revealed significant higher numbers of vital cells among the COAX mats. SIGNIFICANCE: COAX fibers showed improved sustained MNA release compared to conventional fibers and can be seen as potential drug delivery systems in local periodontitis treatment.

Effectiveness of Casein Phosphopeptide-Amorphous Calcium Phosphate (CPP-ACP) Compared to Fluoride Products in an In-Vitro Demineralization Model.

The goal of this study was to evaluate the effectiveness of the toothpaste Tooth Mousse compared to conventional fluoride-based versions in the prevention of enamel and dentin demineralization. Human enamel and dentin samples (n = 120 each) were exposed to artificial demineralization at pH 4.92. During the demineralization process, the samples in the test groups were periodically treated with Tooth Mousse (TM) containing casein-phosphopeptide -amorphous-calcium-phosphate (CPP-ACP) and Tooth Mousse Plus (TMP) containing amorphous-calcium-fluoride-phosphate (CPP-ACPF) to evaluate their protective properties. Fluoride toothpastes containing 1400 ppm amine fluoride (AmF) and 1450 ppm sodium fluoride (NaF) were applied in the positive control groups. Treatment with distilled water (group C-W) or demineralization without treatment (group C-D) served as negative controls. After the demineralization and treatment process, all samples were cut longitudinally and lesion depths were determined at six locations using polarized light microscopy. In TM/TMP groups (enamel: 80/86 µm, dentin: 153/156 µm) lesion depths were significantly smaller compared to the negative control groups C-W/C-D (enamel: 99/111 µm, dentin: 163/166 µm). However, TM and TMP compared to the positive controls AmF/NaF (enamel: 58/63 µm, dentin: 87/109 µm) showed higher lesion depths. The application of TM/TMP (89%/78%) during demineralization led to a reduced number of severe lesions compared to the negative controls C-W/C-D (100%/95%). In this study we demonstrate that Tooth Mousse is less effective regarding prevention of enamel and dentin demineralization compared to fluoride containing toothpastes.

Critical parameters in cultivation of experimental biofilms using the example of Pseudomonas fluorescens.

Formation and treatment of biofilms present a great challenge for health care and industry. About 80% of human infections are associated with biofilms including biomaterial centered infections, like infections of prosthetic heart valves, central venous catheters, or urinary catheters. Additionally, biofilms can cause food and drinking water contamination. Biofilm research focusses on application of experimental biofilm models to study initial adherence processes, to optimize physico-chemical properties of medical materials for reducing interactions between materials and bacteria, and to investigate biofilm treatment under controlled conditions. Exploring new antimicrobial strategies plays a key role in a variety of scientific disciplines, like medical material research, anti-infectious research, plant engineering, or wastewater treatment. Although a variety of biofilm models exist, there is a lack of standardization for experimental protocols, and designing experimental setups remains a challenge. In this study, a number of experimental parameters critical for material research have been tested that influence formation and stability of an experimental biofilm using the non-pathogenic model strain of Pseudomonas fluorescens. These parameters include experimental time frame, nutrient supply, inoculum concentration, static and dynamic cultivation conditions, material properties, and sample treatment during staining for visualization of the biofilm. It was shown, that all tested parameters critically influence the experimental biofilm formation process. The results obtained in this study shall support material researchers in designing experimental biofilm setups.

Effect of biomimetic mineralization on enamel and dentin: A Raman and EDX analysis.

OBJECTIVE: To investigate the effect of an experimental biomimetic mineralization kit (BIMIN) on the chemical composition and crystallinity of caries-free enamel and dentin samples in vitro. METHODS: Enamel and dentin samples from 20 human teeth (10 for enamel; 10 for dentin) were divided into a control group without treatment and test samples with BIMIN treatment. Quantitative analysis of tissue penetration of fluoride, phosphate, and calcium was performed using energy-dispersive X-ray spectroscopy (EDX). Mineralization depth was measured by Raman spectroscopy probing the symmetric valence vibration near 960cm-1 as a marker for crystallinity. EDX data was statistically analyzed using a paired t-test and Raman data was analyzed using the Student's t-test. RESULTS: EDX analysis demonstrated a penetration depth of fluoride of 4.10±3.32µm in enamel and 4.31±2.67µm in dentin. Calcium infiltrated into enamel 2.65±0.64µm and into dentin 5.58±1.63µm, while the penetration depths for phosphate were 4.83±2.81µm for enamel and 6.75±3.25µm for dentin. Further, up to 25µm of a newly mineralized enamel-like layer was observed on the surface of the samples. Raman concentration curves demonstrated an increased degree of mineralization up to 5-10µm into the dentin and enamel samples. SIGNIFICANCE: Biomimetic mineralization of enamel and dentin samples resulted in an increase of mineralization and a penetration of fluoride into enamel and dentin.

Critical physiological factors influencing the outcome of antimicrobial testing according to ISO 22196 / JIS Z 2801.

Bactericidal materials gained interest in the health care sector as they are capable of preventing material surfaces from microbial colonization and subsequent spread of infections. However, commercialization of antimicrobial materials requires proof of their efficacy, which is usually done using in vitro methods. The ISO 22196 standard (Japanese test method JIS Z 2801) is a method for measuring the antibacterial activity of daily goods. As it was found reliable for testing the biocidal activity of antimicrobially active materials and surface coatings most of the laboratories participating in this study used this protocol. Therefore, a round robin test for evaluating antimicrobially active biomaterials had to be established. To our knowledge, this is the first report on inaugurating a round robin test for the ISO 22196 / JIS Z 2801. The first round of testing showed that analyses in the different laboratories yielded different results, especially for materials with intermediate antibacterial effects distinctly different efficacies were noted. Scrutinizing the protocols used by the different participants and identifying the factors influencing the test outcomes the approach was unified. Four critical factors influencing the outcome of antibacterial testing were identified in a series of experiments: (1) incubation time, (2) bacteria starting concentration, (3) physiological state of bacteria (stationary or exponential phase of growth), and (4) nutrient concentration. To our knowledge, this is the first time these parameters have been analyzed for their effect on the outcome of testing according to ISO 22196 / JIS Z 2801. In conclusion, to enable assessment of the results obtained it is necessary to evaluate these single parameters in the test protocol carefully. Furthermore, uniform and robust definitions of the terms antibacterial efficacy / activity, bacteriostatic effects, and bactericidal action need to be agreed upon to simplify communication of results and also regulate expectations regarding antimicrobial tests, outcomes, and materials.

Development of novel electrospun dual-drug fiber mats loaded with a combination of ampicillin and metronidazole.

OBJECTIVE: Our study was performed with the aim of preparing electrospun polylactide fibers with a combination of ampicillin (AMP) and metronidazole (MNZ) and investigating their drug release behavior and the antibacterial effect on Aggregatibacter actinomycetemcomitans and other oral pathogens. METHODS: AMP and MNZ were integrated as a combination in two separate fibers (dual fiber mats - DFW mix) of electrospun PLA fiber mats by means of multijet electrospinning and in a single fiber (single fiber mats - SFW mix). HPLC (high-performance liquid chromatography) was used to measure the released drug quantities. Agar diffusion tests were used to determine the antibacterial effect of the eluates on A. actinomycetemcomitans, Fusobacterium nucleatum, Porphyromonas gingivalis and Enterococcus faecalis. The neutral red test was made to examine the cytocompatibility of the eluates with human gingival fibroblasts (hGFs). RESULTS: The release of the active agents varied with the antibiotic concentrations initially used in the fiber mats, but also with the distribution of the active agents in one or two fibers. Of the total quantity of MNZ (AMP), the SFW mix fiber mats released >60% (>70%) within a span of 5min, and 76% (71%) after 96h. With these drug concentrations released by the fiber mats (≥5m%), an antibacterial effect was achieved on A. actinomycetemcomitans and on all other species tested. Fiber mats and their eluates have no cytotoxic influence on human gingival fibroblasts (hGFs). SIGNIFICANCE: Electrospun AMP/MNZ-loaded polymer fibers are a potential drug delivery system for use in periodontal and endodontic infections.

Study of energy transfer by different light curing units into a class III restoration as a function of tilt angle and distance, using a MARC Patient Simulator (PS).

OBJECTIVE: The MARC Patient Simulator (MARC PS) enables researchers to observe the influence of handling errors on the radiant exposure that is delivered by light curing units (LCUs). Changes in the tilt angle and distance of the light guide exit face in relation to the surface of the composite increment have a distinct effect on the total amount of light delivered during polymerization and may cause insufficient conversion of the material. Therefore, the aim of the present study was to determine the influence of the tilt angle and distance of irradiance on the efficiency of light application by recording the total amount of energy using the anterior tooth sensor of the MARC PS. METHODS: The influence of the tilt angle and distance of the light guide to the sensor surface on the delivered radiant exposure was examined for three different LCUs (Celalux 2 [C2], Bluephase [BP] and Translux Powerblue [TPB]). The measurements were performed for 20 s each with five different tilt angles (α=0°, 5°, 10°, 15°, 20°) and nine different distances (L=1, 2, 3, 4, 5, 6, 7, 8, 9 mm). RESULTS: For all LCUs, a distinct influence of the tilt angle on the delivered amount of fluence was found. At 0° tilt the C2 delivered a total light energy of 38.55 J/cm(2). By increasing the tilt of the light guide the amount of energy applied significantly decreased. At 20° tilt a reduction by 31.2% of the original light fluence was recorded. However, the C2 was the most powerful LCU measured. Even under optimum measurement conditions, the BP delivered a fluence of only 14.8 J/cm(2). At a tilt angle of 20°, though, the light sensor still registered 92.7% of the original output power. Under the same conditions, the TPB delivered 81.4%. With increasing distance of the light guide exit face to the surface of the sensor all LCUs showed a significant loss in delivered light energy. At a distance of 2mm the C2 showed a reduction by 46.7%, whereas total fluence of BP and TPB were reduced by 3.8% and 4.8%, respectively. SIGNIFICANCE: The choice of LCU and the application of an appropriate curing time are important for successful polymerization. Nevertheless, a perpendicular positioning of the light guide as close as possible to the surface of the composite increment is of essential importance in order to ensure sufficient delivery of light.

Antibacterial effect of silver (I) carbohydrate complexes on oral pathogenic key species in vitro.

BACKGROUND: It was the aim of this study to evaluate the antibacterial impact of two silver(I) carbohydrate complexes with tripodal thioglycosides, namely tris[2-(ß-D-thio-glucopyranosyl)ethyl]-amine-silver(I)-nitrate (3) and tris[2-(α-D-thio-manno-pyranosyl)ethyl]-amine-silver(I)-nitrate (4), on five oral pathogenic bacterial strains. Furthermore, cytocompatibility was tested using human gingival fibroblasts (HGF). METHODS: Minimum inhibitory concentrations (MIC) were determined on five oral pathogenic bacterial strains by using the broth microdilution method: Fusobacterium nucleatum (ATCC 10953), Aggregatibacter actinomycetemcomitans (ATCC 33384), Porphyromonas gingivalis (ATCC 33277), Streptococcus mutans (ATCC 25175) and Enterococcus faecalis (DSMZ 20376). Furthermore, antimicrobial efficiency was tested using agar diffusion assays. To evaluate cytocompatibility, human gingival fibroblasts (HGFs) were exposed to AgNO3 and complex 3 followed by a live/dead staining. RESULTS: MIC of the silver(I) complexes ranged between 0.625 and 5.0 mmol/L. The silver complexes 3 and 4 showed higher antibacterial efficiency against all tested species than AgNO3. Antibacterial efficiency of complexes 3 and 4 on F. nucleatum (≥18 mm) and A. actinomycetemcomitans (≥23 mm) was more pronounced than against P. gingivalis (≥15 mm). Complex 3 (20 mM) induced the largest inhibition zones (30 to 31 mm) on Gram-negative strains. For Gram-positive strains, the largest inhibition zones were achieved by complex 3 (20 mM/S. mutans: 28 mm, E. faecalis: 18 mm). Complex 3 had a lower cytotoxic impact on HGFs compared to AgNO3 by the power of ten. CONCLUSIONS: The findings suggest that silver(I) carbohydrate complexes 3 and 4 might function as novel antimicrobial agents for the treatment of periodontal, carious or endodontic diseases.

Template assisted surface microstructuring of flowable dental composites and its effect on microbial adhesion properties.

OBJECTIVES: Despite their various advantages, such as good esthetic properties, absence of mercury and adhesive bonding to teeth, modern dental composites still have some drawbacks, e.g., a relatively high rate of secondary caries on teeth filled with composite materials. Recent research suggests that microstructured biomaterials surfaces may reduce microbial adhesion to materials due to unfavorable physical material-microbe interactions. The objectives of this study were, therefore, to test the hypotheses that (i) different surface microstructures can be created on composites by a novel straightforward approach potentially suitable for clinical application and (ii) that these surface structures have a statistically significant effect on microbial adhesion properties. METHODS: Six different dental composites were initially tested for their suitability for microstructuring by polydimethylsiloxane (PDMS) templates. Each composite was light-cured between a glass slide and a microstructured PDMS template. The nano-hybrid composite Grandio Flow was the only tested composite with satisfying structurability, and was therefore used for the bacterial adhesion tests. Composites samples were structured with four different microstructures (flat, cubes, linear trapezoid structures, flat pyramids) and incubated for 4h in centrifuged saliva. The bacterial adherence was then characterized by colony forming units (CFUs) and scanning electron microscopy (SEM). RESULTS: All four microstructures were successfully transferred from the PDMS templates to the composite Grandio Flow. The CFU-test as well as the quantitative analysis of the SEM images showed the lowest bacterial adhesion on the flat composite samples. The highest bacterial adhesion was observed on the composite samples with linear trapezoid structures, followed by flat pyramids and cubes. The microstructure of dental composite surfaces statistically significantly influenced the adhesion of oral bacteria. SIGNIFICANCE: Modifying the composite surface structure may be a clinically suitable approach to control the microbial adhesion and thus, to reduce the risk of secondary caries at dental composite restorations. Smaller composite surface structures may be useful for accomplishing this.

Antibacterial photodynamic treatment of periodontopathogenic bacteria with indocyanine green and near-infrared laser light enhanced by Trolox(TM).

BACKGROUND AND OBJECTIVES: It has been shown that certain vitamins can significantly enhance the effect of photodynamic anti-tumor therapy. Unfortunately, there is no sufficient information available about the impact of those antioxidants on antimicrobial Photodynamic Therapy (aPDT). The present study is aimed at investigating the antimicrobial effect of the dye indocyanine green (ICG) in the presence of Trolox(TM) , a vitamin E analogue, upon irradiation with near-infrared (NIR) laser light (808 nm) on the gramnegative periodontopathogenic bacteria Aggregatibacter actinomycetemcomitans (A.a.), Porphyromonas gingivalis (P.g.) and Fusobacterium nucleatum (F.n.). METHODS: Bacteria solved in PBS were incubated with ICG (50-500 µg/ml) in the presence and absence of Trolox(TM) (2 mM). Irradiation was performed after 10 minutes of dark-incubation with NIR-laser-light (25-100 J/cm(2) , 810 nm). During treatment, temperature was also recorded inside the bacterial solutions. The treated suspensions were serial diluted and plated onto blood agar plates. After anaerobe cultivation for 5 days the colony-forming units (CFU/ml) were determined. RESULTS: The antibacterial effect was ICG-concentration and exposure dependent. It was found that high ICG-concentrations and light fluence rates caused bacterial reduction due to hyperthermia. Where low ICG-concentrations (<250 µg/ml) and fluence rates only induced minor regression, additional Trolox(TM) -administration significantly enhanced the photodynamic effect. While treatment of A.a. (250 µg/ml ICG, 100 J/cm(2) ) without Trolox(TM) caused no bacterial reduction, additional administration led to total eradication. In the presence of Trolox(TM) reduction to one-fifth of the original ICG-concentration (50 µg/ml) still induced total suppression of P.g. and F.n. at identical fluence (100 J/cm(2) ). Treatment with ICG, NIR-light or Trolox(TM) alone showed no remarkable bactericidal effect. Application of high ICG-concentrations (500 µg/ml) and exposure values (100 J/cm(2) ) caused peak temperatures of 64.53°C. CONCLUSIONS: The results clearly show that Trolox(TM) significantly enhanced the antibacterial effect of ICG upon irradiation with NIR-laser-light. Additional administration of Trolox(TM) may also increase the efficiency of other aPDT systems.

Photodynamic killing of Enterococcus faecalis in dentinal tubules using mTHPC incorporated in liposomes and invasomes.

OBJECTIVES: The present in vitro study investigates the antimicrobial photodynamic efficiency of the photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (mTHPC) incorporated in liposomes (LIP) and highly flexible invasomes (INV) on the endodontopathogenic species Enterococcus faecalis in infected dental root canals. MATERIALS AND METHODS: A total of 48 root canals were prepared mechanically to file size ISO 50 and inoculated with E. faecalis for 48 h. In the test groups, the infected root canals were subjected to aPDT with either mTHPC linked to LIP or INV. The controls were either incubated with 1 % chlorohexidine gel (CHX, positive control) or root canals were irrigated with normal saline (NaCl, negative control). After treatment all canals were mechanically enlarged (ISO 50-110), and the debris of each filing process was subjected to bacterial culture analysis. RESULTS: Both mTHPC formulations showed a significant antimicrobial effect. A bacterial reduction by up to 3.6 log-steps was ascertained for INV directly at the root canal wall. aPDT using INV (ISO 60) was more effective than CHX, which caused a decrease in only 1.2 log-steps. It was found that both liposomal mTHPC formulations were capable to suppress E. faecalis inside the dentinal tubules up to 300 µm. CONCLUSIONS: The results show that mTHPC linked to LIP and INV is capable of efficiently reducing E. faecalis in dental root canals. CLINICAL RELEVANCE: As evidenced, E. faecalis is resistant to several conventional antibacterial treatment measures. In this context, photodynamic treatment with mTHPC delivered by INV is superior to temporary dressing with 1 % CHX gel applied for 24 h.

A 4-week clinical comparison of an oscillating-rotating power brush versus a marketed sonic brush in reducing dental plaque.

PURPOSE: To assess the plaque removal efficacy of an oscillating-rotating power brush relative to a newly-introduced sonic power brush. METHODS: This study used a randomized, examiner-blind, single-center, two-treatment, parallel group 4-week design. Subjects with pre-existing plaque scores of at least 1.75 on the Turesky Modification of the Quigley-Hein Plaque Index (TMQHPI) were evaluated for baseline whole mouth and approximal plaque scores. They received either the oscillating-rotating brush (Oral-B Professional Care 1000, sold as Oral-B Professional Care 600 in some regions, with the Oral-B Precision Clean brush head, D16u/EB20) or the sonic brush (Colgate ProClinical C200 with Colgate Triple Clean brush head) and brushed twice-daily with the assigned brush and a standard fluoride dentifrice for 4 weeks before returning for plaque measurements. Prior to baseline and the Week 4 measurements, participants abstained from oral hygiene for 12 hours and from eating, chewing gum and drinking for 4 hours. RESULTS: A total of 131 subjects were enrolled in the study at baseline, with all completing the study: 65 in the oscillating-rotating group, and 66 in the sonic group. Both brushes significantly reduced plaque over the 4-week study period. The oscillating-rotating brush was statistically significantly more effective in reducing plaque (P < 0.001) than the sonic brush. Compared to the sonic power brush, the adjusted mean plaque reduction scores for the oscillating-rotating power brush were more than five times greater for whole mouth and approximal areas.

Longitudinal micromorphological 15-year results of posterior composite restorations using three-dimensional scanning electron microscopy.

OBJECTIVES: Hybrid composite restorations in posterior teeth were evaluated over 15 years using the semiquantitative Clinical, Photographic and Micromorphologic (CPM) index. It was a further aim to quantitate the surface morphology by three-dimensional scanning electron microscopy (3D-SEM). METHODS: Thirty seven hybrid composite restorations (Ketac-Bond/Visio-Molar X, ESPE, Seefeld/Germany) were longitudinally followed up. Parallel to clinical assessment replicas were taken at baseline, after 1, 5, 10 and 15 years and evaluated by SEM, and profilometrical analyses of 3D-SEM data were computed. The profilometrical results were statistically analysed by ANOVA. The level of significance was set to p<0.05. RESULTS: The semiquantitative micromorphological evaluation exhibited the most considerable deterioration within the first year and up to 5 years of function. Less change was detected during the next 10 years. The profilometrical quantification showed raising depth of the negative marginal ledges with a mean of 27.2µm (range 0.6-94.5µm) after 10 years, with no statistically significant changes from 5 to 10 and 10 to 15 years. The 3D-SEM revealed marginal grooves beneath the level of the ledges (mean 34.5µm after 5 years) within the bonding zone, exposing enamel margins. Leakages, marginal fractures and surface roughness did not seriously deteriorate the quality of restorations. CONCLUSIONS: Hybrid composite restorations of Class I and II cavities surviving the first five years performed well over 15 years of function. Quantitative 3D-SEM profilometrical measurements revealed the dynamics of marginal behaviour over time. CLINICAL SIGNIFICANCE: Long-term parallel clinical and micromorphological evaluation of posterior composite restorations of Class I and Class II cavities documented the clinical safety and acceptable longevity. The longitudinal 3D micromorphologic assessment of the surface changes and of the marginal behaviour revealed deteriorating as well as improving factors hidden in clinical performance.

Colonization of Enterococcus faecalis in a new SiO/SiO(2)-microtube in vitro model system as a function of tubule diameter.

OBJECTIVES: Endodontic pathogens can penetrate deep into dentinal tubules and therefore survive the chemo-mechanical disinfection procedures. Bacterial penetration has been mainly studies using sliced infected human teeth which, besides creating artifacts, can hinder the observation of the inner tubules due to the dense and opaque dentin structure. The aim of the present study was to develop a standardized dentin model by using artificial SiO/SiO2-microtubes of different diameters and lengths to test the penetration ability of Enterococcus faecalis. METHODS: E. faecalis was grown in Schaedler fluid media for 24h and thereafter cell density was settled to 10(3)cells/ml by addition of fresh media. The bacterial solution was then incubated for 2, 3, 5 and 10 days with the SiO/SiO2-microtubes of different diameters (2-5.5µm) and lengths (100-500µm). The colonization of the tubes was evaluated by phase-contrast microscopy and the amount of colonization was determined by using a colonization index (CI; 0-none, 1-mild, 2-moderate, 3-heavy). RESULTS: The diameter of the tubes strongly influences the microbial colonization. After 2 days of cultivation the 5.5µm tubes showed a moderate to heavy colonization (CI 2-3). In comparison, the 2 and 3µm tubes were clearly less colonized at the same point in time. In detail: at day 3, only mild to moderate bacteria colonization (CI 1-2) were found in the 3µm tubes and at day 10 penetration of the 2µm tubes just started. The colonization of the 5.5µm tubes was also influenced by their length. In case of the longer microtubes, though, a smaller share of heavily colonized tubes was observed. SIGNIFICANCE: Our results show that E. faecalis was able to penetrate and reproduce within the standardized SiO/SiO2-microtubes in a short time. To examine the mechanisms of bacterial adhesion and invasion into tubular structures the 2µm tubes could serve as a model system because the diameters are similar to those of dentinal tubules.

Photodynamic antimicrobial effect of safranine O on an ex vivo periodontal biofilm.

BACKGROUND AND OBJECTIVE: The increasing resistance of oral pathogens against antibiotic measures urgently requires new therapeutic strategies. In this context, antimicrobial photodynamic therapy (aPDT) may play a crucial part in the future. The aim of the present study was to compare the antibacterial efficiency of aPDT using the photosensitizer safranine O with that of chlorhexidine (0.2% CHX) on an ex vivo biofilm. METHODS: First the antibacterial activity of both measures against planktonic cultures of Streptococcus gordonii ATCC 33399, Streptococcus mutans ATCC 25175, Fusobacterium nucleatum ATCC 10953, Aggregatibacter actinomycetemcomitans ATCC 33384 and Porphyromonas gingivalis ATCC 33277 was observed. Then a patient specific ex vivo biofilm was established from plaque and saliva samples of patients (n = 19) with chronic periodontitis. The antibacterial effects of aPDT and of 0.2% CHX were determined on the ex vivo biofilms cultivated for 24 and 72 hours. After cultivation of the treated samples on blood agar (2 days) the results were quantified by counting the colony forming units (cfu/ml). RESULTS: Photodynamic treatment with safranine O showed a distinct antibacterial effect on F. nucleatum and P. gingivalis. Whereas S. gordonii was suppressed completely by aPDT, treatment with 0.2% CHX caused only a partial reduction. In the ex vivo biofilm model (24-hour biofilm), aPDT caused a significantly higher bacterial killing than treatment with 0.2% CHX. Compared to the untreated control, there was no significant difference on the 72-hour biofilm for both methods. CONCLUSIONS: The results show that oral-pathogenic species in planktonic solution can be suppressed significantly by aPDT with safranine O. Especially for bacteria in a 24-hour ex vivo biofilm, this method is more effective than treatment with 0.2% CHX. Both antibacterial treatments did not show any significant effect on the biofilm cultivated for 72 hours.

Antibacterial effect of different root canal sealers on three bacterial species.

OBJECTIVE: Bacteria persisting in the root canal system may thwart endodontic therapy. It is therefore interesting to know whether clinically available root canal sealers have an antimicrobial effect. The objective of the present in vitro study was to investigate the antibacterial effect of various sealers on the endodontologically detectable species Enterococcus faecalis (E. faecalis), Fusobacterium nucleatum (F. nucleatum) and Porphyromonas gingivalis (P. gingivalis). METHODS: The antibacterial effectiveness of the sealers was tested by means of the agar diffusion test (ADT) and the direct contact test (DCT). Eight different sealers (AH Plus(®), Hermetic(®), RoekoSeal(®), Sealapex(®), Apexit Plus(®), 2Seal(®), EndoREZ(®) and ProRoot MTA(®)) and two temporary sealers (Calxyl(®) and Gangraena Merz(®)) were tested. At first, 100µl of bacterial suspension (BS) of each individual micro-organism (optical density (OD) 0.5) was applied separately to Schaedler agar plates for the ADT. Subsequently, freshly mixed and set sealer was applied. After 48h of incubation, the inhibition zones were measured. Further, 18mg of sealer were put into each well of 48-well cell culture plates and overlaid with 400µl of Schaedler liquid medium and 100µl of BS (OD 0.5) in monoculture. Bacterial growth was determined by the DCT from the optical density of the liquid by photospectrometry after 2, 4, 6, 8, 10, 12 and 24h. RESULTS: For the application, the sealer Hermetic(®), a significant suppression of the species E. faecalis, F. nucleatum and P. gingivalis was detected in both the ADT and the DCT. AH Plus(®) showed a suppressive effect on E. faecalis and F. nucleatum in the DCT. With all other sealers tested, E. faecalis was not suppressible. RoekoSeal(®), Calxyl(®) and Gangraena-Merz(®) showed no antibacterial effect on the tested species whatsoever. SIGNIFICANCE: We have shown in both ADT and DCT that some root canal sealers suppress the growth of E. faecalis in vitro.

Substrate-free multi-cellular aggregates of human gingival fibroblasts-fabrication, biomechanics and significance for tissue regeneration.

OBJECTIVES: We fabricate multi-cellular aggregates of human gingival fibroblasts (hGFs) using a novel in vivo method that omits supportive flexible substrates. On the basis of the multi-cellular aggregates, constructive and destructive effects of mechanical stimulation are investigated. METHODS: hGFs were seeded onto aligned glass slides (one fixed, one mobile) with an initial gap <30 µm between their connecting edges. After the cells adhere, one of the glass slides is displaced using high precision threads and a piezoelectric element, widening the gap gradually. RESULTS: After several days of gradually widening the gap, multiple multi-cellular hGF aggregates formed, bridging the gap between the glass slides. The effects of discrete displacement events on previously established multi-cellular aggregates ranged from considerable growth and consolidation to collapse and disintegration. A quantitative criterion for assessing the probability for collapse/disintegration of hGF multi-cellular aggregates based on evaluating the meniscus curvature at the free edges before and after displacement is presented and discussed. The curvature is suggested as a representative parameter to characterize the mechanical condition of multi-cellular aggregates, as it is affected by adhesion of cells to the glass slides, cohesion inside the multi-cellular aggregate and the external mechanical load generated by the displacement of the glass slides. SIGNIFICANCE: The presented results clarify the potential and limitations of using mechanical stimulation for initiating and controlling regeneration of (gingival) tissue. Further potential applications include usage as biological substrate for co-culturing hierarchical tissue with multiple cell types (e.g. for vessels) and bio-membranes for filters (e.g. in microfluidics).

Three-dimensional fit of lithium disilicate partial crowns in vitro.

OBJECTIVES: A novel three-dimensional scanning technique was used to investigate the effects a one-step and a two-step impression methods can have on the three-dimensional fit of ceramic partial crowns. METHODS: An acrylic model of a mandibular first molar was prepared to receive a partial coverage all-ceramic crown (mesio-occlusal-distal inlay preparation with reduction of all cusps and rounded shoulder finish line of buccal wall). Type IV plaster replicates were cast based on one-step single viscosity (OS/SV), one-step dual viscosity (OS/DV), and two-step dual viscosity (TS/DV) impressions. Five partial crowns were fabricated per impression method using hot-pressed lithium disilicate ceramics. Then, preparation and restorations were digitized using a non-contact, white-light scanner featuring self-calibrating optics (overall measurement uncertainty of <5µm). Data were entered into quality inspection software which superimposed the records (best-fit-algorithm), calculated fit-discrepancies for every pixel, and colour-coded the results to aid visualization. Furthermore, mean quadratic deviations (RMS) were computed and analyzed statistically with a 1-way ANOVA. Scheffé's procedure was applied for multiple comparisons (α=0.05). RESULTS: Mean RMS-values for marginal (internal) surfaces were: OS/SV 70 (20)µm, OS/DV 78 (34)µm, and TS/DV 107 (52)µm. Differences among impression techniques were statistically significant at p=0.006 (0.001). Qualitatively, occlusal ridges and preparation finish lines were over contoured, whereas inner occlusal boxes and the proximal-occlusal isthmus were under contoured. CONCLUSIONS: OS/SV and OS/DV impressions resulted in statistically significantly smaller marginal and internal discrepancies than the two-step technique. CLINICAL SIGNIFICANCE: Marginal and internal fit of hot-pressed lithium disilicate partial crowns depended on the employed impression technique. One-step impressions are preferred over two-step techniques in many day-to-day clinical situations, especially for the fabrication of partial coverage crown restorations.