Xiangya Huang

Biofilm Formation Capability of Enterococcus faecalis Cells in Starvation Phase and Its Susceptibility to Sodium Hypochlorite

INTRODUCTION Enterococcus faecalis is commonly associated with persistent periapical infections. The physiologic state of the cells in the canal is probably closest to the starvation state. However, the biofilm formation capability of starved E. faecalis cells on human dentin and the susceptibility of the biofilm to 5.25% sodium hypochlorite remain poorly understood. METHODS E. faecalis American Type Culture Collection (ATCC) 29212 in different growth phases were incubated on human dentin and polystyrene blocks. Scanning electron microscopy and biofilm assay were used to investigate the biofilm formation capability of these cells. The susceptibility of the biofilm to 5.25% NaClO was also determined by the plate count method. RESULTS Scanning electron microscopy and biofilm assay showed that starved cells were able to form biofilm on dentin with reduced efficiency as compared with the cells in the exponential phase and stationary phase (p < 0.05). Biofilm grown on dentin harbored more cells than polystyrene (p < 0.05). Biofilms of starved cells were more resistant to 5.25% NaClO than those of stationary cells (p < 0.05), and the impact of 5.25%NaClO on them decreased as the biofilm matured. CONCLUSION E. faecalis cells in the starvation phase could develop biofilm on human dentin, which is responsive to 5.25% NaClO. It may contribute to the predominant role of E. faecalis involved in persistent periapical infections.

A microcomputed tomographic study of canal isthmuses in the mesial root of mandibular first molars in a Chinese population.

Untreated isthmuses can be a cause of endodontic treatment failure. We investigated the anatomic features of the isthmus in the mesial root of mandibular first molars using microcomputed tomography scans. Thirty-six extracted mandibular first molars were collected from the Chinese population and divided into three age groups as follows: 20 to 39 years (group A), 40 to 59 years (group B), and > or = 60 years (group C). Each tooth was scanned and reconstructed, and then the prevalence and type of isthmus were recorded. The percentage of sections showing isthmuses for groups A, B, and C were 50%, 41%, and 24%, respectively. The chi-square test indicated a significant correlation of the distribution of isthmuses with age (p < 0.001). The ratio of partial isthmus to complete isthmus for group C (17.1:1) was significantly higher than group A (5.9:1) and group B (7.0:1) (p < 0.001). By understanding the configuration and location of isthmus, a more efficient endodontic microsurgery can be guaranteed.

Antimicrobial and DNA-binding activities of the peptide fragments of human lactoferrin and histatin 5 against Streptococcus mutans

OBJECTIVE To investigate the killing effect of two salivary antimicrobial peptides, hLF1-11 and P-113, and identify the antibacterial mechanism of the peptides. METHODS The antimicrobial activities of hLF1-11 and P-113 against oral Streptococci strains were determined using the broth microdilution method. The effects of hLF1-11 and P-113 on the bacterial plasma membrane were visualized by scanning electron microscopy. Cell membrane permeability was monitored using the intracellular dye calcein. The subcellular localization of hLF1-11 and P-113 in bacteria was measured by fluorescence light microscopy. An electrophoretic mobility shift assay (EMSA) was performed to evaluate the DNA binding capabilities of hLF1-11, P-113 and MUC7 12-mer. RESULTS Both hLF1-11 and P-113 exerted potent bactericidal activities against all selected oral Streptococci. Streptococcus mutans UA 159 was the most susceptible of the oral bacterial species tested to the antimicrobial effects of the three peptides. The cell membranes of bacteria treated with hLF1-11 or P-113 were still intact after 30 min. hLF1-11 and P-113 could penetrate the bacterial cell membranes and accumulate in the cytoplasm in S. mutans. Both hLF1-11 and P-113 showed DNA binding affinity. CONCLUSIONS Together, our results demonstrate that hLF1-11 and P-113 display antibacterial activity against dental cavity-inducing S. mutans through an intracellular mechanism that could involve DNA binding. Thus, these peptides might be attractive and valuable candidates for development into effective antimicrobial therapies to combat dental caries.

Fatigue Resistance of Nickel-titanium Instruments Exposed to High-concentration Hypochlorite

Introduction The purpose of this study was to introduce a new fatigue test model that simulates the clinical situation for evaluating the corrosion effect of 5.25% sodium hypochlorite (NaOCl) on nickel‐titanium (NiTi) files and to evaluate the effect of 3 different temperatures (22°C, 37°C, and 60°C) on the cyclic fatigue of these files. Methods Three NiTi files (size 25/.04), K3 (SybronEndo, Orange, CA), K3XF (SybronEndo), and Vortex (Dentsply Tulsa Dental Specialties, Tulsa, OK), were subjected to cyclic fatigue tests inside a novel artificial ceramic canal with a curvature of 60° and a 5‐mm radius. A 19‐mm‐long file segment from the tip was introduced into the canal and immersed in water or 5.25% NaOCl at 3 different temperatures, and the number of revolutions to fracture (Nf) was recorded. The fracture surface of all fragments was examined by a scanning electron microscope. Data were analyzed using univariate analysis of variance with the significance level at 0.05. Results The Nf of Vortex files was the highest followed by K3XF and K3 (P < .05) at all conditions. The Nf of all files was highest at 22°C and lowest at 60°C (P < .05). However, no difference in Nf was detected in Vortex files between 22°C and 37°C. The Nf of all files in 5.25% NaOCl was shorter than that in water although there was no statistically significant difference. No pitting or crevice corrosion was observed on the fracture surface. Conclusions NaOCl, 5.25%, does not significantly affect the fatigue behavior of NiTi files. The fatigue resistance should be tested under specific temperature conditions. The austenite finish temperature of a file is important in determining the fracture risk at body temperature. HighlightsA new fatigue test (in zirconium oxide) model that better simulates the clinical situation for the evaluation of the corrosion effect by 5.25% sodium hypochlorite (NaOCl) on nickel‐titanium (NiTi) files is introduced.The effect of 3 different temperatures (22°C, 37°C, and 60°C) on the cyclic fatigue life of conventional superelastic and heat‐treated NiTi files is evaluated.The fatigue life of NiTi files in 5.25% NaOCl is only slightly shorter than in water, with no statistically significant difference.The Vortex file with a reported high austenite finish temperature shows only a slight reduction of cyclic fatigue resistance at body temperature, whereas at 60°C the fatigue resistance is greatly reduced.Contrary to the Vortex file, the fatigue resistance of the K3 and K3XF files decreases clearly at body temperature.

Low Environmental Temperature Influences the Fatigue Resistance of Nickel-titanium Files

Introduction: The purpose of this study was to evaluate the effect of different temperatures (0°C, 10°C, 22°C, 37°C, and 60°C) on the cyclic fatigue life of nickel‐titanium (NiTi) files using a new fatigue test model in zirconium oxide. Methods: Three superelastic NiTi files (EndoSequence [Brasseler USA, Savannah, GA], ProFile [Dentsply Tulsa Dental Specialties, Tulsa, OK], and K3 [SybronEndo, Orange, CA]), and 3 heat‐treated (K3XF [SybronEndo], Vortex [Dentsply Tulsa Dental Specialties], and HyFlex CM [Coltene‐Whaledent, Allstetten, Switzerland]) NiTi files, all size 25/.04, were subjected to cyclic fatigue tests inside a novel, artificial ceramic canal with a curvature of 60° and a 5‐mm radius. The model was immersed in water at 5 different preset temperatures. The number of cycles to failure (NCF) was recorded, and the fracture surface of the fragments was examined by a scanning electron microscope. The data were analyzed using 2‐way analysis of variance with the significance level at 0.05. Results: When the temperature was reduced from 60°C to 0°C, the NCF significantly increased from over 2 to 10 times for the NiTi file groups (P < .01). K3XF had the highest fatigue resistance of all files at 0°C (P < .05). Vortex files had the highest NCF at 10°C–60°C. The NCF of heat‐treated files was significantly higher than superelastic NiTi files at 10°C and 20°C (P < .05). There was no significant difference in the NCF of HyFlex CM at 0°C and 22°C. There was little difference in the fractographic appearance among different temperatures, except that the fraction area occupied by the dimple region of some instruments at 0°C was slightly smaller than at 60°C. Conclusions: Cooling down to low temperatures may be an interesting strategy to improve the fatigue resistance of rotary NiTi files. HighlightsThe effect of different temperatures (0°C, 10°C, 22°C, 37°C, and 60°C) on the cyclic fatigue life of nickel‐titanium (NiTi) files is evaluated using a new fatigue test model in zirconium oxide.When the temperature is reduced from 60°C to 0°C, the number of cycles to failure (NCF) significantly increases from over 2 to 10 times for the NiTi file groups.K3XF has the highest fatigue resistance of all files at 0°C.The Vortex file has the highest NCF at 10°C–60°C.The NCF of heat‐treated files is significantly higher than superelastic NiTi files at 10°C and 20°C.

Selective activities of STAMPs against Streptococcus mutans

The present study aimed to design, synthesize and screen specifically targeted antimicrobial peptides (STAMPs) that can selectively kill Streptococcus mutans (S. mutans) in the biofilm, and to detect protein metabolism, in order to investigate the mechanism of the antibacterial functions of STAMPs against S. mutans. A series of STAMPs were synthesized, and their effects on the selective antibacterial activity of S. mutans on single species and multi-species biofilms under the condition of the planktonic state were studied. The total protein of S. mutans was extracted before and after C11H, and matrix-assisted laser adsorption ionization-time of flight mass spectrometry identification was performed. The antibacterial activity on planktonic S. mutans was increased 3- to 4-fold via C8H, C11H, C12H, C13H, and C14H compared with hLF1-11 (H) alone, and there was no difference between Streptococcus gordonii (S. gordonii) and Streptococcus sanguis (S. sanguis). C8H, C11H, C12H, C13H, and C14H had significant inhibitory effects on the growth of S. mutans biofilm, but there were no significant effects on S. gordonii and S. sanguis biofilms. The number of S. mutans in biofilm decreased at 4 h after C8H, C11H, C12H, C13H and C14H and C8, C11, C12, C13 and C14 had no effect on the growth of planktonic and biofilm states of S. mutans, S. gordonii and S. sanguis species. C11H and C12H exhibited the most obvious effects, followed by C13H and C14H, and then C8H. A total of 21 protein spots with a mean change ratio of 1.5 were identified, all of which were downregulated after C11H. A total of 19 proteins were successfully identified, including cell cycle-relative proteins, nucleic acid metabolism-related enzymes and proteins, virulence factors, protein biosynthesis and regulation, proteins involved in energy metabolism, and proteins with unknown function. In the present study, STAMPs with selective antibacterial activity against S. mutans grown in planktonic or biofilm states but without obvious effects on oral Streptococci and multi-species biofilm were successfully designed and synthesized. Differential protein expression before and after C11H was identified. The mechanism of the antibacterial function was also discussed. Results of the present study laid the foundation for application of STAMPs in the prevention and treatment of dental caries.