Markus Haapasalo

Epidemiology and pathogenesis of Bacillus cereus infections.

Bacillus cereus is a causative agent in both gastrointestinal and in nongastrointestinal infections. Enterotoxins, emetic toxin (cereulide), hemolysins, and phoshpolipase C as well as many enzymes such as beta-lactamases, proteases and collagenases are known as potential virulence factors of B. cereus. A special surface structure of B. cereus cells, the S-layer, has a significant role in the adhesion to host cells, in phagocytosis and in increased radiation resistance. Interest in B. cereus has been growing lately because it seems that B. cereus-related diseases, in particular food poisonings, are growing in number.

Irrigation in Endodontics

The success of endodontic treatment depends on the eradication of microbes from the root-canal system and prevention of reinfection. The root canal is shaped with hand and rotary instruments under constant irrigation to remove the inflamed and necrotic tissue, microbes/biofilms, and other debris from the root-canal space. Irrigants have traditionally been delivered into the root-canal space using syringes and metal needles of different size and tip design. Clinical experience and research have shown, however, that this classic approach typically results in ineffective irrigation. Many of the compounds used for irrigation have been chemically modified and several mechanical devices have been developed to improve the penetration and effectiveness of irrigation. This article summarizes the chemistry, biology, and procedures for safe and efficient irrigation and provides cutting-edge information on the most recent developments.

Isolation of Enterococcus faecalis in previously root-filled canals in a Lithuanian population.

The occurrence of Enterococcus faecalis in root canals of previously root filled teeth with apical periodontitis requiring retreatment was studied in Lithuanian patients. Twenty-five asymptomatic teeth were included in the study. Avoiding contamination microbiological samples were taken from the canals before and after preparation and irrigation with sodium hypochlorite and EDTA. Microbes were isolated from 20 of 25 teeth. E. faecalis was isolated from 14 of those 20 culture positive teeth, usually in pure culture or as a major component of the flora. Second samples taken after preparation revealed growth in 7 of the 20 teeth. Five of the seven cases were E. faecalis in pure culture. Isolation of E. faecalis was not related to the use of any particular root filling material in the original root filling. The results indicate that, rather than previous chemical treatment, it is the ecological conditions present in the incompletely filled root canal that are important for the presence of E. faecalis in these teeth.

Current challenges and concepts of the thermomechanical treatment of nickel-titanium instruments.

INTRODUCTION The performance and mechanical properties of nickel-titanium (NiTi) instruments are influenced by factors such as cross-section, flute design, raw material, and manufacturing processes. Many improvements have been proposed by manufacturers during the past decade to provide clinicians with safer and more efficient instruments. METHODS The mechanical performance of NiTi alloys is sensitive to their microstructure and associated thermomechanical treatment history. Heat treatment or thermal processing is one of the most fundamental approaches toward adjusting the transition temperature in NiTi alloy, which affects the fatigue resistance of NiTi endodontic files. The newly developed NiTi instruments made from controlled memory wire, M-Wire (Dentsply Tulsa Dental Specialties, Tulsa, OK), or R-phase wire represent the next generation of NiTi alloys with improved flexibility and fatigue resistance. The advantages of NiTi files for canal cleaning and shaping are decreased canal transportation and ledging, a reduced risk of file fracture, and faster and more efficient instrumentation. The clinician must understand the nature of different NiTi raw materials and their impact on instrument performance because many new instruments are introduced on a regular basis. RESULTS This review summarizes the metallurgical properties of next-generation NiTi instruments, the impact of thermomechanical treatment on instrument flexibility, and the resistance to cyclic fatigue and torsion. CONCLUSIONS The aim of this review was to provide clinicians with the knowledge necessary for evidence-based practices, maximizing the benefits from the selection and application of NiTi rotary instruments for root canal treatment.

Inactivation of the Antibacterial Activity of Iodine Potassium Iodide and Chlorhexidine Digluconate Against Enterococcus faecalis by Dentin, Dentin Matrix, Type-I Collagen, and Heat-Killed Microbial Whole Cells

The antibacterial activity of chlorhexidine digluconate and iodine potassium iodide on Enterococcus faecalis A197A was tested in the presence of dentin, dentin matrix, dentin pretreated by EDTA and citric acid, collagen, and heat-killed cells of Enterococcus faecalis and Candida albicans. Medications were preincubated for 1 h with each of the potential inhibitors and tested for their antibacterial activity against E. faecalis, strain A197A. Surviving bacteria were sampled after 1 and 24 h of incubation. Dentin matrix and heat-killed microbial cells were the most effective inhibitors of chlorhexidine, whereas dentin pretreated by citric acid or EDTA showed only slight inhibition. Dentin and skin collagen showed some inhibition at 1 h but not after 24 h. Iodine potassium iodide was effectively inhibited by dentin, dentin matrix, and heat-killed microbial cells. Skin collagen and dentin pretreated by EDTA or by citric acid showed little or no inhibitory effect on iodine potassium iodide. Different components of dentin are responsible for the divergent patterns of inhibition of the antibacterial activity of chlorhexidine digluconate and iodine potassium iodide. Chemical treatment of dentin before applying the medication into the root canal may alter the antibacterial effect of the medication.

Antimicrobial Efficacy of Chlorhexidine against Bacteria in Biofilms at Different Stages of Development

INTRODUCTION Detailed knowledge on the nature of the physiological and metabolic phases of biofilm development is important in combating resistant, disease-associated biofilms. The aim of this study was to examine the susceptibility of multispecies biofilms at different phases of growth to root canal irrigants. METHODS The multispecies biofilms were grown from plaque bacteria on collagen-coated hydroxyapatite discs in brain-heart infusion broth for time periods ranging from 2 days to several months. Fresh nutrients were added weekly for the first 3 weeks, followed by a nutrient deprivation phase, by adding fresh brain-heart infusion broth medium only once a month. Biofilms of different age were subjected to 1-, 3-, or 10-minute exposure to 2% chlorhexidine (CHX) or CHX-Plus. After treatment, the volume ratio of dead bacteria in biofilms was assessed by confocal laser scanning microscopy by using a LIVE/DEAD viability stain. Biofilm structure was visualized by scanning electron microscopy. RESULTS The thickness of biofilms increased from 57 μm (2 days) to 155 μm (3 weeks) during biofilm development. It reached a steady state under nutrient-limiting conditions, with thickness of 190 μm (6 weeks) to 201 μm (12 weeks). The proportion of killed bacteria in mature biofilms (3 weeks) was lower than in young biofilms (2 days, 1 and 2 weeks) after treatment with both CHX products (P < .01).The resistance of mature biofilms under the nutrient-limiting phase (6-12 weeks) to CHX remained stable and was similar to 3-week-old biofilm. However, treatment with CHX-Plus for 3 and 10 minutes did not lose effectiveness against biofilm bacteria in mature and nutrient-limited phases. CHX-Plus showed higher levels of bactericidal activity at all exposure times than 2% CHX (P < .01). CONCLUSIONS Bacteria in mature biofilms and nutrient-limited biofilms are more resistant to CHX killing than in young biofilms. The results emphasize the importance of standardization of factors such as biofilm age when studying the comparative effectiveness of disinfecting agents against biofilm bacteria.

V. Functions of S‐layers

Although S-layers are being increasingly identified on Bacteria and Archaea, it is enigmatic that in most cases S-layer function continues to elude us. In a few instances, S-layers have been shown to be virulence factors on pathogens (e.g. Campylobacter fetus ssp. fetus and Aeromonas salmonicida), protective against Bdellovibrio, a depository for surface-exposed enzymes (e.g. Bacillus stearothermophilus), shape-determining agents (e.g. Thermoproteus tenax) and nucleation factors for fine-grain mineral development (e.g. Synechococcus GL 24). Yet, for the vast majority of S-layered bacteria, the natural function of these crystalline arrays continues to be evasive. The following review up-dates the functional basis of S-layers and describes such diverse topics as the effect of S-layers on the Gram stain, bacteriophage adsorption in lactobacilli, phagocytosis by human polymorphonuclear leukocytes, the adhesion of a high-molecular-mass amylase, outer membrane porosity, and the secretion of extracellular enzymes of Thermoanaerobacterium. In addition, the functional aspect of calcium on the Caulobacter S-layer is explained.

Tissue dissolution by sodium hypochlorite: effect of concentration, temperature, agitation, and surfactant.

AIM Sodium hypochlorite is the most commonly used endodontic irrigant because of its antimicrobial and tissue-dissolving activity. The aim of this study was to evaluate and compare the effects of concentration, temperature, and agitation on the tissue-dissolving ability of sodium hypochlorite. In addition, a hypochlorite product with added surface active agent was compared with conventional hypochlorite solutions. METHODS Three sodium hypochlorite solutions from two different manufacturers in concentrations of 1%, 2%, 4%, and 5.8% were tested at room temperature, 37 degrees C, and 45 degrees C with and without agitation by ultrasonic and sonic energy and pipetting. Distilled and sterilized tap water was used as controls. Pieces of bovine muscle tissue (68 +/- 3 mg) were placed in 10 mL of each solution for five minutes. In selected samples, agitation was performed for one, two, or four 15-second periods per each minute. The tissue specimens were weighed before and after treatment, and the percentage of weight loss was calculated. The contact angle on dentin of the three solutions at concentrations of 1% and 5.8% was measured. RESULTS Weight loss (dissolution) of the tissue increased almost linearly with the concentration of sodium hypochlorite. Higher temperatures and agitation considerably enhanced the efficacy of sodium hypochlorite. The effect of agitation on tissue dissolution was greater than that of temperature; continuous agitation resulted in the fastest tissue dissolution. Hypochlorite with added surface active agent had the lowest contact angle on dentin and was most effective in tissue dissolution in all experimental situations. CONCLUSIONS Optimizing the concentration, temperature, flow, and surface tension can improve the tissue-dissolving effectiveness of hypochlorite even 50-fold.

Biocompatibility of two novel root repair materials.

INTRODUCTION The purpose of the present study was to evaluate the biocompatibility of 2 root-end filling materials, Endosequence Root Repair Material Putty (ERRM Putty) and Paste (ERRM Paste) and compare them with gray mineral trioxide aggregate (MTA). METHODS ERRM Putty, ERRM Paste, MTA, intermediate restorative material (IRM), and Cavit G were tested. For cytotoxicity assay, human gingival fibroblasts were incubated for 1, 3, and 7 days with extracts of varying concentrations from materials set for 2 days or 7 days. Cell viability was evaluated by methyl-thiazol-tetrazolium (MTT) assay. For cell adhesion assay, materials set for 7 days were examined under scanning electron microscope directly after setting, after incubation in cell culture medium for 7 days, and after incubation in gingival fibroblast suspension at a density of 5 × 10(4) cells/well for 2 and 7 days. The constituents of crystals formed on surface of materials were determined by energy dispersive analysis by x-ray. RESULTS Cell viability was significantly correlated with the type of material, setting time, and incubation time (P < .001 for all parameters). ERRM Putty and ERRM Paste displayed similar cell viabilities to MTA at all experimental conditions, except that fresh samples of ERRM Paste showed slightly lower cell viabilities than MTA. Cell viabilities with IRM and Cavit G were significantly lower than with the other 3 materials (P < .001). Similar surface crystallographic features and cell adhesion were observed on ERRM Paste, ERRM Putty, and MTA. CONCLUSIONS ERRM Putty and ERRM Paste displayed similar in vitro biocompatibility to MTA.

A New Noninvasive Model to Study the Effectiveness of Dentin Disinfection by Using Confocal Laser Scanning Microscopy

INTRODUCTION The present study was designed to develop a standardized model for quantification of the effectiveness of dentin disinfection by different antibacterial solutions including a new root canal irrigant, Qmix. METHODS Dentinal tubules from the root canal side in semicylindrical dentin specimens were infected with Enterococcus faecalis by centrifugation of the bacterial suspension into the tubules. Scanning electron microscopy (SEM) was used to verify the presence of bacteria in dentin. The outer side of dentin pieces was closed, and the specimens were subjected to 1-minute and 3-minute exposure to sterile water, 1%, 2%, 6% sodium hypochlorite (NaOCl), 2% chlorhexidine (CHX), and Qmix. Confocal laser scanning microscopy (CLSM) and viability staining were used to quantitatively analyze the proportions of dead and live bacteria inside dentin. RESULTS A heavy invasion by E. faecalis was detected by both SEM and CLSM throughout the dentinal tubules. The amount of dead cells in dentin increased with increasing NaOCl concentration and time of exposure (P < .05). Qmix was equally effective in killing bacteria in dentin as 6% NaOCl; more than 40% and 60% of the bacteria were killed by both at 1 minute and 3 minutes, respectively. One percent and 2% NaOCl and 2% CHX killed 20%-30% and 30%-40% bacteria after 1 and 3 minutes of exposure, respectively, with no statistically significant differences among the 3 agents (P > .05). In the control group, which was treated with sterile water, only 4%-6% of the bacteria were dead. CONCLUSIONS Centrifugation helped to create a heavy, evenly distributed infection deep into the dentinal tubules. The new model made it possible to compare the effectiveness of several disinfecting solutions in killing bacteria inside dentin by a noninvasive CLSM method.