Temporal analysis of the spontaneous baroreceptor reflex during mild emotional stress in the rat.

The effect of emotional stress on the spontaneous baroreceptor reflex (sBRR) in freely moving rats was investigated. Six male Wistar rats equipped with an intra-arterial polyethylene catheter were exposed to a 2-min air-jet stress. For time course analysis of the sBRR response to stress, the records of systolic blood pressure (SBP) and pulse interval (PI) were divided into five regions: baseline (BASELINE), acute exposure to air-jet stress (STRESS), immediate recovery (IMMED. RECOVERY), remaining recovery (RECOVERY), and delayed response (DELAYED RESPONSE). In addition to sBRR sensitivity and effectiveness, we introduce the sequence coverage area and its median for evaluation of the sBRR operating range and set point. During exposure to STRESS and IMMED. RECOVERY, sBRR sensitivity was preserved, its effectiveness was decreased, its operating range was enlarged, and the set point was shifted towards higher SBP and lower PI values. According to the joint symbolic dynamics analysis, the SBP and PI relationship became less predictable hence more prone to respond to stress. In RECOVERY the parameters regained baseline values and DELAYED RESPONSE occurred during which re-setting of sBRR was noted. It follows that emotional stress modulates sBRR differentially during the time course of stress and recovery, affecting both linearity and unpredictability of the BP and PI relationship.

Central vasopressin V(1a) and V(1b) receptors modulate the cardiovascular response to air-jet stress in conscious rats.

This study investigates the contribution of central vasopressin receptors in the modulation of systolic arterial pressure (SAP) and heart rate (HR) response to air-jet stress in conscious Wistar rats equipped with a femoral arterial catheter and intracerebroventricular cannula using novel non-peptide and selective vasopressin V(1a) (SR49059) and V(1b) (SSR149415) antagonists. The effects of stress on SAP and HR were evaluated by measuring the maximal response to stress, the latency of the maximal response, the duration of the recovery period, and the increase in the low frequency (LF) short-term variability component. Stress induced a parallel and almost immediate increase in both SAP and HR, followed by enhanced LF SAP variability in the recovery period. Pretreatment of rats with V(1a) antagonist did not affect the maximal increase or the latency of SAP and HR response to acute stress, but shortened the recovery period of SAP and HR and prevented the increase in LF SAP. The V(1b) antagonist reduced the maximal increase in SAP without affecting HR and their latencies, shortened the recovery period of SAP and inhibited the increase in LF SAP variability. These results indicate that both central V(1a) and V(1b) receptors mediate cardiovascular changes induced by air-jet stress in conscious rats.

Prevalence of Enterococcus faecalis and Porphyromonas gingivalis in infected root canals and their susceptibility to endodontic treatment procedures: a molecular study.

INTRODUCTION: Because apical periodontitis is recognizably an infectious disease, elimination or reduction of intracanal bacteria is of utmost importance for optimum treatment outcome. OBJECTIVE: The prevalence of Enterococcus faecalis and Porphyromonas gingivalis in infected root canals was studied Also, the effect of endodontic therapy by using intracanal medicaments, calcium hydroxide paste (CH) or gutta-percha points containing calcium hydroxide (CH-GP) or chlorhexidine (CHX-GP) on these microorganisms was assessed by polymerase chain reaction (PCR) assay. METHODS: Fifty-one patients with chronic apical periodontitis were randomly allocated in one of the fol- lowing groups according to the intracanal medicament used: CH, CH-GP and CHX-GP group. Bacterial samples were taken upon access (S1), after chemomechanical instrumentation (S2) and after 15-day medication (S3). PCR assay was used to detect the presence of selected bacteria. RESULTS: E. faecalis was detected in 49% (25/51) and P. gingivalis in 17.6% (9/51) of the samples. Samples which showed no bacterial presence at S1 were excluded from further analysis. Overall analysis of all 29 samples revealed significant differences between S1 and S2 (p < 0.001), S2 and S3 (p < 0.05), and S1 and S3 (p < 0.001). When distinction was made between the intracanal medications, there was a significant difference in the number of PCR positive samples between S1 and 52, S1 and S3, but not between S2 and S3 samples. CONCLUSION: E. faecalis is more prevalent than P. gingivalis in primary endodontic infection. Intracanal medication in conduction with instrumentation and irrigation efficiently eliminates E. faecalis and P. gingivalis from infected root canals.

Effect of the source of biofilm bacteria, level of biofilm maturation, and type of disinfecting agent on the susceptibility of biofilm bacteria to antibacterial agents.

INTRODUCTION: Biofilm development is a dynamic process that begins with the initial attachment of planktonic bacteria to a surface, eventually leading through different stages to a mature, structurally complex biofilm. The aim of this study was to assess the effect of the source of biofilm bacteria, the level of biofilm maturation, and the type of disinfecting agent on the susceptibility of biofilm bacteria to antibacterial agents. METHODS: Multispecies biofilms from plaque bacteria of 6 donors were grown for up to 8 weeks on collagen-coated hydroxyapatite disks. After 1, 2, 3, 4, and 8 weeks of growth the biofilms were exposed to 1% sodium hypochlorite, 0.2/0.4% iodine-potassium iodide, and 2% chlorhexidine for 1 and 3 minutes. The percentage of killed biofilm bacteria was determined by using LIVE/DEAD viability staining and confocal laser scanning microscopy. One-way analysis of variance was used for statistical analysis. RESULTS: One- and 2-week-old biofilms were moderately or very sensitive to the tested disinfecting agents, which killed 20%-100% of the biofilm bacteria. After 3 weeks of growth the biofilm bacteria were more resistant to the same agents, and only 10%-30% of the bacteria were killed (P< .001). The same pattern of the effect of biofilm age (maturation) on the resistance of bacteria was observed in all 6 biofilms and with all 3 disinfecting agents. CONCLUSION: The change of biofilm bacteria from sensitive to resistant against disinfecting agents occurred between 2 and 3 weeks of biofilm maturation. This development took place simultaneously in all biofilms grown from plaque bacteria from 6 different donors and was independent of the type of disinfecting agent used. The results emphasize the importance of knowing the maturation timeline of each biofilm model used to test the effectiveness of endodontic disinfecting agents against biofilm bacteria.

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.

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.

Bacterial viability in starved and revitalized biofilms: comparison of viability staining and direct culture.

OBJECTIVES: The aim of this study was to enumerate viable bacteria at different growth stages of a multispecies oral biofilm and to compare results obtained with the LIVE/DEAD BacLight Kit (Molecular Probes, Eugene, OR) with those from culturing and plate counting (colony-forming unit counts [CFUs]). METHODS: The multispecies biofilm was grown from plaque bacteria on collagen-coated hydroxyapatite disks in brain-heart infusion broth for 3 weeks (phase І) with a weekly addition of new nutrients. This was followed by a 9-week nutrient-deprivation phase (phase ІІ); after which, the biofilm was reactived again by weekly additions of fresh BHI medium for 4 weeks (phase ІІІ). The number and proportion of live bacteria in biofilm was assessed by culturing and by confocal laser scanning microscopy using a LIVE/DEAD viability stain throughout the experiment. RESULTS: The CFU counts dropped more than four logarithmic steps during phase ІІ. However, viability staining by LIVE/DEAD stain indicated only a 25% drop in viability. The CFU counts increased during phase III, but it took 4 weeks for them to return close to the original CFU numbers. Cell viability, as indicated by the staining, improved from 75% close to the original 100%. CONCLUSIONS: Bacteria in the multispecies biofilm grown under nutrient deprivation became viable but nonculturable but could be brought back to a culturable state after reestablishing sufficient access to nutrients. The results indicate that viability staining better reflected true viability of the biofilm bacteria than culturing during the long starvation phase. The result of this study may have an impact on the interpretation of cultural studies on root canal microbiology/biofilms in vivo.

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.

The synergistic antimicrobial effect by mechanical agitation and two chlorhexidine preparations on biofilm bacteria.

INTRODUCTION: Irrigation of the root canal with antibacterial solutions is considered an essential part of root canal treatment in endodontics. The purpose of this study was to investigate whether mechanical agitation (ultrasonic or sonic) improves the effectiveness of chlorhexidine against biofilm bacteria in vitro. METHODS: Collagen-coated hydroxyapatite (CHA) disks were exposed to dispersed subgingival plaque for 3 weeks at 37 degrees C. The multispecies biofilms established were subjected for 1 and 3 minutes to CHX-Plus (Vista Dental Products, Racine, WI) and 2% chlorhexidine (CHX), with or without mechanical agitation. After treatment, the amount of dead bacteria in biofilms was analyzed by viability staining and confocal laser scanning microscopy (CLSM). The morphology of biofilms, with or without mechanical agitation, was also examined by CLSM. RESULTS: The structure of the biofilm did not show any obvious change when the solutions surrounding the biofilm were exposed to continuous ultrasonic or sonic agitation. The combined use of mechanical agitation and chlorhexidine had a more pronounced antimicrobial effect against the biofilms than either one alone. Sonic activation (EndoActivator; Advanced Endodontics, Santa Barbara, CA) showed the highest levels of bactericidal activity with CHX-Plus after both exposure times. The proportion of killed bacteria also depended on the type of irrigant (p < 0.001) and the time of exposure (p < 0.001). CONCLUSIONS: The low-intensity ultrasonic or sonic agitation that does not disrupt biofilm or disperse the biofilm bacteria improves the action of disinfectants against biofilm bacteria.