Assessment of aeration control strategies for biofilm-based partial nitritation/anammox systems.

The objective of this work was to compare the nitrogen removal in mainstream, biofilm-based partial nitritation anammox (PN/A) systems employing (1) constant setpoint dissolved oxygen (DO) control, (2) intermittent aeration, and (3) ammonia-based aeration control (ABAC). A detailed water resource recovery facility (WRRF) model was used to study the dynamic performance of these aeration control strategies with respect to treatment performance and energy consumption. The results show that constant setpoint DO control cannot meet typical regulatory limits for total ammonia nitrogen (NHx-N). Intermittent aeration shows improvement but requires optimisation of the aeration cycle. ABAC shows the best treatment performance with the advantages of continuous operation and over 20% lower average energy consumption as compared to intermittent aeration.

Efficacy of removal of cariogenic bacteria and carious dentin by ablation using different modes of Er:YAG lasers.

The primary objective of this in vitro study was to evaluate the efficiency of removal of cariogenic bacteria and carious dentin by ablation using two lasers: fluorescence-feedback controlled (FFC) Er:YAG laser and different pulses of Er:YAG laser based on variable square pulse technology (VSPt). The secondary objective was to measure the temperature during laser ablation of carious tissue. Seventy-two extracted human molars were used in this study. Sixty teeth with carious dentin were randomly divided into four experimental groups according to the treatment for caries removal: group 1: 400 µs (FFC group); group 2: super short pulse (SSP group, 50 µs pulse); group 3: medium short pulse (MSP group, 100 µs pulse); group 4: short pulse (SP group, 300 µs pulse) and one positive control group with no treatment. Twelve teeth without carious lesion were used as a negative control group. After caries removal, swabs were taken with cotton pellets and real-time PCR analysis was performed. During caries ablation, a thermal infrared camera was used to measure the temperature changes. In all experimental groups, specimens were free of bacterial contamination after the treatment. In the SSP, MSP and SP groups, temperatures measured during caries ablation were significantly higher compared to temperatures in the FFC group (P<0.001). In this in vitro study, laser treatment for removal of carious dentin and cariogenic bacteria was an efficient treatment modality without causing excessive temperatures that might adversely affect pulp vitality.

Efficacy of removal of cariogenic bacteria and carious dentin by ablation using different modes of Er: YAG lasers

The primary objective of this in vitro study was to evaluate the efficiency of removal of cariogenic bacteria and carious dentin by ablation using two lasers: fluorescence-feedback controlled (FFC) Er:YAG laser and different pulses of Er:YAG laser based on variable square pulse technology (VSPt). The secondary objective was to measure the temperature during laser ablation of carious tissue. Seventy-two extracted human molars were used in this study. Sixty teeth with carious dentin were randomly divided into four experimental groups according to the treatment for caries removal: group 1: 400 µs (FFC group); group 2: super short pulse (SSP group, 50 µs pulse); group 3: medium short pulse (MSP group, 100 µs pulse); group 4: short pulse (SP group, 300 µs pulse) and one positive control group with no treatment. Twelve teeth without carious lesion were used as a negative control group. After caries removal, swabs were taken with cotton pellets and real-time PCR analysis was performed. During caries ablation, a thermal infrared camera was used to measure the temperature changes. In all experimental groups, specimens were free of bacterial contamination after the treatment. In the SSP, MSP and SP groups, temperatures measured during caries ablation were significantly higher compared to temperatures in the FFC group (P<0.001). In this in vitro study, laser treatment for removal of carious dentin and cariogenic bacteria was an efficient treatment modality without causing excessive temperatures that might adversely affect pulp vitality.

Evaluation of cytotoxic and genotoxic effects of two resin-based root-canal sealers and their components on human leucocytes in vitro.

AIM: To evaluate the in vitro genotoxicity and cytotoxicity of two resin-based root canal sealers and to determine the type of cell death they induce. METHODOLOGY: The sealers tested were Epiphany and RealSeal. Each component of the material (Epiphany Primer, Epiphany Thinning Resin, Epiphany Sealant, RealSeal Primer, RealSeal Thinning Resin and RealSeal Root Canal Sealant), components in permutual combinations and all components mixed together were tested on human peripheral blood leucocytes using ethidium bromide/acridine orange viability staining and comet assay. Simultaneously, untreated negative control cultures were analysed in the same manner. DNA damage was evaluated following 4 h of treatment and after 24 h in the absence of the components of the materials. RESULTS: After 4 h of treatment, except thinning resin, each individual component and the different combinations of components induced a significant increase in DNA migration ability (P < 0.05). After 24 h, combination of primer, thinning resin and sealant of both materials caused cell death inducing intense apoptosis. After 24 h, cells exposed to Epiphany Sealant and RealSeal Root Canal Sealant, both in polymerized and unpolymerized form, exhibited a level of DNA damage that was similar to the control. CONCLUSIONS: Primer and thinning resin of both resin-based root canal sealers and their combinations were cytotoxic and induced apoptosis. Both sealants had no significant effect on the viability of the human leucocytes.

In vitro genotoxicity of root canal sealers.

AIM: To evaluate the effect of leakage on differences in genotoxicity of root canal sealers ex vivo according to their main components using two different cytogenetic assays. METHODOLOGY: Six materials of different composition (GuttaFlow, Epiphany, Diaket, IRM, SuperEBA and Hermetic) were tested on human peripheral blood lymphocytes using the comet assay and chromosomal aberration analysis. Prepared materials were eluted in physiological solution for 1 h, 1 day, 5 and 30 days. Thereafter cultures were treated with 8 microg, 4 microg and 2 microg of each sealer. Frequencies of chromatide and chromosome breaks and accentric fragments were determined. Comet assay was used to evaluate primary DNA damage by measuring tail length and tail intensity. Chi-square, Fisher's PLSD (Protected Least Significant Difference) and Kruskall-Wallis non parametric tests were used for statistical analysis. RESULTS: After 1-h elution only the highest dose of Diaket, Hermetic and SuperEBA significantly (P = 0.035, P = 0.048, P = 0.037 respectively) affected the measured cytogenetic parameters. The migration ability of DNA was more strongly affected than induction of chromosomal aberrations. After elutions longer than 24 h none of the tested sealers exhibited a genotoxic effect. CONCLUSION: Under the conditions used in the study all sealers had acceptable biocompatibility in terms of genotoxicity.

Association between oral lichenoid reactions and amalgam restorations.

BACKGROUND: The aim of this study was to perform a clinical assessment of the association between oral lichenoid reactions (OLR) and amalgam restorations and to determine the salivary concentrations of interleukin-6 (IL-6) and IL-8 before and after replacement of the amalgam restorations. METHODS: The study included 20 patients with OLR and 20 healthy volunteers, who were examined between 2001 and 2005 at the Oral Medicine Unit of the Medical Faculty University of Rijeka. All patients were skin patch tested by an experienced physician. Saliva samples were collected, prepared and analysed for IL-6 and IL-8 concentrations using enzyme-linked immunosorbent assay. RESULTS: Sixteen out of 20 patch-tested patients showed a sensitization to inorganic mercury or amalgam. Total replacement of all amalgam fillings was carried out on 20 patients with fillings based on composite resin, gold, porcelain or a combination of these. Sixteen out of 20 patients showed complete healing of OLR; three patients had marked improvement, whereas one patient showed no improvement. Levels of IL-6 detected before replacement were significantly higher than IL-6 levels following the replacement (P = 0.003). The IL-8 levels measured before replacement procedure were significantly higher than the IL-8 levels after replacement of the fillings (P < 0.001). CONCLUSIONS: On the basis of clinical observations, restorative therapy resulted in tissue healing. Following the replacement of amalgam fillings with fillings based on other restorative materials, levels of both IL-6 and IL-8 shifted towards normal, as measured in healthy subjects.

3D finite element model and cervical lesion formation in normal occlusion and in malocclusion.

The aim of this study was to develop a three-dimensional (3D) finite element model (FEM) of the first maxillary premolar in order to compare the stress profiles in the buccal and palatal cervical regions. The 3D geometry of the tooth was reconstructed, the solid model was transferred into a finite element program where a 3D mesh was created, and the stress distribution analysis was performed. Two typical cases have been considered: the tooth under normal occlusion (case I) and the tooth under malocclusion (case II). In case I, larger compressive stresses were found in the cervical enamel and dentine. Tensile stresses were found in the fissure system, adjacent area, and at the vestibular surface of the buccal cusp. The peak values for the principal stress ranged from -259 to +2.25 MPa in the cervical areas. In the case II, larger compressive stresses were found in the palato-cervical enamel and dentine. Tensile stresses were found inside the enamel in the fissure system, adjacent area, at the vestibular surface of the buccal cusp, and in the bucco-cervical enamel. The peak values for the principal stress ranged from -501.947 MPa in palatal region to +82.4 MPa in the buccal region This study implies a role of occlusal forces in development of non-carious lesions. In the case of malocclusion, tensile stresses generated on the cervical areas were higher compared with the stresses generated in the case of normal occlusion and it is probably capable of producing non-carious cervical lesion.

Removal of gutta-percha from root canals using an Nd:YAG laser.

AIM: To examine the use of an Nd:YAG laser in removing gutta-percha fillings from root canals when used in conjunction with eucalyptol, dimethylformamide (DMF) or no solvent. METHODOLOGY: Root-canal fillings (sealer and gutta-percha) were removed with laser irradiation of 20 Hz/1.5 W from 30 roots randomly divided in three groups. In group 1, the solvent was eucalyptol; in group 2, the solvent was DMF; and in group 3, no solvent was used. Laser irradiation was performed until the temperature measured on the root surface increased by 4 degrees C over room temperature. The treatment was deemed complete when the apical foramen was reached with the optical fibre and a reamer. The samples were split longitudinally, and the area of remaining gutta-percha on the root-canal walls was determined with the aid of a computer program. The total number of laser pulses to achieve length and the highest temperature recorded was determined for each tooth. The results were statistically analysed using Student's t-test (P < 0.05) for independent samples. RESULTS: The average temperature increase in group 1 was 9.17 +/- 0.56 degrees C; in group 2, 9.56 +/- 0.28 degrees C; and in group 3, 8.29 +/- 0.41 degrees C. The shortest time to achieve length was in group 3 (6.4 +/- 0.49 min), then in group 1 (6.7 +/- 0.85 min) and group 2 (7.05 +/- 0.79 min). The area of remaining gutta-percha was the largest in group 2 (6.13 +/- 5.76%), whilst the smallest was for group 3 (4.69 +/- 4.03%), but the difference was not statistically significant. The number of pulses was not statistically significant between the groups. CONCLUSIONS: Use of an Nd:YAG laser alone is capable of softening gutta-percha. The addition of solvents did not improve the retreatment, either in terms of the time required for the procedure or in terms of the area of remaining gutta-percha on root-canal walls.

Examination of cytotoxicity and mutagenicity of AH26 and AH Plus sealers.

AIM: To study in vitro the cytotoxic and mutagenic effects of AH26 and AH Plus. METHODOLOGY: Cytotoxic effects on Chinese hamster V79 cells were determined by counting viable cells following incubation with eluations of AH26 and AH Plus. In one set of experiments, the materials were mixed, set for 1 h and then eluted with dimethyl sulphoxide (DMSO) for 1 h, 24 h and 7 days. In the other set, AH26 and AH Plus were mixed and set for 1 h, 24 h and 7 days in physiological saline then crushed and eluted in DMSO for 24 h. The cytotoxic effects of these eluates were evaluated. Three concentrations were chosen to examine the mutagenic effects of AH26 and AH Plus: 5.57, 16.7 and 55.7 microg mL(-1). The structural chromosomal aberration analysis and micronucleus test were performed on human lymphocytes according to standard procedures. RESULTS: Dose-response curves of cell survival were obtained. Both materials were shown to be cytotoxic in doses larger than 55.7 microg mL(-1), except for AH26, after 7 days setting time. AH Plus was also shown to be toxic in concentrations of 16.7 microg mL(-1), except after 7 days setting time. Neither AH26 nor AH Plus induced a significant increase of chromosomal aberrations or micronuclei induction at any setting time or concentration. CONCLUSION: There was no mutagenicity found for AH26 and AH Plus on human lymphocytes in highly controlled conditions in vitro.

Influence of calcium hydroxide root-canal sealer on microbial growth in vitro.

The calcium hydroxide-based filling material Apexit, which is often used in endodontic practice, was evaluated for its antibacterial and antifungal effects against microorganisms isolated from oral cavity (Serratia marcescens, Pseudomonas putida, Staphylococcus aureus, Candida albicans). Two different quantitative techniques were employed--the direct-contact test was used to examine the efficacy of freshly mixed material while the broth-survival test was employed to check the antimicrobial properties of 5-d-old material. Apexit inhibited Gram-negative bacteria more effectively than Gram-positive ones but had none or a very weak inhibitory effect on C. albicans.

Bacterial and fungal microleakage of AH26 and AH Plus root canal sealers.

AIM: To evaluate the penetration of Candida albicans alone and a combination of bacteria through root canals filled with gutta-percha and one or other root canal sealers, AH26 and AH Plus. METHODOLOGY: Eighty teeth were randomly divided into two groups of 40 teeth each and obturated with gutta-percha using either AH26 or AH Plus sealer. A further 10 teeth served as negative controls and 10 as positive controls. The external surface of each root, except the apical 2 mm, was covered with two layers of nail varnish. The teeth were inserted into Eppendorf plastic tubes and suspended in glass bottles containing sterile Schaedler broth. Streptococcus mutans, Streptococcus mitis, Prevotella melaninogenica and Lactobacillus acidophilus were placed in the access cavities of 20 teeth filled with AH26 and 20 with AH Plus. Candida albicans was placed in the access cavities of the other teeth. The culture medium with microorganisms was changed every 7 days. Every 72 h bacterial or fungal growth in the broth was tested up to a period of 90 days. RESULTS: Leakage in the experimental teeth occurred between 14 and 87 days. Leakage was present in 47% of all samples. From the samples with AH26, 45% leaked bacteria and 60% leaked fungi; whilst from the samples with AH Plus, 50% leaked bacteria and 55% fungi. There was no statistically significant difference in penetration of bacteria and fungi between the sealers. CONCLUSION: In this in vitro study, gutta-percha and the sealers AH26 and AH Plus allowed leakage of bacteria and fungi.

Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry detecting NOS in healthy and chronically inflamed pulp.

The aim of this study was to examine the expression of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) activity in human dental pulps and determine whether there are changes of the activity in chronically inflamed pulp tissue. Nineteen pulps with clinical diagnosis of chronic pulpitis were collected during endodontic treatment. The healthy controls were obtained from teeth extracted for orthodontic therapy. The clinical diagnosis was confirmed by histological analysis. Healthy pulps showed stratified odontoblasts in peripheral parts, while in central area there was normal connective tissue. Chronically inflamed pulps showed less expressed stratification of odontoblasts and infiltration of lymphocytes, polymorphonuclear leukocytes, plasma cells and mastocytes. NADPH-d granular reactivity was assessed semi quantitatively under the light microscope by a single observer and scored on an intensity scale from negative reaction to very strong reaction. In healthy human pulps, NADPH-d activity was strong to very strong in odontoblastic layer. Endothelial cells and Schwann cells showed strong NADPH-d reactivity, while the other parts of central area were weakly positive. Similar distribution of reactivity was expressed also in chronically inflamed pulp; moderate to strong reaction was observed in stromal area as result of positive reaction in inflammatory cells and endothelial cells of abundant newly formed capillaries.

Cytotoxic effect of four root filling materials.

The aim of this study was to evaluate the cytotoxic effect of four root canal sealers: AH26, AH Plus, Diaket and Apexit. In the experiment two cell lines, human cervical carcinoma (HeLa) cells and mouse skin fibroblasts (L929), were used. Under aseptic conditions, the sealers were prepared according to the manufacturers' directions, and 0.01 mL of each material was placed in a 24-well plate. The sealers were covered with cell suspension. The cytotoxicity was estimated by determining the number of viable cells by a light microscope, as well as the total number of cells 24 h, 48 h and 120 h after the treatment with mentioned materials. The results obtained in this study showed the high cytotoxcity of the new AH Plus root canal sealer, which was shown to be equally or more toxic to the standard AH26 and Diaket materials. Apexit was the least toxic sealer.

The mutagenic potential of AH+ and AH26 by Salmonella/microsome assay.

The aim of this study was to examine the mutagenic potential of canal sealers AH+ and AH26 by Salmonella/microsome assay. The materials were tested immediately after mixing, 1 hr and 1 month later, respectively. The dimethyl sulfoxide extracts of sealers in amounts of 3.0, 1.5, and 0.75 microliters/plate were used. The plated bacterial strains of Salmonella were TA 98 and TA 100. The results showed that AH+ is mutagenic toward strain TA 100 1 hr after mixing. One month after mixing, mutagenic activity was expressed only in TA 98. Paste A showed strong mutagenicity toward TA 100. AH26 was more mutagenic to the TA 100 immediately after mixing, 1 hr later, and 1 month after it was polymerized. Also it was mutagenic toward TA 98 in the polymerized condition. Further examinations should be conducted to establish a definitive conclusion about mutagenic potential for these two endodontic materials.

Leakage of five root canal sealers.

AIM: The aim of this study was to examine the apical sealing ability of five root canal sealers using a fluid transport model. METHODOLOGY: A comparison of root canal scalers AH26, AH Plus, Diaket, Apexit, and Ketac-Endo were tested on 60 single-rooted teeth. The coronal part of each tooth was removed at the amelo-cemento junction, and also 3 mm of the root tip. Root canals were instrumented using the 'step-back' technique with Gates Glidden drills and irrigated with 2.5% NaOCl. The specimens were divided into five groups of 10 samples each and filled with test materials and gutta-percha points by the cold lateral condensation technique. Ten teeth were used as a control group, out of which five served as negative and five as positive controls. The leakage was measured by the movement of an air bubble in a capillary glass tube connected to the experimental root section. RESULTS: The differences in leakage amongst Ketac-Endo (0.318 microL: SD 0.084), AH26 (0.319 microL; SD 0.075), AH Plus (0.330L; SD 0.085) Apexit (0.360 microL; SD 0.127) and Diaket (0.387 microL; SD 0.140) were not statistically significant (P > 0.05). CONCLUSIONS: Under the conditions of this study, all five sealers produced a satisfactory seal.

Effect of taste and smell on secretion rate of salivary IgA in elderly and young persons.

Two experiments were performed to determine the effect of taste and odor stimuli on secretion rate of salivary IgA in young and elderly individuals. In Experiment 1, three stimuli were applied to the tongue: 1) "flavor" drops (60% sugar, 5% cocoa powder, and 0.1 % Irish cream odor); 2) sugar (60%); and 3) water. In Experiment 2, four different foods (chicken broth, onion soup, corn, and carrots) were tested with and without monosodium glutamate (MSG). The stimuli in both experiments were delivered three times in a one hour period: t=0, t=30 minutes, t=60 minutes. The results of Experiment 1 indicated that application of sugar (taste alone) and flavor (taste and odor combined) to the tongue induced significantly higher secretion rates of sIgA than the application of water in both elderly and young subjects. In addition, flavor application produced significantly higher secretion rates of sIgA than sugar application alone. Secretion rates of sIgA in young persons were significantly higher than those in elderly persons. In Experiment 2, the increase in secretion rate of sIgA at 30 and 60 minutes for each food with MSG was greater than the same food without MSG for the elderly subjects. The increases in secretion rates of sIgA were produced by elevated salivary flow (Experiments 1 and 2) as well as increased absolute concentrations of sIgA (Experiment 1). The elevation of absolute concentrations of sIgA by chemosensory stimuli may involve neural-immune connections. The improvements in salivary flow and secretory immunity by repeated taste and smell stimulation found here have clinical potential for treatment of immune deficiencies and dry mouth which frequently occur in elderly individuals.

Infective endocarditis caused by Veillonella of dental origin.

The purpose of this investigation was to examine whether Veillonella could cause transitory bacteriemia and endocarditis in both pure and mixed cultures when the port of entrance for infection was made in rats' incisors. Incisors of 54 male Zgr: whistar conventional rats were inoculated with pure culture of Veillonella (18 animals) and with mixed culture of S. mutans and Veillonella (18 animals). Remaining 18 incisors (the control group) were treated with saline solution. The animals were sacrificed after 7, 21 and 52 days respectively. Two positive hemocultures were obtained in mixed infection after 21 days of experimental procedure. Histopatological analysis of endocardial tissue revealed changes in 7 (12.96%) cases. Occurrence of acute endocarditis (one case) and chronical (four cases) ones depended on duration of mixed infections. For chronical endocarditis that appears in two animals with pure Veillonela culture we are at a loss of explanation. In conclusion, on the rats model Veillonella can penetrate into circulation in association with S. mutans via the pulp tissue and could be involved in infective endocarditis.

Salivary IgA secretion rate in young and elderly persons.

Immunoglobulin A (IgA) is the dominant immunoglobulin isotype on all mucosal surfaces where it acts as a first line of defense against microbial invasion. Recent investigations suggest that secretory IgA (sIgA) concentrations vary over the day due to a range of variables including dietary factors, daily mood, and exercise. In this study, salivary IgA was determined by ELISA in samples of 48 persons grouped as "young" (20-30 years old) and "elderly" (60-80 years old). Unstimulated, stabilized morning and afternoon saliva was collected during 7 consecutive days. Saliva flow, total proteins, sIgA concentrations, and sIgA secretion rates were determined. The main finding was that saliva flow and sIgA secretion rate were significantly lower in the elderly than in the young. Salivary IgA secretion rate was found to be independent of total proteins secreted in all samples. There is individual variability within a particular age group. It was also found that stress and daily events influence the sIgA secretion rate.