Stem Cell and Oxidative Stress-Inflammation Cycle.

Under a variety of physical and experimental settings, stem cells are able to self-renew and differentiate into specialized adult cells. MSCs (mesenchymal stromal/stem cells) are multipotent stem cells present in a wide range of fetal, embryonic, and adult tissues. They are the progenitors of a variety of specialized cells and are considered crucial tools in tissue engineering. MSCs, derived from various tissues, including cord blood, placenta, bone marrow, and dental tissues, have been extensively examined in tissue repair, immune modulation, etc. Increasing the vitality of MSCs and restoring cellular mechanisms are important factors in treatment success. Oxidative stress harms cellular molecules such as DNA, proteins, and lipids due to the overproduction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in cells and tissues or insufficiency of antioxidant systems that can inactivate them. Oxidative stress has a close link with inflammation as a pathophysiological process. ROS can mediate the expression of proinflammatory genes via intracellular signaling pathways and initiate the chronic inflammatory state. At the same time, inflammatory cells secrete a large number of reactive species that cause increased oxidative stress at sites of inflammation. In inflammatory diseases, the differentiation of stem cells and the regenerative and wound healing process can be affected differently by the increase of oxidative stress. Recent studies have indicated that dental pulp stem cells (DPSCs), as a resource of adult stem cells, are an attractive option for cell therapy in diseases such as neurological diseases, diabetes, cardiological diseases, etc., as well as its treatment potential in pulp inflammation. The future of oxidative stressinflammation cycle and/or ageing therapies involves the selective elimination of senescent cells, also known as senolysis, which prevents various age-related diseases. Most pathologies are implicated on the effects of ageing without exerting undesirable side effects.

Effects of aging and inflammation on catalase activity in human dental pulp.

OBJECTIVES: In this study, it was aimed to examine the catalase activity in clinically healthy and caries-related inflamed symptomatic human dental pulps of young and old individuals. DESIGN: Sixty pulp samples from young and old healthy donors, were collected depending on pulpal status. 48 samples were used for spectrophotometric analysis and 12 samples for immunohistochemistry. Healthy pulps were maintained from non-carries, extracted third molars. Reversible and irreversible pulpitis samples were obtained by pulp extirpation during endodontic treatment. Following homogenization catalase enzyme activity was determined by spectrophotometry. Additionally, two pulp tissue samples from each group were fixed and evaluated for catalase immunoreactivity. RESULTS: Catalase enzyme activity in old healthy pulp samples were significantly higher than healthy young samples (p ≤ 0.05). Reversible and irreversible pulpitis samples indicated significantly decreased activity compared to healthy samples in elderly group (p ≤ 0.05). Young reversible pulpitis samples showed significantly increased catalase activity when compared to irreversible pulpitis and the reversible pulpitis samples in elderly group (p ≤ 0.05). Immunohistochemical evaluation indicated that there was intense catalase immunoreactivity in young patients with reversible pulpitis compared with reversible pulpitis in elderly group. However, weak immunoreactivity was observed in young irreversible pulpitis and elderly reversible pulpitis samples. CONCLUSIONS: The pulp tissues presented different levels of catalase activities against pulpitis and aging.

Age-related Changes in the Alkaline Phosphatase Activity of Healthy and Inflamed Human Dental Pulp.

INTRODUCTION: Alkaline phosphatase (ALP) plays an important role in inducing mineralization events in the dental pulp. This study investigated and compared the ALP levels in healthy and inflamed pulp in young and old human pulp. METHODS: Tissue samples were collected from young (<30 years) and old (>60 years) donors. In both age groups, healthy human pulp (n = 18) were collected from extracted wisdom teeth. For reversible and irreversible pulpitis, pulp samples (n = 18 each) were obtained during endodontic treatment. ALP activity was assessed by spectrophotometry and immunhistochemistry. RESULTS: Regardless of age, reversible pulpitis group samples showed a slight elevation in ALP activity compared with normal healthy pulp. In elderly patients, ALP expression with irreversible pulpitis was significantly higher than those with a healthy pulp (P < .05). CONCLUSIONS: In the hyperemic state, both the young and old pulp shows a slight increase in ALP activity, whereas in irreversible pulpitis, only the old pulp shows significantly elevated ALP levels. Such an increase may trigger calcification events, which may eventually cause difficulties in endodontic treatment procedures in elderly individuals.

Effect of EDTA, sodium hypochlorite, and chlorhexidine gluconate with or without surface modifiers on dentin microhardness.

INTRODUCTION: This study aimed to evaluate the effects of root canal irrigants on the microhardness of root canal dentin in the presence and absence of surface-modifying agents. METHODS: Forty-eight root halves were prepared by longitudinal splitting of the distal roots of 24 freshly extracted mandibular human third molars and embedded in autopolymerizing acrylic resin, leaving the dentin surface exposed. After polishing, the microhardness values of the untreated dentin surfaces were recorded by using Vickers tester at the mid-root level. The root halves were randomly assigned to 6 groups composed of 8 samples each and treated for 5 minutes with one of the following irrigants: 17% EDTA, REDTA, 2% chlorhexidine gluconate (CHX), 2% CHX with surface modifiers (CHX-Plus), 6% NaOCl, or 6% NaOCl with surface modifiers (Chlor-XTRA). After surface treatment, dentin microhardness values were recorded at close proximity to the initial indentation areas. Experimental data were statistically analyzed by using the t test and one-way analysis of variance, followed by Tukey honestly significant difference test at α = 0.05. RESULTS: EDTA, REDTA, NaOCl, and Chlor-XTRA significantly decreased the microhardness of root dentin compared with intact controls (P < .05). CONCLUSIONS: The addition of surface modifiers to the irrigants did not affect the microhardness of the samples.

Chemical and ultramorphologic effects of ethylenediaminetetraacetic acid and sodium hypochlorite in young and old root canal dentin.

OBJECTIVES: The objectives of this study were to evaluate and compare the time-dependent chemical and ultramorphologic effects of ethylenediaminetetraacetic acid (EDTA) and sodium hypochlorite (NaOCl) in young and old dentin. METHODS: Sixty-four teeth scheduled for extraction were collected from young (<30 years) and old (>60 years) patients. In 48 teeth, the dentin was reduced to a powder state and treated with EDTA or EDTA + NaOCl for 1 and 10 minutes, respectively. X-ray diffraction analysis was used to determine the changes in the composition of dentin through dissolution of hydroxyapatite (HAp). In the remaining teeth (n = 16), the root canals were prepared, bisected, and subjected to the same time-dependent treatment regimens. The changes in the number and area of dentinal tubules were calculated by image analysis. The data were analyzed statistically by paired t test and one-way analysis of variance, followed by Tukey honestly significant difference test at P = .05. RESULTS: In both young and old dentin, EDTA significantly decreased the HAp intensity at 1 and 10 minutes, whereas EDTA + NaOCl only decreased that of old dentin at 10 minutes. Pair-wise comparisons revealed that in old dentin, the reduction in HAp intensity after treatment with EDTA and EDTA + NaOCl was significantly greater at 10 minutes than at 1 minute, whereas in young dentin, a significant decrease was only observed in the EDTA/10-minute subgroup. Compared with their 1-minute counterparts, 10-minute treatment with EDTA + NaOCl significantly increased the tubular diameter and tubular area of old dentin. In young dentin, the tubular area and diameter values were not affected by treatment time (P > .05). CONCLUSIONS: In young root dentin, 10-minute treatment with EDTA + NaOCl does not significantly alter the chemical and ultramorphologic structure and thus appears to be unnecessary. In old dentin, extended treatment time with EDTA + NaOCl should be avoided owing to excessive demineralization and erosion. In both types of dentin, EDTA was not effective in complete removal of the smear layer.

The effect of temperature and pH variations on the surface tension of EDTA solutions.

INTRODUCTION: Surface tension of a liquid is one of the major factors that affect the wetting of a solid. The reduction in surface tension could improve the contact of irrigants with the dentinal walls of the root canal system. This in vitro study was conducted to evaluate the effect of pH and temperature variations on the surface tension of EDTA solutions. METHODS: Three solutions, 17% EDTA, REDTA, and EDTA-T, were prepared and adjusted to have a pH of 5.5, 7.5, and 10.5. The surface tension of the test solutions was measured at 22 °C by the pendant drop technique, and the measurement was repeated after heating the solution at 37 °C. Differences among the experimental groups were statistically analyzed using three-way analysis of variance followed by the Bonferroni test for pair-wise comparison. RESULTS: The results of this study showed that there were significant differences in the surface tension values of solutions depending on the pH and temperature (P < .001). The surface tension level of the EDTA solution dramatically decreased when surfactant was added to the EDTA solution in both pH and temperature variations (P < .001). The increased temperature significantly altered the surface tension value at a pH of 5.5 of all EDTA solutions, at a pH of 7.5 of EDTA and REDTA solutions, and at a pH of 10.5 of only REDTA solution (P < .01). CONCLUSIONS: It was concluded that the surface tension of EDTA with and without surfactant is influenced by pH and temperature.

Effect of low-surface-tension EDTA solutions on the wettability of root canal dentin.

OBJECTIVE: This study was conducted to evaluate the effect of reducing the surface tension of ethylenediaminetetraacetic acid (EDTA) solutions on the wettability of root canal dentin. STUDY DESIGN: Forty-two extracted teeth were sectioned at the crown, and the apical third and remaining mid-root portion was bisected longitudinally. The root halves were embedded in resin blocks. The experimental groups were treated with 17% EDTA, EDTA-T, and REDTA alone or followed by 2.5% NaOCl. Surface free energies of samples were calculated by measuring contact angles. Surface tension measurements of all solutions were performed with pendant drop method. RESULTS: The addition of surfactant to the EDTA solution significantly decreased the surface tension of solutions (P < .01). Combined and single use of experimental solutions and NaOCl significantly decreased the water contact angle and increased the surface free energy of root canal dentin (P < .05). EDTA-T alone or combined with NaOCl also increased surface free energy compared with EDTA solution (P < .05). CONCLUSIONS: The use of low-surface-tensioned EDTA compounds alone or in combination with NaOCl increased the wettability of root canal dentin.

Effect of ethylenediaminetetraacetic acid and sodium hypochlorite irrigation on Enterococcus faecalis biofilm colonization in young and old human root canal dentin: in vitro study.

INTRODUCTION: The alterations in dentin tissue depending on increasing age might cause different adhesion capability of bacteria, yielding differences in clinical approaches regarding root canal irrigation. This study, therefore, aimed to evaluate the effects of ethylenediaminetetraacetic acid (EDTA) and sodium hypochlorite (NaOCl) on Enterococcus faecalis biofilm growth in root canal dentin of young and old individuals. METHODS: The root canals of extracted young (<30 years) and old (>60 years) single-rooted human teeth were sectioned at the crown and the apical parts. The root canals of the mid-root sections were enlarged with #2 Gates-Glidden burs. After treatment with 17% EDTA + 2.5% NaOCl, 17% EDTA alone, 2.5% NaOCl alone, or saline, the samples were incubated in E. faecalis suspension for 24 hours. Thereafter, root canal samples were enlarged again with #3 Gates-Glidden burs, and the removed dentin chips were collected. Bacteria were dispersed by using sonication, serially diluted, and then plated for counting on agar plates as colony-forming units. Scanning electron microscopy and confocal laser scanning microscopy investigations were also carried out to examine the biofilm formation on the dentin. Data were analyzed with Kruskal-Wallis test and Mann-Whitney U test with Bonferroni adjustment. RESULTS: Combination of EDTA and NaOCl significantly reduced the amount of intracanal biofilm in both age groups (P < .01). However, the bacterial counts of E. faecalis in the old group were still higher (P < .05). CONCLUSIONS: It might be suggested that root canals from elderly population are more susceptible to canal infection. However, combined application of EDTA and NaOCl significantly reduces the amount of intracanal biofilm.

The zymographic evaluation of gelatinase (MMP-2 and -9) levels in acute and chronic periapical abscesses.

OBJECTIVE: This study investigated the presence and levels of matrix metalloproteinases (MMP)-2 and -9 in periapical abscesses. STUDY DESIGN: Eighteen samples of intracanal exudates containing pus were collected from teeth with clinically and radiographically verified primary or secondary acute and chronic apical abscesses. Pro- and active forms of MMP-2 and MMP-9 levels were analyzed by using substrate gel zymography followed by an image analysis system. Statistical analysis was performed using the Kruskall-Wallis and Mann-Whitney U tests with Bonferroni adjustment. RESULTS: Both forms of MMP-9 were detected in all pus samples and demonstrated marked differences among the experimental groups (P < .05). Primary or secondary acute apical abscess samples demonstrated significantly higher MMP-9 levels compared with MMP-2 levels (P < .01). However, MMP-2 could not be detected in chronic apical abscesses. CONCLUSION: According to the results of this study, gelatinases might affect the pathogenesis of acute and chronic periapical abscesses.

Effect of bleaching agents on surface free energy parameters of resin composite coated with saliva biofilm.

PURPOSE: To assess the effect of 10% carbamide peroxide and 10% hydrogen peroxide bleaching preparations on the surface free energy of resin composite with and without saliva biofilm coating. METHODS: 72 light-cured resin composite samples were used. The samples were either coated with fresh human saliva or left uncoated. Each sample was placed in a plastic assay tube containing 2 ml of either 10% carbamide peroxide (CP), 10% hydrogen peroxide (HP), or phosphate buffer solution. The tubes containing the composite samples were then placed in a dry incubator at 37 degrees C for 1- and 3-day time intervals. After each time interval the samples were rinsed with distilled water and subjected to wetting measurements using a captive bubble technique. Measurements were taken in triplicate and determination of contact angles done by using film negatives on an enlarger. The differences between pre-treatment and post-treatment measurements and between samples coated with saliva and non-coated samples were analyzed statistically for each time period and treatment group. RESULTS: 10% CP reduced octane contact angle of all exposed composite groups after 1 day of treatment regardless of saliva coating. Differences between the pre-bleached and post-bleached groups were statistically significant only for octane contact angles measured in saliva-coated samples (P < 0.05). 10% CP reduced both the octane and air contact angles of all exposed composite surfaces after 3 days of treatment. The reduction was statistically significant only for octane contact angles measured in the saliva-coated samples (P < 0.05). Additionally, 10% CP significantly reduced the surface free energy of saliva-coated samples after 1-day treatment as compared to non-coated samples. 10% HP reduced octane contact angle of all exposed composite groups after 1 day of treatment regardless of saliva coating. The differences between the pre-bleached and post-bleached groups were statistically significant only for octane contact angles measured in the saliva-coated samples (P < 0.05). 10% HP reduced both the octane and air contact angles of all exposed resin composite surface samples after 3 days of treatment regardless of saliva coating. However, the differences between the groups were not statistically significant.