Invasion Of Dentinal Tubules Research Articles

Robust expression of SIRT6 inhibits pulpitis via activation of the TRPV1 channel.

Invasion of dentinal tubules and pulp tissue by pathogenic bacteria may cause infection leading to pulpitis. Sirtuin 6 (SIRT6) is a NAD-dependent protein deacetylase encoded by the SIRT6 gene. The effect of SIRT6 on lipopolysaccharide (LPS)-induced pulpitis and its mechanism of action were discussed in this study. Dental pulp cells (DPCs) were extracted from human teeth and injected with LPS to induce inflammation. The cells injected with LPS showed substantially decreased expression of SIRT6. The overexpression of SIRT6, induced by plasmid-transfection of DPCs with SIRT6 overexpressing vector, led to a marked decrease in proinflammatory cytokines (IL-6, IL-1β, and TNF-α) and deactivation of NF kappa B pathway. Additionally, dentin matrix protein-1 (DMP1), a promoter of inflammation in dental pulp tissues, was downregulated. Further investigation revealed that SIRT6 promotes ubiquitination of the transient receptor potential vanilloid 1 (TRPV1) channel, leading to its degradation and deactivation. The role of TRPV1 in the anti-inflammatory effects of SIRT6 was determined through incubation of SIRT6-expressing dental pulp stem cells (DPSCs) with capsaicin. This incubation counteracted the effect of SIRT6 on cytokines and DMP1. The injection of lentivirus-SIRT6 attenuated LPS-induced pulpitis in vivo by suppressing TRPV1 activity. Thus, SIRT6 inhibits the TRPV1 channel during LPS-induced inflammation of dental pulp. SIGNIFICANCE OF THE STUDY: This study discussed the effect of sirtuin 6 (SIRT6) on lipopolysaccharide (LPS)-induced pulpitis as well as its mechanism of action and found that SIRT6 may be a negative regulator of pulpitis. Additionally, low expression of SIRT6 and high expression of transient receptor potential vanilloid 1 (TRPV1) in LPS-treated human dental pulp cells are closely associated with proinflammatory cytokines, dentin matrix protein 1 expression, and activation of the NF-κB pathway, which indicated that TRPV1 may be a biomarker for pulpitis and the SIRT6-TRPV1-CGRP axis maybe a clinical target due to their role regulating inflammation and neuropathic pain.

Bacterial invasion of dentinal tubules from the external root surface with and without an intact cemental layer- a confocal laser scanning microscopic study

Aim To evaluate the invasion of two bacterial species Streptococcus sanguinis S s and Aggregatibacter actinomycetemcomitans A a in radicular dentinal tubules with and without an intact cemental layer using confocal laser scanning microscopy Methodology intact freshly extracted human teeth were prepared and divided into groups Group S s a S s without cementum b S s with intact cementum and Group A a a A a without cementum b with intact cementum The cemental layer on each root was removed from one side and kept intact on the other side The specimens were incubated in the bacterial suspension for days at C The specimens were sectioned mounted stained with a fluorescent dye and viewed under the Confocal Scanning Electron Microscope at X magnification The penetration of bacteria and presence of live bacteria in dentinal tubules in all the groups was analyzed Results In both the groups there was a significantly higher penetration of bacteria through the exposed dentin as compared to sections with intact cementum However there was a significantly higher penetration of Streptococcus sanguinis as compared to Aggregatibacter actinomycetemcomitans Conclusion An intact cemental layer protects the dentin from invasion of bacterial species These bacteria can lead to reinfection of treated periodontal pockets pulpal inflammation or persistence of periapical infections Therefore management of endodontic periodontic lesions and periodontal therapies should aim at preserving or regenerating a healthy cemental layer

Collagen-like peptide sequences inhibit bacterial invasion of root dentine.

To investigate the effects of peptides derived from the sequence of collagen to inhibit penetration of human or bovine dentine by species of streptococci and enterococci. Blocks of human or bovine root dentine were infected for 14days with bacterial cultures, in the presence or absence of various collagen-like peptide sequences. Invasion of dentinal tubules was determined from microscopic images of histochemically stained dentine thin sections. Extent of invasion was expressed as tubule invasion index (TI), or tubule invasion factor (TIF) which, in addition to the density of invasion, took into account the depth of invasion. Data were analysed by two-way anova. Streptococcus gordonii, Streptococcus mutans and Enterococcus faecalis were associated with heavy invasion (TI >2.5, TIF >4) of human or bovine root dentinal tubules, with E.faecalis being the most penetrative. Incorporation of peptides Gly-Pro-Ala or Gly-Pro-Hyp into the invitro model system significantly reduced (P<0.05) dentine invasion by the three species of highly invasive organisms. Inhibition of bacterial invasion by the peptides was dose dependent, and the peptides did not inhibit bacterial growth in culture. Specific collagen-like peptide sequences inhibited the invasion of dentine invitro by a range of oral bacteria. The peptides likely act as competitive inhibitors blocking bacterial collagen receptors and could potentially allow for target-specific control of dentine infections.

Assessment of dentinal tubule invasion capacity of Enterococcus faecalis under stress conditions ex vivo.

To investigate the dentinal tubule invasion capacity of Enterococcus faecalis under alkaline and energy starvation stress conditions. The root canals from human single-rooted teeth (n=40) were infected with E.faecalis under alkaline (pH 9, 10, 11 and 12) and energy starvation (no glucose, 0.05% glucose and 0.15% glucose) stress conditions. The root canals were prepared in a standard manner and treated to remove the smear layer before incubation. After 4weeks of cultivation, the roots were split vertically into two halves: one half was processed for biofilm formation analysis using a scanning electron microscope; the other half was stained with fluorescent DNA-binding reagents, washed thoroughly and sectioned (100 μm thick), and the depth of tubule invasion by the microorganism was examined by confocal laser-scanning microscopy. The extent of dentine tubule invasion was analysed statistically. The E.faecalis strain resulted in biofilm formation and dentine tubules invasion under all of the stress conditions, except for pH 11 and 12 conditions. However, the tubule penetration distance was markedly reduced in these stress conditions (P<0.01) compared with in tryptic soy broth (TSB) or pH 7 medium. The invasion depth in the middle root dentine was significantly higher than in the apical sections in TSB and energy starvation medium (P<0.01). Ex vivo E.faecalis formed biofilms and colonized dentine under alkaline and glucose starvation stress conditions, but its ability to invade dentine tubules was significantly decreased.

Microbial invasion of dentinal tubules: a literature review and a new perspective

Various features of endodontic microbiology have been investigated using various methods. The aim of the present study was to review the existing literature on endodontic microbiology in dentinal tubules, and to present the features of two cases with endodontic pathology. An electronic search was performed with a search string created ad hoc. Ex vivo and in vitro studies were included, recording the method of detection and characteristics of analyzed teeth. Twenty studies fulfilled the inclusion criteria. Seven of them were in vitro laboratory studies on teeth inoculated after extraction, while 13 were ex vivo studies on extracted, infected teeth. Endodontic bacteria were detected in dentinal tubules, both as single units and as biofilm aggregates. Two similar in vitro cases presented here corroborate the latter findings. A number of techniques have been utilized to observe bacteria in the dentinal tubule ecosystem. Dentinal tubules are favorable niches for microbial survival, either in the form of monomicrobial or polymicrobial communities.

Hyperglycemia and xerostomia are key determinants of tooth decay in type 1 diabetic mice

Insulin-dependent type 1 diabetes mellitus (DM) and oral diseases are closely interrelated. Poor metabolic control in diabetics is associated with a high risk of gingivitis, periodontitis and tooth loss. Salivary flow declines in diabetics and patients suffer from xerostomia. Reduced saliva predisposes to enamel hypomineralization and caries formation; however, the mechanisms that initiate and lead to progression of tooth decay and periodontitis in type 1 DM have not been explored. To address this issue, we analyzed tooth morphology in Akita −/− mice that harbor a point mutation in the Ins2 insulin gene, which leads to progressive hyperglycemia. Mandibles from Akita −/− and wild-type littermates were analyzed by microCT, scanning EM and histology; teeth were examined for amelogenin (Amel) and ameloblastin (Ambn) expression. Mice were injected with pilocarpine to assess saliva production. As hyperglycemia may alter pulp repair, the effect of high glucose levels on the proliferation/differentiation of cultured MD10-F2 pulp cells was also analyzed. Results showed that Akita −/− mice at 6 weeks of age showed chalky white incisors that correlated with marked hyperglycemia and impaired saliva production. MicroCT of Akita −/− teeth revealed excessive enamel wearing and hypomineralization; immunostaining for Amel and Ambn was decreased. A striking feature was invasion of dentinal tubules with Streptococcus mitis and microabcesses that originated in the coronal pulp and progressed to pulp necrosis and periapical periodontitis. High levels of glucose also inhibited MD10-F2 cell proliferation and differentiation. Our findings provide the first evidence that hyperglycemia in combination with reduced saliva in a model of type1 DM leads to decreased enamel mineralization/matrix proteins and predisposes to excessive wearing and decay. Importantly, hyperglycemia adversely affects enamel matrix proteins and pulp repair. Early detection and treatment of hyperglycemia and hyposalivation may provide a useful strategy for preventing the dental complications of diabetes and promoting oral health in this population.

Dentinal tubule invasion and adherence by Enterococcus faecalis

To investigate dentinal tubule invasion and the predilection of Enterococcus faecalis for dentinal tubule walls. The invasion of dentinal tubules in extracted human teeth by E. faecalis was measured ex vivo after 8 weeks of incubation. The canal walls of 16 root sections were either intact or instrumented with or without smear layer present. Extent and maximum depth of tubule invasion were assessed histologically and compared between groups. In the adherence study, 44 vertically split root samples were prepared to expose longitudinally aligned dentinal tubules and fractured orthodentine (OD). Surfaces were exposed to E. faecalis (erythromycin resistant strain, JH2-2 carrying plasmid pGh9:ISS1) and incubated aerobically for 2 h. Samples were processed for analysis using scanning electron microscopy. Bacterial adhesion to tubule walls versus fractured OD was calculated as number of cells per 100 microm(2). The strain of E. faecalis used in this study showed moderate to heavy tubule invasion after 8 weeks. In the adhesion studies, significantly more bacteria adhered to fractured OD than to dentinal tubule walls (ANOVA, P < 0.001). With respect to the tubule wall, adherence was greater in inner versus outer dentine (P = 0.02) and greater when bacterial adhesion was tested in chemically defined medium than in phosphate-buffered saline (ANOVA, P < 0.001). Although E. faecalis readily invaded tubules, it did not adhere preferentially to tubule walls. Initial colonization of dentinal tubules by E. faecalis may depend primarily on other factors.

Bacterial invasion of dentinal tubules beneath apparently intact but hypomineralized enamel in molar teeth with molar incisor hypomineralization

The most common problems for a patient with molar incisor hypomineralization (MIH) are the collapse of enamel and cavitations, loss of fillings, and secondary caries, but most of all, severe hypersensitivity. The aim of this paper was therefore to histologically study possible bacterial invasion of dentinal tubules beneath apparently intact, but hypomineralized enamel in permanent molars with MIH. Five extracted permanent first molars diagnosed with MIH were fixated, demineralized, and sagittally serially sectioned in a bucco-lingual direction in a microtome with a thickness of 4-5 microm. Sections were stained with a modified Brown and Benn staining for bacteria, unstained sections were analysed in field emission SEM. Stained sections from the cuspal areas, below the hypomineralized enamel, the staining indicated the presence of bacteria in the dentinal tubules. The HTX staining showed that the pulp in sections without any findings was normal and free from bacteria or infiltrates from inflammatory cells. In sections where bacteria were found in the cuspal areas or deeper in the dentin, a zone of reparative dentin was found, and in sections from one tooth, the coronal pulp showed an inflammatory reaction with inflammatory cells. In sections adjacent to those without any bacterial staining, the SEM analyses revealed empty dentinal tubules without any odontoblast processes or signs of bacteria. When odontoblast processes were found, the dentinal tubules were filled with bacteria located on the surface of the odontoblast processes. In some areas, a large number of tubules were found with bacteria. No bacteria were found close to the pulp. The odontoblast processes appeared larger in areas where bacteria were found. The presence of bacteria in the dentinal tubules and inflammatory reactions in the pulp indicate that oral bacteria may penetrate through the hypomineralized enamel into the dentin, thus possibly contribute to hypersensitivity of teeth with MIH.

Invasion of dentinal tubules by root canal bacteria

Bacterial invasion of dentinal tubules and the clinical consequences have been recognized for over a century. However, while many components of the infected dentinal tubule microflora have been identified, it is likely that there are etiological agents involved in endodontic infections that have not yet been recognized. Bacterial invasion of coronal dentinal tubules occurs when the dentine is exposed to the oral environment and of radicular dentinal tubules subsequent to infection of the root canal system or as a consequence of periodontal disease. The content and architecture of a dentinal tubule can influence bacterial invasion, with tubule patency being important. This can account for regional variations in bacterial invasion and is particularly seen with dentinal sclerosis, where more advanced sclerotic changes in apical radicular tubules, especially in elderly individuals, limit bacterial invasion in this area. While several hundred bacterial species are known to inhabit the oral cavity, a relatively small and select group of bacteria are involved in invasion of dentinal tubules. Gram‐positive organisms dominate the tubule microflora in both carious and non‐carious dentine. The relatively high numbers of obligate anaerobes present, such as Eubacterium spp., Propionibacterium spp., Bifidobacterium spp., Peptostreptococcus micros, and Veillonella spp., suggests that the environment favors the growth of these bacteria. Gram‐negative obligate anaerobic rods, e.g. Porphyromonas spp., are less frequently recovered; however, with time, fastidious obligately anaerobic bacteria become established as principal components of the microflora and can be found within the deep dentine layers. In the early stages of infection, Gram‐positive bacteria dominate the microflora. The identification of adhesins that mediate these initial interactions of bacteria with dentine is important for understanding the development of tubule infection and in designing adhesion‐blocking compounds. Recent evidence suggests that streptococci and enterococci may recognize components present within dentinal tubules, such as collagen type I, which stimulate bacterial adhesion and intra‐tubular growth. Specific interactions of other oral bacteria with invading streptococci may then facilitate invasion of dentine by select bacteria. It is important therefore that the mechanisms of invasion and inter‐bacterial adhesion are understood to assist development of novel control strategies.

Bacterial adhesins--their role in tubule invasion and endodontic disease.

Bacterial invasion of dentinal tubules is critical to the progression of dental caries and the development of pulp and periapical disease, and may also influence the progression of periodontal disease. However, little is known about the host or bacterial mechanisms involved in tubule invasion. Recent work has demonstrated that bacterial interactions with dentine, and salivary and tissue molecules influence invasion. Salivary molecules such as mucin and immunoglobulin G (IgG) co-aggregate with bacterial cells, which inhibits dentine invasion, while deposition of dentinal tubule fluid molecules e.g. albumin, IgG, or fibrinogen within dentinal tubules also inhibits invasion. Dentine invasion by streptococci has been shown to be associated with a bacterial growth response and adhesion to unmineralized collagen, which are mediated by streptococcal cell-surface antigen I/II polypeptides. These adhesins possess diverse binding properties including binding to salivary glycoprotein, other bacteria, and to collagen. Additionally, some antigen I/II polypeptides facilitate species-specific co-invasion between streptococci and obligate anaerobes that lack the ability to invade by themselves. An understanding of the mechanisms involved in bacterial invasion of dentine should allow development of new control strategies.

Invasion of dentinal tubules by oral bacteria.

Bacterial invasion of dentinal tubules commonly occurs when dentin is exposed following a breach in the integrity of the overlying enamel or cementum. Bacterial products diffuse through the dentinal tubule toward the pulp and evoke inflammatory changes in the pulpo-dentin complex. These may eliminate the bacterial insult and block the route of infection. Unchecked, invasion results in pulpitis and pulp necrosis, infection of the root canal system, and periapical disease. While several hundred bacterial species are known to inhabit the oral cavity, a relatively small and select group of bacteria is involved in the invasion of dentinal tubules and subsequent infection of the root canal space. Gram-positive organisms dominate the tubule microflora in both carious and non-carious dentin. The relatively high numbers of obligate anaerobes present-such as Eubacterium spp., Propionibacterium spp., Bifidobacterium spp., Peptostreptococcus micros, and Veillonella spp.-suggest that the environment favors growth of these bacteria. Gram-negative obligate anaerobic rods, e.g., Porphyromonas spp., are less frequently recovered. Streptococci are among the most commonly identified bacteria that invade dentin. Recent evidence suggests that streptococci may recognize components present within dentinal tubules, such as collagen type I, which stimulate bacterial adhesion and intra-tubular growth. Specific interactions of other oral bacteria with invading streptococci may then facilitate the invasion of dentin by select bacterial groupings. An understanding the mechanisms involved in dentinal tubule invasion by bacteria should allow for the development of new control strategies, such as inhibitory compounds incorporated into oral health care products or dental materials, which would assist in the practice of endodontics.

The effect of tissue molecules on bacterial invasion of dentine.

Bacterial invasion of dentinal tubules is a critical step in the pathogenesis of dental caries and pulp and periapical disease. The purpose of this study was to determine the effect some molecules commonly found in saliva and dentinal tubule fluid may have on the bacterial invasion of dentine. The results showed that invasion of Streptococcus gordonii or Enterococcus faecalis cells was inhibited when the bacterial cells were in solution with mucin, immunoglobulin G (IgG) and serum, and this was related to bacterial cell aggregation, as a result of interaction with agglutinins, and/or inhibition of collagen binding. When dentine was soaked in growth media containing fibrinogen, IgG, albumin or serum prior to inoculation, bacterial invasion was inhibited. It is suggested that this may be due to reduced dentine permeability as a consequence of the deposition of the compounds within dentinal tubules.

Coinvasion of dentinal tubules by Porphyromonas gingivalis and Streptococcus gordonii depends upon binding specificity of streptococcal antigen I/II adhesin.

Cell wall-anchored polypeptides of the antigen I/II family are produced by many species of oral streptococci. These proteins mediate adhesion of streptococci to salivary glycoproteins and to other oral microorganisms and promote binding of cells to collagen type I and invasion of dentinal tubules. Since infections of the root canal system have a mixed anaerobic bacterial etiology, we investigated the hypothesis that coadhesion of anaerobic bacteria with streptococci may facilitate invasive endodontic disease. Porphyromonas gingivalis ATCC 33277 cells were able to invade dentinal tubules when cocultured with Streptococcus gordonii DL1 (Challis) but not when cocultured with Streptococcus mutans NG8. An isogenic noninvasive mutant of S. gordonii, with production of SspA and SspB (antigen I/II family) polypeptides abrogated, was deficient in binding to collagen and had a 40% reduced ability to support adhesion of P. gingivalis. Heterologous expression of the S. mutans SpaP (antigen I/II) protein in this mutant restored collagen binding and tubule invasion but not adhesion to P. gingivalis or the ability to promote P. gingivalis coinvasion of dentin. An isogenic afimbrial mutant of P. gingivalis had 50% reduced binding to S. gordonii cells but was unaffected in the ability to coinvade dentinal tubules with S. gordonii wild-type cells. Expression of the S. gordonii SspA or SspB polypeptide on the surface of Lactococcus lactis cells endowed these bacteria with the abilities to bind P. gingivalis, penetrate dentinal tubules, and promote P. gingivalis coinvasion of dentin. The results demonstrate that collagen-binding and P. gingivalis-binding properties of antigen I/II polypeptides are discrete functions. Specificity of antigen I/II polypeptide recognition accounts for the ability of P. gingivalis to coinvade dentinal tubules with S. gordonii but not with S. mutans. This provides evidence that the specificity of interbacterial coadhesion may influence directly the etiology of pulpal and periapical diseases.

Invasion of dentinal tubules by oral streptococci is associated with collagen recognition mediated by the antigen I/II family of polypeptides.

Cell surface proteins SspA and SspB in Streptococcus gordonii and SpaP in Streptococcus mutans are members of the antigen I/II family of polypeptides produced by oral streptococci. These proteins are adhesins and mediate species-specific binding of cells to a variety of host and bacterial receptors. Here we show that antigen I/II polypeptides are involved in the attachment of oral streptococci to collagen and that they also determine the ability of these bacteria to invade human root dentinal tubules. Wild-type S. gordonii DL1 (Challis) cells showed heavy invasion of tubules to a depth of approximately 200 microm, whereas the abilities of cells of isogenic mutant strains OB220 (sspA) and OB219 (sspA sspB) to invade were 50 and >90% reduced, respectively. Likewise, wild-type S. mutans NG8 cells invaded dentinal tubules, whereas cells of isogenic mutant strain 834 (spaP) did not. The invasive abilities of strains OB220 and OB219 were restored by heterologous expression of S. mutans SpaP polypeptide in these strains. The extents of tubule invasion by various wild-type and mutant strains correlated with their levels of adhesion to type I collagen, a major component of dentin. Furthermore, S. gordonii DL1 cells exhibited a growth response to collagen by forming long chains. This was not shown by ssp mutants but was restored by the expression of SpaP in these cells. The production of SspA polypeptide by S. gordonii DL1, but not production of SspB polypeptide by strain OB220 (sspA), was enhanced in the presence of collagen. These results are the first to demonstrate that antigen I/II family polypeptides bind collagen and mediate a morphological growth response of streptococci to collagen. These antigen I/II polypeptide activities are critical for intratubular growth of streptococci and thus for establishment of endodontic infections.

Regional variation in root dentinal tubule infection by Streptococcus gordonii

The purpose of this study was to investigate the pattern of bacterial invasion of dentinal tubules at different regions in human roots. Specimens were obtained from single-rooted teeth that had their root canals prepared in a standard manner. Roots were then sectioned longitudinally through the canals and the resulting specimens chemically treated to remove the smear layers. Specimens were immersed in a suspension of Streptococcus gordonii for 3 weeks and then prepared for histological analysis. Sections from the cervical, midroot, and apical areas were examined. The pattern of bacterial infection of the cervical and midroot areas was similar, characterized as a heavy infection with bacteria penetrating as deep as 200 microns. Invasion of the apical dentin was significantly different, with a mild infection and maximum penetration of 60 microns.

A scanning electron microscopic evaluation of in vitro dentinal tubules penetration by selected anaerobic bacteria

In vitro root canal dentinal tubule invasion by selected anaerobic bacteria commonly isolated from endodontic infections was evaluated. Dentinal cylinders obtained from bovine incisors were inoculated with bacteria, and microbial penetration into tubules was demonstrated by scanning electron microscopy. The results indicated that all bacterial strains tested were able to penetrate into dentinal tubules, but to different extents.

Penetration of smeared or nonsmeared dentine by Streptococcus gordonii.

The purpose of this study was to investigate the penetration of smeared and nonsmeared dentine by Streptococcus gordonii. Prepared human roots, grouped as either nonsmeared or smeared, were immersed in a suspension of S. gordonii cells for 3 weeks. The roots were then prepared for scanning electron microscopy and histological analysis. Dentine discs prepared from coronal dentine were grouped similarly. Using a fluid filtration apparatus, the hydraulic conductance (Lp) of each disc was determined before and after incubation with bacterial suspension. Scanning electron microscopy evaluation of the roots following infection with bacteria showed no change in the smear layer (P < 0.0001). Histological sections revealed that bacterial penetration of all the nonsmeared samples had occurred, while nine out of 10 smeared samples showed no bacterial penetration (P < 0.0001). The Lp of the nonsmeared discs was significantly reduced by 42% (P < 0.0001) after bacterial penetration. However, the smeared samples revealed a 1% reduction in Lp which was not significant (P > 0.05). The results suggest that dentinal smear layers are an effective barrier to dentinal tubule invasion by S. gordonii.

Radiographic and microbiologic evaluation of posttreatment apical and periapical repair of root canals of dogs' teeth with experimentally induced chronic lesion

The objective of the present study was to evaluate radiographically and bacteriologically apical and periapical repair in dogs' teeth with induced chronic periapical lesions with the use of two different operative techniques (techniques 1 and 2). The study was conducted on 40 root canals of upper and lower premolars from two dogs aged approximately 12 months. Periapical lesions were induced by leaving the root canals exposed to the oral environment for 5 days and then sealing them with zinc oxide-eugenol for 45 days. After this period, radiographic examination revealed the occurrence of a radiolucent lesion and endodontic treatment was started. The two techniques did not differ in terms of chemomechanical preparation, final filling, or type of cement, but differed in terms of irrigating solution and the presence of an antibacterial dressing. Thus 4% to 6% hypochlorite and hydrogen peroxide (10 volumes) were used in technique 1 during chemomechanical preparation and an antibacterial dressing based on calcium hydroxide was applied between sessions, whereas Dakin's fluid (0.5% sodium hypochlorite solution) and a final filling with no antibacterial dressing were used in technique 2. After chemomechanical preparation, the root canals were filled with gutta-percha cones and Sealapex (Sealapex-Sybron, Kerr, Sao Paulo, Brazil), and the animals were killed 270 days after the final filling. Blocks were cut into 6-μm sections and stained by the Brown and Brenn method. Radiographic, histomicrobiologic and statistical analysis permitted us to conclude the following: radiographically there was a marked reduction or even the disappearance of the radiolucent area present before treatment with greater success in the group treated with technique 1 (group I) than in the group treated with technique 2 (group II); the extent of bacterial invasion of dentinal tubules was greater and more intense in group II than in group I; and the amount of microorganisms detected in the ramifications of the apical delta and in the lumen of the root canal was intense in group II and mild or absent in group I.

Scanning electron microscope study on the action of endodontic irrigants on bacteria invading the dentinal tubules

Three groups of 10 maxillary anterior teeth each, which had been exposed to oral media, were flushed with 9 ml of tap water, physiologic saline solution, and alternating irrigation with NaOCl and hydrogen peroxide respectively. Residual caries, necrotic tissue remnants, intertubular cavitation, and dentinal tubule invasion by bacteria were searched for by means of the scanning electron microscope. Cuboidal sodium chloride crystals were very frequently found deposited in the main root canal, in lateral canals, and inside the dentinal tubules. This study discusses the important role NaOCl may play as a solvent of dental plaque and necrotic tissue remnants in the clinical endodontic treatment of infected teeth that had been exposed to oral media.