Alkali-resistant bacteria in root canal systems.

The aim of this study was to isolate and identify alkali-resistant bacteria from the dentin of infected root canals. Bacteria from homogenized dentin powder made up from infected root canal walls from human teeth were cultured on buffer-enriched Brain Heart Infusion agar supplemented with 4% sheep blood (BHI-blood agar), adjusted to pH 7.0, 9.0 or 10.0. Incubation took place for 7 days at 37 degrees C in an anaerobic glove box. Bacterial strains selected according to colony and morphology were subcultured in buffer-enriched BHI broth adjusted to pH 9.0, 10.0 or 11.0 to confirm their growth as alkali-resistant bacteria. Polymerase chain reaction amplification using specific primer sets and 16S rDNA sequence analysis was performed for identification of alkali-resistant isolates. In the present study, 37 teeth extracted from 37 patients were used for preparation of the dentin powder samples. Bacteria were detected in 25 samples when standard BHI-blood agars (pH 7.0) were used. Of these, 29 strains from 15 samples were alkali resistant, 25 strains growing at pH 9.0 and 4 at pH 10.0. The alkali-resistant strains included Enterococcus faecium (10 strains) and Enterococcus faecalis (2 strains), Enterobacter cancerogenus (1 strains), Fusobacterium nucleatum (1 strains), Klebsiella ornithinolytica (2 strains), Lactobacillus rhamnosus (2 strains), Streptococcus anginosus (2 strains), Streptococcus constellatus (3 strains), and Streptococcus mitis (2 strains). Three strains were also identified as bacteria of genus Firmicutes or Staphylococcus at the genus level. The present study showed that many bacterial species in infected root canal dentin were alkali-resistant at pH 9.0 and/or pH 10.0, and belonged mainly to the genus Enterococcus.

Class II antigen-presenting dendritic cell and nerve fiber responses to cavities, caries, or caries treatment in human teeth.

Major histocompatibility complex (MHC) class II molecule-expressing cells are distributed in human dental pulp, and have been shown to accumulate beneath caries lesions. The responses of these cells and nerve fibers were analyzed under 5 different clinical conditions: shallow and deep experimental cavities, active and slow untreated caries, and treated caries. Under deep cavities, class II molecule-expressing dendritic cells displaced the injured odontoblasts during a period of one month, while such a response was not observed in shallow cavities and untreated or treated carious teeth. The class II molecules seen in the neural elements under active caries were no longer detectable in treated carious teeth. However, six months after treatment, clusters consisting of dendritic cells, T-lymphocytes, and nerve fibers still remained locally in the subodontoblastic area. These results indicate that dental pulps respond differently to cavity preparation and restoration between normal and caries conditions, and that immunoresponses persist for many months, even after caries treatment.

A laboratory study of coronal microleakage using four temporary restorative materials.

AIM: The aim of this study was to compare the sealing abilities of Fermin and Canseal with the more popular temporary coronal filling materials, Cavit and Caviton. METHODOLOGY: Standardized access cavities were prepared in 160 intact human permanent molar teeth. They were divided into five groups consisting of 32 samples. The teeth were restored using one of the temporary filling materials, namely: Fermin, Canseal at two powder to liquid ratios, Caviton and Cavit. Thermal cycling and/or load cycling were applied on the samples. Assessment of microleakage utilized methylene blue dye penetration. Grading of the microleakage pattern was from 1 to 3, with 3 providing the best seal. Results were analyzed using two-way anova and by Fisher's PLSD post hoc test (P < 0.05). RESULT: Microleakage along Fermin, Caviton and Cavit samples did not go beyond Leakage Grade 2. Dye penetration into these materials was noted. This was not observed in the two groups of Canseal tested. However, the two groups of Canseal exhibited total leakage notably after being subjected to thermal cycling. There was a statistically significant difference in the microleakage scores obtained between the materials and conditions tested (P < 0.0001). CONCLUSION: Fermin was found to exhibit the best seal amongst the four materials tested followed by Caviton, and Cavit. Thermal cycling influenced the seal of certain types of temporary filling materials more than load cycling.

Penetration of propylene glycol into dentine.

AIM: This study aimed to evaluate penetration of propylene glycol into root dentine. METHODOLOGY: Safranin O in propylene glycol and in distilled water were introduced into root canals with and without artificial smear layer. Dye diffusion through dentinal tubules was determined spectrophotometrically. The time required for dye to exit through the apical foramen using propylene glycol and distilled water as vehicles was also determined. The extent and areas of dye penetration on the split surfaces of roots were assessed using Adobe Photoshop and NIH Image Software. RESULTS: Propylene glycol allowed dye to exit faster through the apical foramen. The area and depth of dye penetration with propylene glycol was significantly greater than with distilled water (P < 0.0001). Smear layer significantly delayed the penetration of dye. CONCLUSION: Propylene glycol delivered dye through the root canal system rapidly and more effectively indicating its potential use in delivering intracanal medicaments.

Evaluation of the surface roughness of compomer by laser scanning microscopy.

The purpose of this study was to evaluate the effect of alcoholic and low pH soft drinks on the surface roughness of compomer restorative materials. There were five tested materials and four immersion media. Specimens were immersed in test solutions for a 10-day period at a temperature of 37 degrees C. Measurement of the surface texture was carried out using a laser scanning microscope (a non-contact laser stylus tracing method). This was also used to produce the Laser Scanning Microscope Image (LSM Image). Specimens immersed in orange juice and whisky displayed higher values for Ra & Rz than specimens immersed in soft drinks and deionized water. LSM Image showed a difference between the control and the examined side, especially for specimens immersed in low pH soft drinks this could be due to the erosive effect of the media. Alcoholic and low pH soft drinks caused deterioration of the materials surface, which may lead to a clinically detectable rough and dull surface.

Artificial Pseudomonas aeruginosa biofilms and confocal laser scanning microscopic analysis.

Bacterial biofilms may be formed at various sites, including mucous membranes, teeth, and infectious lesions. To elucidate the structure and the function of biofilms, artificial biofilms of mucoid-type Pseudomonas aeruginosa organisms (strain PT1252) were made by centrifuging the organisms onto the surface of a coverglass and culturing further in broth media supplied continuously (45 ml/h). The biofilm structure at 4, 8, 12, and 24 h was visualized with fluorescent staining (SYTO9, propidium iodide [PI], and/or fluorescein isothiocyanate-concanavalin A [FITC-ConA]) by confocal laser scanning microscopy (CLSM). It was clearly demonstrated that the number of bacteria (10(4)--10(6)/ml) could be estimated by their fluorescence intensity. Sectional analysis of each biofilm layer (1-microm thickness) made it possible to demonstrate the three-dimensional development of biofilms, and revealed that the biofilms were 9 microm in height after 12 h. The live and dead organisms were differentiated by SYTO9 and PI, respectively, in situ in biofilms, and about 13% of the organisms were dead in 12-h-old biofilms. When 12-h-old biofilms were exposed to ciprofloxacin at minimum bactericidal concentration (6.26 microg/ml) for 90 min, all the organisms were killed, but some organisms (11 +/- 1.3%; n = 3) in 24-h-old biofilms with thicker and denser structure were still alive after exposure for 120 min. These results indicate that the CLSM analysis of artificial biofilms was useful for elucidating bacterial functions in biofilms, and may lead to a new quantitative system for estimating the bactericidal efficacy of antibacterial drugs in biofilms.

Study of the fluoridated adhesive resin cement--fluoride release, fluoride uptake and acid resistance of tooth structures.

The objectives of this study, were to evaluate the fluoride release from fluoridate adhesive resin cement, fluoride uptake into surrounding tooth structures and the effect of their acid resistance. Several specimens were prepared using a plastic ring mould, from extracted human premolars, and prepared from enamel and dentin of the central area of the buccal surface of bovine teeth. The fluoride release rate of fluoridate adhesive resin cement (PN 200) per day was higher than other materials during the 7-day study period. Fluoride released and fluoride uptake by tooth structures was higher in the fluoridate adhesive resin cement. WDX analysis showed the fluoride concentration on dentin contact area was higher than that of enamel after 60 days of immersion in deionized water. The calcium release values were similar for enamel and dentin plates in the various test materials. The present findings indicated the important enhancement of tooth structure acid resistance by fluoridate material.

Changes in the mechanical properties and surface texture of compomer immersed in various media.

STATEMENT OF PROBLEM: Limited information is available about the mechanical behavior of compomer under intraoral conditions. PURPOSE: This in vitro study evaluated changes in the mechanical properties and surface texture of compomer and other materials, used in similar clinical circumstances, when immersed in various media. MATERIAL AND METHODS: Hardness measurement for 5 tested materials and 4 immersion media was obtained with a Vickers hardness testing machine. Compressive strength was measured using an Autograph at a crosshead speed of 0.75 mm/min. All readings were taken for up to a 60-day period. An electron probe microanalyzer was used to give an SEM image. RESULTS: The average compressive strength and Vickers surface hardness showed a significant difference between materials. Results showed an overall increase in the solubility of specimens immersed in low pH soft drinks. CONCLUSION: There was a difference in the mechanical properties and surface texture of the materials tested in this study when they were immersed in various media.

Effect of alcoholic and low-pH soft drinks on fluoride release from compomer.

PURPOSE: The purpose of this study was to evaluate the amount of fluoride released from compomer restorative materials after immersion in various media. MATERIALS AND METHODS: In this test, four materials were used: three compomers (Dyract, Dentsply, Konstanz, Germany; Compoglass, Vivadent, Schaan, Principality of Liechtenstein; and Xeno, Sankins, Tochigi, Japan) and one resin-modified glass ionomer cement (Fuji II LC, GC, Tokyo, Japan). There were four test solutions: one alcoholic (whiskey), two low-pH drinks (Coca-Cola, orange juice), and one deionized water. Over a period of 60 days, the tested specimens were immersed in the test solution for 3 hours every day, then kept in deionized water. The fluoride released was detected by using a fluoride ion selective electrode connected to a microprocessor ion analyzer. The fluoride ion concentration (ppm) of the test solutions and deionized water was recorded after 1, 2, 3, 4, 7, 30, and 60 days. Electron probe microanalysis was used for surface analysis of the fluoride released. RESULTS: When immersed in low-pH soft drinks, compomer showed a significantly higher fluoride release than when immersed in deionized water (p < .0001). For specimens immersed in Coca-Cola, the fluoride release levels (microgram/cm2, mean +/- SD) at 1, 7, and 60 days for Dyract (91.6 +/- 1.8, 39.3 +/- 3.1, 10.5 +/- 0.9), Compoglass (129.5 +/- 0.9, 66.5 +/- 2.7, 19.0 +/- 0.3), Fuji II LC (147.0 +/- 4.2, 50.8 +/- 3.1, 27.6 +/- 3.0), and Xeno (73.6 +/- 3.2, 27.3 +/- 2.1, 6.6 +/- 0.6) demonstrated the trend of significantly lower releases with time in water solution. Over a 60-day period, materials immersed in 100% orange juice released the highest amount of fluoride, which could be attributable to the erosive effect of the medium. Materials immersed in deionized water released the least amount of fluoride. Among the tested compomers, Compoglass released the most fluoride.

Color stability of compomer after immersion in various media.

PURPOSE: The purpose of this study was to evaluate the effect of various media on the color stability of compomer and to compare these results to those of other materials that could be used in similar clinical circumstances. MATERIALS AND METHODS: In this test, six materials (shade A2) were used: four compomers (Dyract, Compoglass F, Xeno, F2000), one composite resin (Clearfil AP-X), and one resin-modified glass ionomer cement (Fuji II LC). There were four test solutions: one alcoholic (whiskey), two low pH soft drinks (Coca Cola, orange juice), and deionized water as a control. A plastic ring mold (9-mm diameter x 1-mm height) was used to prepare 120 disk specimens. For 60 days, the test specimens were immersed in the various media daily for 3 hours then transferred to the deionized water. Color was measured by CIE L* a* b* relative to CIE source against a white background, using a colorimeter. Color change (delta E*) was calculated as delta E* = [(delta L*)2 + (delta a*)2 + (delta b*)2]1/2. Color changes (delta E*) were recorded after 1, 7, 30, and 60 days. RESULTS: The results indicated that compomer and resin-modified glass ionomer were susceptible to discoloration in various solutions over an extended period of time. Composite resin showed minimal perceptible color change. Specimens immersed in whiskey showed a significantly high perceptible color change (p < .0001). Water caused no perceptible color changes.

Teaching of posterior composite restorations in Japanese dental schools.

AIM: This study was conducted to assess the teaching programmes for Class I and II composite restorations in Japanese dental schools to obtain an overview of what is being taught, the relative teaching volume, the criteria for the provision of posterior composite restorations and the placement techniques taught. DESIGN: Questionnaire forms mailed to the operative dentistry teaching departments in all 29 Japanese dental schools. RESULTS: The response rate was 93 per cent, with replies from 27 of the 29 dental schools. Twenty-five (93 per cent) responding schools taught the use of Class I and two schools stated that they did not teach the use of posterior composite restorations. One of the two schools had no plan to teach posterior composites within the next five years. The other school did not answer this question. Most schools anticipated that the proportion of teaching time devoted to posterior composite restorations would increase within the next five years. Diversities and similarities between teaching programmes were noted between Japanese, North American and European dental schools, the Japanese programmes being closer to those in Europe than those in North America. CONCLUSION: The diversities in the teaching of posterior composite restorations in Japanese dental schools are as great as in other parts of the world. Such diversities must affect the overall quality of restorations in general practice.

Endodontic teaching in Philippine dental schools.

AIM: The aim of this study was to evaluate the pattern of undergraduate endodontic teaching in Philippine dental schools. METHODOLOGY: Data were gathered by sending questionnaires to the deans of the 23 dental schools in the country to determine details of the teaching of root canal treatment in permanent teeth. The covering letter requested that endodontic staff complete the questionnaire. RESULTS: Twenty of 23 dental schools returned completed questionnaires. Similarities were observed in the timing of undergraduate endodontic teaching, working length determination, and root canal preparation technique. Irrigating fluids recommended included one or a combination of the following: sodium hypochlorite, hydrogen peroxide, distilled water and EDTA. The root canal medicaments popularly employed were CMCP and eugenol. Most schools used slow-setting zinc oxide eugenol cement as sealer. Differences between schools were noted in the laboratory component of the course. The time allotted for the laboratory exercises, as well as the number of teeth used, differed greatly between each school. An inadequate tutor to student ratio was noted in the majority of schools. Teaching aids were limited and, in most instances, produced by faculty members. Most faculty members teaching endodontics had no specialist training. CONCLUSION: The results of this study have demonstrated that there is a need to review endodontic teaching in the majority of the Philippine dental schools to ensure that the course content and curriculum employed by all schools meet specified standards and that appropriate measures should be considered to enhance the learning experience of students.

WDX study of resin-dentin interface on wet vs. dry dentin.

The purpose of the present study was to determine the resin-dentin Interface conditions in Wet vs. Dry Dentin. Dentin disks were prepared from extracted human premolars. Sectioned dentin surfaces were used for SEM studies of wet vs. dried acid-etched dentin. These specimens were cut perpendicular to the surface into two equal halves. One-half of the sectioned specimen was observed by SEM in three treatment groups and the other half was observed for micromorphological differences in the resin-dentin interface using Wavelength Dispersive X-ray Spectrometer (WDX). SEM photomicrographs of the dentin surface showed the collapse of collagen fibrils in the demineralized layer and enlargement of the tubule orifices. A collagen rich layer approximately 8-10 microns thick (WDX) was observed at the resin-dentin interface when treated with the conventional dry-bonding technique. Dentin surfaces treated by the wet-bonding technique (SB), as observed by SEM, showed an uncollapsed collagen layer, while the collagen-rich layer was approximately 1-2 microns thick (WDX). The present findings suggest that moist bonding is required for optimum infiltration of adhesive resin into the demineralized layer.

Experimental actinomycosis in mice induced by alginate gel particles containing Actinomyces israelii.

The present study aimed to make an animal model for investigating chronic infection. Bacterial cells of Actinomyces israelii (ATCC 10048) were packed in alginate gel particles and injected intra-peritoneally into BALB/c mice. Actinomycotic lesions were induced efficiently in 9 mice out of 12 after 3 or 9 weeks. Actinomycotic lesions were not produced by injecting a bacterial suspension of A. israelii except in one animal. Neither did injection of gel particles without bacteria induce lesions. Bacteria survived in the lesions for at least 9 weeks after the injection, and serum IgG levels against the bacteria were significantly elevated in the animals, indicating that the bacteria were protected from immunological elimination and activated humoral immunity in the animals. Histopathological observation of the lesion by staining revealed that the bacteria in the lesions were acid-fast and seemed to become resistant to phagocytosis. The bacterial masses were surrounded by inflammatory cells, including polymorphonuclear leukocytes and macrophages, and were separated from the host cells by a fringe-like structure similar to the capsular structure of natural sulfur granules. The present study indicated that the use of an alginate gel was effective in inducing actinomycotic lesions in mice.

Immunohistochemical localizations of class II antigens and nerve fibers in human carious teeth: HLA-DR immunoreactivity in Schwann cells.

Nerve fibers and class II major histocompatibility complex (MHC) antigen-expressing dendritic cells have been known to gather in the dental pulp beneath carious lesions. Significant functional interactions presumably occur between the neural and immune elements. The present study analyzed the morphological relationship between class II-expressing cells and nerve fibers in fuman carious teeth, visualized by a HLA-DR monoclonal antibody and a protein gene product 9.5 (PGP 9.5) polyclonal antibody; a confocal laser scanning microscope (CLSM) and an electron microscope were used. In pulps affected by early caries, HLA-DR-positive dendritic cells aggregated mainly in the cell-free zone associated with bundles of PGP 9.5-immuno-reactive nerve fibers. In pulps affected by advanced caries, the accumulated HLA-DR-positive cells and PGP 9.5-immunoreactive nerve fibers showed close association with each other especially beneath the odontoblast layer: the cells even embraced the nerve fibers. Intriguingly, class II molecules were recognized not only in dendritic cells but also in the Schwann cells of non-myelinated nerves in the pulp. Using immuno-electron microscopy, class II molecules were localized on the surface of the non-myelinating Schwann cells and also within some vesicles, whereas myelinating Schwann cells lacked this immunoreactivity. PGP 9.5-immunoreactive nerve fibers were also observed densely in the odontoblast layer, and CLSM revealed an intimate association of the nerve fibers and dendritic cells. The immunoreactivity for HLA-DR in Schwann cells depended upon the severity of the carious lesion. Class II-expressing Schwann cells are suggested to function as antigen-presenting cells in addition to dendritic cells.

Bacterial eradication from root dentine by ultrasonic irrigation with sodium hypochlorite.

The study aimed to evaluate intracanal irrigation procedures in eradicating bacteria from surface, shallow and deep layers of root dentine using extracted human teeth. Artificial bacterial smear layer was successfully produced by rubbing a mixture of dental plaque and artificially decalcified dentine or carious dentine on root canal walls. The reservoir holes were 3.5 mm in depth, 1 mm in diameter prepared 1.5 mm apart and parallel to the root canals on the decrowned planes, in which five separate bacterial species were placed (Actinomyces israelii, Fusobacterium nucleatum, Propionibacterium acnes, Streptococcus mutans and Streptococcus sanguis). Bacterial eradication after irrigation of the prepared canals was determined by bacterial recovery (i) from the root canal surfaces and shallow layers where bacteria were smeared artificially and (ii) from deeper layers of root canal dentine reservoir holes. Ultrasonic irrigation with 5.5% and 12% NaOCl eradicated bacteria from artificial smear layer (P < 0.0001), whilst 12% NaOCl irrigation with a syringe was insufficient. Ultrasonic irrigation with water or 15% EDTA-failed to eradicate bacteria from smeared surfaces. Ultrasonic irrigation with 12% NaOCl killed A. israelii, F. nucleatum, P. acnes, S. mutans, and S. sanguis placed in reservoir channels, although for F. nucleatum, a very small number of bacteria remained in five samples out of 12. Ultrasonic irrigation with less concentrated NaOCl failed to eliminate bacteria completely from reservoir channels in most samples. Ultrasonic irrigation with 12% NaOCl appeared to eliminate bacteria efficiently from surface, shallow and deep layers of root dentine.

Component release from light-activated glass ionomer and compomer cements.

The purpose of this study was to identify and quantify any component released from seven commercially available light-cured or resin-modified glass ionomer and compomer cements. Twenty-one separate cylindrical stainless steel moulds 6 mm in diameter and 1.0 mm deep were filled with one of seven glass ionomer or compomer cements, light activated and then immediately immersed in separate containers of distilled water. Water samples were retrieved over a time period of up to 30 days and retained for analysis. An occlusal cavity 6 mm in diameter was prepared in extracted human third molar teeth with a remaining dentin thickness of 1.6-2.0 mm. A polypropylene chamber was attached to the cemento-enamel junction of each tooth to contain 1 mL of distilled water. Ten teeth were each filled with one of three cements and light activated. Water samples (eluates) were retrieved over a period of time. All samples were analysed by high performance liquid chromatography. Only one component, hydroxyethyl methacrylate (HEMA), was detected in the eluates from both tooth and mould samples. Analysis of diffusion of the HEMA through dentin showed a relatively sustained movement into the pulp space during the first day, with exponential decline thereafter. Our data show that HEMA was released from all of the light activated glass ionomer cements studied and from the compomer, both directly into water and through dentin. This release may be relevant both to the risk of adverse pulpal responses in patients and to the risk of allergy in patients and dental personnel.

Inhibitory effects of metronidazole on anaerobic metabolism of phenylalanine and leucine by Peptostreptococcus anaerobius.

The metabolism of phenylalanine and leucine by Peptostreptococcus anaerobius and the effects of metronidazole on this metabolism were studied. The cells metabolized both phenylalanine and leucine under strict anaerobic conditions and produced hydroxylated products (i.e. phenyllactate from phenylalanine and hydroxyisocaproate from leucine). Other products were phenylpropionate, cinnamate and phenylacetate from phenylalanine; isocaproate, alpha-ketoisocaproate and isovalerate from leucine. Metronidazole inhibited the production of all end-products, with the exception of phenyllactate and hydroxyisocaproate which were increased. Similarly, when the reaction was carried out aerobically, the cells also metabolized both phenylalanine and leucine and all end-products were inhibited again with the exception of phenyllactate and hydroxyisocaproate. Our results suggest that the inhibitory mode of metronidazole is similar to that of oxygen.

Immunolocalization of fibronectin during reparative dentinogenesis in human teeth after pulp capping with calcium hydroxide.

Exposed dental pulp is known to possess the ability to form a hard-tissue barrier (dentin bridge). The exact mechanisms by which pulp cells differentiate into odontoblasts in this process are unknown. Fibronectin has been demonstrated to play a crucial role in odontoblast differentiation during tooth development. This study tested the hypothesis that fibronectin is involved in the initial stages of replacement odontoblast differentiation and reparative dentin formation. We observed its immunohistochemical localization during dentin bridge formation in human teeth, after pulp was capped with calcium hydroxide [Ca(OH)2]. One day after the capping, precipitation of crystalline structures was observed at the TEM level in association with cell debris at the interface between the superficial necrotic zone and underlying pulp tissue. This layer of dystrophic calcification showed positive reaction for fibronectin, and pulp cells appeared to be closely associated with this layer, seven to ten days post-operatively. At 14 days, an alignment of cells, some of which were elongated and odontoblast-like, was observed adjacent to the fibronectin-positive irregular matrix. Between the cells, corkscrew fiber-like fluorescence was visible. At 28 days, the irregular fibrous matrix was followed by the formation of tubular dentin-like matrix lined with odontoblast-like cells. Therefore, it would seem that fibronectin associated with the initially formed calcified layer might play a mediating role in the differentiation of pulp cells into odontoblasts during reparative dentinogenesis, after pulp was capped with Ca(OH)2.

Immunohistochemical localization of HLA-DR-positive cells in unerupted and erupted normal and carious human teeth.

Class II major histocompatibility complex (MHC) antigen-expressing cells are generally associated with the early phase of the immune response. We have studied the distribution of class II-expressing cells in developing, normal, and carious human teeth to clarify when human pulp acquires an immunologic defense potential and how this reacts to dental caries. Antigen-expressing cells were identified immunohistochemically by means of HLA-DR monoclonal antibody. In the pulp of unerupted developing teeth, numerous HLA-DR-positive cells were distributed mainly in and around the odontoblast layer. In erupted teeth, HLA-DR-positive cells were located, for the most part, just beneath the odontoblast layer, with slender cytoplasmic processes extending into the layer. Superficial caries lesions caused an aggregation of HLA-DR-positive cells in dental pulp corresponding to the lesion. In teeth with deeper caries lesions, this aggregation of cells expanded to include the odontoblast layer. Also noted were HLA-DR-positive cells lying along the pulp-dentin border, with cytoplasmic processes projecting deep into the dentinal tubules, where they co-localized with odontoblast processes. These findings suggest that: (1) human dental pulp is equipped with immunologic defense potential prior to eruption; (2) in the initial stage of caries infection, an immunoresponse mediated by class-II-expressing cells is initiated in human dental pulp; and (3) HLA-DR-positive cells trespass deep into dentinal tubules as the caries lesion advances.