Journal of Dental Research

Candida albicans is frequently isolated from the human mouth, yet few carriers develop clinical signs of candidiasis. Oral candidiasis presents clinically in many forms. This reflects the ability of the yeast to colonize different oral surfaces and the variety of factors which predispose the host to Candida colonization and subsequent infection. Colonization of the oral cavity appears to be facilitated by several specific adherence interactions between C. albicans and oral surfaces which enable the yeast to resist host clearance mechanisms. Thus, Candida has been shown to adhere to complement receptors, various extracellular matrix proteins, and specific sugar residues displayed on host or bacterial surfaces in the oral cavity. Oral candidiasis results from yeast overgrowth and penetration of the oral tissues when the host's physical and immunological defenses have been undermined. Tissue invasion may be assisted by secreted hydrolytic enzymes, hyphal formation, and contact sensing. While these and other phenotypic characteristics may endow certain Candida species or strains with a competitive advantage in the oral cavity, it is the host's immune competence that ultimately determines whether clearance, colonization, or candidiasis occurs.

Monomeric resin components from dental composites are toxic to fibroblasts in culture and thus may interfere with the local immune system of the pulp, reducing its effective defense potential, either by cytotoxicity or by a more specific immune mechanism. Therefore, the present study was undertaken to observe the cytotoxic effects elicited by certain unpolymerized components of resin composites upon the function of accessory pulp cells in mitogen-induced proliferation of T-lymphocytes. Accessory cells from the rat incisor pulp were released following enzymatic digestion with collagenase. The assay included incubation of these cells with purified T-lymphocytes from cervical lymph nodes for 72 h in the presence of different concentrations of the resin components. The proliferative T-lymphocyte response was monitored by 3H-thymidine incorporation. Initially, we conducted experiments on spleen cells to determine the proper concentration intervals for suitable testing of the resin components. To assess the individual susceptibility of accessory cells and T-lymphocytes, we pre-treated each of these cells with some of the test materials prior to assay. At low concentrations, urethane dimethacrylate (UDMA), bisglycidyl methacrylate (bis-GMA), triethylene glycol dimethacrylate (TEGDMA), and bis-phenol A (BPA) increased spleen cell proliferation to concanavalin A (con A). Purified T-lymphocytes stimulated by pulpal cells did not show enhanced responses to UDMA, bis-GMA, glycidyl methacrylate (GMA), or N,N-dihydroxyethyl-p-toluidine (DHEpT). At higher concentrations, all substances except camphoroquinone (CAMP) showed inhibitory effects in both test systems. The in vitro study shows that resin components can evoke either immunosuppression or immunostimulation on mitogen-driven proliferation of purified T-lymphocytes and spleen cells.

Using a stereoscopic clearing protocol and scanning electron microscopy, we investigated the extent and nature of microleakage in a total-etch, current-generation dentin adhesive by a wet-bonding technique under different handling conditions. The hypotheses were that inadequate light curing of the primer or incomplete drying of the primer solvent might adversely affect the sealing ability of an acetone-containing adhesive system. The study consisted of three experimental groups: (I) a control group with an adequate light source and with the primer solvent completely dried; (II) an "inadequate-light" group; and (III) an "incomplete evaporation of primer solvent" group. The extent of microleakage after silver staining and clearing of the specimens was scored based on a modified five-point scale. Nonparametric statistical analysis (Kruskal-Wallis ANOVA) followed by a multiple comparison test (Dunn test) indicated significant differences among the three groups (p < 0.05).

SEM examination of the restorative interface revealed that microleakage appeared to be initiated from the bonding resin-hybrid layer interface in all three groups, representing the weak link in the adhesive system. In addition, microleakage was characterized by 5 zones, each delineating a stage in a continuous array of progressively deleterious microleakage patterns variously distributed among the three groups. It was suggested that, while the bonding resin-hybrid layer interface represented the intrinsic weakness in an already much improved dentin adhesive, extrinsic factors such as the adequacy of the curing light and, more importantly, complete removal of the primer solvents can and should be avoided to preserve the structural integrity of the marginal seal.

Many bonding agents require the dentin surface to be acid-etched prior to being bonded. Understanding the stability and morphology of the etched dentin surface is important for improving bond strength and reliability in these systems. In this study, the atomic force microscope was used to quantify dimensional changes that occur to fully hydrated dentin during demineralization with a pH 4.0 lactic acid gel. A high-resolution microtomography instrument, the x-ray tomographic microscope, was also used to quantify the mineral density distribution in the dentin as a function of etching time. The intertubular dentin surface shrank by less than 0.5 μm during etching, while the peritubular dentin receded at an initially rapid linear rate. The dentin surface retained its initial morphology, although it was more porous with the removal of the peritubular dentin. Beneath the etched surface, there were three major zones characterized by mineral density differences. The first zone was a fully demineralized collagen layer, subjacent to which was a partially demineralized zone of roughly constant mineral density. Immediately following the partially mineralized layer was normal dentin. The presence of the partially mineralized layer could be explained in terms of different transport rates in the peritubular and intertubular dentin.

The release of mercury vapor from class I amalgam restorations prepared in human molar teeth was studied during chewing simulations in an artificial mouth of a bi-axial servo-hydraulic mechanical test system. So that the total mercury released from the restoration over a fixed time could be determined, a closed chamber surrounded the envelope of chewing motion. In addition, the influence of sampling frequency on mercury release was corrected by the use of different sampling frequencies over a fixed time interval of mercury release measurement and extrapolation to zero sampling time. Thus, a combination of a closed environment and an extrapolation method to determine the mercury release under continuous sampling was used to determine the mercury released under normal breathing conditions. The measured mercury release rate data were used to calculate the potential daily mercury dose in a patient due to a single amalgam restoration, following the method previously outlined by Berglund. The mercury release from both a conventional and a high-copper amalgam was evaluated at different age intervals after the restoration was placed in the teeth. The results show that while the age of the amalgam and the amalgam type influence the extent of mercury release during the initial non-steady-state conditions, the steady-state value of mercury daily dose due to a single amalgam filling is 0.03 ug/day, which is well below the calculated threshold-limiting value (TLV) of 82.29 μg/day considered dangerous for occupational exposure in the United States.

Several laser systems for the removal of hard dental substances are currently under investigation. However, in most cases, such systems have been demonstrated to be inefficient or have led to undesirable thermal side-effects. This paper reports, for the first time, the removal of enamel and dentin by a picosecond laser system, a solid-state Nd:YLF laser. Very precise cavities can be obtained in the enamel and dentin of extracted human molars when laser pulses are distributed onto well-defined areas of the teeth. Scanning electron microscopy shows that the quality of the cavities is superior to that achieved by other laser systems. The cavity walls are very steep, and their surfaces are characterized by a sealed structure. In contrast to laser systems with longer-duration pulses, picosecond laser pulses ablate with less thermal damage to the surrounding substance. The results of dye penetration tests and polarized microscopy show that even mechanical shock-wave effects are negligible. When the Nd:YLF laser is applied to carious enamel, the ablation rate is found to be about ten times higher than for sound molars, thus making the Nd:YLF laser a caries-selective laser system.

The origin of cariogenesis in occlusal fissures remains elusive because of limited information about both the fissure structure and the morphologic details of carious lesions occurring there. The present study was aimed at reconstructing the coronal structure of human premolars with the aid of computer-assisted image analysis and, on the basis of the reconstructed structures, investigating the configuration of fissures, their proximity to the enameldentin junction (EDJ), and the occurrence and extension of carious lesions around the fissure walls. The coronal portions of the teeth were embedded in polyester resin and then ground off stepwise by hand. Serial images of the enamel contour on successive ground planes were recorded by objective microscopy after it was distinctly demarcated with either 0.5 w/v% carbol fuchsin or 1 w/v% basic fuchsin. Usually, from 150 to 250 photoprints were collected from a single enamel crown to reproduce the details of the fissure structures. The enamel outline (the occlusal and lateral surfaces, fissure walls, and EDJ) and, if present, the outline of caries-attacked areas were traced accurately on those photoprints by means of a digitizing system. The enamel contour data in series were input into an image analyzing system (Nikon COSMOZONE, 2SA). Observation of the computer-drawn coronal enamel allowed us to view the morphologic features of the fissures (shape, divarication, and proximity to EDJ) and to scrutinize the pathway of enamel caries along fissure walls. The results indicate that the computer-assisted reconstruction of enamel crown, in conjunction with the step-by-step grinding technique, is useful in basic and clinical studies of occlusal fissure caries.

Caries at the margins of restorations is difficult to diagnose. In particular, the relevance of both marginal ditching and staining around amalgam restorations is unclear. This clinical study questions the relevance of marginal ditching and color change to the level of infection of the dentin beneath the margins of amalgam restorations. Clinically visible sites (330) on the tooth/restoration margin were selected on 175 teeth. The enamel adjacent to each site was noted as stained (a grey discoloration) or stain-free. One hundred and seventy-eight sites were clinically intact, 83 sites had narrow ditches (< 0.4 mm), and at 49 sites, wide ditches were present (> 0.4 mm). Twenty sites with frankly carious lesions were also included. Plaque was sampled at the tooth-restoration margin, and the dentin was sampled at the enamel-dentin junction below each site. Samples were vortexed, diluted, and cultured for total anaerobic counts, mutans streptococci, lactobacilli, and yeasts. Plaque samples showed that margins with wide ditches (> 0.4 mm) harbored significantly more bacteria, mutans streptococci, and lactobacilli than did clinically intact margins and margins with narrow ditches. There were no significant differences in the degree of infection of the dentin beneath clinically intact restorations and those with narrow ditches, but samples associated with wide ditches and carious lesions yielded significantly more bacteria, mutans streptococci, and lactobacilli. The color of the enamel adjacent to the sample site was irrelevant to the level of infection of the dentin beneath the filling margin, provided a frankly carious lesion was not present. The results suggest that amalgam fillings where margins show wide ditches or carious lesions should be replaced. Narrow ditches and color change alone should not trigger the replacement of a filling.

We adapted an assay that has been used to estimate the strength of eukaryotic cell-cell and cell-extracellular matrix adhesive interactions (McClay et al., 1981) to quantify the strength of bacterial (streptococci, fusobacteria, actinomyces) interactions with salivary receptors. Bacteria are centrifuged onto human submandibular/sublingual or parotid-saliva-coated microtiter wells. Plates are sealed with pressure-sensitive, double-sided tape which allows them to be inverted and centrifuged again. The force required to remove the bacteria from the coated wells is a direct measure of the adhesive strength of the interaction(s) being disrupted. The bacteria-saliva adhesive forces we detected ranged from 1.6 x 10-8 dynes (Streptococcus sanguis 72-40) to > 1.1 x 10-7 dynes (Actinomyces viscosus T14 V). These forces were in the range to withstand the shear stress produced by salivary flow, which we calculated as approximately 6.1 x 10-7 dynes.

The periodontium contains heterogeneous mesenchymal cell populations with various differentiation potentials. The capacity of these cells for tissue formation as well as the origin of their precursors are still not entirely defined. In this study, cells originating from different periodontal tissues were cultured in vitro, and tissue formation in vivo following orthotopic re-implantation was investigated. Cells were recovered from the alveolar bone and periodontal ligament tissue of six minipigs, and cultured cells were then grown on extracted dental roots from the homologous animals by means of co-culture in vitro. Each minipig received 2 roots covered with alveolar bone cells, 2 roots covered with periodontal ligament cells, and 2 control roots (without cells) implanted into palatal bone defects. Intravital fluorochrome labeling was performed, and two minipigs were histologically examined after 2, 4, and 12 weeks in each case. Controls showed widespread resorption and ankylosis, whereas roots covered with cultured periodontal cells exhibited tissue formation in vivo. Alveolar bone cells synthesized a calcified cellular tissue resembling cellular cementum, suggesting that cells within this population might differentiate into cementoblasts when re-implanted with a dental substrate in vivo. Periodontal ligament cells exhibited no calcified tissue formation in vivo, but cells synthesized a connective tissue with orientated fiber bundles attached to both host bone and root, resembling periodontal ligament. Results indicate that cultured cells retain the capacity to form differentiated periodontal tissues after re-implantation, depending on the cells' origin. Our findings also suggest that the alveolar bone contains cementogenic precursors with the potential to differentiate into active cementoblasts in the presence of a dental substrate.

Formation and degradation of dental basement membrane (BM) are important for tooth development. Data on the expression of genes for type IV collagen (the major structural component of the BM) and type IV collagenases [MMP-2 (72 kDa) and MMP-9 (92 kDa)], enzymes that degrade type IV collagen during human tooth development, are lacking. We studied expression of type IV collagen and the MMP-2 and MMP-9 in human fetal teeth (from the 13th to the 20th gestational weeks, covering cap stage through early hard tissue formation). During cap and bell stages, in situ hybridization located transcripts for al type IV collagen chain in the fibroblasts surrounding the enamel organ. No al type IV collagen chain mRNA was detected in tooth germ epithelium or dental papilla. However, type IV collagen immunoreactivity was observed in BM underlying the dental epithelium up to the appositional stage. Transcripts for MMP-2 were located mostly in the cells of the dental papilla and follicle. Transient expression of MMP-2 mRNA was observed in the inner enamel epithelium of late cap/early bell-stage teeth. During early apposition, a high level of MMP-2 was confined to secretory odontoblasts. Transcripts for MMP-9 were detected by the sensitive reverse-transcription polymerase chain reaction (RT-PCR) in developing teeth. Thus, in dental BM, al type IV collagen chain may be of mesenchymal cell origin. Further, MMP-2 but not MMP-9 may participate in remodeling and degradation of BM during human tooth morphogenesis.

Palatal movements play a critical role in regulating oropharyngeal airflow during breathing. We hypothesized that these movements are coordinated with breathing movements via afferent signals from the lung. However, the control of palatal movements in relation to the lung remains unclear. This study was designed to define, by electromyographic techniques, the relationship between palatal movement and lung action during respiration.

We performed tracheotomies on 12 mongrel dogs anesthetized with sodium pentobarbital and found that lung inflation augmented the activity of the levator veli palatini muscle (LVP). Two kinds of discharges were recognized during the expiratory pause following lung inflation. One was a continuous, low-amplitude discharge induced during apnea following lung inflation. The other was a transient, high-amplitude discharge which appeared immediately after lung inflation. Both of these response activities were eliminated by bilateral vagotomy. We thus concluded that palatal movements, which can regulate expiratory airflow resistance and cause switching from nasal to oral airflow, are under the control of vagal afferent signals from the lung.