Changes in hemoglobin concentration and oxygen saturation in human gingiva with decreasing inflammation

Historical and contemporary hypotheses on the development of oral diseases: are we there yet?

Dental plaque is an oral biofilm that much like the rest of our microbiome has a role in health and disease. Specifically, it is the cause of very common oral diseases such as caries, gingivitis, and periodontitis. The ideas about oral disease development have evolved over time. In the nineteenth century, scientists could not identify bacteria related to disease due to the lack of technology. This led to the "Non-Specific Plaque Hypothesis" or the idea that the accumulation of dental plaque was responsible for oral disease without discriminating between the levels of virulence of bacteria. In the twentieth century this idea evolved with the techniques to analyze the changes from health to disease. The first common hypothesis was the "Specific Plaque Hypothesis" (1976) proposing that only a few species of the total microflora are actively involved in disease. Secondly, the "Non-Specific Plaque Hypothesis" was updated (1986) and the idea that the overall activity of the total microflora could lead to disease, was enriched by taking into account difference in virulence among bacteria. Then, a hypothesis was considered that combines key concepts of the earlier two hypotheses: the "Ecological Plaque Hypothesis" (1994), which proposes that disease is the result of an imbalance in the microflora by ecological stress resulting in an enrichment of certain disease-related micro-organisms. Finally, the recent "Keystone-Pathogen Hypothesis" (2012) proposes that certain low-abundance microbial pathogens can cause inflammatory disease by interfering with the host immune system and remodeling the microbiota. In this comprehensive review, we describe how these different hypotheses, and the ideas around them, arose and test their current applicability to the understanding of the development of oral disease. Finally, we conclude that an all-encompassing ecological hypothesis explaining the shifts from health to disease is still lacking.

Discrimination of periodontal diseases using diffuse reflectance spectral intensity ratios

This clinical study was to demonstrate the applicability of diffuse reflectance (DR) intensity ratio R620/R575 in the quantification and discrimination of periodontitis and gingivitis from healthy gingiva. DR spectral measurements were carried out with white-light illumination from 70 healthy sites in 30 healthy volunteers, and 63 gingivitis- and 58 periodontitis-infected sites in 60 patients. Clinical parameters such as probing pocket depth, clinical attachment level, and gingival index were recorded in patient population. Diagnostic accuracies for discrimination of gingivitis and periodontitis from healthy gingiva were determined by comparison of spectral signatures with clinical parameters. Divergence of average DR spectral intensity ratio between control and test groups was studied using analysis of variance. The mean DR spectrum on normalization at 620 nm showed marked differences between healthy tissue, gingivitis, and periodontitis. Hemoglobin concentration and apparent SO(2) (oxygen saturation) were also calculated for healthy, gingivitis, and periodontitis sites. DR spectral intensities at 545 and 575 nm showed a decreasing trend with progression of disease. Among the various DR intensity ratios studied, the R620/R575 ratio provided a sensitivity of 90% and specificity of 94% for discrimination of healthy tissues from gingivitis and a sensitivity of 91% and specificity of 100% for discrimination of gingivitis from periodontitis.

The oral microbial consortium's interaction with the periodontal innate defense system

The oral microbial consortium is the most characterized polymicrobial microbial community associated with the human host. Extensive sampling of both microbial and tissue samples has demonstrated that there is a strong association between the type of microbial community found in the gingival crevice and the status of innate host mediator expression. The strong clinical association between the microbial community and the innate host response in both clinically healthy and diseased tissue suggests that the oral consortium has a direct effect on periodontal tissue expression of innate defense mediators. A preliminary study in germ-free mice has demonstrated that the oral commensal consortium has direct effect on IL-1beta expression, indicating that this microbial community may contribute to the strong protective status of healthy gingival tissue. Likewise, the lipopolysaccharide composition and invasion characteristics of Porphyromonas gingivalis, an oral bacterium strongly associated with periodontitis, suggest that it may be a keystone member of the oral microbial community and facilitate a destructive change in the protective gingival innate host status.

Human Toll-like receptor 4 responses to P. gingivalis are regulated by lipid A 1- and 4'-phosphatase activities

Signal transduction following binding of lipopolysaccharide (LPS) to Toll-like receptor 4 (TLR4) is an essential aspect of host innate immune responses to infection by Gram-negative pathogens. Here, we describe a novel molecular mechanism used by a prevalent human bacterial pathogen to evade and subvert the human innate immune system. We show that the oral pathogen, Porphyromonas gingivalis, uses endogenous lipid A 1- and 4'-phosphatase activities to modify its LPS, creating immunologically silent, non-phosphorylated lipid A. This unique lipid A provides a highly effective mechanism employed by this bacterium to evade TLR4 sensing and to resist killing by cationic antimicrobial peptides. In addition, lipid A 1-phosphatase activity is suppressed by haemin, an important nutrient in the oral cavity. Specifically, P. gingivalis grown in the presence of high haemin produces lipid A that acts as a potent TLR4 antagonist. These results suggest that haemin-dependent regulation of lipid A 1-dephosphorylation can shift P. gingivalis lipid A activity from TLR4 evasive to TLR4 suppressive, potentially altering critical interactions between this bacterium, the local microbial community and the host innate immune system.

Hemoglobin and LPS act in synergy to amplify the inflammatory response

Vascular disruption and bleeding during periodontitis likely increase the levels of hemoglobin in gingival crevicular fluid. The aim of this study was to investigate the effect of hemoglobin on the inflammatory responses of human macrophages stimulated with lipopolysaccharides (LPS) isolated from periodontopathogens. The production of interleukin-1 beta (IL-1beta), IL-6, IL-8, and tumor necrosis factor alpha (TNF-alpha) by macrophages following challenges with Porphyromonas gingivalis and Fusobacterium nucleatum LPS in the presence or absence of human hemoglobin was analyzed by ELISA. The effect of hemoglobin on LPS-binding to macrophages was evaluated with (3)H-LPS. Hemoglobin and LPS from periodontopathogens acted in synergy to stimulate the production of high levels of IL-1beta, IL-6, IL-8, and TNF-alpha by macrophages. Hemoglobin also enhanced LPS-binding to macrophages. This study suggests that hemoglobin contributes to increases in the levels of pro-inflammatory mediators in periodontal sites by acting in synergy with LPS from periodontopathogens, thus favoring the progression of periodontitis.

Environmental cues and gene expression in Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans

Microorganisms typically adapt to environmental cues by turning on and off the expression of virulence genes which, in turn, allows for optimal growth and survival within different environmental niches. This adaptation strategy includes sensing and responding to changes in nutrients, pH, temperature, oxygen tension, redox potential, microbial flora, and osmolarity. For a bacterium to adhere to, penetrate, replicate in, and colonize host cells, it is critical that virulence genes are expressed during certain periods of the infection process. Thus, throughout the different stages of an infection, different sets of virulence factors are turned on and off in response to different environmental signals, allowing the bacterium to effectively adapt to its varying niche. In this review, we focus on the regulation of virulence gene expression in two pathogens which have been implicated as major etiological agents in adult and juvenile periodontal diseases: Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans. Understanding the mechanisms of virulence gene expression in response to the local environment of the host will provide crucial information in the development of effective treatments targeted at eradication of these periodontal disease pathogens.

Oxygen sufficiency in the gingiva of smokers and non-smokers with periodontal disease

BACKGROUND

Epidemiological studies have demonstrated deteriorating effects of smoking on periodontal tissue. The aims of this study were to compare oxygen saturation of hemoglobin in the gingiva (GSo2) of smokers and non-smokers and to evaluate the chronic effect of smoking on gingival oxygen sufficiency.

METHODS

GSo2 was determined using tissue reflectance spectrophotometry in 110 papillary gingival sites of 62 smokers and 100 sites of 60 non-smokers.

RESULTS

No significant difference was found in GSo2 between smokers and non-smokers. In the model of ANOVA with covariates, age (P= 0.0048) and probing depth (P= 0.0012) had significant effects on GSo2. No significant effect was found in either smoking status (P= 0.3557) or the modified gingival index (MGI) (P= 0.3824). The interaction effect between smoking status and the MGI was highly significant (P = 0.0003) indicating that the effect of smoking status on the GSo2 should be compared at each level of the MGI score. GSo2 in healthy gingiva was significantly lower in smokers than non-smokers (P = 0.0014), while smokers showed higher GSo2 than non-smokers in moderately inflamed gingiva (P = 0.0356). The GSo2 in inflamed gingiva was significantly decreased compared with healthy gingiva in non-smokers (P = 0.0044), while smokers showed no significant difference between healthy and inflamed gingiva (P= 0.2772 to 0.8665). GSo2 in smokers was consistently and significantly lower than that of healthy gingiva of non-smokers (P = 0.0391 to 0.0004).

CONCLUSIONS

Smokers exhibit possibly lower function of oxygen sufficiency in healthy gingiva and reduced ability to adapt the function in inflamed gingiva than non-smokers. This suggests that smokers have functional impairments in the gingival microcirculation.

Site-specific attachment level change detected by physical probing in untreated chronic adult periodontitis: review of studies 1982-1997

BACKGROUND

Site-specific attachment level change, detected from sequential physical probing measurements, is currently the most common method of determining the progression/regression or stability of disease status in subjects with chronic adult periodontitis. The sensitivity and accuracy of detection is dependent on the type of probe used, the recording method, the measurement error, and the method of data analysis. In recent years, there has been world-wide interest in developing instruments and methods to minimize measurement error. Published data report disturbingly wide variation in the prevalences and rates of site-specific attachment level change which are difficult to reconcile with biological likelihood. The present paper aims to summarize the salient points from the key studies and to compare the results.

METHODS

The literature between 1982 and 1997 was reviewed for studies in which site-specific attachment level change was detected by physical probing methods in patients with chronic adult periodontitis.

RESULTS

The review documents 23 studies by probe generation, compares methods and results and summarizes the results according to the thresholds and probe type used. The 23 studies used an array of probe types from the 3 probe generations.

CONCLUSIONS

From this review, we conclude that: 1) There are surprisingly few papers which have addressed the question of site-specific attachment level change in untreated chronic adult periodontitis. 2) There are considerable differences in the probes used, in the thresholds achieved, in the number of measurements taken, in the number of subjects and sites studied, and in the duration of the studies. Valid comparisons between studies are, therefore, rarely possible. 3) Only 8 out of 23 papers from 1982 to 1997 have adequate data. Most papers report only losing sites and therefore ignore many of the measurements recorded. Only one paper describes losing sites, gaining sites, and sites showing exacerbation/remission patterns of change. 4) The range of changes described show such variation that it has to be concluded that we cannot reliably detect site-specific attachment level change by physical probing and thus, at the end of the 20th century, we have no clear idea of the natural history of this disease.

Effect of mechanical toothbrush stimulation on gingival microcirculatory functions in inflamed gingiva of dogs

The effect of mechanical toothbrush stimulation on gingival microcirculatory functions was examined with and without removal of supragingival plaque in inflamed gingiva of 6 dogs. After removal of the ligatures, 4 treatment modalities: mechanical stimulation by vibration (MS), removal of supragingival plaque (PR), combination (MS+PR) and no treatment (NT), were administered to each quadrant for 2 weeks. Both quadrants with plaque removal showed a marked decrease in the gingival index score, while slight and moderate decreases were observed in NT and MS quadrants, respectively. Changes in gingival crevicular fluid flow, pocket oxygen tension and hemoglobin oxygen saturation in the gingiva were significant in the MS, PR and MS+PR quadrants. Significant treatment-by-time effects were found for all of the parameters of microcirculatory function between NT and MS quadrants, and gingival crevicular fluid flow between PR and MS+PR quadrants, respectively. These findings suggest that mechanical stimulation with a toothbrush may offer an additional benefit to gingival microcirculatory functions in inflamed gingiva.

Comparisons of modalities of mechanical stimulation with a toothbrush on improvement of oxygen sufficiency in dog gingiva

Mechanical stimulation with a toothbrush was applied to each quadrant of 10 dogs at a force of 200 g for 10 s using following modalities: vibration at attached gingiva, pressurization at attached gingiva, vibration at marginal gingiva and no treatment as a control. Hemoglobin oxygen saturation (SO2) in the gingiva was measured by non-invasive tissue reflectance spectrophotometry. Simultaneously, oxygen tension (pO2) in gingival tissue was monitored with an oxygen microelectrode. Both SO2 and pO2 increased within 10-20 min after stimulation and then slowly returned to the initial level at all treatment sites. The response was most prominent after vibration at attached gingiva. SO2 and pO2 increased by 12% and 42%, respectively, and significant increase continued for 75-85 min. Response after vibration at marginal gingiva was moderate in pO2 and transient in SO2. Pressurization at attached gingiva caused moderate response in SO2, but the increase in pO2 was slight. Control showed little change in both indices. These results suggest that vibration with a toothbrush at attached gingiva may cause a maximal response in improving oxygen sufficiency to gingival tissue.

Virulence factors of Actinobacillus actinomycetemcomitans relevant to the pathogenesis of inflammatory periodontal diseases

There is strong evidence implicating Actinobacillus actinomycetemcomitans as the causative agent of localised juvenile periodontitis (LJP), a disease characterised by rapid destruction of the tooth-supporting tissues. This organism possesses a large number of virulence factors with a wide range of activities which enable it to colonise the oral cavity, invade periodontal tissues, evade host defences, initiate connective tissue destruction and interfere with tissue repair. Adhesion to epithelial and tooth surfaces is dependent on the presence of surface proteins and structures such as microvesicles and fimbriae. Invasion has been demonstrated in vivo and in vitro although the mechanisms involved are poorly understood. The organism has a number of means of evading host defences which include: (i) inhibiting poloymorphonuclear leukocyte (PMN) chemotaxis; (ii) killing PMNs and monocytes; (iii) producing immunosuppressive factors; (iv) secreting proteases capable of cleaving IgG; and (v) producing Fc-binding proteins. Surface components of A. actinomycetemcomitans are potent stimulators of bone resorption and can induce the release of a range of cytokines which can initiate tissue destruction. A number of surface components can also inhibit the proliferation of fibroblasts and their production of components of the extracellular matrix. Little is known, however, regarding the way in which these factors operate in vivo to produce the pathological features of the disease.

Antioxidative activities of some chemotherapeutics. A possible mechanism in reducing gingival inflammation

Inflammatory periodontal diseases are related to dental plaque formation. Increase in the perfusion of the inflamed tissue results in increased oxygen supply. Although oxygen has healing effects, it is bound to be a mediator of peroxidation in biological membranes. Chemotherapeutic agents such as chlorhexidine, listerine, sanguinarine, and cetylpridinium chloride and oral antibiotics such as tetracycline HCl and doxycyline were tested for their antioxidative activities. While doxycycline has the highest antioxidant activity in lower volumes (0.1 ml), sanguinarine, listerine and a pace after them, tetracycline HCl, had similar effects in higher volumes (0.3 and 0.4 ml). The results showed that in addition to their antiseptic or antimicrobial effects, these preparations have an antioxidative activity against spontaneous oxidation.

Mechanical stimulation by toothbrushing increases oxygen sufficiency in human gingivae

We studied the immediate effect of mechanical stimulation with a toothbrush on oxygen sufficiency in human gingivae. Teeth were brushed with a modified Bass technique at various forces (100, 200, and 300 g) for various times (5, 10, and 30 s). Hemoglobin (Hb) oxygen saturation was measured before and intermittently for 60 min after brushing, by non-invasive tissue reflectance spectrophotometry. Hb oxygen saturation increased within a few min after brushing and then slowly returned to the initial level. Toothbrushing at 200 g for 10 s caused the longest-lived increase in Hb oxygen saturation; saturation remained about 6% above the baseline level for more than 25 min. Before brushing, Hb oxygen saturation was significantly lower in inflamed gingivae than in healthy gingivae (p < 0.05). After brushing of inflamed gingivae, the Hb oxygen saturation almost reached the level measured in healthy gingivae before brushing. These findings suggest that stimulation with a toothbrush increases oxygen sufficiency in both healthy and inflamed gingivae.

Changes in oxygen consumption in dog gingiva during induction of experimental periodontitis

The purpose of this study was to examine changes in oxygen consumption in dog gingiva during induction of experimental periodontitis. The disease was induced in adult mongrel dogs during a 16-week period by placement of silk ligatures around selected teeth. The oxygen consumption rate of gingival tissue was determined in vivo by a non-invasive technique, tissue reflectance spectrophotometry. Changes in such clinical parameters as gingival index, plaque index, pocket depth, attachment level, and gingival crevicular fluid flow indicated acute inflammatory responses during the first three weeks after ligation, followed by the appearance of chronic inflammation during the remaining 13 weeks. The oxygen consumption rate increased during the first seven days after ligation and stayed near the maximum level for 2-7 weeks; this was followed by a gradual decrease during the final nine weeks. These results suggest that gingival oxygen consumption increases rapidly with the increase of acute inflammation responses and then decreases slightly with the gradual development of chronic inflammation. Positive correlations were observed between the oxygen consumption rate and other clinical indices. Thus, the tissue reflectance spectrophotometry is a new, useful method for objective, quantitative, and non-invasive assessment of gingival oxygen consumption.