Microbiology of periodontal diseases: introduction

Periodontal disease may associate with breast cancer

The main purpose was to evaluate the association between periodontal disease and the incidence of breast cancer in a prospective study of 3273 randomly selected subjects aged 30-40 years at baseline. Breast cancer incidence was registered from 1985 to 2001 according to the WHO International Classification of Diseases criteria. At baseline, 1676 individuals also underwent a clinical oral examination (Group A) whereas 1597 subjects were not clinically examined but were registered (Group B). The associations between breast cancer, periodontal disease, and missing molars were determined using multiple logistic regression models with several background variables and known risk factors for cancer. In total 26 subjects in group A and 15 subjects in group B had breast cancer. The incidence of breast cancer was 1.75% in subjects who had periodontal disease and/or any missing molars, and 0 in subjects who had periodontal disease but had no missing molars. For periodontally healthy subjects with no missing teeth the breast cancer incidence was 1%. For group B the respective incidence was 0.94%. Female gender (odds ratio (OR) 13.08) and missing any molar in the mandible (OR 2.36) were explanatory variables for breast cancer. Of the subjects with periodontal disease and any missing molars in the mandible 5.5% had breast cancer in comparison to 0.5% of the subjects who had periodontal disease but no missing molars in the mandible (P < 0.02). Chronic periodontal disease indicated by missing molars seemed to associate statistically with breast cancer.

The Hpk2-Rrp2 two-component regulatory system of Treponema denticola: a potential regulator of environmental and adaptive responses

Treponema denticola levels in the gingival crevice become elevated as periodontal disease develops. Oral treponemes may account for as much as 40% of the total bacterial population in the periodontal pocket. The stimuli that trigger enhanced growth of T. denticola, and the mechanisms associated with the transmission of these signals, remain to be defined. We hypothesize that the T. denticola open reading frames tde1970 (histidine kinase) and tde1969 (response regulator) constitute a functional two-component regulatory system that regulates, at least in part, responses to the changing environmental conditions associated with the development of periodontal disease. The results presented demonstrate that tde1970 and tde1969 are conserved, universal among T. denticola isolates and transcribed as part of a seven-gene operon in a growth-phase-dependent manner. tde1970 undergoes autophosphorylation and transfers phosphate to tde1969. Henceforth, the proteins encoded by these open reading frames are designated as Hpk2 and Rrp2 respectively. Hpk2 autophosphorylation kinetics were influenced by environmental conditions and by the presence or absence of a PAS domain. It can be concluded that Hpk2 and Rrp2 constitute a functional two-component system that contributes to environmental sensing.

Destructive and protective roles of cytokines in periodontitis: a re-appraisal from host defense and tissue destruction viewpoints

Periodontal diseases (PD) are chronic infectious inflammatory diseases characterized by the destruction of tooth-supporting structures, being the presence of periodontopathogens required, but not sufficient, for disease development. As a general rule, host inflammatory mediators have been associated with tissue destruction, while anti-inflammatory mediators counteract and attenuate disease progression. With the discovery of several T-cell subsets bearing distinct immunoregulatory properties, this pro- vs. anti-inflammatory scenario became more complex, and a series of studies has hypothesized protective or destructive roles for Th1, Th2, Th17, and Treg subpopulations of polarized lymphocytes. Interestingly, the "protective vs. destructive" archetype is usually considered in a framework related to tissue destruction and disease progression. However, it is important to remember that periodontal diseases are infectious inflammatory conditions, and recent studies have demonstrated that cytokines (TNF-α and IFN-γ) considered harmful in the context of tissue destruction play important roles in the control of periodontal infection. Therefore, in this review, the state-of-the-art knowledge concerning the protective and destructive roles of host inflammatory immune response will be critically evaluated and discussed from the tissue destruction and control-of-infection viewpoints.

Antimicrobial photodynamic therapy may promote periodontal healing through multiple mechanisms

BACKGROUND

Antimicrobial photodynamic therapy (aPDT) as an adjunctive treatment in addition to scaling and root planing for the treatment of periodontitis has been shown to be clinically useful. Its beneficial effect is reported to be due to its potent bactericidal activity. However, aPDT treatment has the potential to inactivate bacterial and host factors that contribute to disease. In this report, we demonstrate that aPDT treatment can simultaneously kill Porphyromonas gingivalis and inactivate its virulence-associated protease. It also inactivates host destructive cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin (IL)-1 beta.

METHODS

We developed a 96-well-based bacterial killing and protease inactivation assay that determined aPDT bactericidal and protease inactivation from the same sample. A cytokine inactivation assay that measured E-selectin expression in response to TNF-alpha and IL-1 beta was developed to measure the ability of aPDT to inactivate cytokine function.

RESULTS

A single aPDT treatment in vitro potently inactivated protease activity and resulted in a 4-log(10) reduction in the viability of P. gingivalis. Dose and time-of-exposure experiments revealed that protease inactivation occurred at lower concentrations of photosensitizer and less time of light exposure. Also, aPDT treatment potently and functionally inactivated IL-1 beta and TNF-alpha.

CONCLUSIONS

aPDT treatment may augment periodontal treatment by increasing bacterial killing, inactivating bacterial virulence factors, and inactivating host cytokines that impair periodontal restoration. Therefore, aPDT treatment may provide a more favorable healing environment.

Mouse model of experimental periodontitis induced by Porphyromonas gingivalis/Fusobacterium nucleatum infection: bone loss and host response

AIM

To compare the effect of oral infection with Porphyromonas gingivalis or Fusobacterium nucleatum versus infection with both bacteria on mouse periodontal tissues, and to characterize the inflammatory response.

MATERIALS AND METHODS

Mice were orally infected with P. gingivalis, F. nucleatum or both. At 42 days post-infection, alveolar bone loss was quantified using micro-computerized tomography. Tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-1beta levels induced by the infection were quantified using the subcutaneous chamber model.

RESULTS

Mice orally infected with F. nucleatum/P. gingivalis exhibited significantly more bone loss compared with that of mono-infected and sham-infected mice. F. nucleatum/P. gingivalis infection also increased the levels of TNF-alpha and IL1beta compared with the levels found in the mono-infected groups.

CONCLUSIONS

Polymicrobial infection with P. gingivalis/F. nucleatum aggravates alveolar bone loss and induces a stronger inflammatory response compared with that observed upon infection with either bacterium alone. The results suggest that oral infection of mice with a mixture of P. gingivalis and F. nucleatum may be superior to mono-infection models of experimental periodontitis.

Grafting of antibodies inside integrated microfluidic-microoptic devices by means of automated microcontact printing

A novel approach to integrating biochip and microfluidic devices is reported in which microcontact printing is a key fabrication technique. The process is performed using an automated microcontact printer that has been developed as an application-specific tool. As proof-of-concept the instrument is used to consecutively and selectively graft patterns of antibodies at the bottom of a glass channel for use in microfluidic immunoassays. Importantly, feature collapse due to over compression of the PDMS stamp is avoided by fine control of the stamp's compression during contact. The precise alignment of biomolecules at the intersection of microfluidic channel and integrated optical waveguides has been achieved, with antigen detection performed via fluorescence excitation. Thus, it has been demonstrated that this technology permits sequential microcontact printing of isolated features consisting of functional biomolecules at any position along a microfluidic channel and also that it is possible to precisely align these features with existing components.

N-acetylcysteine prevents LPS-induced pro-inflammatory cytokines and MMP2 production in gingival fibroblasts

Periodontitis is an inflammatory process that ultimately results in tooth loss. Although the primary etiologic agent for periodontitis is bacteria, the majority of periodontal tissue destruction is thought to be caused by an inappropriate host response. Reactive oxygen species (ROS) have been known to be involved in periodontal tissue destruction. We treated human gingival fibroblasts with lipopolysaccharide (LPS) obtained from E. coli and the periodontopathogens Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis, and examined their inflammatory responses in the presence and absence of the antioxidant N-acetylcysteine (NAC). LPS enhanced ROS production, as well as, expression of pro-inflammatory cytokines such as interleukin-1beta, interleukin-6, interleukin-8 and tumor necrosis factor-alpha, and the production and activation of MMP2. NAC suppressed all LPS-induced inflammatory responses examined, suggesting that LPS-induced ROS may play a major regulatory role in these responses in gingival fibroblasts. In addition, NAC prevented LPS-induced activation of p38 MAPK and JNK but not phosphorylation and subsequent degradation of IkB. These results indicate that NAC exerts anti-inflammatory effects in LPS-stimulated gingival fibroblasts, functioning at least in part via down-regulation of JNK and p38 MAPK activation. Furthermore, this work suggests that antioxidants may be useful in adjunctive therapies that complement conventional periodontal treatments.

Herpesviral-bacterial synergy in the pathogenesis of human periodontitis

PURPOSE OF REVIEW

Periodontitis is an infectious disease, but the specific mechanisms by which tooth-supportive tissues are lost remain obscure. This article proposes an infectious disease model for periodontitis in which herpesviral-bacterial interactions assume a major etiopathogenic role.

RECENT FINDINGS

Epstein-Barr virus type 1, cytomegalovirus and other herpesviruses occur at a high frequency in aggressive periodontitis lesions. Also, herpesvirus-infected periodontitis lesions tend to harbor elevated levels of classic periodontopathic bacteria, including Porphyromonas gingivalis, Dialister pneumosintes, Prevotella intermedia, Prevotella nigrescens, Campylobacter rectus, Treponema denticola and Actinobacillus (Aggregatibacter) actinomycetemcomitans.

SUMMARY

Conceivably, a herpesvirus active infection in the periodontium impairs local defenses, thereby permitting overgrowth and increased aggressiveness of periodontopathic bacteria. In turn, periodontal pathogenic bacteria may augment the virulence of periodontal herpesviruses. It is suggested that interactions among herpesviruses and specific bacterial species constitute an important pathogenetic feature of periodontitis and maybe also of various non-oral infections.

Incorrect Nutrition as a Risk Factor for Periodontal Disease

Knowledge of the cause, prevention, and treatment of periodontal disease has increased rapidly during the past several decades; however, periodontal disease is still a prevalent infection, the treatment of which consumes vast amounts of financial and manpower resources. The intention of this article is to explore the role of nutrition in both the initiation and treatment of periodontal disease and to suggest that dental health professionals should consider nutritional guidance as a part of routine periodontal care.

Co-adhesion and biofilm formation by Fusobacterium nucleatum in response to growth pH

Fusobacterium nucleatum is a Gram-negative anaerobic organism considered to play an important role in the progression of periodontal disease and is commonly found in clinical infections of other body sites. Apart from its metabolic versatility, its cell-surface properties enable it to attach to epithelial cells, collagen, gingival epithelial cells and other bacterial genera, but not with other Fusobacteria. The development of periodontitis is associated with a rise in pH in the gingival sulcus to around 8.5, and this is thought to occur by the catabolism of proteins supplied by gingival crevicular fluid. F. nucleatum is commonly isolated from diseased sites and has also been shown to survive in root canal systems at pH 9.0 after Ca(OH)(2) treatment. In order to survive hostile environmental conditions, such as nutrient deprivation and fluctuating temperature and pH, bacteria form biofilms, which are usually made up of multi-species co-aggregates. We have grown F. nucleatum in a chemostat at a growth rate consistent with that of oral bacteria in vivo and report that, at a growth pH of 8.2, F. nucleatum co-adheres and forms a homogeneous biofilm. Cell-surface hydrophobicity was determined in planktonic and co-adhering cells to characterise the interfacial interactions associated with the response to pH. Cell-surface hydrophobicity was found to increase at pH 8.2 and this was also associated with a decrease in the levels of intracellular polyglucose (IP) and an observed change in the bacterial cell morphology. To our knowledge, these results represent the first study in which F. nucleatum has been shown to co-adhere and form a biofilm, which may be important in the organism's persistence during the transition from health to disease in vivo.

The proteomic profile of Fusobacterium nucleatum is regulated by growth pH

Fusobacterium nucleatum is a saccharolytic Gram-negative anaerobic organism believed to play an important role in the microbial succession associated with the development of periodontal disease. Its genome contains niche-specific genes shared with the other inhabitants of dental plaque, which may help to explain its ability to survive and grow in the changing environmental conditions experienced in the gingival sulcus during the transition from health to disease. The pH of the gingival sulcus increases during the development of periodontitis and this is thought to occur by the metabolism of nutrients supplied by gingival crevicular fluid. In comparison with other plaque inhabitants, F. nucleatum has the greatest ability to neutralize acidic environments. The differential expression of soluble cytoplasmic proteins induced by acidic (pH 6.4) or basic (pH 7.4 and 7.8) conditions, during long-term anaerobic growth in a chemostat, was identified by two-dimensional gel electrophoresis and image analysis software. Twenty-two proteins, found to have altered expression in response to external pH, were identified by tryptic digestion and mass spectrometry. Eight differentially expressed proteins associated with increased energy (ATP) production via the 2-oxoglutarate and Embden-Meyerhof pathways appeared to be directed towards either cellular biosynthesis or the maintenance of internal homeostasis. Overall, these results represent the first proteomic investigation of F. nucleatum and the identification of gene products which may be important in the organism's persistence during the transition from health to disease in vivo.

Benefit of “one-stage full-mouth disinfection” is explained by disinfection and root planing within 24 hours: a randomized controlled trial

OBJECTIVES

The beneficial effects of the one-stage, full-mouth disinfection remain controversial in the scientific literature. This might be due to the fact that an entire mouth disinfection with the use of antiseptics has been confused with a full-mouth scaling and root planing. This parallel, single blind RCT study aimed to compare several full-mouth treatment strategies with each other.

MATERIAL AND METHODS

Seventy-one patients with moderate periodontitis were randomly allocated to one of the following treatment strategies: scaling and root planing, quadrant by quadrant, at two-week intervals (negative control, NC), full-mouth scaling and root planing within 2 consecutive days (FRP), or three one-stage, full-mouth disinfection (FM) protocols within 2 consecutive days applying antiseptics to all intra-oral niches for periopathogens using as antiseptics: chlorhexidine (FMCHX) for 2 months, amine fluoride/stannous fluoride for 2 months (FMF), or chlorhexidine for 2 months followed by amine fluoride/stannous fluoride for another 6 months (FMCHX+F). At baseline and after 2, 4, and 8 a series of periodontal parameters were recorded.

RESULTS

All treatment strategies resulted in significant (p<0.05) improvements of all clinical parameters over the entire duration of the study. Inter-treatment differences were often encountered. The NC group nearly always showed significant smaller improvements than the two CHX groups. The differences between the FRP or FM groups, and the two CHX groups only sporadically reached a statistical significance.

CONCLUSION

These observations indicate that the benefits of the "OSFMD" protocol are partially due to the use of the antiseptics and partially to the completion of the therapy in a short time.

Fibrinogen-neutrophil interactions in response to fMLP and Porphyromonas gingivalis fimbrial peptides

Porphyromonas gingivalis (P.g) is the primary bacterial agent in many forms of chronic periodontitis. Since polymorphonuclear leukocytes (PMNs) are first-line responders to P.g.- induced inflammation, and fibrinogen is important for in vivo PMN in this disease, we have studied the effect of N-formyl-methionyl-leucyl-phenylalanine (fMLP) (an inflammatory stimulus), P.g. fimbriae and fimbrial peptides (based on FimA, the main structural protein of P.g. fimbriae) on PMN-fibrinogen interactions. Freshly isolated human PMNs were allowed to react with FITC-Fibrinogen and various fimbrial peptides (denoted as FimA followed by amino acid number within whole FimA protein), and FITC-Fibrinogen binding was measured using flow cytometry. Freshly isolated neutrophils were also challenged with Fibrinogen and/or fimbrial peptides to measure IL-8 secretion using ELISA. Our studies show that fibrinogen binding to PMNs is enhanced (p < 0.01) in response to fMLP as well as fimbrial peptides (FimA 61-80) containing the motif LTTE (p < 0.01) in a dose dependent manner but not in response to peptides without that motif. We also observed that fMLP and FimA 61-80 have an additive effect on fibrinogen binding to PMNs (p < 0.05), and fMLP and FimA 171-185 significantly inhibit fMLP-induced fibrinogen binding (p < 0.01). To determine of the role of inflammatory cytokines, we examined IL-8 release from PMNs in response to combinations of P. gingivalis fimbriae, fMLP and fibrinogen. In all cases, IL-8 release increased in a dose-dependent manner (p < 0.05). fMLP-fibrinogen effect on IL-8 release from PMNs was synergistic while fimbriae-fibrinogen effect was additive. In summary, PMN priming by fimbrial peptides facilitates fibrinogen-PMN interaction and may increase inflammation.

Porphyromonas gingivalis gingipains mediate the shedding of syndecan-1 from the surface of gingival epithelial cells

Porphyromonas gingivalis gingipains are thought to be critical virulence factors in periodontitis. Increased serum levels of the soluble ectodomains of surface effectors have been reported to occur during bacterial infections. In the present study, we show that the cell surface proteoglycan syndecan-1 was highly expressed on human gingival epithelial cells. Treatments with P. gingivalis culture supernatants consistently mediated the shedding of syndecan-1 from the surface of epithelial cells. Concomitantly, the amount of soluble syndecan-1 detected in the culture medium increased significantly in a time-dependent manner. However, neither a heat-inactivated supernatant nor a supernatant from a gingipain-deficient mutant had a significant effect on syndecan-1 shedding. Such a shedding process may play an important role in the bacterial invasion of periodontal tissue and the modulation of host defences.

Lipoxin signaling in neutrophils and their role in periodontal disease

Endogenous molecules involved in counterregulation of inflammatory responses provide an opportunity to explore new therapeutic approaches based on manipulation of new pathways that may reduce the possibility of unwanted toxic side effects. Lipoxins (LX) are trihydroxytetraene-containing eicosanoids that are generated within the vascular lumen during cell-cell interactions or at mucosa through leukocyte-epithelial cell interactions. Transcellular biosynthetic pathways are the major lipoxin biosynthetic routes where LX are formed in vivo during inflammation and serve as "stop signals" that regulate key steps in leukocyte trafficking. In this review, recent findings in lipoxin generation, impact on the resolution of acute inflammation, and organ protection from neutrophil-mediated injury are presented. Periodontitis, specifically localized aggressive periodontitis, which is recognized as an example of neutrophil-mediated tissue injury, is discussed as a disease model where LX and other endogenous pro-resolution pathway mediators could have potential value.