Milestones in periodontal research and the remaining critical issues

Pathologic interactions in pulpal and periodontal tissues

Both endodontic and periodontal disease are caused by a mixed anaerobic infection. The pathways for the spread of bacteria between pulpal and periodontal tissues have been discussed with controversy. This article is an attempt to provide a rational approach to the perio-endo/endo-perio question based on a review of the relevant literature. In the light of evidence, clinical concepts for the diagnosis and treatment of lesions involving both periodontal and pulpal tissues are discussed.

Postnatal lipopolysaccharide-induced illness predisposes to periodontal disease in adulthood

The long-term consequences of neonatal lipopolysaccharide (LPS) exposure on adult behavioral and neuroendocrine stress responsiveness as well as on the clinical course of periodontal disease were assessed in male Lewis rats. At 3 and 5 days of age, pups were administered either saline (SHAM) or LPS or were left undisturbed. After postnatal treatment, mothers licked LPS-treated pups significantly more. In adult LPS rats of 3-5 months of age, home cage activity indicated changes of the diurnal rhythmicity. Furthermore, SHAM- and LPS-treated animals displayed treatment-specific signs of increased anxiety in social interaction, elevated plus maze, holeboard, and open field tests. At 7 months of age, a dramatic increase of periodontal fiber loss in LPS rats was associated with increased plasma interleukin-6 levels. In contrast, SHAM treatment caused high plasma interferon-gamma cytokine levels and protective effects in periodontal disease. Parameters of the response to novelty were significantly correlated with later disease susceptibility. Thus, LPS-induced early postnatal illness modulates the adult behavioral responsiveness to stress and predisposes to periodontal disease.

Tumor necrosis factor-alpha gene polymorphisms in relation to periodontitis

BACKGROUND

Genetic polymorphisms for cytokines have been proposed as potential genetic markers for destructive periodontal disease. The present aim was to investigate 4 bi-allelic polymorphisms in the TNF-alpha gene in relation to susceptibility for and severity of periodontitis. The polymorphisms were all transitions from G to A, 3 in the promoter positions: -376, -308, -238; and one in the first intron at position +489.

METHODS

90 periodontitis patients and 264 reference control subjects were genotyped and frequencies of genotypes and alleles were analyzed. Also genotype frequencies among severe and moderate periodontitis patients were explored, and the % of teeth with 50% bone loss and the % of teeth without any bone loss for patients with the A allele (A+ genotype) and patients without (A- genotype) were compared.

RESULTS

The distributions of genotypes and frequencies of A allele carriage rates for the 4 TNF-alpha polymorphisms were not different between patients and reference controls; Hardy-Weinberg equilibrium criteria were fulfilled. Also the distribution of A+ and A- genotypes, alone or in combinations, were not different for severe periodontitis compared to moderate periodontitis patients. None of the A+ genotypes showed a significant different bone loss pattern compared to A- genotype patients. Smoking status of the patients did not influence the results.

CONCLUSIONS

Genetic polymorphisms in the TNF-alpha gene at positions -376, -308, -238 and +489 could not be identified as susceptibility or severity factors in periodontitis, irrespective of the smoking status of the patients.

IL-1 genotype and adult periodontitis among young New Zealanders

Several recent studies have investigated the association between interleukin-1 genotype and periodontitis in clinical samples, where generalizability is an issue. The aim of this study was to investigate the association between adult periodontitis and IL-1 genotype in a population-based sample of 26-year-olds. Based on probing depth (PD) measurements, participants were divided into three disease groups: "Severe" (1+ teeth with 5+mm PD; N = 25), "Moderate" (2+ teeth with 4+mm PD; N = 36), and "Controls" (the remainder; N = 800). The "periodontitis-associated genotype" (PAG; Kornman et al., 1997) was present in 20.0% of the "Severe" group and in 34.8% of "Controls", whereas the IL-1A(+4845) [1,1]/IL-1B(+3953) [2,2] genotype was present in 12.0% and 0.9%, respectively. After controlling for sex, smoking status, and plaque levels, we found that those with IL-1B(+3953) [1,1]/IL-1A(+4845) [2,2] had 12.3 times the odds of being in the "Severe" group. Analysis of these data suggests that the IL-1A(+4845) [1,1]/IL-1B(+3953) [2,2] genotype is associated with periodontal disease in this young population. Future periodontal data collections as this cohort ages are required to confirm the predictive value of that genotype.

Periodontal diseases: to protect or not to protect is the question?

For decades, investigations have identified local and systemic humoral immune responses to microorganisms comprising the supra- and subgingival biofilms in the oral cavity. Inflammation and tissue destruction in the periodontium are accompanied by alterations in the quantity, quality, and specificity of antibody. The conundrum in this scenario is the existence of a substantial plasma cell infiltrate at sites of periodontal lesions and a seemingly robust antibody response in the oral cavity and the serum, apparently coincident with progressing disease. Consequently, much effort has been expended to elucidate the critical characteristics of protective humoral responses and to develop strategies for enhancing these unique features. We and others have conducted studies attempting to distinguish disease susceptibility associated with: i) variations in response levels significantly increased to some species with disease, minimal response to others; ii) functional comparisons of antibody subclass differences, genetic regulation, and maturation of responses; iii) microbial and antigenic specificity of the antibody focus on specific pathogens and identification of selected antigens as targets for immunoprotection; and, iv) kinetics of responses during disease and therapeutic interventions linking immune changes with infection and as a measure of treatment success. This report summarizes varied research designs and results, to provide a profile of antibody in health, gingivitis, and periodontitis. These profiles may be used to provide a framework focusing on the humoral response to commensal microorganisms and likely pathogens, as they emerge in the biofilm--etiologic for or in response to disease processes. Models for antibody as a diagnostic adjunct and for predicting protective antibody responses are suggested. These concepts are likely relevant for considering vaccine approaches to periodontitis.

A role for decorin in the structural organization of periodontal ligament

Decorin is a small leucine-rich proteoglycan that interacts with several matrix molecules, including various types of collagen and growth factors, and suppresses the growth of neoplastic cells by an epidermal growth factor (EGF) receptor-mediated pathway. Decorin is abundantly expressed in the periodontal connective tissues during development and tissue maintenance. In periodontal disease, which is one of the most common diseases in the human kind, the level of decorin is decreased in the periodontal connective tissue. Abnormal expression of decorin may also associate with certain inherited disorders that involve increased susceptibility to severe periodontal disease in the early childhood. Therefore, we investigated the periodontal tissues of mice with targeted disruption of the decorin gene. Gross and microscopic analyses showed that decorin-deficient mice appeared to have normal tooth development and eruption, and there were no signs of periodontal disease. However, electron microscopic analysis revealed abnormal morphology and organization of the collagen fibrils in the periodontal ligament. The number of periodontal ligament fibroblasts in the decorin-deficient mice was also increased about two-fold as compared with the wild-type mice. In cell culture, ectopic overexpression of decorin in NIH 3T3 fibroblasts or decorin added exogenously to periodontal fibroblasts suppressed cell growth. However, blocking the EGF receptor tyrosine kinase activity did not prevent the decorin-elicited growth suppression in periodontal fibroblasts. Additionally, decorin did not induce a marked increase in the relative expression of p21 mRNA in periodontal fibroblasts. Therefore, decorin appeared to regulate growth of normal periodontal fibroblasts by a mechanism distinct from that reported for neoplastic cells. The findings demonstrate that decorin plays a role in the organization of collagen fibrils and regulates cell proliferation in the periodontal ligament.

Periodontal disease and atherosclerotic cardiovascular disease: confounding effects or epiphenomenon?

Recent evidence suggests that periodontal disease may predispose to atherosclerotic cardiovascular disease. Data support mechanisms of host-derived local and systemic proinflammatory responses similar to atherosclerosis, consisting of monocytic-derived cytokines and other inflammatory mediators, which are induced by periodontal pathogens and its endotoxin, lipopolysaccharide. These mechanisms may contribute to the start of vascular endothelial dysfunction and further sequelae leading to atherosclerosis. Experimental evidence and biologic plausibility appear to support this proposal. However, clinical evidence from a MEDLINE search from January 1966-December 1999 proposed a weak or no correlation primarily due to confounding factors. The aim of care is to reduce vulnerable pathogens from the infected periodontium by standard treatment; however, new approaches appear promising. Increased awareness of a potential link among infective agents, immunoinflammatory processes, and atherosclerosis may clarify clinical implications.