Lipoxin A4 levels predict site-specific clinical improvements post scaling and root planing and correlate negatively with periodontal pathogens in severe periodontitis.

BACKGROUND: Serving as a stop signal of inflammation, the role of lipoxin A4 (LXA4) in periodontitis remains to be clarified. This study is aimed to examine the changes in LXA4 levels in gingival crevicular fluid (GCF) after scaling and root planing (SRP) and to determine the relationship between LXA4 levels and treatment outcomes and periodontal pathogens in severe periodontitis. METHODS: A total of 74 GCF samples were collected from 21 severe periodontitis participants at the deepest affected sites. These sites were re-sampled at 1, 3, and 6 months after SRP. Besides, GCF samples were also collected from 25 periodontally healthy participants. Clinical parameters including probing depth (PD) and clinical attachment level (CAL) in periodontitis group were recorded. LXA4 levels and periodontal pathogens in the GCF were analyzed by ELISA and PCR, respectively. Correlations between GCF LXA4 levels and treatment effect and periodontal pathogens were assessed. RESULTS: LXA4 levels in GCF significantly increased after SRP (p < 0.05), but remained lower than those observed in healthy individuals (p < 0.05). Sites with lower baseline LXA4 concentrations were more likely to experience greater improvements in PD at 6 months post-SRP (area under the curve [AUC] = 0.792), and the improvements were positively correlated with the increase of LXA4 at these sites post-treatment (p < 0.05). Furthermore, more elevated LXA4 levels were observed in sites that became negative for Prevotella intermedia or Tannerella forsythia after SRP. CONCLUSION: Baseline LXA4 in GCF has the potential to predict the site-specific response of severe periodontal lesions to SRP. The increase of LXA4 levels after treatment was positively correlated with clinical improvements and negatively correlated with the presence of Prevotella intermedia or Tannerella forsythia.

Effect of lipoxin A4 on the osteogenic differentiation of periodontal ligament stem cells under lipopolysaccharide-induced inflammatory conditions.

Lipoxin A4 (LXA4) has been identified as the braking signal of inflammation, but the specific role of LXA4 in regulating the regenerative potential of periodontal ligament stem cells (PDLSCs) remains unclear. The aim of this study was to investigate whether and, if so, how LXA4 improves the osteogenic differentiation of PDLSCs in a lipopolysaccharide (LPS)-induced inflammatory environment. We detected the effects of LXA4 on the osteogenic differentiation of PDLSCs in vitro and explored the bone regenerative potential of LXA4-treated inflammatory PDLSCs in vivo using a calvarial critical sized defect model in male rats. RNA sequencing, real-time PCR and western blot were performed to elucidate the relevant potential mechanisms. Results showed that LXA4 promoted the proliferation, migration and osteogenic differentiation of PDLSCs in vitro, and effectively improved the impaired osteogenic capacity of PDLSCs induced by LPS both in vitro and in vivo. Mechanistically, LXA4 significantly promoted the PI3K/AKT phosphorylation under inflammatory conditions. Additionally, LY294002 (a PI3K inhibitor) blocked the effect of LXA4, suggesting that the PI3K/AKT pathway is a key signaling pathway that mediates the effect of LXA4 on the osteogenesis of inflammatory PDLSCs. These findings indicate LXA4 may be a promising strategy for periodontal regeneration using inflammatory PDLSCs.

Organelle-Specific Mechanisms in Crosstalk between Apoptosis and Ferroptosis.

Apoptosis has been extensively studied, whereas ferroptosis is a newly discovered form of regulated cell death that involves iron-dependent accumulations of lipid hydroperoxides. While these two cell death mechanisms were initially believed to be mutually exclusive, recent studies have revealed cellular contexts requiring a balanced interaction between them. Numerous subcellular sites and signaling molecules within these sites are involved in both processes, either as modules or switches that allow cells to choose on how to proceed. The close relationships between apoptosis and ferroptosis, as well as the possibility of switching from one to the other, are described in this review. To understand the crosstalk between apoptosis and ferroptosis, various organelle-specific mechanisms must be analyzed and compared. The ability to switch apoptosis to ferroptosis by targeting cellular organelles has a great potential in cancer therapy.

Case report: Five-year periodontal management of a patient with two novel mutation sites in ELANE-induced cyclic neutropenia.

Cyclic neutropenia (CyN) is a rare, ELANE-related neutropenia. Oral manifestations are among the initial signs of CyN and an important reason that leads patients to seek professional help. This case report describes a 12-year-old girl with recurrent oral ulcers, severe chronic periodontitis, and pathological tooth migration as the initial and main clinical symptoms of CyN. Two novel mutations in ELANE, c.180T>G (p.I60M) and c.182C>G (p.A61G) associated with CyN were observed. Bioinformatics research indicated lower stability and impaired molecular linkages of the mutant neutrophil elastase (NE) encoded by ELANE. However, the enzyme affinity to the classic substrate Suc-Ala-Ala-Ala-pNA was not substantially changed, suggesting that the impaired integrity and stability of the mutant NE, rather than catalytic deficiency, might be the pathogenic mechanism of ELANE mutation-induced neutropenia. The patient was prescribed scaling and root planing (SRP) and monthly periodontal maintenance without systemic management. Although the routine periodontal treatment was occasionally interrupted by the 2019 coronavirus pandemic, her periodontal devastation remained well-remitted in the 5-year follow-up assessment. The results of this study confirmed the importance of plaque control and proper diagnosis in the periodontal management of such patients and provide better clinical references. In addition, the novel mutations identified in this study expand the spectrum of known ELANE mutations in CyN and further contribute to knowledge regarding its pathogenic mechanism.

Entamoeba gingivalis is associated with periodontal conditions in Chinese young patients: A cross-sectional study.

Background: This study investigated the prevalence and relative abundance of Entamoeba gingivalis (E. gingivalis) in Chinese young patients with different periodontal conditions, and its association with subgingival microbial composition, periodontal parameters, and cytokines in gingival crevicular fluid. Methods: Participants (age: 18-45 years) diagnosed with stage II-IV periodontitis, gingivitis, or periodontal health underwent periodontal examination and sampling. Subgingival plaque was analyzed by 16S+18S sequencing for E. gingivalis detection and microbial analysis. The distribution of E. gingivalis in subgingival plaque was illustrated by fluorescence in situ hybridization. Interleukin-1ß, interleukin-8, and tumor necrosis factor-α in gingival crevicular fluid were measured by multiplexed flow cytometric assay. Results: This cross-sectional study included 120 sites from 60 participants. The prevalence and relative abundance of E. gingivalis were significantly increased in periodontitis (p<0.05). The sites were classified into three subgroups according to the relative abundance of E. gingivalis: negative group (Eg0, n=56); low-abundance group (Eg1, n=32); and high-abundance group (Eg2, n=32). The subgingival microflora in the subgroups showed stepwise changes at both the phylum and genus levels. The microflora compositions were significantly altered from Eg0 to Eg2 (p<0.001). Co-occurrence network analysis showed that Porphyromonas, Treponema, Tannerella, Filifactor, TG5, and Desulfobulbus were highly correlated with E. gingivalis (r>0.6, p<0.001). Correlation analysis showed that E. gingivalis was closely associated with important periodontal parameters and cytokines (p<0.01). Conclusion: E. gingivalis was enriched in periodontitis and closely associated with subgingival microbial dysbiosis, periodontal parameters and cytokines in gingival crevicular fluid. Thus, it may be an important pathogen in periodontal disease.

Hyaline fibromatosis syndrome: a case presenting with gingival enlargement as the only clinical manifestation and a report of two new mutations in the ANTXR2 gene.

BACKGROUND: Hyaline fibromatosis syndrome (HFS) is a rare autosomal recessive disorder caused by mutations in the gene for anthrax toxin receptor-2 (ANTXR2). The clinical features of HFS include skin thickening with nodules, papules and plaques, gingival enlargement, joint stiffness and contractures, and systemic manifestations. Notably, in all patients with HFS reported in the literature, gingival enlargement has never occurred alone. CASE PRESENTATION: A case of a child with gingival enlargement as the only clinical manifestation, who was later diagnosed with HFS, is described. In this case, the absence of skin and joint lesions and other characteristic clinical presentations gave rise to a diagnostic problem. This uncommon condition was clinically indistinguishable from other diseases or conditions that presented with diffuse gingival enlargement. A definitive diagnosis of HFS was reached through genetic analysis. Trio whole exome sequencing revealed compound heterozygous mutations of ANTXR2 in this patient and two new mutations were reported. CONCLUSIONS: The findings of this case serve as an important reminder to clinicians. When dental practitioners encounter gingival manifestations of HFS without accompanied skin or joint involvement, there is a need to pay attention to the differential diagnosis and increase awareness of HFS.

Edentulism and select chronic diseases among adults aged ≥45 years in China, 2011-2018: A longitudinal study.

OBJECTIVES: Information on the association between edentulism and chronic medical conditions in developing countries is lacking. We investigated such information among adults aged ≥45 years in China. METHODS: A national longitudinal data set from the China Health and Retirement Longitudinal Study (CHARLS) 2011-2018 was analysed. A multilevel logistic regression model was applied to analyse the association between edentulism and select chronic diseases. RESULTS: There were 74 240 Chinese adults aged ≥45 years in this study. The prevalence of self-reported edentulism was 8.8% in 2011 and had increased to 16.4% by 2018. CONCLUSION: Edentulism was a factor associated with a higher risk of various self-reported chronic diseases among adults aged ≥45 years in China. Edentulism is one of the comorbidities among ageing people with chronic conditions. Preventive public health policy should consider controlling shared risk factors at an earlier age.

Clinical study of periodontal endoscope-assisted subgingival scaling in the treatment of residual pocket.

OBJECTIVES: To compare the treatment effects of periodontal endoscope-assisted and traditional subgingival scaling on residual pockets. METHODS: A total of 13 patients with periodontitis from Dept. of Periodontics, West China Hospital of Stomatology, Sichuan University were recruited. After 4-6 weeks of initial treatment, the residual pockets with a probing depth (PD) of ≥4 mm and attachment loss (AL) of ≥4 mm and bleeding on probing were examined with traditional (control group) and periodontal endoscope-assisted subgingival scaling (endoscopy group) in a randomly controlled split-mouth design. At baseline and 6 weeks and 3 months after treatment, plaque index (PLI), PD, AL, and bleeding index (BI) were measured. Differences in these clinical parameters within and between groups and patient-reported outcomes were compared. RESULTS: A total of the 694 sites of 251 teeth were included in this trial. Both groups showed significant improvement in each periodontal parameters 6 weeks and 3 months after treatment (P<0.001). For sites in a single-rooted tooth, sites with PD≥5 mm, and sites without vertical alveolar bone resorption and furcation involvement, the PD in endoscopy group was significantly lower than that in the control group at 6 weeks and 3 months after treatment (P<0.05). CONCLUSIONS: Periodontal endoscope-assisted subgingival scaling resulted in better effects than traditional subgingival scaling when the residual pockets were in a single-rooted tooth, with a PD of ≥5 mm but without vertical alveolar bone resorption and furcation involvement.

The combined use of salivary biomarkers and clinical parameters to predict the outcome of scaling and root planing: A cohort study.

AIM: To explore the application of the combined use of baseline salivary biomarkers and clinical parameters in predicting the outcome of scaling and root planing (SRP). MATERIALS AND METHODS: Forty patients with advanced periodontitis were included. Baseline saliva samples were analysed for interleukin-1ß (IL-1ß), matrix metalloproteinase-8 and the loads of Porphyromonas gingivalis, Prevotella intermedia, Aggregatibacter actinomycetemcomitans and Tannerella forsythia. After SRP, pocket closure and further attachment loss at 6 months post-treatment were chosen as outcome variables. Models to predict the outcomes were established by generalized estimating equations. RESULTS: The combined use of baseline clinical attachment level (CAL), site location and IL-1ß (area under the curve [AUC] = 0.764) better predicted pocket closure than probing depth (AUC = 0.672), CAL (AUC = 0.679), site location (AUC = 0.654) or IL-1ß (AUC = 0.579) alone. The combination of site location, tooth loss, percentage of deep pockets, detection of A. actinomycetemcomitans and T. forsythia load (AUC = 0.842) better predicted further clinical attachment loss than site location (AUC = 0.715), tooth loss (AUC = 0.530), percentage of deep pockets (AUC = 0.659) or T. forsythia load (AUC = 0.647) alone. CONCLUSION: The combination of baseline salivary biomarkers and clinical parameters better predicted SRP outcomes than each alone. The current study indicates the possible usefulness of salivary biomarkers in addition to tooth-related parameters in predicting SRP outcomes.

Casticin inhibits invasion and proliferation via downregulation of ß-catenin and reversion of EMT in oral squamous cell carcinoma.

BACKGROUND: Casticin expresses multiple anti-cancer activities, whereas the effect of casticin on oral squamous cell carcinoma (OSCC) is still unclear. ß-catenin signaling plays a crucial role in the epithelial-mesenchymal transition which is closely related to tumorigenesis. Herein, we aimed to study the functions of casticin on invasion and migration of OSCC, and clarify whether the effect of casticin on OSCC has a relationship with ß-catenin signaling. METHODS: Human OSCC cell lines UM1 and HSC-3 were treated with different concentrations of casticin. The cell viability was evaluated by MTT and soft agar colony formation. Transwell assay and wound-healing assay were performed to measure the ability of cell invasion and migration. The protein expression was assessed by Western blotting. RESULTS: Casticin displayed inhibitory activities of cell viability, invasion, and migration on OSCC cell lines. Meanwhile, casticin could reverse EMT process and inhibit the expression of ß-catenin in OSCC. Knock-down or overexpression of ß-catenin could alter the effect of casticin on OSCC. CONCLUSIONS: Casticin impaired invasion and migration of OSCC by inhibition of ß-catenin and reversal of EMT and could be a potential anti-cancer bioactive agent.

Cone-beam computed tomography performance in measuring periodontal bone loss.

The present study aimed to evaluate the performance of cone-beam computed tomography (CBCT) in assessing periodontal bone loss. If effective, CBCT could potentially be a more comfortable and accurate way to evaluate this disease. One hundred and eighty tooth sites from 13 patients were included. Clinical attachment level (CAL) was measured, then CBCT images were acquired prior to periodontal surgery. Three periodontists measured the distance between the cemento-enamel junction and alveolar bone crest at the mesio-buccal, mid-buccal, disto-buccal, mesio-lingual/palatal, mid-lingual/palatal, and disto-lingual/palatal sites. Comparisons of measurements were made among three methods. Inter-observer and intra-observer variances were also analyzed. Statistically significant differences were found between CBCT and CAL + 2.04 mm (P = 0.000), as well as intra-surgical evaluation (P = 0.001). All sites showed differences in CBCT versus intra-surgical measurement and versus CAL + 2.04 comparisons, except the buccal sites (P = 0.187 and 0.147, respectively). This study indicates that the results of CBCT do not agree with results of intra-surgical measurement. As a result, CBCT should be used with caution and only when necessary, to avoid radiation hazards.

[Advances in salivary protein glycosylation and its relationship with systemic and oral diseases].

Protein glycosylation is one of the most important protein post-translational modifications that can affect life activities by endowing the protein with various structural and functional features. Saliva is an easy-to-obtain, noninvasive body fluid that contains components originating from serum, gingival crevicular fluid, and oropharyngeal mucosae. In recent years, understanding of saliva has been constantly updated with the developments in related research. Studies have shown that salivary proteins can be used as diagnostic markers for certain diseases, and changes of protein glycosylation in saliva are generally considered to be related to many diseases. In this review, salivary protein glycosylation and its relationship with systemic and oral diseases were discussed.

Epigenetic Regulations in the Pathogenesis of Periodontitis.

BACKGROUND: Periodontitis is a multifactorial infectious disease that affects a large population worldwide. Oral microorganisms and susceptible host have been proposed to be the prerequisite for the development of periodontitis. Recently, the involvement of epigenetic modifications in the development of periodontitis has been suggested. OBJECTIVES: This review aims to detail recent discoveries involving the epigenetic alterations in periodontitis, and discuss the possible epigenetic mechanisms contributing to the expression of periodontitis- related genes. CONCLUSIONS: The expression of inflammatory cytokines during periodontitis is regulated at epigenetic level by mechanisms such as DNA methylation, histone modification and miRNAs. In addition, periodontal pathogens and their virulence factors could induce epigenetic alterations of periodontal tissues, and thus affect the progression and prognosis of periodontitis. The involvement of epigenetic modifications during periodontitis not only advances our knowledge on the pathogenesis of periodontitis, but may also lead to the identification of potential therapeutic targets of this oral disease.

Enhanced activity of macrophage M1/M2 phenotypes in periodontitis.

OBJECTIVE: Monocytes/macrophages play a key role in mobilizing host defense against microbial infection. The selectivity of gene expression can turn macrophages into M1- or M2-type and the plasticity and differentiation of both M1 and M2 macrophages may play important roles in the development of periodontal disease. Our research aimed to study the association between the ratio of M1/M2 macrophage and inflammatory cytokines IL-1ß, MMP-9, and investigate the expressions of M1-and M2-type macrophages in gingivitis and chronic periodontitis. METHODS: Forty specimens were collected from gingivitis individuals (n=20) and chronic periodontitis (n=20). Probing depth (PD), clinical attachment level (CAL), plaque index (PI) and bleeding on probing (BOP) were recorded. The expressions of M1- and M2-type macrophages are detected with immunohistochemical method and the relative expressions of M1-, M2-type macrophage, IL-1ß and MMP-9 were assayed using real-time polymerase chain reactions. RESULTS: The M1 and M2 peptide were mainly observed in the cytoplasm of gingival connective tissue. The ratio of M1/M2 was significant higher in chronic periodontitis group compared with that in gingivitis one. In addition, the relative expressions of IL-1ß and MMP-9 also increased in periodontitis group and was correlated with the ratios of M1/M2. Meanwhile, PD was positively correlated with ratios of M1/M2. CONCLUSIONS: Periodontal inflammation associates with an enhancement of ratio of M1/M2 phenotypes of macrophages. M1/M2 ratio could provide useful information on the periodontal tissue health status.

A commensal streptococcus hijacks a Pseudomonas aeruginosa exopolysaccharide to promote biofilm formation.

Pseudomonas aeruginosa causes devastating chronic pulmonary infections in cystic fibrosis (CF) patients. Although the CF airway is inhabited by diverse species of microorganisms interlaced within a biofilm, many studies focus on the sole contribution of P. aeruginosa pathogenesis in CF morbidity. More recently, oral commensal streptococci have been identified as cohabitants of the CF lung, but few studies have explored the role these bacteria play within the CF biofilm. We examined the interaction between P. aeruginosa and oral commensal streptococci within a dual species biofilm. Here we report that the CF P. aeruginosa isolate, FRD1, enhances biofilm formation and colonization of Drosophila melanogaster by the oral commensal Streptococcus parasanguinis. Moreover, production of the P. aeruginosa exopolysaccharide, alginate, is required for the promotion of S. parasanguinis biofilm formation and colonization. However, P. aeruginosa is not promoted in the dual species biofilm. Furthermore, we show that the streptococcal adhesin, BapA1, mediates alginate-dependent enhancement of the S. parasanguinis biofilm in vitro, and BapA1 along with another adhesin, Fap1, are required for the in vivo colonization of S. parasanguinis in the presence of FRD1. Taken together, our study highlights a new association between streptococcal adhesins and P. aeruginosa alginate, and reveals a mechanism by which S. parasanguinis potentially colonizes the CF lung and interferes with the pathogenesis of P. aeruginosa.

A review of the literature: antibiotic usage and its relevance to the infection in periodontal flaps.

OBJECTIVE: This study aimed to investigate the systemic antibiotic usage in the perioperative period of periodontal flaps and its relevance to the infection after surgeries through reviewing the papers of the last decade. MATERIALS AND METHODS: A search was conducted for the studies of randomized clinical trials between 2005 and 2014 that reported periodontal flaps in chronic periodontitis patients. Data were extracted and the rate of the systemic antibiotic use, the infection rate after surgeries and the number needed to treat (NNT) to prevent one infected case were calculated. The impact of antibiotic use and materials used in surgeries on the infection was evaluated. RESULTS: Eighty-three trials were included. Antibiotics were used in 73.7% of the patients and 75.4% of the flaps. Infection occurred in only five flaps where enamel matrix proteins (EMD) or EMD + bone grafts were used in intrabony defects. Only 0.170% of the surgeries got infected in total. When all kinds of surgeries were included for analysis, the infection rate was 0.073% for the surgeries using antibiotics, which was lower than the infection rate 0.693% for the surgeries not using antibiotics (p < .05). The infection rate was very low in general. NNT was 203 when all the surgeries were included for analysis. Therefore, the difference of the infection rates between using antibiotics and not might lack clinical significance. CONCLUSIONS: Considering the very low incidence of the infection and the disadvantages of the systemic antibiotic use, we suggest not using systemic antibiotics in the perioperative period of periodontal flaps to prevent infection.

Fine-tuned production of hydrogen peroxide promotes biofilm formation of Streptococcus parasanguinis by a pathogenic cohabitant Aggregatibacter actinomycetemcomitans.

Balanced bacterial biofilm communities help to maintain host health. Disturbance of such balance can lead to bacterial dysbiosis and pathogenesis. However, complex and dynamic bacterial interactions within the biofilm communities are poorly understood. In this study, we used a dual-species biofilm consisting of the periodontal pathogen Aggregatibacter actinomycetemcomitans, and a commensal Streptococcus parasanguinis to investigate bacterial interactions since the two organisms have been found to coexist during the development of localized aggressive periodontal disease. We report that A. actinomycetemcomitans promoted biofilm formation of S. parasanguinis in vitro and in vivo. Protein profiling of S. parasanguinis co-cultured with A. actinomycetemcomitans revealed a significant decrease in the protein level of pyruvate oxidase(PoxL), an enzyme required for the generation of hydrogen peroxide (H2 O2 ). Consistently, the H2 O2 concentration was concurrently decreased. However, the complete removal of H2 O2 impaired the biofilm formation. H2 O2 at a low concentration range regulated by A. actinomycetemcomitans enhanced the biofilm formation. These results demonstrate that A. actinomycetemcomitans promotes the S. parasanguinis biofilm formation through modulating the production of H2 O2 by fine-tuning the expression of poxL, indicating that H2 O2 functions as a signaling molecule. Taken together, this report revealed a previously unknown bacteria-bacteria interaction mechanism.

The expression of human ß-defensins (hBD-1, hBD-2, hBD-3, hBD-4) in gingival epithelia.

OBJECTIVE: The aim of this study was to analyze and compare the expression patterns of human ß-defensin-4 (hBD-4) with those of hBD-1, hBD-2, and hBD-3 in healthy and chronically inflamed gingival tissues. MATERIALS AND METHODS: A total of 96 gingival samples were collected, comprising 46 biopsies from chronic periodontitis (CP) patients and 50 from individuals with healthy tissue. Of these, 21CP and 21 healthy samples were used to examine the protein expression of the hBDs by immunohistochemistry. The remaining 25CP and 29 healthy tissue samples were subjected to real-time reverse transcription polymerase chain reaction to quantify the mRNA expression of the hBDs. RESULTS: All four types of ß-defensin peptides were confined to the gingival epithelia. The percentage of samples positive for hBD-4 mRNA was significantly lower than the percentages for the other three ß-defensins, both in healthy (p=0.003) and in inflamed (p=0.030) gingiva. However, in the case of the relative mRNA expression levels, that of hBD-4 was significantly higher than the levels for hBD-2 (healthy group: p<0.01; CP group: p<0.01) and hBD-3 (healthy group: p=0.004; CP group: p<0.01). CONCLUSIONS: Our study demonstrates differential expression of hBD-1, hBD-2, hBD-3, and hBD-4 in healthy and CP gingiva.

[New finding of the expression of human beta defensin-4 in healthy gingiva].

OBJECTIVE: To investigate the expression and the distribution of human beta defensin (hBD)-4 in healthy gingiva. METHODS: Healthy gingival specimens were collected. The expression of hBD-4 peptides in 18 gingival specimens were detected by immunohistochemistry. The hBD-4 mRNA were determined in freshly isolated gingival tissue by real time reverse transcription-polymerase chain reaction (real time RT-PCR) in 30 gingival specimens. RESULTS: In 18 gingival specimens, hBD-4 peptides were expressed in 13 gingival specimens. In 30 gingival specimens, hBD-4 were detected in 4 gingival specimens by real time RT-PCR. CONCLUSION: The distribution and the expression levels of hBD-4 are different in healthy gingiva. This result may suggest that the hBD-4 play a role in maintaining the periodontal health.

[Susceptibility of porphyromonas gingivalis to metronidazole at different planktonic cell densities and in biofilm].

OBJECTIVE: To compare the susceptibility of Porphyromonas gingivalis to metronidazole at different planktonic cell densities and in biofilm, and to evaluate the role of cell density in antibiotic drug resistance in Porphyromonas gingivalis biofilm. METHODS: The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of metronidazole against Porphyromonas gingivalis were detected by a broth dilution method under a final inocula of 10(6) CFU x mL(-1) and 10(9) CFU x mL(-1) (cell number equal to biofilm). After the initial biofilm formed in the microtiter plate wells, the MIC and MBC of metronidazole to the intact and succedent resuspended biofilm were determined. RESULTS: The MIC and MBC of metronidazole against 10(6) CFU x mL(-1) planktonic Porphyromonas gingivalis were 0.063, 0.125 mg x L(-1) respectively. However, those against 10(9) CFU x mL(-1) planktonic Porphyromonas gingivalis were 25, 50 mg x L(-1). Against intact Porphyromonas gingivalis biofilm, the MIC was 25 mg x L(-1) and MBC was higher than 125 mg x L(-1), those against resuspended biofilm was 25, 125 mg x L(-1) respectively. CONCLUSION: The resistance of Porphyromonas gingivalis to metronidazole increases along with the augment of the bacterial density. Cell density plays an important role in the resistance of biofilm. However, extracellular matrix and the integrity of biofilm may be the other influence factors for the biofilm resistance.