[Effects of periodontitis on bone and tryptophan metabolism of gut microbiota in estrogen-deficient mice]

Objective: To study the effects of periodontitis on bone and tryptophan metabolism of gut microbiota in the context of estrogen deficiency. Methods: Thirty-two female C57BL6/J mice were randomly divided into four groups based on table of random numbers (n=8 in each group): Sham group, in which mice were given sham surgery; Sham_Lig group, in which mice were given sham surgery and were induced to periodontitis by ligating the bilateral maxillary second molars with 5-0 silk threads at the fourth week; Ovx group, in which mice were given bilateral ovariectomy; Ovx_Lig group, in which mice were given bilateral ovariectomy and were induced to periodontitis at the fourth week. After 8 weeks of ligation, the mice of 4 groups were euthanized for collecting the samples of femur, tibia, mandible and skull. Those samples were scanned by micro-CT to measure the bone mineral density (BMD), bone volume versus total volume ratio (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th) and trabecular spacing (Tb.Sp). The cecum contents of 4 groups of mice were collected for gut microbiota 16S rRNA gene sequencing. The tryptophan and its metabolites in intestinal tracts were detected by liquid chromatography-mass spectrometry. Pearson correlation analysis was performed to analyze the correlation between the abundance of gut microbiota and the content of tryptophan and its metabolites. Results: Femur BMD [(82.23±3.97) mg/cm3], BV/TV [(9.25±1.37)%] and Tb.Th [(70.95±5.70) μm] in Ovx_Lig group were significantly lower than Ovx group [(96.30±3.76) mg/cm3 (P=0.004); (14.45±1.55)% (P=0.022) and (87.58±8.02) μm (P<0.001), respectively]. The β-diversity analysis of gut microbiota based on Bray-Curtis distance showed that samples of Ovx_Lig group and Ovx group were obviously grouped. Linear discriminant analysis effect size (LEfSe) showed that Alistipes was the representative genus in Ovx_Lig group. The relative abundance of Alistipes in Ovx_Lig group [(0.42±0.14)%] were significantly higher than that in Ovx group [(0.17±0.05)%] (t=4.45, P<0.001). Tryptophan metabolism analysis showed that the content of kynurenic acid [(531.12±158.60) ng/g] in Ovx_Lig group were significantly higher than that in Ovx group [(400.42±57.96) ng/g] (t=2.19, P=0.046). And the content of indole-3-carbaldehyde [(383.37±144.06) ng/g] in Ovx_Lig group were significantly lower than Ovx group [(701.72±141.93) ng/g] (t=4.45, P<0.001). Correlation analysis showed that relative abundance of Alistipes was positively correlated with kynurenic acid (r=0.32, P=0.088), while negatively correlated with indole-3-carbaldehyde (r=-0.32, P=0.088). Conclusions: Periodontitis can induce bone destruction of femur in estrogen-deficient mice, the mechanism of which may be related to Alistipes in gut and the tryptophan metabolites kynurenic acid and indole-3-carbaldehyde.

[Situational analysis of periodontal disease burden for adults in China from 1990 to 2019 and its incidence trend prediction]

Objective: To analyze the burden and changing trends of periodontal disease in adults of the mainland of China from 1990 to 2019, and to predict the incidence trends of periodontal disease in the next 25 years, with a goal to provide a basis for reducing the burden of periodontal disease and formulating relevant prevention and treatment measures. Methods: Data on the incidence, prevalence, and disability adjusted life years (DALY) rate of periodontal disease among adults in the mainland of China from 1990 to 2019 were extracted from the global burden of disease study 2019 (GBD 2019) database. The estimated annual percent change (EAPC) was used to estimate the temporal trend of periodontal disease, and the age-period-cohort model (APC) was used to predict the age-standardized incidence of periodontal disease in Chinese adults from 2020 to 2044. Results: From 1990 to 2019, the incidence, prevalence, and DALY rate of adult periodontal disease in the mainland of China showed an increasing trend, with EAPCs of 0.3 (95%CI: 0.1-0.6), 0.5 (95%CI: 0.1-0.8), and 0.5 (95%CI: 0.1-0.8), respectively. The incidence and prevalence of periodontitis among the population aged 35-39 years old and 40-44 years old increased the most significantly, with EAPCs of 0.8 and 0.7, respectively, whereas the change in periodontal disease prevalence tended to be stable and the increase trend in prevalence was lower in the elderly group (EAPC=0.4). The incidence (EAPC=2.1), prevalence (EAPC=2.6) and DALY rate (EAPC=2.6) of periodontal disease in females increased more than those in males (EAPC=1.9, 2.4, and 2.4, respectively), of which the prevalence had exceeded that of males in 2019. The APC model predicted that the prevalence of periodontal disease in the period of 2020-2044 in China would still be on an upward trend, and the increase rate would be higher in females than in males. Conclusions: The burden of periodontal disease among adults in China had been increasing over the past 30 years, especially among young and middle-aged adults as well as females, and the incidence of periodontal disease will continue to increase over the next 25 years.

[Standardized nomenclature of oral microorganisms in Chinese: the 2023 update]

Oral microbial community, as an important part of human microbial community, is closely related to oral and general health. Oral microbiological research has become the forefront of international microbiological research. Standardized and unified nomenclature for oral microorganisms in Chinese is of great significance to support the development of oral medicine research. Standardized translation of microbial names is the basis for writing canonical and authoritative professional textbooks and reference books, which helps students to accurately acquire the characteristics and classifications of oral microbes. Unified translation of oral microorganisms is also conducive to academic communication and cooperation, and plays an important role in oral health education and science popularization, which enables oral microbiology knowledge to be accurately disseminated to the public. Therefore, in order to standardize the words in scientific research, funding application, publications, academic exchanges and science popularization within the field of oral medicine, we have fully discussed and revised the Chinese names of oral microorganisms in 2017 edition and ones of newly discovered oral microbes, finally reaching a consensus to form the 2023 edition of Chinese names of oral microorganisms.

[Effects of the kynurenine pathway on the osteogenic differentiation of periodontal ligament stem cells]

Objective: To explore the effect of kynurenine pathway on the osteogenic differentiation of periodontal ligament stem cells (PDLSC). Methods: Unstimulated saliva samples were collected from 19 patients with periodontitis (periodontitis group) and 19 periodontally healthy individuals (health group) in Nanjing Stomatological Hospital, Affiliated Hospital of Medical School, Nanjing University from June to October of 2022. Contents of kynurenine and the metabolites in saliva samples were analyzed by ultra-performance liquid chromatography-tandem mass spectrometry. The expressions of indoleamine 2, 3-dioxygenase (IDO) and aryl hydrocarbon receptor (AhR) were further detected by immunohistochemistry in gingival tissues. The PDLSC used in this study were isolated from extracted teeth for orthodontic treatment in Nanjing Stomatological Hospital, Affiliated Hospital of Medical School, Nanjing University from July to November of 2022. Experiments were then conducted using the cells by incubating with (kynurenine group) or without kynurenine (control group) in vitro. Seven days later, alkaline phosphatase (ALP) staining and assays of ALP activity were performed. Real-time fluorescence quantitative PCR (RT-qPCR) was utilized to detect the expressions of osteogenic related genes ALP, osteocalcin (OCN), runt-related transcription factor 2 (RUNX2), collagen type-Ⅰ (COL-Ⅰ) as well as the kynurenine pathway-associated genes AhR, cytochrome P450 family (CYP) 1A1, CYP1B1. Western blotting was used to detect the expression levels of RUNX2, osteopontin (OPN) and AhR proteins on day 10 and alizarin red staining was performed to observe the formation of mineral nodules on day 21 in control group and kynurenine group. Results: Salivary concentrations of kynurenine [8.26 (0, 19.60) nmol/L] and kynurenic acid [11.4 (3.34, 13.52) nmol/L] were significantly higher in the periodontitis group than in the health group [0.75(0, 4.25) nmol/L, 1.92(1.34, 3.88) nmol/L] (Z=-2.84, P=0.004; Z=-3.61, P<0.001). The expression levels of IDO (18.33±2.22) and AhR (44.14±13.63) in gingival tissues of periodontitis patients were significantly higher than that of the health group (12.21±2.87, 15.39±5.14) (t=3.38, P=0.015; t=3.42, P=0.027). In vitro, the ALP activity of PDLSC in the kynurenine group (291.90±2.35) decreased significantly compared with the control group (329.30±19.29) (t=3.34, P=0.029). The mRNA expression levels of ALP, OCN and RUNX2 in the kynurenine group (0.43±0.12, 0.78±0.09, 0.66±0.10) were decreased compared with the control group (1.02±0.22, 1.00±0.11, 1.00±0.01) (t=4.71, P=0.003; t=3.23, P=0.018; t=6.73, P<0.001), while the levels of AhR and CYP1A1 were increased in the kynurenine group (1.43±0.07, 1.65±0.10) compared with those in the control group (1.01±0.12, 1.01±0.14) (t=5.23, P=0.006; t=6.59, P<0.001). No significant difference was observed in COL-Ⅰ and CYP1B1 mRNA levels between groups. The protein levels of OPN, RUNX2 (0.82±0.05, 0.87±0.03) were reduced and that of AhR (1.24±0.14) was increased in the kynurenine group compared with those in the control group (1.00±0.00, 1.00±0.00, 1.00±0.00) (t=6.79, P=0.003; t=7.95, P=0.001; t=3.04, P=0.039). Conclusions: Over-activated kynurenine pathway in periodontitis patients can promote upregulation of AhR and suppress the osteogenic differentiation of PDLSC.

[Mechanism of obesity affecting periodontal tissue regeneration and therapeutic strategies]

Obesity is an important health problem in our society today, which can lead to the chronic low-grade inflammation state, to be an inducement for many chronic diseases such as hypertension, type 2 diabetes and non-alcoholic fatty liver disease. As a common oral chronic infectious disease, periodontitis is mainly characterized by gingival inflammation, periodontal pocket formation, alveolar bone resorption and tooth mobility. The ultimate goal of periodontitis treatment is to achieve periodontal tissue regeneration in the defect area. As a major risk factor for periodontitis, obesity can alter the periodontal inflammatory microenvironment in multiple ways, affecting the effects of periodontal tissue regeneration ultimately. Therefore, this paper will review the relationship between obesity and periodontal tissue regeneration, mechanism of obesity affecting periodontal tissue regeneration and the therapeutic strategies of periodontal tissue regeneration, providing new ideas for periodontal tissue regeneration treatment in obesity.

Prevalence and Risk Factors of Frailty in Stroke Patients: A Meta-Analysis and Systematic Review

OBJECTIVES

Summarize the existing evidence regarding the prevalence and risk factors of frailty in stroke patients.

DESIGN

A meta-analysis and systematic review.

PARTICIPANTS

Stroke patients in hospitals or communities.

METHODS

We undertook a systematic review and meta-analysis using articles available in 8 databases, including PubMed, The Cochrane Library, Web of Science, Embase, Chinese Biomedical Database (CBM), China National Knowledge Infrastructure Database (CNKI), Wanfang Database, and Weipu Database (VIP) from January 1990 to April 2022. Studies were quality rated using the Newcastle-Ottawa Scale and Agency for Healthcare Research and Quality tool.

RESULTS

A total of 24 studies involving 30,423 participants were identified. The prevalence of frailty and pre-frailty in stroke patients was 27% (95%CI: 0.23-0.31) and 47.9% (95%CI: 0.43-0.53). Female gender (OR = 1.76, 95%CI: 1.63-1.91), advanced age (MD = 6.73, 95%CI: 3.55-9.91), diabetes (OR = 1.34, 95%CI: 1.06-1.69), hyperlipidemia (OR = 1.46, 95%CI: 1.04-2.04), atrial fibrillation (OR = 1.36, 95%CI: 1.01-1.82), National Institutes of Stroke Scale (NIHSS) admission scores (MD = 2.27, 95%CI: 1.72-2.81) were risk factors of frailty in stroke patients.

CONCLUSIONS

Frailty was more prevalent in stroke patients. Female gender, advanced age, diabetes, hyperlipidemia, atrial fibrillation, and National Institutes of Stroke Scale (NIHSS) admission scores were identified as risk factors for frailty in stroke patients. In the future, medical staff should pay attention to the early screening of frailty in high-risk groups and provide information on its prevention.

[Effects of salivary microbiota on tryptophan-aryl hydrocarbon receptor signaling axis in mice with periodontitis]

Objective: To study the effects of salivary microbiota in patients with periodontitis on the tryptophan-aryl hydrocarbon receptor (AhR) signaling axis in mice with periodontitis and to provide theoretical basis as well as new ideas for the influences of periodontitis on systemic metabolism. Methods: Salivary microbiota of 12 healthy individuals and 14 patients with periodontitis were collected in Nanjing Stomatological Hospital, Medical School of Nanjing University from June to December of 2020. According to the random number table method, twenty-four mice were randomly divided into three groups: Sham group (control group), P group (periodontitis patients' salivary microbiota group) and H group (periodontal healthy individuals' salivary microbiota group). The maxillary second molars of all mice were treated with silk thread ligation to induce periodontitis. Phosphate buffer as well as salivary microbiota of periodontal healthy individuals and periodontitis patients were gavaged into periodontitis mice for 2 weeks. The expression of inflammatory factors in mice serum were detected by enzyme linked immunosorbent assay, and the expression of tryptophan and indole metabolites in intestinal tract and serum were detected by liquid chromatography-mass spectrometry. The expression of AhR in intestinal tract of mice was detected by immunohistochemistry and quantitative real time-PCR while gut microbiota constitution was detected by 16S rRNA gene sequencing. The remaining saliva samples of periodontitis patients and periodontal healthy individuals were applied to detect the expression of tryptophan and indole metabolites themselves. Results: The salivary microbiota of periodontitis patients could induce the expression of interleukin-1β [P group: (162.38±39.46) pg/ml, H group: (82.83±20.01) pg/ml; t=4.40, P=0.001) and tumor necrosis factor-α [P group: (361.16±123.90) pg/ml, H group: (191.66±106.87) pg/ml; t=2.54, P=0.030) in serum of periodontitis mice, and reduce the expression of AhR in colon (P group: 1.18±0.05, H group:1.83±0.47; t=3.09, P=0.015) and ileum (P group: 0.80±0.13, H group: 1.18±0.11; t=4.93, P=0.001). After gavage of salivary microbiota of periodontitis patients to the mice, tryptophan (P group: (18.1±3.8)×10⁷, H group: (26.6±6.6)×10⁷; t=2.49, P=0.037] and indole lactic acid [P group: (1.9±0.7)×10⁷, H group: (3.7±0.6)×10⁷; t=4.49, P=0.002) in serum of periodontitis mice were significantly decreased, but was relatively disorder in intestinal tract. However, the expressions of tryptophan and indole metabolites in saliva of periodontitis patients were higher than those of periodontal healthy individuals. There were significant differences in indole propionic acid [P group: (1 239.39±818.72) nmol/L, H group: (56.96±38.33) nmol/L; t=2.83, P=0.022]. What we find noteworthy was that the expressions of indolelactic acid metabolism in saliva, serum and intestinal were consistent, and salivary microbiota of periodontitis patients could reduce the relative abundance of indolelactic acid-producing bacteria in the gut, suggesting that the salivary microbiota of periodontitis patients might affect the expression of AhR through gut microbiota disorder and indolelactic acid downregulation. Conclusions: Salivary microbiota in patients with periodontitis may affect the systemic inflammatory state through down-regulating the expression of tryptophan-AhR signal axis.

[Research progress in the relationship between prediabetes mellitus and periodontitis]

Prediabetes mellitus (Pre-DM) is an intermediate state of hyperglycemia between normal blood glucose homeostasis and type 2 diabetes mellitus (T2DM). More than half of adults in China suffer from Pre-DM. Periodontitis is a chronic inflammatory disease mainly caused by microorganisms in dental plaque. It shares common risk factors and interacts with non-communicable diseases such as diabetes mellitus. Pre-DM may increase the risk of periodontitis, and the latter may also influence the development and progress of diabetes. Oxidative stress, systemic inflammation and intestinal flora are the main mechanisms by which Pre-DM and periodontitis interconnect with each other. This article mainly reviews the relationship between Pre-DM and periodontitis and potential related mechanisms, providing a new basis for the prevention and treatment of both.

[High-fat diet promotes the impact of periodontitis on gut microbiota and glucose metabolism]

Objective: To study whether high-fat diet could aggravate the effect of periodontitis on gut microbiota and glucose metabolism. Methods: Twenty-four male SD rats were randomly and equally divided into four groups based on table of random numbers (n=6 in each group): control group, in which rats were given normal chow diet; periodontitis group, in which periodontitis was induced by ligating bilateral maxillary second molars with 5-0 silk thread; high-fat diet group, in which rats were given high-fat diet; high-fat diet+periodontitis group, in which rats were given high-fat diet and periodontitis was induced at the end of the 8th week. Fasting blood glucose and glucose tolerance were measured at the end of the 12th week. Then the rats were euthanized and the cecum content was collected. The microbial 16S rRNA gene sequencing was performed on the Illumina MiSeq platform. The taxonomy of the sequences was analyzed through RDP Classifier (http://rdp.cme.msu.edu/) against the SILVA (SSU123) 16S rRNA database. Pearson correlation analysis was performed to analyze the correlation between changes in gut microbiota and blood glucose. Results: After 4 weeks of periodontitis induction, the fasting blood glucose levels of the periodontitis group and the high-fat diet group were (4.93±0.28) and (5.25±0.24) mmol/L, respectively, which were significantly higher than that of the control group [(4.56±0.20) mmol/L] (P<0.05) with glucose intolerance. The fasting blood glucose level of high-fat diet+periodontitis group [(5.53±0.14) mmol/L] was significantly higher than that of periodontitis group and high-fat diet group, respectively (P<0.05), with the glucose tolerance curve higher than that of periodontitis group. The 16S rRNA gene analysis revealed that the Bacteroides/Firmicutes ratio in the periodontitis group is (0.37±0.23), which was significantly lower than that of the control group (0.68±0.05) (P<0.05). The relative abundance of Lachnospiraceae_NK4A136_group in the periodontitis group was (14.03±6.38)%, which was significantly lower than that of the control group [(28.21±4.82)%] (P<0.05). The relative abundance of Allobaculum [(4.27±2.67)%], Ruminococcaceae_UCG_005 [(3.70±0.90)%], Blautia [(0.63±0.45)%] in the periodontitis group were significantly higher than those of the control group [(0.60±0.72) %, (0.43±0.16) %, (0.13±0.13) %, respectively](P<0.05). Compared with periodontitis group, the relative abundance of Proteobacteria in high-fat diet+periodontitis group [(3.06±0.90)%] was significantly higher than that of the periodontitis group [(1.40±0.98)%] (P<0.05). The principal coordinate analysis and similarity analysis based on the Bray-Curtis distance showed that samples of the high-fat diet+periodontitis group clustered separately from the periodontitis group and the high-fat diet group. The results of correlation analysis showed that the abundance of Lachnospiraceae_NK4A136_group was negatively correlated with fasting blood glucose and glucose levels after loading for 60 and 120 minutes (r=-0.56, -0.50, -0.42, respectively) (P<0.05). The abundance of Allobaculum, [Eubacterium]_coprostanoligenes_group, Peptococcaceae_uncultured, [Ruminococcus]_torques_group, and several genera belonging to the Proteobacteria were positively correlated with glucose levels after loading for 120 minutes (P<0.05). Conclusions: Periodontitis might be closely related to impaired gut microbiota and glucose metabolism, and the effect could be aggravated by high-fat diet.

[Evaluation of the effects of plaque and inflammation control on treatment of gingival enlargement]

Gingival enlargement or hypertrophy is one of the common clinical symptoms in patients with periodontitis. Plaque stimulation, hormones and drug use could be the promoting factors for the occurrence of gingival enlargements. This paper reviews the literature on the pathogenesis, treatment methods and the effect of plaque and inflammation control in the treatment of various types of gingival hypertrophy. The therapeutic effect of controlling plaque and inflammation on various types of gingival hypertrophy is also discussed and the treatment scheme of gingival hypertrophy is proposed, which may provide reference for clinical work.

[Comparison of subgingival microbial profile of aggressive periodontitis, chronic periodontitis and periodontally healthy individuals]

Objective: To compare the subgingival microbiota of subjects from patients with aggressive periodontitis (AgP), chronic periodontitis (CP) and periodontally healthy (PH) individuals, respectively. Methods: Volunteers were recruited from the Nangjing Stomatological Hospital, Medical School of Nanjing University during December 2013 to December 2014. Ten individuals were included in each of three groups. Preliminary estimation of sampling sites was chosen based on the X-ray and intraoral examination. Then the subgingival plaque samples were collected, the periodontal clinical indices were recorded, genes were extracted and amplified by PCR, and subsequently a DNA library was constructed for 16S rDNA sequencing. The library that can be successfully constructed and sequenced includes: 18 samples from 8 AgP group patients, 31 samples from 10 CP group patients and 10 samples from 8 PH group volunteers. Finally, we analyzed and compared the α-diversity, β-diversity and microbial compositions of samples in each group. Pearson correlation analysis was adopted to evaluate the correlation between the relative abundance of microorganisms and the probing depth (PD). Results: The α-diversity of subgingival flora in AgP group was significantly lower than that in PH group and CP group, respectively (P<0.05). On the phylum level, the abundance of Bacteroides [(36.8±7.4)%] and Spirochetes [(16.0±5.4)%] in AgP group and the abundance of Bacteroides [(37.2±6.3)%] and Spirochetes [(11.8±3.6)%] in CP group were significantly higher than those in PH group [(27.5±11.2)%, (5.2±4.4)%, respectively, P<0.05]. While the relative abundance of Actinomycetes and Proteobacteria [(4.2±3.3)%, (12.9±5.1)%, respectively] in AgP group and that of CP group [(6.1±2.6)%, (12.1±4.0)%, respectively] were significantly higher than PH group [(19.3±13.1)%, (23.0±10.1)%, respectively, P<0.01). The abundance of Spirochetes and Tenericutes in AgP group [(16.0±5.4)%, (1.7±1.2)%, respectively] were significantly higher than that in CP group [(11.8±3.6)%, (0.7±0.6)%, respectively, P<0.05]. At the genus level, Corynebacterium, Actinomycete, Saccharibacteria_norank, Selenomonas and Oribacterium in the subgingival flora of AgP group were significantly lower than that of CP group, while the relative abundance of Actinomycetes, Lentimicrobiaceae_norank, Defluvitaleaceae_UCG_011, Family_XI_unclassified were significantly higher than that of CP group (P<0.05). Principal coordinate analysis showed that samples of each group clustered separately from each other. Linear discriminant analysis revealed that the bacteria enriched in AgP group included Spirochetes, while in CP group included Bacteroidaceae. The result of correlation analysis showed that the abundance of the following genera in AgP group were positively correlated with PD: Treponema_2, Defluitaleaceaeae_UCG_011, Mycoplasma, Catonella, Fretibacterium (r=0.525-0.750, P<0.05). While the relative abundance of Comamonadaceae_unclassified, Streptococcus, Capnocytophaga, Neisseria, Prevotella, Peptococcus, Ralstonia, Bergenia and Actinomycetes were negatively associated with PD (r=-0.617--0.490, P<0.05). In the CP group, the abundance of Dialister, Family_XI_unclassified, Catonella, Peptococcus, Pelospora and Rikenella_RC9_gut group were positively correlated with PD (r=0.430-0.533, P<0.05). Conclusions: There is a clear difference between the subgingival flora of periodontal patients and that of PH individuals. Besides, subgingival flora of AgP and CP are also different, suggesting that these could be two different diseases.

[Detection of Toxoplasma infection in women with gynaecologic neoplasms using ELISA]

OBJECTIVE

To understand the concurrent in Toxoplasma infection among women with cervical cancer.

METHODS

The anti-Toxoplasma IgG, IgM antibodies (Abs) and circulating antigens (CAg) in 247 sera (from 50 cases with cervical cancer in group 1, 59 cases with gynaecological benign tumors in group 2 and 138 cases with other diseases in group 3) were detected by ELISA.

RESULTS

The total positive rates of the CAg and the Abs in the three groups were 44.0% (22/50), 25.4% (15/59) and 20.3% (28/138), respectively. The positive rates were 20.0%, 11.9% and 10.9%, respectively for IgG 20.0%, 13.6% and 8.7%, respectively for IgM and 14.0%, 5.1% and 1.4% respectively for CAg.

CONCLUSION

The Toxoplasma infection rate of the cervical cancer group was higher than those of the other two groups, particularly the positive rates of CAg and IgM.

[Longitudinal study on periodontal disease activity in treated periodontitis patients]

The aim of this study was to estimate the incidence of periodontal disease activity (PDA) in treated periodontitis patients in a longitudinal survey. Seven periodontitis patients with 170 teeth (970 sites) participated in this 6 to 12 month study. After initial therapy, the clinical parameters including attachment level (AL) were recorded as the baseline data and then repeated every two months. Occlusal stents were used for each patient to assure the accuracy and reproductivity of the attachment level measurements. Detection of > or = 2 mm of new AL between two consecutive visits was required to designate a site as PDA. During the study period, 21 sites out of 970 sites showed PDA. For better accuracy, we calculated the yearly PDA rate based on the 6-month data because not all the seven patients finished the 12-month observation. The estimated PDA rate per year was 2.8%. Data also showed that maxillary bicuspids and molars on both jaws were more susceptible to PDA. Interproximal sites and sites with > or = 6 mm pockets before treatment showed significantly greater PDA rate than buccal (lingual) sites and sites with < or = 4 mm initial pocket depth. Our data supports the tooth specific and site specific concept in periodontal disease.