1. Our hypotheses on the relationship between periodontitis and AS are as follows;

   • The prevalence of periodontitis is higher in AS patients group than that of non-AS control group
   • Anti-TNF-α therapy would favorably affect the disease course of periodontitis.

2. Based on our hypotheses, the specific objectives of the present proposal are as follows;

   • The primary objective is to compare the prevalence rate of periodontitis between AS patient group and non-AS group.

   • The secondary objectives will be:

     • To observe the carriage rate of P. gingivalis in AS and non-AS groups
     • To identify clinical parameters associated with the severity of periodontitis in AS group.
     • To compare the progression of periodontitis at weeks 12 and 24 between AS and non-AS groups or between AS patients with and without anti-TNF-α treatment

Inclusion Criteria:

• Age ≥ 18 years
• Subjects giving informed written consent
• In case of AS patients, subjects to meet the 1984 modified New York criteria for AS.
• In case of controls, subjects without a history of inflammatory arthropathy

Exclusion Criteria:

• Subjects having received periodontitis treatment including scaling within 6 months before study participation.
• Subjects with a history of taking antibiotics including prophylactic anti-tuberculosis agents within 3 months before study participation.
• Subjects with a hitory of taking immuno-suppresives (methotrexate, leflunomide, tacrolimus, cyclosporin, or azathioprine) or any dose of glucocorticoids (oral or pareneral) within 3 months before study participation.
• Subjects with a history of diabetes mellitus.
• Subjects with aggressive periodontitis requiring open flap debriment at enrollment immediately.
• Subjects with a hitory of clinical inflammatory bowel disease.
• Subjects with active infection, which can make an influence on the levels of acute phase reactants.
• Subjects with any other condition to render the patient unable to understand the scope of the study or preclude the patient from following the protocol in the physician's opinion.

1. AS group will consist of patients aged 18 years or more who meet the 1984 modified New York criteria for AS.

   i. AS group receiving anti-TNF-α agents will consists of AS patients who have received adalimumab, etanercept, or infliximab before enrollment (or begin anti-TNF-α agents at enrollment) and keep anti-TNF-α agents for 3 months or more after enrollment.

   ii. AS group not receiving anti-TNF-α agents will consists of AS patients who are treated with a non-steroidal anti-inflammatory drug, sulfasalazine, or non-pharmacological therapy and keep non-anti-TNF-α therapy for 3 months or more after enrollment.

2. Control group will consist of age- (± 3 years) and gender-matched volunteers who do not have inflammatory arthropathy.