[Describe the Population from the PICO or describe the selection of studies for a Systematic Review and Meta-Analysis review.]

This systematic review and meta-analysis included studies with patients with moderate to untreated advanced chronic severe periodontitis with and without type 2 diabetes mellitus (>2 years). They were recruited from various clinics, including respective hospitals or universities in countries such as Egypt, India, Brazil and Poland. Exclusion criteria included pregnant women and patients who had antibiotics within the last three months before the interventions.

[Identify the key Intervention and the Comparison from the PICO. For example, review of studies investigating the effects of Vitamin D supplementation on periodontal bone health: all studies had to include a specific intervention (daily vitamin D supplements) directed towards a specific study group (women age >60 years). Try to be as specific as possible and use language that is understandable by as many individuals as possible.]

This systematic review and meta-analysis investigated the effects of omega-3 fatty acids supplementation on periodontal clinical parameters, primarily clinical attachment level (CAL) and periodontal probing depth (PPD). All studies had to include a dietary omega-3 fatty acid supplementation adjunctive to non-surgical periodontal treatment in cohorts aged 40-58 years. Gender distribution was not reported in some studies included, whilst some included only females or both genders. One study specifically included post-menopausal women with an average age of 50 years). All eight studies included are parallel randomised controlled trials. The type of fish oil supplementation used in the studies included mainly EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), which are long-chain omega-3 polyunsaturated fatty acids (omega-3s), quantities ranging from 700mg to 3000mg with or without other supplementation (e.g. alkylglycerols, squalene, Vitamin A and D3) or medication (low dose aspirin: 75mg-100mg). The duration of supplementation ranged from 8 to 26 weeks.

[Identify the Outcome from the PICO. This means the primary disease, condition, or treatment outcome that is thought to be related to the exposure, risk factor, or intervention of interest. One and only one should be identified here. Try to be as specific as possible and use language that is understandable by as many individuals as possible. For example, the main outcome was measurable radiologic reduction in alveolar bone loss following daily vitamin D supplementation with annual evaluations made over a 5 year period—OR—the main outcome was successful resolution of anterior periapical abscess and radiologic evidence of healing following non-surgical retreatment with thermoplastic endodontic material. Evaluations were made at 1 year, between 1 and 3 years, and at 3 years or later following retreatment.]

Clinical attachment loss (CAL) and periodontal probing depth (PPD) were the primary outcomes evaluated in this systematic review and meta-analysis. Secondary outcomes were changes in the sites with PPD>=5mm, the number of sites with bleeding or probing (BOP), and the gingival index (GI). Measurements were taken at the baseline, 12 weeks and 26 weeks intervals for six months studies, whilst they were taken at BL, six weeks and 12 weeks or baseline, four weeks and 12 weeks for three months studies. Clinical parameters were assessed at the baseline and eight weeks for two months of study.

[Typically an effect measure with a confidence interval should appear here. If a meta-analysis was done, provide the key statistical measures used for comparison purposes between studies. Otherwise, briefly summarize the main results reported.]

The pooled estimates revealed a significant overall PPD (periodontal pocket depth) reduction of 0.42 mm (95% CI: 0.15, 0.68, p = .002, I2 = 85%) and CAL (clinical attachment loss) gain of 0.58 mm (95% CI 0.24, 0.92), p = .0007, I2 = 85%). Furthermore, subgroup analysis revealed a significant effect of omega-3 for PPD reduction only for systemically healthy subjects (WMD: 0.52; 95% CI: 0.10, 0.94; p = .002, I2 = 89%). Both systemically healthy (WMD: 0.65; 95% CI: 0.18, 1.11; p = .006, I2 = 90%) and type 2 diabetic subjects (WMD: 0.33; 95% CI: 0.06, 0.60; p = .02, I2 = 0%) presented significant improvements in CAL gain associated with omega-3 supplementation. Subset analysis demonstrated that studies without low-dose aspirin showed significant PPD reduction (WMD: 0.44; 95% CI: 0.03, 0.84; p = .04, I2 = 87%). However, significant CAL gain was observed regardless of the use of low-dose aspirin. Regarding gingival inflammation (BOP and GI), meta-analyses showed a significant reduction only for BOP (WMD: 4.55; 95% CI: 2.00, 7.10; p = .0005, I2 = 0%). Further, subset analysis indicated that the abovementioned improvement was observed only in systemically healthy patients (WMD: 4.77; 95% CI: 0.83, 8.71; p = .02, I2 = 21%).

[What did the author(s) report as the primary findings regarding the relationship between the key study factor(s) and the outcome measure(s).]

The authors of this systematic review and meta-analysis concluded that included randomised clinical trials showed a significant PPD reduction or CAL gain associated with omega-3 fatty acids. They suggest that using omega-3 fatty acid dietary supplementation as an adjunct to non-surgical periodontal treatment can provide additional benefits in CAL gain and PPD reduction, compared with non-surgical periodontal treatment alone in individuals with periodontitis.