Primary outcome
Bleeding, PD
BLEEDING, PLAQUE
In comparison with the FMD group, at 6 months after therapy, the Q-SRP group showed a significant reduction of the GDF-15 levels (p = 0.012) (Table 
Differences among GDF-15, GPx-1, hs-CRP and SP-D at baseline and at each follow-up session. Results are expressed as mean and SD (standard deviation). a, significance between baseline and 30 days; b, significance between baseline and 90 days; c, significance between baseline and 180 days; d, significance between 30 and 90 days; e, significance between 30 and 180 days; f, significance between 90 and 180 days. * P-value significant < 0.008 (Bonferroni corrections). GDF-15, growth differentiation factor 15; GPx-1, glutathione peroxidase 1; hs-CRP, c-reactive proteins; SP-D, surfactant protein DAt 6-months of therapy, the correlation analysis evidenced that there was a correlation between serum GDF-15 and smoking (p = 0.046), % sites with PD ≥ 4 mm (p = 0.022), number of teeth (p = 0.031), BOP (p = 0.044) and PI (p = 0.045). Serum GPx-1 levels were correlated with smoking (p = 0.044), HbA1c (p = 0.045), LDL-cholesterol (coeff. 0.196, p = 0.044), number of teeth (p = 0.041), CAL (p = 0.025) and BOP (p = 0.027); hs-CRP was correlated with HbA1c (p = 0.048), LDL cholesterol (p = 0.019), % sites with PD ≥ 4 mm (p = 0.032), BOP (p = 0.045), and PI (p = 0.039); SP-D levels were correlated with smoking (p = 0.025), number of teeth (p = 0.035); CAL (p < 0.001), BOP (p = 0.016), and PI (p = 0.011) (Table 
Correlation analysis among GDF-15, GPx-1 and the analyzed variables at 6-months of treatment. For sex, males served as a reference. GDF-15, growth differentiation factor 15; GPx-1, glutathione peroxidase 1; hs-CRP, c-reactive proteins; SP-D, surfactant protein D. HbA1c, Glycated haemoglobin; BMI, Body Mass Index, PD, Probing Depth; CAL, Clinical Attachment Loss; BOP, Bleeding on Probing; PI, Plaque Index