ANOVA	Analysis of variance
APJ	Apelin receptor
BOP	Bleeding on probing
CAL	Clinical attachment loss
ELISA	Enzyme-linked immunosorbent assay
G1	Stage I–II periodontitis group
G2	Stage III–IV periodontitis group
GCF	Gingival crevicular fluid
GI	Gingival index
ICC	Intraclass correlation coefficient
L	liter
mm	millimeter
ng	nanogram
nmol	nanomole
NSPT	Non-surgical periodontal therapy
OSI	Oxidative stress index
PBS	Phosphate-buffered saline
PI	Plaque index
PPD	Probing pocket depth
ROS	Reactive oxygen species
SD	Standard deviation
T0	Baseline
T1	1 month after NSPT
T3	3 months after NSPT
T6	6 months after NSPT
TAS	Total antioxidant status
TOS	Total oxidant status
TNF-α	Tumor necrosis factor-alpha
μL	microliter