Table 3. Threshold effect analysis of the skull bone mineral density and periodontitis using piece-wise logistic regression.

Skull BMD, g/cm2	Periodontitis (OR, 95%CI, P)
Fitting by weighted logistic regression model	0.73 (0.59, 0.90) 0.0036
Fitting by weighted two-piecewise linear logistic mode
Inflection point	2.89
< 2.89	0.68 (0.54, 0.86) 0.0012
≥ 2.89	1.77 (0.53, 5.93) 0.3541
Log likelihood ratio test	0.149

^#Periodontitis contained mild, moderate, and severe periodontitis.