Table 4.

Cox proportional hazard models

	Model 1	Model 2	Model 3	Model 4	Model 5
Age	0.886	0.837	0.819	0.657*	0.672*
Female	1.071	1.288	1.164	1.156
Caucasian	1.004	1.144	1.245	1.477
Mandible		0.480+	0.756	0.829
Crowding (LII - mm)			0.544*	0.549+	0.513+
PBM				4.661**	4.397**
Arches	28	28	28	28	28
Failures	28	28	28	28	28
N	37	37	37	37	37
dF	3	4	5	6	3
chi2	0.813	3.549	9.315	17.725	16.786

+ p < 0.010, * p < 0.05 ** p < 0.01