Table 1. Least squares regression analysis on the quality and structural parameters influenced by aging.

	estimated coefficient	standard error	t-values	p-values	standard partial regression coefficient	variance inflation factor
(A) Quality parameters
intercept	1839.20	340.75	5.40	0.0003	0	–
mineral density	−0.89	0.22	−3.99	0.0026	−0.63	1.02
apatite orientation	103.78	73.20	1.42	0.1867	0.26	1.44
AGEs content	−1.66	0.40	−4.10	0.0022	−0.76	1.42
(B) Structural parameters
intercept	233.15	59.78	3.90	0.0005	0	–
degree of occluded tubule lumens	−0.98	0.42	−2.32	0.0272	−0.40	1.06
number of dentinal tubules	−0.24	0.57	−0.43	0.6709	−0.07	1.06