Trace elements can influence the physical properties of tooth enamel

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Table 2 Simple linear and stepwise multiple correlation between trace elements’ concentration in enamel and tooth properties

Correlated properties	Correlated elements	Simple linear regression			Multiple stepwise regression
	Correlated elements	R	B	P	R	B	P
Mechanical properties
Hardness	Ti	0.34	27.00	0.037	0.34	2753.54	0.037
Average crack length	Al	0.67	−18.08	0.005	0.70	−18.08	0.005
Optical properties
Lightness	Fe	0.46	153.60	0.004	NS	NS	NS
˶	Ti	0.47	832.79	0.003	0.47	832.79	0.003
Crystallographic structure
Crystal domain size along a-axis	Cu	0.40	32.87	0.019	NS	NS	NS
Crystal domain size along c-axis	Pb	0.52	−199.11	0.002	0.70	−138.76	0.019
˶	Ti	0.51	−192.05	0.002	˶	−133.19	0.02
˶	Mn	NS	NS	NS	˶	184.01	0.025
Cell lattice parameter along a-axis	Cu	0.35	0.24	0.045	NS	NS	NS
˶	Se	0.59	0.36	<0.001	0.59	0.36	<0.001
Cell lattice parameter along c-axis	Cr	0.38	−6.97	0.031	0.72	−5.79	0.031
˶	Ni	0.40	−0.09	0.02	˶	−0.06	0.047
˶	Se	0.52	0.35	0.002	˶	0.36	<0.001
Carbonate Content
Type A	Fe	0.41	−0.61	0.021	0.41	−0.61	0.021
Type B	Co	0.37	−18.44	0.007	0.77	−16.15	0.011
˶	Ni	0.70	0.47	<0.001	˶	0.46	<0.001
˶	S	0.43	0.01	0.014	NS	NS	NS

R: the correlation coefficient; B: the regression coefficient; P: the significance of Pearson correlation and NS: not significant.