In Genesis 49:12, "teeth whiter than milk" signify the Celestial Spiritual [milk] in the Lord's Natural [teeth], where Judah is here representing the Lord. (Arcana Coelestia 2184-2185).

In Psalms 3:7; 37:12, 58:6; Matthew 8:12, teeth signify the lowest natural things in man: in the genuine sense, their truths, in the opposite sense, their falsities. So the gnashing of teeth signifies the collision of falsities with truths. (Arcana Coelestia 4424[3])

In Exodus 21:27, this signifies truth in the natural, here the ultimate, which is the sensuous. (Arcana Coelestia 9062)

The tooth signifies the corporeal proprium, which is the lowest degree of man. (Arcana Coelestia 10283[12])

'Teeth,' as in Genesis 49:12, in the genuine sense, signify the natural level of life. Any hard part of the body, like bones and cartilage, corresponds to the truths and goods of the lowest natural level. 'Teeth' signify the outer edges of the life of the natural self, or the sensory level. There is a natural sensory will, and a natural sensory understanding. When the sensory levels are separated from the interior of the mind, their supposed truths are really mere falsities, and do violence to truths and destroy them. This situation appears in many passages, because sensory people do not see any truth in its own light, but engage in reasoning and altercations about everything... These altercations are heard in the hells as the gnashing of teeth. Viewed in itself, this is the collision of falsity and truth. This is the meaning of 'gnashing of teeth' in Matthew 8:12, 13:42, 50, 22:13, 24:51, 25:30, and Luke 13:28.

(References: Apocalypse Revealed 435)