9052. 'Tooth for tooth' means if anything [is injured] in the outer part of the understanding. This is clear from the meaning of 'tooth' as the outer part of the understanding, and therefore as natural truth since this composes the life of that part of the understanding. The reason why 'the teeth' have this meaning is that like a mill they grind and so prepare the food which will serve as nourishment for the body, at this point the food which will serve as nourishment for the soul. The food that nourishes the soul is intelligence and wisdom; this food is first received, ground, and prepared by cognitions or knowledge of truth and good in the natural - intelligence and wisdom being what spiritual and celestial food is called, see 56-58, 680, 1480, 4792, 5147, 5293, 5340, 5342, 5576, 5579, 5915, 8562, 9003. From this one may see why it is that 'the teeth' means the outer part of the understanding. What this outer area is becomes clear from what has been shown immediately above in 9051 regarding the inner area of the understanding.
 'The teeth' means natural truth, which belongs to the outer part of the understanding, and in the contrary sense falsity destroying that truth, as is clear from the following places in the Word Natural truth is meant in Moses,
His eyes will be redder than wine, and his teeth whiter than milk. Genesis 49:12.
These words too mention both eyes and teeth together. They refer to Judah, by whom the Lord's Divine Celestial is meant, 6363. 'His eyes' means the Lord's Divine Intellect, 6379, and 'his teeth' the Lord's Divine Natural, 6380, thus also Divine Truth in His Natural.
 In Amos,
I gave you emptiness of teeth in all your cities, and lack of bread in all your places. Amos 4:6
'Emptiness of teeth' stands for scarcity of truth, and 'lack of bread' for scarcity of good.
All this makes plain what the gnashing of teeth is among those in hell, Matthew 8:12; 13:42, 50; 22:13; 25:30; Luke 13:28. It is the clash of falsities with the truths of faith, 4424 (end); for as has been stated, 'the teeth' in the contrary sense means falsity destroying truth, as in David,
Rise up, O Jehovah; save me, O my God! For You will strike all my enemies on the jaw, You will break the teeth of the wicked. Psalms 3:7.
'Breaking the teeth of the wicked' stands for breaking the falsities that the wicked use to destroy truths. In the same author,
As to my soul, I lie in the midst of lions; their teeth are a spear and arrows, and their tongue a sharp sword. Psalms 57:4.
'The teeth of lions' stands for falsities destructive of truths, 'lions' being falsities arising from evil in their power, 6367, 6369.
 In the same author,
O God, destroy their teeth in their mouth; tear out 1 the molars of the young lions. Psalms 58:6.
A nation has come up over My land, strong and innumerable; its teeth are the teeth of a lion, and it has the molars of a fierce lion. It has turned My vine into a waste, and My fig tree into froth. Joel 1:6-7.
'Teeth' and 'molars' stand for falsities destructive of the Church's truths. 'Vine' is the spiritual Church, 1069, 5113, 6376, and 'fig tree' is its natural good, 217, 4231, 5113. The fact that 'teeth' has that meaning is also evident from their being attributed to a nation which will lay waste. In John,
The shapes of the locusts were like horses prepared for war. They had hair like women's hair, and their teeth were like lions'. Revelation 9:7-8.
'The locusts' are those who are steeped in external falsities, 7643, from which it is evident that again 'teeth' are falsities destructive of truths.
1. literally, overthrow