“cleanness of teeth.” An idiom for famine. The people had nothing to eat, so their teeth were clean. This is clear from the context (Amos 4:7-9).
“and lack of food in every town.” One of the great lessons of the Bible is that the behavior of people affects the land that they live on. This lesson is throughout the Old Testament (cp. Deut. 11:13-17; 28:1, 12, 15, 22-25, 38-40; Lev. 18:24-25; Ps. 107:33-34; Jer. 3:2-3; 12:4; 23:10; Amos 4:6-10). (See commentary on Lev. 18:25).
The Hebrew word translated “food” is literally “bread” in the Hebrew text, but here, as in many other places, “bread” is used for food in general.
“but you have not returned to me.” The Bible is very clear that if Israel was faithful to God, they, as well as their animals and land, would be blessed and there would be plenty of food. So, since there was famine, the people should have known what was happening, known that they had abandoned God, and repented and returned to Him. But they were so set on their ungodly ways that they ignored the disasters that were occurring to Israel.