If you are able to expel the food stuck between the teeth but you do not do so and you swallow it, then you have invalidated your fast. If you swallow the food stuck between the teeth involuntarily, then your fast is valid.

Smoking is haram whether in Ramadan or outside Ramadan. Smoking invalidates the fasting because the smoke contains particles that reach the stomach

If you do not eat Suhur or do not wake up for Fajr prayer, this is not counted as a reason for you not to fast. So you have to continue your fast. If you broke your fast, thinking that you did not have to fast, you have to fast another day to make up for it.