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.

Brushing teeth while fasting will not break the fast. So, you can brush your teeth using toothpaste while fasting so long as you are careful to avoid swallowing any of it.

You do not have to take out your braces in order to fast, because nothing goes from it to the stomach. The fact that it causes you to produce more saliva does not mean that it breaks the fast.

If the injection provides nourishment that takes the place of food and drink; it breaks the fast because it is like eating and drinking. If the injection is not a kind of nourishment; this does not break the fast.

Looking at (non-mahram) women is haram because Allah has commanded the believers to lower their gaze. Looking at women does not break your fast, but you have to lower your gaze.

The correct scholarly view is that masturbation is haram. But masturbation at night in Ramadan does not invalidate your fast, either on the day before or the day after.