Black lines on tooth - Decay?!

I do not know how old you are this is an age relevant question. If they are new adult teeth they are going to have large ridges, Used for cutting through the gums. Which in turn makes the cracks or crevices deep.

The dark lines could be decay or they could be stains. When you go to the dentist he will poke at them to tell the difference. If they are soft then they are decay and will need a filling. They have tooth colored composite so it will not be noticeable. However if they are stains they can put on a varnish made special for this purpose, which will help prevent cavities from forming.

If the teeth are not new then chances are they are cavities which are forming and they can either be watched or filled depending on the extent of the decay. As to the size of the filling. It depends on the amount of decay. Keep in mind the size of the filling will always be larger then the original decay because the dentist has to contour the hole to hold the filling.

You should not just cover the lines without the express approval of your dentist. I hope this helps.

I am a dental assistant and mom of 2

the lines are not necessarily decay. The cracks can get decay in them if you do not get sealants in them first. You need to go to the dentist and they will check to see if the fissures go through the enamel. if they don't, you can get them sealed to protect the areas from getting decay.