Why didn't Sauron make use of the dragons?

[Hookbill the Goomba]

I think we have to assume that some Dragons survived after Smoug was defeated. As Thorin says;

There were many Dragons in the North.
Thorin: The Hobbit, An unexpected party

We aren’t told what happened to these dragons though. If the dragons were around in the north which we can guess to ether be the northern waste, blue mountains, or Helcar. These wide lands may be suited to Dragons.
The reasons behind Sauron not using the dragons is perhaps because he did not think that they would be useful in a battle situation, After Smoug was defeated, perhaps the other dragons weren’t considered as much as a threat. Dragons were not very trust worthy, Glourong often desolated even the orcs that were supposed to be helping him, and Perhaps Sauron did not want to risk the same.

[NightKnight]

Either there must have been more than two dragons that survived the War of Wrath, or they bred. There were three dragons mentioned in the Third Age, Smaug, Scatha and the cold-drake that killed Dain I and Frór. The cold-drake can't be Scatha, for Scatha was already dead then, and it can't be Smaug, for he was a fire-dragon.