Temporary fillings, are meant to be as the name implies, temporary. They are generally placed for a number of reasons, including time constraints, sedative effectives(one of the most common ingredients of temporary fillings is Eugenol which has a sedative effect on the nerve of the tooth), and sometimes finances. The problem with temporary fillings is that the seal that they create between the filling and the tooth is weak and subject to breakdown. This can quickly introduce the same bacteria that cause decay underneath the temporary filling in a place where regular oral hygiene can't hold them in check. This can cause rapid decay spreading and the potential that the decay can reach the nerve of the tooth, thus requiring a root canal.
That not withstanding, a little history about temporary material. One of the oldest, and most common types is called IRM (Intermediate restorative material) which was developed by the military back in the Vietnam era as a quick in the field fix for soldiers. At that time it was commnoly colored with dye in either blue or red(as I remember when I was told about this, blue was a tooth that just needed restorative treatment, and red was a tooth that needed either a root canal or extraction). Today, IRM is just one color, white. If you ask some dentists that practice in VA hospitals even today, they still will see some Blue and Red IRM 30 years later!
Word to the wise, get the temporary taken care of sooner than later. What may be a mater of placing a permanent(and less expensive) filling now, can in the future end up being an expensive root canal and crown or extraction in the future.
