Hi there I have an abscessed tooth & was prescribed morphine & t3 (liothyronine). I took T3 (liothyronine) 7hrs ago is it now safe to take a 5mg morphine pill?

Yes. It is now safe to take either another T3 (liothyronine) or the morphine pill if it is very, very bad pain.
Yes. It is a little unusual to be prescribed both of these medicines, particularly if not instructed that one (morphine) for more severe pain) and T3 (liothyronine) for milder pain. However, the T3 (liothyronine) has worn off by now.
Overkill. I have never prescribed morphine for an an abscess in 42 yrs. If T3 (liothyronine) is not working, ask your dr. If taking 2 is ok. Also taking 3 advil between doses of T3 (liothyronine) may help you better and is safer than morphine. I treat the worst abscesses in my community and this formula works well. Also, you need to get the cause of the abscess treated asap! Feel better!
The initial pill. Should have worn off. More importantly you did not state the abscess was drained - that is the most critical thing to have performed. Once abcess is drained....Pain should considerably go down. An antibiotic may be a good idea as well. Ice also on the area may reduce the amount of pain killer required. Hydration is important as well. Consider an antiinflammatory too.