You have overjet or overbite? Cos initially you mentioned overbite and then in your question you mentioned overjet..
Anyway YES splints are useful for treating TMD.
Because there is movement of the teeth the splint might loosen.
Next Steps
If its a splint with wire get it tightened from your dentist. If not visit dentist to make necessary correction in the splint.
Health Tips
Find the real cause for Stress and depression etc. Although splints and braces can cause discomfort, bear in mind it is temporary and its for the better final outcome.