A 38-year-old male complains of an awful toothache in his right lower jaw. He mentions that he hasn't seen a dentist for a couple of years due to the lack of dental insurance. There is no obvious swelling, and his vital signs are within normal limits. On a scale of 1 to 10, he rates his pain as 9. What is the most likely cause of his toothache?
1) Tooth decay
2) Gum disease
3) Tooth sensitivity
4) Tooth fracture