K.G.
Sounds like molars! I've been working in dentistry for 6 years and here is what I know about teething: Molars are harder on them than front teeth as there is more tooth that needs to erupt. The bruising you see is completely normal and is actually called an eruption cyst. Molars can also come almost all the way to the surface only to drop back down again. Totally frustrating for little ones, but again totally normal.
I highly recommend Humphrey's teething pellets. You desolve them in water and then rub it on the gums. They are made of all natural herbs, so there are no harmful chemicals like Orajel and Ambusol have. Also, the numbing medicines have an acid in them that can irritate the gum tissue and make the problem worse over time. They also can numb the throat and make swallowing difficult. Plus, the teething pellets taste really good and kids love it! Motrin works better for teeth pain than Tylenol, so use that when he seems to really be hurting. Hope that helps and that you both get some relief!