Dental implants can replace any of the teeth, either in the back or front. The only routine time a dental implant would not be a recommended form of treatment is to replace wisdom teeth which are not needed in the mouth.
Dental implants at the back of the mouth would be attached to crowns in the same way as front teeth: Dental crowns are attached on the abutment which is attached into the implant (artificial root in the bone). The abutment supports the dental crown which is cemented on permanently.