ltjube_02,
Sure, we'll tell you what ortho and endo does. Ortho is orthodontics (straightening malposed teeth, correcting jaw alignments) and endo is endodontics (root canals of every kind). They don't put in any cavities or make dentures, because as specialists, they are limited to practice only what they specialized in (the stuff I mentioned). After 4 years of dental school, a residency in ortho or endo is 2 to 3 years long.
As far as how many hours they work - from what I've seen, around 40 hours. More if you are just starting your business, less once you are well established. I've seen some orthodontists work 4 day weeks and still earn plenty- at least $200K+. Endo makes lots of money as well - very low overhead, a general estimate would be $1000 for a root canal on a molar (around here). But there isn't too much salary talk around here in dental school, other than the fact that specialists will usually make more than the general dentist.
I don't know too much about radiology other than what I read here on SDN. It sounds like a really competitive medical specialty to get into (need high USMLE scores, top AOA honors, research, etc). That sounds like ortho and endo admissions here in dental school. Programs get around 25 to 40 applicants for every available spot in these specialties. So from the threads I read, it sounds like you can be a radiologist, but still have these crazy hospital hours and be on call, the only consolation being you will make tons of money. Ortho definitely has very little off-hours emergency. If a kid's braces fall off because they bit an apple too hard, it can wait till the office opens on Monday. Wires usually don't snap or break off in the mouth. They may shift around but again, it can wait till Monday. Endo probably has more emergency calls since a tooth can flare up and cause pain at any hour, but I haven't heard of any endodontists at school having to come in at 3 am to start a root canal. Neither specialty is life or death though - people live normal lives with crooked teeth and if a root canal fails for some reason, the tooth can be extracted and the person will still live
There are definitely many jobs and opportunites available for endodontists and orthodontists after they graduate. The hard part is getting through dental school with the right credentials to get into a specialty program.