There are huge differences between residencies. Here is a short synopsis:
Ortho: These guys spend a lot of their time modeling matching polo shirts with their schools ORTHO logo and doodling.
Pedo: these guys spend the best years of their life listening to screaming children and driving around in crappy vans to underserved areas.
OMFS: they are usually elbow deep in HIV and HEPC infected blood yanking out 3rd molars and or rearranging a pts face. After a few months of being on call every other day most become bitter at the ortho guys with their color-coded polo shirts.
ENDO: Only the brightest dental students can enter this elite group, which is committed to applying their intellect to one monotonous task over and over again for the remainder of their career. 2 yrs working as a cigar roller is a prerequisite.
Perio: They are hygienists who train another 2 years learning how to go subgingivally.
Pros: I think they are just plain dentists in disguise.
Public Health: spend 2 years learning about fluoride after which they spend the rest of their time telling people about fluoride.
Dental Radiology: They learn everything there is to learn about radiographs concerning the maxilla, mandible and 32 teeth. They live in awe of Medical radiologists.
General dentists: these guys just fix simple cavities and decide which specialist to refer their patients to.
There is a sub group of general dentist who work exclusively with composite and refer to themselves esthetic dentists. They hope one day to create an ADA accredited esthetic dentistry residency. After the creation of this residency, dental students will have to choose between completing an esthetic dental residency to obtain a license, or graduate with a certificate as an amalgamator.