i know the dictionary says either is okay, but i think that "orientated" sounds completely stupid and uneducated, like someone is making up a word in order to sound smart. i want to cringe any time i hear someone say it. my husband teaches languages and has an english degree, and he says orientated may be technically correct, but he would count it as incorrect in an essay.
use what you want, or what it appears everyone around you uses. either is okay, apparently, but how often do you hear the physicians use the word "orientated"? how often do you hear "orientated" used vs "oriented" in edited or educated language, either written or spoken?
edited to add:
this is what wikipedia's dictionary has to say about orientate:
third person singular
(third-person singular simple present orientates
, present participle orientating
, simple past and past participle orientated
 usage notes
- <li sizcache="0" sizset="4">(british) (transitive) to determine one's position relative to the surroundings; to orient
—john le carré
- he…stood for a moment, orientating himself exactly in the light of his knowledge.
- he came out of the station and took some time to orientate himself.
- (british) (intransitive) to turn to face the east
the term is in wide colloquial use in the uk, although the oxford english dictionary does not define it, simply stating that it is another form of orient
it is widely considered an error in american english.
prescriptivists criticize it as a backformation
it is attested since the mid-19th century.