as far as i know there are no K-9 in the justice department. but i remember a comic with an "bloodhound robodog" (with the size of a vehicle...dredd rode on it on a pursuit of a perp via scent of the "dog")
i think i don't understand your "dentist question"
there is no special "DEA" or something like that. so "sugar crimes" will be fought by "normal" Judges (perhaps some undercover wally judges).
i think dentists are just normal dentists but if a dentist thinks his patient is a regular sugar consumer and DON'T alarm the Justice Department, he is part of the crime.
i use only the prestige classes from the official sourcebooks.
(for Judge Classes look into the Rookies Guide to the Justice Department)
on the other hand..my players are around 6th level...so i am glad they have 1 Tek Judge. i think the prestige classes are pretty lame and only good for NPC (what the hell is going on in a player that takes "Account Judge" as prestige class ?!?!?!)