My dental school had two dental fraternities there as well, Alpha Omega and Psi Omega.
You asked what are dental fraternities, to me, they're only good for parties during dental school.
People at NSU join them, in my opinions, are for the following reasons:
90% social
5% academic (reviews, CV boosters, and practical teachings)
2.5% alumni connections
2.5% philantropies
I remember when the two dental fraternities rushed us, they kept telling us, alumni connections are huge if you want to specialize! I'll tell you what, I've applied to one of the most competitive specialties in dentistry there is and not one interview had asked me about my dental fraternity affliations!
To me, dental fraternities are only good for social purposes.
Don't get confused though, dental fraternity parties are nothing like undergraduate fraternity parties. Undergraduate fraternity parties are CRAZY/INSANE (oh yeah, miss those days!), while dental fraternity parties are "eh, it's alright!"
Join a dental fraternity, is just another means to meet people and have more potential things to do or get involved in. Don't expect to get too much out of it, but it can be fun.