As with everything in dentistry the answer is.... It depends.
Upon graduation you have several options on how to begin your career including the armed forces, IHS, ownership, partnership, associateship, academia, specialization, etc. Since you asked about ownership and associateship I'll post on those two.
I think it is the rare bird that can graduate from dental school and hang out his own shingle for a scratch practice. First of all, no bank will loan you money until you've passed your board and been licensed. Once you have the money figure at least 3-6 months to have your facility outfitted. So for the first 6 months you're going to have to work for someone, not work, or buy an existing practice.
I also think it is the rare person that graduates from dental school with any idea how to run a business. Maybe if you went back to school after being in the work force or owning a business, but for the average guy/gal I think it would be a road of hard knocks learning the business of dentisry.
Out of my class of 77, 2 opened their own office as soon as they could. For one that was 6 months for the other about 9. One IS that rare combination of charisma, confidence, risk taking, and leadership that can make it work and he has done gangbusters. It didn't hurt that he went back to his hometown where everyone knew him and there was only one other older dentist. The other guy took two years to start making a profit. The whole time his wife kept asking him "why are we still living in an apartment DOCTOR Smith?"
I think it is more prudent for the majority of dental graduates to associate with another practice for a length of time (1-5 years depending on how fast a learner you are) to make the mistakes on someone else's tab (and you will make plenty, everyone does).
So how do you find an associateship? The short answer is network. Go to local dental meetings and get to know dentists where you want to live. Another great resource is the dental supply reps. They visit offices on a regular basis and usually know who is looking for help. It also makes them look good if they can help a senior doc find an associatship so they really don't mind helping you out.
How do you find a GOOD associateship? Ask to speak with past employee dentists, go visit and see how things work, ask other dentists about the place. There are lots of dental mills where they promise a new grad a great opportunity and then you end up doing poor dentistry on HMO patients. Many of the large clinics will use you as slave labor.
People graduating in the near future will be in a great position as lots of docs will be thinking about retiring and want to bring in someone to tranistion out of the office. I think it would be ideal to go to work for someone who was willing to mentor you into being a better dentist/businessperson because they want you to enjoy the practice and buy it from them eventually.
Anyway JMH(Long winded)O
Rob