The match works like this. A program decides if they will participate in Match or not. The more programs that participate, the more sense Match will make. Most Ortho, Pedo, OMS, GPR and AEGD programs participate in match, but there are a number in each of those categories that don't participate. If a program is not part of match, they must offer you a position before the match deadlines, because if you take that position, you must drop out of the match.
Match was designed to give every participant only 1 acceptance. This is supposed to eliminate anxiety on both the applicant and program's ends. For example, there is a super candidate for OMS who applies to 10 programs. Every single one of those programs reads his application, thinks he's great, invites him to interview. Without the match process, every single one of those programs wants this guy and accepts him. Now he's got 10 acceptances and has till a certain date (say Jan 15) to tell the 1 program he wants to attend that he's coming, and tell the other 9 he's not going. Until Jan 15, the 9 programs that he's not going to accept can't do anything to fill their spots till this guy actually says he's not coming. So the program is sitting around waiting for him to decide, and the other applicants to those 9 programs are wondering if they're gonna get into those programs and why they haven't heard anything from those programs. What program is going to say "Oh, well we're waiting for this super duper candidate to decide if he's gonna come here before we look at the rest of the losers."
With the match system, the same guy gets invited to interview at the 10 programs, and again they all want him. But this time, each program has to submit a list into the match website of which candidates they would consider for their program and what order they want them in. So even though they all put the guy as their #1 choice, they also enter other candidates they would consider in case they don't get their top picks. Our OMS guy must also submit a list of his 10 programs to the website in the order he wants to attend them in. The website has a deadline, and after the deadline they run an algorithm to match everyone up. Since everyone wanted the hypothetical candidate, he get's his #1 choice, and the 9 other programs who also wanted him, don't get him and get other people from further down their list. Basically, the match forces you to consider all programs and make your decision before an acceptance, not after so everyone can have a chance.
Most post grad programs have very few spots. Most OMS seem to be 2 students per year, Ortho and Pedo programs have between 4 and 5 new students per year (on average), and so on. Without the match system, the OMS program with 2 spots can't send out 5 acceptances b/c what if all 5 accept? They only have room for 2.
If a program is not part of the match (there are a few programs that don't participate), it makes things complicated. Say our guy has his 10 interviews, and 9 of the programs participate in match and 1 doesn't. So the 1 non-match accepts him on the spot, and now he has to decide does he take the acceptance and drop out of match, or give up the acceptance and wait to see what happens in the match? Results of the match are binding and you are supposed to sign a legal contract after match saying you will be attending there, so he can't say yes to the one program and wait and see what match brings him from the other 9. He has to decide beforehand b/c you are only supposed to ever have 1 acceptance. See where the dilemma is?
It's a complicated system, but it works for the most part. Unless you don't get a spot for ortho/OMS/pedo/GPR/AEGD in the match, in which case it's sorta annoying but hey - a DDS ain't a bad backup degree to have.
