Historically, more people have applied to Orthodontics programs than to Oral Surgery programs through Match. However, there are more postions for Orthodontics programs. It could be said that the two are fairly equal in terms of competitiveness at face value. Proposed and recent changes to the application process may change things of course.
For Oral Surgery in 2010:
387 Applicants Participated | 216 Positions Offered | 55.8% Rate
For Orthodontics in 2010:
485 Applicants Participated | 269 Positions Offered | 55.5% Rate
Now, I am by no means downplaying the difficulty of gaining acceptance into these or any other post-graduate program - but, these numbers should offer some semblance of hope for those aspiring towards Orthodontics or Oral Surgery. We can speculate that those that applied were in the top 10% in terms of grades and board scores, but that still would be a generalization. The fact of the matter is folks will get in every year who are not at the very top academically. There are a multitude of other considerations at play. By and large, there are some fairly accepted standards. However, as shown, for those applying, you have a better than 50% chance of matching and getting a position somewhere - and that doesn't even include the unfilled positions for which you don't have to participate in the Match process at all.