You could retake it if you want to go through the pain and anguish of studying again, but I wouldnt do it. Most schools will let the one bad score slide. Your other stats are solid, and I think you'll get plenty of interviews. Once you get the interview, its all about personality. I got a 15 on my PAT, and I still got in. If you dont get in, then obviously, retake the exam.
While "don't re-take it" may be encouraging advice - the bottom line is you want to get in to dental school. It is true that some schools may allow one lower score but most also have a cut-off criteria on each section. I recommend calling the schools that you are interested in and simply asking them.
Don't worry, reading in Dental School is not that important.
When I took it 4 years ago I got a 14 on QR section (math)
Here is what I know from my schools admissions dept. They look at your GPA and overall DAT and then invite you to interview. A 21 is more than enough to get into a school. The interview will then seal the deal.
I think you'll be fine too. I got a 14 in math and nobody even brought it up except the school I am at now. And it was mentioned in a casual joke... "so, you're not very keen on math, huh?" But my average was well below yours. I think you are more than fine to get into most, but not all schools. I think it depends on your goals. I think it would help if you stated what school is your #1 choice so we can better help you on specifics.