Like you, I was very research heavy and didn't have as many shadowing/volunteer hours. I am taking a gap year now (doing biochemistry research at my undergrad institution) and will be attending Penn in the fall. Your GPA is great and your DAT is about average (depending on what schools you are reaching for your AA/TS is 1-2 points lower than some of the top research institutions), but still competitive.
I had oGPA 3.68 and sGPA 3.67 and AA/TS/PAT 23/25/21 (none below 19). I applied to 15 schools, received 7 interviews (went on 5; turned down 2), and was accepted to 3 schools and waitlisted at the other 2. I think you will be fine applying this coming year. There is only so much time in the day and dental admissions know you cannot do everything (i.e. shadow a million hours and do a million hours of research).
I also think the fellowship sounds like an amazing opportunity, especially since you want to go into academic dentistry. Personally, I don't want to go into academic dentistry, so I decided to take one year off (I would have taken no gap year, but I studied abroad and needed to delay a year due to timing). If I was going into academic dentistry, I would definitely consider this opportunity, but not because I think my resume needs building (because I think you could get in next cycle). I would consider it because I want the degree/time off/like the research. On the other hand, if you don't take the fellowship, you will be starting you dental career one year earlier and making a higher salary one year earlier. Also, if you are thinking about an academic career/research, it might be worth looking into DMD/PhD programs. I think this is a decision you can only make and I don't think you could go wrong either way.