I had this same fear when I was getting a root canal a while back. I just did another google search just in case and found this:

Amoxicillin can make birth control pills less effective. Ask your doctor about using a non-hormone method of birth control (such as a condom, diaphragm, spermicide) to prevent pregnancy while taking amoxicillin. Take this medication for the full prescribed length of time. Your symptoms may improve before the infection is completely cleared. Amoxicillin will not treat a viral infection such as the common cold or flu. Do not share this medication with another person, even if they have the same symptoms you have.

- drugs.com (http://www.drugs.com/amoxicillin.html)

As well as this:

Experts rarely agree, and there is a lot of controversy on the significance of the interaction between birth control pills and antibiotics. Amoxicillin is said to interact with birth control pills 1 percent of the time. That is a small number, but for most women, an unplanned pregnancy is a significant event. Most doctors recommend using a back-up method of birth control while you're taking antibiotics and for seven days after the antibiotic course is complete, just to be safe.

- Livestrong.com (http://www.livestrong.com/article/33056-amoxicillin-effects-birth-control/)

So just to be safe I would use condoms if you plan to be sexually active during the course of the treatment, as well as a week after the treatment is finished.

ETA Sorry, reading fail. Gah! Hmm, have you talked to your dentist/doctor about that? I would assume you'd be okay.... but then again I'm not a doctor.

Sorry for the huge comment and reading fail. :(