When I was 9 I broke my two front teeth, it did not hit the root but it was extremely close. The dentist used bonding to fill in the half of the missing teeth.
When I was 11 I went to the dentist for a routine cleaning and I told him there was a sore in my mouth and it hurt really bad. I had an absesed tooth the dentist thought perhaps from the trama of my accident, it was so bad that the root completely died, the dentist performed a root canal on the tooth that absesed. Bonding was still used to fill the halves of the missing teeth.
When I was 18 I got Venners for the two front teeth, no problems with my teeth.
I am now 23 years old and as of a 2 days ago my tooth (the one that has no root) started to throb, it feels sore and it hurts, even hurts when I brush my teeth.
I've always been afraid of losing my tooth that has no root and I have always been self conceious of my teeth even though I have Venners now and no one can see that they are broken.
Could this be something serious, should I visit the dentist or did I perhaps bite down too hard on it or something?
Am I going to loose my tooth?
A little background on my dental hygiene, I have never had a cavity, I brush my teeth like a fiend and use floss and mouthwash.
Please help :(

When you say the tooth with "no root" do you mean the one that had a root canal or did one of the teeth lose it's root due to resorption? When a tooth has had a root canal, the root is still there, there is just no nerve in it.
If you are talking about the tooth that has had the root canal causing you this discomfort you should see your dentist and have him/her take an x-ray of it. You can get secondary infection years later (root canal failed) or the root could be cracked.

There are cases of the dentist not getting ALL of the root, and this can become infected years down the road.

I had it happen once, and it was under a crown, boy you talk about pain!!

I would see the dentist for an x-ray to determine what the problem is.