still require the body's natural immune system and blood stream. Antibiotics
enhance the immune system, but are not a substitution for it.
When bacterial cells are killed, by either method, the cells do not disappear. The body still needs to clean them out, which is the job of the blood and lymph systems. Teeth have no lymph system, unlike everywhere else in the body. As with the pressure buildup, the lack of blood flow into the tooth with fresh, clean blood to remove the infection and dead tissue is not possible.
So, injection of Antibiotics
into the tooth will not help, because you still need that natural flow.
Another difference from the body and the mouth:
The internal body in general is an aseptic enviornment, meaning no bacteria.
Now, one would ask, what about the digestive tract? Remember, the digestive tract is outside the body, completely connected with the outside enviornment by the mouth and anus. Bacteria live and grow outside the body, but are never allowed in. Just as your skin (epithelium) protects what is seen as the body's exterior, a layer of skin (endothelium) protects the digestive tract linings.
Your mouth is part of the external enviornment directly, and as such is teeming with bacteria, even in what would be considered a clean mouth. Your saliva is the perfect enviornment for bacteria to grow, warm and moist. Only the constant flow of fresh saliva keeps a majority of the bacteria controlled. But, since your mouth is not part of the internal body, the immune system has little to no control over what happens.
Your teeth are in a unique position, connected to both the external enviornment and the internal body. The enamel is for teeth what skin is for the rest of the body, the natural barrier between the bacteria outside and the vulnerable tissue inside. Once broken, that layer needs to be replaced for the body to function correctly. Unfortunantly, the cells that created the enamel are located outside of the tooth, and when the tooth erupts into the mouth, they die. Hence the need for a filling, to replace that natural barrier between external and internal enviornment.