I have heard that a dental abscess can cause acne. Because the bacteria from the dental abscess escapes into the body and the body cannot kill it, so it causes pimples. So once the dental problem is fixed, the acne will go away. Is this true?
Acne can be caused by several things, one of which is bacteria. The bacteria involved in acne are called Propionibacterium acnes. This bacteria species usually only colonizes the skin. Its main source of energy are the products of skin glands. In people with overactive glands, they grow to large numbers, and their byproducts lead to the inflammation known as acne.
Dental abscesses are caused by a variety of anaerobic bacteria and the toxins they produce. Propionibacterium acnes would not get to the location of the dental abcess and would not outcompete the anaerobic bacteria in there because it is relatively slow growing while the bacteria causing the dental abscess are fast growing under the conditions present.
Furthermore, there is no need for this anyway. Propionibacterium acnes is present on the skin of most healthy adults.
There is, however, one case report from 1999 linking a case of dental abscess with the appearance of acne. The full case report is not accessible anymore and I can't find any paper citing it. That case report, however, also does not propose the mechanism you describe.
We believe that the presence of our patient's dental infections provoked a follicular inflammatory response resulting in his recalcitrant acne.
I interpret that as them saying that the immune response to the dental abcess might have triggered an immune response to the already present Propionibacterium acnes
Sources and further reading