Would a ct scan see an infection, more specifically a dental infection?

In some cases: CT Scans show differences in bone density. If an infection destroyed some bone, the area would look darker. Some changes are obvious and apparent while others require the experience and training as well as a judgment call of the doctor reading the scan. It will generally not show infections in soft tissue.

PA is needed: Periapical x-ray is good enough to diagnose dental abscess. A tooth infection will often express itself on an xray as a dark circular lesion at the apex. CT scan will also show infection and bone damage. Hope it helps.