Antiseptic would just mean something like alcohol or iodine. Antiseptics became commonplace before antibiotics were discovered. (IOW, widespread acceptance of t

Antiseptic would just mean something like alcohol or iodine. Antiseptics became commonplace before antibiotics were discovered. (IOW, widespread acceptance of the germ theory of disease preceded discovery of antibiotics.) I assume "injection" here is referring to something like a bulb syringe or pipette, neither of which pierce the skin but simply a way to extract and apply a liquid, e.g. antiseptic solution. Because presumably the tooth wounds were so deep, inserting the tip of the syringe into the open wound when applying could be described as injecting, especially in more florid prose.