Prophylactic use of penicillin V in teeth with necrotic pulps and asymptomatic periapical radiolucencies. 
As a result of (1) clinical experience with flare-ups occurring in teeth with necrotic pulps and asymptomatic periapical radiolucencies and (2) on apparent reduction to the incidence of such flare-ups by the administration of penicillin V at the first sign of swelling, this study on the prophylactic administration of penicillin V in similar cases was undertaken.  The subjects were 100 consecutive clinic patients whose teeth had necrotic pulps and asymptomatic periapical radiolucencies.  At the initial visit, all teeth were instrumented completely to the radiographic apex, with 0.5% to 2.54% sodium hypochlorite as the irrigant.  Sterile, dry cotton pellets and ZOE restorations were used.  Alternate patients were given 250 mg of penicillin V and an identical-appearing placebo with instructions to take two tablets every 6 hours for the first 24 hours, followed by one tablet every 6 hours until all tablets were taken.  Pain and swelling were graded by the patients on five-point scales, and flare-ups were scored when either pain and/or swelling necessitated an unscheduled emergency visit.  Fifteen patients developed flare-ups, with significantly more flare-ups in the placebo group (p less than 0.05).  The findings indicate that, in selected cases, prophylactic penicillin can be used to prevent flare-ups.