Four fire engines and around 25 firefighters tackled a fire at King's College Dental Institute in Denmark Hill.
The Institute's staff evacuated around 400 patients and 80 colleagues from the building over seven floors. There were no reports of any injuries.
An area of roofing felt on the building's first floor was destroyed by the fire. Fire crews removed this as they worked to get the blaze under control, successfully preventing the fire from spreading into the building.
Station Commander Brin Powell, who was at the scene, commended the Institute's staff for acting so quickly: "The Institute's staff got the patients and their colleagues out of the building very quickly and they followed their procedures to do this, which kept everyone safe."
The Brigade was called at 1246 and the fire was under control by 1510. Fire crews from Peckham, Brixton, Old Kent Road and New Cross fire stations attended the scene alongside an incident command vehicle.
The cause of the blaze is under investigation.