One hour prior to surgery , patients had to take a single prophylactic antibiotic dose , consisting of 2 g of amoxicillin orally ; after implant placement , patients were randomly allocated to two different groups : protocol A ( no other antibiotic administration ) and protocol B , ( 1 g of amoxicillin in the evening of the day of surgery and 1 g twice a day for the 2 days after ) .