Ball gag
From Voyeurweb's Wiki about Sex
The Ball gag is a type of gag and sometimes used in BDSM play. The ball is strapped into the mouth behind the teeth, with the straps going around the head to secure it in place. Many people are sexually aroused by the sight of gags. After you applied a ball gag to her, she is not able to talk any longer and you have no access to her mouth.