This chapter analyses how teachers, in synchronous videoconferencing lectures of Didactics in Mathematics, manage silence to promote engagement. The epistemology of Mathematics, with its specific semiotic resources, requires special consideration to guarantee an adequate acquisition of contents and teaching procedures. A qualitative approach allows the analysis of multimodal interaction during significant episodes of absence of talk, in a teaching-learning context with different communicative channels, oral for teachers (who are in front of the camera) and written for learners (who use the chat). Results reveal the importance of the multimodal strategies used to repair teachers' and learners' silence in two main situations: the IRF (Initiation-Response-Feedback) cycle initiated by teacher's questions and the teaching exchange when interacting with materials.