The purpose of this study is to investigate how teachers use different types of discourse to support dialogic argumentation. Dialogic argumentation is a collaborative process in which students construct arguments together and examine arguments presented by their peers. Science teachers can use argumentation as a vehicle to help students gain a working understanding of science content and the nature of science and its practices. Whole-class closing discussions from video-recorded lessons are analyzed to study the discourse used to support argumentation by two physics teachers in lower secondary schools. Analysis of discourse includes coding of communicative approach at the episode level and coding of teacher roles of questioning at the level of speaking turns. Student argumentation is also assessed on the basis of dialogicity and complexity of arguments. Findings characterize different ways of orchestrating argumentative discussions. Authoritative episodes were characterized by the presence of the dispenser role, with teachers retaining ownership over ideas and classroom activities to emphasize the correctness of a justification. Dialogic episodes of classroom interaction showed openness to student perspectives, but teachers' use of questioning roles revealed different ways of orchestrating argumentative discussions. The moderator role granted ownership of ideas to students to either pursue a single student's argument in more depth or to directly contrast opposing justifications. Less commonly used were the roles of coach and participant, which teachers used to elicit student justifications in more depth or support students in examining the arguments of their peers. Examination of discourse using multiple frameworks revealed differences in teachers' values and the impact of the use of teacher questioning roles on student contributions to argumentative discussions.