Conflicts between team members

If you succeeded in erasing tension within your improving team, what might the consequences be for productive dissent?

I wouldn't "erase this tension in the retrospective".  Instead I would encourage it to be discussed.  Sometimes tension is needed in order to get a team to higher levels.  This is all part of the Scrum Values of trust, openness, courage, and respect.  While you have talked about it with the individuals, the rest of the team might benefit from discussing it also so that the individuals can see how they impacted everyone else. 

I don't see this as an impediment so why are you trying so hard to remove it?  @Ian's question is spot on.  What is the harm in productive dissent?

I would  

• coach the members and encourage them to resolve the conflicts by themselves. 
• remind them about whole team failure due the conflicts.
• encourage them to find a common ground towards common goal. 
• narrow down to the specific conflicting point(s) and push them to deal with it later (if it is alright)

The above steps always worked for me.  I never had to escalate anything or had to use any common meetings to deal with them until now.  

I think it really depends on the source of the conflict.  Is it personal or professional?  If it's professional or a disagreement on methods, then I think the team needs to be involved to reach consensus, if it's personal, then I you are better off asking the two to resolve it between themselves, but making it clear that you won't let it affect the productivity of the team.