After finishing my PhD in the US, I am now working in a university in an Asian country where I studied for my master. All of my colleagues are 20 years senior than me and are full professors except one. I am wondering what I should call my colleagues. Should I address them as "Teacher" if I've ever taken a class from them? (One of them is my master advisor which is especially awkward for me to call his name.) Or should I address them by their "First Name" to emphasise that our current relationship is not teacher and student anymore? (They usually call each other by First name since they are all in similar age group, seniority, and male?)
By the way, I've been in this position for 1.5 years but I never call them by their first name, it's usually ‘Teacher’ if they previously taught me; or "Teacher xx(Last name)" if they never taught me. Would that be awkward if I just change how I call them now?