Hi, Tolis. Welcome to Opera Lively! When you ask "how often" I'd answer 100% of the time (depending on the opera) for the voice types you mentioned, because all these singers transition between chest and head voices at different points of an opera (that is, according to the notes they need to produce; often when there are notes at or above E4 the singer will need to resonate the voice predominantly in the upper head structures (sinuses). The transition point is called the passagio. This voice teacher, for example, encourages the concept that it is a continuum rather than two separate registers; read her explanation:
http://mollysmusic.org/blog/head-voi...ice-explained/
Even bassos transition. The only category of singers who *might* not transition would be the countertenors who will often keep their voices within the head register, but even countertenors will also use some sort of chest voice which will correspond to their speaking voice (not falsetto) when they are singing lower notes.
The bottom line is, it's the vocal score, and the singer's range and comfort in each register, that will determine where the resonance will be. Of course if an opera role requires no high notes whatsoever, a singer may only use the chest register for that role.
But all singers are capable of transitioning between these registers. So, yes, tenors use chest voice too, and so do all others.
By the way, given that you are from Greece (I think you may be our first member from there), you will enjoy reading the interview I did with the head of the Greek National Opera maestro Myron Michailidis when I visited Athens a few years ago. Here is the link:
http://operalively.com/forums/conten...National-Opera
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