De or het beugelbehandeling?

The correct Dutch article is:

de beugelbehandeling

Rule Words ending in -ing: almost always de. See the rule

How to use beugelbehandeling

the beugelbehandelingde beugelbehandeling
this beugelbehandelingdeze beugelbehandeling
that beugelbehandelingdie beugelbehandeling
our beugelbehandelingonze beugelbehandeling
your beugelbehandelingjouw beugelbehandeling
every beugelbehandelingelke beugelbehandeling
which beugelbehandeling?welke beugelbehandeling?
a big beugelbehandeling / the big beugelbehandelingeen grote beugelbehandeling, de grote beugelbehandeling