De or het letselpreventie?

The correct Dutch article is:

de letselpreventie

Rule Words ending in -tie and -sie: almost always de. See the rule

How to use letselpreventie

the letselpreventiede letselpreventie
this letselpreventiedeze letselpreventie
that letselpreventiedie letselpreventie
our letselpreventieonze letselpreventie
your letselpreventiejouw letselpreventie
every letselpreventieelke letselpreventie
which letselpreventie?welke letselpreventie?
a big letselpreventie / the big letselpreventieeen grote letselpreventie, de grote letselpreventie