Most of the time when you receive a new denture whether it’s implanted or not even a new partial, your speech will be affected, in a way that some people will say they can’t understand what your saying, or you yourself may notice your wording isn’t as clear as before.
This is quite normal and very common.  One of the main reasons is that and especially if your previous dentures were very old,  because the vertical height of the news dentures has been increased to make up for the old dentures been worn down from usage and the deterioration of the bone and tissues in your mouth.
It can also be because the new dentures are larger.  Most of this are necessary evils, but as I mentioned in earlier questions, it all can be remedied, reduced, and adjusted, so in time you should be speaking better.
If this is not the case, and the front top teeth have been positioned where they should not have been, either too far forward or to far backward, then you have a problem.
If the teeth are not where they should be, then you will never be able to speak properly, and the only remedy is to have the dentures remade with the teeth in their proper position, and this will  give the tongue the correct space in which to help you speak properly.
If after the designated amount of time from your practitioner your speech is still not right, request that this be remedied whether by a simple adjustment or having the front teeth repositioned.  There  a few ways this can be done, discuss all the options  with your practitioner.
Thank you,