Hmm, you know upon further reflection, I forgot to complement, the OP on a Job .. "Well Done!" They did there research! There"Vet," told them there dog has an under bite? And they said OK, well ... perhaps I'll go to a Boxer forum, and see what they say??
And I "missed that??" I "forgot about the OP," and went for the obvious ... a "Boxer has an under bite?? Well, yeah no crap, would be the obvious answer!
But ... think about it, how do lot's of us come to that answer? We either read alot or have had Boxers, several or one or two for years (if we are lucky) and 5,10,15,20 years or more of life "experience with Boxers!"
But ... wipe that out and go back to your first Boxer and the vet say's ... "Your dog has an under-bite?? And what do you think then?
The OP did ... "Exactly what I did," ... when I had my issues with my "First Working Line GSD," uh not, a "Boxer!"and I went online and looked for "Answers from trainers that dealt with dog's with serious issues," and if what they did made sense to me ... "I'd do that!"
And well ... I "modified as I saw fit, somethings I had done anyway, but put a spin on them. Human Aggression was my issue but ... I looked online for answers and then used my "Judgement," to determine what was best for me and my dog ... and it worked out fine!
But going way, way, way back ... before the "internet was a "thing??" The "Vet was the first point of point of contact for people with a new dog. But Vet's are "Not," Dog Trainers, they are not "Behaviorist," nor "Confirmation Experts." They are Health Care Experts, that is what they went to school for, "Medical Issues."
When I took my, "Struddell (White Boxer) , into a new vet, my first question ... "was have you worked on Boxer's?" And then of course, the "Ace," question. Now he may or may not have thought the "question was odd?" But he said ... "No problem, we can use something else. It went fine. "
But for the most part ... when people have dog behavioral "Issues?" They have no idea what is going on and who to contact? And there "typical, first point of contact ... would be there vet. This was a slightly different, as it was a "Conformation, thing," but my point is still valid ... they went to "who they know."
A "Good Vet," should be able to point a client, to a "Behaviorist, or a Dog Trainer, or "Confirmation's," (Dog Show Judge) I could not do that job cause to me ... "Every Boxer would look like a winner!") But most likely a local vet, has treated those trainers/owners dog's?
Those are all different discipline?? There is "overlap, between a "Behaviorist and a Dog Trainer?" And long story short ... I "thought, that I was, more of a ,Dog Trainer," than I a "Behaviorist?" But that is another story.
So (New) owners are gonna go first to someone they know and trust? So the Op did that first and then reached out to us. And I just went with the obvious (Boxers have an under-bite) and forgot to say ... "Job Well Done on your research!" And I think you and your new "Doggy are gonna do very well together ... "Welcome Aboard!"