How important is it to have the mouthpiece exactly centred in the middle of the lips when playing the trombone?

About a year before she started playing the trombone my daughter fell over and knocked out one of her top front teeth. The A&E put the tooth back in but too high. I won't go into the full dental details but the end result is that one tooth is considerably higher than the other - it looks the way children's teeth do when they have lost a baby tooth and the adult one is still in the process of coming through. When she plays the trombone the mouthpiece is off centre, away from the side where the tooth is too high.

Her teacher wants her to play with the mouthpiece in a central position but my daughter keeps complaining to me (not to him) that it is more comfortable slightly to one side. Part of me thinks that this is just because she is used to having it slightly to one side and so a new position feels unfamiliar but since I know nothing about brass instruments I did wonder what effect the mis-placed tooth has on the way she "feels" her embouchure (and also possibly on the sound).

I would like to know a bit more about it to try and decide whether I should speak to her teacher or not.

To put things into long-term perspective, in a year or so the dentist wants her to have fairly extensive orthodental treatment (probably involving removing this tooth, realigning the others and cosmetically making one of the others look like a "proper" front tooth) but he wants to wait until more baby teeth have fallen out and her jaw has matured a bit more. No doubt all this will have an effect on her embouchure too.

Playing off-centre would normally be thought inappropriate for someone with symmetrical teeth, but some good brass players have played off-centre, mostly because of similar problems to your daughter's. Moreover, at one time (I don't know the current position) it was quite usual for trumpeters who doubled on cornetto to play the trumpet centrally and the cornetto, of which the standard mouthpiece is very small, well to one side, with no overlap of the parts of the lips involved. I do this when I play my mute cornett, and my horn embouchure is not exactly symmetrical, as I have lost my upper right 2 tooth.

Fundamentally important IMHO

Sure, you can play to a good standard with an off-centre embouchure but it can cause all sorts of problems on the trombone if you don't. As Ken said, some trumpeters, horn players etc do play off centre but not generally trombonists as range becomes a big issue with an off centre embouchure.

Your daughter's teacher is right to make her adjust now at this young age - the longer you leave it, the harder it gets to fix it.

You need to persuade her to move it more centrally. If you don't move it back now then it will cause huge problems if she decides to go to music college or anything like that because she will spend the majority of her time (and probably your money) moving it to a central position and building her range again.

If she does have this orthadontal work done it could seriously hinder her progress so if you move the embouchre to the right place now it will give her one less thing to do when everything is back to normal.