Usually, you will get used to your trays and the lisp will go away, especially if you put the attention into the intention. However, if you happen to have bite ramps, may be the source of a more pronounced lisp. The more you speak with them, the less it will be noticeable.
Keep in mind that most of the time you perceive your lisp stronger than it sounds to others. After all, you are looking after yourself and making yourself better and healthier. Be proud and don't be shy.