So can poorly aligned teeth!
One major cause of lisps and whistling while talking is an overbite. The air escapes while making sounds that involve the tongue pressing against the teeth. Gaps between teeth can cause lisps as well. These can be fixed with orthodontic treatment.
Dental crowding or jaw structure sometimes restrict the tongue’s movement, making slurring or stuttering more likely. Braces can correct that too, giving the tongue all the room it needs to enunciate.
Not all speech disorders can be improved by orthodontic treatment, but for those who have malocclusions, crowding, or crooked teeth, having straight teeth can certainly make it easier to speak clearly. Plus, properly aligned teeth look great, they’re easier to clean, and they even improve digestion!
Don’t let a fear that the braces themselves might make it harder to speak get in the way. It might take some practice to speak clearly around them, but the end result is worth it.