Invisalign® aligners have been designed and created to give them a snug, low profile fit that's unlikely to cause a speech impediment. That said, if you do notice a slight lisp due to your aligners, here is how you may be able to correct the issue.
Orthodontic Treatments & Talking
Any orthodontic treatment or dental appliance that comes in contact with your tongue has the potential to cause slight lisp or speech impediment. Invisalign's thin, sleek design and snug fit, may help to prevent speech difficulties from occurring.
In patients who do experience a slight lisp due to their aligners, the issue typically clears up quickly, as they become more accustomed to wearing their aligners.
If you notice a slight lisp or speech impediment when you first begin your Invisalign treatment, there's a good chance that it's only obvious to you, and will likely be temporary.
The Adjustment Period
As with any orthodontic treatment, when you begin your Invisalign treatment your mouth and tongue will need to adjust to making sounds and forming words with your appliance (aligners) in place. This period of adjustment shouldn't last very long.
After a few days of wearing your aligners your mouth will begin to adjust and any speech impediments you've experienced due to your aligners, should start to clear-up.
Aligners Fitted Incorrectly
In some cases, speech impediments can happen as a result of aligners that are not fitted properly. If you have given yourself a few days to adjust to your aligners, but your speech isn't back to normal, contact your dentist to ensure your aligners are fitted correctly. Your dentist wants your Invisalign treatment to be comfortable, convenient, and problem-free, so be sure to contact your dentist if there is an issue that needs to be resolved.
Correcting a Persistent Lisp
If your adjustment period has passed, and you've had the fit of your aligners double checked, but you're still experiencing a slight lisp, the next step is to practice practice practice.
Chat with your pets, read books out loud to children, converse with friends and family, just keep talking to in order to become more accustomed to speaking while wearing your aligners. There's likely to be specific words that you find more difficult to pronounce. Keep saying those words out-loud while wearing your aligners until it begins to feel natural. The more you practice the easier it should get, and soon your lisp should disappear.