What can cause a lisp after going to the dentist?

Anesthesia: Local anesthesia given during your visit is the most like cause for any difficulty with speech, it should resolve within a couple of hours.

Lisp: What type of procedure did you have done? Is it still there? A little more info would be helpful

Very common: You may speak with a lisp or sound a little muffled after the dental anesthesia, but the issue should resolve within approximately 3-6 hours.

Treatment ?: What treatment did you have? Any anesthesia? A little more info would help with a meaningful answer.

Lisp from?: The only time I have personally experienced having a patient lisp is when prosthetic teeth are improperly positioned on a full or partial denture during the try-in phase (until they are then re-positioned correctly during the same visit. It can also occur if the teeth are not properly adjusted in a protrusive excursion. I guess if not corrected during the visit, can experience afterwards.