What are some reasons that an adult may develop a lisp that they have never had before?

Lisp: the sudden development of a lisp deserves an evaluation of the teeth, tongue, and oral cavity. So a dental exam is in order. Sometimes the thin attachment of the tongue to the floor of the mouth will become snagged between the lower front teeth when the tongue is in function, especially protruded. This functional problem is usually present since birth but can develop with shifting teeth.