Why have i developed a lisp as an adult?

Sigmatism, or lisping: is difficulty pronouncing sibilant sounds like "s" & "z", usually because of improper tongue placement. Of the ~ 7 types of lisps, interdental or frontal lisp from tongue-thrusting is the most common. Physical or psychological factors can cause adult-onset lisp. Evaluations by a primary care physician & a dentist determine if both speech/language & psychotherapy are needed.