useless trivia: What Word Means: A Borneo Camphor Tree?

Questions

---------- percent of the American population has never visited a dentist.?

Forty percent of the American population has never visited a---------- .?

---------- of all people who have ever smoked have now quit.?

Hay fever is the ---------- most prevalent chronic condition in the United States.?

Heroin is derived from the ---------- poppy, Papaver Somniferum, which means the poppy that brings sleep.?