A prophy is preventive in nature for someone who doesn’t have disease. Perio maint/SRP is for a patient that has perio: clinical attachment loss and active disease. The best way to explain is to show. Show patients their bone loss and/or radiographic calculus on their radiographs. If you don’t have an intraoral camera use a mirror to show them supra calculus and/or inflammation and recession of their gingiva. I keep pictures saved on my computer in my operatory of “healthy, gingivitis, mild – severe perio” and show patients that way too. To practice how to explain, when I was in school I would explain to my boyfriend “What perio is” and he would tell me what parts didn’t make sense, so I would adjust my explanation until it made sense to him.