Adults are the market that grows and the one served worst. They search with clear price intent, usually in the evening, and they also compare companies that post aligners out — explaining the process and the supervision is what beats the mail-order model.
For a child it's a parent searching, filtering on eligibility, distance and appointment time. A page that deals with after-school slots and the NHS question recovers enquiries that were heading to whichever practice sits next to the school.
The names of the clear aligner systems are trademarks and awkward to advertise around. Writing about the process, the wear time and the check-ups is safer and ranks just as well — usually better, because it answers the actual question.
Retention is a search almost nobody writes for. "Do I need a retainer forever" gets typed constantly by people two years past treatment, and answering it brings in patients who never had their treatment with you.