In my experience, in the US, an annual checkup is customary. If someone is prone to cavities, then perhaps a more frequent visit is recommended.
Apparently, the American Dental Association recommends visiting the dentist twice per year. In one survey I found, 62.5 % of those surveyed visit the dentist once a year, where 25% visit the dentist twice a year, and 12.5% visited more than twice per year.
The American Academy of Pediatric Dentistry indicates the 6 months is the most common interval for a dental visit.