It seems some big health insurers only have short waiting periods before you can claim on routine dental.
Routine dental can be quite expensive, even if just doing the checkup.
Is there any reason why people don't just take out the basic insurance cover 2 months (if that was the waiting period) prior to a checkup, then cancelling until the next checkup?
Depends how expensive your dental check-up is.
It is unlikely that you'll be covered for the complete cost of your check up — so it'll be down to finding a policy which assist you in claiming an amount greater than your 2 months of contributions.
My health fund recommended about 4 dentists in my area who would "fully cover" my treatment. But seeing as I'd be a new patient, all four of them wanted to do a "pre-appointment", which required me to attend their offices, get x-rays and undergo a basic check up prior to any further work. Surprise-surprise, the xrays wouldn't have been covered, so I reverted to my normal dentist, with whom I was able to claim about $180 off my $220 bill.
If your coverage amount with your regular dentist is $200 for general dental, can you find a policy which requires a 2 month waiting period where your monthly contributions would be less than $100?