[AndyCambs]

I am not with it.
I think the costs advertised at the dentists were something like £8 per month.

An inspection costs £17.50 (including scaling) on the NHS plan.
Fillings, and extractions cost £46.50 (any number of fillings).

So on the basis you'll have two inspections, and two treatments each year, both of which include fillings - that's a total of £93 per year.

using the HSA - £7.70 per month - that works out at £92.40 in total, but then according to the website you only get reimbursed for 75% of the treatment costs. So it would work out more.