If, within two months of completing a course of treatment, you require further treatment within the same charge band or a lower charge band, e.g. an additional filling, you don't have to pay anything extra.
However, if you need further dental treatment after two months of completing an earlier course of treatment, you will have to pay an additional charge.
If your initial treatment is classed as a separate, urgent treatment, it may not be included in any subsequent course of treatment that you require. For urgent dental treatment (including out-of-hours treatment), you will have to pay a separate charge of £16.50.
You will not have to pay for:
denture repairs,
the removal of stitches, or
if your dentist has to stop blood loss.
There is also no charge if your dentist only has to write out a prescription. However, if you pay for prescriptions, you will have to pay the usual prescription charge when you collect your medicines from the pharmacist.
Got this from MHS website. Seems you do need to pay extra 16.5 pounds.