Add together the patient contribution and that which is paid to the dentist. i.e., the full cost (to the government) of the dental appliance.
In Scotland you seem to say the patient pays no nhs contribution, so, the full cost of the particular dental appliance paid by the government to the dentist.
How would adding a contribution made to the government to a payment from the government give you a full cost?
You would need t subtract the contribution from the payment and even then that is inaccurate as the contribution covers other items such as exam, radiographs, any fillings, extractions, root treatments etc.
In Scotland, it is only currently that the fee is waived for the patient; normally they pay 80% of the NHS charge for that item of service (like it used to be decades ago in England)