Sir, in his letter Mr Imran (BDJ 2011; 211: 245) states that I am 'out of touch' and unaware of the NICE guidelines which state that evidence by experience is the least valid of all evidence levels.

I invite Mr Imran to consider that my experience has taught me that the commonest cause of post-operative sensitivity subsequent to an amalgam filling is the failure to use a non-irritant lining of adequate thickness to protect the pulp from thermal changes. Does Mr Imran dispute this? Can my experience be the least valid of all evidence levels?

There is so much verbiage these days. For me 'evidence-based' means 'does it work?' I am reminded of the statement 'the operation was successful but the patient died!'

I accept that where the removal of all the carious dentine would probably produce an exposure, then a wash of calcium hydroxide underneath a non-irritant lining can be very effective. This is because calcium hydroxide has a very alkaline pH of 13.8 which is inhibitive for the cariogenic bacteria. A note is then recorded that the filling should be replaced in two years' time. Secondary dentine thus stimulated to form will permit further excavation of any residual caries without exposure of the pulp. Invariably the tooth will remain vital.

Regarding the application of Duraphat varnish to the perimeter of the cavity, the rationale behind this is that amalgam is the only filling material that advantageously expands when it sets. As it does so, the varnish is squeezed out and replaced by the amalgam, making a more effective seal with the tooth.