I don't think he is talking about 'regrowing teeth', he's talking about repairing a cavity. I know very little about the science of this, so I could be way off

I don't think he is talking about 'regrowing teeth', he's talking about repairing a cavity. I know very little about the science of this, so I could be way off, but I suspect what is happening is. 1) stop further decay 2) allow calcium/mineral/other to build up in the location of the whole. As long as the nerve isn't exposed and deterioration has been stopped, isn't that the same as 'repaired teeth'?