Being familiar with the issue, I once read that a tooth has the capacity to regenerate itself, although I don't recall the information source, it was not the New England Journal of Medicine, having said that, and also due to the fact that I don't have any experience in the field of dentistry, I am just as perplexed about the matter as anyone else. I don't have much to offer, other than to mention that, either teeth do regenerate or, John Armstrong might have an excellent point in this regard. BTW, the whole Armstrong pro or con issue does ostensibly have a middle ground where a modus vivendi can be reached in the sense that while obviously, the two Oswald's aspect is very controverial, even those who poo-poo the idea, would seemingly have to concede that there sure were a hell of a lot of Oswald sighting's at places where Lee Oswald was supposedly somewhere else.
The question of Oswald sightings leading up to the assassination should be held separate to the photograph and apparent evidence of his youth. Although both issues create doubt, there's no necessity for them to be about the same individual. The youth aspect only provides a 'beginning' (with useful bits) to the alleged assassin's life. The sightings provide supposed evidence of 'intentions' and 'leanings'.
My spider senses are telling me the suggestion of three separate Oswald issues; 1 dead Oswald, 1 teenage Oswald photo and 1+ Oswalds via sightings will bring to the opportunist mind the desired freedom to operate ridicule. It may be wrong, but the idea or possibility is not ridiculous.
ST