David's teeth

Can somebody please assist:
As a new - and therefore obsessively observant - DT fan, I noticed in "Blackpool" that David was displaying a somewhat snaggly toothline. Nothing wrong with that: I don't want any white picket fences, with each post identical to its mates. I just noticed it, that's all. [Given the number of scenes when the camera seemed to be filming DI Carlisle from beneath his chin, and given that Carlisle has his mouth open a lot of the time, the uneven teeth were hard to miss!]

Anyhow, it dawned on me, after receiving the dvd, that Casanova had had a bit o' expensive dental work done. His two front teeth seem now to be the same length as the two on either side of them......

AND THEN came the curious line in 'Casanova', when Jack and Rocco are hurriedly leaving the grand house that Jack has just lost by his gambling. The baillifs are all but upon them. Jack makes a throw away remark about having gambled away even his teeth. "They're nice teeth, too" says Jack and bares them for Rocco to see......
So, was Tennant cheekily ad-libbing? Or did Andrew T Davies, the author, give him a pertinent line to say, knowing that DT had spent some down-time having caps or crowns or veneers fitted? Or what?

[i]edited belatedly to correct a couple of errors. And now? I'm actually not at all sure if was right to wonder about whether DT had his teeth done, between Blackpool and Casanove........Ack!!!!!!!They look a bit the same....... [/]