A Doctor needs three things if he's to be effective in his work: a sonic screwdriver, a dashing wardrobe and a key. A very important key.
As each Doctor has changed his attire/flesh/actor, he's also changed his preferred option for accessing the beloved Tardis - from classic cut Yales to spade-shaped devices.
Whovian and dedicated Doctor cosplayer Terrasolo has helpfully charted the evolution of the Tardis key, from the first to the eleventh doctor. There are also details on the eight keys used by the Doctor's companions and friends.
While the shape and details of each key are nearly perfect, Terrasolo notes that the teeth aren't identical - these keys only match the door on his Tardis.
Check out more of Terrasolo's Doctor Who work on his DeviantArt page.
(Click to enlarge)