Comparison of Tyrannosaur denticles (serrations) from the Hell Creek Formation. All of the images are set to the same scale
Some differences are likely associated with position in the mouth and/or feeding wear. So, this may not be a perfect illustration of purely ontogenetic variation.
The adult T. rex denticles are from an unknown position and carina (being from a tooth fragment), the juvenile T. rex denticles are from the distal carina of a right (rear?) maxillary tooth, and the infant T. rex denticles are from the distal carina of a posterior tooth. The Nanotyrannus denticles are also from the distal carina of a posterior(?) tooth.
The Nanotyrannus denticles are noticeably different. That could be because of lack of wear, age of the animal, because it may be a different species, or a combination thereof.