Thistle-tube appearance is a characteristic feature of:: (A) Radicular dentin dysplasia, (B) Coronal dentin dysplasia, (C) Amelogenesis imperfecta, (D) Dentinogenesis imperfecta
Answer is B. Radiographic features of type II (coronal) dentin dysplasia:
The permanent teeth exhibit an abnormally large pulp chamber in the coronal portion of the tooth, often described as ‘thistle-tube’ in shape, and within such areas radiopaque foci resembling pulp stones may be found.
Ref: Shafer's textbook of oral pathology 7th edition page 57