The Defiant "nose" was used in the Deep Space 9 episode "One Little Ship". In that show, a runabout was caught in an anomaly, and "shrunk" to a fraction of its normal size. The "nose" was used in a scene when the runabout was re-entering the Defiant... presumably the actual Defiant model did not have enough detail to look realistic when magnified.
Here's some screen caps:
In real life, the Defiant "nose" was in good shape when received and needs little fix up (although perhaps it should be relit, hmmm). Here's a picture.