The most common and most likely answer to this crossword clue is the 8 letter word OVERBITE
I've seen this crossword clue in Independent
O
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Buddy explains!

The straight part
We know that "how advanced top set is!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case how advanced top set is! = overbite.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does OVERBITE mean?
OVERBITE noun- A malocclusion in which the upper teeth extend over the lower ones.
- To use excessive acid in an etching process, so that the result is too deep.