How teeth are said to appear to explode (5)
I believe the answer is:
erupt
I believe this is a double definition.
'how teeth are said to appear' is the first definition.
(tooth eruption is a dental problem)
'explode' is the second definition.
(erupting is a kind of exploding)
'to' acts as a link.
(Other definitions for erupt that I've seen before include "spout" , "Discharge" , "Break out suddenly and violently" , "Break out like Etna" , "Break out dramatically" .)