One point of transition in tender tooth (8)
I believe the answer is:
bicuspid
'tooth' is the definition.
(I know that bicuspid is a type of tooth)
'one point of transition in tender' is the wordplay.
'one' becomes 'I' (Roman numeral).
'point of transition' becomes 'cusp' (I've seen this in another clue).
'in' is an insertion indicator.
'tender' becomes 'bid' (synonyms).
'i'+'cusp'='icusp'
'icusp' inserted within 'bid' is 'BICUSPID'.
(Other definitions for bicuspid that I've seen before include "Pre-molar tooth" , "CIS bid up the tooth" , "Type of tooth" .)