In order to find the correctly spelt word from the given options, we assess each spelling:
Quintessance: Incorrectly spelt; it does not accurately represent the pronunciation or etymology.
Quintessence: Correctly spelt; it is derived from the Latin 'quinta essentia' meaning 'fifth essence'. It refers to the most perfect or typical example of a quality or class.
Quintesance: Incorrectly spelt; it has an error in reproducing the word 'essence'.
Quintassence: Incorrectly spelt; it mistakenly adds an 'a' altering the word structure.