  We define essential commutative Cartan pairs of $C^*$-algebras generalising
the definition of Renault and show that such pairs are given by essential
twisted groupoid $C^*$-algebras as defined by Kwa\'sniewski and Meyer. We show
that the underlying twisted groupoid is effective, and is unique up to
isomorphism among twists over effective groupoids giving rise to the essential
commutative Cartan pair. We also show that for twists over effective groupoids
giving rise to such pairs, the automorphism group of the twist is isomorphic to
the automorphism group of the induced essential Cartan pair via explicit
constructions.
