Since there are no sources for this person, I am not sure where the death information comes from.
Please see Find a Grave https://www.findagrave.com/memorial/53147313/samuel-dennen and
https://www.findagrave.com/memorial/53147416/keziah-dennen for the burial of this hasband and wife
Samuel's tombstone gives birthdate as 12 Nov 1732 in Gloucester, Mass and Death in 1798 in Minot, Maine
Both are buried in the Sieberling-Whitham Cemetery in Minot, Androscoggin County, Maine, USA