Hi, this baptism has him as Thomas Dent so maybe his parents weren't married at the time:
Name:Thomas Dent
Gender:Male
Baptism Date:27 Apr 1817
Baptism Place:St. Margaret, Barking, Essex, England
Father:Joseph How
Mother:Emma
FHL Film Number:1471843
Reference ID:item 9 p 106
have you tried looking under Dent?
Diddy