The England winger cost £15million when he moved from Blackburn to White Hart Lane in the summer of 2008.
However, a lack of first-team opportunities has led to the 26-year-old making the temporary switch to Blues.
"The aim is to resurrect my career and I love football and just want to have the chance to be playing," said Bentley.
"It has been a difficult time for me the last couple of years. I found it hard not being involved as much as I wanted at Tottenham. They have got some great players and you can find yourself the wrong side of the fence.
"But there was no fall-out with Harry Redknapp and it is time to put things aside, move on - and hopefully I can have a positive effect on Birmingham."
Blues boss Alex McLeish wants Bentley to ensure actions speak louder than words after confirming he will be included in the squad for Sunday's home derby with Aston Villa.
He said: "He has great quality and he is at an age where he has taken stock and it is time for him to show the quality which led to him playing for England.
"It is time for his boots to do the talking. Ron Atkinson always used to say 'don't tell me, show me.'"
McLeish remains hopeful Rangers striker Kenny Miller will make the move to Blues in the next 24 hours. But winger Sebastian Larsson's move to Newcastle looks in doubt after the player failed to agree terms.
The Blues boss said: "Newcastle made a bid but I don't think Seb could agree terms so he is still a Birmingham player."