Found it! If you go under the employee file for a specific employee and find the T4 and RL-1 Reporting tab.  There is Dental Insurance line and it allows you to change the code there. So you don't need to report their specific dental premium payment.

I would like to select a group of employees to have dental benefits?  Looks like sage make you chose each individual employee

I did this but box 45 does not appear on the individual T4 slips. Did it work for you?

Hi Marie, I think the first time you go to do the T4's I think you have to check off Box 45 to add it to the T4 copy.

box 45 show up in the middle of the top of the T4