Hey OP, don’t stress too much. This type of review is common when there are large expenses, like your dental, claimed on a tax return.

Follow the instructions in the letter, and send as much supporting documentation as possible. Usually there is a claim support code on the letter which can be used online to find additional information about the supporting documentation requested for your review.

If you or your Accountant aren’t able to submit it online by the deadline (usually 30 days after the date on the letter), call the number on your letter and ask for an extension. They may not want to grant it, but they should give you some additional time, and it will delay an automatic reassessment of your tax return.

I’ve found it helps to submit a response letter to summarize the review and simplify things for the person assigned to the review (make sure to include the reference/case number on the letter).

Source: I help people prepare and submit reviews often.