The easiest way to get this information might be the treatment success report. This report is designed to show you when a patient has had further treatment on the same tooth as previous treatment in a time period. But you may be able to use it to search a treatment item on the time bases that you need, and it will show you every time that item was completed, the patient, and when that item was completed. I have attached a screen shot of the report run on my system so you can see if it will be any good for you.
If you do like the look of it, to run it:
From the main menu click reports
The in the report manager open, reports about treatment
then highlight "treatment success" and click run
On the report details screen, put in the date range, select the scheme (it is one at a time i'm afraid) then select the code you to look up.
Let me know if that is any good for you, otherwise we can look to see if there is another way to get the information you need.
It is also possible to create your own custom report that will display a list of patients who have had a specific item of treatment between 2 specific dates.
I have attached a copy of a guide showing how to do this.
When you run the query you will need to know the number of the treatment item that you wish to audit on your system.