Very strange. Are you certain that nothing is setting the SourceObject of
the subreport control?

If not, we must assume there is something wrong with the database. Try this
sequence (in order):

1. Uncheck the boxes under:
   Tools | Options | General | Name AutoCorrect
Explanation of why:
   http://allenbrowne.com/bug-03.html

2. Compact the database to get rid of this junk:
   Tools | Database Utilities | Compact/Repair

3. Close Access. Make a backup copy of the file. Decompile the database by
entering something like this at the command prompt while Access is not
running. It is all one line, and include the quotes:
   "c:\Program Files\Microsoft office\office\msaccess.exe" /decompile
       "c:\MyPath\MyDatabase.mdb"

4. Check the Name of both subreport controls. Rename the Dental subreport
control (not the report in the subreport).

5. Open Access (holding down the Shift key if you have any startup code),
and compact again.