Currently when doing letters via email out of the EHR Narratives, you have options for referrer, general dentist and patient. (print / send as email when possible).
There are merge fields for cotherapist, just not an email option.
Scenario - Patient is referred for endo treatment by GP / perio - tooth is non restorable and needs to be extracted - GP preference is that the office send patient directly to oral surgeon. The oral surgeon is the cotherapist but cannot be included via the email option