It's very possible that the procedure code is 'Dentist Limited' and the reason why the Hygienist is unable to post or be an option to select from.
To resolve, please go to Setup / Procedure Codes / Procedure Codes / select the code / Edit / and uncheck the 'Dentist Limited' field and Save.
Note: If the procedure is restricted to be performed only by the dentist practitioner, the box should be checked. If the procedure can be performed by a hygienist, an assistant, or other staff member, the box should not be checked.