Since the receptionist gets the email/call, I recommend providing your CV/resume and contact information so that there isn't much of a back and forth communication between you, receptionist, and dentist.
The easier you make it for the dentist, the easier it is for you to have a shadowing opportunity.
Also, every dentist is different. Once you get a chance to speak with a dentist, make sure you find out what is expected of you. Be smart about it and ask important questions.
If the dentist doesn't allow you to do anything but stand in the corner and watch silently, the experience is worthless imo.
On a side note, if you were to shadow where I work, you would almost have zero time to ask questions directly to the dentist. However, you'll be allowed to help out and learn from assistants.
This will give you a different perspective on dentistry as opposed to a more relaxed office where you can assist the dentist and ask questions during procedures.
I think for this reason it's beneficial to shadow at more than one office to get a broader perspective. (Also to see a variety of procedures)