I had zero connections to dentistry. I called about 10 offices until someone gave me a chance. I noticed that calls definitely will generate a response better than a random email. Ask to speak to the office manager, tell them you're pre-dental and if Dr. Soandso has had shadowing students before. Offer to email a CV with a compelling intro on why you're interested in dentistry. And if they ask when you'd like to come in, say "this week!" otherwise they'll probably forget about it. Once I shadowed there, not only were they willing to have me come back, they also put me in touch with other dentists. And then boom you have a dental network. Good luck!