Unless your boss has to give you permission to take time off to go to the doctor or dentist, I would simply not tell him/her the purpose of the appt. Just say that you have an appt. and that you need to be out of the office.

Otherwise, I would simply ask your boss to stop. "I know you need to let the other staff know when I will be out of the office, but I would be more comfortable if you didn't specify the reason, which is personal information they don't need to have." His messages should read "Since Jane will be out of the office on Friday, here is our revised schedule."

Is your boss doing this for everyone they supervise? If so, I would start by not telling your boss about what you actually do on your own personal time which is totally different compared to if you were going to be out sick for a few days or more which may need to be relayed to the other staff.
Good Luck.

At our company, when a member of the administrative staff is going to take time off, we (the individual) send out an email letting the people we support know that we will be out. In our email message we give out as much, or as little, information as we feel is necessary regarding the reason for the absence and give them the option to contact any other member of the administrative staff for assistance during our absence, including their phone extensions. I agree with J. Charlton's posting, that you should check with HR since "There may be some privacy issues being violated by making a general announcement of your medical needs to others".

I let my main boss know when I will be out of the office and advise him that I will be sending out an "Out of Office" email to my other bosses (and as a courtesy to the staff). This way, he doesn't have to bother and it says what I think is appropriate and gives the staff an opportunity to bring me their urgent tasks.

Your boss may be breaking the law by telling others that you are going to doctor or dentist. Giving that information to others may present privacy issues. What I would do is just ask for time off for personal business (after all, what's more personal than going to doctor or dentist?). You should be sending Out of Office message to the others in the office. In the future, just tell all your coworkers that you are taking time off for personal business.

"I'm kind of embarrassed by my personal details being put out there, so if it's okay with you, just say that I am taking a little personal leave. Thanks for understanding my privacy." If that doesn't work, try talking to his supervisor about HIPAA and about FMLA rules.

I totally agree with Eunice, you should just tell your boss that you will be sending out the email to the dept/staff and only put what you deam important enough for them to know, which is "You will be out of the office". I'm sure they appreciate to only know that you will be out so they know they need to go elsewhere if an issue arises.

Did anyone ever see the movie "Working Girl"? I really did enjoy that movie as it depicted what a professional office and staff should look like, in spite of the ugly things that went on there between the boss and her secretary. Sigourney Weaver told Melanie Griffin that she was never in a meeting, but always on another line, something to that effect. It would irritate me so when someone would come to the office asking for my boss, and my co-workers would say she was out to lunch or at a meeting, whatever. My request to them was to say that she was not available and I would justify to them that it was no one's business what anyone in our office was doing, and that the same response should apply to anyone coming from the outside. Now maybe in an office and between co-workers, you could say a person is out, has an appointment, but the nature of personal business is not for all to know. This boss should show a bit more professionalism. Lead by example. So you need to take the lead and let your boss know that you would appreciate it if what you do on your personal business is not made known to everyone, and to stop making such announcements, and that from now on you will not be giving him detailed reasons for your requested time off. The same would apply if you called in sick, you don't have to tell them what you are sick from, just that you are ill, not feeling well, a generic reason.