Dear Annie: I have a beautiful 3-month-old daughter. We live close to my parents, and they baby-sit “Abby” all the time.

Here’s the problem. At my last dental visit, my dentist told me about a study that says adults with bad oral hygiene can transmit bacteria to children through kissing and sharing utensils, causing tooth infections in the kids.

My mom hasn’t been to a dentist in years. When I told her about the study and suggested she get a checkup, she blew up at me and now refuses to see her granddaughter. I realize my mother has a phobia, but I thought she’d make the effort for Abby’s sake. How can I make her understand that this is not an attack on her, but about the well-being of my daughter? — Clean Teeth in Pennsylvania

Dear Penn: Tooth decay is caused by specific germs and is more common among young children than any other chronic illness. Some of this is caused by poor brushing and flossing, too much sugar in the diet, and relying exclusively on bottled water, which usually doesn’t have fluoride. But it also happens when saliva is transferred to the baby’s mouth by eating from the same spoon, sharing cups and utensils, letting your toddler put your toothbrush in his mouth, or kissing the baby on the mouth if you have poor dental hygiene. Only those with active tooth decay can spread this bacteria. So when you blow on a bite of food, touch it to your mouth and then feed it to your baby, you may be transferring bacteria.

Your mother’s phobia is so severe that she has chosen not to see her grandchild rather than submit to a dentist. This not only damages her relationship with Abby, but risks her physical health, as poor dental hygiene can lead to heart disease. But there is a simpler solution. Please explain all this to Mom and ask her to be careful around Abby. Then wipe the baby’s teeth, tongue and inner cheeks with a clean, wet cloth every few hours, whether she’s around Mom or not.

Dear Annie: I have an etiquette question about holding doors open. How long or at what distance is it appropriate to shut a non-automatic door when someone is obviously going to be walking in after you?

I have waited for people who ended up looking at me weirdly, and I’ve accidentally shut the door on people who were walking faster than I expected. I also have had doors close on me by people who won’t wait regardless of how close I am.

I find it rude not to wait the few seconds to keep the door open, but how much time is too long? — Stuck in the Doorway

Dear Stuck: This is a very subjective question, and there is no exact answer. We’d say hold the door if the person walking behind you would arrive within 10 seconds. If the person has a large number of packages, a bunch of young kids or is disabled, wait longer. Please err on the side of kindness. A few “weird” looks are better than accidentally slamming the door in someone’s face.

Please email your questions to anniesmailbox@comcast.net, or write to: Annie’s Mailbox, c/o Creators Syndicate, 737 3rd Street, Hermosa Beach, CA 90254.