BANGOR, Maine — The plastic knife was no match for the chocolate sheet cake with its thick layer of white icing and purple flowers. Katherine Musgrave, wielding the knife, was getting the frosting all over her hand.

“I’m going to lick my fingers,” Musgrave said in her Southern drawl, eliciting laughter from the 10 people in the room who watched her slice into her birthday cake.

It was unclear what was funnier — the thought of a 90-year-old woman licking her fingers, or Bangor’s best-known and beloved registered dietitian giving in to all that sugary goodness.

Musgrave celebrated entering her 10th decade Monday, the day of her birth in 1920, during an informal lunch party with the doctors, nurses and staff members in the Evergreen Woods offices of Drs. Jane Laeger, Ellen Bentley and Paul Shapero. Laeger and Bentley are gynecologists, and Shapero is an allergist.

Musgrave’s work as an on-site dietitian for the three doctors is, amazingly, one of the jobs she still performs weekly. Musgrave is a professor emerita at the University of Maine and teaches an online course through UMaine’s Division of Lifelong Learning, and can be heard Monday mornings during a nutrition segment on Bangor radio station WZON, during which she discusses ideas for healthy living.

She also runs the nutrition component of corporate wellness programs for several local companies.

UMaine awarded Musgrave an honorary doctorate of science in 2006. In 2002, she was presented the New England University Continuing Education Association Faculty Member of the Year Award.

Longevity runs in Musgrave’s family. Her father and mother lived to 92 and 91, respectively, and two of her three brothers are still alive.

Musgrave regaled partygoers with tales of her upbringing on a farm in Tennessee and the early days of her married life, when she followed her husband across the country from posting to posting in the military.

As Musgrave picked at her cake, she turned serious when asked for her thoughts on the recent shooting death of a 19-year-old man on Cumberland Street in Bangor. An 18-year-old man has been charged in the incident.

“I think these kids who just pick up a gun and shoot have only seen [death] on TV or movies and have no idea about life and death,” Musgrave said. “I think it’s a shame for kids to not know more about life and death and reality. … [But] I think young people today have a lot of good principles. I’m not worried about them. There will be a lot I wish I could look down on, or look up on, whichever way I have to.”

Musgrave cooks dinner — a healthy meal, she said, that includes a protein, complex carbohydrate, and fruit or vegetable — every night for herself and her husband, 91-year-old Stanley Musgrave, whom she married in 1944.

She said she traces her love of food and cooking to her childhood. Her mother hated to cook, she said, and gave her free rein to experiment in the kitchen.

“My feeling is if we can get children, in the first eight years of their lives, to like food and really appreciate food they’ll eat right the rest of their lives,” she said after the party wound down. “As a child I got to feel important, and children would today if parents would take time to let ’em make a few messes in the kitchen and enjoy creating.”

Shapero called Musgrave the office’s “inspiration” and told her to set aside the date in five years for her 95th birthday party.

“I’ll be there,” Musgrave said. “You may have to come get me, but I’ll be there.”