My suggestion for a project is a way for disabled people to brush their teeth. You could use an off of the shelf robotic arm and an electric toothbrush. The arm would need a rotating wrist. The wrist may need other articulation beyond 360 degrees of rotation if the arm itself can't accommodate certain angles to reach the users teeth. The arm could be pre-programmed to brush the different sides of your teeth based on the recommended amount of time dentists say.
Some electric toothbrushes already have a timer in them and shut off on there own when time is up. You could also use large buttons to tell the arm to change to different predefined positions for those people with some remaining arm and hand use. I'm not sure if you'd want to tackle tooth paste dispensing. There are some electric dispensers out there that could utilize toothpaste if you'd want to tackle that another time as a separate project. Toothpaste could also be applied by a caregiver.