Can be differentiated for ELL's by using pictures to demonstrate the history of toothbrushes, and how to properly care for your teeth.
Higher ability students could keep a journal of the experiments complete with pictures.
This is an excellent lesson that can be modified a number of ways. I find that it fits well with Science and Technology Standards 2.4.1 and 2.4.2.
2.4.1: Identify parts of the human body that can be used as tools.
2.4.2: Identify technologies developed by humans to meet human needs. Investigate the limitations of technologies and how they have improved quality of life.
Students could identify how teeth can be considered a tool. They could discuss the toothbrush (and its evolution to items like Sonicare.) The experiments will help them understand the limitations of the toothbrush, and how their choices affect their teeth.