|Lesson 3: Test that Toothpaste!
Prior knowledge / Work:
That gained from completion of Lessons 1 and 2.
Children need to be reminded as to the way in which toothpaste works – mild abrasives, combined with the scrubbing action of the toothbrush, rub away stains and remove debris and plaque from teeth. They must think of a way of mimicking stains on teeth so they can test the toothpastes.
Explain to the children that they are going to test their toothpaste alongside a selection of commercially produced products with a view to seeing how well they remove stains. Discuss with the children how this might be achieved (without using real teeth!). They will need to consider the following:
What surface can be used to mimic the hard surface of the tooth?
The surface of an old bathroom tile (if not too glossy) or that on a coin offer suitable surfaces.
What can be used to create a stain on this surface?
The children can experiment with a range of stains – marker pen works well.
How can we test the toothpastes fairly?
The test must be designed so it can be carried out in the same way for each toothpaste.
How many toothpastes should we use?
It is recommended that the children test their toothpaste and then maybe three additional ones.
Should the test be repeated?
You should always repeat your test, to check if your results are accurate. It is recommended that each toothpaste is tested three times.
What factors will we keep the same?
The amount of stain, the surface, the amount of toothpaste, the type of toothbrush used, the number of brushes with toothbrush and the pressure applied are all factors that the children should identify as needing to be kept the same.
What factors will we change?
The type of toothpaste used.
The way in which the investigation is then carried out will depend on the ability of the children. You may decide on a method as a class and then everyone use that method. Alternatively, small groups of children may devise their own test. The children will have to think about what they are going to measure to decide on the effectiveness of the product. They may decide to brush each stain five times and comment on, or photograph the stain left. They may decide that they will count how many scrubs it takes to remove the stain. They will have to devise a table in which these results are recorded. Class results could be combined and ICT used as a way of recording group results.
The children then carry out their investigation and Worksheet 2 can be used to write up this investigation.
Discuss the children’s results. What problems did they have with the test? How did the homemade toothpaste compare with the other makes?
Discuss with the children how they think main manufacturers test the cleaning power of their products? (Some test them on cow teeth with a range of different, common stains, including tea and coffee).
How would they improve their test if they could repeat it?