Objectives and scope of the toothbrush study

To carry out an LCA, it is essential to define a functional unit. This will serve as a reference and enable the reference flows to be calculated.

Functional unit

Brushing your teeth is a harmless gesture, but one that needs to be defined in order to build a functional unit.

Quality of service

The French health insurance scheme has issued a list of recommendations for 'brushing 'brushing your teeth properly'.

These include

  • that you should brush your teeth twice a day for two minutes;

  • that you should use fluoride toothpaste;

  • that toothbrushes should have soft bristles.

The recommendations suggest that the level of performance is identical between a manual and an electric brush.

Duration of service

The duration of service corresponds to that of the need.

In the toothbrush study, the need starts as soon as the firsts teeth start showing and ends with their disappearance. It would therefore make sense to use a duration of service several decades long. However, to make it easier to calculate the reference flows, a shorter period of time year was chosen. Given the products studied, the two toothbrushes are similar, therefore this choice can’t be selected as a way to compare them.

Conclusion FU

Fundamental

Thus, the functional unit selected is:

‘Ensure that teeth are brushed twice a day for one year, as recommended by the health insurance scheme’.

Brushing hypothesis

Simplifying hypothesis can be used according to the studied cases. 

Regarding the toothbrushes, the quantities of water and toothpaste are excluded from our study.

The health insurance recommandations involve using toothpaste for brushing and a water comsumption to rinse.

Then, both éléments should be present in the referential flows.

A simplifying hypothesis is used, considering that the use of a manual toothbrush and an electric toothbrush induces the same consumption of toothpaste and water.

Since the final objective is to compare the two types of brush, the quantity of water and toothpaste can be excluded from the study.

Whatever the value, if it is identical, it will not affect the comparison.

Reference flow

Reference flows are calculated for each brushing method:

  • manual;

  • electric.

Manual toothbrush

The lifetime of the manual toothbrush is three months.

The reference flow associated with this brushing is therefore four toothbrushes to ensure functional unity.

Electric toothbrush

The electric toothbrush lasts for eight years and the brush head for three months.

To ensure functional unity, it is necessary to use 1/8th of a brush, four brush heads and a quantity of electricity. This is the reference flow.