**7.9 Swelling index**

Film swelling tests are carried out with a simulated saliva solution. Each film sample is weighed and put in a stainless steel wire mesh that has been pre-weighed. In a plastic container, the mesh containing the film sample is immersed in a 15 ml medium. The weight of the film was measured at predetermined intervals until it reached a consistent weight.

$$\text{Swelling index} = \frac{\text{Increase in weight of film} - \text{Initial weight of film}}{\text{Initial weight of film}} \times 100 \tag{4}$$
