Which of the following is NOT a suggested application to increase the effectiveness of topical fluoride?

The option that stands out as not being a suggested application to enhance the effectiveness of topical fluoride is the increase of pH of fluoride. This is because the effectiveness of fluoride tends to be optimized in a slightly acidic environment. Fluoride ions are more readily available for uptake by the enamel in such conditions, and these ions can contribute to remineralization of demineralized enamel.

Increasing the pH to a more neutral or alkaline level can reduce the solubility of fluoride compounds, making them less effective in preventing demineralization or in promoting remineralization. Therefore, maintaining a lower pH is generally recognized as more beneficial for the therapeutic actions of fluoride in dental applications.

On the other hand, increasing fluoride ions in solution, extending exposure time to topical fluoride, and pretreating enamel with phosphoric acid are all techniques that are suggested to enhance the action of fluoride. Increasing fluoride ion concentration can improve its availability for enamel uptake. Prolonging exposure allows for more fluoride to be absorbed and work on the enamel surfaces. Additionally, pretreating enamel with phosphoric acid can enhance fluoride uptake by creating a more porous surface, allowing better penetration of the fluoride.