<prompt> The mechanisms by which fluoride increases caries resistance include all of the following except-Reduction in enamel solubilityDecreased rate of post-eruptive maturationInterference with plaque microorganismsModification in tooth morphology  <response>: The benefits of fluoride in the reduction of dental caries have been known for years, but its exact mechanism of action is not completely understood. The mechanisms by which fluoride increases caries resistance may arise from both systemic and topical applications of fluoride. A number of proposed mechanisms have been identified which are assumed to work simultaneously and can be grouped as follows; 1. Increase enamel resistance or Reduction in enamel solubility 2. Increased rate of post-eruptive maturation 3. Remineralization of incipient lesions 4. Interference with plaque microorganisms 5. Modification in tooth morphology. 