How does a lack of fluoride cause a fissure? Fluoride slows down matrix molecules, and the signals that travel through the matrix. It slows the dentin side down more, as the dentin soaks up about 5 times as much fluoride as the enamel. Now, without enough fluoride, the dentin goes a little too fast. That causes it to get ahead of the enamel. Once the dentin sparks join and leave, the enamel sparks stop moving forward. That leaves a few cells in the center not activated. These cells get left behind when the active ones move up together. A fissure is created in the void above them.

Closure defect hypothesis