Final answer:
Fluoride is the trace mineral needed to preserve tooth enamel. It forms a more resistant compound on the tooth surface, making the enamel less soluble and more resistant to decay.
Step-by-step explanation:
Fluoride is the trace mineral needed to preserve the enamel on teeth. Fluoride plays a crucial role in protecting teeth from decay by forming a more resistant compound called fluorapatite on the tooth surface. This compound makes the enamel less soluble and more resistant to acidic attacks. Fluoride is commonly found in toothpaste, mouthwashes, and is also added to tap water as a preventive measure.