Which of the following conditions can lead to the loss of a tooth?

The correct answer is that a fracture that splits the root incorrectly can lead to the loss of a tooth. When a root fracture occurs, it disrupts the structural integrity of the tooth, compromising its ability to withstand normal chewing forces. If the fracture is severe enough, the tooth may become non-restorable, leading to extraction. Additionally, root fractures often create pathways for bacteria to invade, which can cause further complications such as infection and deterioration of the surrounding bone.

In contrast, while a minor enamel chip, a loose crown, or a worn-down filling may require dental attention, they do not necessarily result in immediate tooth loss. Minor enamel chips can often be repaired with bonding or other cosmetic dentistry treatments. A loose crown can typically be re-cemented without significant damage to the tooth structure. Similarly, a worn-down filling can be replaced, allowing the tooth to remain intact. Therefore, among the given choices, a fracture that splits the root incorrectly is the most serious condition that can directly lead to tooth loss.