What is a common sign of dental caries in its early stages?

Tooth sensitivity is a common sign of dental caries in its early stages because it occurs when the protective enamel layer begins to break down. As the enamel erodes due to acids produced by the bacteria in plaque, the underlying dentin can become exposed. This exposure can lead to sensitivity when the tooth encounters hot, cold, or sweet stimuli, causing discomfort or sharp pain.

In contrast, while swelling of the gums, bad breath, and significantly darkened tooth color may also be associated with oral health issues, they are not specifically indicative of early-stage dental caries. Swollen gums are more commonly associated with gingivitis or periodontal disease rather than caries itself. Bad breath could indicate various problems, including poor oral hygiene or infections, but is not directly linked to the initial stages of caries. Lastly, a significantly darkened tooth color is often a sign of more advanced decay or damage rather than an earliest indicator. Thus, tooth sensitivity stands out as the most relevant early symptom of dental caries.