Final answer:
Dentinal hypersensitivity is most closely related to dentin exposure, a result of enamel loss or gingival recession that can lead to the exposure of the sensitive inner dentin of the teeth.
Step-by-step explanation:
Dentinal hypersensitivity is most related to b. Dentin exposure. When the protective enamel covering is lost due to erosion or decay, the underlying dentin can become exposed. This exposure leads to sensitivity because dentin houses microscopic tubules that connect to the nerve-rich pulp. Conditions such as gingival recession, which often results from chronic gingivitis and can lead to the more serious periodontitis, also contribute to dentin exposure as the gums recede and parts of the tooth that are normally covered become exposed to external stimuli. In summary, while loss of enamel, pulpal necrosis, and gingival recession are related factors, the direct cause of the sensitivity is the exposure of dentin.