**Core Concept**
GLUMA stands for Glyceryl Monothiosemicarbazide, which is a type of intra-canal medicament used in endodontics. It is a disodium salt of a compound that has a chelating action on metallic ions, particularly zinc and calcium, which are present in the dentinal tubules.

**Why the Correct Answer is Right**
GLUMA works by forming a complex with metallic ions, thereby reducing the dentinal hypersensitivity. This is achieved through the chelation of zinc and calcium ions, which are responsible for the transmission of pain signals from the dentin to the pulp. The chelation of these ions reduces the excitability of the dentinal tubules, thus providing relief from hypersensitivity. The mechanism of action of GLUMA is similar to other chelating agents, such as potassium nitrate and strontium chloride.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not relate to the correct definition of GLUMA.
**Option B:** This option is incorrect because it describes a different type of intra-canal medicament, such as calcium hydroxide, which is used for different purposes in endodontics.
**Option C:** This option is incorrect because it is a different type of chelating agent, such as EDTA, which is used for different purposes in dentistry.

**Clinical Pearl / High-Yield Fact**
GLUMA is a popular intra-canal medicament used in endodontics to reduce dentinal hypersensitivity. It works by chelating metallic ions, particularly zinc and calcium, which are present in the dentinal tubules. This makes it an effective treatment option for patients with dentinal hypersensitivity.

**Correct Answer: D.**