**Core Concept:**
Interproximal caries, also known as interdental caries, refers to dental decay that occurs between teeth where the tooth structure is not fully covered by enamel or dentin. The correct method for detecting interproximal caries is crucial for early intervention and prevention of further damage.

**Why the Correct Answer is Right:**
The correct answer is **D**. Silver Diamine Fluoride (SDF) is a solution containing both silver and fluoride ions. When applied to the tooth surface, SDF reacts with the tooth structure, forming a compound that discolours the affected area. This discolouration is a sign of the presence and progression of interproximal caries, making it visible for early detection and treatment.

**Why Each Wrong Option is Incorrect:**
A. **Option A:** Digital X-ray is not specific for detecting interproximal caries. X-rays are primarily used to visualize the root structure and determine the extent of carious lesions. They are not suitable for detecting early interproximal caries due to limited visualization of the interproximal surfaces.

B. **Option B:** Visual examination is important for detecting caries, but it does not specifically highlight the presence of interproximal caries. Visual inspection alone might not be sufficient to confirm the extent and progression of the carious lesion.

C. **Option C:** Fluoride varnish is a preventive agent that strengthens tooth enamel, reducing caries risk. Fluoride varnish does not specifically detect the presence and progression of interproximal caries.

**Clinical Pearl:**
The correct method for detecting interproximal caries is **D** - Silver Diamine Fluoride (SDF) application. SDF application provides a simple, non-invasive method for detecting and monitoring the progression of interproximal caries, allowing for early intervention and prevention of further damage to the tooth structure.

**Correct Answer Explanation:**
Silver Diamine Fluoride (SDF) application is a valuable tool for detecting and monitoring the progression of interproximal caries. When SDF is applied, it converts the affected tooth structure into a darker shade, making the carious lesion visible to the clinician. This visual cue allows for early detection and intervention to prevent further damage to the tooth structure and preserve the tooth.

**Why the Other Options are Incorrect:**
A. Digital X-rays can detect carious lesions, but they are less effective in visualizing the interproximal surfaces. Visual examination alone may not accurately identify the presence and progression of interproximal caries, as the lesions may be subtle and not easily visible.
B. Fluoride varnish is a preventive agent that strengthens tooth enamel, reducing caries risk. Fluoride varnish does not specifically detect the presence and progression of interproximal caries. Its primary function is to reduce caries risk by strengthening tooth enamel.
C. Visual examination of the tooth surface without SDF application is unable to detect the presence and progression of interproximal caries. Detecting caries requires the lesion