**Core Concept**
The maxillary first molar has five roots, with varying lengths and complexities. Understanding the root anatomy is crucial for dental procedures, including endodontic treatment and root canal therapy. In this context, the disto-buccal root is often shorter than the other roots.

**Why the Correct Answer is Right**
The disto-buccal root of the maxillary first molar is typically the shortest root due to its narrower diameter and more limited surface area. This is because the disto-buccal root often has a single canal, whereas the other roots may have multiple canals. The disto-buccal root's shorter length also makes it more susceptible to fracture during dental procedures. In contrast, the mesio-buccal root is often the largest and most complex, with multiple canals and a wider diameter.

**Why Each Wrong Option is Incorrect**
**Option A:** The mesio-buccal root is typically the largest and most complex root of the maxillary first molar, making it the longest rather than the shortest.

**Option C:** The lingual root of the maxillary first molar is usually the second longest root, not the shortest.

**Option D:** While the length of the roots can vary among individuals, the disto-buccal root is generally the shortest root of the maxillary first molar, making this option incorrect.

**Clinical Pearl / High-Yield Fact**
When performing endodontic treatment on a maxillary first molar, it's essential to carefully assess the root anatomy, including the length and complexity of each root, to ensure effective treatment and minimize the risk of root fracture.

**✓ Correct Answer: B. Disto-buccal**