**Core Concept**
Gustafson's ranking is a method used in forensic odontology to estimate age based on the structural changes in the teeth. The ranking involves evaluating the progression of changes in the teeth, including attrition, periodontosis, cementum apposition, and transparency of the roots.

**Why the Correct Answer is Right**
Gustafson's ranking is based on the sequential changes that occur in the teeth with age. The correct order is as follows:
- Attrition is the first change to occur, which is the wearing away of the enamel and dentin due to mastication.
- Periodontosis, also known as periodontal disease, is the second change, which involves the inflammation of the periodontal tissues and the loss of attachment between the tooth and the surrounding bone.
- Cementum apposition is the third change, which involves the deposition of new cementum on the root surface, making the root appear thicker.
- Transparency of the roots is the final change, which occurs due to the resorption of the dentin and the formation of a transparent layer on the root surface.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because attrition is not the last change to occur in the teeth. Attrition is the first change, followed by periodontosis, cementum apposition, and transparency of the roots.

**Option B:** This option is incorrect because periodontosis is not the last change to occur in the teeth. Periodontosis is the second change, followed by cementum apposition and transparency of the roots.

**Option C:** This option is incorrect because cementum apposition is not the last change to occur in the teeth. Cementum apposition is the third change, followed by transparency of the roots.

**Option D:** This option is incorrect because transparency of the roots is not the first change to occur in the teeth. Transparency of the roots is the last change, which occurs due to the resorption of the dentin and the formation of a transparent layer on the root surface.

**Clinical Pearl / High-Yield Fact**
Gustafson's ranking is a useful tool in forensic odontology for estimating age based on the structural changes in the teeth. However, it is essential to note that the ranking is not always straightforward and can be influenced by various factors, including diet, oral hygiene, and genetic predisposition.

**Correct Answer:** D. Transparency over apical 1/3rd of root