**Core Concept:**
Hypertrophy is a process of tissue enlargement primarily driven by an increase in the size of cells (hypertrophy) or the number of cells (hyperplasia) in response to mechanical loading or hormonal effects. In the context of dental structures, hypertrophy primarily affects the cementum layer, which is a non-calcified connective tissue layer that covers the root surface of teeth.

**Why the Correct Answer is Right:**
In the scenario of hypertrophy of cementum, the correct answer refers to the increased size of cementocytes (cells in cementum). The correct answer is D, **"Cementocytes become larger"**. When the root surface of teeth is subjected to mechanical loading (e.g., mastication), hormonal effects, or other stimuli, hypertrophy occurs. This results in increased size of the cementocytes, which leads to thickening of the cementum layer.

**Why Each Wrong Option is Incorrect:**
A) **"Cementocytes become more numerous"** is incorrect because hypertrophy refers to an increase in cell size, not cell number.
B) **"Cementum becomes thicker"** is partially correct, but it does not explain the mechanism behind the hypertrophy.
C) **"Hypertrophy of cementum is not observed"** is incorrect as hypertrophy is a known physiological response in dental structures, particularly in response to mechanical loading.

**Clinical Pearl / High-Yield Fact:**
Understanding hypertrophy of cementum is crucial for dental professionals, especially oral and maxillofacial surgeons and orthodontists. The hypertrophy of cementum can be used as a clinical indicator of dental maturity, especially in forensic odontology when assessing the age of an individual based on dental development.

**Correct Answer:** **"Cementocytes become larger" (Option D)**