**Core Concept**
Gustafson's method is a radiological technique for age determination in adults using the assessment of root resorption and other changes in the dental alveoli. This method relies on the sequential analysis of various dental structures to estimate an individual's age.

**Why the Correct Answer is Right**
The most reliable criterion in Gustafson's method is the resorption of the roots of the teeth. This process is influenced by the decrease in sex hormone levels after menopause, leading to a decrease in bone density and an increase in bone resorption. The rate of root resorption is relatively constant and can be used to estimate age with a high degree of accuracy. The other dental changes observed in Gustafson's method, such as attrition and periodontal recession, are less reliable due to their variability in response to environmental factors.

**Why Each Wrong Option is Incorrect**
**Option A:** Attrition of dental enamel is a variable process influenced by diet, dental hygiene, and other factors, making it an unreliable criterion for age determination.
**Option B:** Periodontal recession is also influenced by various factors, including gum disease, smoking, and genetics, which can lead to inconsistent results.
**Option C:** Cementum apposition is a process that occurs throughout life and is not a reliable indicator of age, as it can be influenced by factors such as diet and hormonal changes.

**Clinical Pearl / High-Yield Fact**
Gustafson's method is a useful tool for estimating age in individuals where other methods, such as radiocarbon dating or DNA analysis, are not feasible. However, it is essential to consider the limitations and potential biases of this method when interpreting results.

**Correct Answer:** C. Cementum apposition is a process that occurs throughout life and is not a reliable indicator of age, as it can be influenced by factors such as diet and hormonal changes.