**Core Concept**
The thickness of enamel in posterior teeth varies along the tooth structure, with the thickest portion being located in the cervical region. This thickness is crucial for resisting the forces of mastication and occlusion. The cervical region is more prone to wear and tear due to the increased surface area exposed to occlusal forces.

**Why the Correct Answer is Right**
The cervical region of posterior teeth has the thickest enamel due to the increased stress concentrations in this area. The enamel in the cervical region serves as a protective barrier against the erosive effects of acids and the abrasive action of food particles. The thickness of enamel in this region allows it to effectively distribute the forces of mastication and occlusion, thereby reducing the risk of enamel wear and fracture.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the incisal edge of posterior teeth is not the thickest region, and it is more prone to wear and tear due to the high concentration of forces during mastication.
**Option B:** This option is incorrect because the occlusal surface of posterior teeth is not the thickest region, and it is more susceptible to wear and tear due to the high forces of occlusion.
**Option C:** This option is incorrect because the buccal or lingual surfaces of posterior teeth are not the thickest regions, and they are not as prone to wear and tear as the cervical region.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the cervical region is more susceptible to enamel wear and tear due to the increased surface area exposed to occlusal forces. This can lead to the development of cervical enamel lesions, which can compromise the integrity of the tooth structure.

**Correct Answer: D.**