**Core Concept**
The bleaching of nonvital teeth involves the use of hydrogen peroxide or other oxidizing agents to break down chromogens and remove stains from the tooth structure. This process requires careful consideration of the potential consequences, particularly those related to the pulp and surrounding tissues.

**Why the Correct Answer is Right**
The most common consequence of bleaching nonvital teeth is **irreversible pulp necrosis**. This occurs due to the penetration of the bleaching agent into the pulp chamber, where it can cause oxidative stress and damage to the pulp tissue. The alkalinity of the bleaching agent can also disrupt the pulp's natural defense mechanisms, leading to necrosis. The severity of this consequence can be influenced by factors such as the concentration and duration of the bleaching agent, as well as the presence of any pre-existing pulp pathology.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while dentin hypersensitivity can be a consequence of bleaching nonvital teeth, it is not the most common consequence. Sensitivity is often a transient issue that can be managed with desensitizing agents or other treatments.
**Option B:** This option is incorrect because **pulpitis** is not a direct consequence of bleaching nonvital teeth. Pulpitis is an inflammatory condition of the pulp, typically caused by bacterial infection or trauma, rather than chemical damage from bleaching agents.
**Option C:** This option is incorrect because **gingival recession** is not a common consequence of bleaching nonvital teeth. Gingival recession is a condition characterized by the loss of gingival tissue, often caused by periodontal disease or other factors unrelated to tooth bleaching.

**Clinical Pearl / High-Yield Fact**
When bleaching nonvital teeth, it is essential to carefully assess the pulp's vitality and consider the potential risks of irreversible pulp necrosis. This can be achieved through the use of diagnostic tests such as thermal testing or electrical pulp testing, as well as the selection of appropriate bleaching agents and techniques.

**Correct Answer: D. Irreversible pulp necrosis.**