Final answer:
The most common side effect of tooth whitening with hydrogen peroxide is pulp sensitivity.
Step-by-step explanation:
The most common side effect of tooth whitening with hydrogen peroxide is pulp sensitivity. This occurs when the hydrogen peroxide penetrates the tooth enamel and reaches the sensitive pulp inside, causing temporary sensitivity or discomfort. However, it is important to note that pulp sensitivity is usually mild and temporary, and it subsides on its own after a short period of time.
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