Which of the following is considered a common dental emergency?

Toothaches and knocked-out teeth are classified as common dental emergencies due to the immediate need for treatment. A toothache typically signifies a more serious underlying issue, such as tooth decay or infection, which can cause pain and potential complications if not addressed promptly. Similarly, a knocked-out tooth represents an urgent situation where timely re-implantation may preserve the tooth, making immediate dental intervention critical.

In contrast, procedures like teeth whitening, regular cleanings, and cavity fillings are important aspects of dental care but are not emergencies. They can usually be scheduled at the patient's convenience rather than requiring immediate attention. Thus, toothaches and knocked-out teeth stand out as situations necessitating urgent care, making this option the most appropriate choice in the context of dental emergencies.