Final answer:
The exception among the dental hygiene interventions listed is setting an ammonia capsule within easy reach during treatment, as it is not a preventative measure but a reactive one. The other options help in preventing medical emergencies from escalating.
Step-by-step explanation:
The exception to dental hygiene interventions that will prevent the escalation of a medical emergency is: B. Set an ammonia capsule within easy reach during treatment. This does not prevent an emergency but rather is a reactive measure intended for use if a patient faints or feels faint. The other interventions, such as resuming the upright chair position slowly and providing a prophylactic antibiotic premedication, are preventative measures aimed at reducing the possibility of an emergency. Moreover, requesting a patient to bring nitroglycerine to the appointment could be crucial for those with heart conditions, and developing patient rapport can help in managing patient anxiety and can lead to better communication regarding health status.