Which of the following is contraindicated when using a dental laser?

In the context of dental laser use, the utilization of a portable oxygen unit is contraindicated primarily due to the risk of fire. Lasers generate intense heat and can ignite materials that are flammable. Since oxygen supports combustion, using an oxygen unit in close proximity to the focused laser light increases the danger of igniting a fire during procedures, potentially putting both the patient and the dental professional at great risk.

The other choices presented are standard practices that are crucial for patient safety and effective laser operation. For instance, switching on the power supply correctly is essential for operational use, while using manual suction devices helps manage smoke and debris generated during procedures. Additionally, proper hand hygiene protocols are vital in any clinical setting to prevent infections and ensure patient safety. Therefore, avoiding the use of a portable oxygen unit is the appropriate choice when handling dental lasers.