Which individual utilized a procedure known as "setting the tubes"?

The correct choice is Kells, who is known for his pioneering contributions to dental radiology, including the technique referred to as "setting the tubes." This method involved the precise arrangement of x-ray tubes to optimize image quality and safety for patients. Kells was instrumental in advancing the application of x-rays in dentistry, and his work laid the foundation for many modern practices in the field.

Kells' innovation marked a significant leap in the way dental professionals approached radiography, allowing for more effective diagnostics and treatment planning. His understanding of the interaction between radiation and materials used in dental settings contributed to improved safety standards and techniques that are still relevant today.