Final answer:
The PC technician should recommend a BIOS password to protect the computer at the dental clinic from bootable disk attacks.
Step-by-step explanation:
The security technique that the PC technician should recommend to protect the computer used at the dental clinic from someone using a bootable disk containing hacking tools is BIOS Password. A BIOS password is set in the computer's BIOS settings, preventing unauthorized access to the computer, even if a bootable disk is used. This adds an additional layer of security to the computer and ensures that only authorized users with the correct password can log in and use it.