A trip to the hygienist might be less daunting than a visit to the dentist, but even so...

By Zoe Smart

...most of us probably spend our time in the hygienist’s chair willing the process to be over.

We are less likely to occupy ourselves examining the equipment used to clean and descale our teeth. But the ultrasonic descalers used today are an impressive piece of medical equipment; the tip of the descaler vibrates at a high frequency of 25 000 to 40 000 cycles a second or even higher, to break down the bacterial matter to which plaque and calculus stick. The efficiency of the cleaning depends on the amplitude of the vibration.

Computers turn high-frequency sound waves into real-time pictures.

Micro erosion through imploding vacuum bubbles

Ultrasonic equipment is widely used in clinical practice for medical diagnosis, for example in monitoring and imaging subcutaneous tissues such as internal organs, tendons and so on. It works by high-frequency sound waves being emitted from an ultrasonic transducer (a hand-held probe) and directed into the body. When a sound wave hits an internal organ, fluid or tissues it bounces back and the transducer records the tiny changes in the sound's pitch and direction. These are measured by a computer and turned into a real-time picture. When entering the body ultrasound causes molecular friction which results in soft tissue heating slightly.

The heat caused by diagnostic medical equipment is so low that it is dissipated by the tissue and is harmless but, as the field of medical diagnostic ultrasonic equipment expands, the need has arisen to establish a means for determining levels of exposure. With that in mind, IEC TC 87: Ultrasonics, published a new edition of IEC 62359, Ultrasonics – Field characterization – Test methods for the determination of thermal and mechanical indices related to medical diagnostic ultrasonic fields, in October 2010. The publication provides improved test methods to determine the relevant indices and exposure parameters resulting from the thermal effects generated by ultrasound, as well as specifying exposure parameters for certain non-thermal effects. TC 87, whose work also covers sectors for defence and the manufacturing industry, is currently working on a new amendment to the second edition of IEC 61157, Standard means for the reporting of the acoustic output of medical diagnostic ultrasonic equipment.

Ultrasonics has been used in dentistry since the mid-1950s to loosen plaque and calculus which, if they are left in place, can have a disastrous effect on gums and teeth. The ultrasonic scaler vibrates at a frequency that breaks down bacterial cell membranes, thus allowing plaque and calculus to be more easily removed.

International Standard IEC 61205, Ultrasonics – Dental descaler systems – Measurement and declaration of the output characteristics is published by TC 87/WG (Working Group) 7: Ultrasonic surgical equipment. It specifies standard methods of measurement and the essential characteristics of ultrasonic dental descalers.

Built-in with Ergo UltraLight Dental descaler uses ultrasonics to ensure effective and painless cleaning of teeth. Photo: Ultrasonic scaler by Amdent
tc-4_ultrasonics_ultrasound_lrg Computers turn high-frequency sound waves into real-time pictures.
tc-4_ultrasonics_portable_machine_lrg A portable ultrasound machine used in medical diagnosis.