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THE problem of possible noxious effects of ultrasonic energy on calcified tissues is important because of its wide use in clinical and dental practice. The conditions of transmitting the ultrasound to bones and teeth and their surroundings are more complex than in soft tissues, being in a certain sense similar to those resulting from absorption of roentgen radiations in bones, causing, for example, selective overheating of bones due to increased absorption of ultrasonic energy and various interface effects on their surface. Coarsening of trabecular bone pattern, periosteal new-bone formation, circumscribed foci of bone sclerosis, localized bone necrosis, pseudocystic and cystic appearances and bone fractures were observed in various experiments on animals<sup>1,2</sup>. Not only were damaging effects on bone noted, but also on the dental germs after 3â 4 W/cm<sup>2</sup> ultrasonic energy<sup>9</sup>. The traumatic capacity of ultrasound in dentistry became the object of intense investigations from the middle 1960's because of the still wider use of ultrasonic dental cutting instruments in practice. Enamel defects and dyscrasias, loss of tooth structures, pink or yellow discolorations, mobile and fractured teeth and missing teeth were often correlated with the intensity and exposure time<sup>3,8</sup>. Thus, it can be concluded that there exists a real danger in application of ultrasound of too high an intensity and of prolonged exposure time. |
