[Suitability of various lasers for interventions from the tympanic membrane to the foot plate (Er:YAG, argon, CO2 s.p.--, Ho:YAG laser].

The Erbium:YAG-laser is a good tool for microresection of bone and soft tissue from the ear drum, to the ossicles and extending to the footplate. The mechanism of ablation is based on the fact that the emission of infrared light is of the same wavelength at which water has its peak of optimal light absorption. 14% of bone is water, just sufficient force for ablation. At 50 mJ impulses the temperature in the centre stays below the coagulation point. 500 impulses of 50 mJoule definitely remain below the acoustic risk. In 44 guinea pigs 500 x 50 mJ caused a temporal threshold shift of maximal 38 dB at 2000 cps which recovered after 90-135 min. In 60 tympanoplasties neither tinnitus nor audiological side effects of the laser application were measured. The ear drum is perforated by 1 (-3) impulses. This can be done even in children after superficial anaesthesia (2% pantocaine drops) to drain the middle ear. The laser perforation of 0.3 mm [symbol: see text] will close after a day and has to be re-opened in the office to avoid tubes. We do not yet know how often general anaesthesia and removal by suction of too viscous mucus remain nevertheless necessary. With the Er:YAG laser parts of the ossicles can be cut out of the intact chain, without contact and trauma, nearly without loss of bone tissue. This allows better radicality in removing cholesteatomas or scars with less destruction. 500 impulses of 50 mJ ablate 32 mg of bone, i.e. the weight of an incus.(ABSTRACT TRUNCATED AT 250 WORDS)