# The Role of Powered Surgical Instruments in Ear Surgery: An Acoustical Blessing or a Curse?
## 5 Generation of Noise and Vibrations by Otological Surgical Instruments and Hearing Loss
### MES Procedures  
#### 5.2.1 Drill Generated Noise Levels  
Many researchers have conducted basic research targeting the problem of measuring the noise levels generated by surgical drills in a non-clinical setting. Among the earliest studies of drill generated noise levels and most frequently cited is that of [PERSON] and [PERSON] (2016), published in 1976. They measured vibrations generated by drills using isolated temporal bones and cadavers, whereafter the data was then converted into equivalent air-borne noise levels. They found that the isolated temporal bones produced lower noise levels than cadavers, and thus concluded that cadavers better simulated real surgical conditions. The maximum equivalent air-borne noise levels were found to be around 100 dB, which falls below the 130 to 140 dB threshold for causing permanent hearing loss from an acute one-time exposure. The same group reported additional results in 1977 ([PERSON] and [PERSON], 2016), looking at different variables focusing on the size of the burr; the type of the burr; (sizes: 2-mm, 4-mm and 6-mm burrs; types: diamond versus cutting burrs); drill rotation speed; and location of drilling. They found that the smaller the burr, the lower the noise levels, as well as that lower noise levels were obtained with diamond burrs, as opposed to cutting burrs with the highest noise level of 108 dB discovered with a 6-mm cutting burr. They further found that drill rotation speed and location of drilling had little effect on noise levels. Several researchers subsequently collected intraoperative in vivo data with the objective of getting a better picture of drill generated noise during real-life conditions. [PERSON] et al. (2018) reported higher in vivo noise levels in 1979 from the contralateral ear (the ear which was not being operated on) of six patients while undergoing a mastoidectomy on the ipsilateral ear (the ear which was being operated on). They reported noise levels in excess of the 108 dB recorded by the [PERSON] group at 116 dBA for 8-mm burrs; 109 dBA for 4-mm burrs; and surprisingly, a dangerously high 125 dBA for 2-mm burrs. [PERSON] and [PERSON] (2018) conducted an in vivo study in 1991 in which they attempted to directly measure the drill-generated noise levels by monitoring intraoperative _electroocchleographic_ (ECoG) noise levels and calculating these levels by using a masking technique. They were able to determine that drill-generated noise levels were present in excess of 90 dBHL at the level of the cochlea, but were unable to determine peak values. Figure 6: Revised system for staging and classifying of middle ear cholesteatomas to be treated by non-TEES based on the PTAM System for Staging and Classification of Middle Ear Cholesteatomas as proposed by the Japan Otological Society (2018) (**a**) The middle ear (P: protympanum; T: tympanic cavity; A: attic; An: antrum; M: mastoid cells). (**b**) Non-powered TEES (orange overlay). (**c**) Powered TEES (yellow overlay). Other researchers collected data on postoperative sensorineural hearing loss in the contralateral ear in order to attempt to eliminate surgical trauma as a possible cause of hearing loss from surgery, while at the same time acknowledging the added distance between the contralateral and ipsilateral ears. [PERSON] and [PERSON] [40] conducted a study on 62 patients and reported in 1985 that they found a minimal difference between the peak noise levels which did not exceed 84 dB in the ipsilateral ear and 82 dB in the contralateral ear. Moreover, they found no hearing loss in the contralateral ear, but did find loss in 16 out of the 62 patients in the ipsilateral ear. They suggested that these results indicated that drill-generated noise levels did not cause sensorineural hearing loss. [PERSON] et al. [41] reported on drill-induced hearing loss in the contralateral ear in 1997 based on determining outer hair cell (OHC) function using distortion-product otoacoustic emissions (DPOAE).