MMP9 and Abnormal mastoid morphology: In the tympanosclerosis animal model, in which the possible role of MMP-9 together with TGF-β1 was investigated, it was reported that TGF-β1 expression increased with the development of tympanosclerosis at 8 weeks, and MMP-9 expression increased slowly from 1 to 4 weeks and decreased at 6 weeks.