# Matrix Metalloproteinases and Temporomandibular Joint Disorder: A Review of the Literature
## 4 Results
### Description of Included Studies  
In 2018, [PERSON] et al. used 39 disc samples from 27 patients to look at MMP-13 expression in TMD. Exclusion criteria for subjects [PERSON]'s study included use of orthodontic appliances, chronic anti-inflammatory use, history of diseases causing impaired immune function, such as HIV, diabetes, or any use of immunosuppressive therapy. The patients, with a mean age of 33.59, then filled out a pain questionnaire, had a clinical examination, and radiographs or CT imaging was performed for diagnostic purposes, placing patients into groupings of either ADDwR or ADDwoR. Surgery was performed on patients and samples were obtained and underwent immunohistochemical staining to analyze for MMP-13 activity. The researchers did not find a significant difference in expression of MMP-13 in samples from patients with TMD, in either the ADDwR or the ADDwoR groupings, when compared to the control group. [PERSON] et al. (2014) analyzed activity of two matrix metalloproteinases and their protein levels in TMD, both MMP-2 and MMP-9. In this study, 45 disc samples from 33 patients (mean age of 32.36 years) were analyzed using immunohistochemical staining. Diagnosis was made using a pain questionnaire and clinical examination, grouping patients into ADDwR and ADDwoR, and selected patients were treated surgically following unsuccessful non-surgical treatment. Following immunohistochemical staining of samples obtained during surgery, MMP-2 was found to be significantly increased in samples from subjects with TMD when compared to the control. It was also found that there was an increase in MMP-2 in samples from patients with ADDwoR when compared to ADDwR, suggesting a correlation between progression of TMD and MMP-2 levels. Levels of MMP-9 showed no significant difference between the TMD disc samples when compared with control disc samples. [PERSON] et al. (2013) used immunohistochemical staining to look at MMP-7 and MMP-9 in disc samples from subjects with TMD. They used 25 disc samples from 25 patients (mean age of 34), which were obtained surgically following unsuccessful non-surgical intervention after diagnosis using a history of present illness, clinical examination, and MRI. They assessed the severity of the disease by looking at unassisted maximum mouth opening and using a visual analog scale to assess pain. Following staining, both MMP-7 and MMP-9 were found to be expressed at levels significantly higher in samples from patients with TMD when compared to control samples. [PERSON] et al. (2011) analyzed the frequency of polymorphisms in genes coding for MMP-1, MMP-3, and MMP-9 proteinases in patients with TMJ degeneration. The study was conducted on 232 individuals, 115 of which had TMJ degeneration and a mean age of 42.82. To diagnose the study group, the researchers used MRI and/or CT scans to image one or both mandibular condyles. Genomic DNA was gathered from epithelial buccal cells and a PCR reaction was performed for MMP-1, MMP-3, and MMP-9 coding genes. A genotype analysis using restriction fragment length polymorphisms was performed, and the frequency of each allele was determined in both groups. Compared to the control group, there was a statistically significant association between the MMP-1 genotype and the TMJ degeneration group. No association was found between the MMP-3 and MMP-9 genotypes and TMJ degeneration.