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Background  Although many studies have focused on the association of the  MMP -9 promoter −1562 C/T polymorphism with the susceptibility and/or severity of chronic periodontitis (CP), results have been inconsistent. Therefore, a meta-analysis of all eligible studies was performed to derive a more precise estimation of the association between this polymorphism and CP risk.    Methods  All relevant studies were identified through a database search in PubMed, Medline, and Web of Science. All the full-text studies with appropriate analytical design, published in English, which evaluated the association of  MMP - 9  promoter −1562C/T polymorphism with CP risk using validated genotyping methods, and with non-duplicated data were selected for this study. A fixed-effect model was used to calculate pooled ORs in the absence of heterogeneity across included trials (P > 0.1 and I 2  < 50 %), otherwise the random-effect model was applied.    Results  In an overall meta-analysis, pooled ORs revealed that T variant in the  MMP - 9  promoter −1562 C/T polymorphism was associated with a significantly decreased risk for CP under all comparison models. In subgroup analyses by ethnicity, pooled ORs showed that a significant association of the  MMP - 9  promoter −1562 C/T polymorphism with CP risk was only detected in Caucasians and Asians but not in mixed population. In the subgroup analysis by severity of CP, pooled ORs indicated that T allele of the  MMP - 9  promoter −1562 C/T polymorphism was associated with decreased susceptibility to severe CP while there was no significant association between this polymorphism and moderate CP.    Conclusions  Our meta-analysis showed that T allele in the  MMP - 9  promoter −1562 C/T polymorphism might be a protective factor for CP, especially in Caucasians and Asians. Moreover, there was a significant association of the MMP-9 promoter −1562 C/T polymorphism with decreased susceptibility to severe CP, while the allelic and/or genotype distributions of this polymorphism were not associated with moderate CP.    Electronic supplementary material  The online version of this article (doi:10.1186/s40064-016-2135-3) contains supplementary material, which is available to authorized users.

A meta-analysis of MMP-9 promoter −1562 C/T polymorphism on susceptibility of chronic periodontitis