Table 1.
Characteristics, unadjusted data, and quality assessment results of included studies.
| References | Country (ethnicity) | Type | Case/control | Source of control | Genotype method | HWE | Smoking status | Newcastle-Ottawa Scale | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| GG | GA | AA | N | Selection (max 4 *) | Comparability (max 2*) | Exposure (max 3*) | |||||||
| (Wohlfahrt et al., 2006) | USA (Caucasian) | SCP | 47/39 | 62/31 | 28/12 | 137/82 | Healthy | PCR | Yes | Mixed | *** | ** | ** |
| (Ozturk et al., 2010) | USA (68% Caucasian)# | CP | 32/76 | 37/91 | 15/36 | 84/203 | Healthy | TaqMan | Yes | Mixed | ** | ** | ** |
| (Schaefer et al., 2010) | Germany and Netherlands (Caucasian) | CP | 187/57 | 304/80 | 115/33 | 606/170 | Healthy | TaqMan | Yes | Mixed | *** | ** | ** |
| (Loo et al., 2012) | China (Asian) | CP | 30/38 | 5/12 | 9/58 | 44/108 | Healthy | PCR | No | No | *** | * | ** |
| (Ikuta et al., 2015) | Japan (Asian) | CP | 9/6 | 24/11 | 8/5 | 41/22 | Healthy | PCR | Yes | NR | *** | * | ** |
| MCP | 3/6 | 8/11 | 2/5 | 13/22 | |||||||||
| SCP | 6/6 | 16/11 | 6/5 | 28/22 | |||||||||
| (Ma, 2016) | China (Asian) | CP | 20/26 | 48/48 | 22/22 | 90/96 | Healthy | PCR | Yes | Mixed | *** | * | ** |
| MCP | 11/26 | 23/48 | 12/22 | 46/96 | |||||||||
| SCP | 9/26 | 25/48 | 10/22 | 44/96 | |||||||||
| (Zupin et al., 2017) | Italy (Caucasian) | CP | 169/41 | 194/80 | 76/34 | 439/155 | Healthy | Illumina | Yes | Mixed | *** | ** | ** |
| SCP | 77/41 | 65/80 | 26/34 | 168/155 | |||||||||
#
68% Caucasians, 27% African Americans, and the remaining composed of other groups; CP, Chronic periodontitis; SCP, Severe chronic periodontitis; MCP, Moderate chronic periodontitis; HWE, Hardy-Weinberg Equilibrium; Mixed, Both smokers and non-smokers; NR, Not reported;
*, it stands for one star in the “star system” (with a maximum of nine stars) of the Newcastle-Ottawa Scale.