## 4 Discussion
This new classification is the product of the World Workshop on the Classification of Periodontal and Peri-implant Diseases and Conditions organized jointly by the American Academy of Periodontology (AAP) and the European Federation of Periodontology (EFP) to create a consensus knowledge base for a new classification to be promoted globally. Furthermore, some aspects such as the surface and position of the implants (anterior or posterior), the type of prosthetic restoration used (removable or fixed), type of retention (screw or cemented), the need for guided bone regeneration before or at the time of implant placement, general oral cavity health conditions were not referred or varied between studies. The techniques of DNA isolation also differ between studies, with some studies obtaining DNA from oral mucosal cells using swabs [22; 23; 24; 25; 34] and others using mouthwashes [21]. Other authors obtain DNA from blood [26; 35]. Within the limits of this systematic review, it might be concluded that there is no obvious association between specific genetic polymorphism of IL-1 and IL-1 RN and peri-implantitis, although a tendency should be underlined showing the potential link between IL-1 genotype and peri-implantitis. For the meta-analysis, it was only possible to include four articles [21; 23; 24; 26] since, in order to obtain a more real result on the true influence of the polymorphism in the disease, allele frequencies were evaluated. The remaining studies were excluded as they did not mention whether the patients were homozygous or heterozygous for the mutated allele, which may influence the interpretation of the results. The common polymorphism in these four studies was IL-1B \(+\)3954, which was evaluated. In the present study, it was found that individuals who had the polymorphism in the IL-1B \(+\)3954 had an almost twice higher risk of developing peri-implantitis (OR 1.986). This result is in agreement with a meta-analysis performed by [PERSON] et al. where the association between IL-1A \(-\)889, ILB \(+\)3954, IL-1B \(-\)511, composite genotype of IL-1A \(-\)889 and ILB \(+\)3954, and TNF-\(\alpha\)\(-\)308 and risk of peri-implant disease (PID) was evaluated [29]. The PID included implant failure/loss, marginal bone loss and peri-implantitis. When a subgroup analysis is performed, it is observed that only IL-1B \(+\)3954 is associated with a higher risk of peri-implantitis (OR 1.87). In a meta-analysis carried out by [PERSON] et al., that included four articles regarding the relationship of IL-1 polymorphisms and peri-implantitis, the composite genotype of IL-1 \(-\)889 and IL-1B \(+\)3954 was associated with increased risk of peri-implantitis (OR 2.34) [19]. The inclusion criteria differed from the present study, which allowed the authors to assess the relationship between the composite genotype and peri-implantitis. In a recent meta-analysis, which evaluated association between interleukin-1 polymorphisms and susceptibility to PID, the authors observed that there was no association between IL\(-\)1A \(-\)889, IL\(-\)1B \(-\)511 and IL\(-\)1 RN (VNTR) polymorphisms and the risk of PID [28]. In contrast, an association was observed between the composite genotype of IL\(-\)1A \(-\)889 and IL\(-\)1B +3954 and PID. In addition, the T allele and CT genotype of IL\(-\)1B +3954 polymorphism were also associated with an elevated risk of PID. In subgroup analysis no association was found between the polymorphisms evaluated and the risk of peri-implantitis [28]. However, the results of the study have to be interpreted with caution because the authors included in the same group of PID, patients with peri-implantitis, patients with marginal bone loss and patients with implant failure. However, bone loss can occur with or without the sign of infection, whereas peri-implantitis is an inflammatory lesion associated with loss of supporting bone around implant [5]. On the other hand, not all implant failures are caused by peri-implantitis and not all peri-implantitis lead to implant loss.