MT1H and periodontitis: Alterations in the expression of the MT1 and MT2 genes can lead to clinical alterations in patients with Down syndrome, such as severe periodontal disease, implant loss, or peri-implantitis; they may be related to the aforementioned role of these molecules in the early stages of bone healing, which can lead to a failure of osseointegration or to the presence of a bone with little strength to withstand the aggressions of the oral environment—this being especially important in the case of both periodontitis and peri-implantitis.