Background/Objectives: This study aimed to establish the regularities of changes in the content of matrix metalloproteinase 8 (MMP-8) and osteoprotegerin (OPG), the most well-known indicators of bone metabolism disorders, in the saliva of children with different severities of chronic kidney disease (CKD) who need orthodontic treatment. This evidence concerns the gene TNFRSF11B and chronic kidney disease.