RAG2 and periodontitis: The prevalence of rag-3 (27 cases) was the most detected followed by rag-4 (20 cases) and rag-1 (14 cases); the lowest occurrence was rag-2 (10 cases) with lower GI and PD/PI/SBI values, showing the rag-3 and rag-4 locus genes might be the predominant genotypes in the patients of orthodontic gingivitis and mild-to-moderate periodontitis in the populations of Shandong region.