XIST and periodontitis: The lncRNAs TUG1, prostate cancer-associated transcript 1 (PCAT1), X-inactive specific transcript (XIST), Fer-1-like family member 4 (FER1L4), growth arrest-specific transcript 5 (GAS5), Prader Willi/Angelman region RNA 6 (PWAR6), osteogenesis impairment-related lncRNA of PDLSCs from periodontitis patients (lncRNA-POIR), Twist1, and antisense non-coding RNA in the inhibitor of cyclin-dependent kinase 4 (INK4) locus (ANRIL) have been reported to enhance osteogenic differentiation of PDL cells [32,45,48,50,51,52,55,56,58,59].