*3.1.8 Telopeptide*

Bone resorption is a basic physiological process that is central to the understanding of many key pathologies, with its most common oral manifestation seen as the alveolar bone destruction in periodontitis [25]. The osteoid matrix consists principally of collagen (90%), other smaller proteins, and proteoglycans. The main structural protein of the bone is type I collagen. Consequently, most available bone resorption markers are based on degradation products of type I collagen. According to Koizumi et al. [26], ICTP (telopeptide) is one of the best markers for clinical use.

## *3.1.9 miRNAs (microRNAs)*

Nowadays, RNAs that do not code for protein have taken on great importance because, in addition to maintaining their importance in the determination of cellular phenotypes [27], now they are recognized as dynamic participants in the performance of cellular activities [28].

It has been mentioned and demonstrated that miRNAs are involved in bone metabolism, in fact, some studies have shown that they are associated with the activator of the nuclear factor receptor kappa-B ligand (RANKL) induced osteoclastogenesis. Within these miRNAs, miR-223 [29] was the first to associate with periodontal tissue, although other miRNAs such as miR-15a, miR-29b, miR-125a, miR-146a, miR148 / 148a, miR-223 and miR-92 have been identified more recently as important in periodontal health and have even been considered potential biomarkers [30].
