PTH and Peri-Implantitis: In particular, the concentrations of TRAcP-5, RANKL, and OPG during symptomatic and asymptomatic periapical cysts have been studied both at the serum and salivary levels; of CTX, OC, and BALP during periodontal diseases and of calprotectin and N-terminal telopeptide (NTx) in patients suffering from peri-implantitis; and of OC, deoxypyridinoline, CTX, N-terminal telopeptides, BALP, and parathyroid hormone in patients suffering from osteonecrosis of the jaw bones related to bisphosphonates.