Behaviour of co-cultured human osteoclastic and osteoblastic cells exposed to endodontic sealers' extracts

Bone tissue is constantly being moulded and shaped by the coordinated action of bone-resorbing osteoclasts and bone-synthesizing osteoblasts. This study addresses the long-term effects of endodontic sealers' extracts (AH Plus™, GuttaFlow™, Tubliseal™, Sealapex™ and RealSeal™) on co-cultures of human osteoclastic and osteoblastic cells.

The sealers were mixed according to the manufacturer's instructions, freshly extracted with culture medium (1.3 cm(2)/ml; 24 h; 37 °C, 5% CO2/air) and diluted (1:20-1:2,500). Co-cultures of osteoclastic and osteoblastic cells, established from precursors present in human peripheral blood mononuclear cells and bone marrow cells, respectively, were exposed to the extracts for 21 days. Co-cultures were characterized for the osteoclastic and osteoblastic response.

The sealers caused a dose-dependent decrease on TRAP and ALP activities, respectively, an osteoclastic and an osteoblastic marker. The resorbing ability of the osteoclastic cells and the expression of osteoclastic and osteoblastic genes were also decreased; in addition, the extracts affected several intracellular signalling pathways. Inhibition was higher during the two first weeks, followed by adaptive cell responses. Osteoblastic response was more sensitive to the extracts' toxicity and showed lower adaptive ability.

A correlation to the clinical situation cannot be predicted; however, the results suggest that the sealers' eluents might disrupt the highly regulated interaction between osteoblastic and osteoclastic cells, compromising the local bone metabolism. Also, the higher susceptibility of the osteoblastic response might be particularly relevant in the initial stages of the healing of periapical lesions, due to the significant role of the bone formation events.