Orthodontic stress Bcl-2 modulation and human odontoblast survival

This study assessed the effect of orthodontic traction on Bcl-2 expression and apoptosis in human dental pulp. It also explored, in absence of noxious stimuli the regeneration of odontoblasts during the entire life of the tooth. Twenty young patients, with Class II malocclusion and severe to moderate crowding, were referred for orthodontic assessment. Whole pulps were removed. Half the pulps were fixed, paraffin-embedded and processed for histology and immunohistochemistry using anti Bcl-2, Caspase 9 cleaved and Caspase 9 not cleaved antibodies. The rest of the samples, both orthodontically treated and not treated dental pulps, were immediately frozen at -80ºC after the extraction and quantitative PCR was performed. Histology showed alterations in pulp microanatomy after 8 months of treatment. Immunohistochemistry depicted a decreasing expression of Bcl-2 in dental pulp over time in the non-treated while a very weak to absent Bcl-2 expression was detected in the orthodontically treated tissues. Active and non-active forms of Caspases, were expressed in both groups of dental pulp, however staining for the non active form was stronger than the corresponding cleaved form in all samples. The increased expression was detected mainly at nuclear level. Real time qPCR results correlated with those of immunohistochemistry and exhibited a decreasing expression of Bcl-2 in the treated samples. Orthodontic traction may inhibit the expression of Bcl-2, favoring the onset of apoptosis and leading us to conclude that the physical stress in the absence of noxious stimuli might make odontoblasts regeneration less likely.