Angiogenesis and healing in immature permanent teeth

Abstract

Dental pulp injury in an immature permanent tooth poses a clinical challenge and healing and apexogenesis are in part determined by the vascularity and angiogenic potential of the tissues. Angiogenesis is critical during development, healing and disease but is complex and dependent on the interaction of angiogenic genes, growth factors and their receptors. The conservative nature of vital pulp therapy makes this treatment desirable but clinical outcomes will only become more predictable when there is better understanding of healing in the pulpal region, particularly regarding angiogenic signalling. This research aimed to characterise cells and tissues in the dental follicle, coronal pulp and apical papilla from healthy immature permanent teeth using immunohistochemistry and, while recognising they are part of a biological continuum, enabled comparisons between coronal and apical regions. Furthermore, the morphology and proliferative behaviour of cells from coronal pulp and apical papilla tissue, as well as their angiogenic gene expression, were investigated in cell culture experiments with and without basic fibroblast growth factor (bFGF). Finally, in a clinical case of dental pulp healing, angiogenic signalling and reparative hard tissues were evaluated. The dental follicle, coronal pulp and apical papilla all contained blood vessels, proliferating cells and evidence of angiogenic signalling necessary for healing and development. Overall it was found that the coronal pulp was significantly more vascular than the apical papilla while the apical cell-rich-zone contained a rich source of vascular and angiogenic factors. Fibroblasts from both regions showed increased proliferation compared with controls when cultured with bFGF, and use of RT2 Profiler™ microarray technology and Real time polymerase chain reaction enabled simultaneous analysis of 84 angiogenic related genes and showed differences in gene expression between coronal and apical regions. Novel genes of interest and potential interest were identified with several known to promote and regulate angiogenesis via VEGF pathways. Treatment with bFGF resulted in significant up-regulation of ANGPT2, BAI1 and HGF genes in coronal fibroblasts, while in apical fibroblasts TGFB2 was significantly down-regulated. In addition, the FLT1 gene was highly expressed in apical cells which may indicate it plays an important role in development and angiogenesis in this region. The results confirm the hypothesis that differences between the coronal pulp and apical papilla are in part due to the angiogenic and growth potential of the two tissues and suggest that different angiogenic pathways may be involved in healing in the crown and apex. Furthermore, these differences might be due to functional differences within the pulp and apical papilla and may contribute to variability in the healing potential of different regions. Following trauma and in the presence of inflammation a case is presented demonstrating the ability of the pulp to retain vitality with the capacity for angiogenic signalling, and the ability of cells to contribute to healing with reparative tissues which appear to be periodontal in origin. This study has increased our understanding of angiogenesis in healing and development, and indicates bFGF may have a role in new therapies aimed at maintenance of pulp vitality and facilitating apexogenesis.