Micro-CT evaluation of tooth, calvaria and mechanical stress-induced tooth movement in adult Runx2/Cbfa1 heterozygous knock-out mice

Abstract

Runx2/Cbfa1 is essential for osteoblast differentiation and bone formation. Runx2 null mice (Runx2^-/-) completely lack mineralized tissue and die soon after birth, whereas Runx2 heterozygous knock-out mice (Runx2^+/-) stay alive but show morphological defects in the skeletal system as observed in cleidocranial dysplasia (CCD) in humans. The aim of this study is to elucidate the role of Runx2 in adult mineralized tissue and also to reveal the distinct features of heterozygous deletion of Runx2 in response to tooth movement. Therefore, we examined the cranium, tooth and the periodontium in adult Runx2^+/- using soft X-ray and micro-CT. In addition, tooth movement induced by mechanical loading was evaluated. In adult Runx2^+/-, crown: root ratio of the first maxillary molar was significantly lower than that of wild type (WT). Irregularities in root morphology was also observed. The cranium was narrow with thin parietal bone compared to WT. Mechanical stressinduced tooth movement was similar between Runx2^+/- and WT in terms of movement distance. However, while rotational movement between the first and third week was increased in WT, it was not altered in Runx2^+/- mice. These data indicate that Runx2 plays a role in cranium and the tooth development in adulthood.