Differentiated analysis of orthodontic tooth movement in rats with an improved rat model and three-dimensional imaging.

Rat models currently available for analysis of orthodontic tooth movement often lack differentiated, reliable and precise measurement systems allowing researchers to separately investigate the individual contribution of tooth tipping, body translation and root torque to overall displacement. Many previously proposed models have serious limitations such as the rather inaccurate analysis of the effects of orthodontic forces on rat incisors. We therefore developed a differentiated measurement system that was used within a rat model with the aim of overcoming the limitations of previous studies. The first left upper molar and the upper incisors of 24 male Wistar rats were subjected to a constant orthodontic force of 0.25 N by means of a NiTi closed coil spring for up to four weeks. The extent of the various types of tooth movement was measured optometrically with a CCD microscope camera and cephalometrically by means of cone beam computed tomography (CBCT). Both types of measurement proved to be reliable for consecutive measurements and the significant tooth movement induced had no harmful effects on the animals. Movement kinetics corresponded to known physiological processes and tipping and body movement equally contributed to the tooth displacement. The upper incisors of the rats were significantly deformed and their natural eruption was effectively halted. The results showed that our proposed measurement systems used within a rat model resolved most of the inadequacies of previous studies. They are reliable, precise and physiological tools for the differentiated analysis of orthodontic tooth movement while simultaneously preserving animal welfare.