In-vivo Effects of Different Orthodontic Loading on Root Resorption and Correlation to Mechanobiological Stimulus in Periodontal Ligament

Orthodontic root resorption (ORR) is a common side effect of orthodontic therapy. High pressure in the periodontal ligament (PDL) generated by orthodontic forces will trigger recruitment of odontoclasts, leaving resorption craters on root surfaces. The patterns of resorption craters are the traces of odontoclast activity under certain orthodontic force. This study aimed to investigate resorptive patterns by: (1) quantifying spatial root resorption under different in-vivo orthodontic loadings using micro-CT imaging technique; and (2) correlating the induced mechanobiological stimulus distribution in PDL with in-silico nonlinear finite element analysis (FEA). This study indicated that the heavy load (225 g) led to a larger total resorption volume than the light load, mainly by having larger individual crater volumes (p < 0.001) than increasing crater numbers, suggesting that intensifying mechanobiological stimulation beyond a certain extent predominantly boosted odontoclast resorption activity rather than recruiting more odontoclasts. Furthermore, buccal-cervical and lingual-apical regions in both light and heavy force groups were found to have significantly larger resorption volumes than other regions (p < 0.005). These data are consistent with our FEA results, suggesting that compressive hydrostatic pressure exceeding human systolic pressure (16 kPa) was more likely to induce resorption