Automated tooth segmentation as an innovative tool to assess 3D-tooth movement and root resorption in rodents

Abstract

Background Orthodontic root resorptions are frequently investigated in small animals, and micro-computed tomography (μCT) enables volumetric comparison. Despite, due to overlapping histograms from dentine and bone, accurate quantification of root resorption is challenging. The present study aims at (i) validating a novel automated approach for tooth segmentation (ATS), (ii) to indicate that matching of contralateral teeth is eligible to assess orthodontic tooth movement (OTM) and root resorption (RR), (iii) and to apply the novel approach in an animal trial performing orthodontic tooth movement. Methods The oral apparatus of three female mice were scanned with a μCT. The first molars of each jaw and animal were segmented using ATS (test) and manually (control), and contralateral volumes were compared. Agreement in root volumes and time efficiency were assessed for method validation. In another n = 14 animals, the left first upper molar was protracted for 11 days at 0.5 N, whereas the contralateral molar served as control. Following ATS, OTM and RR were estimated. Results ATS was significantly more time efficient compared to the manual approach (81% faster, P < 0.01), accurate (volume differences: − 0.01 ± 0.04 mm3), and contralateral roots had comparable volumes. Protracted molars had significantly lower root volumes (P = 0.03), whereas the amount of OTM failed to reveal linear association with RR (P > 0.05). Conclusions Within the limits of the study, it was demonstrated that the combination of ATS and registration of contralateral jaws enables measurements of OTS and associated RR in μCT scans.

Standardized assessment of bone micromorphometry around teeth following orthodontic tooth movement

“…Undecalcified regions were mostly found in proximity to the tooth root and decreased towards the borders of the 100 µm VOI, suggesting that bone resorption was highest in close proximity to the roots but still present in the selected region. In addition, bone resorption was highest at the mesial roots which is in line with a recent 3D analysis showing that intrusion and mesial–palatal tipping was the most common movement of the protracted teeth [ 26 ].…”

3D quantification of in vivo orthodontic tooth movement in rats by means of micro-computed tomography

“…Not only did we observe tipping but also increased bone and root resorption, which has been associated with high OF [6,10]. Although most studies use forces much higher than 25 g [9,28,29], the aforementioned carry-over effect needs to be further confirmed with lower OF.…”

“…Recent methods for real 3D quantification of OTM in mice [28,29] calculate tooth displacement by mirroring the experimental side on the contralateral side. These types of split-mouth models allow for internal controls and reduce sample size.…”

Dynamic Changes in Tooth Displacement and Bone Morphometry in Orthodontic Tooth Movement in Rats: A 3D Analysis

“…Although the measurements became more and more accurate, the evaluation of the dynamic changes induced by OF still remains di cult, as it is hard to nd a reliable reference structure. Previous studies in rats evaluated OTM in an indirect way based on external reference structures such as the contralateral maxilla (splitmouth designs) [19,31] , the incisors [28,32] , the zygomatic arch [17] or the diastema formed between the rst and the second molar [10,15,[33][34][35][36] . However, these methods rely on those reference structures remaining stable during OTM.…”