Periodontal Ligament Hydrostatic Pressure with Areas of Root Resorption after Application of a Continuous Torque Moment

Abstract

Objective: To evaluate the risk of root resorption, individual finite element models (FEMs) of extracted human maxillary first premolars were created, and the distribution of the hydrostatic pressure in the periodontal ligament (PDL) of these models was simulated. Materials and Methods: A continuous lingual torque of 3 Nmm and 6 Nmm respectively was applied in vivo to the aforementioned teeth. After extraction, FEMs of these double-rooted teeth were created based on high-resolution microcomputed tomographics (micro CT, voxel size: 35 microns). This high volumetric resolution made the recognition of very small resorption lacunae possible. Scanning electron micrographs of the root surfaces were created as well. This enabled the investigation of advantages and disadvantages of the different imaging techniques from the viewpoint of the examination of root resorption. Using the FEMs, the same loading conditions as applied in vivo were simulated. Results:The results of clinical examination and simulations were compared using the identical roots of the teeth. The regions that showed increased hydrostatic pressure (Ͼ0.0047 MPa) correlated well with the locations of root resorption for each tooth. Increased torque resulted in increased high-pressure areas and increased magnitudes of hydrostatic pressure, correlating with the experiments. Conclusion: If hydrostatic pressure exceeds typical human capillary blood pressure in the PDL, the risk of root resorption increases.

Effect of low-intensity pulsed ultrasound on orthodontically induced root resorption caused by torque: A prospective, double-blind, controlled clinical trial

“…This could be due to the relatively lower torque magnitude used in this experiment (approximately 5 N/mm) that might not be enough to produce contact of the roots of these premolars with their respective cortical plate. 7,10 In our study, increased root resorption was observed at the apical third, followed by the middle third and cervical third. This is likely because torque results in compressive forces being concentrated at the apex, 10,34 which is more susceptible to root resorption.…”

“…7,10 In our study, increased root resorption was observed at the apical third, followed by the middle third and cervical third. This is likely because torque results in compressive forces being concentrated at the apex, 10,34 which is more susceptible to root resorption. 35,36 Schwarz 37 reported that orthodontic force should not exceed the capillary blood pressure, and areas in which the orthodontic force exceeds the capillary blood pressure show root resorption.…”

“…They observed maximum root resorption at the apical region where orthodontic force exceeded the capillary blood pressure. 10 Bartley et al 8 applied 2.85 N/mm (285 g/mm) of torque and observed more resorption at the apical level than at the middle and cervical level. Casa et al 9 applied 6 N/mm of torque and reported severe root resorption at the apex.…”

“…35,36 Schwarz 37 reported that orthodontic force should not exceed the capillary blood pressure, and areas in which the orthodontic force exceeds the capillary blood pressure show root resorption. 37 Hohmann et al 10 studied the effect of torque on Periodontal ligament (PDL) hydrostatic pressure using finite element analysis. They observed maximum root resorption at the apical region where orthodontic force exceeded the capillary blood pressure.…”

“…5 Torque force induces bucco-lingual rotation of the tooth, 6 and it has been identified as one of the major risk factors for OIRR. [7][8][9][10] Several studies explored potential treatments for OIIRR [11][12][13][14] but the only reported clinically acceptable modality is low-intensity pulsed ultrasound (LIPUS). 15 LIPUS is acoustic pressure waves that can stimulate a variety of cells including cementoblasts, 16 odontoblasts, 17 osteoblasts, 18 chondrocytes, 19 gingival cells, 20,21 and periodontal ligament cells.…”