A Calibration Method Used for Volumetric Measurement of Orthodontically Induced Root Resorption Craters

Effect of local application of bone morphogenetic protein -2 on experimental tooth movement and biological remodeling in rats

Background: This study attempts to detect the potential effects of local bone morphogenetic protein -2 (BMP-2) on orthodontic tooth movement and periodontal tissue remodeling. Methods: Forty adult SD rats were randomly divided into four groups: blank control group, unilateral injection of BMP-2 on the pressure side or tension side of orthodontic teeth and bilateral injection of BMP-2. Their maxillary first molar was moved by a 30 g constant force closed coil spring. 60 μL of BMP-2 with a concentration of 0.5 μg/mL was injected into each part at a time. In addition, three rats were selected as healthy control rats without any intervention. Fluorescent labeled BMP-2 was used to observe the distribution of exogenous BMP-2 in tissues. Micro-CT was used to measure the microscopic parameters of tooth displacement, trabecular bone and root absorption volume. Three different histological methods were used to observe the changes of tissue remodeling, and then the number of osteoclasts and the content of collagen fibers were calculated. Results: Compared with the blank control group, BMP-2 injection reduced the movement distance and increased the collagen fiber content and bone mass (p < 0.01). There was no significant difference in tooth movement distance, BV/TV ratio and BMD between injection sites in unilateral injection group (p > 0.05). In the case of bilateral injection of BMP-2, the osteogenesis is enhanced. Unilateral injection of BMP-2 did not promote root resorption, but double injection showed root resorption (p < 0.01). Conclusion: Our study does show that the osteogenesis of BMP-2 is dose-dependent rather than site-dependent when a certain amount of BMP-2 is applied around orthodontic teeth. Local application of BMP-2 around orthodontic teeth in an appropriate way can enhance bone mass and tooth anchorage without increasing the risk of root absorption volume. However, high levels of BMP-2 may cause aggressive root resorption. These findings are of great significance, that is, BMP-2 is an effective target for regulating orthodontic tooth movement.

Association of orthodontic force system and root resorption: A systematic review

INTRODUCTION

In this systematic review, we assessed the literature to determine which evidence level supports the association of orthodontic force system and root resorption.

METHODS

PubMed, Cochrane, and Embase databases were searched with no restrictions on year, publication status, or language. Selection criteria included human studies conducted with fixed orthodontic appliances or aligners, with at least 10 patients and the force system well described.

RESULTS

A total of 259 articles were retrieved in the initial search. After the review process, 21 full-text articles met the inclusion criteria. Sample sizes ranged from 10 to 73 patients. Most articles were classified as having high evidence levels and low risks of bias.

CONCLUSIONS

Although a meta-analysis was not performed, from the available literature, it seems that positive correlations exist between increased force levels and increased root resorption, as well as between increased treatment time and increased root resorption. Moreover, a pause in tooth movement seems to be beneficial in reducing root resorption because it allows the resorbed cementum to heal. The absence of a control group, selection criteria of patients, and adequate examinations before and after treatment are the most common methodology flaws.

Physical properties of root cementum: Part 17. Root resorption after the application of 2.5° and 15° of buccal root torque for 4 weeks: a microcomputed tomography study

INTRODUCTION

Root resorption is an undesirable consequence of orthodontic tooth movement. The severity is unpredictable, and, despite extensive research, the etiology remains unknown. Torque has been acknowledged as a risk factor for root resorption. The aims of the study were to evaluate and quantify the extent of root resorption after the application of 2.5° and 15° of buccal root torque for 4 weeks.

METHODS

Fifteen patients requiring bilateral extraction of their maxillary first premolars for orthodontic treatment were recruited to the study. By using a standardized experimental protocol, the right and left premolars were randomly subjected to either 2.5° or 15° of buccal root torque. At the end of the 4-week experimental period, the premolars were extracted. A volumetric analysis of root resorption was performed by using microcomputed tomography and measured with specially designed software.

RESULTS

Overall, the amounts of root resorption were comparable after the application of 2.5° or 15° of buccal root torque (P = 0.59). There was a significant difference between the 2 force levels only at the apical region (P = 0.034). More root resorption occurred in areas of compression than in areas of tension. The variables of age and sex were not statistically significant.

CONCLUSIONS

Root resorption was evident after 4 weeks of buccal root torque application. More root resorption was seen at the apical region than at the middle and cervical regions. Higher magnitudes of torque might cause more root resorption, particularly in the apical region. As shown in previous studies, the etiology of root resorption is multi-factorial and cannot be explained by mechanical factors alone.

Detection and size differentiation of simulated tooth root defects using flat-panel volume computerized tomography (fpVCT)

OBJECTIVE

Our aim was to evaluate the capacity of flat-panel volume computerized tomography (fpVCT) to enable the observer to detect and differentiate 3 different sizes of simulated tooth root defects in radiographs.

STUDY DESIGN

Three simulated tooth root defects of different sizes and a defect-free area (160 sites in total) were randomly distributed on the buccal and lingual surface of 20 mandibular premolar roots of Sus scrofa domestica with round burs. For the imaging of the specimens, an fpVCT prototype was used. Findings were evaluated by 3 observers.

RESULTS

Cavity 0 (no lesion) was correctly identified in 53%, cavity 1 in 69%, cavity 2 in 96%, and cavity 3 in 89%. Altogether, the simulated cavities were classified in a correct manner in 77%. The values were compared using receiver operating characteristic curves. The area under the curve (AUC) for cavity 0 versus the pooled results for cavities 1-3 was found to be 0.72. The AUC for the pooled results for 0-2 (no pathologic impact) versus cavity 3 (potential pathologic impact) was 0.94. There was no significant dependence of the results on the observer (P = .37). Results with P < .05 were considered to be significant.

CONCLUSIONS

Flat-panel volume computerized tomography, which is currently used only as a research tool, has a high potential in detection and differentiation at an early stage of external root resorption cavities with pathologic relevance..

Optimization of microCT data processing for modelling of dental structures in orthodontic studies

Dental studies evaluating microCT output often examine resolution as a parameter that affects the data, but many other factors can influence image quality. The objective of this paper is to present the issues involved with the optimization of microCT data acquisition and processing for two biomechanical animal models. The first model evaluates surface and volumetric changes in root structure after in vitro fatigue loading of dog incisors. The second evaluates the in vivo morphometric bone and tooth responses to application of orthodontic force in inbred and transgenic mice. This type of data required specific magnification and noise control microCT settings to segment and render objects with acceptable definition. The proposed procedures enabled high definition rendering of changes in tooth and bone morphology in orthodontic studies. They also allowed for the construction of solid models for finite element analyses.

Physical properties of root cementum: Part 7. Extent of root resorption under areas of compression and tension

INTRODUCTION

The aim of this article was to quantify the extent of root resorption in areas of compression or tension under light and heavy buccal tipping orthodontic forces.

METHODS

The sample consisted of 36 premolars in 16 patients. On 1 side, light (25 g) or heavy (225 g) buccal tipping orthodontic forces were activated for 28 days. The contralateral side in each patient served as the control (0 g). The teeth were extracted, disinfected, imaged under a scanning electron microscope, and analyzed with commercial stereo imaging computer software modified for this study. Buccal and lingual surfaces were divided into 3 equal regions: cervical, middle, and apical. The root surface areas of these regions were documented with straight-on images. Quantification of resorption craters by using volumetric analysis was performed from stereo images taken at +/-3 degrees. The degree of resorption was correlated to the amount of surface area under compression or tension.

RESULTS AND CONCLUSIONS

The buccal cervical region had 8.16-fold more root resorption in the heavy-force group compared with the light-force group (P <.01). The other regions did not seem to have significant differences in the force levels. In the experimental teeth, there was more root resorption in the high-compression regions than in the other regions (P <.01). There were similar amounts of resorption per unit area on the lingual apical and buccal cervical regions. Regions under compression had more root resorption than regions under tension. There was more resorption in regions under heavy compression than in regions under light compression (P <.01). There was also more root resorption in regions under heavy tension than in regions under light tension (P <.01).

Physical properties of root cementum: Part 5. Volumetric analysis of root resorption craters after application of light and heavy orthodontic forces

BACKGROUND

In previous studies on root resorption, resorption was quantified by making histologic cuts or by surface area measurements of resorption craters. The aims of this study were to evaluate the effects of orthodontic force magnitude on root resorption craters with volumetric measurements and also to identify the sites that might be predisposed to resorption.

METHODS

After an experimental time of 28 days, 36 human premolars previously divided into light-force (25 g) and heavy-force (225 g) groups were extracted and prepared for scanning electron microscope imaging. Pairs of stereo images were taken, and 3-dimensional quantitative volumetric analysis was performed with commercial software.

RESULTS AND CONCLUSIONS

The mean volume of the resorption crater in the light-force group was 3.49-fold greater than in the control group; the mean volume of the resorption crater in the heavy-force group was 11.59-fold greater than in the control group ( P < .001). The heavy-force group had 3.31-fold greater total resorption volume than the light-force group ( P < .001). Buccal cervical and lingual apical regions had significantly more resorption craters than the other regions ( P < .001). There was more resorption by volume in the heavy-force group compared with the light-force group and controls. Although more resorption was recorded in the light-force group, the difference in the amount of resorption between the light-force and control groups was not statistically significant. There was significantly more resorption on the buccal cervical and lingual apical regions of the root surfaces than on the other regions, suggesting that high-pressure zones might be more susceptible to resorption after 28 days of force application.

Exploring the third dimension in root resorption

OBJECTIVE

To review and investigate the validity of various 2D quantitative measurement techniques, and to explore the third dimension of root resorption.

DESIGN

A review of the literature involving various quantitative evaluation of root resorption.

RESULTS

Quantitative evaluation of resorption using radiographs has proven to be highly inaccurate because of magnification errors and their inability to be readily repeated and reproduced. Studies using histology sections of samples have proven to be laborious and technique sensitive. Inherent parallax errors and loss of material in data transfer have denied the true understanding of this 3D event.

CONCLUSION

With the evolution in computing technology and digital imaging, the vision of evaluating the extent of root resorption in 3D has materialized. It was demonstrated that 3D volumetric quantitative evaluation of root resorption craters was feasible and its accuracy and repeatability was high.

Root resorption and its association with alterations in physical properties, mineral contents and resorption craters in human premolars following application of light and heavy controlled orthodontic forces

OBJECTIVES

To study the effect of different orthodontic force levels on cementum, investigating from the point of view of its physical properties, alterations in the mineral components, type and location of the resorption craters and the exploration in 3D of space.

DESIGN

In vivo human premolars subjected to heavy and light forces were employed for this study. After a period of movement they were analyzed for hardness and elasticity. Also, the mineral composition measuring Ca, P and F of the cementum root surface was investigated. A new method for volumetric analysis of resorption craters was developed.

RESULTS

There were no significant differences for hardness and elastic modulus between the light and heavy force groups and no significant effects for different tooth positions. Significant inter-individual variation in the Ca, P and F concentrations was noted. Force-related data showed that mean volume of the resorption crater in light-force group was 3.49-fold greater than the control group, and the heavy-force group 11.59-fold more than control group. The heavy force group had 3.31-fold greater total resorption volume then light force group. Buccal cervical and lingual apical regions demonstrated significantly more resorption craters than the other regions. The 2D measurements were strongly correlated to 3D measurements.

CONCLUSION

The application of light and heavy forces did not show any statistically significant differences in hardness and elastic modulus when compared with untreated teeth. The inconsistent increase or decrease of Ca, P and F contents between control and experimental teeth at sites of compression and tension were difficult to explain. There was more resorption by volume in the heavy force group as compared with the light group and controls. Our data also suggested that the high-pressure zones might be more susceptible to resorption after 28 days of force application.

A new method for volumetric measurement of orthodontically induced root resorption craters

This method was designed to quantify root resorption on human premolar root surfaces induced by orthodontic forces by volume. Light (25 g) or heavy (225 g) orthodontic forces were applied to 20 first maxillary premolars in 10 human subjects. The contralateral teeth of the subjects served as controls. All teeth were extracted after 28 d of experimentation and prepared for imaging. A pair of stereo scanning electron microscopy (SEM) images (+/-3 degrees ) of resorption craters was captured and imported into an image analysis software package. The images were aligned and grayscale depth maps of the craters were generated. Correction for errors due to residual tilt and curvature of the cementum surface using shading correction was performed. Thresholding was used to obtain a measure of both the cementum surface height and the average depth of the crater. The depth of the crater was the difference in these values. Crater volumes were obtained by multiplication of the average of this difference by area of the crater. Calibration of this volumetric measurement against standardized calculated known volumes on metallic rods showed good accuracy and reproducibility. In the experimental teeth, heavy forces caused threefold more resorption than light forces (P < 0.01). There was also more root resorption evident in the experimental teeth compared with the control teeth in both the light and heavy force groups.