Multi-nucleated cells remove the main hyalinized tissue and start resorption of adjacent root surfaces

Investigation of Forces and Moments during Orthodontic Tooth Intrusion Using Robot Orthodontic Measurement and Simulation System (ROSS)

The Robot Orthodontic Measurement and Simulation System (ROSS) is a novel biomechanical, dynamic, self-regulating setup for the simulation of tooth movement. The intrusion of the front teeth with forces greater than 0.5 N poses a risk for orthodontic-induced inflammatory root resorption (OIIRR). The aim was to investigate forces and moments during simulated tooth intrusion using ROSS. Five specimens of sixteen unmodified NiTi archwires and seven NiTi archwires with intrusion steps from different manufacturers (Forestadent, Ormco, Dentsply Sirona) with a 0.012″/0.014″/0.016″ wire dimension were tested. Overall, a higher wire dimension correlated with greater intrusive forces Fz (0.012″: 0.561-0.690 N; 0.014″: 0.996-1.321 N; 0.016″: 1.44-2.254 N) and protruding moments Mx (0.012″: -2.65 to -3.922 Nmm; 0.014″: -4.753 to -7.384 Nmm; 0.016″: -5.556 to -11.466 Nmm) during the simulated intrusion of a 1.6 mm-extruded upper incisor. However, the 'intrusion efficiency' parameter was greater for smaller wire dimensions. Modification with intrusion steps led to an overcompensation of the intrusion distance; however, it led to a severe increase in Fz and Mx, e.g., the Sentalloy 0.016″ medium (Dentsply Sirona) exerted 2.891 N and -19.437 Nmm. To reduce the risk for OIIRR, 0.014″ NiTi archwires can be applied for initial aligning (without vertical challenges), and intrusion steps for the vertical levelling of extruded teeth should be bent in the initial archwire, i.e., 0.012″ NiTi.

Light orthodontic force with high-frequency vibration accelerates tooth movement with minimal root resorption in rats

OBJECTIVES

To determine and compare the effects of high-frequency mechanical vibration (HFV) with light force and optimal force on the tooth movement and root resorption in rat model.

MATERIALS AND METHODS

Seventy-two sites in 36 male Wistar rats were randomly assigned using a split-mouth design to control (no force/no vibration) or experimental groups: HFV (125 Hz), light force (5 g), optimal force (10 g), light force with HFV, and optimal force with HFV for 14 and 21 days. The amount of tooth movement, 3D root volume, and root resorption area were assessed by micro-computed tomography and histomorphometric analysis.

RESULTS

Adjunction of HFV with light force significantly increased the amount of tooth movement by 1.8-fold (p = 0.01) and 2.0-fold (p = 0.01) at days 14 and 21 respectively. The HFV combined with optimal force significantly increased the amount of tooth movement by 2.1-fold (p = 0.01) and 2.2-fold (p = 0.01) at days 14 and 21 respectively. The root volume in control (distobuccal root (DB): 0.60 ± 0.19 mm³, distopalatal root (DPa): 0.60 ± 0.07 mm³) and HFV (DB: 0.60 ± 0.08 mm³, DPa: 0.59 ± 0.11 mm³) were not different from the other experimental group (range from 0.44 ± 0.05 to 0.60 ± 0.1 mm³) with the lowest volume in optimal force group.

CONCLUSIONS

Adjunction of HFV with orthodontic force significantly increased tooth movement without causing root resorption.

CLINICAL RELEVANCE

Using light force with HFV could help to identify alternative treatment option to reduce the risk of root resorption.

Orthodontic Loads in Teeth after Regenerative Endodontics: A Finite Element Analysis of the Biomechanical Performance of the Periodontal Ligament

The objective of this study was to analyse the stress distribution in the periodontal ligament and tooth structure of a cementum-reinforced tooth, a dentine-reinforced tooth and an immature tooth during orthodontic loads using a finite element analysis. A finite element model of a maxillary incisor and its supporting tissues was developed. The root was segmented into two parts: a part that represented a root in an immature state and an apical part that represented the tissue formed after regenerative endodontics. The apical part was given the mechanical properties of dentine or cementum. The three models underwent simulation of mesial load, palatal inclination and rotation. The mean stress values and stress distribution patterns of the periodontal ligament of the dentine- and cementum-reinforced teeth were similar in all scenarios. The maturation of the root, with either dentine or cementum, was beneficial for all scenarios, since the periodontal ligament of the immature tooth showed the highest mean stress values. Under the condition of this computational study, orthodontic loads can be applied in teeth previously treated with regenerative endodontics, since the distribution of stress is similar to those of physiologically mature teeth. In vivo studies should be performed to validate these results.

Comparison of surface roughness of root cementum and orthodontically induced root resorption craters from high- and low-fluoridation areas: a 3D confocal microscopy study

Background

Fluoride has a major role in strengthening the structure of enamel against acids. Despite differences between caries and root resorption processes, both events inherently involve acidic dissolution of dental tissues. The aim of the present study was to investigate the effects of water fluoridation levels on the surface roughness of root cementum and resorption craters. The findings provided more insight into the influence of fluoride on the surfaces of intact cementum surface and resorption craters.

Methods

Twenty-eight orthodontic patients were recruited from two cities in Turkey, with high (≥ 2 ppm) and low (≤ 0.05 ppm) water fluoridation. These patients needed bilateral maxillary first premolar extraction as part of their orthodontic treatment and were allocated into two study groups (n = 14 in each group) based on water fluoridation exposure level: the high-fluoride group (HF) and low-fluoride group (LF). 150 g of buccal tipping forces was applied to all maxillary first premolar teeth for 12 weeks with a beta-titanium spring which was reactivated every 4 weeks. All maxillary premolars were removed at the end of the experiment for surface roughness assessment using three-dimensional confocal microscopy and the associated software. The buccal root surface and the largest buccal resorption crater were investigated.

Results

Resorption craters were significantly rougher in LF group compared to HF group (p = 0.002). Craters were rougher than the intact root surfaces (p = 0.000). Cervical and apical regions were significantly rougher than the middle region (p = 0.000 and p = 0.024, respectively).

Conclusions

Higher water fluoridation level of ≥ 2 ppm resulted in significantly smoother root resorption craters than low water fluoridation level of ≤ 0.05 ppm when the teeth were subjected to 150 g of buccal tipping force. Fluoride seems to have a protective role at the interface of root resorption, and further mineral or histological studies may shed light on the exact protective process against root resorption.

Physical properties of root cementum: Part 28. Effects of high and low water fluoridation on orthodontic root resorption: A microcomputed tomography study

INTRODUCTION

Transient inflammatory surface resorption, referred to as orthodontic induced inflammatory root resorption (OIIRR), is an iatrogenic consequence of orthodontic tooth movement. Systemic fluoride has been associated with a reduction of OIIRR. This study aimed to investigate the effects of water fluoridation levels on OIIRR in a clinically applicable human orthodontic model.

METHODS

Twenty-eight patients who required bilateral maxillary first premolar extraction as part of orthodontic treatment were selected from 2 cities with high and low water fluoridation of ≥2 ppm and ≤0.05 ppm, respectively. Patients were separated into high fluoride (HF) and low fluoride (LF) groups on the basis of water fluoridation levels. Bilateral maxillary first premolar teeth were subjected to 150 g of buccal tipping forces for 12 weeks with reactivation every 4 weeks. Teeth were extracted at the end of 12 weeks. Root resorption crater volume was determined using microcomputed tomography and 3-dimensional reconstruction.

RESULTS

HF group showed significantly less mean root resorption volume on the palatal root surface when compared with the LF group (P = 0.025). This difference was specifically displayed at palatal apical regions (P = 0.041). When root resorption volumes from the zones of orthodontic pressure (buccal cervical, palatal apical) were combined, the mean difference between HF and LF groups was statistically significant (P = 0.045).

CONCLUSIONS

Findings of the present study indicated a positive correlation between water fluoridation and the reduction of OIIRR, especially at the zones of orthodontic pressure, using a clinically relevant human orthodontic model.

Craniofacial Bone Tissue Engineering: Current Approaches and Potential Therapy

Craniofacial bone defects can result from various disorders, including congenital malformations, tumor resection, infection, severe trauma, and accidents. Successfully regenerating cranial defects is an integral step to restore craniofacial function. However, challenges managing and controlling new bone tissue formation remain. Current advances in tissue engineering and regenerative medicine use innovative techniques to address these challenges. The use of biomaterials, stromal cells, and growth factors have demonstrated promising outcomes in vitro and in vivo. Natural and synthetic bone grafts combined with Mesenchymal Stromal Cells (MSCs) and growth factors have shown encouraging results in regenerating critical-size cranial defects. One of prevalent growth factors is Bone Morphogenetic Protein-2 (BMP-2). BMP-2 is defined as a gold standard growth factor that enhances new bone formation in vitro and in vivo. Recently, emerging evidence suggested that Megakaryocytes (MKs), induced by Thrombopoietin (TPO), show an increase in osteoblast proliferation in vitro and bone mass in vivo. Furthermore, a co-culture study shows mature MKs enhance MSC survival rate while maintaining their phenotype. Therefore, MKs can provide an insight as a potential therapy offering a safe and effective approach to regenerating critical-size cranial defects.

Microcracks on the Rat Root Surface Induced by Orthodontic Force, Crack Extension Simulation, and Proteomics Study

Root resorption is a common complication during orthodontic treatment. Microcracks occur on the root surface after an orthodontic force is applied and may be related to the root resorption caused by the orthodontic process. However, the mechanisms underlying root resorption induced by microcracks remain unclear. In this study, a rat orthodontic model was used to investigate the biological mechanisms of root resorption caused by microcracks. First, the first molar was loaded with 0.5-N orthodontic force for 7 days, and microcracks were observed on the root apex surface using a scanning electron microscope. Second, to describe the mechanical principle resulting in microcracks, a finite element model of rat orthodontics was established, which showed that a maximum stress on the root apex can cause microcrack extension. Third, after 7 days of loading in vivo, histological observation revealed that root resorption occurred in the stress concentration area and cementoclasts appeared in the resorption cavity. Finally, proteomics analysis of the root apex area, excluding the periodontal ligament, revealed that the NOX2, Aifm1, and MAPK signaling pathways were involved in the root resorption process. Microcrack extension on the root surface increases calcium ion concentrations, alters the proteins related to root resorption, and promotes cementoclast formation.

The miR-155-5p inhibits osteoclast differentiation through targeting CXCR2 in orthodontic root resorption

BACKGROUND AND OBJECTIVE

Root resorption is an unavoidable side effect of orthodontic tooth movement. The mechanism of root resorption is similar to bone resorption; the odontoclasts share similar characteristics with osteoclasts (OCs). MicroRNAs (miRNAs) such as miR-155-5p play an important role in OC differentiation, but the underlying molecular mechanism of miR-155-5p in this process is not fully understood. We found that the miR-155-5p seed sequences were complementary to a sequence conserved in the 3-untranslated region of CXCR2 mRNA. In this study, we explored the molecular mechanism underlying the effect of miR-155-5p on OC differentiation by targeting CXCR2.

MATERIALS AND METHODS

In this study, we divided the orthodontic patients into mild, moderate, and severe groups according to the severity of root resorption. The gingival crevicular fluid (GCF) of patients in different groups was collected, and the expression levels of dentin phosphoprotein (DPP) were detected by ELISA, and the expression levels of CXCR2 and miR-155-5p in GCF were detected by real-time quantitative PCR (qRT-PCR). The relationship between miR-155-5p and CXCR2 was verified by double luciferase. We analyzed changes of CXCR2 and miR-155-5p expression after transfection of miR-155-5p mimic and inhibitor into RAW264.7 cells induced by receptor activator of nuclear factor-κB ligand (RANKL) through qRT-PCR and western blotting. The effect of miR-155-5p on OC differentiation was evaluated by tartrate-resistant acid phosphatase (TRAP) staining. QRT-PCR and western blotting were used to analyze expression of the osteoclastic bone resorption-related enzymes carbonic anhydrase 2 (CA II), matrix metalloproteinase-9 (MMP-9), and cathepsin K. To further confirm the direct targeting effect of CXCR2 by miR-155-5p, we blocked CXCR2 using si-CXCR2 in RANKL-induced RAW264.7 cells.

RESULTS

Dentin phosphoprotein levels were consistent with the trend of miR-155-5p changes, and the trend of CXCR2 expression was opposite to miR-155-5p changes. miR-155-5p can be directly targeted to act on CXCR2. The expression of miR-155-5p was significantly downregulated in differentiated OCs. MiR-155-5p inhibited OC differentiation, and downregulated CA II, MMP-9, and cathepsin K expression at the protein and mRNA levels.

CONCLUSIONS

In summary, the results of this study suggested that miR-155-5p inhibited OC differentiation by targeting CXCR2, thus reducing root resorption in orthodontics. MiR-155-5p can be used as an effective target for avoiding or reducing the degree of root resorption in orthodontic treatment.

Effect of photobiomodulation on external root resorption during orthodontic tooth movement - a randomized controlled trial

OBJECTIVE

The objective of the study was to compare external root resorption during orthodontic tooth movement between patients who were subjected to photobiomodulation and those who were not.

MATERIALS AND METHODS

The study was designed as a split-mouth, single-blind randomized controlled trial conducted on twenty-two orthodontic patients requiring extraction of maxillary first premolars (age group 13-30years). A buccal force was applied to all the premolars using a 0.019″×0.025″ beta-titanium cantilever spring for 28days. The test group premolars were irradiated by indium-gallium-arsenide (InGaAs) diode laser (980nm, 100mW) 0, 3, 7, 11, 15 and 28days after force application. Each premolar was irradiated at ten locations on the buccal and palatal gingiva resulting in a total energy of 10J delivered per tooth. After 28days, the root surface of all the premolars were studied for the number and volume of resorption craters using three-dimensional optical profilometry by a blinded assessor. One-sample Kolmogorov-Smirnov test was used to ascertain normality and Mann-Whitney U test was applied for data analysis.

RESULTS

All twenty-two patients enrolled completed the study. The root surface analysis showed formation of 32.78% less number of resorption craters (P<0.05) and 39.49% less volume of resorption craters (P<0.05) in the test group premolars relative to the control group premolars.

CONCLUSIONS

The results of the present study, therefore, suggest that photobiomodulation reduces external root resorption during orthodontic tooth movement.

TRIAL REGISTRATION/REGISTRATION NUMBER

CTRI/2018/04/013520.

Effects of different wavelengths of low-level laser therapy on orthodontically induced inflammatory root resorption in rats investigated with micro-computerized tomography

INTRODUCTION

The objective of this research was to investigate the effects of different wavelengths low-level laser therapies on orthodontically induced inflammatory root resorption (OIIRR) during orthodontic tooth movement in rats by micro-computerized tomography.

METHODS

Forty Wistar albino rats were divided into 5 groups: control group (A), 405-nm laser group (B), 532-nm laser group (C), 650-nm laser group (D), and 940-nm laser group (E). The left side of group A was used as a positive control (A-PC), and the right side of group A was used as a negative control (A-NC) group. In all groups, the maxillary left first molars were moved mesially by 50 g of force for 14 days. The lasers were performed for 9 minutes on the maxillary left first molar tooth. At the end of the experimental period, OIIRR measurements were performed at the mesial and the distal sides along the mesial root of the maxillary first molars.

RESULTS

The root resorption volume was significantly lower in group A-NC than in groups A-PC, B, and D. The percentage of root resorption was significantly lower in group A-NC than in all other groups. The root resorption volume and the percentage of root resorption in groups C, D, and E were significantly lower than group A-PC. The depth and the width of the lacuna and even the number of mesial lacunae were similar between groups. The distal and the total lacunae were significantly lower in group A-NC than in all other groups except group C.

CONCLUSIONS

The 532-nm, 650-nm, and 940-nm lasers significantly reduced the volume of OIIRR. In addition, the 532-nm laser reduced the number of lacunae both distally and totally than all the other groups.

Root surface microcracks induced by orthodontic force as a potential primary indicator of root resorption

Root resorption is closely related to orthodontic force and affects orthodontic treatment with high incidence; however, the mechanism governing this effect is unclear. Microcracks are associated with bone resorption and may also play an important role in root resorption. This study aimed to assess the occurrence of microcracks on the root surface induced by orthodontic force, analyze the association between force and microcrack development, and propose potential measures to reduce microcracks. Different loads (0.5, 1, or 2 N) were applied between the left first molar and anterior teeth for different durations (1, 3, 7, or 14 days) in a rabbit model. The first molar was dissected and its surface was examined using scanning electron microscopy (SEM), which revealed the presence of microcracks on the compressed side of the root apices. The number, width, and length of microcracks were all positively correlated with the load magnitude and duration. The breaking strength of the root apex was tested by using a digital force tester. In addition, a finite element (FE) model was used to analyze the stress at the root apices and the crack propagation on the root surfaces. FE analysis calculated that the regions of maximum stress at the root apices were consistent with the microcrack regions observed via SEM. These results imply that orthodontic force can directly induce the occurrence and development of microcrack, and may contribute to further root resorption. Therefore, an appropriate interval and direction of orthodontic force may help reduce microcracks and prevent root resorption.

Multiple idiopathic cervical root resorption involving all permanent teeth

Multiple idiopathic external cervical root resorption is a rare condition with numerous predisposing factors that have not yet been clearly elucidated. In addition, its diagnosis and treatment pose challenges for clinicians, and thus, the extraction of the involved teeth is commonly performed. Here, we report a 29-year-old pregnant woman with no contributory medical or family/social history who experienced cervical root resorption that progressed aggressively and involved all permanent teeth. This case is unique owing to the involvement of all teeth. Reports of multiple idiopathic external cervical root resorption are rare in the literature, and the pathogenesis of the condition is poorly understood. This report aims to add an additional case to the existing literature, analyse the underlying mechanisms and provide clinicians with some guidance in diagnosing cervical root resorption.

An unusual case of invasive cervical resorption after piezosurgery-assisted en masse retraction

A 16-year-old patient sought orthodontic correction for profile improvement and labially inclined maxillary incisors. She had Class II malocclusion, protrusive maxillary and mandibular incisors, and increased overjet and overbite with an American Board of Orthodontics discrepancy index value of 25. She was treated with maxillary premolar extractions and miniscrew-supported en masse retraction assisted with piezoincisions. Extraction spaces (7.5 mm per side) were closed with maximum anchorage in 10 months. Total treatment time was 23 months. Twenty-seven months after debonding, a pink spot was noted at the buccocervial region of the left central incisor. Radiographic evaluation on cone-beam computed tomographic scans revealed a severe case of invasive cervical resorption on both central incisors, around which the piezosurgical cuts had been made. Treatment proceeded with a nonintervention approach and the affected teeth were reinforced with a lingual retainer.

Compression and tension variably alter Osteoprotegerin expression via miR-3198 in periodontal ligament cells

Background

Osteoclasts play a critical role in bone resorption due to orthodontic tooth movement (OTM). In OTM, a force is exerted on the tooth, creating compression of the periodontal ligament (PDL) on one side of the tooth, and tension on the other side. In response to these mechanical stresses, the balance of receptor activator of nuclear-factor kappa-B ligand (RANKL) and osteoprotegerin (OPG) shifts to stimulate osteoclastogenesis. However, the mechanism of OPG expression in PDL cells under different mechanical stresses remains unclear. We hypothesized that compression and tension induce different microRNA (miRNA) expression profiles, which account for the difference in OPG expression in PDL cells.

To study miRNA expression profiles resulting from OTM, compression force (2 g/cm²) or tension force (15% elongation) was applied to immortalized human PDL (HPL) cells for 24 h, and miRNA extracted. The miRNA expression in each sample was analyzed using a human miRNA microarray, and the changes of miRNA expression were confirmed by real-time RT-PCR. In addition, miR-3198 mimic and inhibitor were transfected into HPL cells, and OPG expression and production assessed.

Results

We found that certain miRNAs were expressed differentially under compression and tension. For instance, we observed that miR-572, − 663, − 575, − 3679-5p, UL70-3p, and − 3198 were upregulated only by compression. Real-time RT-PCR confirmed that compression induced miR-3198 expression, but tension reduced it, in HPL cells. Consistent with previous reports, OPG expression was reduced by compression and induced by tension, though RANKL was induced by both compression and tension. OPG expression was upregulated by miR-3198 inhibitor, and was reduced by miR-3198 mimic, in HPL cells. We observed that miR-3198 inhibitor rescued the compression-mediated downregulation of OPG. On the other hand, miR-3198 mimic reduced OPG expression under tension. However, RANKL expression was not affected by miR-3198 inhibitor or mimic.

Conclusions

We conclude that miR-3198 is upregulated by compression and is downregulated by tension, suggesting that miR-3198 downregulates OPG expression in response to mechanical stress.

Single Local Injection of Epigallocatechin Gallate-Modified Gelatin Attenuates Bone Resorption and Orthodontic Tooth Movement in Mice

Osteoclastic bone resorption enables orthodontic tooth movement (OTM) in orthodontic treatment. Previously, we demonstrated that local epigallocatechin gallate (EGCG) injection successfully slowed the rate of OTM; however, repeat injections were required. In the present study, we produced a liquid form of EGCG-modified gelatin (EGCG-GL) and examined the properties of EGCG-GL with respect to prolonging EGCG release, NF-E2-related factor 2 (Nrf2) activation, osteoclastogenesis inhibition, bone destruction, and OTM. We found EGCG-GL both prolonged the release of EGCG and induced the expression of antioxidant enzyme genes, such as heme oxygenase 1 (Hmox1) and glutamate-cysteine ligase (Gclc), in the mouse macrophage cell line, RAW264.7. EGCG-GL attenuated intracellular reactive oxygen species (ROS) levels were induced by the receptor activator of nuclear factor-kB ligand (RANKL) and inhibited RANKL-mediated osteoclastogenesis in vitro. An animal model of bone destruction, induced by repeat Lipopolysaccharide (LPS)-injections into the calvaria of male BALB/c mice, revealed that a single injection of EGCG-GL on day-1 could successfully inhibit LPS-mediated bone destruction. Additionally, experimental OTM of maxillary first molars in male mice was attenuated by a single EGCG-GL injection on day-1. In conclusion, EGCG-GL prolongs the release of EGCG and inhibits osteoclastogenesis via the attenuation of intracellular ROS signaling through the increased expression of antioxidant enzymes. These results indicate EGCG-GL would be a beneficial therapeutic approach both in destructive bone disease and in controlling alveolar bone metabolism.

The extent of root resorption and tooth movement following the application of ascending and descending magnetic forces: a prospective split mouth, microcomputed-tomography study

Objective

Various factors have been examined in the literature in an attempt to reduce the incidence and severity of root resorption. The purpose of the present investigation is to test the null hypothesis that there is no difference in relation to force level using gradually increasing (ascending) and decreasing (descending) orthodontic force generated by magnets on the severity of Orthodontically Induced Inflammatory Iatrogenic Root Resorption (OIIRR) and amount of tooth movement.

Methods

Twenty maxillary first premolars from 10 patients were subjected to ascending (25-225 g, magnets in attraction) and descending (225 to 25 g, magnets in repulsion) buccal forces using a split mouth design over an 8-week period. Polyvinyl siloxane impressions were taken at week 0, 4, and 8 to record the tooth movement. After 8 weeks, the teeth were extracted, scanned, with micro-CT in 16.9 µm resolution, and the root resorption craters were localized circumferentially and quantified at each level of the root.

Results

The total volume of OIIRR with ascending force was 1.20 mm3, and with descending force was 1.25 mm3, and there was no statistically significant difference between them. OIIRR on the palatal surface (0.012 mm3) was significantly less than on the buccal surface (0.057 mm3) and than on the mesial surface (0.035 mm3). There is no statistically significant difference in the degree of OIIRR between different level of the root (cervical, middle, and apical) at different surfaces. Moreover, the amount of tooth movement, at 0-, 4-, and 8-week interval, secondary to an ascending and descending force application was not statistically significant.

Conclusions

There is no short-term (8 weeks) statistically significant difference between orthodontic ascending and descending forces, from 25 to 225 g and from 225 to 25 g, respectively, in term of severity and location of OIIRR as well as the amount of tooth movement. The buccal surface of the root showed highest degree of OIIRR compared to other root's surfaces.

Effect of continuous versus intermittent orthodontic forces on root resorption: A microcomputed tomography study

OBJECTIVES:

To compare the extent of root resorption and the amount of tooth movement between continuous orthodontic force and intermittent orthodontic force that was activated in a similar way to a 4-week orthodontic adjustment period.

MATERIALS AND METHODS:

Twenty-five patients who required the extraction of upper first premolars were recruited in this study. A buccally directed continuous force of 150 g was applied to the upper first premolar on one side for 15 weeks. A buccally directed intermittent force (28 days on, 7 days off) of the same magnitude was applied to the contralateral first premolar. The teeth were extracted at the end of the experimental period and processed for volumetric evaluations of resorption craters. The degree of tooth movement and rotation were measured on the study models.

RESULTS:

Continuous force application displayed significantly higher root resorption volume than the intermittent force application ( P < .05), particularly on the buccal and lingual surfaces (P < .05) and the middle third of the root ( P < .01). There was more tipping and rotational movement in the continuous force group.

CONCLUSIONS:

In a 4-week orthodontic adjustment period, intermittent force significantly reduced the amount of root resorption compared with continuous force. Although there was less degree of tooth movement with intermittent force, unwanted rotational movement was avoided. This is crucial in patients who are predisposed to orthodontically induced inflammatory root resorption, and the use of this intermittent regimen should be considered.

Low-Level Laser Action on Orthodontically Induced Root Resorption: Histological and Histomorphometric Evaluation

Introduction: Studies have been conducted to develop a means of preventing, controlling or reducing orthodontically induced root resorption. Phototherapy has demonstrated effectiveness as an anti-inflammatory and, considering the inflammatory origin of this pathology, this study evaluated the effects of laser on root resorption. Methods: The research was conducted among 54 80-day-old male Wistar rats, with weights of 280 ± 40 g. Phototherapy consisted of a diode laser (Ga-Al-As), calibrated with a wavelength of 808 nm, an output power of 100 mW, 2.1 J or 96 J of energy and area of 0.0028 cm². The application was continuous, punctual and with contact. The left first maxillary molar was moved by a super-elastic closed spring with a pre-calibrated and constant force of 25 g. The specimens were irradiated every 48 hours, totaling three or six times, depending on the group to which they belonged. Euthanasia was made in the 7th or 10th day after the onset of movement. The histological and histomorphometric examination was performed with sections of 6 μm stained with hematoxylin and eosin (H&E). Results: Considering the dosimetry studied, when compared the subgroups with the same time of movement, 7 or 10 days, the low-level laser (LLL) has no statistically significant effect on the root resorption. As expected, differences were found between groups with different time of movement. Conclusion: Based on the result, this dosimetry does not seem to be clinically recommended to avoid or reduce inflammatory root resorption, but it also does not induce any root surface alteration.

Orthodontic Forces Induce the Cytoprotective Enzyme Heme Oxygenase-1 in Rats

Orthodontic forces disturb the microenvironment of the periodontal ligament (PDL), and induce craniofacial bone remodeling which is necessary for tooth movement. Unfortunately, orthodontic tooth movement is often hampered by ischemic injury and cell death within the PDL (hyalinization) and root resorption. Large inter-individual differences in hyalinization and root resorption have been observed, and may be explained by differential protection against hyalinization. Heme oxygenase-1 (HO-1) forms an important protective mechanism by breaking down heme into the strong anti-oxidants biliverdin/bilirubin and the signaling molecule carbon monoxide. These versatile HO-1 products protect against ischemic and inflammatory injury. We postulate that orthodontic forces induce HO-1 expression in the PDL during experimental tooth movement. Twenty-five 6-week-old male Wistar rats were used in this study. The upper three molars at one side were moved mesially using a Nickel-Titanium coil spring, providing a continuous orthodontic force of 10 cN. The contralateral side served as control. After 6, 12, 72, 96, and 120 h groups of rats were killed. On parasagittal sections immunohistochemical staining was performed for analysis of HO-1 expression and quantification of osteoclasts. Orthodontic force induced a significant time-dependent HO-1 expression in mononuclear cells within the PDL at both the apposition- and resorption side. Shortly after placement of the orthodontic appliance HO-1 expression was highly induced in PDL cells but dropped to control levels within 72 h. Some osteoclasts were also HO-1 positive but this induction was shown to be independent of time- and mechanical stress. It is tempting to speculate that differential induction of tissue protecting- and osteoclast activating genes in the PDL determine the level of bone resorption and hyalinization and, subsequently, “fast” and “slow” tooth movers during orthodontic treatment.

Observations of the Periodontal Ligament and Cementum in Cats with Dental Resorptive Lesions

The etiology of feline dental resorptive lesions is unknown, but some evidence suggests that interactions between components of the periodontium may be initiating factors in the development of these lesions. In the present study, 22 clinically normal teeth were harvested from 7 cats. The teeth and periodontium were radiographed and examined histologically. In addition, 14 of the 22 teeth were examined histometrically. Two teeth were histologically normal with an open apical foramen and two were normal with a closed apical foramen. Histological evidence of periodontal ligament degeneration without cementum resorption was observed in 8 teeth, and varying degrees of cementum resorption were observed in 10 teeth. Mandibular molar and premolar teeth had distal drift, and mandibular canine teeth had mesial drift. Alterations in the periodontal ligament may represent a preclinical stage of dental resorption.

Circulating dentinal antigen-antibody immune complexes during orthodontic tooth movement in rats

BACKGROUND

The immunogenic potential of dentin has been reported through dentin-reactive autoantibodies detection in human and animal model. This study aimed to investigate the formation and diagnostic value of immune complexes formation after autoantibodies production, and soluble dentin antigens levels associated to root resorption, in the course of orthodontic tooth movement, in rat experimental model.

METHODS

Forty Wistar rats (n = 8 for each group) were submitted to orthodontic tooth movement, in which the maxillary right first molar was mesially moved by applying of 55 g of force for 3, 7, 14, or 21 days. Untreated group was used as control. Circulating autoantibodies to rat dentinal extract, immune complexes, and soluble dentinal antigen levels were determined by immunoenzyme assays. Additionally, dentinal antigens were analyzed by immunoblot.

RESULTS

Higher serum dentin-reactive IgG and immune complex levels were detected in the 14- and 21-day groups (p < 0.05 and p < 0.001 respectively) but not in circulating dentinal antigen levels (p > 0.05), as compared to the control group. Reactivity was found to dentinal components with molecular mass (MM) ~120 and ~150 kDa, by immunoblot.

CONCLUSION

This work represents the first evidence of immune complexes formation and circulating soluble dentin antigens associated to root resorption in orthodontic tooth movement. Immune complexes formation could be used to early diagnosis of external root resorption.

Prevention of root resorption in hypofunctional teeth by occlusal function recovery

OBJECTIVE

To clarify whether occlusal hypofunction is one of the key determinants for root resorption during tooth movement and root resorption is prevented by its recovery.

MATERIALS AND METHODS

The rats were randomly divided into one control and two experimental groups: hypofunctional and recovery groups. In the hypofunctional group, an anterior metal cap and bite plate were attached to the maxillary and mandibular incisors to simulate occlusal hypofunction. In the recovery group, the appliances were removed 7 weeks after their use, and the rats were allowed to bite for 4 weeks after removal. At the age of 16 weeks, the upper first molars were moved and after 0, 7, 14, and 21 days, the maxillae were resected. The resorption area was quantified morphohistologically and tartrate-resistant acid phosphatase (TRAP)-positive cells on the root surface were counted. We also examined the expressions of receptor activator of nuclear factor-κB ligand (RANKL), macrophage-colony stimulating factor (M-CSF), and interleukin (IL)-8 immunohistochemically.

RESULTS

The amount of root resorption and the number of TRAP-positive cells were significantly greater in the hypofunctional group than in the control and recovery groups. Moreover, immunoreactivity for RANKL, M-CSF, and IL-8 was detected in the periodontal ligament and on the root surface in the hypofunctional group.

CONCLUSION

Occlusal hypofunction is one of the critical factors for root resorption; however, root resorption may be prevented by recovery of occlusal function.

Nrf2 activation attenuates both orthodontic tooth movement and relapse

During orthodontic tooth movement, osteoclasts resorb the alveolar bone at the compress side of periodontium. Reactive oxygen species (ROS) works as intracellular signaling molecules of RANKL during osteoclastogenesis, although ROS has cytotoxicity against cells such as lipid oxidation. To deal with oxidative stress, cells have a defense system that is scavenging ROS by augmented antioxidative stress enzymes via transcriptional regulation with nuclear factor E2-related factor 2 (Nrf2). Previously, we reported that augmented antioxidative stress enzymes by Nrf2-gene transfer inhibited bone destruction. In the present study, we examined the effects of Nrf2 activation on osteoclastogenesis and, thereby, orthodontic tooth movement and orthodontic relapse. Mouse macrophage cell line RAW264.7 cells were used as osteoclast progenitor cells and stimulated with recombinant RANKL (100 ng/mL) with or without Nrf2 activator sulforaphane (SFN) and epigallocatechin gallate (EGCG) or ROS scavenger catechin. Osteoclastogenesis, resorption activity, and osteoclast marker gene expression were examined. Intracellular ROS was analyzed by flow cytometry. Maxillary first molars of C57BL6 male mice were moved palatally with 0.012-inch NiTi wire (100-mN force); SFN or EGCG was injected into the palatal gingiva once a week; and phosphate buffered saline was injected on the contralateral side. Tooth movement was monitored using a stone model with precise impression, and the amount of the tooth movement was compared among groups. SFN and EGCG significantly, but catechin weakly, inhibited RANKL-mediated osteoclastogenesis in vitro. Western blot analysis revealed that SFN and EGCG augmented the nuclear translocation of Nrf2 and the expression of anti-oxidative stress enzymes such as HO-1, although catechin did not. SFN and EGCG significantly, but catechin weakly, attenuated the intracellular ROS. Finally, animal experiment revealed that both SFN and EGCG successfully inhibited the orthodontic tooth movement. Additionally, SFN inhibited the relapse. These results suggest that Nrf2 activation could be therapeutic target for the anchorage enforcement in orthodontic treatment and pharmacologic retention against relapse.

Effect of alendronate sodium on tooth movement in ovariectomized rats

OBJECTIVES

The aim of the present study was to evaluate the effect of two different dosages of alendronate on induced orthodontic movement in an experimental model involving rats with osteoporosis following ovariectomy.

DESIGN

Female Wistar rats (Rattus norvegicus) eight weeks of age were divided into four groups (n=12/group): ovariectomized (OVX group); ovariectomized and treated with alendronate sodium at 1mg/kg (Group OVX+ALN1); ovariectomized and treated with alendronate sodium at 2mg/kg (Group OVX+ALN2); and sham operated (control). Three months after ovariectomy, the maxillary right first molar was submitted to movement for five and seven days. After the death of the animals, the maxilla were removed and processed for microscopic evaluation. The maxillary left first molar (without movement) was used for comparison purposes in all groups. The samples were processed for the quantification of alveolar bone and tooth movement.

RESULTS

Intragroup comparisons showed significant movement after five and seven days (p<0.05) for all groups. Comparison among groups revealed greater tooth movement in the OVX group (p<0.05), on day 7.

CONCLUSIONS

Both alendronate sodium doses similarly decreased tooth movement in ovariectomized rats (p>0.05). Movement in ovariectomized+alendronate groups were also smaller than non-ovariectomized rats, however without statistical difference.

Contribution of cone beam computed tomography to the detection of apical root resorption after orthodontic treatment in root-filled and vital teeth

OBJECTIVE

To investigate whether root-filled teeth are similar to vital pulp teeth in terms of apical root resorption (ARR) after orthodontic treatment.

MATERIALS AND METHODS

An original sample of cone beam computed tomography (CBCT) images of 1256 roots from 30 orthodontic patients were analyzed. The inclusion criteria demanded root-filled teeth and their contralateral vital teeth, while teeth with history of trauma had to be excluded to comply with exclusion criteria. CBCT images of root-filled teeth were compared before and after orthodontic treatment in a split-mouth design study. Tooth measurements were made with multiplanar reconstruction using axial-guided navigation. The statistical difference between the treatment effects was compared using the paired t-test.

RESULTS

Twenty posterior root-filled teeth and their contralaterals with vital pulp were selected before orthodontic treatment from six adolescents (two boys and four girls; mean [SD] age 12.8 [1.8] years). No differences were detected between filled and vital root lengths before treatment (P  =  .4364). The mean differences in root length between preorthodontic and postorthodontic treatment in filled- and vital roots were -0.30 mm and -0.16 mm, respectively, without any statistical difference (P  =  .4197) between them.

CONCLUSION

There appears to be no increase in ARR after orthodontic treatment in root-filled teeth with no earlier ARR.

Downregulation of Wnt causes root resorption

INTRODUCTION

There are multiple causes of external root resorption, but absent a disease state, it is most often observed when excessive physical force is used during orthodontic treatment. Even without mechanical stimulation, however, root resorption can still occur. The purpose of this study was to test whether Wnt signaling plays a role in pathologic root resorption, by conditionally deleting Wntless (Wls) from odontoblasts and osteoblasts and then evaluating the phenotypic effects on the maintenance of the root surface.

METHODS

Ten (age, 1 month) and 20 (age, 3 months) OCN-Cre;Wls(fl/fl) mice and their wild-type littermates were evaluated using microcomputed tomography, histology, and immunohistochemistry. Phenotypic alterations in the alveolar bone, dentin, and cementum were characterized and quantified.

RESULTS

In a genetic model of reduced Wnt signaling, we found that RANKL expression is upregulated, and osteoprotegerin expression is downregulated. This molecular disruption results in an increase in osteoclast activity, a decrease in osteoblast activity, and extensive, spontaneous root resorption. A genetic strain of mice in which Wnt signaling is elevated exhibits thicker cementum, whereas, even in the perinatal period, OCN-Cre;Wls(fl/fl) mice exhibit thinner cementum.

CONCLUSIONS

Taken together, these data demonstrate that Wnts regulate cementum homeostasis, and that idiopathic cases of root resorption might have as their etiology a reduction in endogenous Wnt signaling.

Effect of interleukin-4 on orthodontic tooth movement and associated root resorption

OBJECTIVES

Interleukin-4 (IL-4) is a recognized immunomodulatory cytokine that regulates bone homeostasis. However, the influence of IL-4 on orthodontic tooth movement (OTM) and subsequent root resorption is still unknown. Therefore, the purpose of this study was to investigate the effect of IL-4 on tooth movement and its associated root resorption in a mouse model.

MATERIALS AND METHODS

The maxillary first molars of four male mice for each experimental group were subjected to mesial force by a nickel titanium coil spring for 12 days. Control mice were not given appliances and injections. Varying doses of IL-4 were injected locally, adjacent to the first molar. Two sets of experiments were designed. The first set was composed of three groups: the control, treatment with phosphate-buffered saline (PBS), or 1.5 µg/day of IL-4. The second set was composed of five groups: the control, treatment with 0 (PBS only), 0.015, 0.15, or 1.5 µg/day of IL-4. The distance of OTM was measured and tartrate-resistant acid phosphatase positive cells along the loaded alveolar bone and root surface were identified. The root resorption associated with OTM was evaluated by a scanning electron microscope.

RESULTS

The amount of OTM and the number of osteoclasts were significantly decreased in the IL-4-treated mice. Moreover, IL-4 significantly suppressed force-induced odontoclasts and root resorption.

CONCLUSION

IL-4 inhibits tooth movement and prevents root resorption in the mouse model. These results suggest that IL-4 could be used as a useful adjunct to regulate the extent of OTM and also to control root resorption.

Effect of low-intensity pulsed ultrasound on orthodontically induced root resorption in beagle dogs

We investigated the effect of low-intensity pulsed ultrasound (LIPUS) on orthodontically induced inflammatory root resorption in vivo. Ten beagle dogs were treated with an orthodontic appliance to move the mandibular fourth premolars bodily. The orthodontic movement was carried out for 4 wk with a continuous force of 1 N/side; using a split-mouth model, LIPUS was applied daily for 20 min. Fourth premolar and surrounding periodontal tissue were evaluated with micro-computed tomography and hematoxylin and eosin and tartrate-resistant acid phosphatase staining. We calculated the number, volume and distribution of root resorption lacunae and their percentage relative to total root volume, orthodontic tooth movement and periodontal ligament space. There was no significant difference in orthodontic tooth movement between the two sides. LIPUS significantly reduced the number of orthodontically induced inflammatory root resorption initiation areas by 71%, reduced their total volume by 68% and reduced their volume relative to the affected root total volume by 70%. LIPUS induced the formation of a precementum layer, thicker cementum and reparative cellular cementum.

Periodontal microstructure change and tooth movement pattern under different force magnitudes in ovariectomized rats: an in-vivo microcomputed tomography study

INTRODUCTION

The purpose of this study was to evaluate the dynamic changes in the periodontal microstructure and the molar displacement pattern during orthodontic tooth movement in ovariectomized rats.

METHODS

Twenty ovariectomized rats received either 100 or 30 g of orthodontic force to induce mesial movement of the maxillary left first molars over 14 days. Ten healthy rats underwent sham operations as controls. Periodontal ligament thickness, alveolar bone microstructural properties, and displacement of the molar were measured with 6 in-vivo microcomputed tomography scans for each sample.

RESULTS

The ovariectomized rats that received 100 g of orthodontic force had obvious changes in periodontal ligament thickness at day 1 and poor periodontal ligament thickness recovery from days 5 through 14. The bone volume fraction increased and the trabecular separation decreased significantly in this group at day 3, and obvious bone loss was observed at day 14. Molar linear and angular movements were also higher in this group than in the other 2 groups.

CONCLUSIONS

Relatively heavier force applications in ovariectomized rats resulted in poor periodontal ligament thickness recovery and local alveolar bone overcompression, and consequently induced undermining resorption and obvious alveolar bone loss; these led to high rates of tooth movement and molar inclination.

A rat model for orthodontic translational expansive tooth movement

OBJECTIVES

To present the development of an experimental model in rats for translational expansive tooth movement.

SETTING AND SAMPLE

Section of Periodontology at Department of Dentistry Aarhus University. Twenty male Wistar rats in two pilot experimental settings plus seven animals without any intervention serving as controls.

MATERIAL AND METHODS

The second molar (group P1) or the second and third molar (group P2) in the maxillae of the animals were moved buccally using transpalatal β-titanium springs. In the group P2, two spring types (high force and low force) and two preangulations (0° passive or 30° torsion moment) were tested. The amount and type of tooth movement achieved and the resulting skeletal effect were assessed on microCT images, histological analysis was performed on few selected specimens.

RESULTS

Expansive translational root movement amounting half a tooth width was achieved. Comparison of the amount of tooth movement at the right and left side of the maxilla showed that the expansion was rather symmetrical in the P2 group. Skeletal widening of the maxilla contributed in the P2 group to approximately one-third of the total root movement, whereas two-thirds were dental movement.

CONCLUSION

With the model used in the P2 group, further research on translational expansive tooth movement and its effect on the periodontium can be pursued. In models for orthodontic expansion, it is strongly recommended to separately evaluate skeletal and dental effects.

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.

Effect of teriparatide on induced tooth displacement in ovariectomized rats: a histomorphometric analysis

INTRODUCTION

The aim of this study was to evaluate morphologically the effect of teriparatide on induced orthodontic movement of the maxillary first molars in ovariectomized rats.

METHODS

Ovariectomized Wistar rats (n = 16), ovariectomized rats treated with teriparatide (n = 16), and nonovariectomized rats (n = 16) had orthodontic tooth movement for 5 and 7 days. The group treated with teriparatide received a subcutaneous injection (Forteo, Eli Lilly, Indianapolis, Ind; 30 μg/kg/day) for 90 days after the ovariectomy. Histologic sections obtained from the maxilla were prepared for the morphometric analysis of dental movement, the thickness of the periodontal ligament, and the number of osteoclasts in the pressure and tension areas of the apex of the root and alveolar crest in the distal root of the maxillary first molars.

RESULTS

The ovariectomized rats treated with teriparatide had similar responses at 5 and 7 days after the induced dental movements compared with the untreated ovariectomized group. Both ovariectomized groups had greater molar movement on day 7 day compared with the controls (P <0.05). There were no statistically significant differences between groups in the spacing of the periodontal ligament or the number of osteoclasts in the areas studied.

CONCLUSIONS

These data suggest that the treatment of osteoporosis with teriparatide is a good alternative for patients undergoing orthodontic treatment.

Experimental orthodontic tooth movement and extensive root resorption: periodontal and pulpal changes

Previous studies have reported changes both in dental pulp and in periodontal ligament (PDL) following orthodontic tooth movement. However, pulpal changes following extensive root resorption after orthodontic tooth movement have not been studied in detail. The aim of this study was therefore to evaluate inflammatory changes, both in the dental pulp and in the compressed PDL, after experimentally induced extensive root resorption. Extensive root resorption was induced in rats by the activation and re-activation of orthodontic force, with a short intervening period of no force application. The distribution of immune cells, nerve fibres and blood vessels was studied immunohistochemically using antibodies against CD68-immunoreactive (IR) cells, major histocompatibility complex (MHC) class II Ia-expressing cells, CD43-IR cells, protein gene product 9.5 (PGP 9.5), and laminin. In the compressed PDL of experimental first molars, significantly increased density of CD68-IR cells and MHC class II Ia-expressing cells were found, whereas the density of CD43-IR cells were unchanged when compared with control second molars. In the compressed PDL, there was an increased density of blood vessels, but no sprouting of nerve fibres. In the dental pulp, however, no increased density of immune cells or sprouting of nerve fibres was recorded. In conclusion, inflammation after extensive root resorption was confined to the compressed PDL, whereas the dental pulp was unaffected.