An in vivo 3D micro-CT evaluation of tooth movement after the application of different force magnitudes in rat molar

Caffeine induces alveolar bone loss in rats submitted to orthodontic movement via activation of receptor activator of nuclear factor ҡB, receptor activator of nuclear factor ҡB ligand, and osteoprotegerin pathway

INTRODUCTION

Caffeine is a widely consumed substance with several effects on bone metabolism. This study aimed to investigate the effect of caffeine on the bone tissue of rats submitted to orthodontic movement.

METHODS

Twenty-five male Wistar rats underwent orthodontic movement (21 days) of the first permanent maxillary molars on the left side. The experimental group (caffeine; n = 13) and control group (n = 12) received caffeine and water, respectively, by gavage. Microcomputed tomography was performed to analyze orthodontic movement. Histologic analysis of the inflammatory infiltrate and osteoclast count by tartrate-resistant acid phosphatase were conducted. Maxilla tissue was evaluated for receptor activator of nuclear factor ҡB (RANK), RANK ligand (RANKL), and osteoprotegerin by immunohistochemistry.

RESULTS

Caffeine exhibited a lower bone volume/tissue volume ratio (78.09% ± 5.83%) than the control (86.84% ± 4.89%; P <0.05). Inflammatory infiltrate was increased in the caffeine group compared with the control group (P <0.05). A higher number of tartrate-resistant acid phosphatase-positive cells was observed in the caffeine (9.67 ± 1.73) than in the control group (2.66 ± 0.76; P <0.01). Immunoexpression of RANK and RANKL in the caffeine group was greater than the control (P <0.05).

CONCLUSIONS

The use of caffeine thermogenic induces alveolar bone loss in rats submitted to orthodontic movement via activation of RANK, RANKL, and osteoprotegerin signaling pathways.

Early-stage periodontal ligament compression predicts orthodontically induced root resorption in rats

OBJECTIVES

To determine the effect of orthodontic pressure on periodontal ligament (PDL) compression in rats and assess correlation between PDL compression and orthodontically induced root resorption (OIRR).

MATERIALS AND METHODS

Eight female Wistar rats aged 10 weeks underwent surgery to place 2 mini-screws at the center of the palatal plate. 25 cN coil springs connecting the maxillary first molars and mini-screws were applied bilaterally to generate mesial force. Maxillary first molars were assigned to undergo either bodily or tipping movements. Micro-computed tomography (μCT) scans were taken on days 0, 3, 7, and 14, and histological sections were taken on day 14. OIRR was measured from histological sections, and the corresponding PDL compression ratio was quantified using μCT images.

RESULTS

The PDL was compressed by approximately 76% in tipping movement and 55% in bodily movement after 3 days, and by approximately 47% in bodily and tipping movements after 7 days of orthodontic force application. The extent of OIRR in tipping movement was significantly greater than that in bodily movement. A strong positive correlation between OIRR and PDL compression ratio was observed on day 3; however, no correlation was observed on day 7.

CONCLUSIONS

A strong correlation between PDL compression ratio and OIRR was observed at an early stage after the application of orthodontic force regardless of the tooth movement type (bodily or tipping), implying the importance of early stage PDL compression in the induction of OIRR.

The osteoclastic activity in apical distal region of molar mesial roots affects orthodontic tooth movement and root resorption in rats

The utilization of optimal orthodontic force is crucial to prevent undesirable side effects and ensure efficient tooth movement during orthodontic treatment. However, the sensitivity of existing detection techniques is not sufficient, and the criteria for evaluating optimal force have not been yet established. Here, by employing 3D finite element analysis methodology, we found that the apical distal region (A-D region) of mesial roots is particularly sensitive to orthodontic force in rats. Tartrate-resistant acidic phosphatase (TRAP)-positive osteoclasts began accumulating in the A-D region under the force of 40 grams (g), leading to alveolar bone resorption and tooth movement. When the force reached 80 g, TRAP-positive osteoclasts started appearing on the root surface in the A-D region. Additionally, micro-computed tomography revealed a significant root resorption at 80 g. Notably, the A-D region was identified as a major contributor to whole root resorption. It was determined that 40 g is the minimum effective force for tooth movement with minimal side effects according to the analysis of tooth movement, inclination, and hyalinization. These findings suggest that the A-D region with its changes on the root surface is an important consideration and sensitive indicator when evaluating orthodontic forces for a rat model. Collectively, our investigations into this region would aid in offering valuable implications for preventing and minimizing root resorption during patients' orthodontic treatment.

A novel analysis of the formation and resorption changes in dental hard tissue using longitudinal in vivo micro computed tomography

This study was to investigate the new analysis manner of dental hard tissue change using in vivo micro-computed tomography (CT) in rat. Scanning, registration, analyzing, and presenting method to track longitudinal in vivo micro-CT data on dental hard tissues were validated in murine models: formative, dentin thickness after direct pulp capping with mineral trioxide aggregate; resorptive, development of apical bone rarefaction in apical periodontitis model. Serial in vivo micro-CT scans were analyzed through rigid-registration, active-contouring, deformable-registration, and motion vector-based quantitative analyses. The rate and direction of hard tissue formation after direct pulp capping was datafied by tracing coordinate shift of fiducial points on pulp chamber outline in formative model. The development of apical periodontitis could be monitored with voxel counts, and quantitatively analyzed in terms of lesion size, bone loss, and mineral density in resorptive model. This study supports the application of longitudinal in vivo micro-CT for resorptive- and formative-phase specific monitoring of dental hard tissues.

Effects of green tea extract epigallocatechin-3-gallate (EGCG) on orthodontic tooth movement and root resorption in rats

OBJECTIVE

To study the effect of EGCG on tooth movement and root resorption during orthodontic treatment in rats.

METHODS

A total of thirty six male Wistar rats were randomly and equally divided into three groups: control, 50 mg/kg EGCG, and 100 mg/kg EGCG. During the experiment, the subjects were submitted to an orthodontic tooth movement (OTM) model, rats in the experimental groups were given the corresponding dose of EGCG, while rats in the control group were administrated with an equal volume of normal saline solution by gavage. After 14 days of OTM, the rats were sacrificed by transcardial perfusion. Micro-CT of rat maxillaes was taken to analyze OTM distance and root resorption. The maxillary samples were prepared as histological sections for H&E staining, tartrate-resistant acid phosphatase (TRAP) staining and immunohistochemical (IHC) staining to be observed and analyzed.

RESULTS

The OTM distance and root resorption of rats in the dosed group decreased, and the number of TRAP positive cells in their periodontium decreased significantly. The expression level of RANKL was decreased in the EGCG group compared to the control group, while that of OPG, OCN and Runx2 was increased. Effects were more pronounced in 100 mg/kg group than in 50 mg/kg group.

CONCLUSION

EGCG reduces OTM and orthodontic induced root resorption (OIRR) in rats, and is able to attenuate osteoclastogenesis on the pressure side and promote osteogenesis on the tension side.

Dynamic alternations of RANKL/OPG ratio expressed by cementocytes in response to orthodontic‑induced external apical root resorption in a rat model

The aim of the present study was to investigate the alterations in the formation of cementocytes in response to orthodontic forces and to evaluate the contribution of these cells in the biological changes of tooth movement and associated root resorption. A total of 90 Sprague Dawley rats were randomly assigned to the control, high force, and low force groups. Intrusion forces of 10 and 50 g were applied on the rat molar to induce tooth intrusion. The tooth movement was observed from 0 to 14 days by micro-computed tomography, bone histometric analysis, tartrate-resistant acid phosphatase staining, as well as reverse transcription-quantitative PCR and immunofluorescence staining assays. The results suggested that under low force conditions, osteoclasts were distributed at a higher frequency on the bone side than on the root side. Under high force conditions, both sides suffered osteoclast infiltration. In the low force group, the cementocytes exhibited downregulated sclerostin (SOST) and osteoprotegerin (OPG) mRNA levels and a lower receptor activator of nuclear factor-κB ligand (RANKL)/OPG ratio over a certain period of time. The expression levels of these genes were lower compared with those of the osteocytes at each time-point. In the high force group, both cementocytes and osteocytes upregulated the SOST and RANKL/OPG ratio on days 7 and 14, while the cementocytes expressed higher levels of SOST mRNA than those noted in the osteocytes. These data suggested that cementocytes responded to the orthodontic force via modulation of the RANKL/OPG ratio and SOST expression. The biological response of cementocytes contributed to the mechanotransduction and homoeostasis of the roots under compression. Excessive forces may act as a negative factor of this regulatory role. These results expand our knowledge on the function of cementocytes.

Periodontal ligament cells under mechanical force regulate local immune homeostasis by modulating Th17/Treg cell differentiation

OBJECTIVES

Improper orthodontic force often causes root resorption or destructive bone resorption. There is evidence that T helper 17 (Th17) cells and regulatory T (Treg) cells may be actively involved in bone remodeling during tooth movement. In a combination of in vitro and in vivo studies, we investigated the effect of human periodontal ligament cells (hPDLCs) on Th17/Treg cells under different orthodontic forces and corticotomy.

MATERIAL AND METHODS

hPDLCs were cultured in vitro and subjected to different mechanical forces. The expression of interleukin (IL)-6 and transforming growth factor (TGF)-β in the supernatant and the mRNA levels of hypoxia inducible factor (HIF)-1α, Notch1, and TGF-β in hPDLCs were investigated. Supernatants were collected and co-cultured with activated CD4⁺T cells, and the differentiation of Th17/Treg cells was analyzed by flow cytometry. We also established an animal model of tooth movement with or without corticotomy. The tooth movement distance, alveolar bone height, and root resorption were analyzed using micro-computed tomography. Expression of interleukin (IL)-17A, forkhead Box P3 (Foxp3), and IL-6 were analyzed using immunohistochemistry, while osteoclasts were evaluated by tartrate-resistant acid phosphatase (TRAP) staining. The mRNA levels of IL-17A, IL-6, Foxp3, IL-10, HIF-1α, notch1, and C-X-C motif chemokine ligand 12 (CXCL12) in alveolar bone and gingiva were investigated.

RESULTS

Heavy force repressed cell viability and increased the mortality rate of hPDLCs; it also improved the expression of IL-6, declined the expression of TGF-β, and promoted the mRNA expression level of HIF-1α. The expression of TGF-β and Notch1 mRNA decreased and then increased. The supernatant of hPDLCs under heavy force promotes the polarization of Th17 cells. The heavy force caused root resorption and decreased alveolar bone height and increased the positive area of IL-17A immunohistochemical staining and the expression of IL-17A, IL-6, HIF-1α, and Notch1 mRNA. Corticotomy accelerated tooth movement, increased the proportion of Foxp3-positive cells, and up-regulated the expression of Foxp3, IL-10, and CXCL12 mRNA.

CONCLUSIONS

During orthodontic tooth movement, the heavy force causes root resorption and inflammatory bone destruction, which could be associated with increased expression of Th17 cells and IL-6. Corticotomy can accelerate tooth movement without causing root resorption and periodontal bone loss, which may be related to the increased expression of Treg cells.

CLINICAL RELEVANCE

Altogether, this report provides a new perspective on the prevention of inflammatory injury via the regulation of Th17/Treg cells in orthodontics.

Ability of piezocision to retain orthodontically moved teeth in a goat model: A split-mouth study

OBJECTIVES:

to evaluate the effectiveness of piezocision in enhancing retention when performed after orthodontic tooth movement.

METHODS:

Four mature goats had their second incisors removed bilaterally. For each goat, the two sides of the mandible were either treated with piezocision or served as a positive control. Using fixed orthodontic appliance, the first and third incisors on each side were approximated and then retained in place for two weeks. Relapse was measured by the amount of space developed between the approximated incisors after six weeks from the end of the retention period. The periodontal ligament of all incisors was assessed histologically with micro computed tomography and regular hematoxylin and eosin staining.

RESULTS:

A significantly less relapse was observed in the piezocision group than in the control group (p ≤ 0.05). Bone formation occurs in the vicinity and periphery of the periodontal ligament and thus results in the narrowing of the periodontal ligament.

CONCLUSION:

A protocol of post-orthodontic retention involving piezocision can be promising to enhance stability of orthodontic treatment outcome.

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.

Experimental models of orthodontic tooth movement and their effects on periodontal tissues remodelling

OBJECTIVES

The present study aimed to compare two different models of orthodontic tooth movement (OTM) in rats by evaluating tooth movement efficiency and periodontal tissues remodelling.

DESIGN

Fifteen animals were randomly distributed into 3 groups: control group (untreated); ligature appliance (LA) as experimental OTM using a closed coil spring fixed around maxillary first molar by steel ligature; occlusal appliance (OA) as experimental OTM using a closed coil spring attached on the occlusal surface of the maxillary first molar. After 15 days, all animals were euthanized, and the maxilla of each animal was collected for qPCR, micro-computed tomography, and histological analyses.

RESULTS

Interleukin-1 beta, interleukin-6, and tumor necrosis factor-alpha gene expressions were significantly upregulated in the animals of the LA group as compared to the other groups. No significant difference was observed in tooth displacement between both methods. The LA group presented higher linear bone loss and lower values of bone volume fraction, bone mineral density, trabecular number and increased values of trabecular separation compared to the other groups. The birefringent collagen content in the tension side of the periodontal ligament contained significantly lower collagen content in the LA group than in the control group. Furthermore, on the pressure side, the collagen content was significantly lower in the LA and OA groups than in the control group.

CONCLUSIONS

The OA group presented little or no deleterious effect on periodontal tissues compared to the LA group, suggesting its use may be more reliable for OTM induction in rats for 15 days.

In vivo cell proliferation analysis and cell-tracing reveal the global cellular dynamics of periodontal ligament cells under mechanical-loading

Periodontal ligament (PDL) is a uniquely differentiated tissue that anchors the tooth to the alveolar bone socket and plays key roles in oral function. PDL cells can respond rapidly to mechanical stimuli, resulting in accelerated tissue remodeling. Cell proliferation is an initial event in tissue remodeling and participates in maintaining the cell supply; therefore, analyzing cell-proliferative activity might provide a comprehensive view of cellular dynamics at the tissue level. In this study, we investigated proliferating cells in mouse molar PDL during orthodontic tooth movement (OTM)-induced tissue remodeling. Our results demonstrated that the mechanical stimuli evoked a dynamic change in the proliferative-cell profile at the entire PDL. Additionally, cell-tracing analysis revealed that the proliferated cells underwent further division and subsequently contributed to tissue remodeling. Moreover, OTM-induced proliferating cells expressed various molecular markers that most likely arise from a wide range of cell types, indicating the lineage plasticity of PDL cells in vivo. Although further studies are required, these findings partially elucidated the global views of the cell trajectory in mouse molar PDL under mechanical-loading conditions, which is vital for understanding the cellular dynamics of the PDL and beneficial for dental treatment in humans.

The expression of extracellular matrix metalloproteinase inducer (EMMPRIN) in the compression area during orthodontic relapse

OBJECTIVE

This study investigated the expression of extracellular matrix metalloproteinase inducer (EMMPRIN) in the compression area during orthodontic relapse in rat molars.

MATERIALS AND METHODS

Thirty Wistar rats (6 weeks old) underwent orthodontic tooth movement (OTM) of the left first maxillary molar for 21 days, followed by removal of the force device. The contralateral maxillary molar served as a control with no mechanical force stimuli. Animals were sacrificed at 0, 1, 3, 7, and 14 days of relapse after force withdrawal. Tooth relapse and alveolar bone parameters were measured using microcomputed tomography (micro-CT). Maxilla sections were obtained for haematoxylin and eosin (HE), immunohistochemical staining [EMMPRIN, nuclear factor kappa B ligand (RANKL) and vascular endothelial growth factor (VEGF)] and tartrate-resistant acid phosphatase (TRAP). Correlation analyses were then performed.

RESULTS

After force removal, nearly 79.88% of the total relapse occurred within the initial 3 days. The number of osteoclasts clearly increased while the alveolar bone density decreased on the pressure side on Day 3 of relapse. Moreover, the EMMPRIN expression level significantly increased on Day 1, peaked up on Day 3 and decreased on Days 7 and 14. Statistically, a strong positive correlation was found between EMMRPIN expression and the osteoclast number and RANKL and VEGF expression.

CONCLUSION

EMMPRIN was highly expressed on the pressure side during the orthodontic tooth relapse, which could be involved in osteoclastogenesis and alveolar bone resorption in association with RANKL and VEGF expression.

Detection and analysis of enamel cracks by ICG-NIR fluorescence dental imaging

Cracked teeth are the third most common cause of tooth loss, but there is no reliable imaging tool for the diagnosis of cracks. Here, we demonstrate the feasibility of indocyanine green near-infrared fluorescence (ICG-NIRF) dental imaging for the detection of enamel cracks and enamel-dentin cracks in vitro in the first (ICG-NIRF-I, 700-950 nm) and second (ICG-NIRF-II, 950-1700 nm) imaging windows with transmission excitation light, and compared ICG-NIRF with conventional NIR illumination-II (NIRi-II) and X-ray imaging. Dentin cracks were detected by CT scan, while most enamel cracks, undetectable under X-ray imaging, were clearly visible in NIR images. We found that ICG-NIRF-II detected cracks more effectively than NIRi-II, and that light orientation is an important factor for crack detection: an angled exposure obtained better image contrast of cracks than parallel exposure, as it created a shadow under the crack. Crack depth could be evaluated from the crack shadow in ICG-NIRF and NIRi-II images; from this shadow we could determine crack depth and discriminate enamel-dentin cracks from craze lines. Cracks could be observed clearly from ICG-NIRF images with 1-min ICG tooth immersion, although longer ICG immersion produced images with greater contrast. Overall, our data show that ICG-NIRF dental imaging is a useful tool for diagnosing cracked teeth at an early stage.

Functional tooth mobility in young pigs

Mobility is a fundamental characteristic of mammalian teeth, and has been widely used to determine individual tooth prognosis. However, the direction and extent of tooth movement under functional loads are unknown. This study investigated maxillary molar mobility, alveolar bending, and periodontal space (PDL) fluid pressure during mastication and masseter muscle contraction in young pigs, along with PDL space measurements. Twelve three-month-old farm pigs were instrumented with some or all of the following: (1) ultrasonic crystals, one implanted into the pulp chamber of a deciduous maxillary molar and additional crystals glued onto its buccal and palatal alveolar plates; (2) rosette strain gauges affixed to the buccal and palatal of alveolar ridges; (3) a pressure transducer inserted into palatal alveolar bone facing the PDL. Tooth mobility, alveolar bending, and fluid pressure were simultaneously recorded during unrestrained feeding and subsequent masseter muscle stimulation. The PDL widths were measured using micro-CT. The results indicate that during the power stroke of mastication, (1) the molar displaced buccally and apically (192 ± 95 µm) regardless of the side of chewing; (2) compressive bone strain was greater on the buccal than on the palatal alveolar plate; and (3) PDL pressure increased during the power strok (3.63 ± 0.80 kPa). Masseter contraction produced similar results but with generally lower values. The PDL widths were larger than the range of tooth mobility, and showed no correlation with the mobility. Thus occlusal function causes buccal tipping and intrusion of maxillary molars with concomitant compression of the buccal alveolar plate and raised pressure within the PDL space.

A Novel Analysis via Micro-CT Imaging Indicates That Chemically Modified Tetracycline-3 (CMT-3) Inhibits Tooth Relapse after Orthodontic Movement: A Pilot Experimental Study

Objective

To evaluate the effect of chemically modified tetracycline-3 (CMT-3) and simvastatin on tooth relapse after orthodontic movement in rats using a novel analysis method employing high-resolution micro-CT (Micro-CT) images. In addition, the correlation between bone density and orthodontic relapse was also evaluated for each experimental group.

Methods

Forty adult male Wistar rats had stainless steel springs installed on their left upper first molars in order to generate tooth movement for 18 days. After this initial period, the animals were divided into three groups: (1) 30 mg/kg of CMT-3; (2) 5 mg/kg of simvastatin; and (3) 0.5% carboxymethylcellulose, and each group was treated for 20 days. Micro-CT images were analyzed (conventional method and 3D reconstruction) on the 7th and 18th days following spring fixation and finally, 20 days after treatment either with CMT-3 or simvastatin (38th day). Bone mineral density (BMD) of the mesial and distal roots of the upper first molar was also analyzed.

Results

The difference was statistically significant between the groups as to recurrence (p=0.048), and the post hoc test identified the value of p=0.007 between the control group and the CMT-3 group. Simvastatin was not able to inhibit tooth relapse. The bone mineral densities of both the mesial and distal roots were different between the three groups, after the 20th day of drug use (p=0001 and p < 0001).

Conclusion

Our findings support the initial evidence that CMT-3 is able to prevent relapse after tooth movement. Future trials in humans should evaluate such treatment as a promising approach to preventing this common phenomenon.

Clinical Relevance

Considering the results obtained, CMT-3 can be used to avoid relapse after tooth movement.

Tissue response resulting from different force magnitudes combined with corticotomy in rats

OBJECTIVES

To evaluate the amount of hyalinization and root resorption after application of light and heavy forces during corticotomy-assisted tooth movement.

MATERIALS AND METHODS

Forty-eight male Wistar rats were used. Eight animals were the control group (day 0). The other 40 animals were randomly divided into two groups using the split-mouth technique: (1) corticotomy combined light force (CLF) and (2) corticotomy combined heavy force (CHF). Nickel-titanium closed coil springs that generated 10 g (light force) and 50 g (heavy force) were used for maxillary first molar movement. three-dimensional root volume was evaluated at 0, 14, and 28 days. Percent hyalinization was analyzed at 0, 3, 7, 14, 21, and 28 days by histomorphometric analysis.

RESULTS

The CHF group showed significantly lower cervical root volume than the CLF group at 28 days. Compared with day 0, the CHF group showed significantly less root volume in both distobuccal and distopalatal roots at 28 days. The hyalinization percentages in the CHF group were significantly higher than the CLF group at days 3 and 21.

CONCLUSIONS

Heavy force combined with corticotomy produced more periodontal ligament hyalinization and root resorption than the light force combined with corticotomy.

The circadian expression of osteogenic factors in periodontal tissue loading mechanical force: new concepts of the personalized orthodontic care

Objective

The need for orthodontic treatment continues to increase. Strategies that shorten the treatment course and reduce discomfort are most welcome in clinic. Circadian rhythm plays important role in various physiological processes, including bone formation. This study intended to depict a possible circadian releasing property of the osteogenic factors within the periodontal tissue during orthodontic treatment, which may direct a more efficient and satisfactory orthodontic treatment to the patient.

Methods

Primary periodontal ligament cells (PDLCs) were obtained from the Sprague-Dawley (SD) rats. An equibiaxial strain value of 12% was applied on rat PDLCs (rPDLCs). After 2 h stimuli of 10^-7 M dexamethasone (DX), the osteogenic genes' expressions were detected by real-time polymerase chain reaction (RT-PCR) at Zeitgeber times 0, 4, 8, 12, 16, 20, and 24. An orthodontic appliance was placed on 45 SD rats. Animals were maintained under 12-h light/dark periods and euthanized at 9 time points over the diurnal cycle. The orthodontic sensitive tissues of the mesial root of the maxillary first molar were collected for RT-PCR and immunohistological assay.

Results

The rPDLCs displayed typical fibroblastic spindle shape, and subcultured steadily in vitro. Induced by DX, the mRNA expression of Col-1, OPN, and IBSP within the loaded/unloaded rPDLCs oscillated as that of the main clock gene Per-1. The osteogenic genes' expressions as well as the protein releases sustained a circadian oscillation trend in vivo.

Conclusions

This study indicates the existence of a circadian rhythm of the osteogenic factors within the orthodontic sensitive tissues, which highlights the importance of precise timing of force loading in further orthodontic treatment. Thus, a periodicity pattern of orthodontic traction at night may prove a more efficient tooth movement while minimizing the treatment window and discomfort complains.

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.

Dynamic Evaluation of Orthodontically-Induced Tooth Movement, Root Resorption, and Alveolar Bone Remodeling in Rats by in Vivo Micro-Computed Tomography

Background

The aim of this study was to dynamically evaluate tooth movement, root resorption, and remodeling of alveolar bone using different forces to cause tooth movement in rats.

Material/Methods

12-week-old male Sprague-Dawley rats were selected. Nickel-titanium (Ni-Ti) coil springs (20 g, 50 g, and 100 g forces) were placed for mesial movement of the left first maxillary molar teeth. Tooth movement, root resorption, and microarchitectural parameters of the trabecular bone were evaluated by in vivo micro-CT. Histological examination was used to observe the root resorption, alveolar bone remodeling, and changes in osteoclasts from day 0 to day 14.

Results

The tooth movement distance increased significantly over the initial 3 days in the 3 groups. The 20 g force group showed more tooth movement than in the 50 and 100 g force groups after 14 days (P<0.05). From days 7 to 10, root resorption lacunae appeared in the 3 groups and then stabilized, and the 100 g force group produced more lacunar resorption than in the anther 2 groups (P<0.05). Compared to day 0, the trabecular thickness and bone volume fraction on the pressure side gradually decreased from day 7 to day 14. The structure model index increased significantly from day 3 to day 14. Histological examination showed remarkable root resorption craters and osteoclasts positive for tartrate-resistant acid phosphatase in the root resorption lacunae in the 50 g and 100 g groups from day 7 to day 14.

Conclusions

A 100 g heavy force can be used to establish a root resorption model in rats.

A Novel Method to Quantify Longitudinal Orthodontic Bone Changes with In Vivo Micro-CT Data

Orthodontic tooth movement (OTM) is the result of region-specific bone modeling under a load. Quantification of this change in the alveolar bone around a tooth is a basic requirement to understand the mechanism of orthodontics. The purpose of this study was to quantify subregional alveolar bone changes during orthodontic tooth movement with a novel method. In this study, 12 Sprague-Dawley (SD) rats were used as an orthodontic model, and one side of the first upper molar was used to simulate OTM. The alveolar bone around the mesial root was reconstructed from in vivo micro-CT images and separated from other parts of the alveolar bone with two semicylinder filters. The amount and rate of OTM, bone mineral density (BMD), and bone volume (BV) around the root were calculated and compared at 5 time points. The results showed that the amount of tooth movement, BMD, and BV can be evaluated dynamically with this method. The molar moved fastest during the first 3 days, and the rate decreased after day 14. BMD decreased from day 0 to day 14 and returned from day 14 to day 28. BV deceased from day 0 to day 7 and from day 14 to day 28. The method created in this study can be used to accurately quantify dynamic alveolar bone changes during OTM.

Reduced Orthodontic Tooth Movement in Enpp1 Mutant Mice with Hypercementosis

Previous studies revealed that cementum formation is tightly regulated by inorganic pyrophosphate (PPi), a mineralization inhibitor. Local PPi concentrations are determined by regulators, including ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), which increases PPi concentrations by adenosine triphosphate hydrolysis. Orthodontic forces stimulate alveolar bone remodelling, leading to orthodontic tooth movement (OTM). To better understand how disturbed mineral metabolism and the resulting altered periodontal structures affect OTM, we employed Enpp1 mutant mice that feature reduced PPi and increased cervical cementum in a model of OTM induced by a stretched closed-coil spring ligated between the maxillary left first molar and maxillary incisors. We analyzed tooth movement, osteoclast/odontoclast response, and tooth root resorption by micro-computed tomography, histology, histomorphometry, and immunohistochemistry. Preoperatively, we noted an altered periodontium in Enpp1 mutant mice, with significantly increased periodontal ligament (PDL) volume and thickness, as well as increased PDL-bone/tooth root surface area, compared to wild-type (WT) controls. After 11 d of orthodontic treatment, Enpp1 mutant mice displayed 38% reduced tooth movement versus WT mice. Molar roots in Enpp1 mutant mice exhibited less change in PDL width in compression and tension zones compared to WT mice. Root resorption was noted in both groups with no difference in average depths, but resorption lacunae in Enpp1 mutant mice were almost entirely limited to cementum, with 150% increased cementum resorption and 92% decreased dentin resorption. Osteoclast/odontoclast cells were reduced by 64% in Enpp1 mutant mice, with a predominance of tartrate-resistant acid phosphatase (TRAP)-positive cells on root surfaces, compared to WT mice. Increased numbers of TRAP-positive cells on root surfaces were associated with robust immunolocalization of osteopontin (OPN) and receptor-activator of NF-κB ligand (RANKL). Collectively, reduced response to orthodontic forces, decreased tooth movement, and altered osteoclast/odontoclast distribution suggests Enpp1 loss of function has direct effects on clastic function/recruitment and/or indirect effects on periodontal remodeling via altered periodontal structure or tissue mineralization.

Atorvastatin inhibits osteoclastogenesis and arrests tooth movement

INTRODUCTION

In addition to their cholesterol-lowering effects, the statin class of drugs appears to enhance osteogenesis and suppress bone resorption, which could be a clinical concern during orthodontic treatment. In this animal study, we aimed to determine whether atorvastatin (ATV) affects orthodontic tooth movement (OTM) through osteoclast inhibition. Furthermore, we analyzed the potential adverse effects of ATV on long-bone turnover and endochondral ossification.

METHODS

Rats were administered ATV (15 mg/kg) or saline solution via gavage (n = 12 animals/group), starting 2 weeks before initial OTM. Tooth displacement was measured after 7, 14, and 21 days. Histologic sections of the maxilla and femur were obtained after 14 and 21 days of OTM and stained (hematoxylin and eosin; TRAP assay) for histomorphometric analysis.

RESULTS

ATV was associated with significant (P <0.05) reductions in OTM and osteoclast counts. Independently of drug administration, OTM increased the number of osteoclasts and reduced the bone-volume ratio compared with the control maxillae without OTM. Long-term statin administration did not appear to affect femoral endochondral ossification.

CONCLUSIONS

This experimental study showed that the long-term use of ATV can significantly promote osteoclast inhibition and slow the OTM in the first week in rats. Under physiologic conditions, the drug did not affect bone turnover and endochondral ossification.

Microarchitecture and Biomechanical Evaluation of BoneCeramic Grafted Alveolar Defects during Tooth Movement in Rat

OBJECTIVE

BoneCeramic can regenerate bone in alveolar defects, but it remains unknown whether it is feasible to move a tooth through BoneCeramic grafting sites. The objective of this study was to investigate three-dimensional real-time bone responses and micromechanical properties in the grafting sites during orthodontic tooth movement.

METHODS

Sixty 5-week-old rats were randomly assigned into three groups to receive BoneCeramic, natural bovine cancellous bone particles (Bio-Oss), and no graft, respectively, after the extraction of the left maxillary first molar. After 4 weeks, the maxillary left second molar was moved into the extraction for 28 days. Dynamic bone microstructures and root resorption were evaluated using in vivo micro-computed tomography and histology. Stress distribution of tooth roots and biomechanical properties of corresponding bone tissue were examined by finite element methods and nanoindentation. Mixed-model analysis of variance was performed to compare the difference among time points with Bonferroni post hoc tests at the significance level of P < .05.

RESULTS

The BoneCeramic group had the least amount of tooth movement and root resorption volume and craters, highest bone volume fraction, trabecular number, mean trabecular thickness, microhardness, and elastic modulus, followed by Bio-Oss and the control group. The highest stress accumulated in the cervical region of the mesial roots.

CONCLUSION

BoneCeramic has better osteoconductive potential and biomechanical properties and induces less root resorption compared with Bio-Oss grafting and naturally recovered extraction site.

Approach towards the porous fibrous structure of the periodontal ligament using micro-computerized tomography and finite element analysis

The periodontal ligament (PDL) is a porous and fibrous soft tissue situated around the tooth, which plays a key role in the transmission of loads from the tooth to the alveolar bone of the mandible. Although several studies have tried to characterize its mechanical properties, the behaviour of this tissue is not clear yet. In this study, a new simulation methodology based on a material model which considers the contribution of porous and fibrous structure with different material model formulations depending on the effort direction is proposed. The defined material model was characterized by a non-linear approximation of the porous fibrous matrix to experimental results obtained from samples of similar species and was validated by rigorous test simulations under tensile and compressive loads. The global PDL response was also validated using the parameters of the characterization in a finite element model of full human canine tooth obtained by micro-tomography. The results suggest that the porous contribution has high influence during compression because the bulk modulus of the material depends on the ability of interstitial fluid to drain. On the other hand, the collagen fibres running along the load direction are the main responsible of the ligament stiffness during tensile efforts. Thus, a material model with distinct responses depending of the load direction is proposed. Furthermore, the results suggest the importance of considering 3D finite element models based of the real morphology of human PDL for representing the irregular stress distribution caused by the coupling of complex material models and irregular morphologies.

A micro-CT study of microstructure change of alveolar bone during orthodontic tooth movement under different force magnitudes in rats

The dynamic changes of the microstructure of alveolar bone during orthodontic tooth movement in rats was explored by employing micro-computed tomography (micro-CT) system and to provide theoretical reference for clinical orthodontic treatment. Ten rats were selected randomly as control among 70 adult female Wistar rats, and the other 60 rats were divided into 25-g and 75-g groups of equal number. Orthodontic appliance with force of 25 g and 75 g was installed to perform the molar mesial movement. Microstructural parameters for trabecular bone mesial to the distobuccal root were evaluated at different time points using micro-CT system. Moreover, distance for mesial movement of the molar were measured. Microstructural parameters for trabecular bone of two groups showed no significant changes from day 0 to day 3 (P>0.05); from day 3 to day 7, bone mineral density (BMD), bone volume/total volume (BV/TV) and trabecular thickness (Tb.Th) decreased significantly (P<0.05), whereas trabecular separation (Tb.Sp) and structure model index (SMI) increased significantly (P<0.05); from day 7 to day 14, in 25-g group, BMD, BV/TV and Tb.Th increased significantly (P<0.05), while Tb.Sp and SMI decreased significantly (P<0.05). Correspondingly, in 75-g group, changes of parameters did not carry any statistical significance (P>0.05). Furthermore, the 75-g group showed larger distance than 25-g group only at day 14 (P<0.05). In conclusion, in order to maintain the health of periodontal tissues, adequate time for repair and recovery is needed to ensure reasonable remolding of alveolar bone and healthy movement of the orthodontic tooth.

Types of tooth movement, bodily or tipping, do not affect the displacement of the tooth's center of resistance but do affect the alveolar bone resorption

OBJECTIVE

To investigate how types of tooth movement, bodily or tipping, influence the displacement of the center of resistance in teeth and alveolar bone resorption.

MATERIALS AND METHODS

Ten-week-old female Wistar rats were divided into eight groups of different factors, as follows: type of movement (bodily and tipping) and force magnitude (10, 25, 50, and 100 cN). The maxillary left first molars were moved mesially with nickel-titanium coil springs for 28 days. Micro-computed tomography (micro-CT) images were taken before and after tooth movement. The position of the center of resistance was determined by using finite element models constructed from the micro-CT image. The displacement of the center of resistance and the volume of alveolar bone resorption were measured.

RESULTS

The displacement of the center of resistance showed no significant difference between the bodily and tipping groups. The displacements of the center of resistance were increased with force magnitude at 10 and 25 cN, whereas they were not further increased at 50 and 100 cN. On the other hand, cervical alveolar bone resorption was significantly greater in the tipping group than in the bodily group.

CONCLUSIONS

Displacement of the center of resistance was not influenced by the types of tooth movement. However, volume of cervical alveolar bone resorption was greater in the tipping movement group than in the bodily movement group.

BoneCeramic graft regenerates alveolar defects but slows orthodontic tooth movement with less root resorption

INTRODUCTION

BoneCeramic (Straumann, Basel, Switzerland) can regenerate bone in alveolar defects after tooth extraction, but it is unknown whether it is feasible to move a tooth through BoneCeramic grafting sites. The objective of this study was to investigate 3-dimensional real-time root resorption and bone responses in grafted sites during orthodontic tooth movement.

METHODS

Sixty 5-week-old rats were randomly assigned to 3 groups to receive BoneCeramic, natural bovine cancellous bone particles (Bio-Oss; Geistlich Pharma, Wolhusen, Switzerland), or no graft, after the extraction of the maxillary left first molar. After 4 weeks, the maxillary left second molar was moved into the extraction site for 28 days. Dynamic bone microstructures and root resorption were evaluated using in-vivo microcomputed tomography. Stress distribution and corresponding tissue responses were examined by the finite element method and histology. Mixed model analysis of variance was performed to compare the differences among time points with Bonferroni post-hoc tests at the significance level of P <0.05.

RESULTS

The BoneCeramic group had the least amount of tooth movement and root resorption volumes and craters, and the highest bone volume fraction, trabecular number, and mean trabecular thickness, followed by the Bio-Oss and the control groups. The highest stress accumulated in the cervical region of the mesial roots.

CONCLUSIONS

BoneCeramic has better osteoconductive potential and induces less root resorption compared with Bio-Oss grafting and naturally recovered extraction sites.

The effect of simvastatin on relapse of tooth movement and bone mineral density in rats measured by a new method using microtomography

PURPOSE

To evaluate the effect of simvastatin on relapse of tooth movement in rats using microtomography (micro CT), as well as the correlation of bone density with the orthodontic relapse.

METHODS

Twenty-five adult male Wistar rats, divided into two groups, had stainless steel springs installed on left maxillary first molar. The molars were moved for 18 days, and after removing the springs, were applied by oral gavage, 5mg/kg of simvastatin in the experimental group for 20 days. Tooth relapse was assessed with a micro CT scanner, and the images chosen through the Data Viewer software 1.5.0.0 had their measurement guides made and checked by the software Image ProR plus 5.1, and compared by Mann-Whitney test. After rats were sacrificed, bone mineral density was evaluated by micro CT through the software CT Analyzer 1.13 and compared by independent T-test, as well as by Spearman correlation test.

RESULTS

Relapse and bone mineral density (BMD) was lower in the experimental group than in the control group, however without a statistically significant difference.

CONCLUSION

Simvastatin did not inhibit the relapse of tooth movement in rats, and there was no correlation between bone density and orthodontic relapse.

Effects of different types of tooth movement and force magnitudes on the amount of tooth movement and root resorption in rats

OBJECTIVE

To investigate differences in the amount of tooth movement and root resorption that occurred after tipping and bodily movement of the maxillary first molar in rats.

MATERIALS AND METHODS

Ten-week-old female Wistar rats were divided into two groups according to type of tooth movement and subdivided into four subgroups according to the magnitude of applied force. Nickel-titanium closed-coil springs exerting forces of 10, 25, 50, or 100 g were applied to the maxillary left first molars to induce mesial tooth movement. We designed a novel orthodontic appliance for bodily tooth movement. Tooth movement distance and root resorption were measured using microcomputed tomography and scanning electron and scanning laser microscopy.

RESULTS

The amount of tooth movement in the bodily tooth movement group was less than half that in the tipping tooth movement group. The greatest amount of tooth movement occurred in the 10-g tipping and 50-g bodily tooth movement subgroups, and the amount of tooth movement decreased with the application of an excessive magnitude of force. Conversely, root resorption increased when the heavier orthodontic force was applied in both groups. Root resorption in the tipping tooth movement group was approximately twice that in the bodily tooth movement group.

CONCLUSIONS

Root resorption in the tipping tooth movement group was more pronounced than that in the bodily tooth movement group. Although the amount of tooth movement decreased when extremely heavy forces were applied, root resorption increased in both the tipping and bodily tooth movement groups in rats.

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.

Comparisons of the chondroitin sulphate levels in orthodontically moved canines and the clinical outcomes between two different force magnitudes

The aims of this study were to compare the chondroitin sulphate (CS) levels in gingival crevicular fluid (GCF) of moved canines using either 70 or 120 g of orthodontic force, and to compare the rate of tooth movement and the amount of pain between these two force magnitudes. Sixteen patients (6 males and 10 females; aged 16.91 ± 2.99 years), with class I malocclusion, who required orthodontic treatment with first premolar extractions, were recruited. The force magnitudes used to move the maxillary canines distally were controlled at 70 and 120 g on the right and the left sides, respectively. GCF samples were collected with Periopaper(®) strips before and during orthodontic tooth movement. Competitive ELISA with monoclonal antibody was used to measure the CS levels. The distance of tooth movement and the amount of pain assessed by visual analog scale (VAS) scores were evaluated. The medians of CS levels during the loaded period were significantly greater than those during the unloaded period (P < 0.05). The differences between the medians of CS levels of 70 g and 120 g retraction force during each 1 week period were not significant. There was no significant difference in the rates of canine movement between these two force magnitudes. However, using 120 g, the medians of VAS scores were significantly greater than those with 70 g (P < 0.05). Collectively, 70 g retraction force appears to be sufficient and more suitable than 120 g force as it causes no difference in biochemically-assessed bone remodelling activity, the same rate of tooth movement, reduced pain and better comfort.

Soft diet causes greater alveolar osteopenia in the mandible than in the maxilla

OBJECTIVE

To investigate changes in the bony microstructure of the upper and lower alveolar bone during masticatory loading induced by soft diet feeding in growing rats.

DESIGN

Three-week-old male Wistar rats were randomly divided into two groups. Rats were fed with either pellets [control group (n=6)] or a soft diet [experimental group (n=6)] for nine weeks. 3D-microstructure of the alveolar bone of the first molar region (M1) was examined by micro-CT analysis.

RESULTS

Micro-CT images showed increased marrow spaces of the inter-radicular alveolar bone around the rat mandibular M1 in the experimental group compared with that in the control group. The bone volume/tissue volume ratio, trabecular thickness, trabecular number, mean intercept length, trabecular width and trabecular star volume for the mandibular M1 inter-radicular alveolar bone were lower in the experimental group than in the control group. Marrow space star volume was increased in the experimental group compared with the control group.

CONCLUSIONS

These results suggest that alveolar osteopenia is more extensive in the mandible than the maxilla in rats that experience low masticatory loading during growth.

Experimentally determined mechanical properties of, and models for, the periodontal ligament: critical review of current literature

Introduction. This review is intended to highlight and discuss discrepancies in the literature of the periodontal ligament's (PDL) mechanical properties and the various experimental approaches used to measure them. Methods. Searches were performed on biomechanical and orthodontic publications (in databases: Compendex, EMBASE, MEDLINE, PubMed, ScienceDirect, and Scopus). Results. The review revealed that significant variations exist, some on the order of six orders of magnitude, in the PDL's elastic constants and mechanical properties. Possible explanations may be attributable to different experimental approaches and assumptions. Conclusions. The discrepancies highlight the need for further research into PDL properties under various clinical and experimental loading conditions. Better understanding of the PDL's biomechanical behavior under physiologic and traumatic loading conditions might enhance the understanding of the PDL's biologic reaction in health and disease. Providing a greater insight into the response of the PDL would be instrumental to orthodontists and engineers for designing more predictable, and therefore more efficacious, orthodontic appliances.

Tooth movement and root resorption; the effect of ovariectomy on orthodontic force application in rats

OBJECTIVE

To quantify the amount of tooth movement and orthodontically induced root resorption (OIRR) in ovariectomized rats.

MATERIALS AND METHODS

Five 10-week-old female Wistar rats undergoing ovariectomy (OVX) were investigated as the experimental group, and the other five without ovariectomy served as the control group. Four weeks after ovariectomy, 25-g nickel-titanium closed-coil springs were applied mesially to the maxillary left first molars. Micro-computed tomography was taken at day 0, 1, 3, 7, 14, 21, and 28. At day 28, the molars were extracted. The surface area of root resorption craters, depth, and volume were measured using electron and laser scanning microscopes.

RESULTS

Tooth movement gradually increased with time throughout 28 days. There was a significant difference in the amount of tooth movement between the control group and the OVX group. For OIRR, the OVX group showed wide and shallow root resorption craters scattered on the mesial root. The deep resorption craters were observed on the distal roots distributed in the cervical, middle, and apical thirds of the roots. Statistically significant differences were found between the control and the OVX groups in the depth and the volume of root resorption craters in the distal roots and the total volume of root resorption craters in all three roots.

CONCLUSION

Ovariectomy affected not only tooth movement but also OIRR. Tooth movement in the OVX group was more rapid than the control group. Furthermore, the amount of OIRR in the OVX group was more severe than the control group.