Estrogen protects dental roots from orthodontic-induced inflammatory resorption

Influence of anti-sclerostin monoclonal antibody in the repair of post-extraction sockets of ovariectomized rats

OBJECTIVE

This study assessed the impact of an anti-sclerostin monoclonal antibody (Scl-Ab)-based osteoporosis drug on the post-extraction alveolar repair of ovariectomized rats.

DESIGN

Fifteen female rats were randomly distributed into three groups: CTR (healthy animals), OST (osteoporosis induced by ovariectomy), and OST+Scl-Ab (osteoporosis induction followed by Scl-Ab treatment). Ovariectomy or sham surgery was performed 30 days before baseline, and Scl-Ab or a vehicle was administered accordingly in the groups. After seven days, all rats underwent the first lower molar extraction and were euthanized 15 days later. Computed microtomography, histological analysis, and collagen content measurement were performed on post-extraction sockets and intact mandibular and maxillary bone areas.

RESULTS

Microtomographic analyses of the sockets and mandibles did not reveal significant differences between groups on bone morphometric parameters (p > 0.05), while maxillary bone analyses resulted in better maintenance of bone architecture in OST+Scl-Ab, compared to OST (p < 0.05). Descriptive histological analysis and polarization microscopy indicated better post-extraction socket repair characteristics and collagen content in OST+Scl-Ab compared to OST (p < 0.05).

CONCLUSIONS

Scl-Ab-based medication did not accelerate alveolar bone formation but exhibited better post-extraction repair characteristics, and collagen content compared to ovariectomized animals only.

Protective Effect of Bovine Milk Extracellular Vesicles on Alveolar Bone Loss

SCOPE

Bovine milk extracellular vesicles (MEVs) have demonstrated therapeutic potential in regulating bone cell activity. However, the outcome of their use on alveolar bone loss has not yet been demonstrated.

METHODS AND RESULTS

This study evaluates the effect of oral administration of MEVs on ovariectomized (OVX) mice. There is a reduced height of the alveolar bone crest in OVX mice by MEVs treatment, but the alveolar bone parameters are not altered. OVX mice are then submitted to a force-induced bone remodeling model by orthodontic tooth movement (OTM). MEVs-treated mice have markedly less bone remodeling movement, unlike the untreated OVX mice. Also, OVX mice treated with MEVs show an increased number of osteoblasts and osteocytes associated with higher sclerostin expression and reduce osteoclasts in the alveolar bone. Although the treatment with MEVs in OVX mice does not show differences in root structure in OTM, few odontoclasts are observed in the dental roots of OVX-treated mice. Compared to untreated mice, maxillary and systemic RANKL/OPG ratios are reduced in OVX mice treated with MEVs.

CONCLUSION

Treatment with MEVs results in positive bone cell balance in the alveolar bone and dental roots, indicating its beneficial potential in treating alveolar bone loss in the nutritional context.

Targeting phosphatidylinositol-3-kinase for inhibiting maxillary bone resorption

Previous studies have suggested a role of phosphatidylinositol-3-kinase gamma (PI3Kγ) in bone remodeling, but the mechanism remains undefined. Here, we explored the contribution of PI3Kγ in the resorption of maxillary bone and dental roots using models of orthodontic tooth movement (OTM), orthodontic-induced inflammatory root resorption, and rapid maxillary expansion (RME). PI3Kγ-deficient mice (PI3Kγ-/- ), mice with loss of PI3Kγ kinase activity (PI3KγKD/KD ) and C57BL/6 mice treated with a PI3Kγ inhibitor (AS605240) and respective controls were used. The maxillary bones of PI3Kγ-/- , PI3KγKD/KD , and C57BL/6 mice treated with AS605240 showed an improvement of bone quality compared to their controls, resulting in reduction of the OTM and RME in all experimental groups. PI3Kγ-/- mice exhibited increased root volume and decreased odontoclasts counts. Consistently, the pharmacological blockade or genetic deletion of PI3K resulted in increased numbers of osteoblasts and reduction in osteoclasts during OTM. There was an augmented expression of Runt-related transcription factor 2 (Runx2) and alkaline phosphatase (Alp), a reduction of interleukin-6 (Il-6), as well as a lack of responsiveness of receptor activator of nuclear factor kappa-Β (Rank) in PI3Kγ-/- and PI3KγKD/KD mice compared to control mice. The maxillary bones of PI3Kγ-/- animals showed reduced p-Akt expression. In vitro, bone marrow cells treated with AS605240 and cells from PI3Kγ-/- mice exhibited significant augment of osteoblast mineralization and less osteoclast differentiation. The PI3Kγ/Akt axis is pivotal for bone remodeling by providing negative and positive signals for the differentiation of osteoclasts and osteoblasts, respectively.

RANKL+ senescent cells under mechanical stress: a therapeutic target for orthodontic root resorption using senolytics

In dentistry, orthodontic root resorption is a long-lasting issue with no effective treatment strategy, and its mechanisms, especially those related to senescent cells, remain largely unknown. Here, we used an orthodontic intrusion tooth movement model with an L-loop in rats to demonstrate that mechanical stress-induced senescent cells aggravate apical root resorption, which was prevented by administering senolytics (a dasatinib and quercetin cocktail). Our results indicated that cementoblasts and periodontal ligament cells underwent cellular senescence (p21⁺ or p16⁺) and strongly expressed receptor activator of nuclear factor-kappa B (RANKL) from day three, subsequently inducing tartrate-resistant acid phosphatase (TRAP)-positive odontoclasts and provoking apical root resorption. More p21⁺ senescent cells expressed RANKL than p16⁺ senescent cells. We observed only minor changes in the number of RANKL⁺ non-senescent cells, whereas RANKL⁺ senescent cells markedly increased from day seven. Intriguingly, we also found cathepsin K⁺p21⁺p16⁺ cells in the root resorption fossa, suggesting senescent odontoclasts. Oral administration of dasatinib and quercetin markedly reduced these senescent cells and TRAP⁺ cells, eventually alleviating root resorption. Altogether, these results unveil those aberrant stimuli in orthodontic intrusive tooth movement induced RANKL⁺ early senescent cells, which have a pivotal role in odontoclastogenesis and subsequent root resorption. These findings offer a new therapeutic target to prevent root resorption during orthodontic tooth movement.

Effect of orthodontic treatment on the periapical radiolucency of endodontically treated teeth: a CBCT analysis

BACKGROUND

This study aimed to evaluate periapical radiolucency of endodontically treated teeth before and after orthodontic treatment using cone-beam computed tomography (CBCT).

METHODS

Patients who underwent orthodontic treatment at Wonkwang University Daejeon Dental Hospital between January 2009 and June 2022 were included based on the following criteria: root canal treatment, and availability of CBCT images taken before and after orthodontic treatment with an interval of > 1 year between both scans. Patients with primary teeth or orthodontic tooth extractions were excluded. The size of the periapical radiolucency (SPR) of the endodontically treated tooth was evaluated using CBCT. Pre-orthodontic treatment CBCT images and the latest post-orthodontic treatment CBCT images were analyzed. The selected teeth were further categorized based on the orthodontic duration, CBCT interval, the patient sex and age, the tooth type and position (maxilla or mandible), and quality of root canal obturation. Statistical analyses were performed to evaluate changes in SPR using the paired t-test and multiple regression analysis.

RESULTS

In total, 115 teeth (37 anterior teeth, 22 premolars and 56 molars) from 61 patients (age, 14-54 years) were included, with 39 teeth from male patients and 76 teeth from female patients. The age was ranged between 14 and 54 years old, and mean age was 25.87 years old. The mean CBCT interval and orthodontic treatment period were 43.32 months and 36.84 months, respectively. Seventy-five teeth showed good obturation quality, 80 were not used as anchors during orthodontic treatment, and 71 were maxillary. The SPR size increased after orthodontic treatment for 56 teeth and decreased for 59 cases. The average change in SPR was -0.102 mm and the difference was not significant. Significant decrease of SPR were observed between female patients (p = 0.036) and maxillary teeth (p = 0.040).

CONCLUSION

Orthodontic treatment had no significant impact on the changes in the SPR in endodontically treated teeth in most categories. However, there was a significant difference among females and the maxillary teeth. In both categories, the size of radiolucency decreased significantly.

Role of mechano-sensitive non-coding RNAs in bone remodeling of orthodontic tooth movement: recent advances

Orthodontic tooth movement relies on bone remodeling and periodontal tissue regeneration in response to the complicated mechanical cues on the compressive and tensive side. In general, mechanical stimulus regulates the expression of mechano-sensitive coding and non-coding genes, which in turn affects how cells are involved in bone remodeling. Growing numbers of non-coding RNAs, particularly mechano-sensitive non-coding RNA, have been verified to be essential for the regulation of osteogenesis and osteoclastogenesis and have revealed how they interact with signaling molecules to do so. This review summarizes recent findings of non-coding RNAs, including microRNAs and long non-coding RNAs, as crucial regulators of gene expression responding to mechanical stimulation, and outlines their roles in bone deposition and resorption. We focused on multiple mechano-sensitive miRNAs such as miR-21, - 29, -34, -103, -494-3p, -1246, -138-5p, -503-5p, and -3198 that play a critical role in osteogenesis function and bone resorption. The emerging roles of force-dependent regulation of lncRNAs in bone remodeling are also discussed extensively. We summarized mechano-sensitive lncRNA XIST, H19, and MALAT1 along with other lncRNAs involved in osteogenesis and osteoclastogenesis. Ultimately, we look forward to the prospects of the novel application of non-coding RNAs as potential therapeutics for tooth movement and periodontal tissue regeneration.

Enhancement of orthodontic tooth movement and root resorption in ovariectomized mice

Background/purpose

As the number of patients with osteoporosis requiring orthodontic treatment is increasing with the aging of society, it is necessary to evaluate the relations between bone metabolism in old age and orthodontic tooth movement (OTM). However, the effects of changes in bone metabolism due to osteoporosis on OTM and root resorption are still unclear. Therefore, we investigated the effects of OTM and root resorption in a mouse ovariectomy (OVX)-induced osteoporosis model.

Materials and methods

Eight-week-old female wild-type mice underwent OVX or sham surgery (Sham) as controls. One month after treatment, a nickel titanium coil spring was used to apply a mesial force to the maxillary left first molars of OVX or Sham mice for 12 days. The distance between the maxillary first molar and the second molar changed due to OTM and osteoclast formation was evaluated. The odontoclast formation and root resorption along the root surface of the distobuccal root of the first molar was also evaluated by histological analysis and scanning electron microscopy.

Results

Distance of tooth movement and osteoclast formation were significantly increased in OVX mice compared to Sham controls. Furthermore, root resorption in the mesial surface of the distal molars induced by orthodontic force was significantly increased in OVX mice.

Conclusion

The amount of OTM was significantly increased, and the accompanying root resorption was also increased in OVX mice. Therefore, attention should be paid to the risk of root resorption associated with orthodontic treatment in patients with osteoporosis.

Does the rate of orthodontic tooth movement change during the estrus cycle? A systematic review based on animal studies

BACKGROUND

As the fluctuation of sex hormone levels in menstruating women results in periodical effects in bone metabolism, understanding the implications for tooth movement could be of benefit to the orthodontist. This type of research presents practical and ethical problems in humans, but animal models could provide useful information. Our objective was to systematically investigate the available evidence on the question whether the rate of orthodontic tooth movement varies between the different stages of the estrus cycle in animals.

METHODS

Unrestricted searches in 7 databases and manual searching of the reference lists in relevant studies were performed up to February 2021 (Medline [PubMed], CENTRAL [Cochrane Library; includes records from Embase, CINAHL, ClinicalTrials.gov, WHO's ICTRP, KoreaMed, Cochrane Review Groups' Specialized Registers, and records identified by handsearching], Cochrane Database of Systematic Reviews [Cochrane Library], Scopus, Web of Knowledge [including Web of Science Core Collection, KCI Korean Journal Database, Russian Science Citation Index, SciELO Citation Index and Zoological Record], Arab World Research Source [EBSCO] and ProQuest Dissertation and Theses [ProQuest]). Our search focused on prospective controlled animal studies, whose samples included female subjects of any species that were quantitatively comparing the amount of tooth movement in the different stages of the estrus cycle. Following study retrieval and selection, relevant data was extracted, and the risk of bias was assessed using the SYRCLE's Risk of Bias Tool.

RESULTS

From the finally assessed records, 3 studies met the inclusion criteria. Two of the studies experimented on Wistar rats, whereas the other on cats. Tooth movement was induced by expansion or coil springs. The rate of orthodontic tooth movement was increased during the stages of the estrus cycle when oestrogen and/or progesterone levels were lower. The risk of bias in the retrieved studies was assessed to be unclear.

CONCLUSION

Hormonal changes during the estrus cycle may affect the rate of orthodontic tooth movement. Although these animal experiment results should be approached cautiously regarding their translational potential, it could be useful to consider the possible impact of these physiological changes in the clinical setting until more information becomes available. Registration: PROSPERO (CRD42021158069).

Does exogenous female sex hormone administration affect the rate of tooth movement and root resorption? A systematic review of animal studies

Background

The long-term use of contraceptive methods that contain estrogens, progestogens or combinations of the above among women aged 15 to 49 years is extensive. Both estrogens and progestogens affect bone metabolism.

Objective

To systematically investigate and appraise the quality of the available evidence from animal studies regarding the impact of exogenous administration of female sex hormones on the rate of orthodontic tooth movement and root resorption.

Search methods

Search without restriction in seven databases (including grey literature) and hand searching were performed until May 2021.

Selection criteria

We looked for controlled animal studies investigating the effect from exogenous administration of formulations containing female sex hormones on the rate of orthodontic tooth movement and root resorption.

Data collection and analysis

After study retrieval and selection, relevant data was extracted, and the risk of bias was assessed using the SYRCLE’s Risk of Bias Tool. The quality of available evidence was assessed with the Grades of Recommendation, Assessment, Development, and Evaluation.

Results

Three studies were identified, all being at unclear risk of bias. Overall, administration of progesterone and the combinations of estradiol with norgestrel and desogestrel were shown to significantly decrease the rate of orthodontic tooth movement when given for longer periods (>3 weeks). Inconsistent information was detected for shorter periods of consumption. Estradiol, with desogestrel use, resulted in less root resorption. The quality of the available evidence was considered to be low.

Conclusions

Exogenous administration of female sex hormones may decelerate in the long term the rate of tooth movement and decrease orthodontically induced root resorption in animals. Until more information becomes available, an orthodontist should be able to identify a patient consuming such substances and understand the potential clinical implications and adverse effects that may arise.

Registration

PROSPERO: CRD42017078208; https://clinicaltrials.gov/.

Effect of ovariectomy-induced osteoporosis on the amount of orthodontic tooth movement: a systematic review of animal studies

BACKGROUND

Understanding the impact of osteopenia and osteoporosis on orthodontic tooth movement could be of benefit to the orthodontist, but research in humans presents practical and ethical problems. The ovariectomized animal model could provide useful information on osteoporosis.

OBJECTIVE

To compare the amount of tooth movement during or after the application of orthodontic forces between ovariectomized animals and control or sham-operated subjects.

SEARCH METHODS

Unrestricted searches in seven databases and manual searching of the reference lists in relevant studies were performed up to February 2021 (PubMed, Central, Cochrane Database of Systematic Reviews, Scopus, Web of Science, Arab World Research Source, ProQuest Dissertations, and Theses Global).

SELECTION CRITERIA

We searched for studies quantitatively comparing the amount of tooth movement during or after the application of orthodontic forces between ovariectomized animals and control or sham-operated subjects.

DATA COLLECTION AND ANALYSIS

Following study retrieval and selection, relevant data were extracted, and the risk of bias was assessed using the SYRCLE's Risk of Bias Tool. Exploratory synthesis and meta-regression were carried out using the random effects model.

RESULTS

Thirteen studies were finally selected and no specific concerns regarding bias were identified. During the active period, ovariectomy was associated with a statistically significant acceleratory effect on the rate of orthodontic tooth movement compared to non-treated rats (3 weeks; 4 studies, 0.15 mm more movement in the ovariectomized rats; 95 per cent confidence interval: 0.10-0.19; P = 0.000). Exploratory meta-regression showed that this difference could increase over time. Following force discontinuation, no statistically significant differences were observed [3 weeks; 1 study (median ± SE), Ovariectomy group: 0.30 ± 0.04 mm; Sham operation group: 0.18 ± 0.03; P = 0.1558].

CONCLUSIONS

Ovariectomy-induced osteoporosis may affect the rate of orthodontic tooth movement. Although animal studies should be approached with caution regarding their translational potential, the safe practice would suggest that one should consider potential implications.

REGISTRATION

PROSPERO (CRD42018118003).

Effects of Histamine Receptor Antagonist Cetirizine on Orthodontic Tooth Movement

Many patients regularly take histamine receptor antagonists, such as cetirizine, to prevent allergic reactions, but these antiallergic drugs may have inadvertent effects on orthodontic treatment. In previous studies, histamine has been shown to modulate the sterile inflammatory reaction underlying orthodontic tooth movement. Pertinent effects of histamine antagonization via cetirizine during orthodontic treatment, however, have not been adequately investigated. We thus treated male Fischer344 rats either with tap water (control group) or cetirizine by daily oral gavage corresponding to the clinically used human dosage adjusted to the rat metabolism (0.87 mg/kg) or to a previously published high dosage of cetirizine (3 mg/kg). Experimental anterior movement of the first upper left molar was induced by insertion of a nickel-titanium (NiTi) coil spring (0.25 N) between the molar and the upper incisors. Cone-beam computed tomography (CBCT), micro-computed tomography (µCT) images, as well as histological hematoxylin-eosin (HE), and tartrate-resistant acid phosphatase (TRAP) stainings were used to assess the extent of tooth movement, cranial growth, periodontal bone loss, root resorptions, and osteoclast activity in the periodontal ligament. Both investigated cetirizine dosages had no impact on the weight gain of the animals and, thus, animal welfare. Neither the extent of tooth movement, nor cranial growth, nor root resorption, nor periodontal bone loss were significantly influenced by the cetirizine dosages investigated. We, thus, conclude that histamine receptor antagonist cetirizine can be used during orthodontic treatment to prevent allergic reactions without clinically relevant side effects on orthodontic tooth movement.

Inhibitory Effects of 4-Hexylresorcinol on Root Resorption Induced by Orthodontic Tooth Movement

Root resorption during orthodontic tooth movement (OTM) is caused by an imbalance between the bone turnover rate and applied mechanical stress. The administration of 4-hexylresorcinol (4HR) increases the bone turnover rate and factors associated with bone formation. Thus, 4HR may show protective activity against root resorption during orthodontic tooth movement (OTM). A total of 40 rats (male: 20; female: 20) were included in this study, and the mandibular first molar was subjected to excessive orthodontic force. The experimental group (n = 20) received 12.8 mg/kg of 4HR every 2 weeks. The controls (n = 20) received a solvent without 4HR. Both groups had the same sex distribution. On Day 28 after the initiation of OTM, all the animals were sacrificed for micro-computed tomography analysis, Western blot analysis, and immunohistochemistry. The ratios of the root length and root volume to the total volume were significantly higher in the experimental group compared to those in the control group (p < 0.05). The expression levels of OPG, RANKL, alkaline phosphatase, and Runx2 in the experimental group according to Western blotting were significantly higher in the experimental group compared to those in the control group (p < 0.05). Their expression was mainly found in the periodontal ligament area. In conclusion, the administration of 4HR decreased the root resorption caused by OTM and increased the expression levels of OPG, RANKL, alkaline phosphatase, and Runx2.