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Experimental orthodontic pain drives anxiety state through the induction of alterations to the neuronal architecture in hippocampus

BMC Neuroscience volume 26, Article number: 26 (2025) Cite this article

Abstract

Background

To explore the effect and mechanism of hippocampus on experimental orthodontic pain-induced anxiety.

Methods

Herein, we document a novel modeling method whereby the nickel–titanium (Ni–Ti) orthodontic wire was fixed stably in the oral cavity of mice with a ligation technique to induce stable distal movement of maxillary incisors to mimic orthodontic tooth movement. At the experimental endpoint, serum corticosterone assay, Golgi staining and Micro-CT were performed in each group after oral-facial mechanical pain sensitivity assessment and open field test.

Results

The mechanical pain sensitivity of experimental tooth movement pain (ETMP) mice had an apparent increased elicited following tooth movement. And anxiety-like behavior was developed: reduced the time proportion of center zone and the total moving distance in the open field test and the elevated serum corticosterone levels in ETMP mice relative to control group mice. The Golgi staining in ventral hippocampal CA1 revealed that neural spine density, dendritic length and number of dendrites are reduced markedly in ETMP mice compared with the control group.

Conclusion

Experimental orthodontic pain drives emotional anxiety through the plasticity changes in decreased neuronal complexity and reduced spine density in ventral hippocampal CA1 in mice.

Peer Review reports

Background

Orthodontic pain, an inflammatory pain caused by tooth movement, is the most common complication in orthodontic treatment. Typically, orthodontic pain peaks within 1–2 days and gradually subsides [1]. Clinical studies have demonstrated that orthodontic pain can induce negative emotions in patients, such as anxiety [2, 3], which in turn could exacerbate the perception of pain [4]. The combination of orthodontic pain and anxiety can have a significant impact on patients’ normal behavior, social life, and daily activities, especially in terms of eating and sleeping [5], leading to reduced compliance during orthodontic treatment and ultimately, patient dropout [6, 7]. Therefore, it is of interest to assess emotional anxiety and its relationship with pain during orthodontic treatment, and reducing or eliminating the orthodontic pain and controlling the anxiety along with it [8, 9].

As everyone knows, some complex looped connections structures located at medial rim of the brain, named limbic system [10], whose brain regions (like hippocampus and amygdala) are involved in formation and expression of “pain sensation-emotion-cognition” [11]. Some dental researchers have realized that the connection between orthodontic pain and negative emotions may be explained by the role of limbic system [12]. An animal study in rats confirmed orthodontic tooth movement (OTM) activated the amygdala by high c-Fos expression and the reduction in Fos-IR cells in the central amygdala (CeA) [13], which is similar to the result that the lesion of CeA can attenuate orthodontic pain during OTM in rats [14]. Although hippocampus is widely believed by its role in declarative and episodic memory [15], for example, tooth inflammatory pulpal pain or orthodontic pain may induce memory and learning impairment in rat [16,17,18]. Actually, as an important part of the limbic system, hippocampus also is emerged as a critical node in emotional affective aspects of pain, particularly in anxiety and depression [19,20,21]. Hippocampus plays a crucial role in emotional regulation [22], integrating information and driving existing synaptic plasticity through changes in synaptic molecules to affect emotions. In addition, hippocampus is not only a necessary pathway for pain transmission but also plays an important role in processing pain information [23].

Yet, the important role of hippocampus in the processing and development of orthodontic pain and its relationship with anxiety is seemed to have been ignored and largely unclear. A new mouse behavior model of pain induced by experimental tooth movement was applied in this study to preliminary explore the effect and mechanism of hippocampus on experimental orthodontic pain-induced anxiety.

Materials and methods

Experimental animals and grouping

The animal use protocol listed below has been reviewed and approved by the Institution Animal Care and Use Committee (IACUC), Sun Yat-sen University (Approval number: SYSU-IACUC-2023-000281). Eighteen SPF male C57BL/6 wild-type mice (age: 8 weeks, weight: 24–26 g), from the experimental Animal Center of Sun Yat-sen University, were randomly divided into three groups, including one control group without orthodontic force application and two experimental tooth movement pain (ETMP) groups, further divided into 2 days (2D) and 5 days (5D) groups based on the duration of force application, with six mice in each group. The feeds were softened with sterile water to facilitate ingestion, the body weight and daily food intake of mice would be monitored daily throughout the test period.

Establishment of mouse incisor movement model

The modeling process as follows (Fig. 1): (1) Anesthesia: after weighing, 0.4% pentobarbital sodium is administered at 0.12 mL/10 g by intraperitoneal injection for anesthesia. (2) Pretreatment of the maxillary incisor: an electric engraving knife (Deguqmnt, China) is used to grind a 0.08 mm deep fixation groove on the labial side of both maxillary incisors near the gingival margin. (3) Ligature wire fixation: two 0.08 mm diameter ligature wires (Ligature A and B) are chosen. Ligature A was threaded through the proximal space between bilateral maxillary incisors, then ligated at the neck of the incisors, allowing ligature B to be fixed at the distal of this incisor. The other incisor is operated similarly. (4) Placement of the nickel–titanium (Ni–Ti) orthodontic wire: A 0.15 mm diameter Ni–Ti orthodontic wire (Wuhang Metal Materials Co., Ltd., China) was cut, and both free ends of the Ni–Ti orthodontic wire were fixed to the distal of both incisors by ligature B. The Ni–Ti orthodontic wire formed a “U-shape” and was fixed close to the palate in the mouse’s mouth. In this step, the "U-shape bottom" was located between the first molars to ensure consistent force application (approximately 7 g) during the experiment. (5) Auxiliary fixation: to enhance the fixation effect, a thin layer of flowable resin (3 M Unitek, USA) was applied to the Ni–Ti orthodontic wire, ligature wire, and contacting incisor surfaces, shaped with a probe and then light-cured.

Fig. 1
figure 1

The diagrammatic sketch of this mouse incisor movement model. (1) Ligature A was threaded through the proximal space between bilateral maxillary incisors, then ligated at the neck of the incisors. (2) The ligature B was fixed on the distal side of the maxillary incisors by ligature A. (3) The Ni–Ti orthodontic wire was fixed on the distal surface of the maxillary incisors by ligature B. (4) The Ni–Ti orthodontic wire became U-shaped, and the “U-shaped bottom” was located between the first molars

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Orofacial mechanical pain sensitivity test

To reduce the effect of non-painful stimuli on behavior test, experimental mice all have received habituation and grasping training 3 days before modeling; to ensure consistent baseline pain response before behavior test, each group of mice underwent a single behavioral test 1 day before modeling. The test process as follows: mice were placed in the palm and their heads were restrained between two fingers. Touch-Test™ monofilaments (Shanghai Rui Shi, China) were used to apply graded mechanical stimulation to the cheeks of the mice in ascending order, and their behavioral responses were observed, including head withdrawal reflexes or facial grooming behaviors (scratching face or head) [24, 25]. Each filament was applied five times with 30-s intervals. When three out of the five trials resulted in a head withdrawal reflex or facial grooming behavior, it was considered a positive result and recorded. The mechanical intensity at this point was the minimum stimulus intensity at which the mouse exhibited a pain response, also known as the mechanical pain reflex threshold.

Open field test

Experimental mice were gently removed from their cages with their backs facing the experimenter and quickly placed in the center of the open field test box (40 cm × 40 cm × 35 cm). The experimenter then left immediately. The PhenoScan (Clever Sys, USA) system was used to observe and record the behavior of the experimental mice in the test box for a duration of 5 min. We would pay attention to the behavioral trajectory of mice, the time spent in the central zone (as a percentage of total duration) and the total distance traveled by mice in the test box.

Tissue collection and processing

Serum

After each group of mice was deeply anesthetized by intraperitoneal injection of 1.5 times the anesthetic dose of pentobarbital sodium, blood was collected by the eyeball blood collection method. Serum was obtained by centrifugation at 3000 rpm for 5 min and detected using a serum corticosterone ELISA kit (Servicebio, China). Given that dysregulation of the hypothalamic-pituitary adrenal (HPA) axis can lead to anxiety-like behaviors and that serum corticosterone serves as the primary glucocorticoid end product in rodents [26, 27], we compared serum corticosterone levels between ETMP mice and control mice.

Brain tissue

After the eyeball blood collection, mice were euthanized by intracardiac perfusion with 0.9% saline. Brains were then removed and placed in Golgi staining solution in the dark for 2 weeks. After staining, brain tissue was sectioned at 120 μm thickness using a vibrating microtome (Leica, Germany) and sections mounted on gelatin-coated slides.

We traced each neuron using Axio Imager (MicroBrightField, USA) at low (40×) magnifications, and representative images from the ventral CA1sub region of the hippocampus were taken (5 different brain slices in each group, 2 cells per brain slice). Neuronal images were analyzed by using Fiji software (NIH, USA) with the NeuronJ plugin [28], and dendritic lengths and number of the branches were calculated. Neuronal arborization were subjected to Sholl analysis: counting the number of crossings by dendrites of concentric circles spaced at a distance of 25 μm within a distance of 300 μm from the soma [29]. Blind group counting of the dendritic spines were performed by different experimenters and photographed at high (100×) magnifications.

Maxilla

After euthanizing the mice, maxillary specimens were collected and fixed in 4% paraformaldehyde solution for 24 h. They were then transferred to 0.1% paraformaldehyde solution for subsequent Micro-CT scanning (Bruker, Germany). Afterwards, maxillary specimens were decalcified in Tris-buffered ethylene diamine tetra-acetic (EDTA) solution (10%, pH = 7.4) for 2 weeks at 4 °C. After demineralization, the specimens were paraffin-embedded. 5-µm thick transverse sections of the maxillary alveolar bone were obtained using a rotating microtome (Leica, Germany) for HE staining.

Statistical analysis

Statistical analysis was performed using GraphPad Prism 8.0.1. The Shapiro–Wilk normality test evaluated the normality of experimental data in each group, and the Brown-Forsythe test assessed homogeneity of variance. Group differences were evaluated using One-Way ANOVA. All data are presented as mean ± standard deviation (SD), with n representing the sample size.

Results

Successful establishment of the tooth movement model

At the experimental endpoint (Fig. 2A), no experimental mice died, and the applied Ni–Ti orthodontic wires did not detach. The examination of the extent of tooth movement always showed 0 mm on the control group, in all examined animals, while bilateral maxillary incisors of experimental animals exhibited visible distal movement gap (Fig. 2B), same as the Micro-CT three-dimensional reconstruction images (Fig. 2D). The Ni–Ti orthodontic wire induced a significant distance between bilateral maxillary incisors by on average of 0.41 mm (SD = 0.01 mm) after as early as 2 days and a tooth movement of 0.67 mm (SD = 0.05 mm) after 5 days (Fig. 2E). HE staining showed typical bone resorption characteristics that continuous alveolar bone destruction on the distal side of incisors, while lightly stained newly-formed immature alveolar bone tissue was formed on the other side (Fig. 2C). These results indicated that mice were successfully developed as tooth movement models in this novel modeling method. From the weight history of the mice (Fig. 2F), we found the ETMP mice have weight loss only at 1–2 days during the whole experiment: the initial weight loss of ETMP mice (on day 1, control mice: 25.07 ± 0.58, ETMP mice: 23.00 ± 0.56, P < 0.0001; on day 2, control mice: 25.22 ± 0.56, ETMP mice: 24.15 ± 0.65, P = 0.012) followed by a returned to normal levels (on day 3, control mice: 25.08 ± 0.44, ETMP mice: 24.55 ± 0.56) after adapting to orthodontic force application, compared with control mice. No abnormal eating behavior (Supplementary Fig. 1) and no tissue damage (Fig. 2B) was observed during the stay of the Ni–Ti orthodontic wire in the oral cavity of mice.

Fig. 2
figure 2

Profiles of Ni–Ti orthodontic wire-induced tooth movement model. A Time course of the experiments. B Gross appearance of the maxilla specimens 5 days after orthodontic force application; vertical view (left), front view (right). C HE staining appearance of the periodontal tissue of unilateral incisor in control, 2D and 5D groups. The rectangle in the middle microphotographs indicates the region of the high magnitude microphotograph on the tension and pressure sides. Scale bars: 100 μm. AB, alveolar bone; PDL, periodontal ligament; MI, maxillary incisor. D Reconstructed Micro-CT images of the maxilla specimens on day 5. E The extent of tooth movement after 2 and 5 days of OTM with the Ni–Ti orthodontic wire compared to the control group, in which tooth movement was always 0 mm. F Daily changes in body weight throughout the 5-day observation period in both experimental and control groups. *P < 0.05, ****P < 0.0001; n = 6 per group

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Mice in the ETMP group developed orthodontic pain and induced anxiety-like behavior

ETMP mice showed a significant decrease in pain reflex threshold, compared to controls (Fig. 3A). Baseline values before experiment were very consistent ensuring no difference between groups (control mice: 3.88 ± 0.10, ETMP mice: 3.88 ± 0.10). Compared with the control group, the reflex threshold to mechanical stimulation of the cheek area was significantly reduced in the ETMP group mice after tooth movement (on day 2, control mice: 3.92 ± 0.12, ETMP mice: 1.77 ± 0.29, P < 0.0001; on day 5, control mice: 3.92 ± 0.12, ETMP mice: 2.12 ± 0.37, P < 0.0001). In the open field test behavior trajectory diagram (Fig. 3B), it can be seen that, whether in terms of trajectory density in the central area (yellow) or the number of times passing through it, or the overall trajectory density (yellow plus red) in the whole diagram, the ETMP group mice showed significantly lower (fewer) values than the control group. Through statistical analysis, compared with the control group, the total distance of horizontal movement (control group: 18,419 ± 4645, 2D group: 12,861 ± 3413, 5D group: 9152 ± 3485, compared with 2D group P = 0.039, compared with 5D group P = 0.003) and the time spent in the central area of the open field test box(control group: 15.05 ± 2.58, 2D group: 6.58 ± 2.68, 5D group: 4.82 ± 2.01, compared with 2D group P < 0.001, compared with 5D group P < 0.0001; Fig. 3C) in the ETMP group were significantly reduced. The ELISA test results of serum corticosterone in mice showed that the corticosterone content in the serum of ETMP group mice was significantly higher than that of the control group (control group: 11.09 ± 8.11, 2D group: 44.82 ± 19.93, 5D group: 67.27 ± 29.35, compared with 2D group P = 0.040, compared with 5D group P = 0.003; Fig. 3D). In summary, mice in the ETMP group developed orthodontic pain and induced anxiety-like behavior.

Fig. 3
figure 3

Mice in the ETMP group developed orthodontic pain and developed anxiety-like behavior. A Effects of orthodontic force on mechanical pain sensitivity in mice. B The trajectory diagram of mouse in each group in open field test. C The total moving distance and the time proportion of center zone of mouse in each group in the test box. D Effects of orthodontic pain on the expression levels of serum corticosterone in mice. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001; n = 6 per group

Full size image

Experimental orthodontic pain can induce changes in the structure of hippocampal neurons in mice

Under a 40× field of view (Fig. 4A), stained neurons in all groups have clear cell bodies and dendritic morphology. The intersection number graph at a distance of 300 μm from the neuron cell body from Sholl analysis showed that, ETMP mice had a reduced number of intersection points of neurons compared to controls (2D at 250–275 μm from soma, 5D at 175–300 μm from soma; Fig. 4B). Through statistical analysis, the number of dendrites (control group: 6.71 ± 0.95, 2D group: 5.29 ± 0.76, 5D group: 4.86 ± 1.07, compared with 2D group P = 0.019, compared with 5D group P = 0.003;) and total length (control group: 1718 ± 70, 2D group: 1550 ± 72, 5D group: 975 ± 95, compared with 2D group P = 0.004, compared with 5D group P < 0.0001; Fig. 4C) in ETMP mice neurons were significantly reduced compared with the control group. Under a 100× field of view (Fig. 4D), it can be observed that the morphology of dendritic spines gradually changed from stubby or mushroom to immature long or filopodial-like with the increase of force application time. Correspondingly, the number of dendritic spines also significantly decreased (control group: 5.17 ± 0.75, 2D group: 4.17 ± 0.75, 5D group: 2.67 ± 0.52, compared with 2D group P = 0.042, compared with 5D group P < 0.0001; Fig. 4E).

Fig. 4
figure 4

Effect of orthodontic pain on neuronal complexity and dendritic spine in ventral hippocampus CA1. A Schematic photomicrographs of neurons (40×) with the allocation of dendrites between repeated 25 μm-spaced concentric rings. B The number of intersections by dendrites of concentric circles spaced at a distance of 25 μm within a distance of 300 μm from the soma. ****P < 0.0001, compared with 2D group; ####P < 0.0001, compared with 5D group; n = 10 per group. C The total dendrite length and number of dendrites in ventral hippocampus CA1 in mice. D Schematic photomicrographs of dendritic spine (100×). E Density statistics of dendritic spines in mice of each group. *P < 0.05, **P < 0.01, ****P < 0.0001; n = 10 per group

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Discussion

A novel mouse behavior model of pain induced by experimental tooth movement was applied in this study, which is a new attempt. Compared to the molars, incisor periodontal tissues have a richer sensory receptor [30], making the animal model of incisor movement more suitable for experimental studies on orthodontic pain. When external mechanical forces are applied to teeth to induce movement, they trigger a series of inflammatory pain responses in the periodontal tissues [31]. As pain signals are transmitted upward through the trigeminal ganglion, the trigeminal nucleus in the medulla oblongata sends fibers to activate the facial nucleus. The activated facial nucleus, in turn, controls facial muscles via the facial nerve, resulting in behaviors such as facial grimacing or eye-closing. This mechanism explains why some orthodontic patients involuntarily exhibit grimacing expressions or eye closure when experiencing pain after orthodontic force application [32, 33]. It also provides a theoretical basis for assessing pain levels in animal models of orthodontic pain by observing facial expressions or behavioral responses [34]. In 1998, Yamashiro et al. pioneered the use of facial grooming behavior to assess pain in rats undergoing experimental tooth movement, a method widely recognized by scholars [35]. Subsequently, this approach has been progressively adopted and refined in animal studies investigating orthodontic pain, emotional alterations, and behavioral changes [36]. In this experiment, we evaluated the orthodontic pain response of the ETMP group by observing and recording the head retraction response or facial grooming behavior of mice when facing graded mechanical stimulation on the cheeks. The results of the oro-facial mechanical pain sensitivity test showed that the pain reflex threshold of the ETMP group mice to cheek mechanical stimulation was significantly lower than that of the control group, indicating that orthodontic pain was formed during the incisor movement process mediated by Ni–Ti orthodontic wire in this model. A clinical study found that during the alignment stage after placing the arch wire, pain would be generated, which would also affect the patient’s anxiety state and the expression level of cortisol hormone [37]. Similarly, in the open field experiment of the ETMP group mice, both the time occupancy in the central area and the total horizontal movement distance were significantly reduced, while the serum corticosterone content was significantly increased, indicating that experimental orthodontic pain could induce anxiety-like behavior in mice.

Hippocampus, as an important component of the limbic system, also plays a key role in pain-emotion, especially in anxiety and depression [19, 20]. Studies have shown that hippocampus lesions can improve anxiety-like behavior in rats [19, 38]. Among them, the ventral hippocampus (vHPC) is a vital part in the network processing emotional information [39]. It is closely connected with other limbic and cortical areas of the brain and participates in emotional activities [22]. For example, ventral hippocampal CA1 (vCA1) area can receive signal input from the posterior basolateral amygdala (BLA), the amygdala-hippocampal innervation, playing essential roles in processing anxiety-associated events [40]. The connection between the vHPC and the prefrontal cortex (PFC) may also be an important pathway for modulating anxiety-related behavior [41]. The number of neuronal intersections, total dendritic length, and dendritic number in vCA1 region of the ETMP group mice were significantly reduced compared to normal mice, indicating that the dendritic structure of neurons in this area has changed and the complexity has decreased. The dendritic structure of neurons is crucial for determining the number and type of synaptic connections a neuron possesses and controls how synaptic inputs are integrated to produce coding outputs [42]. Reduced neuronal dendritic branching caused by experimental orthodontic pain means that neurons will receive less signal input and neurogenesis, which weakens the collaborative anti-anxiety effects of vCA1 region and other cortical-limbic systems, ultimately leading to the development of anxiety. At the same time, as a synapse marker, dendritic spines are considered to be morphological markers of excitatory synapses and indicators for assessing the health and development of normal excitatory circuits [43]. Consistent with previous results, the density and size of dendritic spines in vCA1 region of ETMP group mice were significantly reduced with increasing force application time, suggesting weakened synaptic strength and reduced neuronal excitatory transmission, eventually leading to anxiety-like behavior in mice. Based on these results, we believe that the harmful stimulus of experimental orthodontic pain passes through hippocampus, leading to plastic changes such as reduced neuronal complexity and decreased dendritic spines in vCA1 region, ultimately causing anxiety in mice. Of course, insufficient nutrients intake could lead to various consequences, including energy deficits and systemic changes that can affect hippocampal function. Considering this, it would be relevant to know the ETMP mice undergoing orthodontic treatment were able to consume food properly and no tissue damage.

Some scholars believe that the impact of pain on hippocampal neurons may be a built-in strategy to alleviate pain [44]. Hippocampus is also well-known for its role in learning and memory. In a mouse model of Complex Regional Pain Syndrome (CRPS), mice exhibit anxiety-like behavior, mechanical hyperalgesia, and impaired working memory, accompanied by neuronal plasticity changes in the brain (hippocampal region) [42]. Chronic persistent pain is often associated with cognitive deficits and aversive emotional states (such as anxiety and depression). Functional and structural changes in hippocampus (such as reduced hippocampal neurogenesis) may be closely related to memory deficits and aversive emotional states in chronic pain patients [22]. Some studies suggest that when hippocampus is involved in pain information processing, changes in hippocampal neuron development and related hippocampal learning mechanisms may be associated with the development of persistent pain; impairing hippocampal neurogenesis can reduce the occurrence of pain behavior or decrease its severity, while upregulation of hippocampal neurogenesis can prolong persistent pain [45].

Limitations

Obviously, whether the changes in hippocampal neurons caused by experimental orthodontic pain are mediated by neurotransmitters released from glial cells (such as microglia and astrocytes), or how this change will affect the interaction between hippocampus and other limbic or cortical areas of the brain, leading to the development of anxiety, requires further experimental exploration.

Conclusions

In the process of hippocampus participating in and integrating orthodontic pain information, the nociceptive stimulus of orthodontic pain would lead to plastic changes such as reduced neuronal complexity and decreased dendritic spines in vCA1, ultimately resulting in an anxiety state.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Abbreviations

ETMP:

Experimental tooth movement pain

OTM:

Orthodontic tooth movement

CeA:

Central amygdala

vHPC:

Ventral hippocampus

vCA1:

Ventral hippocampal CA1

BLA:

Basolateral amygdala

PFC:

Prefrontal cortex

CRPS:

Complex regional pain syndrome

References

  1. Ireland AJ, Ellis P, Jordan A, Bradley R, Ewings P, Atack NE, et al. Comparative assessment of chewing gum and ibuprofen in the management of orthodontic pain with fixed appliances: a pragmatic multicenter randomized controlled trial. Am J Orthod Dentofacial Orthop. 2016;150(2):220–7.

    Article  PubMed  Google Scholar 

  2. Cozzani M, Ragazzini G, Delucchi A, Barreca C, Rinchuse DJ, Servetto R, et al. Self-reported pain after orthodontic treatments: a randomized controlled study on the effects of two follow-up procedures. Eur J Orthod. 2016;38(3):266–71.

    Article  PubMed  Google Scholar 

  3. Wang J, Tang X, Shen Y, Shang G, Fang L, Wang R, et al. The correlations between health-related quality of life changes and pain and anxiety in orthodontic patients in the initial stage of treatment. Biomed Res Int. 2015;2015: 725913.

    PubMed  PubMed Central  Google Scholar 

  4. Lin W, Farella M, Antoun JS, Topless RK, Merriman TR, Michelotti A. Factors associated with orthodontic pain. J Oral Rehabil. 2021;48(10):1135–43.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  5. Banerjee S, Banerjee R, Shenoy U, Agarkar S, Bhattacharya S. Effect of orthodontic pain on quality of life of patients undergoing orthodontic treatment. Indian J Dent Res. 2018;29(1):4–9.

    Article  PubMed  Google Scholar 

  6. Krishnan V. Orthodontic pain: from causes to management—a review. Eur J Orthod. 2007;29(2):170–9.

    Article  PubMed  Google Scholar 

  7. White AM, Giblin L, Boyd LD. The prevalence of dental anxiety in dental practice settings. J Dent Hyg JDH. 2017;91(1):30–4.

    PubMed  Google Scholar 

  8. Hare J, Bruj-Milasan G, Newton T. An overview of dental anxiety and the non-pharmacological management of dental anxiety. Primary Dent J. 2019;7(4):36–9.

    Article  Google Scholar 

  9. Tizzoni R, Veneroni L, D’Aloia A, Tizzoni M, Clerici CA. A case series analysing patients with dental anxiety: a patient-centered model based on psychological profiling. F1000Research. 2019;8:1843.

    Article  PubMed  Google Scholar 

  10. Rajmohan V, Mohandas E. The limbic system. Indian J Psychiatry. 2007;49(2):132–9.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  11. Zhang XH, Zou H, Zhou YR, Feng CC, Ju ZY, Zhou J, et al. Research advances in the limbic system involved in acupuncture treatment of chronic pain. Zhen ci yan jiu Acupuncture Res. 2020;45(4):339–45.

    Google Scholar 

  12. Long H, Wang Y, Jian F, Liao LN, Yang X, Lai WL. Current advances in orthodontic pain. Int J Oral Sci. 2016;8(2):67–75.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  13. Novaes AP, da Rocha MJ, Leite-Panissi CR. Tooth movement activates the central amygdala and the lateral hypothalamus by the magnitude of the force applied. Angle Orthod. 2010;80(1):111–5.

    Article  PubMed  PubMed Central  Google Scholar 

  14. Qiao H, Gao Y, Huang Q, Jia R. The central nucleus of the amygdala lesion attenuates orthodontic pain during experimental tooth movement in rats. Brain Behav. 2020;10(1): e01506.

    Article  PubMed  Google Scholar 

  15. Eichenbaum H. Memory: organization and control. Annu Rev Psychol. 2017;68:19–45.

    Article  PubMed  Google Scholar 

  16. Raoof R, Esmaeili-Mahani S, Abbasnejad M, Raoof M, Sheibani V, Kooshki R, et al. Changes in hippocampal orexin 1 receptor expression involved in tooth pain-induced learning and memory impairment in rats. Neuropeptides. 2015;50:9–16.

    Article  CAS  PubMed  Google Scholar 

  17. Raoof M, Esmaeili-Mahani S, Nourzadeh M, Raoof R, Abbasnejad M, Amirkhosravi L, et al. Noxious stimulation of the rat tooth pulp may impair learning and memory through the induction of hippocampal apoptosis. J Oral Facial Pain Headache. 2015;29(4):390–7.

    Article  PubMed  Google Scholar 

  18. Li HS, Ke J, Zhao GZ, Wu LA, Kou JP, Liu HC. Effects of Danggui-Shaoyao-San on the influence of spatial learning and memory induced by experimental tooth movement. Chin Med J. 2015;128(14):1948–55.

    Article  PubMed  PubMed Central  Google Scholar 

  19. Barkus C, McHugh SB, Sprengel R, Seeburg PH, Rawlins JN, Bannerman DM. Hippocampal NMDA receptors and anxiety: at the interface between cognition and emotion. Eur J Pharmacol. 2010;626(1):49–56.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  20. Mutso AA, Radzicki D, Baliki MN, Huang L, Banisadr G, Centeno MV, et al. Abnormalities in hippocampal functioning with persistent pain. J Neurosci. 2012;32(17):5747–56.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  21. Liu W, Ge T, Leng Y, Pan Z, Fan J, Yang W, et al. The role of neural plasticity in depression: from hippocampus to prefrontal cortex. Neural Plast. 2017;2017:6871089.

    Article  PubMed  PubMed Central  Google Scholar 

  22. Thompson JM, Neugebauer V. Cortico-limbic pain mechanisms. Neurosci Lett. 2019;702:15–23.

    Article  CAS  PubMed  Google Scholar 

  23. Yang S, Chang MC. Chronic pain: structural and functional changes in brain structures and associated negative affective states. Int J Mol Sci. 2019;20(13):3130.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  24. Andrade-González RD, Perrusquia-Hernández E, Montes-Ángeles CD, Castillo-Díaz LA, Hernández Campos ME, Pérez-Martínez IO. Encoding signs of orofacial neuropathic pain from facial expressions in mice. Arch Oral Biol. 2022;135: 105369.

    Article  PubMed  Google Scholar 

  25. Dolensek N, Gehrlach DA, Klein AS, Gogolla N. Facial expressions of emotion states and their neuronal correlates in mice. Science (New York, NY). 2020;368(6486):89–94.

    Article  CAS  Google Scholar 

  26. Lam VYY, Raineki C, Wang LY, Chiu M, Lee G, Ellis L, et al. Role of corticosterone in anxiety- and depressive-like behavior and HPA regulation following prenatal alcohol exposure. Prog Neuropsychopharmacol Biol Psychiatry. 2019;90:1–15.

    Article  CAS  PubMed  Google Scholar 

  27. Kinlein SA, Phillips DJ, Keller CR, Karatsoreos IN. Role of corticosterone in altered neurobehavioral responses to acute stress in a model of compromised hypothalamic-pituitary-adrenal axis function. Psychoneuroendocrinology. 2019;102:248–55.

    Article  CAS  PubMed  Google Scholar 

  28. Meijering E, Jacob M, Sarria JC, Steiner P, Hirling H, Unser M. Design and validation of a tool for neurite tracing and analysis in fluorescence microscopy images. Cytometry A. 2004;58(2):167–76.

    Article  CAS  PubMed  Google Scholar 

  29. Ferreira TA, Blackman AV, Oyrer J, Jayabal S, Chung AJ, Watt AJ, et al. Neuronal morphometry directly from bitmap images. Nat Methods. 2014;11(10):982–4.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  30. Jayawardena CK, Takahashi N, Takano Y. A unique localization of mechanoreceptors in the periodontal tissue of guinea pig teeth. Arch Histol Cytol. 2002;65(3):233–44.

    Article  PubMed  Google Scholar 

  31. Lew KK. Attitudes and perceptions of adults towards orthodontic treatment in an Asian community. Commun Dent Oral Epidemiol. 1993;21(1):31–5.

    Article  CAS  Google Scholar 

  32. Rahu MA, Grap MJ, Cohn JF, Munro CL, Lyon DE, Sessler CN. Facial expression as an indicator of pain in critically ill intubated adults during endotracheal suctioning. Am J Crit Care. 2013;22(5):412–22.

    Article  PubMed  PubMed Central  Google Scholar 

  33. Schmidt KL, Cohn JF. Human facial expressions as adaptations: evolutionary questions in facial expression research. Am J Phys Anthropol. 2001;116(Suppl 33):3–24.

    Article  Google Scholar 

  34. Liao L, Long H, Zhang L, Chen H, Zhou Y, Ye N, et al. Evaluation of pain in rats through facial expression following experimental tooth movement. Eur J Oral Sci. 2014;122(2):121–4.

    Article  PubMed  Google Scholar 

  35. Yamashiro T, Satoh K, Nakagawa K, Moriyama H, Yagi T, Takada K. Expression of Fos in the rat forebrain following experimental tooth movement. J Dent Res. 1998;77(11):1920–5.

    Article  CAS  PubMed  Google Scholar 

  36. Yozgatian JH, Zeredo JL, Hotokezaka H, Koga Y, Toda K, Yoshida N. Emotional stress- and pain-related behaviors evoked by experimental tooth movement. Angle Orthod. 2008;78(3):487–94.

    Article  PubMed  Google Scholar 

  37. Aksoy A, Cesur MG, Dağdeviren BH, Özkaynak YA, Karacin G, Gültekin F. Assessment of pain, anxiety, and cortisol levels during the initial aligning phase of fixed orthodontic treatment. Turk J Orthodontics. 2019;32(1):34–40.

    Article  Google Scholar 

  38. Deacon RM, Bannerman DM, Rawlins JN. Anxiolytic effects of cytotoxic hippocampal lesions in rats. Behav Neurosci. 2002;116(3):494–7.

    Article  PubMed  Google Scholar 

  39. Gergues MM, Han KJ, Choi HS, Brown B, Clausing KJ, Turner VS, et al. Circuit and molecular architecture of a ventral hippocampal network. Nat Neurosci. 2020;23(11):1444–52.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  40. Pi G, Gao D, Wu D, Wang Y, Lei H, Zeng W, et al. Posterior basolateral amygdala to ventral hippocampal CA1 drives approach behaviour to exert an anxiolytic effect. Nat Commun. 2020;11(1):183.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  41. Padilla-Coreano N, Bolkan SS, Pierce GM, Blackman DR, Hardin WD, Garcia-Garcia AL, et al. Direct ventral hippocampal-prefrontal input is required for anxiety-related neural activity and behavior. Neuron. 2016;89(4):857–66.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  42. Tajerian M, Leu D, Zou Y, Sahbaie P, Li W, Khan H, et al. Brain neuroplastic changes accompany anxiety and memory deficits in a model of complex regional pain syndrome. Anesthesiology. 2014;121(4):852–65.

    Article  CAS  PubMed  Google Scholar 

  43. Rochefort NL, Konnerth A. Dendritic spines: from structure to in vivo function. EMBO Rep. 2012;13(8):699–708.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  44. Forkmann K, Wiech K, Ritter C, Sommer T, Rose M, Bingel U. Pain-specific modulation of hippocampal activity and functional connectivity during visual encoding. J Neurosci. 2013;33(6):2571–81.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  45. Apkarian AV, Mutso AA, Centeno MV, Kan L, Wu M, Levinstein M, et al. Role of adult hippocampal neurogenesis in persistent pain. Pain. 2016;157(2):418–28.

    Article  PubMed  PubMed Central  Google Scholar 

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Acknowledgements

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Funding

This work was supported by the National Natural Science Foundation of China (No.82271021), the Guangdong Basic and Applied Basic Research Foundation, China (No. 2021A1515010460), Fundamental Research Funds for the Central Universities, Sun Yat-sen University (23qnpy143) and the Science and Technology Projects in Guangzhou, China (No. 2024A03J0098).

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Author notes

  1. Hongrui Que and Yuxuan Wang contributed equally to this work.

Authors and Affiliations

  1. The Third Affiliated Hospital of Sun Yat-Sen University, Guangzhou, China

    Hongrui Que, Yuxuan Wang, Yi Feng, Shaoqin Tu, Jiaming Wei, Chiyuen Cheung, Nan Wei, Zheng Chen & Hong Ai

  2. Department of Stomatology, Shenzhen Sixth People’S Hospital (Nanshan Hospital) Huazhong University of Science and Technology Union Shenzhen Hospital, Shenzhen, People’s Republic of China

    Yuxuan Wang

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  1. Hongrui Que
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Contributions

ZC and HA made substantial contributions to conception and design. HRQ and YXW made substantial contributions to acquisition and analysis of data, and been involved in drafting the manuscript. YF, SQT and JMW been involved in revising the manuscript critically for important intellectual content and helped with interpretation of data. CYC and NW helped with experimental modeling and acquisition of data. All authors read and approved the final manuscript.

Corresponding authors

Correspondence to Zheng Chen or Hong Ai.

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Ethics approval and consent to participate

The Sun Yat-sen University of Medical Sciences ethics committee provided ethics approval for the current study (Approval number: SYSU-IACUC-2023-000281). The authors confirmed that all the methods were performed in accordance with the relevant guidelines and regulations. The study was reported in accordance with ARRIVE guidelines.

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Que, H., Wang, Y., Feng, Y. et al. Experimental orthodontic pain drives anxiety state through the induction of alterations to the neuronal architecture in hippocampus. BMC Neurosci 26, 26 (2025). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12868-025-00945-9

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BMC Neuroscience

ISSN: 1471-2202

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