Mechanism analysis of periostin in osteoclasts differentiation of dental follicle: Two case reports

Abstract

BACKGROUND

This study analyzed the dental follicle and alveolar bone of two patients with tooth eruption disorders, aiming to provide some reference for exploring the etiology and selecting treatment plans of this disease from the perspective of the influence of extracellular matrix on osteoclasts differentiation in dental follicle.

CASE SUMMARY

Collect dental follicle and alveolar bone tissue from one patient with single tooth eruption disorder and one patient with full permanent tooth eruption disorder, respectively. Simultaneously collect the dental follicle and alveolar bone tissue of obstructed teeth that need to be extracted due to orthodontic treatment as the control group. Hematoxylin and eosin (HE) staining was used to observe the morphology of dental follicle cells. Immunohistochemical staining was used to observe the expression of periostin, receptor activator of nuclear factor kappa B ligand (RANKL), and osteoprotegerin (OPG) protein in dental follicle and alveolar bone tissue. And observe the eruption of teeth after removing resistance from the crown of the permanent tooth germ.

CONCLUSION

HE staining of two cases of dental follicle tissues showed that the volume of dental follicle cells decreased, the nuclei were condensed, and there seemed to be cellular fibrosis. The immunohistochemical staining showed that both the dental follicle and alveolar bone tissue exhibited increased expression of periostin, decreased expression of RANKL and OPG proteins, and decreased RANKL/OPG ratio. After removing resistance, the permanent tooth germ often appears to have normal eruption. Tooth eruption disorders may be accompanied by abnormal remodeling of periostin, which affects the differentiation function of osteoclasts in the dental follicle and leads to metabolic imbalance of alveolar bone, resulting in tooth eruption disorders. Whether it is a single or full permanent tooth eruption disorder, once the coronal resistance is removed, the teeth can often erupt normally.

Key Words: Tooth eruption disorder; Dental follicle; Osteoclast differentiation; Periostin; Case report

Core Tip: This study analyzed the periostin and bone metabolic factors in the dental follicle and alveolar bone of two patients with tooth eruption disorders. And the results suggest that tooth eruption diseases may be accompanied by abnormal remodeling of periostin, which can affect the differentiation function of osteoclasts in the dental follicle, leading to an imbalance in alveolar bone metabolism and resulting in tooth eruption disorders. This provides some reference for the etiology and treatment of tooth eruption disorders from a new research perspective of the effect of extracellular matrix on the differentiation of osteoclasts in dental follicle.

INTRODUCTION

Tooth eruption disorder refers to the condition where the development of the tooth root is basically completed, but the eruption period is significantly later than that of normal teeth[1]. Once the resistance of the dental crown is removed, teeth can usually erupt normally, indicating that excessive stress may be a key factor in preventing tooth eruption. The dental follicle, as an essential organ for tooth eruption, is the loose fibrous connective tissue surrounding the developing tooth germ[2]. When teeth erupt, a certain amount of stress is generated between the dental follicle, alveolar bone, and gingiva as the tooth germ develops and occlusal movement occurs. Then promote the secretion of various factors in the dental follicle, recruit macrophages into the dental follicle and fuse to form osteoclasts, leading to alveolar bone resorption and eruption channels formation[3]. This indicates that normal tooth eruption requires a certain amount of stress to act on the dental follicle and stimulate the differentiation of osteoclasts by recruiting macrophages. However, why does the dental follicle have different effects on the activation function of osteoclasts during tooth eruption disorders? The reason for this may be that excessive stress alters the molecular regulatory mechanism of the dental follicle, leading to abnormal differentiation of osteoclasts. At present, research on tooth eruption disorders both domestically and internationally mainly focuses on changes in cytokines during tooth eruption[4,5]. On the contrary, there have been no reports on how the dental follicle perceives stress to initiate osteoclast differentiation, how the morphology and function of dental follicle cells change when stress increases, and how the corresponding alveolar bone changes at this time.

Extracellular matrix is a three-dimensional network composed of large molecules and minerals synthesized and secreted by cells, distributed on the cell surface or between cells, supporting and connecting tissue structures, regulating tissue development and cellular physiological activities[6,7]. If remodeling is disrupted, it can easily lead to fibrosis in fibroblasts. Periostin, as a multifunctional extracellular matrix protein, is mainly expressed in fibrous connective tissue subjected to sustained mechanical stress[8]. It can sense stress and convert it into biological signals, regulating tissue cell function. Recent studies have shown that periostin is expressed in the dental follicle and can promote the differentiation of dental follicle cells[9]. This suggests that periostitis protein may be a key extracellular matrix that can sensitively sense stress changes during tooth eruption, and can serve as an important indicator for dynamically observing the morphology and osteoclast differentiation function of dental follicle cells.

This study collected dental follicle and alveolar bone tissue specimens from one case of single tooth and one case of full permanent tooth eruption disorder. Hematoxylin and eosin (H&E) staining methods was used to observe the morphology of dental follicle cells. And immunohistochemical staining methods was used to observe the periostin, receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG) protein expression. The objective aims to offer guidance for the etiological exploration and treatment options of this type of disease from the perspective of abnormal dental follicle morphology and osteoclast differentiation caused by excessive extracellular matrix sensing stress.

CASE PRESENTATION

Chief complaints

Single tooth eruption disorder: A 12-year-old female patient with good overall health came to our pediatric dental department for treatment due to the failure of the left maxillary first premolar (tooth 24) to erupt.

Full mouth tooth eruption disorder: A 10-year-old male patient with overall good health came to our pediatric dental clinic for treatment because none of his permanent teeth had properly erupted or replaced.

History of present illness

Both patients showed no history of systemic diseases or other abnormalities during examination.

History of past illness

Parents of the two patients stated that they were full-term natural birth, and her/his mother had not smoked, drunk or contracted infectious diseases during pregnancy. They denied that the patients have bad eating habits and hobbies, and denied the orthodontic treatment history.

Personal and family history

General health and oral specialist examinations were conducted on family members to understand the corresponding medical history and genetic characteristics of related diseases. The results showed that no related diseases were found.

Physical examination

Single tooth eruption disorder: The intraoral examination revealed permanent dentition without tooth 24. But several abnormal tooth shaped tissues can be observed in the affected area.

Full mouth tooth eruption disorder: The intraoral examination of the patient revealed deciduous dentition, deciduous tooth 54, 64 and 85 were caries, and no obvious abnormality in the remaining deciduous teeth.

Laboratory examinations

HE staining: The HE staining results of dental follicle tissues from the two patients with tooth eruption disorder showed that the volume of dental follicle cells decreased, the nuclei were condensed, and there seemed to be cellular fibrosis (Figure 1).

Figure 1 Morphological changes in dental follicles of patients with tooth eruption disorders. A: The hematoxylin and eosin staining results of dental follicle tissues from the two patients with tooth eruption disorder showed that the volume of dental follicle cells decreased, the nuclei were condensed, and there seemed to be cellular fibrosis; B: The result of hematoxylin and eosin staining of normal dental follicle tissue in the control group (×200).

Immunohistochemical staining: Two cases of immunohistochemical staining showed that both the dental follicle and alveolar bone tissue exhibited increased expression of periostin, decreased expression of RANKL and OPG proteins, and decreased RANKL/OPG ratio (Figures 2 and 3).

Figure 2 Detection of relevant proteins in dental follicle tissue. A: Immunohistochemical staining results of dental follicle tissue from two patients with tooth eruption disorders. The expression of periostin protein increases, while the expression of nuclear factor kappa B ligand and osteoprotegerin protein decreases, and the ratio of nuclear factor kappa B ligand/osteoprotegerin decreases; B: Immunohistochemical results of normal dental follicle tissue in the control group (×200).

Figure 3 Detection of relevant proteins in alveolar bone tissue. A: Immunohistochemical staining results of alveolar bone tissue from two patients with tooth eruption disorders. The expression of periostin protein increases, while the expression of nuclear factor kappa B ligand and osteoprotegerin protein decreases, and the ratio of nuclear factor kappa B ligand/osteoprotegerin decreases; B: Immunohistochemical results of normal alveolar bone tissue in the control group (×200).

Imaging examinations

Single tooth eruption disorder: The results of cone beam computed tomography showed that image aggregates resembling undersized teeth were visible above the impacted tooth 24 (Figure 4A). Based on the analysis of clinical and imaging examination results, the preliminary diagnosis is peripheral odontoma. Under local anesthesia, we performed extraction according to the standard of peripheral odontoma and fully exposing the obstructed permanent tooth germ.

Figure 4 Imaging examination of the patient with single tooth eruption disorder. A: Preoperative observation of tooth 24 coronal odontoma; B: First eruption of teeth observed one month after surgery; C: Three months after surgery, most of the teeth have already erupted.

The patient returned to our department for follow-up one month after surgery, and imaging showed no abnormalities above the crown region of tooth 24 (Figure 4B).

The patient had the second follow-up visit three months after the surgery. Oral examination showed that tooth 24 had almost fully erupted, and imaging data indicated no abnormalities in root development (Figure 4C).

Full mouth tooth eruption disorder: His panoramic radiograph examination showed that the number of permanent tooth embryos was normal, the root of teeth 16, 26, 36, 46 were curve, root development of teeth 12-22, 32-42 was basically complete, and no obvious abnormalities were observed in alveolar bone (Figure 5A). Panoramic radiographs examination of his twin sister showed no abnormality in the replacement of primary and permanent teeth (Figure 5B). Within one year, the patient will have their retained deciduous teeth and crown alveolar bone removed in batches, fully exposing the obstructed permanent tooth germ. Two years later, the patient was returned to our clinic and the panoramic radiograph examination showed that all permanent teeth have basically erupted (Figure 5C).

Figure 5 Imaging examination of the patient with full mouth permanent tooth eruption disorder. A: The number of permanent tooth embryos was normal, the root of teeth 16, 26, 36, 46 were curve, root development of teeth 12-22, 32-42 was basically complete, and no obvious abnormalities were observed in alveolar bone; B: His twin sister showed no abnormality in primary and permanent teeth replacement; C: Remove crown resistance for 2 year, the panoramic radiograph examination showed that all permanent teeth have basically erupted.

FINAL DIAGNOSIS

The first patient was diagnosed with single tooth eruption disorder; the second patient was diagnosed with multiple tooth eruption disorders.

TREATMENT

The first patient underwent tooth extraction under local anesthesia according to the standard of peripheral odontoma and fully exposing the obstructed permanent tooth germ.

For the second patient, the retained deciduous teeth and crown alveolar bone were extracted in batches within one year, completely exposing the obstructed permanent tooth germ.

OUTCOME AND FOLLOW-UP

The patient with single tooth eruption disorders was followed up one month after surgery, and imaging showed no abnormalities above the crown of the obstructed tooth. Three months after the surgery, the patient's oral examination during the follow-up showed that the obstructed teeth had erupted normally.

The patient with multiple tooth eruption disorders was followed up two years later, and oral examinations showed that all permanent teeth had mostly erupted.

DISCUSSION

The main manifestations of tooth eruption disorders are retention of single or multiple primary teeth, delayed eruption of permanent teeth, and tooth impaction[10,11]. Once the excessive stress on the crown of the obstructed tooth is removed, such as surgical removal of odontoma, extraction of retained deciduous teeth, and removal of bone above the obstructed tooth, the teeth can often erupt normally. This indicates that when the stress on the crown of the tooth germ is too high, it may affect the osteogenic differentiation ability of the tooth follicle by altering the morphology of the tooth follicle cells and molecular signal transduction mechanisms, leading to decrease in the potential for tooth eruption[12-14]. However, it is currently unclear what changes occur in dental follicle cells when subjected to excessive stress. This study observed the morphological changes of dental follicle cells through HE staining, and the results showed that when tooth eruption was hindered, the volume of dental follicle cells decreased, the nuclei were condensed, and there seemed to be cellular fibrosis. The results indicate that excessive stress on the dental crown may lead to fibrosis of dental follicle cells, thereby affecting the differentiation function of osteoclasts in the dental follicle. Nevertheless, it is currently unclear how the dental follicle sensitively perceives stress changes, why excessive stress can lead to fibrous changes in dental follicle cells, and how molecular mechanisms regulate the differentiation process of osteoclasts in dental follicles.

Extracellular matrix is a three-dimensional network composed of large molecules and minerals synthesized and secreted by cells, distributed on the cell surface or between cells, supporting and connecting tissue structures, regulating tissue development and cellular physiological activities[15,16]. If remodeling is disrupted, it can easily lead to fibrosis in fibroblasts[17]. The properties of fibroblasts in dental follicles suggest that there is a crucial regulatory role played by extracellular matrix during tooth eruption. Periostin, as a multifunctional extracellular matrix protein, is mainly expressed in fibrous connective tissue subjected to sustained mechanical stress[18]. It can sense stress and convert it into biological signals, regulating tissue cell function. The detection of periostin in the periodontal tissue of extracted mandibular teeth in mice revealed a decrease in periostin expression after loss of stress stimulation[19]. Recent studies have shown that periostin are expressed in the dental follicle and can promote the differentiation function of dental follicle cells. In this study, we found that the expression of periostin in the group with tooth eruption disorders was significantly higher than that in the control group, indicating that periostin is a key extracellular matrix for sensing stress changes during eruption and can be used as an important indicator for dynamically observing changes in tooth eruption. If the stress is too high, it may lead to dysregulation of periostin remodeling, affecting the osteoclast differentiation function of the dental follicle.

The RANKL/OPG ratio is an important indicator for measuring osteoclast differentiation[20]. An increase in the ratio indicates active osteoclast differentiation, while a decrease in the ratio indicates the opposite. The RANKL in osteoclasts is mainly expressed by stromal cells and osteoblasts, and can be activated by many factors[21]. The RANK in osteoclasts is located on the surface of the precursor cell membrane and is the only target receptor for RANKL to stimulate osteoclast activation[22]. OPG is a natural inhibitor of RANKL, which binds to RANKL and competitively blocks RANKL/RANK binding, inhibiting osteoclast differentiation and maturation[23]. RANKL positive signal is widely expressed in various tissues of tooth eruption, but the location and intensity of expression are inconsistent at different stages[24]. Animal experiments have shown that RANKL/OPG increases and osteoclasts become active during the middle stage of tooth eruption in mice, but in the early and late stages of eruption, there are relatively fewer osteoclasts in the alveolar bone, RANKL/OPG decreased, consistent with the level of bone resorption activity[25]. In this study, the ratio of RANKL/OPG in the dental follicle and alveolar bone tissues of the eruption disorder group was found to decrease synchronously. From this point, we preliminarily speculate that excessive pressure on the dental crown may lead to dysregulation of extracellular membrane protein remodeling, driving fibrosis of dental follicle cells. Thus, by changing the RANKL/OPG ratio, it affects the differentiation of osteoclasts during tooth eruption, leading to obstacles in tooth eruption.

CONCLUSION

The pathogenesis and treatment of tooth eruption disorders have always been a hot topic in the field of dentistry, but currently the limited treatment include drug-induced tooth eruption, alveolar bone repair surgery and orthodontic traction. Drug induced tooth eruption is achieved by using exogenous hormone drugs to promote tooth germ development and induce smooth eruption of blocked teeth. This method is only suitable for situations where local factors cause difficulty in tooth eruption and drugs may affect tooth germ development. Alveolar bone repair is the surgical removal of abnormal bone tissue that hinders the normal eruption of teeth to promote tooth eruption. This method is suitable for tooth eruption disorders caused by jaw deformities, but it involves excessive trauma. Orthodontic traction is the process of gradually adjusting the position of teeth using fixed or functional orthodontic appliances under the guidance of a professional physician. This method has a narrow range of indications and a long treatment period.

With the research of gene therapy and tissue engineering technology in the process of tooth eruption, it can be predicted that future treatment plans should include precise and effective site strikes to promote tooth re-eruption. This study observed the morphology of dental follicle cells and analyzed the expression of periostin, RANKL, and OPG protein in dental follicle and alveolar bone. In order to explore the molecular signal transduction mechanism of tooth eruption disorder from the perspective of extracellular matrix perception affecting cell morphology and function, and to open up novel research ideas for the protection and treatment of abnormal tooth eruption. In future research, we will expand clinical samples and establish in vitro animal models to further observe the effects of periostin on osteoclast differentiation and alveolar bone remodeling in dental follicle, providing more experimental evidence for the treatment of tooth eruption disorders.

ACKNOWLEDGEMENTS

The authors are grateful to the patients and their family members for their kind cooperation and participation.