An ex vivo culture model for orthodontically induced root resorption

Mechanical force regulates root resorption in rats through RANKL and OPG

Background

External root resorption is one of common complications of orthodontic treatment, while internal root resorption is rarely observed, and the difference between pulp and periodontal tissues during orthodontic treatment is still unknown. The purpose of this study was to evaluate the effects of orthodontic forces on histological and cellular changes of the dental pulp and periodontal tissues.

Methods

Orthodontic tooth movement model was established in Forty-eight adult male Wistar rats. The distance of orthodontic tooth movement was quantitatively analyzed. The histological changes of pulp and periodontal tissues were performed by hematoxylin–eosin staining, tartrate-resistant acid phosphate staining was used to analyze the changes of osteoclast number, immunohistochemistry analysis and reverse transcription polymerase chain reaction were used to examine the receptor of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) expression. The width of tertiary dentine was quantitatively analyzed. Tartrate-resistant acid phosphate staining and the erosion area of osteo assay surface plate was used to evaluate osteoclast activity.

Results

The orthodontic tooth movement distance increased in a force dependent manner, and reached the peak value when orthodontic force is 60 g. Heavy orthodontic force increased the RANKL expression of periodontal ligament srem cells (PDLSCs) which further activated osteoclasts and resulted in external root resorption, while the RANKL expression of dental pulp stem cells (DPSCs) was relatively low to activate osteoclasts and result in internal root resorption, and the dental pulp tend to form tertiary dentine under orthodontic force stimulation.

Conclusions

Heavy orthodontic forces activated osteoclasts and triggered external root resorption by upregulating RANKL expression in rat periodontal tissues, while there was no significant change of RANKL expression in dental pulp tissue under heavy orthodontic forces, which prevented osteoclast activation and internal root resorption.

Tissue-specific biomarkers in gingival crevicular fluid are correlated with external root resorption caused by constant mechanical load: an in vivo study

OBJECTIVES

This study investigated the association of changes in cementum protein-1 (CEMP-1), dentine phosphoprotein (DPP), and c-terminal cross-linked telopeptide of type I collagen (CTX-I) levels in human gingival crevicular fluid (GCF) under constant load with external root resorption volume and amount of tooth movement.

MATERIALS AND METHODS

In total, 11 healthy adult patients (mean age, 23.5 years [range, 18.3-37.7]; four men and seven women) were enrolled. GCF samples were obtained from premolars at T0, T1 (1 day), T2 (1 week), T3 (2 weeks), T4 (4 weeks), and T5 (8 weeks) under constant 100-gm buccal tipping force. Opposite premolars were used as controls. Teeth were extracted at T5, followed by quantification of external root resorption volume and histological analysis.

RESULTS

In the test group, T5/T0 ratios of CEMP-1 and DPP levels, differential CEMP-1 levels between T5 and T0, and differential DPP levels between T2 and T0 correlated positively with root resorption volume (r = 0.734, 0.730, 0.627, and 0.612, respectively, all p < 0.05). CEMP-1 levels at T0 and T3 correlated negatively with root resorption volume (r = -0.603 and -0.706; all p < 0.05). CTX-I levels at T5 correlated positively with the amount of tooth movement (r = 0.848, p < 0.01).

CONCLUSIONS

Alterations in CEMP-1 and DPP levels in human GCF at specific timepoints during orthodontic treatment may be associated with different degrees of external root resorption.

CLINICAL RELEVANCE

This study demonstrates that changes in the levels of tissue-specific biomarkers in GCF may facilitate early detection of external root resorption during orthodontic tooth movement.

Intermittent parathyroid hormone promotes cementogenesis via ephrinB2-EPHB4 forward signaling

Intermittent parathyroid hormone (PTH) promotes periodontal repair, but the underlying mechanisms remained unclear. Recent studies found that ephrinB2-EPHB4 forward signaling mediated the anabolic effect of PTH in bone homeostasis. Considering the similarities between cementum and bone, we aimed to examine the therapeutic effect of PTH on resorbed roots and explore the role of forward signaling in this process. In vivo experiments showed that intermittent PTH significantly accelerated the regeneration of root resorption and promoted expression of EPHB4 and ephrinB2. When the signaling was blocked, the resorption repair was also delayed. In vitro studies showed that intermittent PTH promoted the expression of EPHB4 and ephrinB2 in OCCM-30 cells. The effects of PTH on the mineralization capacity of OCCM-30 cells was mediated through the ephrinB2-EPHB4 forward signaling. These results support the premise that the anabolic effects of intermittent PTH on the regeneration of root resorption is via the ephrinB2-EPHB4 forward signaling pathway.

The role of EphB4/ephrinB2 signaling in root repair after orthodontically-induced root resorption

INTRODUCTION

This study aimed to investigate the effect of EphB4/ephrinB2 signaling on orthodontically-induced root resorption repair and the possible molecular mechanism behind it.

METHODS

Seventy-two 6-week-old male Wistar rats were randomly divided into 3 groups: blank control group, physiological regeneration group (PHY), and EphB4 inhibitor local injection group (INH). A root repair model was built on experimental rats of the PHY and INH groups. The animals in the INH groups received a daily periodontal local injection of EphB4 inhibitor NVP-BHG712, whereas the blank control group and PHY groups received only the vehicle.

RESULTS

Histologic staining and microcomputed tomography analysis showed that root regeneration was inhibited in the INH group compared with the PHY group with a greater number of osteoclasts. Immunohistochemical staining showed active EphB4/ephrinB2 signaling activities during root regeneration. The cementogenesis-related factors cementum attachment protein, alkaline phosphatase, osteopontin, and runt-related transcription factor 2, and osteoclastic-related factors RANKL and osteoprotegerin were affected by regulated EphB4/ephrinB2 signaling.

CONCLUSIONS

These findings demonstrated that the EphB4/ephrinB2 signaling might be a promising therapeutic target for novel therapeutic approaches to reduce orthodontically-induced root resorption through enhancement of cementogenesis.

Developing a Tooth in situ Organ Culture Model for Dental and Periodontal Regeneration Research

In this study we have realized the need for an organ culture tooth in situ model to simulate the tooth structure especially the tooth attachment apparatus. The importance of such a model is to open avenues for investigating regeneration of the complex tooth and tooth attachment tissues and to reduce the need for experimental animals in investigating dental materials and treatments in the future. The aim of this study was to develop a porcine tooth in situ organ culture model and a novel bioreactor suitable for future studies of periodontal regeneration, including application of appropriate physiological loading. The Objectives of this study was to establish tissue viability, maintenance of tissue structure, and model sterility after 1 and 4 days of culture. To model diffusion characteristics within the organ culture system and design and develop a bioreactor that allows tooth loading and simulation of the chewing cycle. Methods: Twenty-one porcine first molars were dissected aseptically in situ within their bony sockets. Twelve were used to optimize sterility and determine tissue viability. The remainder were used in a 4-day organ culture study in basal medium. Sterility was determined for medium samples and swabs taken from all tissue components, using standard aerobic and anaerobic microbiological cultures. Tissue viability was determined at days 1 and 4 using an XTT assay and Glucose consumption assays. Maintenance of structure was confirmed using histology and histomorphometric analysis. Diffusion characteristics were investigated using micro-CT combined with finite element modeling. A suitable bioreactor was designed to permit longer term culture with application of mechanical loading to the tooth in situ. Result: XTT and Glucose consumption assays confirmed viability throughout the culture period for all tissues investigated. Histological and histomorphometric analysis confirmed maintenance of tissue structure. Clear microbiological cultures indicated maintenance of sterility within the organ culture system. The novel bioreactor showed no evidence of medium contamination after 4 days of culture. Finite element modeling indicated nutrient availability to the periodontium. Conclusion: A whole tooth in situ organ culture system was successfully maintained over 4 days in vitro.

The effect of low intensity pulsed ultrasound on dentoalveolar structures during orthodontic force application in diabetic ex-vivo model

OBJECTIVE

This study aimed to investigate the effect of the low intensity pulsed ultrasound (LIPUS) on the dentoalveolar structures during orthodontic force application in ex-vivo model using mandible slice organ culture (MSOC) of diabetic rats.

DESIGN

18 male Wistar rats with a mean weight (275 g) were randomly divided into three main groups: 1) normal rats, 2) Insulin treated diabetic rats, and 3) diabetic rats. Diabetes mellitus (DM) was induced by streptozotocin. Four weeks later, rats were euthanized, mandibles were dissected, divided into 1.5-mm slices creating mandible slice organ cultures (MSOCs). MSOCs were cultured at 37 °C in air with 5 % CO₂. The following day, orthodontic spring delivering a 50-g of force was applied to each slice. In each group, rats were randomly assigned to 2 subgroups; one received 10 min of LIPUS daily and the other was the control. Culture continued for 7 days, and then the sections were prepared for histological and histomorphometric analysis.

RESULTS

For all study groups (Normal, Insulin Treated Diabetic and Diabetic), LIPUS treatment significantly increased the thickness of predentin, cementum, and improved bone remodeling on the tension side and increased odontoblast, sub-odontoblast, and periodontal ligaments cell counts and bone resorption lacunae number on the compression side.

CONCLUSIONS

Application of LIPUS treatment for 10 min daily for a week enhanced bone remodeling and repair of cementum and dentin in normal as well as diabetic MSOCs.

Effects of estrogen on root repair after orthodontically induced root resorption in ovariectomized rats

INTRODUCTION

This study aimed to investigate the effects of estrogen on root repair after orthodontically induced root resorption.

METHODS

Seventy-two 6-week-old female Wistar rats were randomly divided into 3 groups: ovariectomy only (OVX), ovariectomy plus estradiol injection (OVX + E2), and sham operation (control). E2 was administrated to all the experimental animals after the establishment of the root repair model. One-way analysis of variance with the Tukey post-hoc test was used to analyze the experimental results.

RESULTS

Micro-computed tomography and hematoxylin and eosin staining showed that the total volumes of resorption lacunae were significantly smaller in the control and OVX + E2 groups than those in the OVX group. Alkaline phosphatase and tartrate-resistant acid phosphatase stainings suggested that the cementoblastic activities and the amount of new cementum formation were inhibited while the activities of osteoclasts were obvious in the OVX group. The immunohistochemistry stainings revealed that the osteoprotegerin to receptor activator of nuclear factor-кB ligand ratio and the phosphorylated extracellular signal-regulated kinases to extracellular signal-regulated kinases ratio of the control and OVX + E2 groups were significantly greater than those of the OVX group.

CONCLUSIONS

These findings demonstrated that estrogen administration might be a solution to reduce orthodontically induced root resorption through the activation of extracellular signal-regulated kinase-1/2 pathway and enhancement of cementogenesis.

A Comparison of Osteoblast and Osteoclast In Vitro Co-Culture Models and Their Translation for Preclinical Drug Testing Applications

As the population of western societies on average ages, the number of people affected by bone remodeling-associated diseases such as osteoporosis continues to increase. The development of new therapeutics is hampered by the high failure rates of drug candidates during clinical testing, which is in part due to the poor predictive character of animal models during preclinical drug testing. Co-culture models of osteoblasts and osteoclasts offer an alternative to animal testing and are considered to have the potential to improve drug development processes in the future. However, a robust, scalable, and reproducible 3D model combining osteoblasts and osteoclasts for preclinical drug testing purposes has not been developed to date. Here we review various types of osteoblast-osteoclast co-culture models and outline the remaining obstacles that must be overcome for their successful translation.

Ultrasound Enhances Dentoalveolar Remodeling in an Ex Vivo Orthodontic, Ovariectomy-Induced Osteoporotic Model

The aim of the study was to investigate the effects of low-intensity pulsed ultrasound (LIPUS) on dentoalveolar structures during application of force to a cultured mandible slice taken from an ovariectomized rat model of osteoporosis. Rats were divided based on whether they had ovariectomy and/or LIPUS application into four groups: control osteoporosis group, control normal group, ultrasound-treated osteoporosis group and ultrasound-treated normal group. The mandibles were dissected, sliced and cultured before application of a 0.5-N force. Tissue specimens from five rats per group received LIPUS; the remaining rats served as untreated controls. Tissue sections were evaluated histologically and histomorphometrically. Osteoporosis significantly affected the alveolar bone without any effect on the dentin-pulp complex. LIPUS enhanced osteoporotic alveolar bone remodeling and increased cementum and predentin thickness. Furthermore, LIPUS application significantly increased odontoblast and periodontal ligament cell counts (p < 0.05) in both groups. Therefore, LIPUS enhances alveolar bone remolding and increases cementum and predentin formation in osteoporotic rat mandible slice organ cultures.

Dental pulp cells promote the expression of receptor activator of nuclear factor-κB ligand, prostaglandin E2 and substance P in mechanically stressed periodontal ligament cells

OBJECTIVE

This study investigated the expression of receptor activator of nuclear factor-κB ligand (RANKL) in periodontal ligament (PDL) cells co-cultured with dental pulp (DP) cells following mechanical stress in vitro. Furthermore, the expression of prostaglandin (PG) E₂ and substance P (SP) by the PDL cells and by the DP cells were also examined.

DESIGN

PDL and DP cells were obtained from 10 rats. The experimental group consisted of PDL cells subjected to centrifugal force as mechanical stress and co-cultured with DP cells. The 3 control groups of PDL cells were: 1) PDL cells without mechanical stress, 2) PDL cells treated with mechanical stress and 3) PDL cells co-cultured with DP cells. The 2 control groups of DP cells were: 1) DP cells without mechanical stress and 2) DP cells co-cultured with PDL cells. In each group, both cells were examined at day 1 and day 3, and mRNA levels of RANKL by PDL cells were analyzed using Real time quantitative Reverse Transcription (RT)-PCR. Furthermore, RANKL expression was observed using Immunofluorescence staining. PGE₂ and SP expression levels by PDL cells and DP cells were characterized by ELISA analysis.

RESULTS

The expression of RANKL by PDL cells under mechanical stress increased by co-culture with DP cells. PGE₂ and SP expressions were increased in the group of PDL cells subjected to mechanical stress and co-cultured with DP cells.

CONCLUSION

DP cells may facilitate the expression of RANKL in PDL cells under mechanical stress via PGE₂ and SP.

Autotransplantation and surgical uprighting of impacted or retained teeth: A retrospective clinical study and evaluation of patient satisfaction

OBJECTIVES

This retrospective clinical study aimed to determine the success rate of autotransplanted impacted or retained teeth along with a patient satisfaction survey and to analyze the influence of relevant clinical and radiographic parameters.

SUBJECTS AND METHODS

Fifty-seven teeth (37 canines, 10 molars, seven premolars, three incisors) in 45 patients (median 15 years) were evaluated over a mean of 1.6 years. The success criteria were pocket probing depth ≤3.5 mm, mobility grade ≤ II, Periotest ≤30 and complete alveolar bone healing. The influencing parameters were oral hygiene, smoking, periodontal screening index, occlusal/proximal contacts, horizontal position, dental age, pulp obliteration and degree of displacement. Furthermore, bone height was measured.

RESULTS

The overall success rate was 74%, along with a high patient satisfaction. The survival rate was 96% after a mean follow-up of 1.6 years. The favorable factors were proper oral hygiene, non-smoking, good general periodontal condition, proximal contacts and pulp obliteration. An increase in or maintenance of bone level was found in 96%.

CONCLUSIONS

Autotransplantation of impacted or retained teeth is an appropriate treatment, if orthodontic alignment has failed, especially in growing patients.