British Orthodontic Society, Chapman Prize Winner 2003. A novel in vitro culture model to investigate the reaction of the dentine-pulp complex to orthodontic force

THE EFFECT OF BISPHOSPHONATE RISEDRONATE HYDROGEL ON ALKALINE PHOSPHATASE AND OSTEOCLASTS DURING RELAPSE MOVEMENT

Objectives: To analyze the effect of risedronate hydrogel on enzyme alkaline phosphatase (ALP) and osteoclast/osteoblast ratio during tooth relapse movement Materials and methods: The research design is experimental with time series. The lower incisors of 75 guinea pigs are distally moved using open coil spring. The guinea pigs were divided into three groups: without risedronate (group A; n = 25); given 250 µmol/L of risedronate hydrogel (group B; n = 25), and given 500 µmol/L of risedronate hydrogel (group C; n = 25). Risedronate were applied intrasulcularly in the mesial part of the gingival sulcus every 3 days. After 14 days of stabilization, the open coil spring was removed (bisphosphonate administration was continued). The relapsed teeth and ALP levels on days 0, 3, 7, 14, and 21 were measured. The osteoclast/osteoblast ratio was measured by hematoxylin and eosin staining. ANOVA test was used to determine the difference in the three groups and their interactions with concentration and time. Results: There was a significant difference in osteoclast/osteoblast ratio on day 3 (p = 0.019, p

Tissue Engineering for Periodontal Ligament Regeneration: Biomechanical Specifications

The periodontal biomechanical environment is very difficult to investigate. By the complex geometry and composition of the periodontal ligament (PDL), its mechanical behavior is very dependent on the type of loading (compressive versus tensile loading; static versus cyclic loading; uniaxial versus multiaxial) and the location around the root (cervical, middle, or apical). These different aspects of the PDL make it difficult to develop a functional biomaterial to treat periodontal attachment due to periodontal diseases. This review aims to describe the structural and biomechanical properties of the PDL. Particular importance is placed in the close interrelationship that exists between structure and biomechanics: the PDL structural organization is specific to its biomechanical environment, and its biomechanical properties are specific to its structural arrangement. This balance between structure and biomechanics can be explained by a mechanosensitive periodontal cellular activity. These specifications have to be considered in the further tissue engineering strategies for the development of an efficient biomaterial for periodontal tissues regeneration.

Advanced in Vitro Experimental Models for Tissue Engineering-based Reconstruction of a 3D Dentin/pulp Complex: a Literature Review

OBJECTIVE

Experimental procedures have been used to monitor cellular responses at the dentin/pulp interface. Aiming to divert from in vivo studies and oversimplified two-dimensional assays, three-dimensional (3D) models have been developed. This review provides an overview of existing literature, regarding 3D in vitro dentin/pulp reconstruction.

MATERIAL & METHODS

PubMed, Scopus, Cochrane Library and Web of Science- were systematically searched for attributes between 1998 and 2020. The search focused on articles on the development of three-dimensional tools for the reconstruction of a dentin/pulp complex under in vitro conditions, which were then screened and qualitatively assessed. Article grouping according to mode of implementation, resulted in five categories: the customised cell perfusion chamber (CPC) (n = 8), the tooth bud model (TBM) (n = 3), the 3D dentin/pulp complex manufactured by tissue engineering (DPC) (n = 6), the entire tooth culture (ETC) (n = 4) and the tooth slice culture model (TSC) (n = 5).

RESULTS

A total of 26 publications, applying nine and eight substances for pulp and dentin representation respectively, were included. Natural materials and dentin components were the most widely utilized. The most diverse category was the DPC, while the CPC group was the test with the highest longevity. The most consistent categories were the ETC and TSC models, while the TBM presented as the most complete de novo approach.

CONCLUSIONS

All studies presented with experimental protocols with potential upgrades. Solving the limitations of each category will provide a complete in vitro testing and monitoring tool of dental responses to exogenous inputs.

CLINICAL RELEVANCE

The 3D dentin/pulp complexes are valid supplementary tools for in vivo studies and clinical testing. Graphical Abstract.

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.

[Progress on clinical application of orthodontic-implant combined therapy]

For complex implant cases, simple implantation could not achieve the desired therapeutic effect, and a multidisciplinary approach has become a general trend. Orthodontic treatment before implantation creates favorable conditions for subsequent implantation by increasing restoring three-dimensional space, improving occlusion of patients. It also stimulates the increase of autologous soft and hard tissue while biological potential of periodontal ligament is fully developed. The choice of operation time is vital to keep the level of soft and hard tissue at the implantation site, which improves the curative effect of implantation in terms of function and aesthetics. In this article, the orthodontic-implant combined therapy is briefly reviewed focusing on the three-dimensional space optimization, implant site enhancement by orthodontic extrusion and delayed orthodontic space opening.

A novel ex vivo culture model for inflammatory bone destruction

Pathological alterations in the balance of bone metabolism are central to the progression of inflammatory bone diseases such as periodontal disease. We have developed and characterized a novel ex vivo murine mandible model of inflammatory bone destruction. Slices of mandible were cultured for 14 days in the presence or absence of P. gingivalis lipopolysaccharide (LPS) or pro-inflammatory cytokines. Following culture, cell viability and tissue histomorphometry were assessed with quantification of matrix proteins, resident osteoclasts, ligament cells, monocytes, macrophages, and neutrophils. In the absence of inflammatory factors, culture viability, osteoclasts, and matrix components were maintained. LPS or TNFα stimulation demonstrated an increase in cellular proliferation, monocyte cells, osteoclast differentiation, and matrix degradation. Pathophysiological bone metabolism can be induced via exposure to LPS and direct influence of TNFα within the model despite the absence of systemic circulation, providing a model for inflammatory bone destruction and investigation of the effects of novel therapeutics.

Dental tissue repair: novel models for tissue regeneration strategies

Studies have shown that dentin matrices contain reservoirs of bioactive molecules capable of directing tissue repair. Elucidating the release mechanisms of such endogenous growth factors will enhance our understanding of dentinpulp regeneration and support the development of novel treatment modalities to enhance dentin repair following trauma and disease. Current clinical practice using new materials which are perceived to maintain pulpal viability require biological evidence to assess their therapeutic benefit and there is a need for better effective methods of assessing therapeutic approaches to improving dentin regeneration at the cellular and tissue level. Experimental modelling of dentin regeneration is hampered by the lack of suitable models. In vivo and in vitro studies have yielded considerable information on the processes taking place, but are limited, due to the cost, ethics and lack of cell/matrix interactions. Novel organotypic models, whereby cells and tissues are cultured in situ may provide a more suitable model system to facilitate dental tissue engineering and regeneration.

An ex vivo culture model for orthodontically induced root resorption

OBJECTIVES

Root resorption is a ubiquitous although undesirable sequela to orthodontic treatment. Current methods to investigate the pathophysiology have certain limitations. In pursuit to understand and develop treatment modalities for orthodontically induced root resorption, the ability to manipulate cells within their natural extracellular matrix in a three dimensional organotypic model is invaluable. The study aimed to develop a laboratory-based organotypic model to investigate the effect of orthodontic forces on the periodontium.

METHODS

Mandibular slices of male Wistar rats were maintained in Trowel-typed cultures at 37°C in 5% carbon dioxide in air for 7 days with test specimens subjected to compressive forces at 50 g and 100g by stainless steel springs. Tissue architecture and cell viability were maintained under culture conditions.

RESULTS

Osteoclast numbers increased significantly in both test groups whilst odontoclasts increased in the 50 g group. Immunohistochemistry demonstrated increased dentine sialoprotein expression in both test groups, suggesting changes in mineralization-related activity due to mechanical strain.

CONCLUSION

The study showed initial cellular and molecular changes of key markers that relate to root resorption in response to mechanical loading.

CLINICAL SIGNIFICANCE

Severe root resorption may occur when forces applied are heavy or transmitted over an extended period and could lead to mobility and tooth loss. This ex vivo model can be used to investigate cellular and molecular processes during orthodontic tooth movement which may advance the clinical management of root resorption.

The effect of low intensity pulsed ultrasound in a 3D ex vivo orthodontic model

OBJECTIVES

This study investigated the effects of low intensity pulsed ultrasound (LIPUS) on dentoalveolar structures during orthodontic force application using a novel organ culture system.

METHODS

Mandibles were dissected from 28-day-old male Sprague Dawley rats, sliced into 1.5mm and cultured at 37°C and 5% CO(2), prior to application of a 50g force to each mandible slice. Slices were randomly divided into three groups of control, 5 and 10min LIPUS application and cultured for five days before histological and histomorphometrical analysis.

RESULTS

Cementum and predentine thickness and subodontoblast and periodontal ligament cell counts were increased in the ultrasound groups, with increases statistically significant in the 10min treated groups. Odontoblasts remained viable during LIPUS exposure and osteoclast activity was increased by LIPUS.

CONCLUSIONS

LIPUS may influence remodelling of the dentine-pulp complex and associated tissues during orthodontic force application ex vivo.

Early effects of orthodontic forces on osteoblast differentiation in a novel mouse organ culture model

OBJECTIVE

To develop a mouse orthodontic organ culture model and examine early-induced changes in osteoblast differentiation markers within the periodontal ligament (PDL) and alveolar bone.

METHODS

Mandibles from 4- to 12-week-old transgenic mice were dissected and hemisected. A conventional superelastic orthodontic spring (25 grams) was bonded to the incisor and first molar on one side of the mandible; the other side served as a control. Dissected mandibles were cultured for 6 hours and then were histologically analyzed for proliferation (BrdU immunostaining) and fluorescent protein expression. Additionally, an in vivo model using the same methods was applied to 3.6 Col1-GFP transgenic mice.

RESULTS

In vitro, after 6 hours of orthodontic loading, a significant increase was noted in 3.6Col1-GFP- and BSP-GFP-positive cells within the tension side of the PDL compared with unloaded controls. On the compression side, a significant decrease in positive cells in 3.6Col1-GFP mice was observed in the PDL compared with unloaded controls. In vivo, the same tendencies were found.

CONCLUSION

This novel in vitro mandibular tooth movement organ culture model coupled with transgenic mouse technology provides a powerful tool for delineating initial cellular and molecular events of orthodontic tooth movement.

Molecular characterization of young and mature odontoblasts

The odontoblast is the secretory cell responsible for primary, secondary and tertiary reactionary dentinogenesis. We provide evidence that the changes in secretory activity of odontoblasts reflect differential transcriptional control and that common regulatory processes may exist between dentine and bone.

INTRODUCTION

Based on the hypothesis that differential dentine secretion (primary and secondary dentinogenesis) is associated with changes in the transcriptional control within the cell, we have investigated the transcriptome of odontoblasts at young and mature stages and subsequently used this information to identify key regulatory intracellular pathways involved in this process.

MATERIALS AND METHODS

We used microarray analysis to compare the transcriptome of early stage (primary dentinogenesis) and late stage (secondary dentinogenesis) odontoblasts from 30 month old bovine teeth. Secondarily, we used post-array sqRT-PCR to confirm the differential expression of 23 genes in both populations of odontoblasts. Finally, immunohistochemistry was performed on bovine and murine tissues with antibodies to DMP1 and anti-phospho p38 proteins.

RESULTS

DMP-1 and osteocalcin gene expression were up-regulated in the mature odontoblasts, whereas collagen I, DSPP, TGF-beta1 and TGF-beta1R gene expression were down-regulated. Microarray analysis highlighted 574 differentially regulated genes (fold change>2 - p<0.05). This study supports further existing similarities between pulp cells and bone cells. Using post-array Sq-RT-PCR we characterized transcript levels of genes involved in the p38 MAP kinase pathway (PTPRR, NTRKK2, MAPK13, MAP2K6, MKK3). Differential p38 gene activation was confirmed by immunohistochemistry for p38 protein in murine teeth. Finally, immunohistochemistry for DMP1 indicated that odontoblasts involved in primary and secondary dentinogenesis may coexist in the same tooth.

CONCLUSION

As established in bone cells, the transcriptome of the odontoblast was shown here to evolve with their stage and functional maturity. Identification of the involved signalling pathways, as highlighted for p38, will enable the deciphering of physiology and pathology of mineralised tissue formation.

VEGF and odontoblast-like cells: stimulation by low frequency ultrasound

OBJECTIVE

Vascular endothelial growth factor (VEGF) has been implicated in the regulation of dental pulp and dentine repair. Therapeutic ultrasound was shown to be effective for fracture repair. We investigated whether low frequency ultrasound influences the production of VEGF by odontoblast-like cells. Moreover, we examined the direct effects of VEGF on odontoblast-like cell proliferation.

DESIGN

MDPC-23, an established odontoblast-like cell line, was exposed to increasing intensities of 30kHz ultrasound using an ultrasonic tip probe.

RESULTS

After 24h cell culture, WST-1 analysis of cell viability and number showed a dose-dependent decrease in the number of viable cells with increasing ultrasound power. However, the relative concentration of VEGF as analysed by ELISA and normalised to cell number was significantly increased in the culture supernatants indicating an ultrasound-induced stimulation of odontoblastic VEGF secretion. Analysis of VEGF gene expression by sqRT-PCR revealed the expression of the main VEGF isoforms in the MDPC-23 cells, i.e. VEGF(120) and VEGF(164) as well as to a minor extent VEGF(188). Low power ultrasound increased gene expression of all VEGF isoforms. Addition of recombinant VEGF to the cell cultures significantly stimulated cell proliferation. Gene expression of the VEGF receptors Flt1/VEGFR1 and KDR/VEGFR2 was detected in the MDPC-23, suggesting the possibility that VEGF may act on the odontoblast-like cells in an autocrine manner.

CONCLUSIONS

Our results indicate that ultrasound promoted VEGF expression and production by odontoblast-like cells and that VEGF may have autocrine effects on these cells. It is proposed that ultrasound may influence odontoblast activity and dentine repair by modulating production of endogenous growth factors in the dentine-pulp complex.

Short-term in vitro effects of low frequency ultrasound on odontoblast-like cells

In this study, the effects of low frequency ultrasound (US) were examined on odontoblasts, the primary cell responsible for dentinogenesis and dentine repair. An established odontoblast-like cell line, MDPC-23, was subjected to 30 kHz ultrasound at three different power settings. US induced a marginal level of cell death (3% to 4%) at lower amplitudes rising to 25% cell death at the highest power tested. The latter was reflected in a 30% decrease in cell attachment after 4 to 24 h of culture, while the number of adherent cells was reduced by approximately 10% to 15% in the lower power groups. Cell replication after 24 h, as measured by BrdU incorporation, showed no significant changes in the US-treated groups. Gene expression analyses demonstrated a moderate dose-dependent increase in the expression of GAPDH (glyseraldehyde-3-phosphate dehydrogenase)-normalised collagen type I, osteopontin (OPN), transforming growth factor-beta1 (TGFbeta1) and the heat shock protein (hsp) 70. The greatest change was found in the expression of the small hsp 25/27, which showed a two- to six-fold increase following US treatment. No significant effects were observed for alkaline phosphatase (ALP) and core-binding factor A1 (CBFA1/Runx2) expression levels. This is the first report describing US effects on odontoblasts. Further studies are warranted to elucidate US effects on odontoblast function and to evaluate US as a therapeutic application in dentine repair.

Differential Gene Expression of Periodontal Ligament Cells After Loading of Static Compressive Force

BACKGROUND

Compressive force is an important mechanical stimulus on the periodontal ligament (PDL) and is closely related to therapeutic tooth movement. In this study, early or late response genes related to the compressive stress in PDL cells were evaluated. Particularly, the expression of interleukin (IL)-6, IL-8, and alkaline phosphatase (ALP) was studied.

METHODS

The primary cultured cells from PDL were grown in a three-dimensional collagen gel, and received a continuous static compressive force (1.76 g/cm(2)). The expressed genes were screened by cDNA microarray assays for 2 or 12 hours after the initiation of the mechanical force application. The genes of interest that showed significant changes in expression in the cDNA microarray assay were analyzed further by quantitative reverse transcriptase polymerase chain reaction (RT-PCR), enzyme-linked immunoabsorbent assays (ELISA), and ALP assays.

RESULTS

ALP, IL-6, and IL-8 were selected among the genes that significantly changed expression (/M/ >0.7) and subsequently were confirmed by quantitative RT-PCR. The secreted protein concentrations for IL-6, IL-8, and ALP activity were measured at 72 hours after application of continuous static compressive force. The protein level of IL-6 was significantly increased at 72 hours (P <0.001), but there was no significant change in IL-8 (P >0.05). ALP activity was decreased approximately 41.5% compared to the control (P = 0.015).

CONCLUSIONS

Considering that IL-6 is a potent osteoclast activator and the compressive side of PDL during orthodontic tooth movement shows the resorption of calcified tissue, the changed expression of IL-6 and ALP in response to the static compressive force in PDL cells may contribute to the orthodontic tooth movement or alveolar bone remodeling.