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Human Tooth Culture: a Study Model for Reparative Dentinogenesis and Direct Pulp Capping Materials Biocompatibility

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Human Tooth Culture: a Study Model for Reparative Dentinogenesis and Direct Pulp Capping Materials Biocompatibility Human Tooth Culture: A Study Model for Reparative Dentinogenesis and Direct Pulp Capping Materials Biocompatibility Odile Te´ cle` s, Patrick Laurent, Virginie Aubut, Imad About Laboratoire IMEB-ERT 30, Faculte´ d’Odontologie, Universite´delaMe´ diterrane´ e, 27 Boulevard Jean Moulin, 13355 Marseille Cedex 05, France Received 6 April 2006; revised 26 June 2007; accepted 26 June 2007 Published online 12 September 2007 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.b.30933 Abstract: In a previous work, based on an in vitro entire tooth culture model of human immature third molars, we demonstrated that perivascular progenitor cells can proliferate and migrate to the injury site after pulp exposure. In this work, we investigated the differentiation of cells after direct capping with biomaterials classically used in restorative dentistry. Histological staining after direct pulp capping with Calcium Hydroxide XR1 or MTA revealed early and progressive mineralized foci formation containing BrdU-labeled sequestered cells. The molecular characterization of the matrix and the sequestered cells by immunohistochemistry (Collagene type I, Dentin sialoprotein, and Nestin) clearly demon- strates that these areas share common characteristics of the mineralized matrix of reparative dentin formed by odontoblast-like cells. This reproduces some features of the pulp responses after applying these materials in vivo and demonstrates that the entire tooth culture model reproduces a part of the early steps of dentin regeneration in vivo. Its future development may be useful in studying the effects of biomaterials on this process. ' 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 85B: 180–187, 2008 Keywords: entire tooth culture; osteodentin; odontoblast; differentiation; reparative dentinogenesis INTRODUCTION Several studies have suggested the presence of progeni- tor stem cells in the pulp and several origins of these cells During tooth development, inductive epithelial-mesenchy- were suggested. These include the sub-odontoblast cells in mal interactions lead to the differentiation of ectomesen- the layer of Ho¨hl, fibroblasts, undifferentiated mesenchymal chymal pulp cells into odontoblasts, highly differentiated cells from the pulp core, and vascular-derived pericytes.2 postmitotic cells.1 The pulp progenitor stem cells have been shown to be mul- In pathological conditions such as moderate carious tipotent. It has been shown that the adult human dental lesions or cavity preparation, the odontoblasts have the pulp contains a rapidly proliferative subpopulation of cells ability to respond to injury and upregulate their secretory capable of differentiating into adipocytes and neural-like activity leading to the deposition of reactionary dentin.2,3 cells.5 In vitro, they can differentiate into odontoblast-like When the intensity of the injury leads to odontoblast death, cells secreting a mineralized matrix having the mineral and a new generation of odontoblast-like cells replace the ne- molecular characteristics of dentin.6 We have recently crotic cells and secrete a reparative dentin matrix that iso- developed a new human entire tooth culture model to study lates the underlying healthy pulp from the exposure site.4 the early steps of dentin regeneration. In case of pulp expo- In this case, the lesions are clinically treated by applying a sure, this model showed that perivascular pulp progenitor 1 pulp capping material such as calcium hydroxide XR or cells proliferate in response to odontoblast injury and 1 Mineral Trioxide Aggregate (Pro Root MTA ) directly migrate to the pulpal injury site whereas teeth cultured onto the pulp core (direct pulp capping). with dentin cavities did not show any perivascular prolifer- ation.7 Thus, reproducing the major difference of pulp response to dentin cavities and pulp exposure in vivo. How- Correspondence to: I. About (e-mail: [email protected]) ever, it is still unclear if the migrating cells in this model Contract grant sponsors: Ministe`re de l’e´ducation nationale; de l’enseignement supe´rieur et de la recherche´; Universite´ de la Me´diterrane´e (Bonus Qualite´ Recher- are able to differentiate into odontoblast-like cells. che-Universite´). The purpose of this study was to find out if cells are Ó 2007 Wiley Periodicals, Inc. able to differentiate and secrete a mineralized matrix in 180 HUMAN ENTIRE TOOTH CULTURE AND REPARATIVE DENTINOGENESIS 181 this entire tooth culture model and to find out if the they were cultured in the same medium without BrdU for obtained pulp response corresponds to that observed in vivo 1, 14, or 28 days (n 5 5 per group and per material). A after restoration with classically used direct pulp capping control group was restored with agar-containing MEM me- materials. dium and cultured under the same conditions (n 5 5). The teeth were cultured in 12-well tissue plates (Falcon1, Bec- MATERIALS AND METHODS ton Dickinson, USA) in Minimum Essential Medium (MEM) supplemented with 10% fetal bovine serum and 2 M b Materials m -glycerophosphate. The crowns were fixed to a metal- lic wire with a sealant (Embrace1, Pulpdent, USA). The For the preparation of the culture media, all materials were wire was suspended on the two adjacent plates. The apical purchased from Cambrex (Cambrex Bio Science, Walkers- part of the teeth was dipped in 4 mL of culture medium ville, MD). Chemicals were obtained from Sigma-Aldrich without touching the bottom of the culture wells in order to (Sigma Aldrich Chemicals Corp, St. Louis, MO) unless facilitate the diffusion of the medium through the apical otherwise precised. part without any direct contact with the restorative material (Figure 1). The culture medium was changed every day. Teeth Thirty-five unimpacted immature human third molars Histology freshly extracted for orthodontic reasons were obtained At the end of the culture periods, the teeth were fixed in from 15- to 18-year-old adolescents in compliance with 4% formol solution and routinely processed on longitudinal French legislation (informed patients and parents consent sections as described previously.7 and Institutional Review Board approval of the protocol used). The teeth were used to study the differentiation of Scanning Electron Microscopy pulp progenitor cells after preparation of pulpal cavities. Only teeth showing one to two third root formations were Scanning electron microscopy (SEM) examination was per- used. formed to examine the details of the pulpal mineralization on deparaffinated and rehydrated 7 lm-thick sections. Sam- ples both from MTA and calcium hydroxide were sputter- Antibodies coated with gold (JEOL, JCS 1100, Tokyo, Japan) and Polyclonal antibodies against the type I collagen were pur- examined using a FEI type QUANTA 200 (FEI, France, chased from Southern Biotechnology Associates. (Birming- LIMEIL BREVANNES, France). ham, AL). Polyclonal antibodies against dentin-sialoprotein were given by Dr. Butler (University of Texas, USA). Immunohistochemistry Monoclonal antibodies against nestin were purchased from To investigate the cell differentiation, odontoblast molecu- Chemicon (Chemicon International, CA) and those against lar markers were examined. This was performed on rehy- BrdU were from Sigma-Aldrich (Sigma Aldrich Chemicals drated paraffin embedded sections with antibodies against Corp, St. Louis, MO). collagen I, dentin sialoprotein, and nestin. Primary antibod- ies were diluted in PBS containing 0.1% bovine serum al- Tooth Culture bumin (BSA). The incubation with primary antibodies was performed overnight at 48C at the following concentrations: The extracted teeth were immediately transported to the anti-BrdU antibodies were used at 10 lg/mL, anticollagen I laboratory in minimum essential medium (MEM) supple- antibodies at 40 lg/mL, and anti-nestin antibodies at 5 lg/ mented with 300 UI/mL penicillin, 300 lg/mL streptomy- mL. Anti-dentinsialoprotein antibodies were diluted 1:100 1 cin, and 0.75 lg/mL amphotericin B (fungizone ). The in PBS. The staining was revealed using the labeled strep- teeth were cleaned with sterilized instruments after elimi- tavidin-biotin kit (LSAB) (DakoCytomation, Carpinteria, nating the periodontal ligament and the dental sac. Exposed CA) according to the manufacturer’s instructions. Controls pulpal cavities were prepared with diamond truncated burs were performed by incubations with unrelated primary anti- (reference 878.2872) mounted on a high-speed (300,000 bodies. All controls gave negative results. rpm) dental hand-piece and sterile saline cooling. The bur was left at speed until pulp penetration then it was Mineralization Morphometric Measurements retracted. This penetration was reached upon the disappear- ance of the hard tissue resistance. The teeth were restored These were performed with an Image Processing System with classically used pulp capping materials on a random IPS 32 version 4.32 (Samba technologies, Grenoble, basis: Mineral Trioxide Aggregate (Pro Root MTA1)or France). The measurements were done on three representa- calcium hydroxide XR1 according to the manufacturers’ tive hematoxylin-eosin stained sections per tooth. instructions. For BrdU-labeling, the teeth were incubated Image analysis was used to quantify the foci surface, with BrdU-containing medium (1 mg/mL) for 1 day. Then, their mean distance from the exposure and the pulp cham- Journal of Biomedical Materials Research Part B: Applied Biomaterials 182 TE´ CLE` S ET AL. Figure 1. Entire tooth culture system.
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