Alveolar ridge dimensional changes following ridge preservation procedure with novel devices: part 3 - histological analysis in non-human primate model.

OBJECTIVES: This study sought to investigate the histological changes following tooth extraction, ridge preservation and augmentation, using novel devices designed to obturate the oral orifice of extraction sockets (SocketKAP™) and provide structural support for sockets with defective bony walls (SocketKAGE™) in a non-human primate model. MATERIAL AND METHODS: Six Macaca fascicularis were imaged by cone beam computed tomography to register their preoperative alveolar bone. Three teeth were extracted in each animal, yielding intact socket walls and were divided into three intervention groups: unassisted healing negative control (Group A); SocketKAP™ (Group B); filled with anorganic bovine bone mineral (ABBM) + SocketKAP™ (Group C). Three additional teeth were extracted in each animal, followed by surgical resection of the entire buccal alveolar bone and divided into three groups: negative control (Group D); SocketKAP™ + SocketKAGE™ (Group E); ABBM + SocketKAP™ + SocketKAGE™ (Group F). Animals were euthanized after 12 weeks, and treatment sites were examined by histology and histomorphometric analysis. RESULTS: Control sockets with unassisted healing (Groups A and D) underwent severe loss of bone width, height and total area (approximately 40-60% loss). Application of SocketKAP™ in sites with intact walls, as well as SocketKAP™ plus SocketKAGE™ in sites with defective buccal walls lead to higher preservation of alveolar bone height after 12 weeks post-intervention. Addition of ABBM leads to the highest degree of alveolar bone dimensional preservation. Control sites with unassisted healing (Groups A and D), as well as sites treated with extraction socket devices (Groups B and E) without ABBM yielded higher percentage of vital bone, compared with sites filled with ABBM (Groups C and F). No adverse histological responses were noted to SocketKAP™ or SocketKAGE™ devices. CONCLUSIONS: SocketKAP™ + SocketKAGE™ devices proved effective in reducing post-extraction alveolar bone resorption mediating favorable wound healing within sockets. Addition of ABBM was associated with reduced volumetric loss, although the bone fill was characterized by less mature as well as more woven bone.

Alveolar ridge dimensional changes following ridge preservation procedure with novel devices: Part 1--CBCT linear analysis in non-human primate model.

AIM: This study sought to investigate dimensional changes to the alveolar bone following extraction and application of novel devices used for obturation of socket orifice (socket cap) and space maintenance in sockets with facial dehiscence (socket cage). MATERIAL AND METHODS: Six Macaca fascicularis had six teeth each removed according to the following intervention groups (groups A-C intact alveolar bone; D-E facial dehiscence): negative control (A); socket obturated with cap (B); filled with anorganic bovine bone mineral (ABBM) + socket cap (C); dehiscence negative control (D); socket cap + socket cage (E); ABBM + socket cap + socket cage (F). Serial CBCT scans at preoperatively, 6 and 12 weeks following intervention were compared to quantify linear alveolar bone alterations. RESULTS: Without therapeutic intervention, intact sockets exhibited significant reduction in width at the crestal 2 mm of the ridge crest within 6 weeks. Compared with the negative control sites which lost up to 52% of crestal bone width, sites treated with socket cap + ABBM lost at most 4% of bone width at the crestal 2 mm. Similar results were seen in the dehiscence groups, with the combination of socket cap + socket cage + ABBM maintaining the greatest socket width and height dimensions. CONCLUSIONS: Results from the current non-human primate study suggest that the socket cap and socket cage devices, when used in conjunction with xenograft proved effective in minimizing post-extraction socket width loss and height seen in both intact sockets and sockets with facial dehiscence defects.

Role of the epithelial cell rests of Malassez in the development, maintenance and regeneration of periodontal ligament tissues.

Periodontitis is a highly prevalent inflammatory disease that results in damage to the tooth-supporting tissues, potentially leading to tooth loss. Periodontal tissue regeneration is a complex process that involves the collaboration of two hard tissues (cementum and alveolar bone) and two soft tissues (gingiva and periodontal ligament). To date, no periodontal-regenerative procedures provide predictable clinical outcomes. To understand the rational basis of regenerative procedures, a better understanding of the events associated with the formation of periodontal components will help to establish reliable strategies for clinical practice. An important aspect of this is the role of the Hertwig's epithelial root sheath in periodontal development and that of its descendants, the epithelial cell rests of Malassez, in the maintenance of the periodontium. An important structure during tooth root development, the Hertwig's epithelial root sheath is not only a barrier between the dental follicle and dental papilla cells but is also involved in determining the shape, size and number of roots and in the development of dentin and cementum, and may act as a source of mesenchymal progenitor cells for cementoblasts. In adulthood, the epithelial cell rests of Malassez are the only odontogenic epithelial population in the periodontal ligament. Although there is no general agreement on the functions of the epithelial cell rests of Malassez, accumulating evidence suggests that the putative roles of the epithelial cell rests of Malassez in adult periodontal ligament include maintaining periodontal ligament homeostasis to prevent ankylosis and maintain periodontal ligament space, to prevent root resorption, to serve as a target during periodontal ligament innervation and to contribute to cementum repair. Recently, ovine epithelial cell rests of Malassez cells have been shown to harbor clonogenic epithelial stem-cell populations that demonstrate similar properties to mesenchymal stromal/stem cells, both functionally and phenotypically. Therefore, the epithelial cell rests of Malassez, rather than being 'cell rests', as indicated by their name, are an important source of stem cells that might play a pivotal role in periodontal regeneration.

Investigation of the Cell Surface Proteome of Human Periodontal Ligament Stem Cells.

The present study examined the cell surface proteome of human periodontal ligament stem cells (PDLSC) compared to human fibroblasts. Cell surface proteins were prelabelled with CyDye before processing to extract the membrane lysates, which were separated using 2D electrophoresis. Selected differentially expressed protein "spots" were identified using Mass spectrometry. Four proteins were selected for validation: CD73, CD90, Annexin A2, and sphingosine kinase 1 previously associated with mesenchymal stem cells. Flow cytometric analysis found that CD73 and CD90 were highly expressed by human PDLSC and gingival fibroblasts but not by keratinocytes, indicating that these antigens could be used as potential markers for distinguishing between mesenchymal cells and epithelial cell populations. Annexin A2 was also found to be expressed at low copy number on the cell surface of human PDLSC and gingival fibroblasts, while human keratinocytes lacked any cell surface expression of Annexin A2. In contrast, sphingosine kinase 1 expression was detected in all the cell types examined using immunocytochemical analysis. These proteomic studies form the foundation to further define the cell surface protein expression profile of PDLSC in order to better characterise this cell population and help develop novel strategies for the purification of this stem cell population.

Epithelial cell rests of Malassez contain unique stem cell populations capable of undergoing epithelial-mesenchymal transition.

The epithelial cell rests of Malassez (ERM) are odontogenic epithelial cells located within the periodontal ligament matrix. While their function is unknown, they may support tissue homeostasis and maintain periodontal ligament space or even contribute to periodontal regeneration. We investigated the notion that ERM contain a subpopulation of stem cells that could undergo epithelial-mesenchymal transition and differentiate into mesenchymal stem-like cells with multilineage potential. For this purpose, ERM collected from ovine incisors were subjected to different inductive conditions in vitro, previously developed for the characterization of bone marrow mesenchymal stromal/stem cells (BMSC). We found that ex vivo-expanded ERM expressed both epithelial (cytokeratin-8, E-cadherin, and epithelial membrane protein-1) and BMSC markers (CD44, CD29, and heat shock protein-90ß). Integrin α6/CD49f could be used for the enrichment of clonogenic cell clusters [colony-forming units-epithelial cells (CFU-Epi)]. Integrin α6/CD49f-positive-selected epithelial cells demonstrated over 50- and 7-fold greater CFU-Epi than integrin α(6)/CD49f-negative cells and unfractionated cells, respectively. Importantly, ERM demonstrated stem cell-like properties in their differentiation capacity to form bone, fat, cartilage, and neural cells in vitro. When transplanted into immunocompromised mice, ERM generated bone, cementum-like and Sharpey's fiber-like structures. Additionally, gene expression studies showed that osteogenic induction of ERM triggered an epithelial-mesenchymal transition. In conclusion, ERM are unusual cells that display the morphological and phenotypic characteristics of ectoderm-derived epithelial cells; however, they also have the capacity to differentiate into a mesenchymal phenotype and thus represent a unique stem cell population within the periodontal ligament.