Abstract
Background and Objective. Dental stem cell-based tissue engineered constructs are emerging as a promising alternative to autologous bone transfer for treating bone defects. The purpose of this review is to systematically assess the preclinical in vivo and in vitro studies which have evaluated the efficacy of dental stem cells on bone regeneration. Methods. A literature search was conducted in Ovid Medline, Embase, PubMed, and Web of Science up to October 2014. Implantation of dental stem cells in animal models for evaluating bone regeneration and/or in vitro studies demonstrating osteogenic potential of dental stem cells were included. The preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines were used to ensure the quality of the search. Modified ARRIVE (Animal research: reporting in invivo experiments) and CONSORT (Consolidated reporting of trials) were used to critically analyze the selected studies. Results. From 1914 citations, 207 full-text articles were screened and 137 studies were included in this review. Because of the heterogeneity observed in the studies selected, meta-analysis was not possible. Conclusion. Both in vivo and in vitro studies indicate the potential use of dental stem cells in bone regeneration. However well-designed randomized animal trials are needed before moving into clinical trials.
1. Introduction
Bone is a multifunctional organ that provides protection, structure, and mechanical support to the body [1]. The integrity of human bone is challenged by infections, trauma, congenital malformation, and surgical removal of tumor [2–4]. Repair and regeneration of bone are a series of biological events involving a number of cell types and signaling pathways in a temporal and spatial sequence [2–6]. When these natural mechanisms/events are compromised, bone grafting is commonly used to augment bone repair and regeneration. Autologous bone grafting has been considered as a “gold standard” because it possesses osteogenesis (osteoprogenitor cells), osteoinduction (BMPs, growth factors), and osteoconduction (scaffold) [7]. However, limitations such as a limited supply, resorption, donor site morbidity, deformity, chronic infection, and rejection demand other alternative treatment approaches [7, 8].
Cell-based bone tissue engineering emerges as a potential alternative as it aims to generate new cell-driven, functional tissue rather than to fill a defect with a nonliving scaffold. It is a combination of principles of orthopedic surgery with biology, physics, material science, and engineering [7]. Classic bone tissue engineering is comprised of osteogenic cells (to form bone tissue matrix), morphogenic signals (help the cells to be the desired phenotype), biocompatible scaffold (to mimic an extracellular matrix niche), and vascular supply (to meet the nutrient supply and clearance of the growing tissue) [7, 8]. Stem cells play a pivotal role in bone tissue engineering [9–15].
Multipotent mesenchymal stromal cells (commonly referred to as mesenchymal stem cells, MSCs) are the most frequently used cell population in tissue engineering because of its multilineage potential, multiple sources, and ability to self-renew [16, 17]. Bone marrow-derived mesenchymal stem cells (BMMSCs) are being considered as a gold standard [7, 9, 16, 17]. However, because of the difficulty to harvest a sufficient cell number as well as the pain and morbidity involved during the harvesting procedure, researchers have been exploring other sources/locations for MSCs. Many anatomical locations have been researched to yield MSC populations [1, 7, 18, 19]. One of the potential sources identified was the dental/oral tissues. Research on using MSCs of dental origin has increased exponentially in the last decade [20–22].
Dental stem/progenitor cells were isolated, characterized, and categorized into six major types [22, 23]: (1) dental pulp-derived stem cells/postnatal dental pulp stem cells (DPSCs), (2) stem cell from exfoliated human dentition (SHED), (3) stem cell from the apical papilla (SCAP), (4) periodontal ligament-derived stem cells (PDLSCs), (5) dental follicle-derived stem cells (DFSCs), and (6) gingival mesenchymal stem cells (GMSCs). The major attractions towards using dental MSCs are ease of access, less invasive approach for harvest, ability to produce higher colony forming units (CFUs), and a higher cell proliferation rate and survival time than bone marrow-derived MSCs [24, 25].
A significant body of literature has been published in the past five years on various types of dental MSCs and its applications [24]. However, there is still limited evidence regarding the capacity of dental MSCs for bone regeneration. An in-depth review and understanding of preclinical in vitro and in vivo studies is a prerequisite to assess the efficacy of dental MSCs and to translate their use into the clinics [26]. Thus the aim of this paper is to perform a systematic review of the literature on dental MSCs for bone regeneration, including in vitro and in vivo studies.
2. Materials and Methods
2.1. Review Protocol
We focused our review question to address: “Do dental-derived stem cells possess osteogenic potential and regenerate bone defects in in vitro and in animal models”?
2.2. Search Strategy
A comprehensive literature search published up to September 2014 was performed on the article databases: Ovid Medline, Embase, PubMed, and Web of Science. The search strategy used a combination of medical subject headings (MeSH) terms and keywords for Medline, PubMed, Web of Science, and EMBASE. The keywords and MeSH terms used for the search were stem cells, mesenchymal stromal cells, progenitor cells, tooth, dental pulp, dental sac, periodontal ligament, deciduous tooth, neural crest, gingiva, SCAP, DPSC, DFSC, GMSC, PDLSC, SHED, bone repair, bone regeneration, bone transplantation, bone substitute, bone tissue engineering, tissue engineering, bone reconstruction, bone defect, osteogenesis, tissue scaffolds, bioreactor, bone morphogenetic protein, intercellular signaling peptide, in vitro, in vivo, animal model, and preclinical. In addition, a hand search strategy was performed by the authors from the citation/reference list of the primary studies and reviews.
2.3. Outcomes Measure
(i)Osteogenic potential/calcified nodule formation/mineralized tissue formation with evidence of osteocyte/osteoblast confirmed by either histology or alkaline phosphatase (ALP) assay or histochemical staining for in vitro studies.(ii)New bone formation/bone regeneration/defect closure/defect bridging/hard tissue formation (bone)/mineralized tissue or calcified tissue (evidence of osteoblast/osteocyte) confirmed at least by histology or radiography for in vivo studies.
2.4. Inclusion Criteria
The selection was limited to the studies which should have(i)used at least one type of stem cell derived from dental tissue,(ii)studied either osteogenic potential or bone regeneration,(iii)evaluated at least one of the outcomes mentioned above.
2.5. Exclusion Criteria
Studies those used Mesenchymal stem cells derived from mandibular bone, maxillary bone, palatal bone, alveolar bone, buccal mucosa. Conference proceedings, abstracts, expert opinion, and letters were excluded from the initial search phase. The manual examination of titles and abstracts further excluded studies that did not meet the inclusion criteria. Odontogenic/periodontal ligament/cementum/dentin regeneration systematic reviews, clinical studies, and non-English articles were omitted after the proofreading of full-text articles.
2.6. Screening Methods and Data Extraction
The studies were selected and screened by two authors (Murali Ramamoorthi and Mohammed Bakkar). Disagreements between the reviewers were resolved by consensus with all the authors. Data were extracted based on authors, year of publication, population characteristics (animal species, gender, age, weight, number of animals, stem cell source, intervention, defect location and dynamics, scaffold/carrier/cues, period of observation, and evaluation methods) for in vivo studies, experimental characteristics (stem cell source, osteogenic medium, scaffold/carrier/cues, and evaluation methods) for in vitro studies, and methodological characteristics (study quality/risk bias assessment) for both in vivo and in vitro studies.
2.7. Study Quality Assessment
As there are no established sets of criteria/guidelines for assessing the quality or risk of bias for in vivo and in vitro studies [27–32], we assessed the quality of all selected full-text articles using the ARRIVE (animal research: reporting in in vivo experiments) guidelines [27] for in vivo and a modified ARRIVE combined with CONSORT (consolidated reporting of trials) guidelines for in vitro experiments, based on the previous studies [25, 26, 28–30]. The evaluation was based on a predefined grading system of the checklist for in vitro studies (Table 1) and (Table 2) for in vivo studies.
The quality of the articles was assessed by the authors using a checklist of ARRIVE (animal research: reporting in in vivo experiments) guidelines for in vivo studies and using modified ARRIVE and CONSORT (consolidated reporting of trials) guidelines for in vitro studies (the evaluation was based on predefined grading system) (Table 2).
Risk of bias is commonly used to assess clinical trials. Thus we included a risk of bias assessment, as suggested by Bright et al. [25] and the Cochrane Review handbook to improve the quality of our review on dental MSCs. The parameters used were (i) power calculation to determine the samples, (ii) allocation concealment, randomization/replication/multiple experiments done to show consistency, and (iii) blinding in allotment/evaluation of results. A simple Yes or No was used to score selected articles, based on these parameters above.
2.8. Statistical Analysis
Because of heterogeneity of sources of dental MSCs, different animal species, diverse defect characteristics, various evaluation times, and different scaffolds/cues among our selected 137 articles, a (statistical) meta-analysis for quantitative review was not possible. We were able to perform a qualitative systematic review.
3. Results
3.1. Search Results
A total of 1,914 articles were retrieved from the literature search; 1,480 were excluded because of duplication. Four hundred and thirty-four articles were eligible for title and abstract screening. 227 articles were excluded as they did not meet the inclusion criteria. Thus 207 articles were qualified for full-text evaluation. 70 articles were excluded after proofreading the full text. The reasons for exclusion were as follows: odontogenic/dentin/cementum/periodontal ligament regeneration (), clinical studies (), reviews (), language restrictions (), and multiple reports of the same experiment (), thus leaving 137 full articles to be included in this systematic qualitative review. The outline of articles selection is summarized in a flow chart (Figure 1). The details of the included studies are described in Table 3.
3.2. Characteristics of the Selected Studies
Out of 137 articles, 80.5% of the studies were published between 2010 and September 2014. Dental pulp-derived (35.5%) and periodontal ligament-derived (30.4%) stem cells were more predominantly studied among the eight different dental sources of stem cells reported in this review. Detailed characteristics (year, source, species, scaffolds/cues, medium, transplanted cell number, evaluation methods, and conclusion of the study) of these studies are shown in Tables 4 and 5.
Five different species of animals (rat/mice, dog, minipig, rabbit, and sheep) were used for the in vivo experiments. A total of 704 animals were used to study the osteogenic potential/bone regeneration of dental stem cells. Out of 65 in vivo studies, 46 used either rats or mice, 13 used dogs, two used minipigs, three used rabbits, and one used sheep to transplant dental stem cells. In 39 out of 65 studies, the dental stem cell source was from humans. Then 13 studies used dental MSCs from dogs, seven from a rat source, two from rabbits, two from minipigs, one from porcine, and one from sheep. The defect type and location were not uniform. Twenty-four studies used subcutaneous implantation on animals, 12 in periodontal defects, nine in mandibular defects, seven in critical-size defects of the calvarium, three in the renal capsule, and one in maxillary sinus augmentation as a defect model to observe osteogenic potential or bone formation in vivo.
In the selected in vitro studies, 85 of the 96 studies used dental MSCs from humans. The remaining 11 studies obtain dental stem cells from rats (7), porcine (1), dog (1), chimpanzee (1), and macaque nemestrima (1). Four in vitro studies used a bioreactor in their experiments. Ninety studies used osteogenic induction medium with serum, while four studies used serum-free medium and two studies used human serum. Nine in vitro studies and five in vivo studies compared the osteogenic potential of different dental derived stem cells. Most of the studies compared the osteogenic potential of PDLSC and GMSC (3 in vivo, 3 in vitro). All these six studies confirmed that PDLSC showed better osteogenic potential compared to GMSC. Based on the included studies that compared osteogenic potential of multiple dental stem cells, PDLSC showed better osteogenic differentiation, followed by DPSC and SHED.
Almost all of the selected studies employed histology (in vivo) or ALP assay and histochemical staining (in vitro) to evaluate the outcomes. Among the 65 in vivo studies, only six studies reported no in vivo bone formation seen with dental stem cells (DFCS-2, DPSC-3, and PDLSC-1). The comparisons of in vivo osteogenic differentiation of different dental stem cells are shown in Table 6. The total number of studies in each type of dental stem cell in this comparison is increased due to the five in vivo studies compared to the osteogenic behavior of different dental stem cells.
3.3. Quality Assessment of the Selected Literature
In general, most of the studies included some information related to the animals they used. However the majority of the literature lacked the quality based on ARRIVE guidelines. Only two studies reported a sample size calculation, four studies reported blinding in assessment of the outcomes, and 17/65 studies mentioned randomization in their articles. None of the sixty-five studies mentioned the 3Rs (replacement, reduction, and refinement) in their articles. However, one study mentioned that they followed the ARRIVE guidelines.
In 96 in vitro studies, only one study mentioned the power calculation to sample size. Blinding in evaluation was reported in one in vitro study. Sixteen selected in vitro studies gave information that they repeated their experiments or measurement more than once. Supplemental Tables i, ii, iii, and iv (in Supplementary Material available online at http://dx.doi.org/10.1155/2015/378368) summarize the quality of the in vitro and in vivo studies selected in this review.
4. Discussion
The purpose of this review was to summarize the role of dental-derived stem cells (dental MSCs) and their effects on the osteogenic differentiation potential and bone regeneration. Both in vivo and in vitro studies were included in this review. In total, 137 studies were qualitatively reviewed. No randomized controlled trials (RCTs) were found in in vivo studies. The in vitro studies were mainly experimental studies on the osteogenic differentiation or factors enhancing/decreasing the osteogenic potential of various dental stem cells. Dental MSCs used in these studies were derived from the dental pulp, apical papilla, dental papilla, gingiva, dental follicle, dental-neural crest, and periodontal ligament.
The literature stated that dental pulp stem cells were the first to be identified as having mesenchymal properties in the year 2000 by Gronthos and coworkers [33]. To date, four clinical studies were reported using dental stem cells for bone regeneration [9, 22, 24]. Due to the paucity of published clinical studies, we did not include clinical studies in this review. We strongly believe that an in-depth appraisal of the literature on preclinical in vivo and in vitro studies is a prerequisite to understanding the efficacy of a new therapeutic approach before its translation into human use. Dental stem cells such as DPSC, SHED, PDLSC, SCAP, and DFSC fulfill the requirements for mesenchymal stem cell as described by the International Society for cellular therapy [34], that is, adhering to plastic, multilineage differentiation potential, positive to stromal cell markers (CD73, CD90, CD105, STRO1, Nanog) and absence of hematopoietic markers (CD14, CD34, CD45).
4.1. SCAPs
The soft tissue covering the root apex of developing teeth serves as a source for SCAPs. All the studies reported in humans are a source for obtaining SCAPs for their experiments. The four in vivo studies conducted in rats and mice revealed ectopic bone-like tissue formation seen at 12 weeks. The in vitro study by Wang and colleagues [35] found an interesting observation, that insulin growth factor 1 (IGF-1) enhanced the osteogenic differentiation but weakened the odontogenic differentiation of SCAPs. Studies by Wu and coworkers [36] confirmed that basic-fibroblast growth factor b FGF inhibited the osteogenic differentiation of SCAP.
4.2. DFSCs
Among the four in vivo studies conducted in rats/mice, two studies [37, 38] reported a lack of new bone formation by using DFSCs. However the in vitro study conducted by Tsuchiya et al. reported an osteogenic potential with DFSCs in an appropriate osteogenic induction medium. The two failed studies used porcine or rat as their stem cell source [37, 38]. The study done by Honda et al. [39] demonstrated bone formation similar to intramembranous ossification in rat critical sized calvarial defects. In vitro studies showed that BMP-9 and BMP-6 promoted osteogenesis of DFSCs. A later report [40] mentioned that 37°C to 40°C was optimal for osteogenesis and DFSCs lost its osteogenesis at 41°C.
4.3. GMSCs
Two different sources were used in the studies (human, dog). Rats/mice and dogs were used to study the bone regeneration effect. All studies showed that GMSCs were capable of undergoing osteogenic differentiation and forming new bone in the defect area. The cell number used to transplant ranged from 1 × 106 to 5 × 106.
4.4. SHEDs
Being a biological waste, SHEDs are an interesting candidate for stem cell therapies. Studies showed that they were capable of rapid proliferation and more frequent population doubling than bone marrow-derived MSCs. In vitro studies confirmed the osteogenic differentiation that rigid scaffolds supported osteogenesis, and bovine fibroblast growth factor inhibited osteogenesis. Almost all the in vivo studies used scaffolds; HA/TCP was the most frequently used carrier. All the in vivo studies confirmed the osteogenic differentiation and bone regeneration potential of SHEDs. A recent report showed that 5-year cryopreserved SHEDs were able to proliferate and undergo osteogenesis without immune reaction in a 9 mm mandibular defect in dogs [41].
4.5. DPSCs
Stem cell derived from dental pulp was the most studied dental stem cell for bone regeneration. Among the twenty in vivo studies, three reported that DPSCs were not able to regenerate new bone in subcutaneously implanted mice. Two studies by Annibali et al. in 2013 and 2014 [42, 43] failed to show new bone formation using human DPSCs. Zhang et al. in 2008 [44] demonstrated no evidence of bone formation in mice with rat DPSCs. Almost all the studies used scaffold. Laino et al. in 2005 [45] was able to generate in vitro living autologous bone (LAB) tissue from DPSCs, on subcutaneous implantation in rats LAB remodeled to lamellar bone in 4 weeks.
4.6. PDLSCs
PDLSC studies showed diverse source in obtaining periodontal ligament cell. More than half of the in vivo studies used dogs as a source to obtain PDLSCs, and the periodontal defect model was widely used to assess the osteogenic potential. Seo et al. [46] showed human PDLSCs failed to generate new bone in rat periodontal defects after 8 weeks of observation. Ibandronate, simvastin, VEGF, LMHF, BMP 2, and BMP 6 all seemed to enhance osteogenic potential of PDLSCs [47–50]. Silvério et al. [51] in 2010 demonstrated deciduous derived PDLSCs promoted more mineral nodule formation compared to PDLSC derived from permanent teeth in vitro.
Studies by Yamada et al. [52] showed PDLSCs derived from dog and puppy sources were able to generate 10 mm diameter mandibular defects with high vascularity. Wang et al. [53] demonstrated SHEDs have more osteogenic potential than DPSC in mice. Studies confirmed that PDLSC had more osteogenic and bone formation potential than GMSCs [54, 55]. However, Yang et al. [56] studies showed GMSCs had better osteogenic potential than PDLSCs in inflammatory conditions. On average, the 3rd cell passage was used in most of the studies and the addition of scaffolds or growth factors (except b-FGF) improved osteogenesis of the dental stem cells. Although some studies used critical sized defect, most of these studies used either a small size defect or subcutaneous implantation. This jeopardized the extrapolation on outcomes in clinical situations.
Among the various osteogenic induction and growth factors (BMP, IGF, dexamethasone, VEGF, EGF, and FGF) used in the selected studies, it lacks information about the cost effectiveness, safety, and clinical relevance information. Future research should aim to address these parameters.
Most of the selected studies used FBS for culturing dental stem cells. Serum supplementation is important in ex vivo expansion of these cells for clinical use. Using serum containing medium during stem cell culture for human cell therapy is unsafe as it may transfer viral/prion disease, xenogenic antibodies especially if repeated infusions are needed [57]. While FBS based medium may be acceptable for preclinical studies, xeno-free medium is required for expanding these cells in large scale good manufacturing practices (GMP) for clinical applications [57–59]. Furthermore human cells have the possibility to take up animal proteins and present them on their membranes; thus initiating xenogeneic immune response leads to rejection [58]. As the serum condition can significantly affect cell response, it is important to obtain research data with more clinical relevance [58, 59]. Future studies are recommended to compare the safety and efficacy, surface antigen expression, stemness, growth potential, osteogenic differentiation potential of different dental stem cells cultured in FBS, serum-free medium, allogenic human serum, autologous human serum, plasma rich protein, and plasma lysate.
To increase the scientific validity of animal studies, experiments should be appropriately designed, analyzed, and reported transparently. This not only maximizes scientific knowledge, but also is for ethical and economic reasons [30]. The robustness of the research increases by using sufficient animals to achieve scientific objectives and using appropriate statistical analyses to maximize the validity of the experimental outcomes [31]. Using the NC3Rs (National Center for replacement, refinement and reduction of animals in research) ARRIVE guidelines, we performed a detailed analysis of the quality of reporting and statistical analysis of the included in vivo studies. The analysis revealed a number of issues relating to reporting omissions. The majority of the articles reported age of the animals used. However, there was a lack of information about the weight, gender, and housing conditions of the animals used. The availability of online supplementary results offered by many journals to include additional information results negates the argument that researchers are constrained by the page limit [26, 31]. In some of the in vivo studies (), the number of animals were simply not reported anywhere in the methodology, results, or discussion sections. Reporting the number of animals is essential to replicate the experiments or to reanalyze the data. Furthermore, 63 of 65 studies did not mention how the sample size was chosen. Determining sample size by power size or simple calculations help to design an animal research with an appropriate number of animals to detect a biologically important effect [28–32]. We cannot rule out that the researchers may have calculated/determined the number of animals but did not report that in the article. However, reporting omission can be easily rectified, as incomplete reporting means potentially flawed research [28].
In vitro preclinical research is the basic foundation for any new therapeutic approach. Although it may not replicate a dynamic environment, in vitro research provides valuable information for future research steps. The methodological quality analysis of the selected in vitro articles revealed the possibility of selection bias. Most of the articles lacked randomization, blinding, sample size calculation, and repetition of the experiments. This affects the scientific validity of experimental results. Although CONSORT guidelines are designed to be used in RCTs, we found it reasonable to apply these guidelines to in vitro studies to emphasize the quality and importance of avoiding bias in reporting or in research, because all phases of research process are interlinked [26, 28, 32]. An inadequate sample size might report incorrect results, which could eventually result in failed animal studies or clinical trials. Comparing the performance of dental stem cells with autologous bone grafts or adipose-derived MSCs or BMMSCs will be an interesting approach. Immune modulation property shown by most of the dental stem cells may provide a solution for graft rejection.
To date few clinical cases of bone tissue engineering used dental stem cells [9, 22, 24]. The main reason for the slow progress is attributed to the extrapolation of outcome from preclinical studies. Based on our observation with the selected literatures and guidelines [26–32, 60], we believe that animal study design should include well defined inclusion and exclusion criteria (study setting), a period to test the participating animals short term ability to adhere to the experimental/treatment regimen (run in period), process of random allocation of animals to the different study groups (randomization), reporting of baseline characteristics (age, sex, and weight) for the all animals in the experimental and control group, animal housing conditions, blinding in outcome assessment and data analyses, clear reporting of number of animals enrolled, followed up, and any addition or number of animals dropped out (attrition), disclosing any adverse effects to the animals during and after intervention/experiment, reporting sample size and methods used to do sample size calculation, and reporting confidence interval in addition to value (for the effect estimate and precision). These parameters will minimize the risk of confounding and selection bias. It also ensures that the outcome of the study is not affected by conscious or unconscious bias or factors unrelated to biological action. Thus improving the internal and external validity of the study. Further well designed and conducted animal randomized control trials (RCTs) will help us to generate high level of scientific evidence similar to human RCTs.
In summary, although selected studies showed dental stem cells have remarkable potential for use in bone regeneration, further well designed preclinical studies addressing optimal differentiating factors, culture medium, critical sized defect model, comparison of osteogenic potential of different dental progenitor cells, biological activity, cost effectiveness, efficacy, and safety of dental stem cells are required before clinical translation.
5. Conclusion
Several dental tissues identified by this review possessed dental MSCs with an osteogenic differentiation in vitro and in vivo. Regenerating lost bone tissue was feasible with dental MSCs. The easy accessibility to obtain dental MSCs made them an attractive alternative to BMMSCs for use in clinical trials to evaluate their safety and efficacy. However the current limitation, based on the quality of the literature, requires better designed in vitro or randomized control animal trials before going into clinical trials.
Abbreviations
| AdBMP2: | Adenovirus carrying bone morphogenetic protein |
| ALP: | Alkaline phosphatase |
| b FGF: | Basic fibroblast growth factor |
| BMMSC: | Bone marrow derived mesenchymal stromal cell |
| BMP: | Bone morphogenetic protein |
| Cap: | Calcium phosphate |
| CBB: | Ceramic bovine bone |
| cDPSC: | Dental pulp stem cell derived from chimpanzee |
| Col: | Collagen |
| CSD: | Critical sized defect |
| CT: | Computed tomography |
| DFSC: | Dental follicle stem cell |
| DLX2: | Distal less homeobox 2 |
| DPSC: | Dental pulp stem cell |
| ECM: | Extracellular matrix |
| EMD: | Enamel matrix derivative |
| F: | Female |
| FBS: | Fetal bovine serum |
| FCS: | Fetal calf serum |
| FGF: | Fibroblast growth factor |
| GCF: | Genipin chitosan framework |
| GCM: | Growth culture medium |
| GFP: | Green fluorescent protein |
| GDPB: | Granular deproteinized bone |
| GMSC: | Gingiva derived mesenchymal cell |
| HAP: | Hydroxy apatite |
| HGCCS: | Nanohydroxyl apatite coated genipin chitosan conjugated scaffold |
| IGF-1: | Insulin growth factor |
| ISCS: | Intrafibrillar silicified collagen scaffold |
| ITS: | Insulin transferring selenous acid |
| Kg: | Kilogram |
| LMHF: | Low magnitude high frequency |
| LST: | Laser sintered |
| m: | Month |
| M: | Male |
| MAO: | Mono arc oxygen |
| Na; na: | Not available |
| nHAC: | Nanohydroxyl apatite collagen |
| OIM: | Osteogenic induction medium |
| PCL: | Polycaprolactone |
| PDMS: | Polydimethyl siloxane |
| PET: | Positive emission tomography |
| PLCL: | Poly(L-lactide-co-epsilon-caprolactone) |
| rh: | Recombinant |
| RGD: | Arginine-glycine-aspartic acid tripeptide |
| SAPN: | Self-assembling peptide nanofibre hydrogel |
| SC: | Subcutaneous |
| SCAP: | Stem cell from apical papilla |
| SCID: | Stem cell from inflamed pulp |
| SEM: | Scanning electron microscope |
| SHED: | Stem cell from human exfoliated dentition |
| Ti: | Titanium |
| TCP: | Tricalcium phosphate |
| TNF-α: | Tumor necrosis factor-alpha |
| VEGF: | Vascular endothelial growth factor |
| Wk: | Week |
| WJCMSC: | Wharton jelly of umbilical cord stem cells. |
Conflict of Interests
No conflict of interests exists.
Acknowledgments
The authors would like to thank the following funding agencies: Natural Sciences and Engineering Research Council (NSERC) of Canada and the Canada Research Chairs.
Supplementary Materials
The details of the quality score and risk of bias assessment grading achieved by the final included studies were briefed in the supplementary material. Supplementary Table i , ii, shows the details of the quality score achieved by the selected invitro & invivo studies in each domain [ the characteristics of each domain for invitro and invivo were described in Table 1, 2 in main text]and Tables iii & iv shows the risk of the bias assessment grading for the selected studies.