Tissue Regeneration on Rise: Dental Hard Tissue Regeneration and Challenges—A Narrative Review

Background As people live longer, there is an increasing need for hard tissue regeneration and whole-tooth regeneration. Despite the advancements in the field of medicine, the field of regenerative dentistry is still challenging due to the complexity of dental hard tissues. Cross-disciplinary collaboration among material scientists, cellular biologists, and odontologists aimed at developing strategies and uncovering solutions related to dental tissue regeneration. Methodology. A search of the literature was done for pertinent research. Consistent with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) 2020 Statement, the electronic databases looked at were PubMed, Science Direct, Scopus, and Google Scholar, with the keyword search “hard dental tissue regeneration.” Results Database analysis yielded a total of 476 articles. 222 duplicate articles have been removed in total. Articles that have no connection to the directed regeneration of hard dental tissue were disregarded. The review concluded with the inclusion of four studies that were relevant to our research objective. Conclusion Current molecular signaling network investigations and novel viewpoints on cellular heterogeneity have made advancements in understanding of the kinetics of dental hard tissue regeneration possible. Here, we outline the fundamentals of stem hard dental tissue maintenance, regeneration, and repair, as well as recent advancements in the field of hard tissue regeneration. These intriguing findings help establish a framework that will eventually enable basic research findings to be utilized towards oral health-improving medicines.


Introduction
Hard tissues comprise dental enamel, cementum, and bone [1].Tey are also known as calcifed tissues because hard tissues include calcium-phosphate minerals [1].With an aging population worldwide, there is a greater demand than ever for hard tissue regeneration and repair [2,3].Malunions, abnormalities, and fractures of the bones have become major global health issues [4,5].In 2004, the US gross domestic product was 7.7%, or $849 billion, after missed wages and medical expenses for those with musculoskeletal illnesses [6].With an aging population, this cost is rising rapidly [6].Autografts are the best option, but their limited supply and potential for donor site morbidity limit their use.Te risk of infection and the increased incidence of nonunion with host tissues present difculties for allografts.
Smart biomaterials, along with tissue engineering structures, present intriguing alternatives to autogenous bone grafts with a plethora of potential applications [3,7,8].
Te most prevalent disease afecting other hard tissues in humans is tooth caries.Dental caries signifcantly impairs oral and general health, lowers quality of life, and signifcantly increases public health expenses [9,10].In the US, more than 200 million dental cavity restorations are performed annually, with a $46 billion cost associated with these treatments in 2005 [10].As life expectancy and the percentage of tooth retention in seniors rise, the need is growing quickly [11].Mineral loss results from acidogenic bacteria fermenting carbohydrates to create acids, which causes caries [12].Restorations made to treat dental cavities frequently deteriorate over time, primarily as a result of secondary (recurrent) caries [13].In addition, more than half of all restorations are replacements for failed restorations [14].
Te ongoing increases in tooth loss due to specifc bacteria that adhere to teeth metabolize carbohydrates into acid and cause dental caries necessitates the development of novel techniques for tooth regeneration [15].Conventional dental implants possess a limited lifespan and eventually may be required to be replaced even though metal crowns, porcelain, and resin-based composites have been demonstrated to be quite efective in retaining hard tooth tissues.Under this perspective, there can be signifcant benefts from developing new techniques for repairing damaged dental hard tissues [15].
Te goal of the hard dental tissue regeneration process is to restore the pulp, cement, dentin, and enamel of each individual hard component as well as the entire tooth.Owing to complexity of the dental hard tissues, it becomes challenging to replace a lost tooth with a bioengineered structure that is functional.Tis complexity and challenge calls for the collaboration of biologic, genetic, or bioengineering approaches [16].A variety of requirements, including precise dental occlusion, proprioception, appropriate tooth-to-tooth contact, communication of chewing duties, and cosmetic restoration, must be addressed in the construction of the bioengineered teeth [17].Optimizing the orientation and interactions of the epithelial mesenchymal cell layers with the extracellular matrix is crucial for the creation of teeth with a predetermined form.Creating scafolds by 3D printing, cell seeding, or other techniques is one strategy to achieve the required distribution of cells inside the matrix [18].
Dentistry and regenerative medicine hold countless assurance for the discipline of dental hard tissue regeneration, which aims to replace or restore lost or damaged dental structures such as cementum, dentin, and enamel [1,19,20].Human teeth are prone to a variety of problems that can cause them to lose their structure and function, such as decay, trauma, and wear and tear.In traditional dental treatments, artifcial restorations such as crowns and fllings are frequently placed after diseased tissue has been removed.Tese methods might not be as functional or long lasting as they could be [1].
Te goal of dental hard tissue regeneration is to circumvent these constraints by encouraging the dental structures' organic growth and repair processes.Dental hard tissue regeneration is an intriguing new area in dentistry that may lead to more natural, long-lasting treatments for diseases and damage to the teeth.Better dental treatments and results for patients could result from ongoing study in this area, improving their quality of life and oral health in the process.Hence, the goal for this review is to present a narrative review on dental tissue regeneration.

Methods
A literature search for relevant studies was completed.Te electronic databases searched were PubMed, Science Direct, Scopus, and Google Scholar, utilizing the search keyword "hard dental tissue regeneration" in accordance with the 2020 Statement of Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) [21].A review of the relevant literature on directed hard dental tissue regeneration was conducted in order to select only those studies that met the review's inclusion criteria.We only took into consideration papers that were published in English.Furthermore, the only materials taken into consideration were original publications, reports, and case series.Textbooks, brief messages, letters, abstracts, interim reports, and book chapters were excluded.
Duplicates of every study found using the search procedures were removed after importing them all into an Endnote library.Te articles that met the selection criteria were assessed separately by the frst and second authors.To settle any disagreements, the third author, who acted as the third reviewer, was consulted.Following this screening, two additional reviewers (the original two authors) examined the chosen records in detail and independently decided whether or not to include them in the review.A third author was again approached in case of any disagreement.Te same two reviewers extracted the data into a standard data format.Te PRISMA fow diagram shown in Figure 1 was used to present articles that satisfed the eligibility requirements and those that were discarded during the study selection process.

Results
Using the search method outlined in this study, 476 studies in total were found through database analysis.A total of 222 duplicate articles were removed.Articles without any bearing on guided hard dental tissue regeneration were excluded from consideration.Te articles were also excluded for the following reasons: policy statements, thorough reviews, and brief messages.Finally, four studies that were pertinent to our research issue were included in the review.
Despite the fact that there have been a lot of review publications on tooth engineering techniques published recently, we found that only four of them have addressed issues related to dental hard tissue regeneration [1,[22][23][24] and ten have addressed issues related to hard dental tissues and their genesis [25][26][27][28][29][30][31][32][33][34].Tese studies provided good descriptions of a number of topics pertaining to dental hard tissue regeneration, yet only one study specifcally addressed the connection between the efcacy of the regeneration 2 Scientifca procedure and the characteristics of biomaterials and/or stem cells.Te remaining ten studies illustrate the tooth formation process, which begins during embryogenesis and moves through several stages during pregnancy, childhood, and adolescence until permanent teeth erupt (Table 1).Te recent developments in the investigation of many facets and methods of hard dental tissue regeneration are the main topic of this review.Te results of the advancement are compared to the problems that this feld of study is currently facing.
Te included review's fndings showcased current developments in hard dental tissue regeneration techniques, highlighted the regeneration of the entire tooth, and described the primary methods for creating scafolds that are acceptable and ofer the right conditions for stem cell development.Stem cells were able to completely contribute to the regeneration of the hard dental tissues and the entire tooth, regardless of the technique used, i.e., scafold-based or scafold-free approach [1,[22][23][24].Knowledge of the signaling pathways infuencing dental tissue genesis could lead to creating innovative cell culture methods and scafolds with specifc functions.Due to the acellular nature of enamel, which makes it impossible to replicate in vitro using a purely cell-based method, functionalized biomaterials are likely to be crucial to the regeneration of hard dental tissues such as dentin and cementum, as well as enamel  6 Scientifca [25,[27][28][29][30]33]. Researchers have studied and evaluated a great number of potentially suitable biomaterials but only a relatively small number of these have been applied in clinical trials.Furthermore, review reports and in vitro experiments made up nearly all of the studies contained in this review.Several issues and constraints limit the generalizability of what has been learned about dental tissue regeneration through these investigations.Review reports are vulnerable to bias due to the selection of the included studies.A distorted interpretation of the literature may result from review writers' deliberate or inadvertent favouritism of studies that corroborate their theories or from their disregard of studies with contradicting fndings.To examine the impact of diferent biomaterials or growth factors on dental tissue regeneration, in vitro research frequently uses cell or tissue cultures.Tese studies might not accurately capture the intricate milieu of the oral cavity while allowing for carefully monitored settings and in-depth molecular investigations.Terefore, research on the regeneration of hard tooth tissue has enhanced our understanding of regenerative therapies, yet there are a number of methodological limitations and issues with generalizability associated with these studies.Te discipline must advance, and research fndings must be translated into practical, benefcial medical treatments by addressing these limitations through enhanced study designs, standardized methodologies, and rigorous clinical trials.

Te Cellular and Molecular Processes Involved in Tooth
Development.Developmental and stem cell biologists who research adult tissue regeneration and embryonic morphogenesis have long been interested in teeth because they ofer a superb framework for interpreting the molecular principles of organogenesis [30].In the past few years, molecular signaling networks and new ideas about cellular heterogeneity have helped us learn a lot more about the changing interactions between epithelial and mesenchymal cells that happen during tooth development and homeostasis [30].
Te process of developing teeth begins in the embryonic stage and continues in stages during infancy, childhood, and puberty, culminating in the eruption of permanent teeth.Te formation of dental tissues is inter-related to one another as one tissue directs the development of the other [25,27,35].Early odontogenesis is characterized by an epithelial-mesenchymal interaction, which is also a model for the formation of other organs such as hair follicles and exocrine glands [31].Te epithelium is derived from the embryonic endoderm, while the mesenchyme is derived from the cranial neural crest.Placodal thickenings of the mouth epithelium along the dental lamina initialize the cellular condensation of the underlying mesenchyme.Subsequently, the tooth primordium undergoes multiple morphological stages, ultimately maturing into a bell stage, bud, and cap.Te mesenchyme produces the pulp, periodontal apparatus, and hard materials such as cementum and dentine, whereas the epithelium creates enamel [27].
Subsequently, reciprocal induction begins in the mesenchyme, and epithelial components lose their inductive odontogenic capacity.Numerous molecules interacting in signaling pathways form a signaling program that controls these reciprocal crosstalks.Families that act as morphogenetic inducers, such as Wingless/Int1, Ectodysplasin, Hedgehog, and Bone Morphogenic Proteins are prominent examples of these factors [26,28,31].Signaling centers, which also regulate morphogenesis and coordinate tissue connections, are in charge of determining the size of a single tooth.Cellular signaling also afects tooth shape in addition to tissue variables such as mesenchymal condensation, epithelial contraction, and bone biomechanics [31,32].
Several recognized stem cell niches exist throughout the development of teeth.Epithelial stem cells reside in the apical end of the advancing epithelium, known as the cervical loop.Tese cells remain active until the tooth root begins to form [22]. Stem cells aid in the continuous growth of teeth, such as the incisors of mice.Te double-layered epithelial root sheath of the hertwig, which elongates the cervical loop, functions as a signaling hub for the formation of tooth roots.It is important to remember that the interaction between the growing alveolar bone and tooth production dictates how teeth form, and this should be considered when constructing whole tooth regeneration techniques [31,33].
Comprising nonvascularized hard tissues such as dental pulp, soft, vascularized enamel, and dentin, the adult tooth is a complicated organ.Intimately connected to dentin, the dental pulp contains odontoblasts, pericytes, dental pulp stem cells, and other cellular groupings.Nerves allow the pulp and oral environment to convey sensory information, while blood vessels that pierce the pulp provide nutrition to its resident cells.In cases of severe dental damage (e.g., deep cavities), odontoblasts, their progenitors, and dental pulp stem cells can be isolated from the tooth pulp to promote dentin repair [36].Te periodontal ligament, a sophisticated attachment tissue that binds the tooth to the alveolar jawbone and contains odontogenic stem cells, surrounds the tooth [29,34].

Tissue Engineering Triad.
Te multidisciplinary discipline of tissue engineering employs engineering and biological science ideas to create biological replacements that have the potential to enhance, preserve, or repair tissue and organ functioning [37].Te foundation of tissue engineering is the regenerative process of biological tissues using growth agents, scafolds, and progenitor and stem cells [37,38].Scafolds containing the appropriate cells and signaling molecules must be employed to initiate the development of new dental tissue that can homogenize with the surrounding tissues [39][40][41].
It has been discovered that stem cells of diverse origins are necessary for tissue regeneration.Stem cells include both adult and embryonic stem cells [42].Te source of Scientifca immature, undiferentiated cells known as embryonic stem cells is the inner cell mass of blastocysts [43,44].Tese cells are capable of perpetual self-renewal and growth.Adult stem and progenitor cells that are still undiferentiated possess the capacity to develop into distinct tissue types [45].Tey protect the tissues they dwell in, including blood, skin, bone, and tooth pulp, from breaking down structurally [46].
Growth factors were suggested to be the third crucial element in the triad of tissue engineering and are considered necessary for the process of regeneration.Tey interact with the extracellular matrix in the surrounding area after being released from cells, immediately ofering themselves to cell surface receptors.When growth factors attach to certain cellmembrane-linked receptors, a number of activities and pathways in tissue engineering are initiated [47][48][49][50].Tese comprise the following: adhesion, development, proliferation, migration, survival, and diferentiation into the target cell type.It has been demonstrated that a protein known as bone morphogenetic protein-2 (BMP-2) can convert dental pulp stem/progenitor cells into odontoblasts [47].It has also been demonstrated that BMP-4 promotes the diferentiation of human embryonic stem cells into dental epithelium, which gives rise to teeth [51].Transfroming growth factor (TGF) also hastens the mineralization process, which dental pulp stem cells control, in addition to helping odontoblast-like cells proliferate [47].Generally, angiogenesis in the processes of repair and regeneration, wound healing, and growth are all dependent on these growth factor-mediated cell responses [50].

Tooth Regeneration.
Te ultimate goal of regenerative dentistry is believed to be the replacement of an organ with a whole tooth.For patients, this course of treatment might be their best chance to restore damaged or missing teeth without having to undergo prosthodontic or implantology procedures that require artifcial replacements.A complete tooth could be created using a hybrid technique.For instance, a metal or ceramic implant could be used to join a bioengineered tissue structures like a tooth crown or the periodontal ligament, or a prosthetic crown could be joined with a biologically regenerated tooth root, or "bio-root."In the next several years, creating a complete tooth (a "biotooth") from scratch utilizing just cells and tissues is most likely the aim.Tis approach is still challenging inspite of the advancements in the basic and translational research [34,[52][53][54][55].
Autogenous dental cells from individuals in need of tooth regeneration would be the best way to generate entire teeth.Various approaches to the application of these cells for whole-tooth bioengineering have been established.Combining adult stem cells with teeth embryonic progenitor cells was one idea.Adult stem cells are to demonstrate dental mesenchymal ability and function as a tooth inducer in association with the mesenchymal cells.Alternatively, they should have odontogenic competence and operate as dental epithelium when combined with mesenchymal cells.Young et al. began culturing cells from unerupted porcine tooth buds as early as 2002 [56].Te aggregates were either implanted or generated in vitro on biodegradable scafolds.As a result, a simple dental crown made of pulp, dentin, and enamel formed.Subsequently, rat and human cells might be used to create bioengineered tooth-like structures that are comparable to these [57,58].Ohazama et al. employed an inductive embryonic dental epithelium, which was frst implanted under the renal capsule and subsequently placed into adult jaws in 2004, in conjunction with adult mesenchymal stem cells (MSCs) that were not attached to the teeth [59].Teeth broke through the surface and developed, including the root.Moreover, there was an increase in bone formation.Te production of tooth-bud-like structures in vitro was limited to MSCs generated from adipose tissue [60].To create a whole tooth outside of an embryo, Angelova et al. combined embryonic mouse tooth mesenchyme with human gingival epithelial cells [61].

Enamel Regeneration.
Te amelogenesis and structure of dental enamel, the hardest tissue in the body of a human, is a highly organized tissue that covers the outer layer of the tooth crown.Tis material is unique in its mechanical and structural properties due to its high hydroxyapatite content, the way apatite crystals are arranged into enamel prisms, and the way these prisms line up in a picket-fence pattern within a tissue that is very tough and fexible [62][63][64][65].Te inner cells of the enamel organ diferentiate from specialized epithelial cells known as ameloblasts, which produce enamel [66].Tey exhibit polarization and elongation with a protonated Golgi apparatus and endoplasmic reticulum in order to produce and release enamel proteins and to infux phosphate and calcium ions into the enamel matrix that is forming [67,68].Te three primary proteins found in growing teeth are enamelin, amelogenin, and ameloblastin.Enamel formation requires the presence of enamel proteins [69].Tis list now includes an enzyme known as amelotin and a novel protein known as odontogenic ameloblast associated.Tese were found in the maturation stage of amelogenesis and in the junctional epithelium [70][71][72][73].Ameloblasts undergo reabsorption of water and degradation of enamel proteins during the mature stage of amelogenesis, following the development of the enamel matrix [67,68].Ultimately, the adult enamel turns acellular as it goes through apoptosis.Since enamel is not biomineralized like other hard tissues such as bone and dentin, it cannot repair itself if it is broken [74,75].Terefore, cellular remineralization of surface demineralized defects is largely, if not entirely, responsible for the reparative healing of damaged enamel [76].
Te goal of this research was to restore enamel faws resulting from caries, trauma, or other causes by developing artifcial materials with a hardness similar to enamel [77].Regretfully, the majority of materials in use today lack the lost tissues' mechanical, physical, and aesthetic qualities [78].Enamel tissue engineering is encountering numerous challenges in spite of the pressing need for tooth enamel regeneration [79][80][81].Among these difculties are the complex posttranslational protein changes required for crystal growth and the recapitulation of the unique motions 8 Scientifca of ameloblasts during the formation of hydroxyapatite crystals into enamel prisms [82,83].After all these studies and fndings, there is still no feasible plan for cell-based in vivo enamel tissue engineering [74].Te main challenge remains producing artifcial enamel with the right anatomy to replace lost enamel-forming cells and replicate the prismatic and interprismatic features found in natural enamel [84].
4.5.Formation and Regeneration of Dentin.Treatment regarding dentin-pulp complex is most frequently associated with dentin regeneration.It is highly desirable to fnd ways to preserve pulp vitality because it is necessary for tooth stability and homeostasis.Te primary treatment for preserving pulp vitality at the moment is pulp capping; however, this commonly comes with permanent pulp infammation and reinfections [85].Terefore, it would be ideal to use novel techniques and biomaterials for the pulpdentin compound regeneration.
In conventional endodontic therapy, hard tissue development at the apex is created by cleaning and sealing the pulp gap with calcium hydroxide.Tis formation of the hard tissue creates a barrier for a root-flling substance.Tis is done by apexifcation.Because this process does not encourage more root formation, the weak and fragile root canal walls persist, making teeth more vulnerable to subsequent problems [86].One regenerative endodontic method being studied to circumvent these limitations is remyelization.In this instance, bleeding is produced in order to seal the dental canal and form an endogenous clot of blood that serves as a support structure for the recruitment of growth factors, matrix proteins, and stem cells.Because of root development, apical closure, and the preservation of the tooth's vitality, this process results in the regeneration of the pulpdentin complex [87,88].But because mesenchymal stem cells were present in the blood that was invading, the resultant tissue is more bone-like and associated with connective tissue than the planned pulp-dentin complex [89].
Te use of biological printing along with dental progenitor and stem cells employing clinical methods of 3D biofabrication and restoration of oral tissues is now recommended as an alternative to standard dental restorations.It was possible to construct scafolds with precise, repeatable microarchitectures by using bioinks.Tese unique dentinderived extracellular matrix hybrid cell-laden hydrogel bioinks, which were synthesized from alginate and dentin matrix proteins, were examined and showed excellent printability and cell survival at diferent doses.In addition, the hybrid hydrogels showed that they could be embedded with dentin molecules that are soluble in acid, which improved stem/progenitor cells from apical papilla's odontogenic diferentiation and efciently engineered the pulpdentin complex [90].
4.6.Cementum Formation and Regeneration.Te periodontal complex is composed of the alveolar bone, cementum, gingiva, and periodontal ligament.Cementum regeneration occurs directly as a result of treating this compound.Scafolds used in periodontal complex regrowth not only provide the injured tissue with the support it needs but also frequently serve as a vehicle for bioactive substances like proteins, growth factors, or gene vectors that promote the process of healing and attract nearby stem cells to become involved and settle in.Te goal of creating multicompartment scafolds is to address the various difculties associated with regenerating several tissues on a single scafold in periodontal lesions [91].Furthermore, contemporary research includes cell-based scafolds, such as cell sheets, in addition to synthetic scafolds.To use this method, in a lab dish, numerous cell types crucial to periodontal regeneration are cultured until robust cell-cell connections and extracellular matrix synthesis occur.Tis makes it possible to implant the cell sheet as a substance that resembles a scafold [92].
Te regenerating potential of retro mineral trioxide (MTA), a calcium silicate cement combined with tricalcium phosphate, was examined in a study by Fakheran et al.Tey found that it produced signifcantly more new bone and cementum than the control group that was not treated.In addition, the use of biodegradable tricalcium phosphate improves the low rate of biodegradation of MTA [93].An inorganic calciumphosphatebased scafold material loaded with BMP-2 was utilized by Wei et al. in a preclinical investigation to treat gum disease in dogs [94].By itself, the calcium phosphate-based biomaterial signifcantly increases the regeneration of mineralized tissue and improves the adherence of the teeth to the surrounding tissue as compared to an untreated control and a deproteinized bovinebone mineral utilized as a commercial control.When BMP-2 is added, these promising outcomes could even be increased two-and threefold in terms of the height and area of the remineralized tissues.Unexpectedly, encapsulated BMP-2 had a greater impact on osteogenesis than on oncementogenesis [94].Wang et al. followed the multicompartment scafold technique using a bilayered material containing growth factors.Te hybrid material consisting of a fbrobblast growth factor-2loaded propylene-glycol alginate gel (PLGA) on the root surface for ligament repair and a BMP-2-loaded (PLGA/calcium phosphate cement) for periodontal regeneration was evaluated in vivo on nonhuman primates [95].Te authors of a promising rodent study corroborated the fndings of the prior examination by demonstrating signifcantly enhanced cementum and periodontal ligament regeneration in addition to high vascularization of the newly formed periodontal ligament [95,96].
Cementum has more fuoride than other mineralized tissues, which makes it a great target for catalysis to promote tissue mineralization and speed up cementum regeneration by depositing minerals on the surfaces of tooth roots [97].In addition, Yang et al. have created collagen scafolds that include fuorine-containing amorphous calcium phosphates (FACPs) to support the growth of mineralized tissue on tooth-root surfaces that have precise dimensions on a micron scale.Te FACP-collagen scafold was created via the recently created 3D scafolding method known as Bioskiving, which makes use of decellularized tendon tissues.Tis made it possible to create hierarchical structures that resemble cementum but with distinctive alternating collagen lamella patterns [37].Specifcally, to arrange the micro-and Scientifca nanostructures of collagen constructs in three dimensions, the approach can tear away tendon-derived structures (tendon-decellularized structures) and stack sheets of collagen lamellae in alternate orientations [97,98].

Clinical Application of the Study
Despite notable advancements in the regeneration of hard dental tissues, there remain several fundamental challenges in implementing the notion of the "processed tooth" in clinical practice.Designing the architecture of bioengineered teeth will require taking into account several crucial factors to achieve this challenging goal.A study on hard dental tissue regeneration may have clinical applications for the creation and use of innovative regenerative therapies to treat tooth injuries or dental caries.Application of a combination of stem cells, growth factors, and bioactive scafolds to encourage dentin and enamel regeneration in an efort to repair the tooth's damaged structure and function is gaining alot of attention lately.In general, the clinical use of hard dental tissue regeneration presents opportunities for enhancing future research and interdisciplinary approaches to improve tooth restoration and repair, as well as the overall results of dental treatment.

Conclusion
Te use of biopolymeric substances to isolate and regenerate particular periodontal tissues (alveolar bone, cementum, or periodontal ligaments) for the unique dimensions of spatial boundaries has been the focus of numerous attempts in periodontal dental tissue engineering to date.Te emergence of mineralized tissue might be particularly promoted by the biopolymer process outlined in this review by means of spatiotemporal control of tissue development towards periodontal issues employing their structures, biological substance immobilization, which lose controls by modifcation of chemicals, and manufacturing methods for 3D design.By gaining an understanding of signaling pathways infuencing the genesis of dental tissue, new approaches to cell culture and the creation of scafolds with specifc functions could be sparked.Given that enamel is an acellular tissue that cannot be replicated in vitro using a purely cellbased method, functionalized biomaterials are likely to be crucial to other dental tissues and hard dental tissues such as dentin and cementum are growing again.Despite the fact that a number of potentially useful biomaterials have already been examined and evaluated, up until this point, only a few of them have been employed in clinical trials.Future research in stem cell-based techniques will probably focus on biomaterials that enable the release of multiple drugs in a progressive and as-needed approach to tailor the diferent cascade events that take place amid cementogenesis, dentinogenesis, and enamel formation, respectively.

Figure 1 :
Figure 1: PRISMA fowchart of the study selection process.

Table 1 :
Research articles included the review.

Table 1 :
Continued.s tooth production process can take up too many years when it occurs in vivo.Growth-stimulatory signaling molecules could resolve this issue.Controlling the size, shape, and colour of the dental crown is one of the other issues that still have to be resolved, but these can be resolved using current clinical dentistry techniques.Lastly, there is a signifcant chance that cells cultured outside of the human body could develop into cancerous cells.Te majority of stem cell treatments have this risk, and research is currently being conducted in order to mitigate the chance of cancer