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The ultimate goal of dental stem cell research is to construct a bioengineered tooth. Tooth formation occurs based on the well-organized reciprocal interaction of epithelial and mesenchymal cells. The dental mesenchymal stem cells are the best explored, but because the human odontogenic epithelium is lost after the completion of enamel formation, studies on these cells are scarce. The successful creation of a bioengineered tooth is achievable only when the odontogenic epithelium is reconstructed to produce a replica of natural enamel. This article discusses the untapped sources of odontogenic epithelial stem cells in humans, such as those present in the active dental lamina in postnatal life, in remnants of dental lamina (the gubernaculum cord), in the epithelial cell rests of Malassez, and in reduced enamel epithelium. The possible uses of these stem cells in regenerative medicine, not just for enamel formation, are discussed.Laboratory Investigation advance online publication, 14 September 2015; doi:10.1038/labinvest.2015.108.

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MINI REVIEW

Odontogenic epithelial stem cells: hidden sources

Sivan Padma Priya

1,2

, Akon Higuchi

3,4,5

, Salem Abu Fanas

, Mok Pooi Ling

, Vasantha Kumari Neela

, PM Sunil

9,10

TR Saraswathi

, Kadarkarai Murugan

, Abdullah A Alarfaj

, Murugan A Munusamy

and Suresh Kumar

8,13

The ultimate goal of dental stem cell research is to construct a bioengineered tooth. Tooth formation occurs based on the

well-organized reciprocal interaction of epithelial and mesenchymal cells. The dental mesenchymal stem cells are the best

explored, but because the human odontogenic epithelium is lost after the completion of enamel formation, studies on

these cells are scarce. The successful creation of a bioengineered tooth is achievable only when the odontogenic

epithelium is reconstructed to produce a replica of natural enamel. This article discusses the untapped sources of

odontogenic epithelial stem cells in humans, such as those present in the active dental lamina in postnatal life, in

remnants of dental lamina (the gubernaculum cord), in the epithelial cell rests of Malassez, and in reduced enamel

epithelium. The possible uses of these stem cells in regenerative medicine, not just for enamel formation, are discussed.

Laboratory Investigation advance online publication, 14 September 2015; doi:10.1038/labinvest.2015.108

New treatments for many developmental and degenerative

disorders are currently emerging from regenerative medicine,

specifically stem cell therapy, which has proven successful in

many diseases by providing replacement cells without genetic

modification. It is believed that stem cells can be directed to

reach a destination if injected or loaded locally to facilitate

repair or regeneration.1 Dental caries and periodontal problems

are two of the most common health problems, afflicting not

only the affected individuals but also the economies of

developed countries. The dental structures are functionally

restored with biocompatible materials, without tissue

regeneration. The complex nature of tooth formation (odon-

togenesis), based on the organized reciprocal interaction of

the odontogenic epithelial and cranial neural crest-derived

ectomesenchymal tissues, has maintained the functional

regeneration of whole teeth, along with their supporting

structures, as an unattainable goal in the field of human tooth

bioengineering.2 There are many more reports about mesenchy-

mal stem cells (MSCs) than about odontogenic epithelial stem

cells (OEpSCs).3 The OEpSCs are defined as the stem cells

involved in tooth development (odontogenesis), which are of

outer ectodermal (epithelial) origin and interact reciprocally

with the odontogenic MSCs of ectomesenchymal origin. There

are sources of OEpSCs that have never been discussed, and

their possible retrieval and applications in stem cell research

should be revealed.3 This article seeks to describe the possibility

of using OEpSCs as another source of dental stem cell (DSCs).

Role of OEpSCs during Odontogenesis

The role of OEpSCs during odontogenesis is indispensable. In

2012, Jussila and Thesleff4 discussed the signaling networks

and complexity of the regulation involved in odontogenesis

including regeneration of human teeth. Human teeth are

developed by the well-organized reciprocal interaction of

outer ectoderm and cranial neural crest cells (CNCCs)

derived from ectomesenchymal cells. The CNCCs are from

neural ectoderm (epithelium), which are migrate to the

mesenchyme by a process called epithelial-mesenchymal

transition (EMT). The CNCCs are more specialized cells

because of their ability to form the greater part of the

Department of Basic Medical Science, Ajman University of Science and Technology– Fujairah Campus, Al Fujairah, United Arab Emirates;

Department of Surgical Sciences,

Ajman University of Science and Technology, Ajman, United Arab Emirates;

Department of Chemical and Materials Engineering, National Central University, Jhong-li,

Taoyuan, Taiwan;

Department of Botany and Microbiology, King Saud University, Riyadh, Saudi Arabia;

Department of Reproduction, National Research Institute for Child

Health and Development, Tokyo, Japan;

Department of Surgical Sciences, Ajman University of Science and Technology, Ajman, United Arab Emirates;

Department of

Obstetrics and Gynaecology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Selangor, Malaysia;

Department of Medical Microbiology and Parasitology,

Universiti Putra Malaysia, Slangor, Malaysia;

Department of Oral Pathology, Sri Anjaneya Institute of Dental Science, Calicut, India;

Director of Stem Cell and Regenerative

Medicine Lab, Malabar Medical College, Calicut, India;

Department of Oral Pathology, Tamil Nadu Government Dental College, Chennai, India;

Division of Entomology,

Department of Zoology, School of Life Sciences, Bharathiar University, Coimbatore, India and

Genetics and Regenerative Medicine Research Center, Universiti Putra

Malaysia, Selangor, Malaysia

Correspondence: Professor SP Priya, MDS, Department of Basic Medical Science and Department of Surgical Sciences, Ajman University of Science and Technology, Ajman,

United Arab Emirates or Professor A Higuchi, PhD, Department of Chemical and Materials Engineering, National Central University, No. 300, Jhongda RD., Jhongli 32001,

Taoyuan, Taiwan or Professor S Kumar, PhD, Department of Medical Microbiology and Parasitology, Universities Putra Malaysia, Slangor, Malaysia.

E-mail: priyaganu@yahoo.com or higuchi@ncu.edu.tw or sureshkudsc@gmail.com

Received 20 January 2015; revised 22 May 2015; accepted 29 May 2015; published online 14 September 2015

www.laboratoryinvestigation.org | Laboratory Investigation | Volume 00 2015 1

Laboratory Investigation (2015), 1– 9

craniofacial structures and the remarkable multilineage

differentiation property persisting even in adult tissue.

Figure 1 shows the contents of tooth germ and their

relations during embryogenesis, which describes the primary

tooth in cap stage and the permanent tooth in bud stage of

the odontogenesis. The dental lamina (DL) bestows both the

primary and permanent teeth during embryogenesis. These

embryonic stage cells with the ability to proceed with the

odontogenesis exist even up to the fifth year of postnatal life

in the third molar region, but are kept hushed till initiated.

The stem cell population at these stages can be explained from

the fact that (i) the DL and enamel organ (EO) have OEpSCs,

(ii) the dental papilla (DP) has dental pulp stem cells

(DPSCs), and (iii) the dental follicle (DF) has DF progenitor

cells (Table 1).

The DL is a band of ectodermal ingrowth from the outer

ectoderm into the mesenchyme in the region of the future

dental arch. These odontogenic epithelial ingrowths are the

main source of the OEpSC and tooth buds in the respective

place for teeth called as EO, the function of which is not only

restricted to enamel formation but also to induct the

ectomesenchymal cells to form other tissues of the teeth.

The EO progresses during different stages of odontogenesis

namely bud, cap, and bell, constantly interacting with the

ectomesenchymal cells named as DP and DF. EO with DP and

DF are collectively named as the tooth germ (Figure 1). The

EO is the inducer for the DP to differentiate the odontoblasts

to secrete dentin. The presence of the dentin is the

stimulation for the EO to differentiate the enamel-secreting

ameloblasts. The absence of EO will make no dentin and the

dentin absence will prevent enamel formation.

The cervical region of EO forms Hedwig' s epithelial root

sheath (HERS) after crown completion. This sheath of

OEpSCs is important to induct the root dentin formation as

they are doing in the crown. After dentin formation in the

root, the HERS dissociates and disintegrates to allow the outer

DF cells to contact the dentin to differentiate and secrete the

cementum. This process establishes the periodontal attach-

ment between the cementum and the alveolar bone around

the developing root. These HERS cells might undergo

apoptosis or EMT to rest inside the periodontal ligament as

epithelial cells rest of Malassez (ERM).5 Animals like mouse

having continuously growing anterior teeth possess the HERS

throughout the life for unceasing enamel and root formation.

However, the active HERS is not available in human after root

completion. Humans have two sets of teeth, 20 deciduous and

32 permanent teeth. This same scenario of odontogenesis is

repeated for each tooth including the third molar, which is

initiated by around 5– 6 years of postnatal life. The permanent

molars without predecessor teeth are formed by the extension

of the DL along with the growth of the jaws.

DENTAL STEM CELLS (DSCs)

DSCs collectively include the cells of epithelial and mesenchy-

mal origin. Studies related to mesenchymal DSCs of

Figure 1 Developing deciduous tooth in cap stage with permanent tooth

bud and successional DL in fetus during embryogenesis. The DL, the

ingrowth inside the mesenchyme, demonstrates the continuity between

the outer epithelium and the EO of the primary (deciduous) in cap stage

and permanent (successional) tooth in bud stage. The diverse group of

cells in tooth germ is composed of the outer ectoderm-derived DL, which

generates the EO and the CNCCs derived DP and DF cells. These primitive

cells of the embryonic stage are present up to the fifth year of postnatal

life for the formation of the third molar. This explains the presence of the

DSC in postnatal life. The stem cell population at these stages can be

explained as the DL and EO are having OEpSC, the DP having DPSC and

DF having DFPC cells. CNCC, cranial neural crest cell; DF, dental follicle;

DL, dental lamina; DP, dental papilla; DSC, dental stem cell; EO, enamel

organ; EO-P, enamel organ for permanent teeth; OE, outer ectoderm/

epithelium; SDL, successional dental lamina.

Table 1 Sources and types of dental stem cells

Dental stem cells (DSCs) Acronym Type Source

Dental pulp stem cells (DPSCs) DPSCs MSCs Dental pulp

Stem cells from human exfoliated

deciduous teeth (SHED)

SHED MSCs Dental pulp

Stem cells from apical papilla (SCAP) SCAP MSCs Developing

root end

Periodontal ligament stem cells

(PDLSCs)

PDLSCs MSCs Periodontal

ligament

Dental follicle progenitor cells (DFPCs) DFPCs MSCs Around

developing tooth

Gingiva-derived mesenchymal

stem cells (GMSCs)

GMSCs MSCs Gingiva

Epithelial cell rests of Malassez (ERM) ERM EpSCs Periodontal

ligament

Dental pulp pluripotent-like

stem cells (DPPSCs)

DPPSCs MSCs Dental pulp

EpSCs, epithelial stem cells; MSCs, mesenchymal stem cells.

Odontogenic epithelial stem cells

S Padma Priya et al

2Laboratory Investigation | Volume 00 2015 | www.laboratoryinvestigation.org

classification, types, methods of isolation, characterization,

advantages, and disadvantages have been explored in several

articles.6,7 DSCs are particularly attractive for their superior

advantages, such as being amenable to ethical collection

practices,7 easy to access,7 and comparatively potent8and

having a high proliferation rate and a greater cell number

than is common for stem cells,8,9 with plenty of sources being

available at all stages of life.8 Furthermore, many cell lines can

be retrieved that are demonstrating good compatibility and

attachment to a variety of biomaterials.10,11 DSCs are

comparatively cost effective.12 The DSC sources located so

far in teeth are listed in Table 1.3,9,13–17

Many reports have described the multi-potentiality and

possible applications of mesenchymal DSCs in dental and

non-dental tissue regeneration.18– 23 DSCs are not just

reproducing the pulp and periodontium. Several studies

demonstrated their potential to become osteoblast, adipocyte,

myoblast (smooth muscles and functional (beating) cardiac

cells), endothelial cells, chondroblasts, melanocyte, corneal cells,

retinal cells, pancreatic islet cells, neurons, and hepatocytes.18–24

Their uniqueness of development from CNCCs explains their

multilineage differentiation characteristics.

Clinical trials related to the osteogenic properties of DPSCs

that included 3 years of follow-up25 and related to periodontal

tissue regeneration26 (72 months of follow-up) are the only

two studies reported in humans. Clinical trials reported by

Nakashima and Iohara27 have initiated successful pulp

regeneration with DPSCs. The ability to form bone, muscle,

fibrous connective tissue, and nerves will be applied in the

regenerative facial reconstruction for developmental defects of

cleft palate and cleft lip in near future.

The regeneration of functional dental tissues form DSCs is

more complicated than that of non-dental tissues. The

research results from animal studies are not applicable for

humans, because changes in dental structures are one of the

cardinal signs of evolution and the maturation of dental

tissues in animals is faster than that in humans. Animals and

humans have anatomically dissimilar tooth making animal

models limited in comparison with the human dental tissue.

The time of initiation, eruption, and root completion of each

tooth vary even in the human dentition with little correlation

between them.24 Table 2 explains permanent tooth develop-

ment from the time of initiation of tooth bud to root

completion. Initiation indicates the availability of the active

DL and the surrounding ectomesenchyme at different stages

of life. The end of root completion conveys the end of

availability of HERS, which are then replaced by ERM in

humans.5 As deciduous teeth initiation and completion

occurs during the fetal and in infant stage, the discussion of

HERS and ERM as the cell source is under ethical issue and

not with better scope. However, the deciduous teeth are

loaded with DPSC, SHED, PDLSC, GMSC, ERM, and the

SCAP till root completion. Exfoliating teeth (SHED) are an

excellent source of DSC if the vital cells are preserved

properly. The time lapse between the initiation and the

completion of root indicates the time taken for normal tooth

development in humans. The time taken for the permanent

teeth completion varies from 7.8 to 12.5 years, which raises

many questions regarding functional bioengineered tooth

in human.

OEpSCs AND THEIR POSSIBLE SOURCE

The oral ectoderm ingrowth (DL) during development is the

main source for the OEpSCs. The possible sources of OEpSCs

in postnatal life include the active DL present in the

retromolar region of the human jaw for 5– 6 years,24 the

remnants of DL in the gubernaculum cord (GC) present

above any erupting tooth,24 the epithelial cell rests of Malassez

(ERM)3,24,28 covering the root of all teeth, and the reduced

enamel epithelium (REE),24,29 which is a tissue layer covering

the newly erupting tooth, the junctional epithelium (JE)29

surrounding the neck of the teeth, and the HERS near the

incomplete root ends.

Figure 2 shows the location of DSCs of mesenchymal and

epithelial origin (OEpSCs) in postnatal life. This schematic

presentation is the histology to be expected in a 12– 13-year-

old human in the posterior mandible molar region indicating

the different stages of odontogenesis for different teeth. The

availability of OEpSCs at this stage of life is expected from

remnants of DL, GC, ERM, SCAP, and JE where JE is derived

from REE. OEpSCs can also possibly become trapped in the

dental pulp region and may initiate the formation of dentin

inside pulp commonly known as pulp stones.

Dental Lamina (DL) and Gubernacular Cord (GC)

The DL is a continuous thickening of the oral ectoderm,

forming an ingrowth into the mesenchyme in the region of

the future dental arch at 45– 48 days of human intrauterine

life to develop tooth buds.24 DL acquires this potential for

odontogenesis at 30– 35 days of development but collaborates

with the underlying ectomesenchyme by 52– 56 days of

development.24,29 The ectomesenchyme gains the power to

induce odontogenesis from dental and non-dental epithelium

(and even from outer skin).24,29 Overexpression of DL is

correlated with supernumerary tooth formation30 and also

with abnormal manifestations of odontogenic cysts and

tumor formation.31 Animal studies have proven the avail-

ability of the active DL, even in the edentulous space

(diastema) of the jaws and its ability to form a bud without

progressing. It has been shown that knockout mutations of

genes required for odontogenesis cannot prevent the forma-

tion of dental epithelium.32,33 Additionally, it has been

suggested that evolutionarily lost teeth can reappear, running

counter to Dollo' s law of the irreversibility of evolution.34,35

This proves the persistence and potential of the odontogenic

epithelium for millions of years.

The human DL yields permanent tooth buds in different

stages of life, indirectly indicating that the DL becomes

active in different stages of life (listed in Table 2). After tooth

bud formation, the DL is programmed for apoptosis. There

Odontogenic epithelial stem cells

S Padma Priya et al

www.laboratoryinvestigation.org | Laboratory Investigation | Volume 00 2015 3

may be certain remnants of the DL present in the dental arch,

called 'cell rests of Serres' (Figure 3), to which many

odontogenic tumors and cysts of the jaws are attributed.

These remnants detach from the stalk-like extension provided

for the tooth bud by replacing the tissue with the fibrous

condensation known as the GC, which aids tooth eruption.

Table 2 Permanent dentition: the timing of tooth initiation and root completion and the time elapsed between stages

a,b

Permanent teeth Initiation Emergence into the

oral cavity (years)

Root completion

(years)

Time elapsed from

initiation to emergence (years)

Male Female Male Female Male Female

Incisor

Upper

C18 –20th week of IUL 8.3 7.4 10.6 9.3 8.9 8

L 9.1 8.1 11.1 9.7 9.9 8.7

Lower

C 7.3 6.7 9.2 8.1 7.9 8.3

L 8.1 7.3 9.9 8.8 8.7 7.9

Canine

Upper 11 9.4 13.7 11.9 11.6 10

Lower 10.9 9.2 13.5 11.4 11.5 9.8

Premolar

Upper

1 11.1 9.7 13.5 11.8 11.7 10.2

2 11.6 10.6 13.8 12.6 12 11

Lower

1 11.2 9.9 13.3 11.9 11.8 10.5

2 11.9 10.6 14 12.8 12.5 11

Molar

Upper

1 20th week of IUL 7.8 7.2 10.1 9.2 8.2 7.8

2 First year of PNL 12.4 11.8 14.6 13.6 12.4 11.8

35 –6 years of life 17.4 17.8 18.2 18.8 12 12.2

Lower

1 20th week of IUL 7.8 7.2 10 9.2 8.2 7.8

2 First year of PNL 12.5 11.8 14.8 13.8 12.5 11.8

35 –6 years of life 17.4 17.7 18.3 18.3 12 12.2

C, Central; L, Lateral; IUL, Intrauterine Life; PNL, Postnatal Life.

This table explains permanent tooth development from the time of initiation of tooth bud to root completion. Initiation indicates the availability of the active DL

and the surrounding ectomesenchyme at different stages of life. The end of root completion conveys the end of availability of HERS and then replaced by ERM in

human.5 As deciduous teeth initiation and completion occurs during the fetal and in infant stage, discussing them as a source is under ethical issue, and hence,it

has not been considered in the table. The time lapse between the initiation and the completion of root indicates the time taken for normal tooth development in

humans. The permanent teeth completion varies from 7.8 to 12.5 years. This table is prepared from the available sources related to the study on the stages of

tooth development at different age.24 As the population-based differences have been very well noticed with tooth development, differences can be noticed in

different populations in the age of eruption and completion. DL, dental lamina; ERM, epithelial cell rests of Malassez; HERS, Hertwig's epithelial root sheath.

Odontogenic epithelial stem cells

S Padma Priya et al

4Laboratory Investigation | Volume 00 2015 | www.laboratoryinvestigation.org

This cord-like fibrous tissue is reported to contain remnants

of the DL.24 The pericoronal tissues of the third molar region,

which includes the GC, have been best explored, including the

potential for odontogenic epithelial cell proliferation, associ-

ated histopathological changes in asymptomatic impacted

molars.36 The retromolar area is the most common site for

pathology reported in the jaw.37 It is suggested that the

periodic clinical evaluation of asymptomatic impacted molars

and their removal, including removal of the pericoronal

tissue, is important to prevent complications. The presence of

embryonic-stage DL in the retromolar area in the postnatal

oral environment, which is exposed to unavoidable physical,

mechanical, and chemical (microbial and inflammatory

cytokines) trauma, can explain the extensive pathology

reported. These DL rests may represent a new source of

OEpSCs.

There are many wisdom teeth removed owing to a lack of

space and associated complications (1.3 million/year in the

USA).38 Third molar tooth germ isolated from human donors

has been verified for potential use as another source of

embryonic stem cell-like cells, with fewer transgenic manipu-

lations required for induction.39 Studies have even verified

that dissociated tooth germ maintains its odontogenic

potential upon re-aggregation.40 Research on dental tissue

during organogenesis will settle debates about the develop-

ment of many organs undergoing the same interactions if

performed systematically at the interdisciplinary level.

Currently, no research has testified the viability of the DL

in postnatal life.

The isolation of OEpSCs from the active DL (from young

children) raises ethical issues. Tracing the 'cell rests of Serres ' is

difficult because their persistence is questionable, but the GC

can be easily located on the gingiva over the erupting tooth

(Figure 2). The time of the tooth eruption reveals the

availability of the GC (Table 2). The quantity and quality of

OEpSCs from the GC must be investigated, because not much

Figure 2 Radiograph and schematic representation of the posterior

region of mandible of 12 and half-year-old child. Location of the dental

stem cells of mesenchymal and epithelial origin in postnatal life is shown

where the different levels of tooth development in the molar region of

the posterior mandible reveal epithelial stem cells (OEpSCs) and

mesenchymal stem cells in postnatal life. The webbed presentation

expected from the ERM around the root, SCAP in the unclosed root apex,

the EO of the developing tooth, DL remnants in the GC, and the JE

derived from REE all represent odontogenic epithelial stem cells (OEpSCs).

OEpSCs can also become trapped in the dental pulp region very

minimally and may initiate the formation of pulp stones. AB, alveolar

bone; C, cementum; D, dentin; DF, dental follicle; DL, dental lamina; DP,

dental papilla; DPSCs, dental pulp stem cells; E, enamel; EO, enamel

organ; ERM, epithelial rests of Malassez; GC, gubernacular cord; JE,

junctional epithelium; OE, outer/oral epithelium; PDL, periodontal

ligament; REE, reduced enamel epithelium; SCAP, stem cells of apical

papilla.

Figure 3 Remnants of DL or the 'cell rests of Serres.' The DL is the band

of ingrowth of the outer OE inside the mesenchyme for the tooth bud

formation. The continuity of the OE and the DL is obvious during the

early stage of the development. The continuity will be disturbed because

of the initiated apoptosis at later stage. The ultimate goal of the DL is

tooth bud formation in the respective region of the different teeth at

different stage of life. The DL cells are to be eliminated by apoptosis after

the tooth bud formation in respective regions. However, a few of them

can be trapped at the subepithelial or intra-alveolar level and may be

responsible for many odontogenic epithelial tumors and cysts. These

remnants of DL are named 'cell rests of Serres.' The stem cell population

in these rests are odontogenic epithelial stem cells (OEpSCs). DL, dental

lamina; EO, enamel organ; OE, oral epithelium.

Odontogenic epithelial stem cells

S Padma Priya et al

www.laboratoryinvestigation.org | Laboratory Investigation | Volume 00 2015 5

relevant research has been performed yet regarding the

availability of the stem cells. Further research will unveil the

contents and importance of OEpSCs on GC in tooth

eruption, which is crucial to be explored regarding unerupted

or impacted tooth.41

The unique feature of the upper four incisors is that they

originate from the frontal lobe along with the forebrain,

sharing the embryonic cell source (the neural ectoderm cells

and CNCCs) of ocular development. Melanotic ectodermal

tumors of infancy or retinal anlage tumors occur in the upper

jaw anterior region, which histologically mimics the neural

retina and the retinal-pigmented epithelium.42 This may

indicate tumor development that recapitulates the retina from

an earlier developmental stage. Whether the primitive ocular

tissue becomes trapped and travels with the dental arch or the

dental epithelium dedifferentiates to acquire a primitive nature

has not been investigated systematically. If the GC and ERM

from these areas are proved to contain OEpSCs, this might lead

to successful formation of the pigmented and neural elements

of retinal tissue. Mead et al 43 reported that the DPSCs

(mesenchymal cells) promote the regeneration of retinal

ganglia. It is renowned that the head and neck regions

share the common CNCC-derived ectomesenchyme during

development.

Epithelial Cell Rests of Malassez (ERM)

After enamel formation, the outer and inner enamel epithelia

of the EO at the cervical region join to form Hertwig's

epithelial root sheath (HERS) to assist in root formation, and

they will later cease to exist owing to apoptosis.5,24 A few cells

are trapped in the periodontal ligament space close to the root

surface, serving as the ERM.5,44 These cell rests are associated

with many cysts and tumors of odontogenic epithelial

origin.45 Recent research has demonstrated the role of the

ERM in contributing to periodontal regeneration and the

turnover of ERM cells throughout life.46 The ERM exhibit a

unique ability called the EMT. These cells are epithelial cells

but live in the connective tissue environment with the ability

to differentiate into mesenchyme-related tissues by losing

their basal lamina.17,46 These abilities raise the question of

whether the cells should be named as cell rests.

The ability of the ERM to undergo EMT, their multi-

potentiality, and their differentiation into ameloblast-like cells

have been studied by Xiong et al. 17 An ERM cell line from

human periodontium has been successfully established for

further research.47 The millions of extracted teeth can be

collected for the ERM to study the EMT, which is a vital

process happening during development, tissue repair, and

cancer generation.

If the teeth extraction is performed before root completion

for orthodontic purposes or because of pathologically

impacted teeth, active HERS can be collected from the root

tip. ERM can be collected from the root surface of any

extracted teeth or from the socket lining.47

Reduced Enamel Epithelium (REE) and Junctional

Epithelium (JE)

After the completion of enamel formation, the EO collapses

into a REE, which covers the enamel and prevents the dental

follicular cells from forming a hard tissue over it and

facilitates the eruption of the tooth by producing proteolytic

enzymes to clear the surrounding tissues.24 REE becomes part

of the JE once the tooth erupts inside the oral cavity.48 REE is

the lining epithelium for dentigerous cysts, the most common

type of odontogenic cyst in young adults.37 The JE of

bioengineered tooth was proven to be odontogenic in origin

and to have epithelial stem cell potential reported by

Yajima-Himuro et al 49 in 2014.

REE can be obtained from the tissue covering any erupting

crown and from the JE of erupting or recently erupted teeth.24

For use as a source of REE, the JE should be undisturbed by

any disease process or surgical intervention; otherwise, the

sulcular epithelium might have replaced the REE. The tooth

development stages at 4– 6yearsinthehumananterior

mandible demonstrate their relationships between the devel-

oping permanent tooth and the resorbing deciduous teeth.24

OEpSCs are present in the REE, HERS, and in the DL

remnants in the GC. DPSCs are present in the DP and DF of

the developing permanent tooth and in the pulp of the

resorbing deciduous teeth. The close proximity of the resorbing

roots with open pulp and the REE can explain the possible

amalgamation of OEpSCs with the pulp of the deciduous teeth

during exfoliation.

VIABILITY OF THE FUTURE PROSPECTS OF OEpSCs

Studies regarding the potential of OEpSCs to be present in

postnatal DL, REE, and JE have been discussed by several

investigators.24– 47 The GC could be one more source that is

yet to be explored.

Studies have also focused on the odontogenic potential of

non-dental structures from the oral cavity and from extra-oral

structures. The studies reporting the odontogenic potential of

the oral mucosa50 raise the question whether the remnants of

DL ('cell rests of Serres') may be trapped in the oral mucosa. A

report about stem cells from human exfoliated deciduous teeth

(SHED-mesenchymal) containing epithelial stem cells51 again

raises the possibility of entrapment of REE of the successor

teeth below the deciduous teeth and also entrapment of

epithelial cells inside the pulp during odontogenesis, which is a

common finding correlated with the pathogenesis of pulp

stone formation.52 This also is another possible source of

OEpSCs. Wang et al 53 reported that the inducted human

keratinocytes form enamel by turning into ameloblasts in 2010.

Studies addressing epithelial stem cells in the formation of

ameloblast or ameloblast-like cells and their ability have

examined in bone marrow stem cell-derived ameloblast-like

cells,54 enamel formation by sub-cultured odontogenic cells

from the porcine EO,55 fully functional tooth regeneration

from the mouse tooth germ,56 human adipose-derived stem

cells induced to form a tooth bud,57 human gingival tissue as

Odontogenic epithelial stem cells

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6Laboratory Investigation | Volume 00 2015 | www.laboratoryinvestigation.org

a source for whole tooth bioengineering,58 the self-renewal

and multilineage potential of dental epithelial cells,59 the

formation of epithelium by induced pluripotent stem cells

from dental mesenchymal cells,60 non-keratinocyte cells

induced to form dental epithelial cells,53 and characterization

of dental epithelial cells,61 in addition to many detailed

reviews of tooth bioengineering.61,62 Existing reports of

in vitro and in vivo studies in animal and human tissues have

provided the information necessary for further research to

reach the bioengineered tooth popularly referred as the third

dentition. OEpSC-derived enamel for clinical trials will be

studied in the near future.

OEpSCs in Tissue Engineering and Regenerative

Medicine

The ultimate goal of the use of OEpSCs in tissue engineering

and regenerative medicine is the formation of enamel

identical to natural enamel for the bio-tooth, which will

become a reality in the near future.

Ikeda et al 56 reconstructed the fully functional bioengi-

neered tooth by transplanting the bioengineered tooth germ

into the jaw bone of mouse. The tooth germ was

reconstructed with the original tooth germ derived from

epithelial and MSCs. They suggested the use the third molar

tooth germ for tooth engineering in human. Sonoyama et al 63

also engineered fully functional tooth with the biomaterial

scaffold to develop the dentin and root below the artificial

porcelain crown using the SCAP cells in swine. Functional

bio-tooth engineering for human use has been challenged by

nature because of the limited sources of OEpSCs. The

difficulty faces in (i) achieving the desired size and shape of

the enamel, dentin and root/roots with the perfect junctions

and periodontal attachments, (ii) the long duration of tooth

formation (Table 2), and (iii) establishing the functional

occlusion. Finally, the most challenging aspect will be

performing clinical trials in the human oral environment

augmented with functional and microbial insults.

The enamel is a nonliving tissue similar to hair and nails,

supported by the underlying connective tissue. Dentin is the

supportive tissue; serving with a junction having merely

physical and mechanical in nature.24 There are 5– 12 million

enamel rods in the permanent teeth and 50 000– 90 000s of

dentinal tubules per square millimeter of dentin.64 This highly

organized structure of teeth must be formed by the

synchronized reciprocal work differentiating at different

times and rates. Re-creation of the enamel is possible only

with transplantation of naturally formed tooth germ that has

already been completely programmed. Third dentition

remains the dream of dentists.

One advantage of the nonliving nature of the enamel is that

a scaffold of the desired shape can be designed with strong

biocompatible nanoparticles and then incorporated with the

bioengineered enamel during tooth engineering. Because the

desired shapes can be produced, exciting possibilities in

regenerative therapy for dental cavities include inlays of

bioengineered enamel (such as computer-aided design and

computer-aided manufacturing porcelain inlays).

OEpSCs will have a major role in the tooth engineering

where the crucial role of OEpSCs during the formation of

dentin, root, cementum, and periodontal tissues can be used

to regenerate these tissues. Research can be designed for

cementum-coated implants to simulate the periodontium,

pulp-capping biomaterials enriched with OEpSCs for dentin

formation, and guided tissue regeneration of the period-

ontium with OEpSC reinforcement.

Non-dental Derivation from OEpSCs

Non-dental derivations from oral mucosal epithelial stem

cells are routinely successful. Clinical trials have been reported

for the use of tissue-engineered oral mucosal epithelium to

fabricate corneal epithelium in humans by Nishida et al ,65 and

successful animal trials have been reported to produce

esophageal epithelium by Takagi et al 66 and tracheal

epithelium by Kanzaki et al. 67 However, bioengineered teeth

and enamel have not yet been generated for humans.

Endodermal-epithelial interactions in the posterior molars

have been discussed for many years in the context of

odontogenesis. If these interactions are proved, the possibilities

of endodermal organ engineering from DSCs will be

undeniable.68 The regeneration of non-dental tissues of critical

value, such as the cornea, cardiac cells, neurons, pancreatic

islets, and retina, from oral and DSCs will have favorable results

in the near future because of their embryonic origin.18–23,43

The current treatment protocols for dental defects by either

the fillings with biocompatible materials or the tooth

replacement with dental implants are well established with

standard techniques, which are economically affordable and

ethically safe. Clinical studies on human dental tissue

regeneration should target acceptable and easy procedures

for application in regenerative medicine with nano-structured

materials as reported by Mitsiadis et al. 69 and Mitsiadis and

Papagerakis.70

CONCLUSIONS AND PERSPECTIVES

DSCs will provide promising results in regenerative therapy,

not just for dental structures but also for many vital

structures. OEpSCs sourcing from DL, ERM, REE, and JE

have yielded positive results, but the most promising OEpSC

source is the ERM. The GC has yet to be explored. The GC

from the upper anterior region must be investigated for the

potential to form retinal tissue. The DL is the only embryonic

tissue available late in postnatal life in the third molar region

that can be used for studies related to organogenesis.

Exfoliating teeth in children and the third molar or its tooth

germ with the pericoronal tissue of adults are the best sources

of OEpSCs. Public awareness can be generated to encourage

their preservation in tooth banks. Promising research areas

for study in the near future are the nanomaterials incorpo-

rated with OEpSCs for regenerative therapy in dentistry and

the ability of the ERM to form retina and to undergo the EMT

Odontogenic epithelial stem cells

S Padma Priya et al

www.laboratoryinvestigation.org | Laboratory Investigation | Volume 00 2015 7

owing to their developmental biological properties. A

bioengineered tooth is possible only by using the fully

programmed tooth germ. Human clinical trials with well-

controlled and monitored research works with transplanted

tooth germ may provide remarkable results. Endoderm-

derived oral tissues with stem cell potential in humans

may help with the tissue engineering of endodermal cells

such as pancreatic islets. The tissue available in dental

structures is likely sufficient to form many organs, not just

bioengineered teeth.

Stem cells have yielded promising therapeutic results for

many incurable diseases. Soon, thanks to stem cell therapy,

dental filling materials will undergo revolutionary changes.

Concurring expert scientists from different fields joining

together and conducting concurrent studies with the same

protocols in many parts of the world will lead us to rapid

success. The suggestions of this article about the search for

sources of OEpSCs may project like hypothesis but research

on them will also hopefully lead us to new horizons.

ACKNOWLEDGMENTS

This research was partially supported by the Ministry of Science and

Technology, Taiwan, under the grant numbers 103-2120-M-008-001 and

102-2221-E-008-112-MY2. This work was also supported by the Landseed

Hospital project (NCU-LSH-102-A-003 and 103LSH-NCU-1), the National

Defense Medical Center Project (102NCU-NDMC-01), and the Cathay General

Hospital Project (102NCU-CGH-02, 103CGH-NCU-A3, CGH-MR-A10204 and

CGH-MR-A10301). A Grant-in-Aid for Scientific Research (number 15K06591)

from the Ministry of Education, Culture, Sports, Science, and Technology of

Japan is also acknowledged. We acknowledge the International High Cited

Research Group (IHCRG #14-104), Deanship of Scientific Research, King Saud

University, Riyadh, Kingdom of Saudi Arabia.

DISCLOSURE/CONFLICT OF INTEREST

The authors declare no conflict of interest.

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... This anatomic structure may be found in all the groups of permanent teeth in patients with normal dental eruption (6). Running through within it is the GuCo, composed of fibrous tissue associated with remnant epithelial cells of the dental lamina that link the epithelial portion of the dental follicle of the permanent tooth to the gingiva, functioning as an eruptive pathway (4,9). ...

... A relationship between the GuCa and the etiology of odontogenic tumors was described in the literature (4). Due to the fact that the gubernaculum dentis presented remnant epithelial cells of the dental lamina in its histological composition, this structure was pointed out as one of the origins of the adenomatoid odontogenic tumor (AOT) and of the odontoma (5,9,10). In the literature researched, no clear association of the ameloblastoma odontogenic tumor and of the Dentigerous Odontogenic Cysts with GuCa was found. ...

... The association of the AOT with GuCo was proposed by different authors (2,5,9). This hypothesis perhaps explains the fact that this tumor is rarely associated with deciduous teeth (5). ...

Thaís Silva Cerqueira
Kariza Vargens Diniz Correia

The aims of this review of the literature were to conceptualize the gubernacular canal, by an approach to its function, importance and characteristics of its image in Cone Beam Computed Tomography. The bibliographic survey of scientific articles was conducted in the following databases: PubMed, Bireme, Scielo and Google Scholar. The gubernacular canal, which carries the gubernacular cord within it, is an anatomic structure that starts in the dental follicle and goes through to the alveolar bone crest behind the deciduous tooth. This set appears to play an important role in the tooth eruption process, serving as guide to the permanent tooth in the eruptive trajectory, in addition to being a possible factor in the etiology of odontogenic tumors. Therefore, knowledge about and visualization of this canal in terminological exams such as Cone Beam Computed Tomography are relevant in dental clinical practice to help with the diagnosis of tumors and abnormalities in the eruptive process, thus enabling early intervention when necessary.

... However, unlike other mineralized tissues of the human body, enamel cannot be regenerated due to its acellular nature. Although several cell sources were shown to have amelogenic capacity including keratinocyte stem cells, epithelial cell rests of Malassez (ERM) from periodontal ligament, odontogenic oral epithelial stem cells (OEpSCs), adipose tissue-derived mesenchymal stem cells (AT-MSCs), and iPSCs [87][88][89][90][91][92]. ...

... Thus, it is of major interest to find tissue sources able to generate dental epithelial cells which can be differentiated into enamel-secreting ameloblasts. Aside from iPSCs, examples for this are epithelial cells from the skin or gingiva as well as epithelial rests of Malassez, which can be found in the PDL, co-culture of these cells with different types of dental mesenchymal cells can lead to ameloblast differentiation or even formation of enamel-like structures [58,87,89]. ...

With increasing life expectancy, demands for dental tissue and whole-tooth regeneration are becoming more significant. Despite great progress in medicine, including regenerative therapies, the complex structure of dental tissues introduces several challenges to the field of regenerative dentistry. Interdisciplinary efforts from cellular biologists, material scientists, and clinical odontologists are being made to establish strategies and find the solutions for dental tissue regeneration and/or whole-tooth regeneration. In recent years, many significant discoveries were done regarding signaling pathways and factors shaping calcified tissue genesis, including those of tooth. Novel biocompatible scaffolds and polymer-based drug release systems are under development and may soon result in clinically applicable biomaterials with the potential to modulate signaling cascades involved in dental tissue genesis and regeneration. Approaches for whole-tooth regeneration utilizing adult stem cells, induced pluripotent stem cells, or tooth germ cells transplantation are emerging as promising alternatives to overcome existing in vitro tissue generation hurdles. In this interdisciplinary review, most recent advances in cellular signaling guiding dental tissue genesis, novel functionalized scaffolds and drug release material, various odontogenic cell sources, and methods for tooth regeneration are discussed thus providing a multifaceted, up-to-date, and illustrative overview on the tooth regeneration matter, alongside hints for future directions in the challenging field of regenerative dentistry.

... In another study, the efficiency of reprogramming was higher in immature cells when compared to that in the mature cells 21 . According to some studies, ERM cells are immature with stem cell-like features and properties 15,22 . Hence, they may have a higher potential to generate pluripotent stem cells than keratinocytes derived from other types of stratified squamous epithelium. ...

The DNA demethylating agent, 5-Azacytidine (5Aza), and histone deacetylase inhibitor, valproic acid (Vpa), can improve the reprogramming efficiencies of pluripotent cells. This study aimed to examine the roles of 5Aza and Vpa in the dedifferentiation of epithelial cell rests of Malassez (ERM) into stem-like cells. Additionally, the ability of stem-like cells to differentiate into mesenchymal cells was evaluated. ERM was cultured in embryonic stem cell medium (ESCM) with 1 µM of 5Aza, or 2 mM of Vpa, or a combination of 5Aza and Vpa. The cells stimulated with both 5Aza and Vpa were named as progenitor-dedifferentiated into stem-like cells (Pro-DSLCs). The Pro-DSLCs cultured in ESCM alone for another week were named as DSLCs. The stem cell markers were significantly higher in the DSLCs than the controls (no additions). The mRNA and protein levels of the endothelial, mesenchymal stem, and osteogenic cell markers were significantly higher in the Pro-DSLCs and DSLCs than the controls. The combination of a demethylating agent and a deacetylated inhibitor induced the dedifferentiation of ERM into DSLCs. The Pro-DSLCs derived from ERM can be directly reprogrammed into mesenchymal-like cells without dedifferentiation into stem-like cells. Isolated ERM treated with epigenetic agents may be used for periodontal regeneration.

... Besides, stem cell markers such as Oct-4, CD44 and K15 have been demonstrated in odontogenic lesions as well (18,19). In addition, odontogenic epithelium, such as remnants of dental lamina, the epithelial cell rests of Malassez and reduced enamel epithelium, has been thought to be hidden sources in regenerative medicine because of the existence of stem cells in them (20). What's more, Marrelli et al. have isolated MSC-like cells from human periapical cysts (21). ...

Background: Dentigerous cyst (DC) is a bone destructive disease and remains a challenge for clinicians. Marsupialization enables bone to regenerate with capsules maintaining, making it a preferred therapeutic means for DC adjacent to vital anatomical structures. Given that capsules of DC derive from odontogenic epithelium remnants at embryonic stage, we investigated whether there were mesenchymal stem cells (MSCs) located in DC capsules and the role that they played in the bone regeneration after marsupialization. Methods: Samples obtained before and after marsupialization were used for histological detection and cell culture. The stemness of cells isolated from fresh tissues were analyzed by morphology, surface marker and multi-differentiation assays. Comparison of proliferation ability between Am-DCSCs and Bm-DCSCs were evaluated by Cell Counting Kit-8 (CCK-8), fibroblast colony-forming units (CFU-F) and 5'‐ethynyl‐2'‐deoxyuridine (EdU) assay. Their osteogenic capacity in vitro was detected by Alkaline phosphatase (ALP) and Alizarin Red staining (ARS), combined with Real-time polymerase chain reaction (RT-PCR) and immunofluorescence (IF) staining. Subcutaneous ectopic osteogenesis as well as cranial bone defect model in nude mice were performed to detect their bone regeneration and bone defect repair ability. Results: Bone tissue and strong ALP activity were detected in the capsule of DC after marsupialization. Two types of MSCs were isolated from fibrous capsules of DC both before (Bm-DCSCs) and after (Am-DCSCs) marsupialization. These fibroblast-like, colony forming cells expressed MSC markers (CD44+, CD90+, CD31-, CD34-, CD45-), and they could differentiate into osteoblast-, adipocyte- and chondrocyte-like cells under induction. Notably, Am-DCSCs performed better in cell proliferation and self-renewal. Moreover, Am-DCSCs showed greater osteogenic capacity both in vitro and in vivo compared with Bm-DCSCs. Conclusions: There are MSCs residing in capsules of DC, and the cell viability as well as osteogenic capacity of them are largely enhanced after marsupialization. Our findings suggested that MSCs might play a crucial role in the healing process of DC after marsupialization, thus providing new insight into the treatment for DC by promoting the osteogenic differentiation of MSCs inside capsules.

... Besides, stem cell markers such as Oct-4, CD44, and K15 have been demonstrated in odontogenic lesions as well [18,19]. In addition, odontogenic epithelium, such as remnants of the dental lamina, the epithelial cell rests of Malassez, and reduced enamel epithelium, has been thought to be hidden sources in regenerative medicine because of the existence of stem cells in them [20]. What is more, Marrelli et al. have isolated MSC-like cells from human periapical cysts [21]. ...

Background Dentigerous cyst (DC) is a bone destructive disease and remains a challenge for clinicians. Marsupialization enables the bone to regenerate with capsule maintaining, making it a preferred therapeutic means for DC adjacent to vital anatomical structures. Given that capsules of DC are derived from odontogenic epithelium remnants at the embryonic stage, we investigated whether there were mesenchymal stem cells (MSCs) located in DC capsules and the role that they played in the bone regeneration after marsupialization. Methods Samples obtained before and after marsupialization were used for histological detection and cell culture. The stemness of cells isolated from fresh tissues was analyzed by morphology, surface marker, and multi-differentiation assays. Comparison of proliferation ability between MSCs isolated from DC capsules before (Bm-DCSCs) and after (Am-DCSCs) marsupialization was evaluated by Cell Counting Kit-8 (CCK-8), fibroblast colony-forming units (CFU-F), and 5′-ethynyl-2′-deoxyuridine (EdU) assay. Their osteogenic capacity in vitro was detected by alkaline phosphatase (ALP) and Alizarin Red staining (ARS), combined with real-time polymerase chain reaction (RT-PCR) and immunofluorescence (IF) staining. Subcutaneous ectopic osteogenesis as well as cranial bone defect model in nude mice was performed to detect their bone regeneration and bone defect repairability. Results Bone tissue and strong ALP activity were detected in the capsule of DC after marsupialization. Two types of MSCs were isolated from fibrous capsules of DC both before (Bm-DCSCs) and after (Am-DCSCs) marsupialization. These fibroblast-like, colony-forming cells expressed MSC markers (CD44+, CD90+, CD31−, CD34−, CD45−), and they could differentiate into osteoblast-, adipocyte-, and chondrocyte-like cells under induction. Notably, Am-DCSCs performed better in cell proliferation and self-renewal. Moreover, Am-DCSCs showed a greater osteogenic capacity both in vitro and in vivo compared with Bm-DCSCs. Conclusions There are MSCs residing in capsules of DC, and the cell viability as well as the osteogenic capacity of them is largely enhanced after marsupialization. Our findings suggested that MSCs might play a crucial role in the healing process of DC after marsupialization, thus providing new insight into the treatment for DC by promoting the osteogenic differentiation of MSCs inside capsules.

Mesenchymal and epithelial stem cells were identified in dental tissues; however, knowledge about the odontogenic stem cells is limited, and there are some questions regarding their temporo-spatial dynamics in tooth development. Objective: Our study aimed to analyze the expression of the stem cell markers CD146 and p75NTR during the different stages of odontogenesis. Methodology: The groups consisted of 13.5, 15.5, 17.5 days old embryos, and 14 days postnatal BALB/c mice. The expression of CD146 and p75NTR was evaluated by immunohistochemistry. Results: Our results showed that positive cells for both markers were present in all stages of tooth development, and the number of positive cells increased with the progression of this process. Cells of epithelial and ectomesenchymal origin were positive for CD146, and the expression of p75NTR was mainly detected in the dental papilla and dental follicle. In the postnatal group, dental pulp cells were positive for CD146, and the reduced enamel epithelium and the oral mucosa epithelium showed immunostaining for p75NTR. Conclusions: These results suggest that the staining pattern of CD146 and p75NTR underwent temporal and spatial changes during odontogenesis and both markers were expressed by epithelial and mesenchymal cell types, which is relevant due to the significance of the epithelial-ectomesenchymal interactions in tooth development.

Suchandra Chowdhury
Shyamasree Ghosh

Stem cells (SC) are the progenitor cells with the ability to self-renew and differentiate into various lineages. They find importance in stem cell therapy, gene therapy, and tissue engineering. While embryonic stem cells (ESCs) are bestowed with the hallmark property of self-renewal and ability to differentiate into different lineages, the mesenchymal stem cells (MSCs) reveal restricted lineage potential as compared to the ESCs. In this chapter, we discuss the different types of stem cells including ESCs, adult stem cells, stem cells from umbilical cord blood, tissue-specific stem cells (TSSCs), induced pluripotent cells, cancer stem cells, and stem cell plasticity.

Suchandra Chowdhury
Shyamasree Ghosh

The process of isolation and culture of the stem cells finds importance in both biomedical aspect and drug discovery. In this chapter, we discuss about the different types of stem cells, their sources, methods of isolation and culture. We also discuss the three-dimensional (3D) culture of biomaterials, which aid in the 3D cell culture and their subsequent changes with respect to the biophysical or biochemical properties over time (i.e., fourth dimension) which is the basis of 4D culture. The 3D cultures mimic the real-life system of cells in their microenvironment in vivo and their communication with other cell types and the extracellular matrix (ECM) which finds importance in the giving near perfect to actualization results in the tests for drug discovery and is finding importance in today's biology.

Uncontrolled activation of the Hedgehog (Hh) signaling pathway, operating through GLI transcription factors, plays a central role in the pathogenesis of cutaneous basal cell carcinoma and contributes to the development of several malignancies arising in extracutaneous sites. We now report that K5-tTA;tetO-Gli2 bitransgenic mice develop distinctive epithelial tumors within their jaws. These tumors consist of large masses of highly proliferative, monomorphous, basaloid cells with scattered foci of keratinization and central necrosis, mimicking human basaloid squamous cell carcinoma (BSCC), an aggressive upper aerodigestive tract tumor. Like human BSCC, these tumors express epidermal basal keratins, and differentiation-specific keratins within squamous foci. Mouse BSCCs express high levels of Gli2 and Hh target genes, including Gli1 and Ptch1, which we show are also upregulated in a subset of human BSCCs. Mouse BSCCs appear to arise from distinct epithelial sites, including the gingival junctional epithelium and epithelial rests of Malassez, a proposed stem cell compartment. Although Gli2 transgene expression is restricted to epithelial cells, we also detect striking alterations in bone adjacent to BSCCs, with activated osteoblasts, osteoclasts, and osteal macrophages, indicative of active bone remodeling. Gli2 transgene inactivation resulted in rapid BSCC regression and reversal of the bone remodeling phenotype. This first-reported mouse model of BSCC supports the concept that uncontrolled Hh signaling plays a central role in the pathogenesis of a subset of human BSCCs, points to Hh/GLI2 signaling as a potential therapeutic target, and provides a powerful new tool for probing the mechanistic underpinnings of tumor-associated bone remodeling.

Tooth development results from sequential and reciprocal interactions between the oral epithelium and the underlying neural crest-derived mesenchyme. The generation of dental structures and/or entire teeth in the laboratory depends upon the manipulation of stem cells and requires a synergy of all cellular and molecular events that finally lead to the formation of tooth-specific hard tissues, dentin and enamel. Although mesenchymal stem cells from different origins have been extensively studied in their capacity to form dentin in vitro, information is not yet available concerning the use of epithelial stem cells. The odontogenic potential resides in the oral epithelium and thus epithelial stem cells are necessary for both the initiation of tooth formation and enamel matrix production. This review focuses on the different sources of stem cells that have been used for making teeth in vitro and their relative efficiency. Embryonic, post-natal or even adult stem cells were assessed and proved to possess an enormous regenerative potential, but their application in dental practice is still problematic and limited due to various parameters that are not yet under control such as the high risk of rejection, cell behaviour, long tooth eruption period, appropriate crown morphology and suitable colour. Nevertheless, the development of biological approaches for dental reconstruction using stem cells is promising and remains one of the greatest challenges in the dental field for the years to come.

Despina S. Koussoulakou

The ancestor of recent vertebrate teeth was a tooth-like structure on the outer body surface of jawless fishes. Over the course of 500,000,000 years of evolution, many of those structures migrated into the mouth cavity. In addition, the total number of teeth per dentition generally decreased and teeth morphological complexity increased. Teeth form mainly on the jaws within the mouth cavity through mutual, delicate interactions between dental epithelium and oral ectomesenchyme. These interactions involve spatially restricted expression of several, teeth-related genes and the secretion of various transcription and signaling factors. Congenital disturbances in tooth formation, acquired dental diseases and odontogenic tumors affect millions of people and rank human oral pathology as the second most frequent clinical problem. On the basis of substantial experimental evidence and advances in bioengineering, many scientists strongly believe that a deep knowledge of the evolutionary relationships and the cellular and molecular mechanisms regulating the morphogenesis of a given tooth in its natural position, in vivo, will be useful in the near future to prevent and treat teeth pathologies and malformations and for in vitro and in vivo teeth tissue regeneration.

Hyun Nam
Ji-Hye Kim
Jae-Won Kim
Gene Lee

Human Hertwig's epithelial root sheath/epithelial rests of Malassez (HERS/ERM) cells are epithelial remnants of teeth residing in the periodontium. Although the functional roles of HERS/ERM cells have yet to be elucidated, they are a unique epithelial cell population in adult teeth and are reported to have stem cell characteristics. Therefore, HERS/ ERM cells might play a role as an epithelial component for the repair or regeneration of dental hard tissues; however, they are very rare population in periodontium and the primary isolation of them is considered to be difficult. To overcome these problems, we immortalized primary HERS/ ERM cells isolated from human periodontium using SV40 large T antigen (SV40 LT) and performed a characterization of the immortalized cell line. Primary HERS/ERM cells could not be maintained for more than 6 passages; however, immortalized HERS/ERM cells were maintained for more than 20 passages. There were no differences in the morphological and immunophenotypic characteristics of HERS/ERM cells and immortalized HERS/ERM cells. The expression of epithelial stem cell and embryonic stem cell markers was maintained in immortalized HERS/ERM cells. Moreover, immortalized HERS/ERM cells could acquire mesenchymal phenotypes through the epithelial-mesenchymal transition via TGF-β1. In conclusion, we established an immortalized human HERS/ERM cell line with SV40 LT and expect this cell line to contribute to the understanding of the functional roles of HERS/ERM cells and the tissue engineering of teeth.

Source: https://www.researchgate.net/publication/281778650_Odontogenic_epithelial_stem_cells_Hidden_sources

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