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Table7.2 Turnover time ofepithelia ofdifferent regions.
Epithelium Turnover time (days) Factors affecting
Cheek 4– 25 Cytokines:
Gingiva 41– 57
Skin 52– 75
Gut 14
EGF, epidermal growth factor; KGF, keratinocyte growth factor; IL, interleukin;
TGF, transforming growth factor.
1) EGF
2) KGF
3) IL- 1
4) α- T G F
5) β- T G F
Drugs:
Chemotherapeutic drugs
7.8 The Epithelial andConnective Tissue Junction
7.8.1 Basement Membrane
The epithelial layer is attached to the basement membrane through hemidesmosomes. The basement membrane consists of a basal lamina and a reticular lamina, which consist of various proteins such as laminin and collagen type IV by epithelial cells, while the reticular lamina entails
reticular fibres produced by connective tissue components.
The junction at which connective tissue papillae interdigitate with the epithelial rete ridges is
wavy. This pattern increases the surface area, enhances the attachment and distributes forces over
a larger area, providing a larger area for metabolic exchange between the epithelium and connective tissue. Masticatory mucosa has a larger number of papillae per unit area, while lining mucosa
has a lesser number of papillae per unit area and is shorter. The basal lamina, situated between the
basal cells and lamina propria, is not evident on H&E- stained sections but can be enhanced by
periodic acid– Shiff (PAS) reaction, which appears magenta red in colour. The basal lamina on
which basal cells reside is about 50– 60 nm thick mat- like assembly(2).
The basal lamina has three zones: (i) lamina lucida, (ii) lamina densa and (iii) lamina fibroreticularis (Table7.3).
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7.9 Connective Tissue: Lamina Propria andSubmucosa
The relatively thin zone of connective tissue that separates the mucosal epithelium from more
deeply situated submucosal fibrous connective tissues (submucosa) is called lamina propria
(Figure7.5). At sites such as the anterior hard palate, the maxillary alveolus and the mandibular
alveolus, the subepithelial connective tissues merge with the periosteum of the bone to form dense
fibrous mucoperiosteum. The lamina propria, which is close to the overlying epithelium, contains
small- diameter blood, lymphatic vessels and nerve endings. Lamina propria is divided into the
superficial papillary and the deeper reticular layers or zones. The superficial papillary layer abuts
the mucosal epithelium (rete ridges), and the deeper reticular area merges with the submucosa.
Lamina propria comprises cellular elements such as fibroblasts, macrophages, mast cells and
inflammatory cells. The extracellular matrix of the lamina propria and the submucosa comprises
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Lamina
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Table7.3 The three zones of basal lamina(1).
Lamina lucidum (LL) Lamina densa (LD) Lamina fibroreticularis (LF)
● Synthesised by epithelium
● Clear band
● Thinner than LD
● Inconspicuous with tissue
preservation methods
● Can be an artefact
incorporated during tissue
dehydration
● Proteins attachment cell to
BL: hemidesmosomelinked membrane proteins
and laminin- 332
● A dense mat- like structure
● Synthesised by the epithelium
● Homogeneous
● Fine fibrillar planar
assemblage of ECM molecules
● Network of collagen type IV
and laminins
● Proteins: heparan sulphate
proteoglycan, nidogen and
fibulin
● Anchoring fibrils: collagen
type VII inserted
● Adaptable connection
Some components are
manufactured by CT cells
like fibroblasts
between the BL and CT
BL, basal lamina; CT, connective tissue; ECM, extracellular matrix; LD, lamina densa; LF, lamina fibroreticularis;
LL, lamina lucida.
Papillary
layer
propria
Reticular
layer
Submucosa
Figure7.5 Lamina propria. The historical section of palatal mucosa showing approximate boundaries of
the papillary and reticular layers in the lamina propria. Source: With permission of Pocket Dentistry.
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collagen (type I and III) and elastic fibres. Elastic fibres are most prominent in the buccal and
alveolar mucosa. The ground substance consists of protein– carbohydrate complexes of two
classes– proteoglycans and glycoproteins, free water and transudate derived from the vasculature.
The role of the ground substance includes functions relating to cell– cell interactions, cell mobility,
diffusion and tissue– water homeostasis(1, 2).
7.10 Blood Supply ofOral Mucosa
The blood supply of the oral mucosa is abundant and results from the arteries running parallel to
the submucosa or in the deeper reticular layer(22). There are many regional modifications. Blood
flow is maximum in the gingival tissue. The venous drainage occurs in the internal and external
jugular veins (Table7.4).
Table7.4 Blood supply tothe oral mucosa.
Oral mucosa region Blood supply (artery)
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Lining mucosa
Soft palate
Floor of mouth
Masticatory mucosa
Maxillary:
Buccal gingiva
Labial gingiva
Palatal gingiva
Mandibular:
Buccal gingiva
Labial gingiva
Lingual gingiva
Hard palate
Specialised mucosa
Tongue
Maxillary (terminal branches)
Facial
Ascending palatine
Submental
Lingual
Facial
Ascending palatine
Lingual (sublingual)
Maxillary
Facial (submental branch)
Lingual
Maxillary and lingual
Posterior superior alveolar (gingival and perforating branches)
Infraorbital (labial branches) and anterior superior alveolar
(perforating branches)
Greater palatine branches
Maxillary (buccal branch)
Inferior alveolar (perforating branches)
Mental
Incisive branches
Inferior alveolar (lingual + perforating branches)
Main lingual
Greater palatine
Lingual
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7.11 Sensory Nerves andReceptors
Three sensory endings in the oral mucosa are Merkel’s disks, Meissner’s corpuscles and free nerve
endings, allowing the mucosa to perceive and respond to temperature, touch and pain (Table7.5).
The number of sensory receptors is higher in the anterior than in the posterior part of the oral
cavity. Multiple receptors are responsible for the perception of each sense.
A specialised receptor present only in the oral mucosa is the taste bud and the taste system’s
chief sensory unit. Taste buds are intraepithelial goblet/barrel- shaped structures in the soft palate
and pharynx, but mainly in the fungiform, foliate and circumvallate papillae. Taste buds constitute
30– 80 stave/spindle- shaped cells of epithelial origin(23, 24). Each one has a taste pore, which
opens to the external milieu and is present just below the surface of the epithelium. There is
regional variation in the sensitivity of taste: sweet at the tip of the tongue, salty and sour at the
lateral surfaces of the tongue, and bitter and sour at the posterior tongue.
7.12 Structural Variations inOral Mucosa
Based on the variations in the structure, the oral mucosa can be classified as lining mucosa,
masticatory mucosa or specialised mucosa(1, 7).
7.12.1 Lining Mucosa
Lining mucosa covers the underside of the tongue, inside of the lips, cheeks, floor of the mouth
and alveolar processes, and a part of the gingiva and soft palate is lining mucosa. This is covered by
stratified squamous non- keratinised epithelium. The epithelial layer is thick, comprising several
layers of cells. Lamina propria has active role in sensing and is flexible. Collagen fibres and elastic
fibres are evident and are responsible for the extensibility.
Table7.5 Nerve supply ofthe oral mucosa.
Region Innervation Nerves
Oral mucosa Nociceptive innervation Maxillary and mandibular
Salivary glands Secretomotor
parasympathetic fibres
Tongue posterior 1/3,
including circumvallate
and foliate papillae
Anterior fungiform
papillae
Hard palate Maxillary nerve branches:
divisions of trigeminal nerve
Facial and glossopharyngeal
nerve
Glossopharyngeal
Chorda tympani
Greater palatine
Lesser palatine
Nasopalatine
Sphenopalatine
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7.12.2 Masticatory Mucosa
Masticatory mucosa covers the free and attached gingivae, the hard palate and part of the dorsum
of the tongue. The stratified squamous epithelium covering the masticatory mucosa is thick and
ortho- keratinised. Sometimes, gingiva and hard palate show para- keratinisation. The surfaces can
bear various forces and are inextensible and abrasion. The interface between the epithelium and
lamina propria shows mechanical attachment with numerous elongated papillae, preventing the
epithelium from being stripped off under shear force. The lamina propria is thick and comprises
collagen bundles.
The gingival epithelium is relatively thick and keratinised but thin and non- keratinised as it
forms the gingival sulcus and the junctional epithelial attachment.
7.12.3 Specialised Mucosa
The ‘specialised mucosa’ refers to features found on the dorsum of the tongue in the form of
papillae. These include the filiform papillae, fungiform papillae, circumvallate papillae and
foliate papillae. The other special features include the presence of taste buds within the mucosal
epithelium. Taste buds are associated with circumvallate papillae, foliate papillae and some
fungiform papillae and may also be found within the epithelium of the soft palate. Functionally,
however, the dorsum of the tongue is covered by masticatory mucosa.
Filiform Papillae: These form the bulk of the tongue papillae(24) covering the anterior part of the
tongue and resembling hair(25). They are cone- shaped structures with connective tissue cores
covered by a thick keratinised epithelium forming a tough, abrasive surface. Filiform papillae
are the smallest yet most abundant papillae. They help in the compression and breakdown of
food. Elongation of these papillae results from more keratinisation. Sometimes, there is hyperplasia of these papillae, leading to a condition called hairy tongue. Non- keratinised, flexible epithelial
areas between the filiform papillae make the tongue an extensible organ. The papillae contain
trigeminal nerve endings communicating temperature, texture and pain information(8).
Fungiform Papillae: They are present exclusively on the anterior tongue. They are morphologically
fungus like. There are an average of 195 fungiform papillae on the tongue surface of an individual, with 87% of them positioned on the anterior 2 cm of the dorsum of the tongue(24). The
papillae are smooth and round and appear red because the connective tissue core present
ishighly vascular. The superior surfaces show the presence of taste buds. Encapsulated nerve
endings resembling Meissner’s corpuscles of skin are in the most apical parts of the connective
tissue papillae(7).
Circumvallate Papillae: These are dome- shaped papillae 8– 12, positioned anteriorly adjoining the
sulcus terminalis embedded into the tongue dorsum(25). The papillae are encircled by a deep,
circular groove/moat into which the ducts of glands of Ebner minor salivary glands are drained.
Glands of Ebner are the only minor purely serous salivary glands in the oral cavity. A connective
tissue core is covered by the keratinised epithelium, whereas lateral walls are covered by
non- keratinised epithelium as they encompass taste buds. Excretory ducts of serous glands
openinto the trenches surrounding the papillae. Apical areas show a lesser number of taste
buds. On average, the papillae contain over 100 taste buds(25).
Foliate Papillae: These are located at the posterior lateral margins of the tongue. They consist of
parallel ridge- like structures formed by mucosal folds alternating with deep grooves. They are
keratinised and have numerous taste buds (around 100)(25) in their lateral walls.
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7.13 Age Changes inthe Oral Mucosa
Many changes keep occurring in the oral mucosa as an individual ages. Senile changes in the
OMM of older individuals are often described as ‘atrophic’/‘friable’, i.e. atrophic epithelium with
flat basement membrane. Reasons that can explain such occurrence include systemic diseases,
medications, nutritional deficiency (iron/B complex vitamins) and a combination of factors.
Alterations occurring at the microscopic level are reflected clinically in the OMM, which can be
considered senescence signals.
7.14 Functions ofOral Mucosa
OMM performs several functions, mainly protective sensory functions, speech and swallowing,
and secretarial functions.
7.14.1 Protective Function
The unique feature of the OMM is its function as a gatekeeper of the alimentary canal (26).
Theoral mucosa is constantly exposed to mechanical, chemical and biological stimuli. The OMM
plays a crucial role in mastication and defending the underlying tissues from all stimuli, including
various antigens such as microorganisms, foreign particles like dust and noxious molecules from
food. The noxious substances also include carcinogenic elements (alcohol, tobacco, betel nut, etc.).
The oral epithelium acts as a physical and immune barrier against all these physiological as well as
pathogenic agents, including the entry of the oral cavity’s normal bacterial flora that may cause
infection (4). Multilayered epithelium, cell– cell junctions, dendritic cells and T- helper 17 cells
(Th17) are all responsible for achieving the role of the OMM in immunological defence mechanisms.
7.14.2 Sensory Function andRole inSpeech andSwallowing
The OMM has sensory innervation from three branches of the trigeminal nerve. There are three
types of sensory endings in the oral mucosa: Merkel’s disks, Meissner’s corpuscles and free nerve
endings. Various sensations perceived by the OMM are temperature, touch, pain and proprioception. In addition, five basic gustatory sensations are also perceived by the OMM(23). The touch
sensation warrants the synchronisation of movements by the tongue, lips and soft palate for speaking. It is necessary to identify objects/foodstuffs affecting masticatory function and commencing
the reflex of swallowing. The ubiquitous G- protein- coupled receptors (GPCRs) mediate various
sense receptors (sweet, umami and bitter) while salty and sour taste are mediated by transient
receptor potential in ion channels. The trigeminal nerve communicates with the filiform papillae
and several nerve endings in the OMM. The information is presented to the insula of the gustatory
cortex, and a gustotopic map is generated. Each individual taste has a ‘hot spot’ in the insular,
which reacts to a specific taste(23).
7.14.3 Secretion
The main secretion in the mouth is saliva produced by major and minor salivary glands, which
helps in lubrication and protection. Minor salivary glands are found in the oral submucosal region.
Sebaceous glands are found on the lips, labial and buccal mucosa, which secrete a fatty substance
(sebum) and have a role in immunity, lubrication and buffering.
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References
7.15 Summary
OMM lines the oral structures extending from the vermilion border to the palatopharyngeal folds
posteriorly. It can be classified into three different types: lining, masticatory and specialised.
Histologically, a surface squamous stratified epithelium (oral epithelium) is present with an underlying superficial (lamina propria) and a dense deeper connective tissue (submucosa). The principal
functions of the OMM include secretion, sensory function and protection from mechanical,
chemical and biological stimuli.
References
1 Nanci A. Ten Cate’s Oral Histology Development, Structure and Function, 8th edition. St. Louis:
Elsevier; 2013.
2 Brizuela M, Winters R. Histology, Oral Mucosa. [Updated 2023May 8]. In: StatPearls [Internet].
Treasure Island (FL): StatPearls Publishing; 2023.
3 Shroeder HE. Differentiation of Human Oral Stratified Epithelia. Basel: S Krager; 1981.
4 Squier CA, Kremer MJ. Biology of oral mucosa and esophagus. J Nat Cancer Instit Monogr.
2001;29:7– 15.
5 Wertz PW. Roles of lipids in the permeability barriers of skin and oral mucosa. Int J Mol Sci.
2021;22(10):5229.
6 Squier CA, Johnson NW, Hopps RM. Human oral mucosa: development, structure, and function.
Oxford, UK: Blackwell Scientific; 1976.
7 Garant PR. Oral Cells and Tissues. Chicago: Quintessence Pub. Co; 2003.
8 Jones PH. Epithelial stem cells. Bioessays. 1997;19:683– 90.
9 Watt FM. Epidermal stem cells: markers, patterning and the control of stem cell fate. Philos Trans
R Soc Lond B Biol Sci. 1998;353:831– 7.
10 Green H, Djian P. Consecutive actions of different gene- altering mechanisms in the evolution of
involucrin. Mol Biol Evol. 1992;9(6):977– 1017.
11 Schmitz G, Müller G. Structure and function of lamellar bodies, lipid- protein complexes involved
in storage and secretion of cellular lipids. J Lipid Res. 1991;32(10):1539– 70.
12 Kingsley C, Kourtidis A. Critical roles of adherens junctions in diseases of the oral mucosa.
TissueBarriers. 2023;11(2):2084320.
13 Samiei M, Ahmadian E, Eftekhari A, Eghbal MA, Rezaie F, Vinken M. Cell junctions and oral
health. EXCLI J. 2019;18:317– 30.
14 Liu W, Cui Y, Wei J, Sun J, Zheng L, Xie J. Gap junction- mediated cell- to- cell communication in
oral development and oral diseases: a concise review of research progress. Int J Oral Sci.
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15 Kowalczyk AP, Green KJ. Structure, function, and regulation of desmosomes. Prog Mol Biol Transl
Sci. 2013;116:95– 118.
16 Skerrow D, Skerrow CJ. Tonofilament differentiation in human epidermis, isolation and
polypeptide chain composition of keratinocyte subpopulations. Exp Cell Res. 1983;143(1):27– 35.
17 Barrett AW, Scully C. Human oral mucosal melanocytes: a review. J Oral Pathol Med.
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19 Meleti M, Vescovi P, Mooi WJ, van der Waal I. Pigmented lesions of the oral mucosa and perioral
tissues: a flow- chart for the diagnosis and some recommendations for the management. Oral Surg
Oral Med Oral Pathol Oral Radiol Endod. 2008;105(5):606– 16.
20 Kingsmill VJ, Berkovitz BK, Barrett AW. An immunohistochemical analysis of human Merkel cell
density in gingival epithelium from dentate and edentulous subjects. Arch Oral Biol.
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21 Wang SS, Tang YL, Pang X, Zheng M, Tang YJ, Liang XH. The maintenance of an oral epithelial
barrier. Life Sci. 2019;15(227):129– 36.
22 Kamrani P, Sadiq NM. Anatomy, Head and Neck, Oral Cavity (Mouth) [Updated 2023 August 14].
In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023
23 Gravina SA, Yep GL, Khan M. Human biology of taste. Ann Saudi Med. 2013;33(3):217– 22.
24 Miller IJ, Jr, Preslar AJ. Spatial distribution of rat fungiform papillae. Anat Rec. 1975;181(3):679– 84.
25 Triantafyllou A, Coulter P. Structural organization of subgemmal neurogenous plaques in foliate
papillae of tongue. Hum Pathol. 2004;35(8):991– 9.
26 Senel S. An overview of physical, microbiological and immune barriers of oral mucosa 2021.
IntJMol Sci. 2021;22(15):7821.
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8
Cellular Mechanisms ofAgeing ofOral Tissues
Jeremy Lau, Agnieszka Frydrych and Omar Kujan
UWA Dental School, The University of Western Australia, Perth, Western Australia, Australia
8.1 Introduction
Ageing is characterised by progressive changes in body’s tissues or organs(1). It is a time- related
decline in physiological function necessary for survival and fertility. Ultimately, ageing leads to
death. In literature, the terms ageing and senescence are often used interchangeably. However,
there is difference between them. Ageing relates to a progressive decline with time, while senescence occurs throughout life including embryogenesis. In society, the features most often associated
with ageing include hair loss, loss of skin elasticity, decline in strength, decreased immune competence and a range of medical conditions including atherosclerosis and cataract formation(1).
Ageing can be discussed in terms of chronological age, biological age, sociological age and successful ageing. Chronical age relates to the time lapsed since birth and is a simplified means to
measure one’s age. The definition of calling someone elderly or old is somewhat arbitrary, with the
World Health Organisation considering an older person as over 60 years of age(2). Biology relates
to the presence or absence of disease. Prevalence of several disorders increases with age in particular cardiovascular disease, cancer, stroke and dementia. However, not all elderly develop these
conditions. Sociological relates to perceived normal behaviour for a particular age group. For
instance, those playing elite sports or going clubbing may be perceived as being younger. Successful
ageing notes variability in the ageing process. It may harbour new opportunities and can lead to
productive function.
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8.2 Hallmarks ofAgeing
The original cellular and molecular hallmarks of ageing comprise: altered intercellular communication, stem cell exhaustion, cellular senescence, mitochondrial dysfunction, genomic instability,
loss of proteostasis, epigenetic alterations, telomere attrition and deregulated nutrient sensing(3)
(Figure8.1). At the 2022 Copenhagen meeting on ageing, five additional hallmarks were proposed
including compromised autophagy, microbiome disturbance, altered mechanical properties,
splicing dysregulation and inflammation(4).
Pathological Basis of Oral and Maxillofacial Diseases, First Edition. Edited by S. R. Prabhu, Syed Ali Khurram,
Omar Kujan and Merva Soluk Tekkesin.
© 2025 John Wiley & Sons Ltd. Published 2025 by John Wiley & Sons Ltd.
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Cellular
senescence
Mitochondrial
dysfunction
Genomic
Instability
proteostasis
Loss of
Epigenetic
alterations
Stem cell
exhaustion
Altered
intercellular
communication
Compromised
Autophagy
Microbiome
Disturbance
Mechanical
Properties
Splicing
Dysregulation
Altered
Inflammation
Telomere
attrition
Deregulated
nutrient-sensing
Unknown
Figure8.1 New hallmarks of ageing. Source:(4) / Impact Journals, LLC / CC BY 4.0.
8.3 Cellular, Molecular andPhysiological Mechanisms ofAge- related
Changes inTeeth andPeriodontal Tissues
With ageing, changes to the teeth occur in various layers including the enamel, dentine- pulp complex and cementum. Clinically, common changes include physiological wear such as attrition and
abrasion. The ageing of enamel is considered a complex multifaceted process(5). The enamel
becomes more brittle and becomes prone to chipping and fracturing with age(6). It is also less
permeable in older adults due to ionic exchange with the oral environment, which can lead to
physiochemical changes(7).
In the dentine, formation of secondary dentine occurs throughout life. This leads to a reduction in
the size of the pulp and, in some cases, complete calcification of the pulp chamber. Dentinal sclerosis
may also result due to the production of peritubular dentine. Sclerosis of radicular dentine affects the
properties of tooth roots and may lead to increased risk of fracture particularly during extractions(8).
Over time, the pulp becomes less vascular and less cellular and reduces fibroblast density(9).
The pulp also has a decreased response to injury with poorer healing potential. Telomere shortening, DNA damage and oncogene activation are considered the main drivers of the dental pulp
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