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5. SUPPORTING STRUCTURE prof Tilak2024.pdf
1. Structure and function of Dental
hard tissues and Tooth
supporting structures
Professor WM Tilakaratne
BDS, MS, FDSRCS, FRCPath, PhD
2. Learning outcomes
Understand the structure of dental hard tissues
and tooth supporting structures
Review properties of tooth supporting structures.
Relate the significance of various structures to
clinical dentistry
Summarize the age changes in dental hard tissues
3. Enamel
• Enamel is the protective covering of the
tooth and the hardest tissue in the human
body secreted by ameloblasts. These cells
are lost after enamel formation hence no
renewal of enamel.
4. Ameloblasts
• Secrete matrix proteins which are
responsible for creating extracellular
environment favourable for mineral
deposition.
• Shows a unique life cycle with different
phenotypic changes according to the stage
of development.
5. Chemical composition of enamel
• Inorganic: 96% (Permanent), 93%
(Deciduous)
• Mineral composition: Hydroxyapatite,
Fluoapatite and carbonate apatite
• Intercrystalline spaces: Amorphous calcium
carbonate, Mn, Zn, Cu, Mg, Al etc
7. Morphology of enamel
• Enamel rods
• Enamel inter-rod space
• Rod sheath
• Striae of Retzius
• Hunter-Schreger bands
• Cross striation of rods
• Gnarled enamel
• DEJ and enamel spindles
• Enamel lamellae and tufts
• Surface enamel
8. Striae of Retzuis
Striae of Retzuis represents incremental
growth. In ground cross sections they appear
like concentric growth rings similar to those
found in trees. In ground longitudinal sections
they appear to be dark lines extending from
the DEJ to the tooth surface, where they end
in shallow furrows known as perikymata (or
9. Enamel Tufts, Lamellae and Spindles
• Enamel tufts originate from the DEJ, run a short distance in the
enamel. They represent protein (enamelin) rich areas in the enamel
matrix that fail to mature. They are formed during the formative
stages of enamel.
• Lamellae extend from the enamel surface toward the
dentinoenamel junction and may sometimes extend to dentin.
Consist of organic material, with little mineral content. Usually
developed in planes of tension.
• Enamel spindles originate from odontoblastic process which cross
the DEJ. Before enamel forms, some developing odontoblastic
processes extend into the ameloblast layer, and when enamel
formation begins become trapped to form enamel spindles.
12. Enamel surface
• Perikymata: Striae of Retzius extend from
DEJ to the outer surface and end in shallow
furrows.
• Surface consists of a structure less surface
layer without rods.
• As the tooth erupts, it is covered by pellicle
consisting of debris from enamel organ and
soon replaced by salivary pellicle.
13. Enamel Rod structure
• Rods extend from DEJ to the outer surface.
• Each rod is formed by secretory products of
four ameloblasts.
• One forms the rod head.
• A part of two ameloblasts form the neck.
• Tail is formed by four ameloblasts.
14. Reduced enamel epithelium
• It represents the epithelial covering of the
enamel after its formation is completed. REE
is derived mainly from the ameloblast and
stratum intermedium layers of the enamel
organ, but it also may include remnants of
stellate reticulum and outer enamel
epithelium.
Primary enamel cuticle, also called
Nasmyth's membrane, is a thin
membrane of tissue also known as
reduced enamel epithelium
15. Clinical implications
• Leads to diseases with structural
abnormalities (Amelogenesis imperfecta).
• Chronological hypoplasia
• Changes in chemical structure and
composition.
• Remnants such as REE lead to cyst
formation.
16. Dentine
Physical properties
• Pale yellow
• Darker with age
• Harder than bone and cementum, softer than enamel.
• Much more resistant to propagation of cracks than enamel
(higher fracture toughness)
• Greater compressive, tensile and flexural strength than
enamel
• Permeable (permeability depends on the size and patency
of the tubules)
• Permeability decline with age.
• Elastic (slight deformation)
• Less mineralized than enamel (more radiolucent)
17. Chemical properties
• 70% inorganic, 20% organic and 10% water by
weight.
• 50% inorganic, 30% organic and 20% water by
volume.
Inorganic matrix
• Inorganic mineral component: calcium hydroxyapatite
crystals.
• Hydroxyapatite similar in shape, but very much
smaller than those in enamel.
• Trace elements: fluoride.
• Crystallites in the mineralised dentine are found on
and between the collagen fibrils.
18. Organic matrix
• Composition similar to bone.
• Fibrils (collagen)embedded in an amorphous ground
substance.
• 90% collagen ( mostly type 1)
• Traces of type III and type V collagen
• Most of the collagen fibrils in dentine run parallel to
the pulpal surface.
• In mineralised dentine collagen fibrils are of larger
diameter (100 nm) and are more closely packed than
in predentine.
21. Regional variations in dentine structure
and composition
• The properties and composition of mineralised
dentine vary with distance from the predentin to
the enamel–dentine junction.
• The mineral content of dentine decreases and the
thickness of mineral crystals increases towards
the enamel–dentine junction.
• Hardness and elastic modulus decrease towards
the DEJ.
• The most peripheral region beneath the enamel:
mantle dentine.
• Predentin is the innermost unmineralised layer
22. MANTLE DENTINE
• It is slightly (approx. 5%) less
mineralised.
• The collagen fibrils are largely oriented
perpendicular to the enamel–dentine
junction.
• The dentinal tubules branch profusely in
this region
• Mineralisation in the presence of
matrix vesicles
• Varies in width from 20 μm to 150 μm
23. Interglobular
dentine
• Incomplete fusion of
calcospherites.
• Beneath the mantle layer
in the crown and the
granular layer in root.
• Dentinal tubules pass
without deviation through
interglobular areas
26. Age-related and posteruptive
changes
• Related to age: secondary dentine and
translucent dentine.
• Response to a stimulus (caries or attrition):
tertiary dentine, sclerotic dentine and dead
tracts.
27. Secondary dentine
• Structure is very similar to that of primary
dentine
• Change in direction of the dentinal tubules
• The same odontoblasts continue to lay
down similar dentine and the tubules of
primary and secondary dentine are
continuous.
• Slower rate of deposition
• Secondary dentine formation begins at the
completion of root formation as the tooth
comes into occlusion.
• Secondary dentine forms most rapidly on
the pulpal floor.
• Its continuing deposition leads to smaller
pulp chambers and narrower root canals
28. Translucent Dentine
• With ageing, tubules become
completely occluded with
peritubular dentine to form
translucent dentine.
• At the root apex and
increases linearly with age
• Used in forensic dentistry
to help determine the age
of a person
29. Tertiary dentine
• Due to external stimuli.
• Few and/or irregularly arranged
tubules; or it may be relatively
atubular.
• No continuity of dentinal tubules
between normal dentine and
tertiary D.
• Variety of names (irregular
secondary dentine, reparative
dentine, reactionary dentine, and
osteodentine)
• production by newly
differentiated mesenchymal cells
30.
31. Sclerotic dentine
• Dentinal tubules fill in response to external
stimuli (slowly advancing caries or severe
attrition)
32. Clinical considerations
Permeability of dentine
• Tubular structure allows substances applied to its
outer surface being able to reach and affect the
dental pulp.
• Ex: bacteria of dental caries and the toxins
– dental materials, or etchants
depends on:
• Exposure of the dentine surface ( caries, attrition,
abrasion or trauma)
• Patency of the tubules (peritubular dentine,
exogenous material)
• Sealed off from the pulp (tertiary dentine)
• Outward movement of interstitial ‘dentinal’ fluid
• Intact odontoclasts layer ( barrier)
33. Response to external
stimuli
Caries, attrition
• Deposition of tertiary dentine
provides a barrier to the progress
of caries and toxins.
• Secondary dentine -barrier
Cavity preparation
• Drilling through dentine open a
pathway towards the pulp.
• Depth, age (younger less dentine
thickness, less amount of
peritubular dentine).
• Heat during drilling
34. Adhesion of dental
materials to dentine
• New materials adhere to
enamel and dentine.
• Less pulpal injury and
improved aesthetic results.
• Adhesion to dentine is more
complex than that to enamel.
– high organic and water content
– tubular architecture,
– Its heterogeneity,
– its age changes and its reactions to
caries.
– a smear layer
35. Endodontics
• The continuous deposition of
secondary dentine throughout
life
• Deposition of tertiary dentine
• Leads to oobliteration of the
pulp chamber and root canals
Endodontics applications
37. 1st hypothesis:
• No free nerve endings in outer parts of dentine.
• Application of local anaesthetics to the surface does not abolish
the sensitivity.
2nd hypothesis:
• No evidence to show odontoblast process is analogous to a nerve
fibre and conduct impulses..
• Odontoblast procesess do not extend to the enamel–dentine
junction.
• Application of local anaesthetics to the surface does not abolish
the sensitivity.
• Odontoblasts have not been shown to be synaptically connected
to nerve fibres.
3rd hypothesis:
• The most plausible hypothesis
• Fluid movement through the dentinal tubules depolarise nerve
endings at the pulp–predentine junction and in the
subodontoblastic neural plexus
39. Role of the supporting
apparatus?
• Protects the teeth from masticatory
forces – facilitates normal oral function
preventing premature loss of teeth
41. Gingiva
• Part of the masticatory
mucosa which covers
the alveolar process
and surrounds the
cervical portion of the
tooth.
42. The gingivae – Comprise:
• Free Gingival margin (the visible edge of the
gingiva)
• Gingival sulcus (crevice):0.5-3 mm deep
• Free gingiva (FG) – a mobile cuff of gingiva,
above alveolar crest
• Free gingival groove (FGG)
• Attached gingiva (AG) – a band of 1-9 mm in
height, bound to the underlying alveolus &
cementum by collagen fibres of DG complex
• Muco-gingival junction (MJG)
44. Alveolar mucosa & MGJ
• Alveolar mucosa- Dark red, located apical to
the MGJ. Loosely bound to the underlying
bone – movable
• MGJ – Where AG joins the oral mucosa.
45. Gingival Crevice & GCF
• Gingival sulcus (crevice) – Between FG and
tooth crown in health.
• Clinical probing depths 0.5-3mm (20 –25 g
probing pressures).
• Crevice washed out by GCF (GCF flows out at a
rate of 0.2 µl / hour. GCF contributes about 1ml
/ day to saliva)
46. Contents of the GCF in health?
• Same as serum, except for RBC
• Viable neutrophils (PMNLs) can be collected
• With inflammation,
GCF Transudate ------>More like an
Inflammatory exudate during inflammation
(Increased flow rate & volume due to local
components of inflammatory process)
47. The epithelium covering the free
gingiva -
1 Oral epithelium (OE) - faces the oral cavity.
2 Oral sulcular epithelium (OSE) - faces the tooth
without being in contact with the tooth surface.
3 Junctional epithelium (JE) - provides the contact
between gingiva and the tooth.
49. How is structure of JE related to function?
• Non-keratinized JE – permeable (tissue
defence mechanisms possible) –permeability
allows GCF carrying PMNLs, complement &
antibody as components of immune-inflam:
response ). Manifested by infiltration of
inflammatory cells
How is the integrity of the JE maintained?
• High cellular turn over (Divides faster than
any other normal epithelium)
• 2-6 days (JE) Vs 1 month (OE)
50. Clinical relevance of JE:
• Apical migration of JE – 1st clinical indicator
of periodontal attachment loss;
Results in formation of a true pocket.
• JE – key to determine when gingivitis
progresses to periodontitis.
51. Gingival Connective Tissue
predominant tissue component of gingiva (also in
PDL)
Components
• Ground substance, blood, lymph & neural
tissue.
• Major components of CT fibres - collagen
fibre bundles.
52. Fibres in GCT
• Collagen fibres - most predominant and most
important type
• Reticulin fibres - found at the epithelium-CT
and endothelium-CT interface
• Oxytalan fibres - in gingiva & PDL. Function is
unknown
• Elastic fibres - only in association with blood
vessels
54. Dento-gingival fibres (DGF)
• Embedded in the cementum of the supra-
alveolar portion of the root. Project from the
cementum into the free gingival tissue of
facial, lingual & interproximal surfaces, in a
fan-like configuration.
55. • Dento-periosteal fibres (DPF)-
Embedded on the same portion of the
cementum as DGF, but run their course
apically in the tissue of attached gingiva.
57. Circular fibres (CF) –
• Run their course in the free gingiva and
encircle the tooth in a cuff- or ring-like
fashion.
58. Trans-septal fibres (TF)
Embedded in the cementum of adjacent
teeth. Run straight across supra-
alveolar cementum of approximating
teeth.
59. Purpose of collagen fibres in GCT
Maintain a tight gingival cuff & tight adaptation of
gingiva to tooth – restrict subgingival microbial
colonization.
All fibre bundle groups reinforce the interdental
papilla and provide resilience and tone necessary
for maintaining integrity of the dentogingival
attachment.
60. Age changes of gingiva
Age and inflammation related changes
• The level of the junctional epithelium relative
to the tooth surface shifts apically with age
and it is believed inflammation is an
important factor that contributes to this apical
migration. This apical shift is gradual and if it
is accelerated then it is a pathological
condition referred to as gingival recession.
61. Age changes of gingiva
• With age – progressive apical migration
of the dento-gingival junction.
• Increased height.
62. Root Cementum
• Thickness - varies at different levels of the
root. Thinner coronally (0.05-0.1mm at CEJ)
and thicker apically (0.2-1mm)
• Thickest at the root apex
• Thinnest cervically
64. Classification of cementum
• 1) Acellular (primary) cementum
• 2) Cellular (secondary) cementum
Primary/Acellular Cementum
• Forms next to the dentine & around
inserting PDL fibres (sharpey’s fibres)
65. Secondary Cementum
• Found mainly in the apical area & overlying
the acellular cementum
• Formed during functional needs (e.g.
compensatory tooth eruption due to
attrition)
• Cementocytes are numerous
66. Cementum formation
• Cementum formation - occurs throughout
life, slowly (surface being covered by a
layer of uncalcified matrix or
precementum) -This allows for continual
reattachment / new attachment of the
PDL fibres.
67. Incremental lines of cementum
Rhythmic deposition.
• Periods of activity alternating with periods of
quiescence.
• Periods of decreased activity - associated with
incremental lines.
68. Functions of the cementum
• Prime function: To give attachment to
collagen fibres of PDL (Anchors the PDL
fibres to root surface)
• Protects root dentine
70. • Pattern 1 - cementum overlaps (60%-
predominant arrangement).
• Pattern 2 - C & E meet at a butt joint
(30%)
• Pattern 3 - C&E fail to meet (10%).
• Clinical implication ?- Pattern 3 will lead
to sensitivity with the slightest root
exposure.
• (In a given tooth, can have even all 3
types, but one type can predominate).
71. Resorption and repair of
cementum
• Cementum - less susceptible for resorption
than bone under same pressure (eg: with
orthodontic loading)
• But, most roots of permanent teeth, show
small localized areas of resorption - by
odontoclasts)
• Cause of resorption ? Not clear, Micro-
trauma? – a possibility
72. Cementicles
• Small globular masses of cementum
found on 35% (appro.) of human roots.
• Not always attached to the cemental
surface.
• May be located free in the PDL.
73. Cementicles
FC – Free cementicle
SC-sessile cementicle
May result from micro-trauma (When
extra stress on the Sharpey’s fibres
causes a tear in the cementum.
Commoner in apical and middle 1/3 of
the root and root furcation areas.
74. Hypercementosis
• Cementum deposits continuously and slowly
throughout life.
• Chronic periapical inflammation - hypercementosis
(localized)
• Hypercementosis in all teeth - Paget’s disease
• Clinical implications :Difficult extractions.
75. Periodontal Ligament (PDL)
• Dynamic structure
• Soft, richly vascular, dense & fibrous
cellular connective tissue
• Occupies between the root of the
tooth & the alveolus.
• PDL : 0.2-0.4 mm wide.
76. PDL- boundaries & structural
relationship with tissues around
• Above alveolar crest, PDL is continuous with
the connective tissue of the gingiva.
• At the apical foramen- continuous with the
dental pulp.
77. Clinical implications
• Gingivitis sometimes progresses to
periodontitis.
• Any pulpal infection through apical
foramen – infection of apical PDL
(endo-perio lesion).
78. Functions of PDL
1) Provides attachment between tooth
(via cementum) & alveolar bone.
2) Resists, displaces occlusal forces.
3) Protects dental tissues from damage
caused by excessive occlusal load
(especially at the apex)
79. 4) Allows normal function by “physiological”
mobility (up to 0.2 mm).
This slight mobility of teeth – essential for
function. Tooth mobility - largely determined
by the width, height & quality of the PDL
5) Provides sensory input for reflex jaw activities
via mechanoreceptors
6) PDL- responsible for mechanisms to maintain
the functional position of a tooth.
Functions of the PDL, cont--
80. Functions of the PDL, cont--
• 7) Its cells form alveolar bone &
cementum (also maintain & repair both
structures).
• 8) Neurological control of mastication
(by mechano-receptors). Type II
mechano-receptors: primary mechano-
receptors in PDL
81. • Shape of the PDL space - hour-glass
appearance (Narrowest at the mid root
level - where it acts as a fulcrum during
orthodontic load).
• Width of the PDL - varies according to
functional state of the periodontal
tissues.
82. • Non-functional & un-erupted teeth -
narrower space – minimal physiological
mobility.
• Teeth subjected to heavy occlusal stress
- increased space.
• Age changes ? PDL narrows with age
slightly.
83. Structure of the PDL
1) Fibres:
• Arranged collagen fibre system
84. PDL fibres A) Transseptal (Gin), (B) Alveolar crest, (C)
Horizontal, (D) Oblique, (E) Apical, and (F) Interradicular
Structure of the PDL
85. Specific functions of oblique fibres:
• Form a suspensory ligament which
translate pressure on the tooth into
tensional forces on the alveolar wall.
86. • Other than distinctive bundles -numerous
randomly oriented collagen fibres - makes a
fibrous plexus.
• Rate of turn over of collagen in PDL - faster
than virtually all other connective tissues.
Highest turnover towards the apex.
• Reason for high turn over? Maybe functional
demands - occlusal stress needing remodeling.
87. All Fibres of the PDL
• Mainly collagenous (90% of all PDL fibres)
• Oxytalan & reticuline fibres (small amounts)
• Collagen of the PDL - Mainly type I
• (Type I- major protein component of most
connective tissues (including bone & skin).
88. Main components in ground
substance in PDL
• Hyaluronidase; glycosaminoglycans-
mainly.
• Proteoglycans
• Glycoproteins
• All ground subs components - secreted
by fibroblasts.
89. Functions of Ground
substance -
1) Ion and water binding & exchange.
2) Control of collagen fibrillogenesis.
3) Fibre orientations.
90. Cells of the PDL
• Fibroblasts: most predominant connective tissue cell
• Osteoblasts
• Cementoblasts
• Osteoclasts
• Cementoclasts
• Undifferentiated mesenchymal cells
• Defense cells
• Epithelial cells (Cell Rests of Malassez).
91. Bone resorption
• During orthodontic tooth movement?
• A PDL placed under pressure will result
in bone resorption whereas PDL under
tension results in bone formation.
92. Alveolar Bone
• That part of the maxilla or mandible which
supports and protects the teeth.
• Arbitrary boundary - level of the root apices
(separates alveolar bone from the body of the
mandible / maxilla).
93. Alveolar bone-
• Finer at the margins (coronally), thicker
towards the root apex.
• Dense facial & lingual cortical plates – meet
at the alveolar crest.
• Al crest situated 1-1.5 mm apical to CEJ.
• Radiographically, radio opaque line (lamina
dura)- dense cortical bone lining the alveolar
socket).
95. • Radiographyically, loss of continuity of
lamina dura- The 1st sign of bone
demineralization, often occurs at
interdental alveolar crest
• Cortical bone thickness varies –
• Thinnest - mandibular incisor region
• Thickest - mandibular molar
96. Functions of alveolar bone
• Distribute and absorb forces generated by
mastication and other tooth contacts.
• Serves as an attachment apparatus for the
teeth.
• Provides a framework for bone marrow.
• Acts as a reservoir for ions (especially Ca).
97. Alveolar bone
• Alveolar bone - provides strength (allows
it to remodel according to functional
demands.
• Al bone - tooth-dependent bone.
• Anodontia - poorly developed.
• Following tooth extraction - atrophies.
98. Cell types in bone - 5 types
1) Bone forming cells- osteoblasts
Found on the surface. Cells are “trapped”
in their own secretions.
2) Osteocytes - When osteoblasts
subsequently get incorporated into the
matrix – called osteocytes.
99. • 3) Large multi-nucleated cells - osteoclasts -
responsible for bone resorption.
• 4) Osteoprogenitor cells - mesenchymal
fibroblast-like cells. Regarded as forming a
stem cell population to generate osteoblasts
(Situated near blood vessels of the PDL).
100. • 5) Bone-lining cells (flattened,
undifferentiated, inactive osteoblasts)-
• Provide a lining to the bone surface,
when al bone is not being deposited or
resorbed (throughout a considerable
part of adult life).
• No important function - may be related
to ion exchange.
101. Bone resorption
• Bone turnover is controlled by the RANK/RANK-L/OPG
system.
• RANK expressed by osteoclasts.
• RANK-L (RANK-ligand) is a ligand that binds to RANK,
and is expressed by bone stromal cells, osteoblasts and
fibroblasts.
• Binding of RANK-L to RANK results in osteoclast
differentiation and activation, leading to bone resorption.
• IL-1β and TNF-α regulate the expression of RANK-L.
• OPG (osteoprotegerin): binding inhibits resorption.
