৪৮তম বিশেষ বিসিএস [স্বাস্থ্য] ⎯ ডেন্টাল অংশ [Archived]

Here's a bullet-point comparison between enamel and dentin composition:

Enamel
- Inorganic: 96% (Hydroxyapatite)
- Organic: 1-2% (Amelogenin, enamelin)
- Water: 2-3%
- Hardest tissue in the body
- No collagen
- Avascular, non-vital

Dentin
- Inorganic: 70% (Hydroxyapatite)
- Organic: 20% (Mainly Type I collagen)
- Water: 10%
- Less hard than enamel, but resilient
- Contains collagen
- Vital tissue (contains odontoblast processes)

Structural and organizational features of Enamel:

1. Striae of Retzius
- Incremental growth lines seen in longitudinal sections
- Represent rhythmic enamel deposition during development
- Clinical relevance: perikymata on enamel surface are external manifestations

2. Perikymata
- Shallow grooves on enamel surface (mainly in cervical region)
- Correspond to Striae of Retzius
- Wear away with age or abrasion

3. Neonatal Line
- Prominent Striae of Retzius seen in enamel of teeth formed at birth
- Separates pre- and postnatal enamel
- Useful in forensic and developmental studies

4. Cross Striations
- Seen perpendicular to enamel rods
- Indicate daily enamel deposition (approx. 4 µm/day)

Reference:
Orban’s Oral Histology & Embryology (Chapter 3: Enamel)

Enamel Rods – Key Points:

- Basic structural unit of enamel
- Also known as enamel prisms
- Each rod is cylindrical and extends from DEJ to enamel surface
- Composed of hydroxyapatite crystals arranged longitudinally
- Enamel rods are perpendicular to the dentinoenamel junction (DEJ) in most areas
- In the cervical region, rods tilt slightly apically
- Rods have a keyhole or fish-scale shape in cross-section
- Surrounded by rod sheath, which contains more organic material
- Crystals are tightly packed in the head of the rod and loosely in the tail

Clinical relevance:
- Direction of rods must be considered during cavity preparation to avoid unsupported enamel
- Rod direction affects bonding and etching outcomes

Reference:
The Textbook of Oral Anatomy by Bhalaji (Chapter: Enamel)
Orban’s Oral Histology and Embryology (Chapter: Enamel Rods)

Dentinoenamel Junction (DEJ) – Key Points
(From Textbook of Oral Anatomy by Bhalaji, Chapter: Enamel & Dentin)

— The DEJ is the interface between enamel and dentin.
— It appears scalloped in permanent teeth, enhancing mechanical adhesion between enamel and dentin.
— The concavity of the scallop faces dentin; convexity faces enamel.
— It prevents enamel shearing forces during mastication.
— Acts as a structural and functional bond between hard (enamel) and slightly elastic (dentin) tissues.
— Enamel tufts and spindles often arise near or at the DEJ.

1. Enamel Tufts
- Definition: Small, brush-like structures extending from the DEJ into the enamel (1/3rd depth).
- Origin: Hypomineralized areas with increased organic content.
- Appearance: Tuft-like, seen in transverse sections.
-Clinical Significance: May serve as areas of stress relief; not clinically visible or pathological.

2. Enamel Lamellae
- Definition: Thin, leaf-like vertical structures that extend from enamel surface towards the DEJ, and sometimes beyond.
- Clinical Relevance: May act as pathways for caries or fracture lines.

3. Enamel Spindles
- Definition: Short, linear defects formed by trapped odontoblastic processes during early enamel formation.
- Location: Found at DEJ, especially in cusp tips.
- Appearance: Seen in ground sections as small dark dots or lines.
- Significance: May relate to dentin sensitivity; not structurally significant.

Types of Dentin - Discussion:

1. Primary Dentin
- Forms before root completion
- Makes up bulk of dentin
- Laid down at a regular rate

2. Secondary Dentin
- Forms after root completion
- Deposited slowly throughout life
- Reduces pulp chamber size gradually

3. Tertiary Dentin (Reparative/Reactive)
- Formed in response to injury or stimuli
- Irregular structure
- Protects pulp from further damage

4. Mantle Dentin
- Outer layer of primary dentin
- First dentin formed
- Less mineralized, contains collagen fibers perpendicular to DEJ

5. Circumpulpal Dentin
- Lies beneath mantle dentin
- Bulk of primary dentin
- More mineralized than mantle dentin

6. Interglobular Dentin
- Areas of hypomineralization in dentin
- Located near mantle dentin
- Result of defective mineralization

7. Predentin
- Unmineralized organic matrix
- Lies adjacent to odontoblasts
- Mineralizes to become dentin

Reference :Orban's & Ten cate

Dentinal Tubules:

- Microscopic canals running through dentin from pulp to DEJ
- Contain odontoblastic processes and fluid
- Allow nutrient and signal transport between pulp and dentin
- Diameter varies: wider near pulp, narrower near DEJ
- Responsible for dentin sensitivity (fluid movement stimulates nerve endings)
- Tubule density varies by location; more tubules in crown than root
- Tubules branch and interconnect, forming a complex network
- Mineralization around tubules forms peritubular dentin, which is highly mineralized

Incremental Lines of Dentin (growth lines) reflect the rhythmic pattern of dentin formation:

1. Lines of von Ebner
- Daily incremental lines
- Spaced about 4 μm apart
- Indicate daily matrix deposition
- Found in primary and secondary dentin

2. Contour Lines of Owen
- Also called Andresen lines
- Represent metabolic disturbances
- More prominent than von Ebner lines
- Irregular spacing

3. Neonatal Line
- Found in dentin and enamel of teeth formed at birth
- Marks the physiological stress during birth

4. Imbrication Lines
- Sometimes used synonymously with von Ebner lines

Reference:
The Textbook of Oral Anatomy by Orban (Chapter: Dentin)
Ten Cate’s Oral Histology (Chapter: Dentin)

Composition of Cementum
Reference: Ten Cate’s Oral Histology, Chapter 9: Periodontium)

➤ Inorganic content:
- About 45–50% of cementum
- Composed mainly of hydroxyapatite crystals

➤ Organic content:
- About 50–55%
- Mostly Type I collagen (90%)
- Small amounts of Type III and XII collagen
- Proteoglycans, glycoproteins (e.g., osteopontin, bone sialoprotein), non-collagenous proteins
- Embedded Sharpey’s fibers (from periodontal ligament)

➤ Cells:
- Acellular cementum: No cells
- Cellular cementum: Contains cementocytes in lacunae with canaliculi directed toward PDL.

Functions of Cementum
(Reference: Ten Cate’s Oral Histology, Chapter: periodontium)

— Anchorage
• Provides attachment for the periodontal ligament (Sharpey’s fibers), anchoring the tooth to the alveolar bone.
— Protection
• Covers and protects the underlying dentin, preventing sensitivity and bacterial penetration.
— Repair
• Participates in repair and regeneration of the root surface after resorption or injury.
— Compensation
• Compensates for occlusal wear by continuing to deposit cementum at the apical region, helping maintain tooth length.
— Adaptation
• Adapts to functional stress by forming cellular cementum in areas under pressure.

See Table 6.1 Differences in AEFC and CIFC from Chapter:6 Cementum of ORBAN'S Oral Histology and Embryology.

Cementoenamel Junction (CEJ)
(Reference: Ten Cate’s Oral Histology, Chapter: Periodontium)

Definition:
The CEJ is the anatomical boundary where enamel of the crown meets the cementum of the root.

Types of CEJ Relationships:
1. Cementum overlaps enamel – ~60–65% (most common)
2. Edge-to-edge (butt joint) – ~30%
3. Gap between enamel and cementum – ~5–10% (exposes dentin → may cause sensitivity)

Clinical Significance:
- Variations may influence sensitivity, restorative margin placement, and scaling techniques.
- A gap at CEJ can cause dentinal hypersensitivity.
- Knowledge of CEJ is crucial in periodontal therapy.

Sharpey’s Fibers
(Reference: Ten Cate’s Oral Histology, 9th Edition, Chapter: Cementum & Periodontium)

Definition:
Sharpey’s fibers are terminal portions of the principal collagen fibers of the periodontal ligament (PDL) that insert into the cementum and alveolar bone.

Key Features:
- Composed of Type I collagen.
- Embedded into both cementum and alveolar bone.
- Help anchor the tooth securely in its socket.
- More mineralized in bone than in cementum.
- Denser in acellular cementum compared to cellular cementum.

Function:
- Provide attachment between tooth and bone.
- Help resist forces of mastication.
- Contribute to proprioception.

More common at the orifice of pulp chamber or within the root canal.
※ ref  Tencate's oral Histology 9th edition page 190 

the neural termination of periodontal  ligament follows 3 ways 
1. branch out like trees 
2.spindle ship like Ruffini's corpuscles
3. Coiled
※ Ref  AK Das page 143 

Undifferentiated mesenchymal cells in periodontal ligaments may  Converts into
1. Fibroblasts 
2. Osteoblast
3. Cementoblast
※ Ref  Ten cate 9 edition page 210 

Mast cells is a content of lamina propria 
Lymphatic and minor salivary glans are content of submucous. 
The Basal layer of oral epithelium contain tonofilaments and Markel cell 
Ref. Orban's 15th. Pg- 197

glossy pigmented, pink spongy and porus  is a feature of disease or inflamed gingiva 
※ Ref  Ten cate 9th edition is 283 Orban's 15th edition page 210 

Body of odontoblast - odontoblastic layer
Capillary network - pulp core layer and odontoblastic layer 
Plexus of Raskhow - cell free zone 
Undifferentiated mesenchymal cell - cell rich zone

the lining mucosa of oral cavity is non keratinized  in nature 
※ ref. ten cate  9th edition page 282

Dorsum of  the tongue is covered by specialized mucosa 
※ ref. ten cate 9th edition is page 278 

Filiform papilla is devoid of Taste buds 
※ ref.  Ten cate 9th edition page 278

Stensen's - duct of parotid gland- serous

গ. Kidney, lungs and skin play important role in water balance 
Ref. Ak das page -175

the concentration of IgA in saliva is greater than that of other immunoglobulin  and Association with lower level of dental caries suggest that it is active against the cariburing bacteria 
Ref. Oral Bioscience - ferguson p-144

the concentration of immunoglobulin  A in saliva is greater than that of other immunoglobulin  and it is association  with low level of dental career suggests  that it is active against the cariogenic bacteria

contain of sub-mucosa 
1. Salivary glands
2. Bloods vessels 
3. Nerves 
4. Adipose tissue
Ref. Orbans 14th ed. Page _196

Alveolar group of periodontal fibers 
1. Alveolar crest group
2. Horizontal group
3. Oblique group
4. Apical group 
5. Interradicular group
Ref. AK das page- 141

Maxillary:

Parmanent lateral incisor- Most variable tooth after 3rd molars.

Deciduous lateral incisor-No prominent cingulam. Lingual fossa is deeper.

Mandibular :

Permanent Central incisor-Smallest in all permanent teeth. Bileterally symmetrical only incisor that is both mesio- incisal and disto-incisal are right angle &sharp.Mamelons wear soon after eruption due to mastication



Deciduous Central incisor-Smallest tooth in human dentition and first tooth to erupt into oral cavity. No mammelons &developmental groove are seen.
Root is twice as long as crown


Ref: A K DAS, Arathi Rao

First indication of tooth formation is localised proliferation of oral epithelium at about 12mm C. R stage (6th week of embryonic life). 

It occurs in the lateral region of Both maxillary & mandibular processes..

Proliferation of oral epithelium continues across the midline at the front of mouth & forms a horseshoe shaped structure called primary epithelial band. 



Ref: Scott & Simon

Palmer's Notation/ Zsigmondy's method:
Oldest &used in most countries.


Dane system /Hderup system: popular in Norway, Denmark,Sweden, Finland & Iceland.


FDI system: Two digit system specially designed for computer recording.
1st digit indicates the  quadrant.(both permanent &deciduous). 
2nd digit indicates the individual tooth within the quadrant.


Ref: A  K DAS

Maxillary deciduous first molar:

1.Most Atypical tooth of all molars in human dentition.
2.Looks like an intermediate between a premolar & molar. Basically resembles a premolar.
3.Smallest molar in the mouth.
4.Well developed cervical ridge& more prominent mesially forming molar tubercle of Zuckerkandl. 
5. Occlusal surface is trapezoidal.

Ref: A K DAS

Characteristics of dentition in different races:

A.Mongoloid( Eskimos,American,Indian,chinese)-

1.High prevalence of shovel shaped incisors.
2. Low prevalence of Carabelli's tubercle 
3Frequently absent lower 3rd molar.
4. Five cusped lower 2nd molar is frequent.

B. Negros-
1.Mandibular 3rd molar rarely absent.
2. Supernumerary premolars are common.
3. Dento-alveolar prognathism is characteristic. 
4. Five cusped lower 2nd molar is frequent as mongoloid.

C. White people-
1. Carabelli's tubercle much more frequent than mongoloid &Negro races.
2.Mandibular 3rd molar more frequent than mongoloid but less frequent than Negros.


Ref: Scott & Simon

Characters such as size,shape & Fissure pattern of the teeth are genetically determined.

In human dentition, teeth showed  minimum genetic and racial variable in parmanent dentition are Canines,Central incisors & 1st molars.. 

Ref: Scott &Simon

Permanent teeth are more retarded than deciduous teeth
Ref- Scott& Simon 


Difference between permanent &deciduous teeth:

Ref- A K DAS

Mandibular permanent  1st molar generally has 5 cusp. Distal cusp may absent &look like second molar.
Sixth cusp named tubelculum sextum is seen on distal marginal ridge Between distal cusp and distolingual cusp.
Seventh cusp b named tuberculum intermedium  is seen on distal cuspal Ridge of mesio lingual cusp.

Ref: A K DAS

Canine:

Most stable teeth in dental arch,
Root are thickest & longest.
Last teeth to be lost &least affected by caries.
Four corner stones of dental arches.
Helps to support facial musculatures.
Act as a guide-post in occlusion.

Ref : A K DAS

Teeth are buried due to excessive fibrous gingival tissue in hereditary gingival fibromatosis. Complete eruption is failed & only their tips show in the mouth.This condition is known as pseudoanodontia.

Hereditary ectodermal dyplasia-- anodontia with systemic defect

Down syndome- Hpydondia.

Cleidocranial dysplasia- Hyperdontia(additional teeth)

Ref: Cawson's oral pathology