Understanding Dental Enamel

• The presentation covers the histology of enamel and intended learning outcomes.
• The session aims to enable students to describe the composition and structure of enamel.
• Students will learn how enamel structure relates to its function.
• Distinguishing the clinical appearance of enamel over a lifetime.
• Apply knowledge to interpret the clinical significance of enamel in health and disease.

Assessment

• Formative assessment includes workbooks and quizzes to support learning.
• Summative assessment covers e-assessment for Oral Dental Sciences.

Histology of teeth tissues

• Enamel
• Dentine
• Pulp
• Cementum
• Bone (alveolar)
• Periodontal ligament
• Gingiva

Why learn enamel histology?

• To effectively support, maintain, and improve oral health for patients.

Knowledge Check

• Consider where enamel is located.
• Recall the embryonic origin of enamel.
• Consider how the embryonic origin links to enamel structure and properties.
• Refer to lectures on Oral Embryology and Tooth Morphology.

Enamel composition

• Enamel is 96% inorganic minerals, and 4% organic material.
• Calcium hydroxyapatite (Ca5(PO4)3OH) is the majority mineral, with carbonate and fluoride as minorities.
• The organic content includes fibrous material (collagen), water, and some proteins.

Overview of Enamel Structure

• Key components include enamel rods (prisms), interrods, and crystallites (calcium hydroxyapatite).
• Enamel structure is linked to amelogenesis.
• Incremental lines
• Prismless enamel (rod-less)
• Dento-enamel junction and other microscopic features are important.

Enamel Rods

• Millions of enamel rods (prisms) make up the structure of enamel.
• Rods are tightly packed and organized in a 'keyhole shape in cross-section.
• Each rod contains millions of calcium hydroxyapatite crystallites, the mineral/inorganic content.
• Enamel rods in cross-section: the head of the keyhole is 5mm in diameter, the tail is 9mm long

Enamel Rods Structure Details

• The keyhole shape reflects the head and tail of the enamel rod.
• The head orients toward the occlusal/incisal surface, the tail toward the cervical region.
• The tail is also known as an interrod
• Rod and interrod surrounded by an organic sheath.

Enamel Crystallites

• Millions of crystallites (hydroxyapatite) tightly pack each rod in keyhole shapes.
• Crystallites are extremely long, thin, and ribbon-like, running the thickness of the enamel.
• Crystallites orient parallel to the long axis of the rod in the head, and diverge slightly in the tail.
• Crystallite arrangement enhances enamel strength.

Enamel Rod Orientation

• Rod direction varies to account for tooth shape.

• Rods direct more horizontally-apically at the cervical margin.

• Rods are almost vertical at the cusp tips.

• Enamel thickness varies, thickest at cusp tips and incisal edges, thinnest at cervical margins.

• Enamel rods run from the dento-enamel junction (DEJ) to the enamel surface.

• Rods traverse in an s-shape manner.

• Rods position perpendicular to dentine at the DEJ.

• Rods are twisted at the cusps forming gnarled enamel.

• Structural features add to the strength of enamel.

• Rod direction is a key consideration in cavity preparation.

• It avoids unsupported enamel to prevent fracture and failure.

Enamel Rods and Amelogenesis

• Ameloblasts form enamel rod structure during amelogenesis.
• Each enamel rod (and interrod) is formed by one ameloblast.
• Ameloblast lifecycle is significant because enamel becomes inert, lacking cells during its life.
• Amelogenesis patterns result in incremental lines.

Incremental Lines

• Incremental lines represent the pattern of amelogenesis occurring in waves during active and rest growth phases.

• The rings of growth in teeth are called Stria of Retzius similar to growth rings in trees.

• These lines may be detected clinically as normal subtle features or as more distinct features

• Stria of Retzius are visible under a microscope in ground sections of enamel, appearing as growth rings/lines.

• Perkymata are edges of the Stria of Retzius visible as shallow furrows on the enamel surface.

• Perkymata are located where incremental lines reach the surface on labial/buccal surfaces.

• Perkymata are most marked when newly erupted and gradually wear over time.

• Perkymata are visible clinically.

Prismless Enamel

• Some enamel areas have unstructured enamel known as prismless/aprismatic.

• The very first and last formed enamel shows no usual prism structure.

• The crystals are parallel with the surface in 'prismless' enamel.

• 'Prismless' enamel is 30 microns wide at the surface and highly radio-opaque.

• Due to more fluoride and carbon it's harder and less soluable.

• This enamel type is key for demineralisation/remineralisation

• 'Prismless' enamel is seen in primary dentition and 70% of permanent dentition, mainly in cervical regions.

• A clinical consideration: It may interfere with optimal etching.

Dentine-Enamel Junction (DEJ)

• The junction between enamel and dentine forms following dentinogenesis and amelogenesis.
• Scalloped appearance under a microscope is thought to strengthen the bond between two materials.

Structural Features at the DEJ

• Enamel Tuft thought to result from abrupt changes in direction of enamel rods.
• Such change is because of the scalloped boundary of enamel at DEJ.
• Possibly supports the bond between dentine and enamel
• No known clinical significance
• Seen in traverse sections of enamel

Enamel Spindles

• Enamel Spindles are extensions of dentine tubules into enamel.
• They may result from odontoblast processes extending into the ameloblast layer. It become trapped since dentine starts to form before enamel.
• These spindles possibly contribute to minor sensitivity.

Microscopic Features

• Features only visible under a microscope help to grasp the histological structure

• Light and dark bands under a light microscope are Hunter-Schreger Bands.

• Observed in longitudinal section running upwards from dentine.

• Cross-sections appear as growth rings.

• Lamellae appear as cracks in enamel due to developmental defects.

• Lamellae appear as jagged lines on the crown surface.

• Lamellae extend inwards, possibly reaching the dento-amamel junction.

• Lamellae result from ameloblasts ceasing enamel production.

• Lamellae can be mistaken for cracks in enamel, and vice versa.

Functions of Enamel

• Protection
• Eating
• Ion exchange
• Inability to repair or feel injury
• Smile

Function Linked to Structure

• Functions:
  • Protects the tooth/pulp.
  • Facilitates eating: chewing, biting etc.
  • Cannot repair or feel injury.
  • Enables remineralization and demineralization via ion exchange.
  • Provides an aesthetically pleasing 'pearly whites' smile.
• Structure:
  • Thickest at cusp tips, occlusal and incisal surfaces.
  • Covers the entire crown.
  • Inert tissue (no living cell due to limited ameloblast lifecycle).
  • The hardest biological tissue.
  • Highly mineralized.
  • A white translucent crystalite structure.
  • Consists of permeable 'micropores.'

Changes in Enamel Over a Lifetime

• Over time enamel is subject to tooth wear, including attrition, abrasion, and erosion.

• Perkymata wear away, and scratches and cracks develop

• Color changes occur with reduced translucency as underlying dentine turns yellow.

• The aging process leads to reduced 'permeability' and exchange of ions (Ca, PO, F-).

• Exposure to topical fluoride on younger teeth has clinical significance in early enamel lesions.

• As a mineralized structure, enamel undergoes demineralization (mineral loss) and remineralization (mineral uptake).

• Acidic conditions favor demineralization.

• Alkaline conditions favor remineralization with fluoride and calcium phosphate uptake.

• Enamel has a critical pH of 5.5.

• Lacking living cells, enamel cannot repair itself or feel injury.

• This lack allows early dental caries stages to progress unnoticed.

• Enamel composition and structure is relevant for clinical carie prevention and treatment.

Clinical Application

• The clinical application covers preventive and restorative care.

• Fluoride incorporated into enamel (fluorapatite) has a critical pH of 4.5.

• Lower than hydroxyapatite, and more resistant to acids and demineralization

• Acid etching removes minerals from the enamel surface, creating 'tags'.

• 'Tags' enable the bond to fill in and stick the composite.

• There is significance of the DEJ in caries

• Focus on breakdown of enamel

• Consider progression of caries into dentine and pulp

• Note lesion size differences in enamel versus dentine at the DEJ...

• Radiopaque structures of enamel, dentine, and alveolar bone signify mineralization.

• A radiolucent enamel area indicates interproximal caries without breaching the DEJ.

Structural Abnormalies

• Clinically distinct: an exaggerated line representing the distinction between enamel that form before birth and after birth.

• Neo-natal line usually reflects disturbances in amelogenesis at birth (perinatal).

• Other instances may be systemic distubances during amelogenesis or tetracycline stating

• Defects in the enamel structure due to disturbances during amelogenesis.

• Can be due to Local instances such as from trauma

• Can be Systemic disturbances that affect all the teeth forming at the time such as

  • Fluorosis (too much fluoride)
  • Exposure to tetracycline,
  • Nutritional deficiencies
  • Molar-incisor hypomineralisation affects

• It can be Genetic factors, also may affect all teeth suh as amelogenesis imperfecta affecting these defects.

• They result in significant clinical implications

Structural Abnormalities in Enamel

• Defects during amelogenesis result in enamel causing hypoplasia or enamel hypomineralisation.
• These defects are collectively known as molar-incisor hypomineralisation.
• The impact ranges from minimal to significant clinical implications.

Explore dental enamel composition and its characteristics. Learn about age-related changes, fluoride's role, and enamel's inability to self-repair. Understand the orientation of enamel rods and their significance in dental procedures.