Oral Histology6: Enamel & Dentin

Flashcards covering key terminology and concepts related to enamel and dentin from the DMD700 Oral Histology lecture.

Enamel

Avascular structure covering the tooth, consisting of interlocking rods, non-vital, and not renewable.

Avascular

Lacking blood vessels; characteristic of enamel.

Ameloblasts

Cells responsible for the formation of enamel.

Hydroxyapatite

A crystalline calcium phosphate that constitutes about 95% of enamel.

Striae of Retzius

Incremental lines in enamel resulting from rhythmic deposition.

Neonatal line

A notable line of Retzius associated with birth indicating a change in nutrition and environment.

Enamel tufts

Cracks in the enamel surface extending from the DEJ toward the enamel.

Enamel lamellae

Cracks in the surface of enamel visible to the naked eye.

Dentinoenamel junction (DEJ)

The interface where dentin meets enamel.

Dentin

Living, sensitive hard tissue that makes up the bulk of the tooth.

Odontoblasts

Cells responsible for the formation of dentin.

Sclerotic dentin

Dentin with obliterated tubules believed to protect the pulp.

Secondary dentin

Dentin formed in response to mastication after the crown has engaged in occlusal function.

Tertiary dentin

Also known as reparative dentin; forms in response to pulpal stimulation or injury.

Incremental lines

Lines formed in dentin due to the periodic deposition of dentin.

Dentinal tubules

Microscopic channels in dentin containing odontoblast processes.

Peritubular dentin

Highly mineralized dentin surrounding the dentinal tubules.

Intertubular dentin

Dentin found between the dentinal tubules.

Granular layer of Tomes

Granular appearing layer of dentin underlying the cementum covering the root.

enamel 

avascular, lacks nerve supply, not renewable 

enamel rods

keyhole shaped ameloblasts that lay down enamel

enamel

95% inorganic mineral substance primarily composed of hydroxyapatite and 5% water and organic matter

hydroxyapatite

crystalline calcium phosphate found on bone dentin and cementum 

organic component of mature enamel

protein called enamelin

enamel: gray as…

dentin: yellow

enamel thickness

ranges from thin knifelike edge at cervical margins to 2.5 mm over occlusal or incisal surfaces

rod structure

extend from DEJ to enamel outer surface

one enamel rod

formed by 4 ameloblasts

keyhole/ raquet/fish shaped

enamel rod shape used to maximize space of crystalline matter to ensure structural integrity and strength. the more crystal=less organic material=harder to degrade

rod orientation of each part of the crystal 

crystals in the head follow the long axis of the rod 

crystals from the tail are perpendicular to the head 

rod orientation 

rods are perpendicular to the DEJ and curve toward cusp tips 

parts of a rod

sheath surrounding surface with a core at the center

the sheath contains more organic material than the core

interrod enamel

enamel running between the crystalline rod structures with the purpose of filling the space with even more enamel

ordered correctly 

perpendicular at cervical region and intertwined at cusp tips

enamel rod pattern

because enamel rods interdigitate 

the hunter-schreger bands phenonenon occurs 

hunter-schreger band phenomenon

banding appearing in the 1/2 -2/3 thickness of the tooth due to lights bouncing off interdigitated enamel rods

outer enamel

prismless enamel with no banding effect due to completely perpendicular enamel rods

incremental lines in enamel 

due to rythmic changes in deposition of enamel 

Lines of Retzius or striae

lines of entrapped air molecules accentuating developmental lines

most famous line of Retzius due to major changes in nutrition and environment

neonatal lines

prenatal enamel 

has fewer defects than post natal enamel 

enamel lamellae

cracks in the surface of enamel that are visible to the naked eye

enamel lamellae

extend from surface DEJ, are a possible avenue for bacteria, and can be due to impact or temperature

enamel tufts 

areas of disorganized enamel rods mixed with enamalin located at DEJ. thought to be areas of more dentin like structure between layer seperation

enamel spindles

extensions of dentinotubles that arise in DEJ and extend to enamel

enamel spindles are

shorter and thinner that enamel tufts 

enamel tufts

enamel spindles

enamel surface

smooth or with fine ridges called perikymata or imbrication lines on facial surfacethat cover the outer layer of the tooth, providing protection and aesthetic quality.

imbrication lines/perikymata

permeability of enamel

caused by…

leakage around restorations

decomposition of tooth

lamellae, cracks, tufts and spindles

microlamellae

irregular surfaces

microlamellae

minute spaces around enamel rods that increase tooth permeability and can harbor bacteria.

etching

dilute acids that alter surface enamel and provide adherence to enamel rods 

peripheral enamel rods…

resist demineralization to a greater extent than rod core

attrition

tooth on tooth contact wear

abrasion

caused by external forces like brushing

erosion

caused by acid wear 

abfraction

loss of structure due to occlusal force imbalances

dentin

body of the tooth

dentin is living

true

dentin coverings at

root is covered by cementum

crown covered by enamel

dentin is like bone…

as it is made of mostly organic matrix of collagen fibers and mineral hydroxyapatite crystals

dentin classification

based on time of development

primary, secondary, tertiary

dentin

bulk of tooth made of 70% hydroxyapatite, 20

5% organic collagen and 10% water

dentin is has less ____ and is ____ than enamel

mineral 

softer 

radiolucency of dentin

more than enamel and less than pulp 

dentin resilience 

due to dentino tubules present in matrix the elasticity and strength make for a material that resists mastication forces and prevents fractures.

where is dentin first laid

initial dentin is formed at cusp tips and activates more odontoblasts to activate along the DEJ eventually being moved towards the pulp as the tooth develops.

what is present in a dentinotubuole

odontoblast processes dentinal fluid and extracellular matrix substances

predentin

band of newly formed unmineralized dentin at pulpal border 

dentin formation

stage 1: organic matrix is deposited

stage 2: mineral substance is added

predentin is evidence of 

step 1 of dentin formation

mineralization occurs at

the predentin-dentin junction

mantle dentin

first primary dentin formed, deposited at the DEJ extending pulpally, serves as a covering over the rest if dentin, and nearly free of defects

globular dentin/ interglobular dentin 

beneath mantle dentin, exists only in the crown, contains hypomineralized areas 

circumpulpal dentin

beneath globular dentin forms the bulk of primary dentin with thick areas in crown and thin areas in roots

order of layers of primary dentin

circumpulpal, globular, mantle

primary dentin

makes up the bulk of dentin in a tooth 

dentinotubules from primary and secondary dentin

form an s curve

odontoblast INITIALLY have multiple processes that secrete

mantle dentin

as odontoblast elongate

they branch at right angles giving dentin vitality

dentin area 

surface is much larger than pulp interface 

larger surface area makes

dentinotubles much closer together at the pulp and sparse on the surface area

peritubular dentin

dentinal matrix immediately surrounding the tubule

intertubular dentin

dentin between dentinotubules 

peritubular dentin is more

mineralized than intertubular dentin

when peritubular dentin proliferates

dentinaltubles diameter shrinks

secondary dentin

formed internally to primary dentin

is a normal response to mastication

occurs with aging

when does secondary dentin form

after crown has started masticatory function and roots are nearly complete

secondary dentin forms _____ than primary dentin

slower

a slow rate of dentin formation 

preserves pulp from being obliterated

tubules from primary and secondary dentin

are Continuous

secondary dentin can also be laid

above pulp horns to appose occlusal forces

tertiary dentin/reparative dentin

is formed in response to injury or irritation of the dental pulp

forms at the site of odontoblast activation

can be deposited rapidly 

appears irregular

cells found in tertiary dentin

odontoblasts, fibroblasts, blood cells

tertiary dentin is deposited slowly and forms more regular dentin due to

fewer or less intense stimuli

reparative dentin

closely associated with bone and can be referred to as osteodentin

sclerotic dentin

formed when dentin tubules are obliterated

forming sclerotic dentin

increases with age

protects pulp

eliminated permeability to pulp