Lesson 8 - Part 2 Flashcards
Describe the composition of dentin
- 70% Inorganic mineral - Primary dentin, major component of crown and root - Hydroxyapatite crystals
- 20% Organic collagen fibers - and small amounts of protein
- 10% Water
Describe the physical properties of dentin
- More radiolucent than enamel
- More radiopaque than pulp
- Resilient to impact of mastication
- Dentin is pale yellow in color
- Dentin has greater compressive and tensile strengths than enamel
- Dentin is readily permeable due to dentinal tubules
How is dentin formed?
- Dentin is formed by odontoblasts
- Odontoblastic process is an extension of the odontoblastic cell throughout the dentin from DEJ to the pulpal surface
The walls of dentinal tubules are called __________
peritubular dentin
The dentin between dentinal tubules are called _________
intertubular dentin
The outermost layer of dentin is called _________
mantle dentin
*first dentin formed
The layer of dentin around the outer pulpal wall is called __________
circumpulpal dentin
The dentin formed before the completion of the apical foramen is ___________
primary dentin
*formed BEFORE functional eruptive phase
The dentin formed after the completion of the apical foramen is __________
secondary dentin
The dentin formed as a result of injury is ___________
tertiary dentin
Describe the microscopic appearance of dentin
Cross section of dentinal tubules, composed of peritubular dentin containing odontoblastic processes and surrounded by intertubular dentin.
Describe Peritubular dentin
- Dentinal matrix surrounding the dentinal tubule
- Hypermineralized (40%)
- Aging teeth: due to external stimuli, may fill tubule completely with minerals called Sclerotic Dentin
Describe Intertubular dentin
- Main body of dentin, between and around the dentinal tubules
- Few changes throughout life
- Intertubular dentin is Less calcified than intratubular dentin
Describe Imbrication Lines (VonEbner)
- Incremental deposition of dentin and mineralization
- Resulting in hesitation lines with alteration in matrix/mineralization
- NEONATAL line is most obvious from abrupt change in environment at birth
Describe primary dentin1.
- All dentin formed BEFORE functional eruptive phase
- Primary dentin =mantle dentin +circumpulpal dentin
- Primary dentin constitutes the bulk of dentin in crowns and roots of teeth
Describe mantle dentin (type of primary dentin)
- First primary dentin formed at the DEJ
- Serves as a covering (mantle) over the rest of dentin
- Free of developmental defects
- mantle dentin is intertwined with enamel creating a scalloped DEJ –increased adherence (enamel spindles – terminal ends of odontoblastic processes)
Describe Circumpulpal dentin (type of primary dentin)
- Circumpulpal dentin lies directly adjacent to mantle dentin
- Circumpulpal dentin is the bulk of the primary dentin
- Thickness of circumpulpal dentin - 6 to 8 mm in crown, 2 to 6 mm in root
Describe secondary dentin
- Secondary Dentin is dentin formed DURING functional eruptive phase
- Dentin formed after tooth in clinical occlusion - Functional eruptive phase
- Dentin formed when apical foramen/root near completion
- Functional occlusion: signals the rate of formation of dentin to slow down
- Prevents the dentin to continue to grow rapidly and therefore obliterate the pulp
- Tubules of 1st and 2nd dentin are continuous
- Less mineralized than primary dentin
- Noted for regular tubular pattern
- Odontoblastic layer lines the dentin-pulp interface
Describe Tertiary/Reparative Dentin
- Pulpal stimulation - Attrition, Abrasion, Caries, Restorative procedure
- Forms only at site of odontoblastic activation
- Odontoblasts in the area of the affected tubules might perish due to injury - result is Undifferentiated mesenchymal cells of the pulp to become odontoblasts - result is Tertiary dentin tries to seal off the injured area
Describe dead tracks
- Dentinal tubules that are empty due to death of the odontoblasts
- Pathway for bacteria to the pulp
- Rapid penetration of decay with insufficient time for reparative dentin
Describe Sclerotic Dentin
- sclerotic dentin, is often found in association with the chronic injury of caries and is noted as the tooth ages. In this type of dentin, the odontoblastic processes die and leave the dentinal tubules vacant.
- These hollow dentinal tubules then become retrofilled and finally occluded by a mineralized substance similar to peritubular dentin.
List the causes of dentinal hypersensitivity
- Caries
- Cavity preparation
- Attrition
- Recession
- Aggressive hand instrumentation
- CEJ formation
Describe how CEJ formation can lead to dentinal hypersensitivity
enamel and cementum do not meet, leaving exposed dentin on root surface
Describe the Hydrodynamic mechanism of Dentinal hypersensitivity
- Changes in the dentinal fluid
- Evaporation/loss of dentinal fluid
- Movement of the fluid
- Ionic changes in the fluid
- Changes in dentinal fluid are transmitted to afferent axon present in some tubules
- Sending a message from pulp of pain
- Treatment: block exposed open ends of the dentinal tubules
What are the clinical considerations of dentin?
- Exposed dentin readily absorbs stains due to increased porosity, “sponge” for stain
- Hand instrumentation & prophy jet can remove dentin causing increased exposure and sensitivity
- Exposed dentin is rougher in surface texture than enamel
Describe aging and dentin
- With increased age, the diameter of the dentinal tubule narrows because of deposition of peritubular dentin.
- This narrowing may be related to the decreased ability of pulp to react to various stimuli with age.
- Odontoblasts also undergo cytoplasmic changes, including a reduction in organelle content with age.
- Dentin becomes more exposed as a result of both attrition and gingival recession, which may or may not lead to dentinal hypersensitivity.
- Apart from dentin that is resorbed during the shedding of primary teeth, the dentin formed is mostly stable during the life of the tooth.
- However, in a few cases it can become resorbed in permanent teeth (but the cause is unknown [idiopathic]) and can involve either internal resorption or external resorption process. - It can be noted radiographically
