Enamel and dentine caries structure Flashcards
what is caries
localised ,chemical dissolution of tooth surface rough by metabolic activity in a microbial deposit covering tooth surface at any given time
how is caries promoted
frequent dietary supply of fermentable carbohydrates
Dietary habits are thought to induce ecological imbalance within dental biofilm with acidogenic and aciduric bacterial plaque species dominating
Dental caries lesions develop at relatively protected sites in the dentition where dental biofilms are allowed to accumulate and mature over time
what are the sites of caries
pits,grooves, and fissures in occlusal surfaces during eruption,approximal surfaces cervical to contact point/area and along gingival margin
what is acidogenic?
organisms produce acidic metabolites and reduce environmental PH
what is aciduric
organisms capable of growth at acidic PH levels that are often toxic to others
what is the composition of enamel
Highly mineralized, mineral component comprises 95% of tissue by weight
Principle mineral component is calcium hydroxyapatite - contain impurities such as carbonate and magnesium
what is the composition of dentine?
Dentine forms bulk of tooth- not highly mineralised as enamel
Dentine significant organic components of 20%
Water content 10% is high compared to enamel
what is the physicial properties of human enamel and dentine
Enamel hardest tissue in body
Withstands shearing and impact forces
Abrasion resistance high but brittle
how is thee a loss of dentine support
due to progression of caries in dentine, unsupported enamel can fracture resulting in cavitation at tooth surface
how does the properties of enamel vary
Properties of enamel vary at different regions from within tissue: hardness and density decrease from surface towards ADJ
Flexible dentine and compressible helps support overlying enamel- due to organic matrix and tubular architecture
what properties does dentine have when exposed?
poor abrasion resistance,poor resistance to crack propagation and present a poor barrier to diffusion of bacterial by products under caries lesion
describe the structure of enamel
microporous solid composed of tightly packed crystals
Developmental defects - small irregular fissures and micro-pores can be seen histologically within surface zone
Tiny micro channels about 0.5-1.5 micrometres in diameter involved in lesion development - diffusion processes
Openings of striae of retzius at surface via perikymata grooves act as larger diffusion pathways
what is found in the microstructure of enamel
HAP tightly packed within prisms- packaging of crystals slightly looser along prism periphery/boundary (hexagonal)
- Crystal packing tight at microscopic level- crystal separated from neighbours by tiny inter crystalline spaces frilled with water and organic material (prism rods arrangement)
- Prisms perpendicular to ADJ
Intercrystalline spaces together form a fine network of diffusion pathways referred to as micro-pores and open on surface enamel.
how does enamel dissolution occur
occurs by exposure to acid formed by overlying plaque biofilm and by proteolytic action of bacteria on protein content
Acid will penetrate more readily where there is greater porosity : tend to progress down paths provided by prism boundaries
what are prism boundaries
Prism boundaries - main highways through enamel allowing diffusion of molecules form the surface
describe acid dissolution in enamel
irregular psims outlines although central demineralisation and destruction in prism cores is also seen
where does caries progress more rapidly
along hypomineralized areas within enamel including prism boundaries and incremental lines: cross straitons and strait of retzius
describe dentine in cross section
- Large numbers of small,parallel dentinal tubules in a mineralised collagen matrix
-Inner part of tubules contain long processes of cells response formin the tissue,the odontoblast as well as small volume of extracellular fluid - Tubules per cross sectional area and diameters change - extend inwards from ADJ near enamel towards the pulp becoming wider and greater in number
- Superficial dentinal tubules occupy approx 1% of the dentine volume compared to 30% of the deeper dentine volume,
- Deeper dentine is more porous and permeable to bacteria and chemicals than superficial dentine.
what is the early enamel caries called
white spot lesions
how is early enamel caries developed
- Enamel mineral dissolves in presence of acid protons produced by plaque biofilm
- Plaque biofilm can shift ecologically to become cariogenic so it produced and retain low PH at tooth surface
- Repeated demineralisation and remineralisation can give rise to initial caries lesion if equilibrium tips towards acid dissolution and mineral loss
Early stages- opaque white spot lesion
why is there a white spot in early enamel caries
because subsurface enamel becomes porosus as a result of mineral being dissolved by acid produced by plaque bacteria
As porosity increases the lesion may take up stain and knwn as brown post lesion.
Cavitate exposing dentine
LHS- longitudinal section through enamel lesion- lesion has a wedge shape
describe the 4 characteristic zones on enamel caries
1.Translucent - deepest and least affected
2.Body of lesion= most affected part with greatest porosity
3.Intact surface zone= underneath plaque biofilm
4.Dark zone= separated body of leion from translucent zone
describe the pore volumes in each characteristic zone
what does the reminerlasition of enamel caries lesions require
requires calcium and phosphate ions to diffuse to prior subsurface though relatively intact surface zone
Not seem possible to maintain necessary supersaturation in lesion fluid and remineralisation of lesion body is not obtained to any significant degree in vivo
describe the dental caries microstructure
- Purely chemical process with dissolution of HAP by acid
In dentien, caries more complex
Dentine is composite of mineral and caries 3 stage process - Mineral removed by bacterial acid
- Ground substance fills spaces between collagen fibres by enzymes
Enzymatic removal of collagen meshwork, forms scaffold around detinal tubutles
Intertubular dentine= apartie crystals are smaller, less calcium and more carbonate than those in name and more soltulbel
what is interlobular dentine
apartie crystals are smaller, less calcium and more carbonate than those in name and more soltulbel
what is peritubular dentine
- less soluble than intertubular dentine
- Differs from intertubular dentin by lakcign collagenous fibrous matrix
5-12% more mineralized than intertubular enine
how is the initial poplar response activated
ctivated by bacterial acids and cell wall components such as LPS and soluble plaque metabolic products which diffuse towards pulp against natural direction of pulp tissue fluid movement
how does the dentine pulp complex react to irritation
- combination of inflammaiton an promotion of mineralisation
- Various types of pulp cell react and complex series of antibacterial, immune, vascular and localised inflammatory responses are activated
how is pulp vitality preserved?
Core of operative dentistry and offers bioloigcal based concept reduces intervention and maintains the pulps developmental ,defence and proprioceptive
what is reactionary dentine?
dentin forming in response to milder irritation, up regulation of existing odontoblast activity form dentine with irregular appearance with fewer tubules than circumpulpal dentine
what is reparative dentine?
dentin forming in response to stronger stimuli which original odontoblasts in associated regions have destroyed and calcified tissue has been formed by newly differentiated ‘odontoblast-like’ cells. More irregular than circumpulpal
what is tertiary dentine?
- Hard tissue deposited on pulpal surface in response to external stimulus
- Restricted to region beneath irritation and provides barrier to progress of caries and toxins
what is sclerotic dentine?
Tissue formed when dentinal tubules fill in as a response to an external stimulus such as under slowly advancing caries or beneath area of severe attrition.
- Presence of this tissue under a carious lesion can reduce the permeability of the dentinal tubules which communicate with the pulp.
what is followed by caries lesions progression
- eventual cavitation,
- bacterial invasion of dentinal tubules commences
- External bacterial stimuli move towards pulp
- Inflammatory response continues to intensify
- Dental pulp has innate ability to heal if challenge is removed and tooth is suitably restored
- Without preventative treatments lesions may progress further with irreversible inflammation of pulp tissue and eventually loss of vitality of subsequent bacterial colonisation of the pulp by proteolytic gram negative facultative anaerobic bacteria.
- Bacteria form colonies and biofilms within dentinal tubules
what are the effects of bacteria upon the pulp-dentine complex
- pulp tissue remained vital
- New dentine was laid down at exposure site
- no pulpal infection or periapical lesions formed
- pulps die because of bacterial infections
what causes the pulp to die?
Bacterial infiltration of dentinal tubules and subsequent penetrating into pulp space
what is the aim then treating carious sessions
avoid exposing pulp to lessen risk of bacterial infection and preserve to odontoblast to facilitated reactionary dentinogenesis
why should we isolate tooth using rubber dam when treating deep carious lesions?
To prevent sliavry bacterial contamination.preparing aseptic working field is fundamental to optimal maintenance of pulp vitality.
what is important to ensure when restoring a deep carious lesion?
Ensure restoration provide adequate coronal seal to prevent microleakage and risk of pulpal pathology
describe proximal caries lesion progression
(a)the red lines outline the ‘inverted cone’ cross-sectional histological shape of the enamel lesion, and
(b)the blue arrows indicate the lateral direction of spread of the lesion having crossed the amelodentinal junction (ADJ) into dentine.
(c)the white dotted lines show how the extent of the spread of the dentine lesion subjacent to the ADJ is associated with the same lateral extent of the enamel lesion on the tooth surface,
(d)both governed by the activity of the plaque biofilm at the tooth surface.
Looking at the image on the RIGHT
The surface lesion shown is an arrested brown spot lesion, its boundaries clearly aligned with the inverted cone of the enamel lesion beneath.
In BOTH CASES the lesion has reached the dentine which has been affected and looks brown. The path of the lesion in dentine (and therefore its appearance) is dictated by the dentine structure. We can see that the dentine lesion is tracking down the dentinal tubules and following their primary curvature.
Note: this type of lesion often develops below the contact point; relatively shielded where plaque can remain stagnant & mature.
How is caries spread into dentine?
stage 1; plaque layer forms on the enamel surface + time + fermentable carbohydrates, no F- causes releases or organic acids
Stage 2: acid dissolution of enamel prisms at prisms boundaries and cores, loss of mineral and increase in porosity allows acid attack to advance through the enamel
Stage 3: Spreads along the ADJ laterally
Stage 4: Dentinal tubules decrease in volume as sclerotic dentine is deposited and reactionary dentine on the plural wall
Stage 5: Enamel surface cavities, plaque bacteria invade the lesion and penetrate dentinal tubules (infected dentine)
what can accumulate in deep occlusal fissures
food debris and dental plaque accumulates in deep occlusal fissures and produce acid from fermentable carbs
what cares are inaccessiblee for cleaning using a toothbrush
Deep fissures
describe cone shaped lesions
- penetrate nearly perpendicular towards ADJ
- Lesions precede cavitation and occur without apparent break in enamel surface
- Results form surface enamel having high F- content and being relatively resistant to caries dissolution
- Spread of such enamel lesions may produce larger hidden dentine lesions- occult caries and more frequent in teeth with deep pits/fissure patterns
why do we restore teeth?
- Protect pulp-dentine complex and arrest lesion activity by sealing coronal part with adhesive dental material- removes symptoms of acute reversible pulpitis.
- Maximise longevity of tooth restoration complex by removing enough soft dentine to place a durable restoration of sufficient bulk and resilience while maintaining sufficient surrounding tooth support for restoration
- Restore function,form and aesthetics of tooth
- Use of adhesive restorative materials reduces the need for dental hard tissues removal for retention and resistance cavity form
- Good peripheral seal of adhesive restorative material to sound dentine and/or enamel cavity walls reduces the viability of remaining bacteria and their cariogenicity; carious tissue removal simply to remove bacteria in order to halt the caries process is not sufficient.
- Lesions with surface cavitation that cannot be managed by making them cleansable should be considered non cleansable and therefore active.
- Patients caries risk assessment and response to preventive management are important in decisions regarding operative intervention vs non operative control measures.
what happened sheen you removes soft dentine
deform with pressure and be easily scooped up with a sharp hand excavator with little force being applied. The dentien consistency described as caries infected dentin and can apear moist in constituency
how Is leather dentine described
can be easily lifted using excavator without much force- caries affected dentin,
how is firm dentine described
physically resistant to hand excavation requiring some pressure to be exerted through an instrument to lift it
what is hard dentine
sound dentine; scratchy sound can be heard when a straight probe is taken across dentine.
briefly describe cavity prep
- Periphery (ADJ) – prepare to hard
- Cavity floor facing pulp:
Shallow (outer third) - prepare to firm
Moderate (mid third) - prepare to leathery (remove soft infected, leave deeper leathery ‘affected’ dentine)
Deep (inner third/quarter) – prepare to soft (remove most contaminated ‘infected’ wet, soft dentine while leaving some deeper soft dentine)
what layers do we consider when caries process progresses through dentine towards pulp
Layer 1: caries infected dentine
Most coronal layers of the dentine become exposed to the oral environment through an open carious cavity through enamel,allowing bacteria and saliva access to the dentine. Gross disruption of the organic fibrillar matrix of dentin so it is not recognisable as possessing dentinal tubules,peritubular and intertubular dentine and it is heavily inifltaed with bacterial colonies.
At this stage, proteolytic bacteria are using type 1 collagen protein as food substrate.
As you descend deeper through the infected layer the colonies of bacteria become fewer, and the recognised structure of the dentine becomes more visible at the microscopic level, and less disrupted.
Layer 2: This is known as the caries-AFFECTED dentine and it is much closer to the pulp in position, and there is a recognisable dentine structure, although it is affected by the incipient acid wave of demineralisation which precedes the bacterial invasion as it proceeds down the dentinal tubules towards the pulp. This acid demineralisation means that the dentine is slightly demineralised as the hydroxyapatite crystals are being dissolved, and it is therefore slightly softer in comparison to normal dentine. It is possible to see isolated bacteria in superficial zones of the affected dentine, but it is not heavily infiltrated.
Layer 3: This is the normal dentine structure with dentinal tubules and there will be evidence of the dentinal tubules becoming reduced in size with sclerotic dentine inside the tubules providing a more impenetrable barrier to the invading bacteria.
As the caries gets deeper to the pulp this layer becomes increasingly thinner and so the risk of direct pulpal exposure becomes so much greater.
what is the aim of treating caries
The aim is to preserve a dentine barrier over the pulp thus avoiding pulp exposure. Demineralised, but structurally intact dentine that can be remineralised should be preserved. However, clinical discrimination between these layers of infected and affected dentine is difficult especially in rapidly advancing lesions.
how is deep cares defined
radiographic evidence of caries reaching inner third or inner quarter of dentin but still with well defined zone of radiopaque dentien separation infecting demineralised dentine form pulp
Extremely deep caries = caries penetrating entire thickness of dentine without radiopaque zone separating lesion from pulp. Pulp exposure is unavoidable.
Microorganisms penetrate to the critical zone of tertiary dentine including the pulp.
how is IM caries managed?
- Non selective removal to hard dentien- hard sound dentine remains so demineralised removed
- Selective removal from firm dentine - leathery dentine pulpally , feeling of resistance to hand excavator. - Treatment of choice in shallow or moderate cavitated dentine lesions
- Selective removal to soft dentine= recommended in deep cavitated lesions , soft carious tissue is left over pulp , whilst peripheral carious dentien si prepared to ahrd dentien
Stepwise excavation= carious tissue removal in 2 stages
1st- soft carious tissue left only ober pulp whistle peripheral dentien prepared to and dentine
Provisional restoration durable for 6-12 months.
Lesion removed and further excavation on pulpal aspect carried out to firm dentien prior to definitive restorations
describe selectief removal to soft dentine
- single visit technique
- unsupported enable is trimmed
- hard dentine and sound enamel is left t periphery
- all caries at ADJ is removed
- Soft caries on pulpal floor is left until all walls are clear
- plupal wall is excavated using large hand excavator or lose rose head bur in slow speed handpicked, removing softest dentine whilst being careful not to expose pulp
- more deeply places soft infected dentine is left behind
- very wet,heavilty infected dentine had been removed
what happens if caries is left untreated?
Left untreated, caries will advances through enamel into dentin stimulating pulpitis . if conservatory managed, pupla recovery may occur even in deep lesions
Pulp exposure may be avoided in vital,asymptomatic or mild symptomatic teeth with radiographic deep caries by selective removal of caries and restoration in ½ visit
