3Physiologic regular secondary dentin Primary DSecondary D
4Physiologic regular secondary dentin This is the type of dentin formed under Physiologic conditions after complete root formation.It is deposited continuously as long as the pulp is vital.It is formed at a lower rate and is separated by a darkly stained line from primary dentinIt has less number of tubules.It occurs in the entire pulpal surface.Higher deposition at the roof and floor of the pulp chamber.
6Physiologic regular secondary dentin The size of the pulp cavity decreases and obliteration of the pulp hornsThe course of the dentin canals is more irregular
7Pathologic irregular secondary dentin It is also known as tertiary or reparative dentinThis type of dentin is formed as a protection for the pulp against severe stimulus (pathological conditions or irritations), such asAttritionCariesPreparationsIt is formed at a localized area (e.g. pulp horn)Some UMC in the subodontoblastic layer differentiate to new odontoblast to form dentin.
8Pathologic irregular secondary dentin The number of the tubules is reduced.Tertiary dentin has frequently twisted tubulesSome areas doesn’t contain tubulesReparative dentin is separated from other types by a darkly stained line.
10Types of reparative dentin Osteodentin: The odontoblasts (cells) are included in the formed dentin
11Types of reparative dentin Atubular dentin: areas without tubules
12Types of reparative dentin Vasodentin: entrapped blood vessels
13Types of secondary dentin irregularCause: severe stimuli, severe attrition, erosion, deep caries,Site of formation: located (eg pulp horn)Tubules: wavy and twisted course, decrease in number or atubularRegularCause: mild stimuli (slow attrition, slowly progressing caries)Site of formation: entire pulpal surface (thicker on pulp roof and floor)Tubules: wavy course, decrease in number
14Types of secondary dentin RegularLine of demarcation: stain darkClinically:The increase of the dentin thickness and the closure of the pulp horns make it much less possible to expose the pulp chamber during preparation.IrregularLine of demarcation: stain darkClinically:Functions as a barrier for against caries.
15Transparent (Sclerotic) dentin Sclerotic dentin can be seen as physiological change (elderly dentin) or pathological change (caries, attrition, deep fillings, ) in primary or secondary dentin.Partial or complete obliteration of the dentin tubules, at first thickining of peritubular dentin, then complete obliteration of the tubules with intertubular d.Higher mineralized, harder and denser than normal dentinAppears light in transmitted light and dark in reflected light.
16Transparent (Sclerotic) dentin Young dentinAdult dentinSclerotic dentin
18Dead tractsSevere stimulation to dentin leads to destruction or disintegration of the odontoblastic process and odontoblasts.The dentin tubules are empty and filled with air.Most often in areas of narrow pulp horns due to odontoblastic crowding. In ground section they appear black.Often surrounds with sclerotic dentin.
22Vitality and sensitivity of dentin Vitality of dentin is its ability to react following physiological or pathological stimuli.Forming secondary or tertiary dentin, feeling pain are signs of being vital.Several theories have been cited to explain the mechanism involved in dentinal sensitivity & vitality:The transducer theory,the conduction theory,the modulation theorythe Brännström's hydrodynamic theory.
23The transducer theoryThe transducer theory contend that the odontoblast and its process are capable to mediate neural impulse in the same way as nerve cells.Contra:But investigations have proved that no pain is experienced in exposed dentin by application of substance known to bare nerve endings.The measurement of membrane potential of the odontoblasts shows clearly that this potential is very low to contribute in the pain excitation.
25The conduction theoryThe conduction theory (intratubular innervation theory) contend that dentin is richly innervated and those nerves mediate the impulse to the brain.Some new studies show that predentin and the first layer of circumpulpal dentin (0.2mm) is innervated with nerve fiber from the raschkows plexus.The fibers run parallel ro the tomes fiber in the dentin tubules.The density of those fiber is much higher in the coronal dentin than cervical dentin. Root dentin doesn’t include such fibers.
27The conduction theorySome authors contend that those fibers end at the DEJ, but can not be seen in histological slides.Contra:It is uncapable to explain the higher sensitivity at the cemento-enamel junction than that felt at other areas.
29The hydrodynamic theory The “hydrodynamic theory”, developed in the 1960’s is the widely accepted physiopathological theory of Dentin Sensitivity.Temperature, physical osmotic changes or electrical and chemical stimuli and dehydration are the most pain-inducing stimuli.According to this theory, those stimuli increase centrifugal fluid flow within the dentinal tubules, giving rise to a pressure change throughout the entire dentine.
30The hydrodynamic theory The movement stimulates intradentinal nerve receptors sensitive to pressure (BARORECEPTORS), which leads to the transmission of the stimuli .This simulation generates pain.
31The hydrodynamic theory Berman describes this reaction as:“The coefficient of thermal expansion of the tubule fluid is about ten times that of the tubule wall. Therefore, heat applied to dentin will result in expansion of the fluid and cold will result in contraction of the fluid, both creating an excitation of the 'mechano-receptor'.”