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الكلية كلية طب الاسنان
القسم ترميم ومعالجة الاسنان
المرحلة 4
أستاذ المادة احمد غانم مهدي الهلال
4/17/2011 5:08:42 PM
Histology of Dentin Caries
Zones of dentinal caries (most clearly distinguished with slow caries and under microscope)
Zone 1: Normal dentin
• It’s the deepest area.
• The tubules filled with odontoblastic processes; no crystals in the lumens.
• The intertubular dentin has normal cross-banded collagen (no degradation).
• No bacteria present.
• Stimulation of dentin produces pain.
Zone 2: Sub-transparent dentin
• It’s a zone of demineralization of the intertubular dentin.
• Initial formation of very fine crystals in tubule lumen at advancing front.
• Normal cross-banded collagen (no degradation).
• Odontoblastic processes damaged.
• No bacteria present.
• Stimulation of dentin produces pain.
• Remineralization is possible
Zone 3: Transparent dentin:
• It’s a zone of carious dentin that is softer than normal dentin.
• Slightly greater demineralization of intertubular dentin.
• Larger crystals fill tubule lumens.
• Normal cross-banded collagen (no degradation).
• Odontoblastic processes damaged.
• No bacteria present.
• Stimulation of dentin produces pain.
• Remineralization is possible.
Zone 4: Turbid dentin
• It’s a zone of bacterial invasion.
• Widening and distortion of tubules which are filled with bacteria.
• Very little mineral present.
• Collagen is irreversibly denatured.
• Cannot remineralize.
• Caries removal must include this.
zone.
Zone 5: Infected dentin
• It’s the outermost zone.
• Decomposed dentin filled with bacteria.
• Collagen and mineral seem to be absent.
• No recognizable structure to dentin.
• Caries removal must include this zone.
During tooth preparation, dentin is distinguished from enamel by:
1. Color: dentine is normally yellow-white and is slightly darker than enamel, in older patients the dentin is darker and becomes brown or black in cases of exposed dentin to oral fluids and old restorative materials or slowly advancing caries.
2. Reflectance: dentin surface is more opaque and dull, so it’s less reflective to light than enamel which appears shiny.
3. Hardness: dentin is softer than enamel, so sharp explorer tends to catch and hold in dentin.
4. Sound: when moving an explorer tip over the tooth, enamel surface provide a sharp, higher pitched sound than enamel.
Sensitivity of dentin:
Although dentin is sensitive to thermal, tactile and osmotic stimuli across its (3-3.5 mm) thickness, it’s neither vascularized nor innervated, except for about 20% of tubules that have nerve fibers penetrating inner dentine by few microns, Therefore odontoblast and its processes are the possible stimulus receptors.
Mechanism of pain transmission:
A variety of physical, thermal, chemical, bacterial, and traumatic stimuli are transmitted through the dentinal tubules, though the precise mechanism of the transmissive elements of sensation has not been conclusively established.
The most accepted theory of pain transmission is the hydrodynamic theory, which accounts for pain transmission through small, rapid movements of fluid that occur within the dentinal tubules. Because many tubules contain mechanoreceptor nerve endings near the pulp, small fluid movements in the tubules arising from cutting, drying, pressure changes, osmotic shifts, or changes in temperature account for the majority of pain transmission.
Dentinal tubules are normally filled with odontoblastic processes and dentinal fluid (a transudate of plasma). When enamel or cementum is removed during tooth preparation, the external seal of dentin is lost and the tubules become fluid-filled channels from the cut surface directly to the pulp.
Dentin must be treated with great care during restorative procedures to minimize damage to the odontoblasts and pulp. Air-water spray should be used whenever cutting with high-speed handpieces to avoid heat generation. The dentin should not be dehydrated by compressed air blasts; it should always maintain its normal fluid content.
Whenever dentin has been cut or abraded, a thin altered layer is created on the surface. This smear layer is only a few micrometers thick and is composed of denatured collagen, hydroxyapatite, and other cutting debris. The smear layer serves as a natural bandage over the cut dentinal surface because it occludes many of the dentinal tubules with debris called smear plugs.
Hydrodynamic theory:
It proposed that a stimuli (air, cold, heat, or cutting) cause’s rapid dentinal fluid movement, causing displacement of odontoblast bodies and the nerve endings in the pulp are deformed, this response is interpreted as pain.
As we approach near the pulp, the tubule density and diameter is increased, leading to increased permeability, thus increasing the volume and flow rate of fluid. This explains why deeper tooth preparations are associated with more sensitivity.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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