Dentin 2 PDF

Dentin 2 DENTIN ENAMEL 2 1  Dentin 2 Age changes of dentin 1. Changes in primary dentin. a) Transparent/ translucent / sclerotic dentin....

Dentin 2 DENTIN ENAMEL 2 1  Dentin 2 Age changes of dentin 1. Changes in primary dentin. a) Transparent/ translucent / sclerotic dentin. b) Dead tracts 2. Regular Secondary dentin. 3. Tertiary dentin. Changes in primary dentin: a- Transparent/ translucent sclerotic dentin It is a regressive alteration in the tooth hard substance which characterized by calcification of dentinal tubules where the odontoblastic processes undergo fatty degeneration then calcification,the most likely source of calcium salts is the fluid of dentinal lymph within tubules. It occurs as a manifestation of normal aging process so it is prevalent in older individual as well as a result of dentin injury by slow caries or abrasion (mild stimuli). This dentin has uniform refractive index because dentinal tubules are occluded by widening of peritubular zones and odontoblastic processes become reduced in diameter. It appear translucent when viewed by transmitted light, it appear dark when transmitted by reflected light. Sclerotic dentin will leads to occlusion of the dentinal tubules by calcified deposit. This increased mineralization of the tooth leads to: Decrease the conductivity of the odontoblastic processes. Slows down carious process. (defensive). Prolong the pulp vitality Decrease permeability of dentin. Increase the brittleness of dentin. 2  Dentin 2 b- Dead tracts In case of sever stimulation to dentin, the odontoblastic processes in the affected area are completely destroyed or damaged. In dried ground section, these empty dentinal tubules are filled with air, they appear black in transmitted light and white in reflected light, this optical phenomenon is due to difference in the refractive index of the affected tubules and the normal tubules. Dentin areas characterized by degenerated odontoblastic processes (dead tract) bounded by narrow zone of sclerotic dentin. It should be noted in dried ground section of normal dentin, the death of odontoblasts crowded in narrow pulpal horn leaving empty tubules which may be filled with air, and these tubules give an appearance similar to dead tract. 3  Dentin 2 Regular secondary dentin: Secondary dentin develops after root formation has been completed and represents the continuing deposition of dentin along the entire pulp surface, but much slower deposition of dentin by odontoblasts. It has tubular structure, but less regular. The tubules often change their direction And continue in wavier course, the number of dentinal tubules per unit area is fewer than primary dentin. With continuous deposition of secondary dentin, the surface of the pulpal wall gradually diminished, the odontoblasts become more and more crowded, when crowding reach maximum, many of cells degenerate and the remaining cells rearrange themselves on the wall of the pulp. This type of dentin formation increased by mild stimulus reaching the pulp as slow attrition, slowly progressive caries. The pulp cavity gradually decreased with continuous deposition of regular secondary dentin. These change in pulp size called ʺpulp recessionʺ. Making the liability of pulp exposure during cavity preparation lesser to occur. Between the primary and secondary dentin, there is often darkly staining line (line of demarcation) where the DTs: 1. Change their direction. 2. Continue in wavier course. 3. Decrease in Number. 4  Dentin 2 Difference between 1ry & 2ry dentin in the dentinal tubules ✓ Number of DTs per unit area is fewer in secondary dentin, because: With continuous deposition of secondary dentin, the surface area of the pulpal wall gradually diminished. Evidence suggests that the tubules of 2ry D sclerose (fill with calcified material) more readily than those of 1ry D to reduce permeability protecting the pulp. Irregular secondary dentin (Reparative& reactionary dentin),(Tertiary dentin): It occurs when stimulus to dentin is more pronounced as abrasion, caries or cavity preparation. Unlike primary or secondary dentin that forms along the entire pulp border, it is formed on the exact area corresponding to pulpal end of exposed tubules. This action to seal off zone of injury. 5  Dentin 2 Histologically: Tubules are fewer in number, less regular in arrangement. ►Tubular: ✓ Tubules are fewer in number, less regular in arrangement or irregularly twisted. ►Atubular dentin: when tubules are irregularly scattered and irregularly twisted. Some area may not contain tubules. ✓ Because of sever stimulation, the odontoblastic process are exposed and the odontoblasts cell damaged. ❖ These injured cells may either: Continue to form dentin which will be irregular called reactive dentin Completely degenerated and replaced by undifferentiated cells form pulp which form reparative dentin ►Osteodentin: ✓ when the dentin forming cells are often included in the rapidly forming matrix, then these cells degenerate and vacate the space that they were occupied ►Vasodentin: entrapped blood vessel. ❖ Because of sever stimulation ,the odontoblastic process are exposed and the odontoblast cells affected. These injured cells may either: ✓ Continue to form dentin which will be irregular called reactive dentin. ✓ Completely degenerated and replaced by undifferentiated cells form pulp which form reparative dentin. 6  Dentin 2 CLINICAL CONSIDERATIONS 1. Dentin sensitivity may not be a symptom of caries unless pulp is inflamed 2. Air driven cutting instrument cause damage of odontoblasts at pulp periphery. 3. Indirect pulp capping by using cavity lining material as Ca(OH)2 stimulate reparative dentin formation. 4. Permeability of dentin: ✓ The tubular structure possibility of dentin allows for the of substances applied to its outer surface being able to reach and affect the dental pulp. ✓ The poor pulpal response to some restorative materials is more likely to be due to the poor marginal seal of that material, allowing microleakage and presence of bacteria on the surface of dentin. 5. The color of the tooth Related to the translucency of the enamel and the thickness of the dentin. The increased thickness of the dentin contributes to the “yellowing” of the teeth with age and serves to insulate the dental pulp, making vitality testing more difficult. 6. The deposition of localized tertiary dentin Not only reduces the volume of the pulp chamber but also alters its shape. This makes endodontic procedures more difficult and increases the possibility of iatrogenic accidents, for example, perforations. 7. When 1mm3 of dentin is exposed, about 30,000 living odontoblasts are damaged, so cavity preparation should be conservative and use sealing material which is not irritant. 8. The smear layer Debris from dentin instrumentation. Reduces the permeability of dentinal tubules because some debris enters the tubules obliterating them. The entry of smear into the dentinal tubules is dependent on both 1. Size of the smear particles. 2. Diameter of the dentinal tubules. Advantages Disadvantages ❑ It reduces permeability ❑ It interferes with dentin bonding procedures. ❑ Reduces infiltration of noxious agents ❑ Smear layers cannot be removed by irrigation. into the tubules and perhaps the pulp ❑ Can be removed or modified by some form of acid conditioning. However, The removal of smear by acids can damage the pulp. 7  Dentin 2 Dentin Sensitivity & theories that explains it ►Dentin Sensitivity: Enamel and cementum are non-sensitive. Dentin is sensitive, but not uniformly. Most sensitive at ADJ and quite sensitive close to the pulp. Three theories have been proposed to explain dentin sensitivity: 1) Direct neural stimulation. 2) Odontoblastic transduction theory. 3) Fluid or hydrodynamic theory. 1) Direct neural Dentin contains nerve endings, which respond directly when dentin stimulation (the oldest) is stimulated. It proposed that odontoblastic process 2) Odontoblastic is excited by stimulus. transduction theory: Then the impulse is transmitted from ADJ to nerve endings in contact with odontoblast cell body. It is the most popular and accepted one. Proposed that various stimuli as heat, cold, air affect fluid movement inside dentinal tubules which stimulate nerve endings in plexus of Rashcow Supporting: 3) Fluid or hydrodynamic 1. When dentin is first exposed , theory: small blebs of fluid can be seen on cavity floor. 2. When the cavity is dried with air or cotton wool, a greater fluid loss is induced, leading to more movements and more pain. 8