Dentin - Growth and Formation

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Dentin Hypersensitivity

Dentin hypersensitivity is a common dental condition characterized by sharp, transient pain or discomfort in response to external stimuli such as hot, cold, sweet, or acidic substances, or even by physical contact like brushing or flossing. This pain occurs when the dentin, which is the layer beneath the tooth enamel and cementum, becomes exposed due to various factors such as gum recession, enamel loss, or root exposure.

Dentin hypersensitivity is defined as “pain derived from exposed dentin in response to chemical, thermal, tactile, or osmotic stimuli, which cannot be explained as arising from any other dental defect or disease.” It is a common problem among dental patients and is considered one of the most frustrating dental issues. Various treatments have been suggested for its alleviation, but they are often insufficient and not very successful until the cause is identified.

Common terms used to refer to dentin hypersensitivity include:

Dentin Hypersensitivity Symptoms

Dentin hypersensitivity, also known as tooth sensitivity, is a common dental issue that results in sharp, transient pain or discomfort when teeth are exposed to specific stimuli. The symptoms can range from mild to severe, and may affect one or multiple teeth. These symptoms include:

It’s important to note that dentin hypersensitivity can have several potential causes, including gum recession, tooth decay, enamel erosion, or aggressive tooth brushing. If you’re experiencing any of these symptoms, it’s essential to consult with a dental professional for a proper diagnosis and treatment plan.

How Does Dentin Transmit Sensations of Pain?

Scanning electron microscope (SEM) results show that sensitive dentin has a higher number of dentinal tubules and larger tubule size compared to non-sensitive dentin. Sensitive dentin has approximately eight times the number of tubules found in non-sensitive dentin. Moreover, the tubules in sensitive dentin are thicker. The rate of dentinal fluid flow is dependent on the fourth power of the tubule’s radius, and this difference plays a significant role in the development of dentinal hypersensitivity in clinical conditions.

Phases of Dentinal Hypersensitivity Development

According to SEM finding, Dentinal hypersensitivity develops in two phases:

  1. Lesion localization: In the first phase, dentinal tubules become exposed due to enamel loss caused by attrition, abrasion, erosion, and abfraction. However, dentinal exposure primarily occurs because of gingival recession and cementum loss on the root surface. It is important to note that not all exposed dentin is sensitive. However, the calcified smear layer in sensitive dentin is thinner compared to non-sensitive dentin, leading to increased fluid movement and, consequently, a pain response.
  2. Lesion initiation: In the second phase, the tubular plug and smear layer play a crucial role. Present on the surface of exposed dentin, they consist of protein elements and sediments derived from salivary calcium phosphates, sealing the dentinal tubules inconsistently and transiently. When the tubular plugs and smear layer are removed, the dentinal tubules and pulp become exposed to the external environment.

Both mechanical and chemical factors are effective in removing the smear layer from dentinal tubules, as indicated by laboratory research. However, clinical investigations show that mechanical factors alone are not sufficient for removing the smear layer. When combined with acidic foods or drinks, the smear layer is more likely to be removed.

Theories Explaining Dentinal Hypersensitivity

Theories that explain how Dentin Hypersensitivity is caused include:

  1. Direct Innervation Theory: This theory implies that nerve endings enter dentin through the pulp and extend to the dentin-enamel junction (DEJ), directly transmitting pain caused by mechanical stimuli. However, there is little evidence to support this theory, as there is not much proof of nerve presence in the superficial dentin where sensitivity is highest.
  2. Odontoblast Receptor Theory: According to this theory, odontoblasts act as pain receptors and transmit signals to pulpal nerves. This theory has been largely dismissed because the cellular matrix of odontoblasts is not capable of exciting and producing neural impulses. Moreover, no synapses have been found between odontoblasts and pulpal nerves.
  3. Fluid Movement/Hydrodynamic Theory: This Theory is the most widely accepted explanation for dentin hypersensitivity. It is based on the movement of fluid within dentinal tubules and suggests that these tubules are open between the dentin surface exposed to the environment and the pulp. This theory proposes that thermal and physical changes near the exposed dentin create an osmotic stimulus, resulting in fluid movement inside the dentinal tubules. This fluid movement stimulates a baroreceptor, leading to neural discharge in a process called the hydrodynamic theory of pain. Fluid movement can be either toward the pulp or away from the dentin. Cooling, drying, evaporation, and hypertonic chemical stimuli cause dentinal fluid to flow away from the dentin-pulp complex, increasing pain, while heating causes fluid to flow toward the pulp.

Causes of Dentin Sensitivity

Dentin hypersensitivity is a common dental issue that causes discomfort or pain in response to various stimuli. There are several factors that can contribute to the development of dentinal hypersensitivity:

To reduce the risk of dentinal hypersensitivity, it’s essential to maintain proper oral hygiene, use a soft-bristled toothbrush, avoid overconsumption of acidic foods and beverages, and address any underlying dental or medical issues.

For successful treatment of dentinal hypersensitivity, it is critical to accurately diagnose the condition and identify its cause. Diagnosis starts with investigating the patient’s medical history and conducting a physical examination. Basic questions about the onset of dentinal hypersensitivity, pain intensity, pain stability, and factors that affect sensitivity are asked. During the examination, techniques such as air pressure water spray or percussion with an instrument may be used to recreate the stimulating factors and assess the patient’s pain level.

Can Dentin Hypersensitivity Be Cured?

While dentin hypersensitivity, also known as tooth sensitivity, can be treated and managed, it may not be completely curable. The treatment approach depends on the underlying cause of the sensitivity. Here are some treatment options for dentin hypersensitivity:

Though dentin hypersensitivity may not be completely curable, it can be effectively managed and treated with proper dental care and treatment.

Dentinal Fluid

Dentinal fluid is a clear, colorless fluid found within the dentinal tubules, which are microscopic, tube-like structures present in the dentin layer of the tooth (that lies beneath the enamel and surrounds the pulp chamber, where the tooth’s nerves and blood vessels reside).

Dentinal Fluid Composition

Dentinal fluid is mainly composed of water, which accounts for approximately 75% of its total weight. It also contains a variety of dissolved substances, such as proteins, peptides, ions (calcium, potassium, sodium, and others), and organic molecules. These key organic molecules include:

Dentinal Fluid Function

Dentinal fluid plays several crucial roles in maintaining tooth health and function:

Dentin Etching

Dentin etching is a process used to remove the smear layer before applying adhesive. This method typically involves the use of phosphoric acid, which effectively eliminates the smear layer when used in the correct concentration. Using a low concentration of phosphoric acid (e.g., 0.13% to 20%) may result in a less aggressive etching effect, leaving the smear layer partially intact. On the other hand, a high concentration (e.g., 65%) can lead to dentin demineralization and reduced bond strength. Clinically, the ideal concentration of phosphoric acid is typically between 30% and 40%.

Different types of dentin-etching systems include Etch-and-rinse adhesive systems, as well as Self-etch adhesives system. Following is a description of each of these two systems:

  1. Etch-and-rinse adhesive systems: In these systems, the smear layer is completely demineralized and rinsed away, meaning it does not negatively affect the etch-and-rinse adhesive process. However, long-term dentin collagen degradation has been shown to be more pronounced with etch-and-rinse adhesives compared to self-etching adhesives. This is likely due to the aggressive demineralization of phosphoric acid, which exposes more dentin collagen fibrils, activating matrix metalloproteinases (MMPs) and leading to collagen degradation over time.

To address the drawbacks of phosphoric acid, alternative etchants have been developed, such as Multi Etchant  by Yamakin, Osaka, Japan), Shofu Enamel Conditioner (by Shofu, Kyoto, Japan), and an experimental zirconium oxynitrate conditioner (by Ivoclar Vivadent, Schaan, Liechtenstein). These alternatives demonstrate higher dentin bond strength compared to phosphoric acid.

Another approach to minimize dentin collagen degradation is reducing the etching time. Although the depth of dentin demineralization is related to etching time, no adverse effect on dentin bond strength has been observed when the etching time is shortened to 5 seconds.

  1. Self-etch adhesives system: Unlike etch-and-rinse adhesives, self-etch adhesives do not require a separate etching step, as they contain acidic monomers that simultaneously condition and prime the dental substrate. This approach offers several advantages, including shorter application time, fewer steps, and less technique sensitivity, resulting in more reliable clinical performance, although reliability may vary depending on the specific product.

Self-etch adhesives are less aggressive with respect to dentin than phosphoric acid etching, resulting in a more superficial interaction with dentin and preserving largely obstructed tubules with a smear layer. This provides an additional clinical benefit to using self-etch adhesives. 

Dentin with Smear Layer

The smear layer is a thin film of debris created on the surface of the dentin during tooth preparation procedures, such as cutting or grinding. It consists of organic and inorganic components, including hydroxyapatite crystals and denatured collagen. 

The smear layer’s thickness typically depends on the size of the abrasive particles used. Larger abrasive particle sizes result in thicker smear layers, ranging from 0.9 to 2.6 μm for the SiC-ground smear layer and 1.0 to 2.8 μm for the diamond bur-cut smear layer.

The density or denseness of the smear layer, which indicates the degree of compaction, is also influenced by the preparation instruments. A dense smear layer is observed when prepared using diamond burs, while a loosely organized smear layer is detected when prepared using SiC paper.

The formation of a smear layer is an unavoidable consequence of tooth preparation, but its presence may have implications for the adhesion of restorative materials and the overall success of dental treatments. The smear layer can form smear plugs that block the orifices of dentinal tubules, decreasing dentin permeability by up to 86%. Despite this, fluids from the dentinal tubules can still permeate through the layer due to its micro-porous structure.

The presence of the smear layer on dentin can interfere with the adhesion of restorative materials, such as dental adhesives or cements. This is because the layer acts as a barrier, preventing direct contact between the adhesive and the dentin. Therefore, it has been suggested that the smear layer should be removed before applying a bonding agent or the restorative materials. Phosphoric acid is often used for the complete removal of the smear layer in etch-and-rinse adhesives and partial removal in self-etching adhesives. The concentration and application time of the etchant should be carefully controlled to achieve optimal results without damaging the dentin.

Dentin with Calcium Hydroxide

Calcium hydroxide is a white, odorless powder that, when mixed with water, forms a paste. This dental material can reduce dentin hypersensitivity by forming secondary dentin. When applied to exposed dentin, calcium hydroxide can provide the appropriate stimulus needed by odontoblasts to form a dentin new layer beneath the existing dentin layer, thus helping to reduce sensitivity.

The paste is usually left in place for a period before final restoration. Applying calcium hydroxide to exposed dentin can also help seal off dentin tubules responsible for transmitting pain or sensitivity sensations.

Using dentin with calcium hydroxide can be an effective treatment for dentin hypersensitivity, but it may not be suitable for everyone. This treatment may not be effective in cases where sensitivity is caused by more severe underlying dental problems or extensive tooth decay.

Toothpaste for Dentin Hypersensitivity

Dentin hypersensitivity is a common dental problem that results from the exposure of dentinal tubules due to factors such as tooth decay, trauma, age-related changes, gum recession, or enamel loss. Toothpaste specifically designed for dentin hypersensitivity can help alleviate the pain and discomfort associated with this condition.

There are two primary mechanisms by which these toothpastes work to reduce dentin hypersensitivity:

  1. Nerve Depolarization: blocking the pain response.
    Some toothpastes contain potassium ions, such as potassium nitrate or potassium citrate, which help to depolarize the nerve endings within the dentinal tubules. By interrupting the transmission of pain signals to the brain, these toothpastes can effectively reduce the sensation of pain or discomfort caused by external stimuli.
  2. Tubule Occlusion: sealing the ends of the dentinal tubules.
    Some toothpastes work by physically blocking the exposed dentinal tubules, thus isolating the nerve endings from external stimuli. Ingredients like bio-glasses, arginine combined with particulate calcium, and metal ions like strontium and stannous, contribute to this tubule occlusion process. When these ingredients come in contact with saliva, they form a protective layer over the exposed dentin, reducing sensitivity.Stannous fluoride (SnF2) is a popular ingredient in toothpastes for dentin hypersensitivity, as it not only helps with tubule occlusion but also provides protection against cavities by strengthening tooth enamel. Clinical studies demonstrate the efficacy of SnF2 toothpaste. However, formulating toothpastes with SnF2 can be challenging due to its potential to cause staining and the need to protect it from oxidation or hydrolysis. To overcome these challenges, Anhydrous Glycerin bases are used, and stain prevention agents like sodium tripolyphosphate (STP) are added to the formulation.Upon exposure to the aqueous oral environment, tubule openings at the dentin surface become occluded by precipitates of stannous hydroxides and oxides, along with particulates from the toothpaste and saliva-derived proteins and ions, leading to a reduction in tubular fluid flow.

When choosing a toothpaste for dentin hypersensitivity, it is essential to select one that has been clinically proven to be effective. Some popular brands include Sensodyne, Pronamel, Parodontax, Colgate Sensitive, and Elmex Sensitive, among others. In addition to using a specialized toothpaste, maintaining good oral hygiene practices like regular brushing, flossing, and dental check-ups can also help manage dentin hypersensitivity effectively.

Fluoride as a Treatment for Dentinal Hypersensitivity

Fluoride, a naturally occurring mineral, have long been recognized for its role in preventing tooth decay and promoting the remineralization of enamel and dentin. Additionally, various clinical trials have demonstrated that fluoride solutions can also effectively reduce dentin hypersensitivity.

Fluoride works to alleviate dentinal hypersensitivity through two main mechanisms:

  1. Remineralization: Fluoride promotes the remineralization process, which helps to strengthen the enamel and dentin. By reinforcing these tooth layers, fluoride prevents the exposure of the underlying dentin and reduces the likelihood of dentinal hypersensitivity.
  2. Tubule Occlusion: When fluoride is applied to the exposed dentin, it forms calcium fluoride crystals inside the dentinal tubules. These crystals obstruct the tubules, creating a barrier that isolates the nerve endings from external stimuli such as temperature changes, acidic substances, or mechanical forces. As a result, the movement of fluid within the dentinal tubules is reduced, which in turn diminishes the nerve response and alleviates hypersensitivity.

Scanning electron microscopy (SEM) has shown granular precipitates appearing in the peritubular dentin after fluoride application. These precipitates, comprised of calcium fluoride crystals, reduce dentinal permeability by forming inside the dentinal tubules. These crystals are partially insoluble in saliva.

There are several fluoride formulations used to treat dentinal hypersensitivity:

These fluoride formulations can be found in toothpaste, mouthwash, or as professional applications by a dentist. The choice of fluoride formulation depends on the severity of the condition, the patient’s individual needs, and the preference of the dental professional.

Dentin Hypersensitivity: Nerve Desensitization

Dentin hypersensitivity is a common issue experienced by dental patients. One of the treatment methods for this condition is nerve desensitization, which focuses on reducing sensitivity by blocking the transmission of pain signals from the dentin to the nerves within the tooth. It is essential to note that the success of nerve desensitization treatment may vary depending on the underlying cause of the sensitivity.

Two primary approaches to achieve nerve desensitization include:

  1. Blocking the dentin tubules: this approach uses desensitizing agents, such as potassium nitrate, fluoride, or oxalates, to block the exposed dentinal tubules. These agents can form a protective barrier over the dentin, preventing external stimuli from reaching the nerve endings and triggering pain.
  2. Promoting the deposition of minerals in the dentin: this approach aims to strengthen the tooth structure and reduce sensitivity by encouraging the remineralization of the exposed dentin. Fluoride treatments can facilitate this process, as they help promote the formation of more robust, acid-resistant tooth enamel and dentin.

Lasers can also be employed for nerve desensitization. They selectively target and ablate nerve endings in the tooth, helping to decrease sensitivity without affecting the surrounding tissue or causing tooth damage. Laser treatment can be particularly beneficial for patients who have not responded well to other desensitization treatments.

Other treatments for nerve desensitization may involve using desensitizing toothpaste or prescription mouthwash containing fluoride or other desensitizing agents. These products can provide relief by either blocking the dentinal tubules or promoting remineralization.

It is essential to consult with a dental professional to determine the most suitable treatment option for dentin hypersensitivity, as the success of nerve desensitization treatment may vary depending on the underlying cause of the sensitivity.

Dentin Hypersensitivity Medications

Several medications can help manage dentin hypersensitivity:

It is important to note that these medications may provide temporary relief; therefore, the underlying cause of sensitivity should be identified, and appropriate treatment should be administered.

Does Dentin have Nerves?

Dentin itself does not have nerves. However, dentin is a vital tissue that is closely connected to the dental pulp, which contains blood vessels, connective tissue, and nerves. 

The odontoblasts, which are cells responsible for forming dentin, have long processes called odontoblastic processes that extend into the dentinal tubules. These odontoblastic processes are not nerves, but they are sensitive and can transmit sensations to the nerves in the dental pulp when stimulated. This transmission of sensations is what leads to the pain and discomfort associated with dentin hypersensitivity.