Application of Laser in Pulp Capping

With the development of common lasers in the mouth, scientists have found that they have unique advantages and play an important role in improving the success rate of direct pulp capping. This article gives an overview of the theoretical basis, advantages, clinical treatment procedures, and application prospects of laser application in direct pulp capping.

When laser acts on tissues, there are three main effects: absorption, transmission and reflection. In the treatment of diseased tissues, the absorption effect of laser mainly occurs, and its influencing factors include the wavelength of laser, tissue characteristics, etc. The wavelength of laser is the key to its success in special treatment. Different types of lasers have different penetrating ability to tissues. Weak penetrators play a role in the shallow layer of tissues, and vice versa. Cell reactions induced by laser heating are mainly denaturation or inactivation of proteins and enzymes, which can be used for disinfection and sterilization. When low-energy laser irradiates biological tissues, it can directly produce heat, promote the metabolism of tissues in the heat-producing area, and improve their blood supply and nutrition. Biomolecules absorb laser photon energy and convert it into chemical energy, which is called photochemistry. Photodynamic therapy (PDT) refers to the change of function and morphology of cells or biomolecules in the body by laser irradiation with the participation of photosensitizers, leading to injury or necrosis.

When the laser illuminates the object, the photon transmits the momentum to the absorber, and the pressure applied to the irradiated portion is called the light pressure. There are two kinds of pressure effects caused by laser irradiation: one is the pressure formed by the radiation pressure of the laser itself, which is often called the primary pressure; the other is the internal flow generated by the back-stamping and vaporization of the airflow formed by the laser irradiation of the biological tissue. Vaporization pressure, thermotropic expansion pressure, and electrostrictive pressure, etc., such pressure is often referred to as secondary pressure. The phenomenon that a biological tissue absorbs laser energy and converts light energy into mechanical energy is called a photoinduced pressure effect. The weak laser has a small photon energy and a small power density, so its pressure effect can be ignored. A laser is an electromagnetic wave. The interaction between laser and biological tissue is essentially the function of electromagnetic fields and biological tissues. When the biological tissue absorbs laser energy, if the field strength exceeds 105V/cm2, the biological material can be ionized; if the field strength exceeds 106V/cm2, the binding force between the atoms can be destroyed to cause tissue damage.

When a low-energy laser illuminates a biological tissue, it does not directly cause irreversible damage to the biological tissue, and its bio-stimulating effect is directly generated by radiation rather than thermal effects. The magnitude of the laser energy density determines the excitation or inhibition of biological tissues, and the energy density is expressed as an excitatory effect, and vice versa. The effect of low-dose lasers in biological tissues is cumulative, and the final effect depends on the total energy of the laser, but the number of laser irradiations has a threshold, and the effect produced does not increase indefinitely as the number of illumination increases. It has been reported that low-energy laser can activate the mononuclear macrophage system of the body. In the process of irradiation, it mainly enhances humoral immunity. After stopping the irradiation, it mainly enhances cellular immunity; this can reduce the hypercoagulable state of the body blood and improve various kinds. Enzyme activity, including sugar metabolism and important enzymes in the mitochondrial respiratory chain, promotes sugar utilization and ATP production, thereby correcting metabolic acidosis and electrolyte imbalance.

At present, direct pulp capping, pulpotomy and root canal therapy are the most effective methods to treat pulp exposure. Some clinicians believe that direct pulp capping is the first choice of treatment. If the treatment fails, they can choose other treatment methods. Direct pulp capping is a method of preserving vital pulp by blocking bacterial leakage and promoting the formation of dentin bridge by placing biocompatible materials on the pulp exposed by accidental pulp perforation or dental trauma during the treatment of deep caries. In the treatment of direct pulp capping, there are many factors affecting the secretion of dentin in the third stage, such as the degree of pulp damage, the presence of debris in the pulp exposure environment, the nature of pulp capping materials, the presence of inflammation and contamination in the pulp before treatment, and so on, thus affecting the success rate of treatment. Retrospective studies have shown that direct pulp capping has a high success rate in the treatment of pulp exposure caused by trauma, but a low success rate in the treatment of pulp exposure caused by bacterial contaminated caries. In recent years, it has been found that laser can improve the success rate in the treatment of pulp exposure. As an adjuvant treatment of direct pulp capping or pulpotomy, laser has the following advantages.

Fungicidal function: During the whole preparation process of the cavity, laser can play a bactericidal role, and has a bactericidal effect on the exposed pulp and its surrounding environment. Hemostatic function: The traditional method of pulp hemostasis and decontamination is to rinse with sodium hypochlorite in large quantities. If the amount of bleeding is small, the area covered with Ca (OH) 2 directly after rinsing. If the amount of bleeding is large, the area treated with iron sulfate hemostasis is compressed with aldehyde preparation. However, the traditional treatment is time-consuming and ineffective. Assist in sealing dentin tubule function: Laser can remove the stain layer of dentin, make pulp capping material close to the dentin tubule, ensure the tightness of the interface, prevent bacteria from entering; Laser may cause the surface of dentin to melt, the formation of molten particles can seal the dentin tubule, reduce the sensitivity of pulp, thereby reducing the pulp capping material stimulation to the pulp, also. It prevents bacteria from entering dentinal tubules. The damage to pulp is less when the section of pulp tissue is treated. In traditional pulpotomy, digger and ball drill may lead to distraction and twist of pulp tissue, which may lead to secondary inflammation. The size of pulp perforation is not limited when the pulp is exposed. Traditional treatment requires enlargement of pulp perforation to meet the requirements of instrument operation. The results show that when the diameter of pulp perforation is 0.1-1.5 mm, the laser treatment effect will be better. In the treatment of traumatic teeth with serious pulp surface contamination, laser can control the depth of carbonization and has hemostatic function, which is helpful to the treatment before crown breaking and bonding. Low-energy laser has biological stimulating effect and can be used in direct pulp capping. It can reduce inflammation of pulp, promote cell proliferation and control local calcification of pulp.

The clinical treatment procedure for laser application to direct pulp capping is: correct diagnosis, control indications. Local anesthesia and placement of rubber barriers. Prepare cavities. It is possible to use a high-speed or low-speed machine tool and a manual instrument to prepare a cavity; when approaching the pulp, it is recommended to use a holmium laser at the same time to achieve hemostasis and sterilization. Treatment of exposed pulp. This step is the most critical and it is recommended to apply non-contact processing. Place the capping material. The pulp capping material includes mineral trioxide agglomerates (MTA), photocurable calcium silicate preparations (TheraCalLC), calcium hydroxide preparations (Dycal, etc.), and glass ionomer cements. Filling. A dentate material is conventionally applied to the pulp capping material. (7) Forming a dentin bridge.

Clinical studies combining microscopy with laser technology need to be further developed. The combination of microscope and laser technology can make the operation more precise, and the placement of the pulp material is more precise, which may expand the indications of direct pulp capping (such as relaxing the size of the perforation hole) and increase the success rate of treatment. In addition, laser application to direct pulp capping may cause adverse reactions, such as unsuitable energy, excessive operating time and poor technology, can cause excessive absorption of laser energy in the tooth tissue, hyperthermia of the pulp Even coagulation and necrosis of deep pulp and secondary inflammatory reactions can occur. Therefore, the clinical application of the type of laser and its parameters requires further research. At present, many scholars believe that the application of low-energy laser in oral therapy may have broad prospects.

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