**2. Dental laser systems and the basics of the work**

#### **2.1. Basic processes of laser radiation and tissue interaction**

One of the main difficulties of all starting dental laser using is the depth of penetration of laser to the tissue and its effects on the principal constituents of the tissue. In order to clarify these questions, it is necessary to consider the process of light penetration in the tissue and the biological effects on the tissue [9, 22].

The process of laser penetration in the biological tissues is extremely complicated. This was connected to others with their nonhomogeneous structure. From the dental point of view, it is very necessary to deliver precisely a respective dosage of laser energy to a given tissue [2, 20].

This energy will be absorbed and transformed into other forms of energy. The laser passing through the upper layers of the tissue is reflected, scattered, and partially absorbed [23]. A degree of these processes is dependent upon tissue type and in the case of the epidermis. It can differ from the case of the skin or oil gland irradiation. In order to define the tissue laser radiation interaction, some considerations should be addressed with respect to the physical parameters and the structural features of the irradiated tissue [10, 12]. The absorption limit and its width are conditional upon the tissue structure, water, hemoglobin, enamel, dentin, pulp cavity, etc. [24].

Anyhow, the process of laser tissue radiation interaction is determined by the wavelength, power, and the irradiation time. The primary characteristics of this interaction are illustrated in **Figures 1** and **2**. **Figure 1** shows the primary physical phenomena, transmission, reflection, scattering, and absorption which occur including the biological tissue.

If there are two materials, one is white and the second black, in the sunlight, the white body will reflect more light waves than the black one and it will be cooler than the black body, which absorbs more solar energy. The radiation of the tissue involves the release of these four processes simultaneously [11, 25].

For example, the laser source with an output power of 30 mW emits 1016 photons per second. Theoretically, that means 10<sup>16</sup> photons penetrate in the tissue every second [15]. Accordingly, it does not matter if a given point is irradiated for 1 second or for 1 minute. The alike situation

Laser Dental Treatment Techniques http://dx.doi.org/10.5772/intechopen.80029 21

The point is to select the wavelengths in bands where the processes of effective transmission in tissues for biostimulation purposes are predominant as well as for cutting, coagulation, defects, etc.

occurs when we shine a given point on the wall with an electric torch [1, 5, 27].

**Figure 3.** Characteristic of absorption of the laser light for the main tissue components [13].

**Figure 2.** Transmission values of the main wavelengths for selected parts of the skin.

The transmission and the absorption of the laser in the given tissue are dependent, apart from its wavelength, and upon its power, it is not dependent on irradiation time. The spot size of the laser beam and its intensity will be the same regardless of how long this laser is on [26].

**Figure 1.** Illustration of the basic phenomena always accompanying the light-tissue interaction [28].

**Figure 2.** Transmission values of the main wavelengths for selected parts of the skin.

For example, the laser source with an output power of 30 mW emits 1016 photons per second. Theoretically, that means 10<sup>16</sup> photons penetrate in the tissue every second [15]. Accordingly, it does not matter if a given point is irradiated for 1 second or for 1 minute. The alike situation occurs when we shine a given point on the wall with an electric torch [1, 5, 27].

The point is to select the wavelengths in bands where the processes of effective transmission in tissues for biostimulation purposes are predominant as well as for cutting, coagulation, defects, etc.

**Figure 3.** Characteristic of absorption of the laser light for the main tissue components [13].

**Figure 1.** Illustration of the basic phenomena always accompanying the light-tissue interaction [28].

scattering, and absorption which occur including the biological tissue.

these questions, it is necessary to consider the process of light penetration in the tissue and the

The process of laser penetration in the biological tissues is extremely complicated. This was connected to others with their nonhomogeneous structure. From the dental point of view, it is very necessary to deliver precisely a respective dosage of laser energy to a given tissue [2, 20]. This energy will be absorbed and transformed into other forms of energy. The laser passing through the upper layers of the tissue is reflected, scattered, and partially absorbed [23]. A degree of these processes is dependent upon tissue type and in the case of the epidermis. It can differ from the case of the skin or oil gland irradiation. In order to define the tissue laser radiation interaction, some considerations should be addressed with respect to the physical parameters and the structural features of the irradiated tissue [10, 12]. The absorption limit and its width are conditional upon the tissue structure, water, hemoglobin, enamel, dentin, pulp cavity, etc. [24]. Anyhow, the process of laser tissue radiation interaction is determined by the wavelength, power, and the irradiation time. The primary characteristics of this interaction are illustrated in **Figures 1** and **2**. **Figure 1** shows the primary physical phenomena, transmission, reflection,

If there are two materials, one is white and the second black, in the sunlight, the white body will reflect more light waves than the black one and it will be cooler than the black body, which absorbs more solar energy. The radiation of the tissue involves the release of these four

The transmission and the absorption of the laser in the given tissue are dependent, apart from its wavelength, and upon its power, it is not dependent on irradiation time. The spot size of the laser beam and its intensity will be the same regardless of how long this laser is on [26].

biological effects on the tissue [9, 22].

20 Prevention, Detection and Management of Oral Cancer

processes simultaneously [11, 25].

**Figure 2** shows in detail the transmission of the major important laser wavelengths in particular constituents of the skin tissue, while **Figure 3** illustrates the optical absorption characteristics of water, hemoglobin, and melanin and shows precisely the primary constituents of the tissue where absorption covers 100%.

**3. Clinical applications and descriptions**

ing intact dentins [19, 31, 32] (**Figures 5**–**8**).

**Figure 5.** Decay present on the facial of the maxillary left lateral incisor.

**Figure 6.** The erbium laser used to remove the decay. No anesthesia was required.

treatment (see **Figures 10**–**14**).

**3.1. Laser treatment of hard tooth substance (enamel and dentin)**

The carious material contains a higher content of water compared with other surrounding dental healthy hard tissues. As a result, the ablation efficiency of caries is higher than other healthy tissues. There was a possible selectivity in removing carious material by using Er:YAG laser because of the various energy dose requirements to ablate the carious and also healthy tissue leaving those healthy tissues minimally affected. It was found that the Er:YAG laser can ablate the carious dentin effectively with the minimal thermal damage to the other surround-

Laser Dental Treatment Techniques http://dx.doi.org/10.5772/intechopen.80029 23

The laser can remove infected and softened carious dentin to the same degree as the bur treatment [33]. However, the lower degree of vibration was remarked with the Er:YAG laser

**Figure 4** displays the curves of the absorption by the principal components of teeth tissues and laser wavelengths. The biggest absorption occurs with wavelength of approximately 2900 nm. This is the radiation generated by Er:YAG laser and CO<sup>2</sup> laser radiation—10,600 nm ranks second, respectively. The abovementioned dependence for particular tooth tissues.

The time duration of treatment session on a given point is significant since it determined the total number of the photons penetrated in the tissue [25]. Photons emitted by laser source do not penetrate into deeper tissue layers even if a given point is irradiated for a longer time [5, 29]. If we mention the above example with the electric torch, we can see that the laser beam will not reach further and it is not more intensive, no matter whether the laser is on for an hour or for a minute.

In spite of this explanation, the treatment effect is obtained in a deeper layer after the long period of laser irradiation. This phenomenon occurring is similar to the exponential dependence between the transmitted energy (total number of photons transmitted during a therapeutic session) and the depth of penetration [3, 29].

The relation between the time duration of a treatment session and therapeutic effects can be explained by the penetrating photons that initiate the chain reaction which transfers the biological effects of the therapeutic session to the deeper tissue layers and at sides [30].

**Figure 4.** Characteristics of laser beam absorption as the function of wavelength for the main components of the tooth [26].
