Laser in Dentistry PDF

A laser (Light Amplification by Lasers in Stimulated Emission of Dentistry Radiation), Population inversion in which the number of atoms or molecules in the upper energy levels is higher than that in the lower ones. This cannot be achieved by direct excitation of atoms and molecules...

A laser (Light Amplification by Lasers in Stimulated Emission of Dentistry Radiation), Population inversion in which the number of atoms or molecules in the upper energy levels is higher than that in the lower ones. This cannot be achieved by direct excitation of atoms and molecules Laser to the lasing state since this will Requirements give at best 50% excited states and no population inversion will be 1- Stimulated achieved Emission 2-Population inversion Laser properties These properties are Laser radiation has the following important characteristics over ordinary light source. They are: i) monochromaticity (photons have the same wavelength), ii) directionality or parallelism (not divergent), iii) coherence (photons propagate in phase), and iv) brightness (high intensity). ❑ A ruby laser is an example of a three- energy level solid-state laser that uses the synthetic ruby crystal as its laser medium. ❑ Ruby laser is the first successful laser developed by Maiman in 1960. ❑ It emits deep red light of wavelength 694.3 nm. ❑ In a ruby laser, a single crystal of ruby (Al2O3: Cr3+) in the form of cylinder acts as a laser medium or active medium. ❑ The laser medium (ruby) in the ruby laser ❑ In a ruby laser, we use flashtube is made of a host of sapphire (Al2O3) as the energy source or pump which is doped with small amounts of source. The flashtube supplies energy to the laser medium chromium ions (Cr3+). (ruby). ❑ The ruby has good thermal properties. ❑ Given E1 is the ground state or lower energy state, ❑ the energy level E2 is known as metastable state, and ❑ the energy level E3 is known as pump state. ❑ Let us assume that initially most of the electrons are in the lower energy state (E1) and only a tiny number of ions are in the excited states (E2 and E3) (Figure 4-12). ❑ When light energy is supplied to the laser medium (ruby), the electrons in the lower energy state or ground state (E1) gain enough energy and jumps into the pump state (E3). ❑ The lifetime of pump state E3 is very small (10-9 sec) so the electrons in the pump state do not stay for long period. After a short period, they fall into the metastable state E2 by releasing radiationless energy. ❑ The lifetime of metastable state E2 is 10-3 sec which is much greater than the lifetime of pump state E3. ❑ Therefore, the ions reach E2 much faster than they leave E2. This results in an increase in the number of electrons in the metastable state E2 and hence population inversion is achieved. ❑After some period, the ions in the metastable state E2 fall into the lower energy state E1 by releasing energy in the form of photons. This is called spontaneous emission of radiation. When the emitted photon interacts with the electron in the metastable state, it forcefully makes that ion fall into the ground state E1. As a result, two photons are emitted. This is the stimulated emission of radiation. ❑When these emitted photons again interact with the metastable state electrons, then 4 photons are produced. Because of this continuous interaction with the electrons, millions of photons are produced. ❑In an active medium (ruby), a process called spontaneous emission produces light. The light produced within the laser medium will bounce back and forth between the two mirrors. This stimulates other electrons to fall into the ground state by releasing light energy. This is called stimulated emission. Likewise, millions of electrons are stimulated to emit light. Thus, the light gain is achieved. The amplified light escapes through the partially reflecting mirror to produce laser light.  Some other solid- state lasers ❑ Similar laser systems that are commonly used in dentistry are: Er:YAG laser in which erbium (chemical symbol: Er) in the form of the trivalent ion Er3+ is used as the laser-active dopant in yttrium aluminum garnet (YAG). Er:YAG laser emits light with a wavelength of 2.940 μm, which is in the infrared region. used in the form of the trivalent ion Er3+ as the laser-active dopant. Erbium belongs to the so-called rare earth metals including, among other 17 elements, neodymium (Nd3+), europium (Eu3+), gadolinium (Gd3+), holmium (Ho3+), and yttrium (Y3+) - that appear in low concentrations in the ground. All the laser-active rare earth ions are lanthanides. Therefore, lasers based on rare-earth-doped gain media are sometimes called lanthanide lasers. ❑ (Er,Cr:YSGG) laser is erbium, chromium-doped yttrium, scandium, gallium and garnet that emits at a wavelength of 2.780 μm and is highly absorbed by water. ❑ Similarly, Nd:YAG laser consists of Nd3+ ions in yttrium- aluminum- garnet host where Nd3+ ions substitute yttrium (Y3+) ions in the host YAG host matrix giving laser emission at 1.064 μm that falls in the infrared region. ❑ Nd:YAP laser has the chemical formula Nd3+: YAlO3, with the addition of a chemical material called perovskite giving laser emission at 1.340 μm that falls in the infrared region. ❑ GaAlAs laser is another important laser in the near infrared region is giving mainly laser photons at 980 nm. ❑ Another important dental solid- state laser is KTP laser. KTP stands for the Potassium Titanyl Phosphate (KTP), and this crystal is used as the laser medium, producing a wavelength of 532 nanometers in the visible region. The KTP laser only targets the oxyhemoglobin in our blood, thereby leaving surrounding structures and tissue unaffected. Helium- Neon Laser Gas Lasers ❑ As a demonstration of the four – energy level laser, we will discuss the He-Ne laser in which population inversion of Ne, which is the lasing species, will be achieved by energy transfer from electrically excited He* atoms. ❑ In our demonstration we selected the He-Ne laser system in which He is excited by an electrical discharge. ❑ Energy transfer to the Ne atoms then gives the excited Ne atoms which are the laser emitting species. ❑ In this case a mixture of the two gases in the ratio (He: Ne = 10: 1) is put in an optical cavity and a pair of parallel mirrors is put as in Figure 4-10. One of the parallel mirrors is partially transparent and the other is totally reflecting.  Carbon dioxide (CO2 ) laser ❑ The transitions leading to laser emission in carbon dioxide lasers are not electronic transitions but vibrational transitions within the ground electronic state of CO2 molecule. ❑ The three possible vibrational modes in CO2 are the symmetric stretching, the bending mode, and the asymmetric stretch. ❑ Pumping is by electric discharge through a mixture of CO2, N2 and He gases resulting in the efficient production of the first vibrational state of nitrogen. ❑ The first vibrational state of nitrogen selectively populates the first vibrational excited asymmetric stretch mode. ❑ The energy of this state matches the first vibrational state of N2 permitting resonant energy transfer to occur (See Figure 4-14). ❑ Helium atoms serve in depopulating lower vibrational energy level ❑ The main laser emissions occur at about 10.6 and 9.4 m. ❑ The tremendous potential power of CO2 lasers, arising from the high efficiency of the lasing transition, is a key reason for their use in welding, cutting, and drilling materials. ❑ One application of particular importance for CO2 lasers is the cutting of titanium metal, an especially hard material for mechanical tools to cut. ❑ CO2 laser has attained popularity in surgical applications to cut and cauterize tissue because of the absorption of infrared radiation by water in the tissues. ❑ Hydroxyapatite, the main constituent of enamel and dentin, has a very strong absorption peak in the IR region around 10 μm.  The CO2 laser is THE ONLY practical soft-tissue surgical laser that uses the laser beam directly to cut, ablate and photo-thermally coagulate the soft tissue. IR CO2 laser - Well absorbed by enamel and dentin - Welding ceramic materials to enamel Human Teeth and its Chemical Constituents Water absorbs in the UV region (below 200 nm) and in the IR region at 2.94 μm. Hydroxyapatite, the main constituent of enamel 96% and dentin has a very strong absorption peak in the IR region around 10 μm. 3%  Some Other Applications of Lasers Selective bond breaking BCl3 + C6H6 → C6H5 − BCl2 + HCl ❑ This reaction normally proceeds only above 600C in the presence of a catalyst. ❑ Exposure to 10.6 m CO2 laser radiation results in the formation of products at room temperature without a catalyst. ❑ The commercial potential of this procedure is considerable since heat-sensitive compounds, such as pharmaceuticals, may be made at lower temperatures than in conventional reactions. The laser can be used selectively. It is tuned to the absorption frequency of a particular molecule and drives a reaction that differs from thermal chemistry using normal heat sources. Using finely tuned laser radiation we can selectively excite and react to a chosen molecule in the presence of a non-absorbing species, which may be a different molecule or an isotopic variant of the same molecule.  Laser capture microdissection (LCM) ❑ Laser capture microdissection is a technique that can be used to isolate small histologically homogeneous cell populations (or even single cells) from tissue sections in a form suitable for analysis by molecular biological techniques. ❑ The LCM system is now commercially available, and in addition to its simplicity, it has the advantage of preserving the tissue’s original morphology while avoiding contamination from surrounding tissue. LCM system is basically an inverted microscope fitted with a low power near IR laser. Tissue sections are mounted on standard glass slider, and a transparent ethylene-vinyl acetate film is then placed over the dry ❑ The IR laser provides enough thermal energy to transiently melt the thermoplastic film in a precise location, binding it to targeted cells. ❑ The laser diameter can be adjusted from 7.5 to 30 m so that individual cells or cluster of cells can be selected. ❑ Because the plastic film absorbs most of the thermal energy and the pulse duration is a fraction of a second, little or no detectable damage to the biological environment occurs.  Laser welding of detached eye retina The retina is the light-sensitive layer which forms a sort of carpet on the inside of the eye. It sometimes happens – especially in old age – that this carpet becomes detached from the eyeball and floats in the surrounding liquid. In the area of detached retina, vision is lost. The modern technique of repair of the detached retina uses the properties of pulsed laser which can be focused into a very tiny spot near the fault line where detachment has occurred. The heat liberated by this light then acts as spot welding, and with a number of these “molten” contact points the retina is cemented back on the inner surface of the eye.  Laser lithotripsy of calculi ❑ Laser lithotripsy is an effective means to fragment stones within the gallbladder and the common bile duct. ❑ The objective of the procedure is to crush stones into fragments that are small enough to be passed naturally (diameter less than 2 mm). ❑ The fragmentation of the stone with a pulsed dye laser is found to result in a bright flash of light. Time–resolved spectroscopy indicates a continuum and broad banded lines due to neutral and singly ionized calcium, suggesting that plasma is generated in the fragmentation process. ❑ As it expands, the plasma produces a shock wave in the stone to cause it to break. Another approach is to use a Ho: YAG laser operating at 2.1 µm. ❑ The absorption of this line by water results in superheated steam with subsequent pressure inside the stone causing its breakdown. The advantages of this last technique are: i) it works with all types of stones, and ii) it has the effect of reducing risk of damage to tissue surrounding a stone. ❑ In dye-laser application, it is better to use different wavelengths according to the color of stone which is related to its composition. ❑ Black stones, referred to as pigmented, are composed primarily of calcium bilirubinate. ❑ White or slightly tanned stones, referred to as cholesterol stones, are composed of cholesterol monohydrate. ❑ Brown, or mid, stones are a mixture of cholesterol stones and calcium salts, bile acids, fatty acids, proteins, and phospholipids.