Usos y fundamentos del láser en periodoncia e implantología oral / Uses and fundamentals of laser in periodontics and oral implantology

El primer dispositivo láser fue desarrollado por Maiman en 1960. Desde entonces, el láser es ampliamente usado en medicina y cirugía, debido a su capacidad de emitir energía altamente concentrada y controlable sobre los tejidos a ser tratados. Para obtener el efecto biológico deseado, la energía debe absorberse en los tejidos y, al ser transformada en calor, se consiguen distintos efectos, dependiendo de la temperatura a la que se eleve el tejido. En caso de exceso de neergía láser aplicada, se elevará la temperatura del tejido por sobre los 200º C y se llegará a la carbonización y, en consecuencia, al daño tisular. Por esta razón, el clínico debe controlar los parámetros de energía, el diámetro del rayo y el tiempo o la duración de la exposición, para obtener un resultado satisfactorio, teniendo en cuenta que el rango de ablación varía con la composición y la estructura del sitio quirúrgico. Es muy importante tener en cuenta que diferentes longitudes de onda tienen diferentes coeficientes de absorción en los diferentes tejidos. Los láseres más utilizados en odontología para el desarrollo de tratamientos periodontales, incluyendo cirugía periodontal, poseen longitudes de onda que pertenecen al rango visible e invisible del espectro electromagnético. Podemos mencionar el láser de Erbium:YAG (2.940 nm), dióxido de carbono (10.600 nm), Nd:YAG (1064 nm), diodo (810-980 nm) y el láser e argón, con dos longitudes de onda (488 nm, de color azul, y 514 nm, verde azulada). Los láseres de argón, diodo y Nd:YAG tienen alta afinidad por componentes de la sangre y tejidos pigmentados y, por consiguiente, muy buena absorción en ellos. Los láseres de erbium:YAG y dióxido de carbono son altamente absorbidos por el agua, principal componente de los tejidos blandos. La razón por la que no existe un dispositivo láser que sea 100 por ciento eficiente en todos los tejidos, se debe a la composición del tejido y al tipo de interacción física de la luz.

Usos y fundamentos del láser en periodoncia e implantología oral / Uses and fundamentals of laser in periodontics and oral implantology

El primer dispositivo láser fue desarrollado por Maiman en 1960. Desde entonces, el láser es ampliamente usado en medicina y cirugía, debido a su capacidad de emitir energía altamente concentrada y controlable sobre los tejidos a ser tratados. Para obtener el efecto biológico deseado, la energía debe absorberse en los tejidos y, al ser transformada en calor, se consiguen distintos efectos, dependiendo de la temperatura a la que se eleve el tejido. En caso de exceso de neergía láser aplicada, se elevará la temperatura del tejido por sobre los 200º C y se llegará a la carbonización y, en consecuencia, al daño tisular. Por esta razón, el clínico debe controlar los parámetros de energía, el diámetro del rayo y el tiempo o la duración de la exposición, para obtener un resultado satisfactorio, teniendo en cuenta que el rango de ablación varía con la composición y la estructura del sitio quirúrgico. Es muy importante tener en cuenta que diferentes longitudes de onda tienen diferentes coeficientes de absorción en los diferentes tejidos. Los láseres más utilizados en odontología para el desarrollo de tratamientos periodontales, incluyendo cirugía periodontal, poseen longitudes de onda que pertenecen al rango visible e invisible del espectro electromagnético. Podemos mencionar el láser de Erbium:YAG (2.940 nm), dióxido de carbono (10.600 nm), Nd:YAG (1064 nm), diodo (810-980 nm) y el láser e argón, con dos longitudes de onda (488 nm, de color azul, y 514 nm, verde azulada). Los láseres de argón, diodo y Nd:YAG tienen alta afinidad por componentes de la sangre y tejidos pigmentados y, por consiguiente, muy buena absorción en ellos. Los láseres de erbium:YAG y dióxido de carbono son altamente absorbidos por el agua, principal componente de los tejidos blandos. La razón por la que no existe un dispositivo láser que sea 100 por ciento eficiente en todos los tejidos, se debe a la composición del tejido y al tipo de interacción física de la luz. (AU)

Putative photoacoustic damage in skin induced by pulsed ArF excimer laser.

Argon-fluoride excimer laser ablation of guinea pig stratum corneum causes deeper tissue damage than expected for thermal or photochemical mechanisms, suggesting that photoacoustic waves have a role in tissue damage. Laser irradiation (193 nm, 14-ns pulse) at two different radiant exposures, 62 and 156 mJ/cm2 per pulse, was used to ablate the 15-microns-thick stratum corneum of the skin. Light and electron microscopy of immediate biopsies demonstrated damage to fibroblasts as deep as 88 and 220 microns, respectively, below the ablation site. These depths are far in excess of the optical penetration depth of 193-nm light (1/e depth = 1.5 micron). The damage is unlikely to be due to a photochemical mechanism because (a) the photons will not penetrate to these depths, (b) it is a long distance for toxic photoproducts to diffuse, and (c) damage is proportional to laser pulse intensity and not the total dose that accumulates in the residual tissue; therefore, reciprocity does not hold. Damage due to a thermal mechanism is not expected because there is not sufficient energy deposited in the tissue to cause significant heating at such depths. The damage is most likely due to a photoacoustic mechanism because (a) photoacoustic waves can propagate deep into tissue, (b) the depth of damage increases with increasing laser pulse intensity rather than with increasing total residual energy, and (c) the effects are immediate. These effects should be considered in the evaluation of short pulse, high peak power laser-tissue interactions.

Comparative efficacy of continuous and pulsed argon laser ablation of human diseased ventricle.

We compared the tissue lesions obtained in a saline medium using single continuous argon laser discharges with paired sequential continuous laser discharges in nine segments of diseased human ventricle resected from patients with and without ventricular tachycardia (VT) at cardiac surgery. Single continuous argon laser discharges were delivered to separate sites on the endocardial surface of the tissue segments for periods of 10, 20, and 30 seconds at laser beam power of 5 W (group IA) and 8 W (group IIA). Paired sequential argon laser discharges of 5, 10, and 15 seconds in duration were delivered to separate sites at a laser power of 5 W (group IB) and 8 W (group IIB). Gross and microscopic examination of each tissue lesion and its dimensions were performed. Laser irradiation of excised human ventricle resulted in a circular discrete burn at the site of application. Histologic examination showed crater formation due to tissue vaporization with the crater lining consisting of charred tissue and a zone of coagulation necrosis. Analysis of lesion dimensions in groups IA and IIA showed comparable lesion depth and diameter with single continuous and paired sequential laser discharges at energies of 50 J (p greater than .2), 100 J (p greater than .2), and 150 J (p greater than .2). Similarly, lesion depth and diameter were comparable in groups IB and IIB at the same energies. We conclude that paired sequential argon laser discharges may be used to produce comparable tissue lesions to single continuous argon laser discharges in diseased human ventricle.

Protective eye filters for endolaser therapy with the indirect ophthalmoscope.

I have developed two protective caps that fit on the viewing windows of the indirect ophthalmoscope. These caps contain filters that absorb the argon laser beam and protect the operator's eyes during endolaser treatment.

The effects of varying lengths and powers of CO2 laser pulses transmitted through an optical fiber on atherosclerotic plaques.

We have studied the changes induced in atherosclerotic arteries by a CO2 laser beam delivered through a silver halide optical fiber. We found that the crater depth and diameter correlate with the total energy delivered and with the mode of delivery. Short-duration high-power pulses caused shallower and narrower craters and less damage to the arterial wall compared to the same energy delivered as low-power pulses of long duration. Thus, high-power pulses for short periods may be an effective and safe procedure for evaporization of atherosclerotic plaques.

Low-energy long-exposure laser therapy in the management of choroidal melanoma.

Low-energy (0.2-0.4 W) long-exposure (10-30 s) argon green and krypton red laser applications were used in the treatment of 29 selected choroidal melanomas. In 11 cases laser treatment was the only therapy used. In 18 cases laser was used as an adjunct to local surgical resection of the tumour. The technique gives promise of being useful in the management of relatively flat choroidal melanomas of up 4 mm in thickness.

Effects of XeCl excimer laser on the eyelid and anterior segment structures.

We evaluated the in vitro and in vivo effects of an XeCl excimer laser on the eyelid and anterior segments of the eye. The wavelength of this laser was successfully transmitted through a quartz fiberoptic system. The action of the XeCl excimer laser through our system was more photocoagulative than photoablative.

Threshold for lens damage during Q-switched Nd:YAG laser iridectomy. A study of rhesus monkey eyes.

Clinical and pathologic examinations were performed after 18 iridectomies had been created in six eyes of three rhesus monkeys using increasing Q-switched neodymium (Nd):YAG laser energy, pulses per burst, and number of bursts. Treatment parameters bracketed the threshold for lens damage during iridectomy. Iridectomy with one or two bursts of one or two Q-switched pulses at 5 to 6.2 mJ per pulse was achieved without lens damage. Slight increase of pulse energy or an increase to three pulses per burst (without pulse energy increase) caused local damage to the underlying lens. Marked increase of any of the treatment parameters caused slightly larger iridectomies and slightly larger, localized damage of the underlying lens. Synechiae developed between the monkey posterior iris surface at the iridectomy and the damaged area in 80% of the lens lesions. In monkeys, the small pulsed laser iridectomies created with pulses of energies up to 6.5 mJ became occluded during the healing process.

Endothelial damage from retrocorneal mode-locked neodymium:YAG laser pulses in monkeys.

Laser pulses were focused 0.85 to 1.60 mm from the rhesus monkey corneal endothelium using a mode-locked laser at 3.3 and 4.5 mJ. Sixteen slightly off-axis pulses were applied with no contact lens on the eye. Corneal damage was studied clinically and by scanning electron microscopy. The retrocorneal distance for a 50% incidence of endothelial damage (LD 50 = lesion distance, 50%) for 3.3 mJ mode-locked pulses was found to be 1.60 mm. All mode-locked pulses of 4.5 mJ focused 0.85 to 1.60 mJ from the endothelium caused damage. In comparison, Q-switched pulses of 12 mJ or less are not likely to damage the cornea if focused more than 0.75 mm from the endothelium. The severe, early effect of mode-locked pulses is edema of endothelial cells in a 0.2- to 0.3-mm diameter circular zone surrounding a 0.1-mm diameter denuded zone with a small central break of Descemet's membrane. By two months, mild and moderate lesions heal with little or no distortion of the endothelial mosaic. Irregular enlargement of endothelial cells surrounding and covering the previously denuded area of severe lesions is caused by both mode-locked and Q-switched treatment. In no case was there clinically significant, persistent damage in the healed monkey corneas.

Endothelial damage thresholds for retrocorneal Q-switched neodymium:YAG laser pulses in monkeys.

Laser pulses were focused within 1 mm of the rhesus monkey corneal endothelium using the Coherent Model 9900 laser at energies of 3, 6, 9, and 12 mJ. Sixteen slightly off-axis pulses were applied with no contact lens on the eye. Corneal damage was studied clinically and by scanning electron microscopy. Q-switched pulses of 12 mJ or less are not likely to damage the cornea if focused more than 0.75 mm from the endothelium. The retrocorneal focal distance for a 50% incidence of endothelial damage for 6, 9, and 12 mJ pulses was found to be less than 0.5 mm. For 3 mJ pulses, it was less than 0.25 mm. The severe early effect of suprathreshold pulses is edema of endothelial cells in a 0.2- to 0.6-mm diameter circular zone surrounding a small central pit through Descemet's membrane. At two months, irregular enlargement of endothelial cells surrounding and partially covering the persistent pit exists at sites of severe damage. The extent of the longer-term change is proportional to the severity of the original insult, but in no case was there clinically significant, persistent damage in the healed corneas.

Shock-wave effect on anterior segment structures following experimental neodymium:YAG laser iridectomy.

The short-pulse laser may prove superior to the argon laser in producing noninvasive iridectomies. Little is known of the effects of the laser shock-wave on anterior segment structures adjacent to the iris. To investigate this question, iridectomies were produced in two owl monkeys using a neodymium (Nd):YAG laser and tissues were evaluated by light microscopy and scanning and transmission electron microscopy. For purposes of comparison, one eye received an iridectomy produced by an argon laser. Results indicate that while clean iris colobomas can be produced with a well-focused Nd:YAG laser, its shock-wave affects tissues in both the trabecular meshwork and corneal endothelium if the iridectomy is located within 0.8 mm of the limbus. No damage to the trabecular meshwork or corneal endothelium was evident after the argon laser iridectomy.

Laser treatment of upper gastrointestinal hemorrhage.

The goal of laser treatment of the visible vessel or bleeding ulcer is to stop the bleeding to allow healing of the ulcer base. Adjuvant techniques including the use of vasoconstrictive agents, tissue adhesives, and tissue injection hold future promise in complementing laser therapy. Laser photocoagulation appears to be an effective method of treatment. At this time, however, the therapy of this serious clinical problem is evolving. As experience increases and as new technology and techniques are applied, the development of an effective treatment for the bleeding peptic ulcer or visible vessel is even more promising.

[Flattening of hypertrophic scars by punctiform argon ion laser coagulation in several sessions]. / Abflachung hypertropher Narben durch punktförmige Argon-Ionen-Laserkoagulation in mehreren Sitzungen.

11 hypertrophic scars were treated by different argon ion laser techniques. The observation period is 0.5-3 years. Punctiform coagulation zones of 2-3 mm diameter, interspersed by untreated areas of scar tissue of 2 mm length, which are by lasered 6 weeks later in a second laser session, has proved most successful. Laser sessions are repeated in this manner until sufficient flattening of the hypertrophic scar is achieved. A low power density and very brief multiple interrupted radiation periods for controlling the thermal effect are useful. It is assumed that small superficial coagulation necroses produced by the argon ion laser will result in subsequent scar tissue being formed in other directions while decreasing the collagen formation, eventually resulting in flattening of the hypertrophic scar.

The effect of thermal mode Nd:YAG laser radiation on vessels and ocular tissues. Experimental and clinical findings.

Ultrastructural examination of mesenteric vessels of pigmented rabbits after irradiation with the thermal mode of Nd:YAG laser showed an excellent hemostatic effect. Clinical experience parallels those findings.

Aplicaciones del rayo laser en endoscopía digestiva / Use of laser in digestive endoscopy

La aplicación endoscópica del Nd: Yag laser en el control del sagrado digestivo está adquiriendo especial significado en un seleccionado grupo de pacientes con alto riesgo. Lesiones mucosas, como los pólipos benignos y malformaciones vasculares pueden ser tratadas exitosamente. En lesiones gastrointestinales obstructivas malignas avanzadas e inoperables, que son accesibles a la visión endoscópica, la cirugía por laser es extremadamente útil como procedimiento paliativo. Los resultados en early cáncer gástrico, endoscópicamente vaporizados son estimulantes. El sistema laser es caro y requiere complejas conexiones de agua y electricidad, además de la asistencia de un técnico competente. Se trata de resolver estos problemas que pueden cambiar dramáticamente el futuro de la endoscopía terapéutica del laser