Michal Nemec

Endodontic Treatment with Application of Er:YAG Laser Waveguide Radiation Disinfection

OBJECTIVE The objective of this study is to examine the ability of Er:YAG laser radiation. Using a movable waveguide helps to obtain an antibacterial effect, not only in root canal walls but also in the surrounding tissues. BACKGROUND DATA Conventional endodontic treatment is not fully effective due to microbial colonization of root canal walls dentin in premolars and molars. Various laser systems seem to be effective to kill the remaining microbial content in the root canal. The problem is in the flexibility of laser system tips. MATERIALS AND METHODS The Er:YAG laser system was designed with a fluorocarbon polymer-coated silver hollow glass waveguide. Root canal systems of 44 premolars and molars were treated endodontically, using a step-back technique; 10 teeth were then treated with calcium hydroxide paste, and 22 teeth were irradiated by a movable waveguide. Before and after treatment, the colony-forming units were counted to determine 21 various microorganisms. RESULTS Classical enlargement and shaping of the root canal is effective in 60%. Application of calcium hydroxide prepares sterile root canal in 80%. Er:YAG laser irradiation via movable waveguide (energy of 100 mJ, 30 pulses, repetition rate 4 Hz) can ensure residual disinfection of the root canal. CONCLUSION Application of Er:YAG laser radiation through a flexible waveguide helps to attain antibacterial effect, not only in the root canal walls, but also in the surrounding tissues. Therapeutic doses of laser radiation guarantee one-step disinfection, including of anaerobic microorganisms.

Erbium:YAG laser lithotripsy by use of a flexible hollow waveguide with an end-scaling cap.

An Er:YAG laser light delivery system composed of a polymer-coated silver hollow waveguide and a quartz sealing cap has been developed for calculus fragmentation. Sealing caps with various distal-end geometries were fabricated, and the focusing effects of these caps for Er:YAG laser light were measured both in air and in water. Owing to the high power capability of the quartz a beam of sealing caps, Er:YAG laser light with an output energy of 200 mJ and a repetition rate of 10 Hz was successfully transmitted in saline solution by use of the system. Calculus fragmentation experiments conducted in vitro showed that the delivery system is suitable for medical applications in lithotripsy. We also found that the cap with a focusing effect is more effective in cutting calculi. The deterioration of the sealing caps after calculus fragmentation is also discussed.

Ceramic Bracket Debonding by Tm:YAP Laser Irradiation

OBJECTIVE The aim of this study was to prepare a simple and reliable method for ceramic bracket debonding, ensuring minimal changes in the enamel structure and an acceptable temperature rise in the pulp. BACKGROUND DATA Ceramic bracket debonding is based on the principle of degrading the strength of adhesive resin between the tooth and ceramic bracket. The search for a safe and efficient method of adhesive resin removal following debonding has resulted in the introduction of a wide range of instruments and procedures, among which proper use of laser irradiation can be promising. METHODS The debonding of two types of ceramic brackets utilized a diode-pumped Thulium:Ytterbium-Aluminium-Perovskite (Tm:YAP) microchip laser generating irradiation at a wavelength of 1998 nm (spot size 3 mm; focused by lens), with two power settings (1-2 W). Loss of enamel and residual resin on teeth, as well as rise in temperature inside the tooth were subsequently investigated in detail. RESULTS A 1W power of irradiation during a 60-sec period resulted in a temperature rise from 3 to 4°C in the approximate root location. This power is also suitable for debracketing from the point of view of damage to enamel lying below the bracket. Only a slight damage to the enamel was registered by SEM compared to conventional bracket removal. CONCLUSIONS Use of a Tm:YAP laser (wavelength 1998 nm, power 1 W, irradiance 14 W/cm(2), interacting time 60 sec) which is at the same time compact and small enough to be used in the dental practice, together with moderate cooling, could be an efficient tool for debracketing.

Resonantly pumped, high peak power Er:YAG laser

The high peak power hybrid Er:YAG laser, resonantly pumped at the wavelength of 1532 nm was developed. The fused silica acousto-optic modulator driven by 10 W of RF power was deployed as the Q-switch for such a laser. For the best case of Q-switching regime the pulses of 110 kW peak power (4 mJ, 37 ns) were reached at the pump power of 7.8 W and the repetition rate of 500 Hz.

Optical properties and surface structure comparison of tooth whitening using four laser systems and chemical action agents

The purpose of the study is to evaluate the effect of various laser techniques for bleaching teeth in office vital whitening. Hydrogen peroxide (30% concentration) and carbamide peroxide (10% solution) were used for chemical activation of bleaching process. Extracted non-carcious upper central incisors were exposed to laser radiation. Four different laser systems (Nd:YAG laser SHG, wavelength 0.53 μm, CTE:YAG laser, wavelength 2.7 μm, Nd:YAG laser, wavelength 1.06 μm, and alexandrite laser, wavelength 0.75 μm) were applied to accelerate the speed of the process. The end of chemical exposition was verified by the change of bleaching agent color. The color change was determined by stereomicroscope (Nikon SMZ 2T, Japan), the quality of surface structure was checked by scanning electron microscope Joel (Japan). The speed of bleaching rnaged from 630 s (chemical methods only) to 250-340 s (chemicals + alexandrite laser radiation). The Alexandrite laser application was considered an elective process to decrease the time of bleaching without modifying the surface.

Diode pumped Tm:YAP laser for eye microsurgery

Pulsed tunable diode-pumped Tm:YAP laser was characterized and used for preliminary investigation in eye microsurgery. By means of Lyot filter, the laser emission was tuned between a high (120 cm-1 @ 1940 nm) and two times lower (50 cm-1 @ 2040 nm) value of radiation absorption in water. In the interaction experiment, the eye tissue (in vitro) was irradiated with tunable Tm:YAP laser radiation, and the effects of cutting and coagulation depth in wavelength range from 1940 nm up to 2040 nm were investigated. The results were documented by optical microscope.

Laser action in bulk Cr:ZnSe crystals

Cr:ZnSe laser active material is one of the favourite possibility how to generate broadly tunable mid-infrared laser radiation at room-temperature. The aim of this study was to demonstrate and analyze pulsed as well as continuous-wave laser action in bulk Cr:ZnSe crystals grown by the floating-zone method or by the Bridgman method. The absorption spectra of Cr:ZnSe were measured to be from 1500 to 2000 nm, therefore various lasers were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser (generated wavelength 1658 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm), and diodepumped Tm:YAP laser (generated wavelength 1980 nm). In the first case, the Cr:ZnSe crystal grown by the Bridgman method was investigated. In the second case, the Cr:ZnSe crystal grown by the floating zone method was studied. In both cases, the homogeneity of the active Cr:ZnSe crystals was found reasonable good. The emission spectrum was from 2000 up to 2800 nm. The Cr:ZnSe laser generated radiation was broadly continuously tunable in the range from 2050 nm up to 2750 nm. The generated radiation beam spatial structure was close to TEM00.

V:YAG saturable absorber for flash-lamp and diode-pumped solid state lasers

V:YAG saturable absorber was used for efficient Q-switching and mode-locking of Nd:YAG and Nd:YAP flash-lamp or diode pumped lasers operating in 1.3 mm region. Crystals of Yttrium-Aluminum Garnet (YAG) doped with three-valence vanadium V3+ in tetrahedral position (V:YAG) were grown using of Czochralski method in reducing protective atmosphere. High purity oxides were used for crystal growth (Y2O3 (5N), Al2O3 (5N), V2O5 (4N)). Concentration of V2O5 in the melt reached up to 1 wt. %. Discs of the diameter 5 or 10 mm and of various thickness were machined from grown V:YAG crystals. The discs were both sides polished and AR coated so that minimum reflectivity at 1.08 and 1.34 microns was reached. The initial transmission of the saturable absorber was dependent on the samples thickness and its annealing process. We report stability improvement of passively mode-locked (by these V:YAG crystals) Nd:YAP flash-lamp pumped lasers. The maximum output energy 53 mJ at wavelength 1340 nm was obtained for Nd:YAP flash-lamp pumped laser operating at repetition rate 5 Hz. Mode-locked train envelope width was measured to be 22 ns (FWHM). Individual pulses inside the train were shorter than 1 ns. Also results with composite Nd:YAG rod Q-switched by V:YAG crystal and with Nd:YAG/V:YAG monolith rod under CW longitudinal diode pumping was obtained and compared. These laser systems represent new powerfull sources in the near infrared region.

Passively Q-switched resonantly pumped Er:YAG laser

A preliminary investigation of the passively Q-switched resonantly pumped Er:YAG laser system operating at wavelength 1645 nm has been performed. The output characteristics of the designed and constructed laser, i.e., the output energy, temporal profile, and spatial beam structure were registered. The Er:YAG laser crystals longitudinally pulse-pumped by Erbium glass laser radiation (repetition rate 0.5 Hz, wavelength 1535 nm) were investigated. The passive Q-switch was a Co:MALO (Co2+:MgAl2O4) crystal. To optimize the system, three Er:YAG crystals with various in Erbium/Yttrium concentration and length were studied in the free-running regime. The curved pumping mirror of linear hemispherical oscillator had a high transmittance at the pumping wavelength and maximal reflectance at the generating wavelength around 1645 nm. The output flat dielectric coupler reflectance was 90 % at 1645 nm. Out of the three Er:YAG active laser crystals, the best output characteristics in free running regime were reached for the medium with Er3+ concentration 0.2 at.% Er/Y and length 25 mm. For the Q-switching, three saturable absorbers Co:MALO with various length, that is various transmission, were investigated. These crystals had no anti-reflection layer and were placed between the active crystal and output mirror. The laser resonator length was 162 mm. For an incident pump energy of 131 mJ, the 1.6 mJ Q-switched single pulse energy with 58 ns pulse duration (FWHM) was obtained. The corresponding peak power was 28 kW. The spatial beam structure was close to the fundamental profile.

High repetition rate, tunable, Q-switched diode pumped Tm:YLF laser

The aim of work was to characterize a simple oscillator consisted of Tm:YLF crystal end-pumped by a fiber coupled diode laser and active Q-switch with tunability option. About 7 W with near 35% slope efficiency was demonstrated in a free-running mode. The divergence angle was about 4.3 mrad and estimated parameter M2 < 1.3. Continuous tuning by means of Lyot’s filter, consisted of 2 quartz plates in the range of 1879.0–1939.4 nm with less than 1-nm linewidth, was achieved. For the best case (10-ms pump pulse duration, 42-A pump current corresponding to 266 mJ of pump energy), the Q-switched energy was 10.5 mJ with pulse duration of 22 ns corresponding to near 0.5 MW peak power. The 2.5 W of average power with 12.6-kW peak power and 2000-Hz repetition rate was demonstrated for cw pumping regime.