In prosthodontics, 3D printing primarily relies on intraoral scanners equipped with a handheld camera, computer, and software. These scanners capture and reconstruct the three-dimensional geometry of the dental arch. Traditional plaster models of teeth are typically obtained through an impression process, where the choice of appropriate impression material is determined by the desired model type. Subsequently, the dental impression is covered with plaster in the laboratory. Three-dimensional (3D) printing, formerly an industrial technology with a development history spanning over forty years, is based on creating a 3D model of any shape from a digitally prepared scan, employing an addition of selected material. The thickness of the layers in the printing process depends on the technology of the used printer and the quality of the print. The layers are systematically applied, and cured, and, after this process, a complete model is generated. 3D printing can be utilized to prepare models for various applications, including prosthodontics, orthodontics, surgery, and more. Our study aimed to assess stereolithography-printed models in vitro and in vivo over the last three years.
The aim of our study was 3D objectification of stereolithography prepared printed models. Patients during clinical treatment were scanned by an optical scanner. Data from scanner were transferred to the STL files and then stereolithographic models were prepared. Method of optical triangulation, photogrammetric methods and mathematical model analysis were used for measurements. The surface profile was also evaluated. After three years, the quality of STL models was smooth and homogeneous and it was directly connected with the type and structure of filaments. Clinical applications demonstrated also treatment options for patients with nausea, rare diseases, or with small space between upper and lower jaw.
KEYWORDS: Teeth, Semiconductor lasers, Diodes, Temperature metrology, Infrared lasers, 3D modeling, Laser dentistry, Scanning electron microscopy, Hydrogen, Electron microscopes
The study describes a diode system which activates a home-bleaching agent for discolored teeth. The techniques involve pastes utilizing 16 % hydrogen and carbamide peroxide. Two different laser diodes operating at 445 nm and 1.7 um were used. The exposition power densities used were up to 10 W/cm2. For bleaching, stereolithographic models and trays were prepared. Bleaching technique was activated laser irradiation lasting for 100 s, bleaching. After the bleaching process, the enamel surface was with the scanning electron microscope. This process resulted in a 2-3 shade change measurement in one treatment.
3D scans of dental arches and the 3D print technique in orthodontics have become every important part of clinical practice. The aim of our study was 3D objectification of stereolithography system (SLA) printed models in comparison with Fused Deposition Modeling (FDM), Polyjet (PJ) technology, and Selective Laser Sintering (SLS). The 50 scans of upper dental arches of medical students were prepared using 3Shape TRIOS 3. After then SLA 3D Printer Formlabs 2 built step by step layers of an upper dental arch model using liquid polymer hardened by laser beam (blue 405 nm laser). The study compared precision of 3D SLA, PDM, PJ and SLS models along all 3 axes.
In the last decade, lasers found a number of indications in dentistry. However, there is still one problem: the narrow spectrum of usefulness for individual radiation wavelengths. The aim of our study is to demonstrate the use of a compact three-frequency pulsed Nd-YAG laser for more than one treatment, namely disinfection, coagulation, selective ablation, and soft tissue removal. The laser wavelengths and the maximal energies achieved were the following: 1.06 um, 1.32 um, 1.44 um and 830 mJ, 425 mJ, and 200 mJ, respectively. It has been found that all of the investigated wavelengths exhibit disinfection properties. Moreover, radiation of 1.06 um wavelength removes soft tissue and exhibits also coagulation properties. Radiation of 1.44 um is most useful for selective ablation of initial caries and disinfection, and 1.32 um radiation can be used for precise ablation when higher energy is applied.
The analysis of the disinfection effect of Nd:YAG laser radiation was investigated for patients with high
concentration of Streptococcus mutans in saliva (positive result in Saliva-check mutans test). For the interaction the
Nd:YAG laser system generated separate switchable wavelengths with the maximum output energies 1.1, 0.6, and
0.3 J for wavelength 1.06 μm, 1.32, μm and 1.44 μm, respectively, was used. Our study proved that after the laser
irradiation the Saliva-check test showed negative presence of Streptococcus mutans. The disinfection effect was
confirmed for all used radiation wavelength. For 1.44 μm this effect was reached with a smallest energy density.
The goal of the study was investigation of Er:YAG radiation (wavelength 2.94 μm) interaction with various metal
and ceramic brackets and adhesive materials. The source of radiation was a free-running Er: YAG laser generating
pulses with energy 280 mJ, 250 μs long and repetition rate 6 Hz (mean power 1.7 W). During the treatment lasting
140 s, water cooling was implemented and only the brackets were irradiated. It has been observed that the brackets
were removed easily after the Er:YAG laser irradiation, and temperature rise was limited also for metal brackets.
SEM investigation has confirmed less damage of enamel in comparison with non-irradiated samples.
Third molar extractions in general anesthesia have become a standard procedure in dentistry. There is an effort to shorten
healing time and decrease the number of complications as well as increase comfort after the treatment. Low-level lasers
are known for their analgesic, anti-inflammatory, and stimulatory effect. The aim of the study is to evaluate the effect of
low-level laser after surgery in general anesthesia reducing the patient's discomfort, i.e. mainly pain, and also, to
monitor the biostimulation process. Our study included 79 patients treated at the Department of Maxilofacial Surgery,
diagnosed with third molar retention. Diode low-level laser radiation (wavelength 830 nm, output power 270 mW, probe
aperture of 6.4 mm2) with dose ~ 3 mJ was applied. The control group was treated by using placebo - red light. The
exposure time was 11 seconds immediately after the suture; the treatment was repeated every day for the following 3
days. To evaluate the effect of laser biostimulation, the objective markers for immunological determination of healing -
sIgA and lysozyme in non-stimulated saliva of patients - were used. The sIgA decreases after laser application from
546.91 mg/l to 304. 91mg/l and in the control group from 602.25mg/l to 425.62 mg/l. The results were statistically
significant. The level of lysozyme decreases from 54.27 mg/l to 2.45mg/l after laser biostimulation, from 304.371mg/l to
11.08mg/l after placebo effect. The study has confirmed a low-level laser healing effect not directly related to pain.
The goal of the work was the investigation of powerful Er: YSGG radiation (wavelength 2.79 um) interaction with
ivory and dentin. The main goal was an investigation of powerful Er: YSGG radiation interaction with ivory and dentin. As source of radiation was used a free-running or Q-switched Er: YSGG laser generating 250 us or 100 ns long pulses with pulse energy of 123 mJ or 41 mJ, respectively. The lens with the focal length 85 mm was used for concentration of the radiation on interacting material. The ablation rate was checked for case of both above mentioned regimes as well as for the cases of without and with water cooling of interacting material. It was found that for long pulse with the energy density of 176 J/cm2 the ablation rate was 0.033 mm3/J (without water cooling), while for short 100 ns with the energy density of 46 J/cm2 the ablation rate was 0.012 mm3/J (with water cooling).
The comparison of tissue quality and its restoration after contact, non-contact, and non-contact scanned Er:YAG
(2940 nm) laser radiation ablation was evaluated. Laser setting for contact ablation was 250 mJ/pulse, pulse repetition
rate 15 Hz, average power 3.75 W. For non-contact ablation these values were 600 mJ/pulse, 6 Hz, 3.6 W. The
scanning ablation was provided in non-contact mode (1440 pulses/1 cavity). All cavities were filled by sonic activated
composite resin. Microleakage was assessed quantitatively by the degree of dye penetration. Cavity prepared by
contact mode with sonic-activated composite filling protects microleakage formation.
The aim of study is to compare the ablation effect of contact and non-contact interaction of Er:YAG and CTH:YAG laser radiation with artificial enamel caries lesion. The artificial caries was prepared in intact teeth to simulate demineralized surface and the laser radiation was applied. Contact and non-contact ablation was compared. Two laser systems Er:YAG 2.94 μm and CTH:YAG 2.1 μm were used. The enamel artificial caries were gently removed by laser radiation and flow Sonic fill composite resin was inserted. Scanning electron microscope was use to evaluate the enamel surface.
The investigation of tensile strength needed for bracket debonding was the aim of study. A diode pumped Tm: YAP
microchip laser generating a continuous 2um radiation with the maximum output power of 4W was used for debonding
purposes. The group of 60 brackets was debonded using classical and laser irradiation methods - the doze from 1W to 4
W, 60s. The tensile strength without laser irradiation was in the range from 39.6 N (full ceramic bracket group) to 63.7 N
(ceramic bracket with metal slot group). After irradiation the tensile strength was decreased from 35.1 N (full ceramic
bracket group) to 48.8 N (ceramic bracket with metal slot group). The results of our study generally agree with the
previous studies, substantiating the fact that lasers can be used effectively to thermally soften the adhesive resin for
removal of ceramic brackets. From the practical point of view is conclusion that during laser irradiation, thermal
ablation occurs and the bracket is removed from the enamel together with the rest of the adhesive resin. Laser
debonding is easier and little heat diffusion occurred.
The study demonstrates the possibility of using Tm:YAP laser radiation for the removing ceramic brackets. The amount
of enamel loss and residual resin on teeth has been evaluated. A diode-pumped Tm:YAP microchip laser generating at
wavelength 1.9 μm was used for the debonding process. The transmission and absorption measurement of the basic
elements - bracket, adhesive resin, and enamel was analyzed to explain the source of the heat and bracket debonding.
Quantitative measurements are made for visualizing enamel surface before and after a self-ligating bonding technique.
Temperature rise observation during the debonding procedure - from 0.5 to 2 W power - has improved the accuracy of
assessment. The results were evaluated by CCD camera and scanning electron microscope. From the measurements it is possible to conclude that continuously running small diode pumped Tm:YAP microchip laser having output power 1W can remove the ceramic bracket without enamel iatrogenic damage.
The study demonstrates the possibility of using laser radiation for the ceramic bracket removing. Three laser radiations
were examined for this effect and the removing possibility and velocity together with enamel and root damage were
investigated. A diode pumped Tm:YAP microchip laser generating a wavelength 1.9 μm, diode pumped Nd:YAG laser
with 1.44 μm wavelength, GaAs diode with 0.808 μm were used for the debonding purpose. The measurement of
transmission and absorption of the basic element - bracket, adhesive resin, and enamel was also made with the goal to
explain the source of the heat and bracket debonding. The explanation of the debonding effect is also presented.
From the results it is possible to conclude that continuously running diode pumped microchip Tm:YAP laser having
output power 1W can be a good candidate for ceramic bracket debonding procedure.
Ceramic brackets are an aesthetic substitute for conventional stainless steel brackets in orthodontic patients. However,
ceramic brackets are more brittle and have higher bond strengths, which can lead to bracket breakage and enamel damage
during classical type of debonding.
This study examined the possibility of laser radiation ceramic brackets removing as well as the possible damage of a
surface structure of hard dental tissue after this procedure. Two types of lasers were used for the experiments - a laser
diode LIMO HLU20F400 generating a wavelength of 808 nm with the maximum output power 20W at the end of the
fiber (core diameter 400 &mgr;m, numerical aperture 0.22). As a second source, a diode-pumped Tm:YAP laser system
generating a wavelength of 1.9 &mgr;m, with up to 3.8 W maximum output power was chosen. For the investigation,
extracted incisors with ceramic brackets were used. In both cases, laser radiation was applied for 0.5 minute at a
maximum power of 1 W. Temperature changes of the irradiated tissue was registered by camera Electrophysics PV320.
After the interaction experiment, the photo-documentation was prepared by the stereomicroscope Nikon SMZ 2T, Japan.
The surface tissue analysis was processed in "low vacuum" (30 Pa) regime without desiccation. This technique was used
to record back-scattered electron images. Selecting the appropriate laser, resin, and bracket combination can minimize
risks of enamel degradation and make debonding more safe.
Free running and Q-switch infrared Er:YAG laser radiations were compared in the case of hard tissue preparation. The
interaction energy of 40 mJ in pulse 200 us long yielding to the interaction intensity 62 kW/cm2, and the energy of 20 mJ
in 100 ns long pulse yielding to the interaction intensity 62 MW/cm2 was used for the case of free running, and Q-switch
regime, respectively. For the radiation delivery, waveguide transfer system was used. It consisted of input lens (40 mm
focal length), a cyclic olefin polymer coated silver hollow glass waveguide (700/850 um diameter), and output lens (55
um focal length). For the interaction experiment the samples of the extracted human teeth cut into longitudinal sections
and polished were used. The thickness of the prepared samples ranged from 5 to 7 mm. The methods were compared
from the point of prepared cavity shape (SEM), inner surface, and possibility of selective removal of carries. The
composite filling material was used to reconstruct the cavities.
For the purpose of micro-selective preparation which is part of the modern dentistry four various methods were examined: ablation by Er:YAG laser radiation (free-running or Q-switching regime), preparation of tissues by ultrasonic round ball tip, and by the classical dental drilling machine using diamond round bur. In the case of Er:YAG laser application the interaction energy 40 mJ in pulse of 200 us yielding to the interaction intensity 62 kW/cm2, and 20 mJ in pulse of 100 ns yielding to the interaction intensity 62 MW/cm2 was used for the case of free running, and Q-switch regime, respectively. For comparisson with the classical methods the ultrasound preparation tip (Sonixflex cariex TC, D-Sonicsys micro) and dental driller together with usual preparation burrs and standard handpiece were used. For the interaction experiment the samples of extracted human teeth and ebony cut into longitudinal sections and polished were used. The thickness of the prepared samples ranged from 5 to 7 mm. The methods were compared from the point of prepared cavity shape (SEM), inner surface, and possibility of selective removal of carries. The composite filling material was used to reconstruct the cavities. The dye penetrating analysis was performed.
The Er:YAG laser at 2940 nm has been proposed for use in dental cavity preparation and removal of carious enamel and dentin. The purpose of the present study was to determine the effect of the Er:YAG laser ablation in treating dental caries after a period from 5 to 11 years. For this study, 133 cavities were chosen, and for their reparation of it the three restorative materials were used. Baseline examination was made in the following intervals: one week, 1 year, and from 5 to 11 years after cavity preparation and placement of filling material. Clinical assessments were carried out in accordance with the US Public Health Service System. The follow-up included: the marginal ridge, marginal adaptation, anatomic form, caries, color match, cavo surface margin discoloration, surface smoothness, and postoperative sensitivity. Er:YAG laser ablation is an excellent method for treating frontal teeth, i.e., incisors, canines, premolars, and initial occlusal caries of molars. However, visual control of non-contact therapy is necessary. Er:YAG laser ablation is safe, and it strongly reduces pain. The laser treatment markedly decreases the unpleasant sound and vibration.
μThe study describes the preclinical experience with laser-activated bleaching agent for discolored teeth. Extracted human upper central incisors were selected, and in the bleaching experiment 35% hydrogen peroxide was used. Three various laser systems and halogen-light unit for activation of the bleaching agent were applied. They were Alexandrite laser (wavelength 750 nm and 375 nm - SHG), Nd:YAG laser (wavelength 1.064 m), and Er:YAG laser (wavelength 2.94 μm). The halogen-light unit was used in a standard regime. The enamel surface was analyzed in the scanning electron microscope. The method of chemical oxidation results in a 2-3 shade change in one treatment. The halogen-light units produced the same effect with shorter time of bleaching process (from 630 s to 300 s). The Alexandrite laser (750 nm) and bleaching agent helped to reach the desired color shade after a shorter time (400 s). Alexandrite laser (375 nm) and Nd:YAG laser had no effect on the longevity of the process of bleaching. Overheating of the chemical bleaching agent was visible after Er:YAG laser activation (195 s). Slight surface modification after bleaching process was detected in SEM.
The success of endodontic treatment depends on the methods used
for shaping, cleaning, disinfecting, and sealing of a root canal.
In the last few decades, big progress has been achieved in the
application of the following methods: manual instrumentation,
sonic and ultrasonic devices, and rotary instruments. The
procedures used in the root canal system preparation result in a
smear layer creation. The aim of this study was to give more
precision to the smear layer removal using laser radiation. The
root canal systems of 20 human teeth were treated endodontically.
As laser radiation sources, Er:YAG laser system generating a
wavelength of 2940 nm (rep. rate 1.5 Hz, spot size diameter
320 um, number of pulses 55, energy 100 mJ) and Alexandrite
laser system generating a wavelength of 375 nm (rep. rate 1 Hz,
spot size diameter 320 um, number of pulses 200, energy
1 mJ) were used. As a delivery system, a hollow glass waveguide
with the special X-ray contrast cover was used. The flexible
waveguide was moved via root canal and the laser radiation cleaned
the wall surface. After application of Er:YAG laser radiation, the
smear layer was fully removed, the surface was clean and smooth,
and in the SEM investigation the open dentinal tubules were
visible. No cracks were determined. The surface modifications were
also not observed after endodontic preparation as well as
Alexandrite laser radiation therapy. The whole treatment can be
checked by X-ray machine.
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.
Objective of the study was the evaluation of X-ray image quality of cyclic olefin polymer-coated silver hollow glass waveguide (COP/Ag) in root canal, using a dental digital radiography method for an endodontic treatment. Er:YAG laser system was used. The wavelength generated was 2.94 micrometers and the length of the generated pulses was around 250 usec. The radiation was delivered to the investigated tissue by a cyclic olefin polymer-coated silver hollow glass waveguide (COP/Ag) with an inner diameter equal to 700 micrometers and the length of 10 cm. The fluence used in the experiments was in the range of 19 up to 45 J/cm2. The root canal systems of 10 extracted premolars and molars were treated endodontically using a step-back technique with K-type endodontic files. Isometric X-ray images were captured via fixed-point measurement method. Digital images were taken before treatment, with conventional files and with an insertion of the COP/Ag hollow glass waveguide. A density histogram, characterizing the density spread across the image was established. An aluminum step wedge, 50 mm long x 20 mm wide, having thickness range from 0.5 mm to 5 mm was used as a marker to check the quality of radiopacity. The overall dimensions were adjusted in relation to the sensor size as a control. COP/Ag hollow glass waveguide was slightly visible in root canal system. An isometric image, histogram, and pseudocolor picture help to detect the position of waveguide in the root canal.
Presence of more dental alloys in oral cavity often causes pathological symptoms. Due to various and multi-faced symptomatology, they tend to be a source of significant problems not only for the patient but also for the dentist. Metal ions released from alloys can cause subjective and objective symptoms in mouth. The aim of this study was detection of metal elements presence in saliva. There were 4 groups of examined persons: with intact teeth (15 individuals) with metallic restorations, pathological currents 5-30 (mu) A, multi-faced subjective symptomatology and uncharacteristic objective diagnosis (32 patients), with metallic restorations and no subjective symptoms (14 persons) and with metallic restorations, without pathological currents and with problems related to galvanism (13 patients). Presence of 14 metal elements was checked by inductively coupled plasma mass spectrometer with laser ablation. Nd:YAG laser detector was used. There were significant differences in content of silver, gold and mercury between persons with intact teeth and other three groups. There were no differences found between subjects with and without galvanic currents, and presence of subjective and objective symptoms.
Pulsed Er:YAG laser removal of dentin and enamel tissue is effective. One of the dangers of this laser ablation is tooth overheating by the laser energy combined with heat related changes in pulp and side effects around the cavity margins. The purpose of present study was to determine the effect of the Er:YAG laser ablation in treating dental caries after a period of 5 years. During dry laser ablation, the temperature in the pulp chamber rose, and there is insufficient time for the tooth structures to dissipate the heat between the pulses. The addition ofwater mist during irradiation can speed up ablation of enamel and dentin. Water mist cools the surface sufficiently to prevent undesirable physical changes. From our results it follows that Er:YAG laser ablation is an excellent method for treating of frontal teeth - incisors, canines, premolars and initial occiusal caries of molars. However visual control of non-contact therapy is necessary. Compound, intricate cavity shape close to pulp cavity can not be prepared with laser radiation. Therefore the working time is much longer in comparison with the classical drilling machine. Low tooth sensitivity to laser ablation, preparation without unpleasant noise and vibration create a new technique, which is very successful for small and medium caries.
The aim of this study was to evaluate the different frequencies of low-level laser radiation on healing process after human molar extractions. Frequencies of 5 Hz, 292 Hz and 9000 Hz were used in experiments. Monitoring of secretory IgA and albumin level in saliva and changes in bone density were used as objective markers of biostimulatory effect. Subjective evaluation of therapy was observed using scale. Changes of sIgA, albumin levels and bone density were compared in group of 150 patients. Differences in levels of the saliva markers were found to be significant comparing irradiated and non-irradiated groups, as well as comparing groups irradiated by various modulatory frequencies. We observed significant differences between the increase of sIgA res. Albumin and subjective treatment feelings. Bone density after extraction and six-months after surgical treatment was examined using the dental digital radiovisiography. There were detected no significant differences between bone density in irradiated and non- irradiated groups perhaps due to our used therapy diagram.
The purpose of this study was to observe the response of surrounding tissues on long-term presence of coated titanium implants under loading. The protective layer based on hydroxy apatite was created by the method of pulsed laser deposition with KrF excimer laser on the kernel from pure titanium. The coating thickness was about 1 m. Implants were inserted into the mandible of minipigs up extracted premolars. After 14 weeks of healing without loading the metal-ceramic crowns were cemented and implants were moved in to the occlusion. Six months after the crown application the experimental animals were sacrificed and from the bone blocks with implants were manufactured microscopic ground sections. The implant position in the bone were determined by radiovisography. The bone structure around the implants were viewed in the microscope using transmitted light. Observation after six months long functional loading acknowledged the presence of newly formed bone around all implants. In no samples were found any inflammatory or regressive changes. Osseointegration of both surface types was similar.
For medical applications tunable solid state laser system emitting a visible light in a region from 710 to 775 nm was developed. Laser head of this system was composed of alexandrite crystal rod (4 mm in diameter, 90 mm of length), two dielectric mirrors and tuning element (dispersing prism or thin-film polarizer). For Q-switching, three different optics shutters were proved: a saturable NC-dye or LiF crystal, LiNbO3 Pockels cell, and rotating prism. Maximum output energy in free-running and Q-switching regime was 400 mJ and 70 mJ, respectively. The pulse duration was 70 microsecond(s) in the free-running and 45 - 250 ns in Q-switching regime. The output free running laser radiation was guided via a multimode quartz fiber (1 m of length, core diameter 600 micrometers ) or via a special fluorocarbon polymer-coated silver hollow glass waveguide (0.62 m of length, inner diameter 1 mm). At first, this radiation with a laser fluence of 2.5 J/cm2 was used for an ablation of a dental calculus. Next, the laser radiation propagation in a root canal and its effect on bacteria was proved. The dissipated energy measurement was made inside and outside of the tooth. From the results follow that the alexandrite laser could be useful for medical applications.
The objective of this study was to compare the penetration effect of the near and mid-infrared laser radiation. For this reason the Er:YAG, Nd:YAG, and alexandrite laser systems were used in the experiments. The spread of the laser radiation energy in the hard dental tissue surrounding the root canal was evaluated and the possible bactericidal effect of these various laser wavelengths was analyzed. During the measurements, three experimental arrangements were used. The energy transport through the tooth tissue was observed for the frontal and side experimental layout. It was demonstrated that due to the absorption in the hydroxyapatite and water content in the dentin, the Er:YAG laser radiation is fully, and the Nd:YAG is partly absorbed in the root canal's wall. On the other hand, it was proved that the alexandrite laser radiation spreads through the canal system space and leaks into the surrounding tooth tissues. All laser radiation can be efficiently used for killing dental bacteria but the spreading of their radiation in the tooth tissues is different.
A tunable solid state laser system has been developed emitting visible light in the region from 710 to 775 nm, which can be used for medical applications. The laser head of this system is composed of alexandrite crystal rod, two dielectric mirrors, and a tuning element. The maximum reached output energy in the free running multimode regime was 400 mJ with the pulse duration of 70 micrometers . The output laser radiation was guided via a multimode quartz fiber or via a special fluorocarbon polymer-coated silver hollow glass waveguide. At first, this radiation with laser fluency of 2.5 J/cm2 was used for the ablation of dental calculus. Next, the laser radiation propagation in the root canal and its effect on bacteria was proved. The dissipated energy measurement was made inside and outside the tooth. Hence, the alexandrite laser could be useful for medical applications in dentistry.
Er:YAG laser system generating radiation in a free-running, long-pulse mode regime with the output energy up to 610 mJ and the wavelength in the mid-IR region was designed. As delivery systems, a fluorocarbon polymer-coated and a cyclic olefin polymer-coated silver hollow glass waveguides were used and the comparison of the radiation transmissions of these two waveguides and the articulated arm delivery system was made. ALl the delivery systems were ended by the focusing optics or by a special sapphire tip, for a non- contact and a contact treatment in the real applications, respectively. The output energy from these systems was in the range from 100 mJ up to 450 mJ. In the applications, the laser radiation was directed at a dental or an eye tissue. In the dental procedure, the differences between the contact and non-contact Er:YAG laser hard dental tissue preparation and also between the delivery system - articulated arm and waveguide-were verified. The influence of laser energy and number of pulses on profile and depth of drilled cavity was investigated. In the ophthalmologic surgery the contact and non-contact laser-phacoablation was investigated. The result show that the Er:YAG laser system could be a useful instrument in ophthalmology and dentistry.
The differences between a contact and non-contact Er:YAG laser hard dental tissue preparation were verified. The influence of laser energy and number of pulses on a profile and depth of a drilled cavity was investigated. The delivery systems used were an articulated arm and a cyclic olefin polymer-coated silver hollow glass waveguide with or without a special sapphire tip. In the case of the non-contact preparation, the laser radiation was directed onto the dental tissue by focusing optics (CaF2 lens) together with the cooling water spray in order to ensure that the tissues will not be burned. The water spray was also used during the preparation when the waveguide with a sapphire tip was used to deliver the radiation. For the evaluation of shapes, depth and profiles of the prepared cavities the metallographic microscope, photographs from the light microscope and scanning electron microsec were used. From the result it follows that great differences exist in the laser speed, value of energy, the profile, and depth of the cavities prepared by the contact and non-contact preparation. In the case of contact ablation the procedure is quicker, the energy fluence needed is lower and more precise cavities with larger diameters are produced.
The aim of study was to evaluate the effect of low-level laser radiation on the healing process after human lower molar extraction. Frequencies of 5 Hz, 292 Hz and 9000 Hz were used in this experiment. Monitoring the secretory IgA and albumin levels in saliva and changes in bone density were used as a marker of biostimulatory effect. Bone density after extraction and six month after surgical treatment was examined using the dental digital radiography. Wound closure was followed by healing of bone structure in extraction site. Changes of secretory IgA, albumin levels and bone density were compared in groups of patients with laser treatment and control group without any laser therapy. Differences in levels of the saliva markers were found to be significant comparing irradiated and non-irradiated groups, as well as comparing groups irradiated by various modulatory frequencies. Density of alveolar bone was examined on five slices acquired from every digital radiography image. Histogram were evaluated wit a computer program for microscopic image analysis. Density differences were verified in area of the whole slice. There were no significant differences found between bone density in irradiated and non irradiated groups perhaps due to our used therapeutical diagram.
Aim of study was to evaluate osseointegration of the KrF laser hydroxyapatite coated titanium alloy Ti6Al4V dental implants. For deposition KrF excimer laser in stainless- steel deposition chamber was used. Thickness of HA films were round 1 μm . Mini-pigs were used in this investigation. Implants were placed vertically into the lower jaw. After 14 weeks unloaded osseointegration the metal ceramic crowns were inserted. the experimental animals were sacrificed (1 year post insertion). The vertical position of implants was controlled with a radiograph. Microscopical sections were cut and ground. Sections were viewed using microscope with CCD camera. 1 year osseointegration in lower jaw confirmed by all implants presence of newly formed bone around the all implants. Laser-deposited coating the layer of fibrous connective tissue was seen only seldom. In the control group (titamium implant without cover) the fibrous connective tissue was seen between implant and newly formed bone.
The goal of the study was to verify differences between the alexandrite and Er:YAG laser energy distribution in the root canal and in the surrounding dentin and bone tissues. For the experiment, two lasers were prepared: the Er:YAG laser (λ=2.94 μm) with a delivery system fluorocarbon polymer-coated silver hollow glass waveguide ended by a special sapphire tip and the alexandrite laser (λ=0.75 μm) with a silicon fiber. The Er:YAG laser was operated in a free-running mode, the length of the generated pulses was 250 μsec and the output energy ranged from 100 to 350 mJ. The pulse length of the free- running alexandrite laser was 70 μsec and the output energy was ranged from 80 up to 200 mJ. For the experiment prepared root canals of molars were used. It was ascertained that the radiation of the alexandrite laser passes through the root canal and hits the surrounding tissue. Nocardia asteroids, Filaments, Micrococcus albus, Lactobacillus sp and Streptococcus sanguis colonies were treated by the Er:YAG or alexandrite laser radiation. The surface was checked by scanning electron microscopy. From the result it follows that the Er:YAG laser destroyed microbial colonies but the differences is in the depth of the affected area.
The evaluation of a cavity profile prepared in hard tissue by the radiation of Er:YAG dental laser with either a fluorocarbon polymer-coated silver hollow glass waveguide or an articulated arm as a delivery system is the objective of present study. Shape of holes in the enamel, dentin and ivory were studied for different energy (from 70 mJ to 450 mJ/pulse) and number of pulses (from 1 to 10). Scanning electron microscopy, photographs and X-ray microtomography were used for analysis of results. Differences between contact and non- contact preparation were studied. As the results it was found that the shape of cavity made by the waveguide delivery system is wider and flatter in comparison with the cavities prepared with the help of mirror arm. Bottom surface of the cavity has a smooth relief, edge of cavity is sharply determined. With the contact preparation the hole could be made with better precision and with comparatively smaller value of energy.
Pulsed laser deposition technique allow to 'tailor' bioceramic coat for metal implants by the change of deposition conditions. Each attribute is influenced by the several deposition parameters and each parameter change several various properties. Problem caused that many parameters has an opposite function and improvement of one property is followed by deterioration of other attribute. This study monitor influence of each single deposition parameter and evaluate its importance form the point of view of coat properties. For deposition KrF excimer laser in stainless-steel deposition chamber was used. Deposition conditions (ambient composition and pressures, metallic substrate temperature, energy density and target-substrate distance) were changed according to the film properties. A non-coated titanium implant was used as a control. Films with promising mechanical quality underwent an in vitro biological tests -- measurement of proliferation activity, observing cell interactions with macrophages, fibroblasts, testing toxicity of percolates, observing a solubility of hydroxyapatite (HA) coat. Deposition conditions corresponding with the optimal mechanical and biochemical properties are: metal temperature 490 degrees Celsius, ambient-mixture of argon and water vapor, energy density 3 Jcm-2, target-substrate distance 7.5 cm.
The aim of contribution is to evaluate the effects of low- level laser radiation on healing process after human molars extraction in lower jaw using frequency 5 Hz, 292 Hz and 9000 Hz. Changes in bone density and monitoring of secretory IgA and albumin levels in saliva were used as a marker of biostimulatory effect. Bone density after extraction and 6 month after surgical treatment was examined using the dental digital radiography. Bone healing was followed by osseointegration of bone structure in extraction wound. Changes of bone density, secretory IgA and albumin levels were compared in groups of patients with laser therapy and control group without laser therapy. Differences in levels of the saliva markers (sIgA and albumin) were found to be significant comparing irradiated and non-irradiated groups, as well as comparing groups irradiated by various modulatory frequencies. Density of alveolar bone (histogram) was examined on five slices acquired from every RVG image. Histograms were evaluated with computer program for microscopic image analysis. Differences of density were verified in area of the whole slice. There were no significant differences found between the bone density in irradiated and non irradiated groups perhaps due to our used therapeutical diagram.
The aim of our study was to verify the efficiency of delivery systems for Er:YAG laser radiation which could be used in dentistry. The influence of increasing energy and number of pulses on a profile and depth of drilled holes was investigated. Er:YAG laser was operating in a free-running mode, generating a length of pulses 200 microsecond with a maximum energy of 500 mJ. The delivery systems investigated were an articulated arm and a fluorocarbon polymer-coated silver hollow glass waveguide. The prepared hard tissues were a sliced part of enamel, dentine and ivory. The laser radiation was directed on them by focusing optics (CaF2 lens) together with the cooling water to ensure that the tissues will not be burned. For the evaluation of shapes, depth and profiles of the prepared cavities the metallographic microscope, x-ray microtomograph and scanning electron microscope were used. From the results it was observed that the profile and depth of the cavities prepared by the laser radiation delivered by the various systems (waveguide or articulated arm) are not the same. The laser radiation delivered by waveguide produces a larger diameter cavity with a lower depth. The holes are smoother and without side effects.
The aim of the clinical study is to evaluate Er:YAG laser ablation after two year-long clinical treatment. One hundred fifty cavities were volunteered for checking. Three restorative materials were used following manufacturer's directions. For the experiment, an Er:YAG laser drilling machine was applied. The laser delivered energy from 100 to 450 mJ, repetition rate from 1 to 4 Hz. The length of the generated pulses was 200 microseconds. During our experiments cooling of the teeth was achieved by fine water mist. The number of pulses was from 16 to 489. Caries of enamel and dentin were treated. Old insufficient fillings were also removed (not amalgam or metal alloys). The experiments followed the guidelines of the Declaration of Helsinki (1964), Tokyo (1975), Venice (1983) and Hong-Kong (1989). Clinical evaluation of fillings after 6, 12, 18 and 24 months based on ADA recommendation was used. Eight criteria were applied for the restoration control. Composite resins and glassionomers could be used as filling materials.
The subject of this work follows changes of the sIgA and albumin levels in the saliva of 48 patients treated after the extraction of their lower molars with either diode or He-Ne biostimulatory laser, using different modulatory frequencies (5 Hz, 292 Hz, 9000 Hz). The results were compared to the sIgA and albumin levels in the saliva of the control, i.e. not- treated group. For the tests radial immunodiffusion (RID) method was used (commercial RID kit of the Binding Site, Birmingham, Great Britain). Appropriately chosen laser beam modulatory frequency should influence the increase in the sIgA and albumin levels against the base level. In our study, this hypothesis was confirmed in the group treated with the frequency of 292 Hz and 9000 Hz (both diode GaAIAs, 670 nm, red, 20 mW, energy density 1.5 Jcm2) on albumin levels and 9000 Hz on sIgA levels. The changes of the levels of the watched markers versus the control group were at this frequencies (292 Hz and 9000 Hz) statistically significant. At the others used frequencies (5 Hz diode laser and 5 Hz He-Ne laser) the changes of the levels of the watched markers versus control group were statistically insignificant. The aim of this study was to contribute to the evaluation of specific modulatory frequencies (5 Hz, 292 Hz, 9000 Hz) for therapeutical use in a given pathological case of the oral cavity. We can conclude that using frequency 9000 Hz had best immunomodulatory effect.
In vivo experimental results of hydroxyapatite coated real dental prostheses in unloaded conditions are presented. Implants were covered by method of laser ablation. Coated and reference prostheses were implanted into jaw of minipigs. Osseointegration and quality of new bone formation were studied.
This study compares bond shear strength between hard dental tissues and composite resin filling material after a classical acid etching treatment procedure and Er:YAG laser surface conditioning. The retention of composite resin was evaluated for three cases: (1) the flat dental substrate without any conditioning, (2) the classical drilling machine prepared surface with acid etching and (3) the Er:YAG laser conditioning of enamel and dentin. None significant differences between bond shear strength of the classical drilling machine prepared surface with acid etching in comparison with the laser radiation conditioning were found.
The subject of this work follows changes of the sIgA and albumin levels in the saliva of the patients treated after the extraction of their lower molars with either diode or He-Ne biostimulatory laser, using different modulatory frequencies. The results were compared with the sIgA and albumin levels in the saliva of the control, i.e. not- treated group. Appropriately chosen laser beam modulatory frequency should influence the increase in the sIgA and albumin levels against the base level. In our study, this hypothesis was confirmed in the group treated with the frequency of 9000Hz. The changes of the levels of the watched markers versus the control group were however statistically insignificant. The aim of this study was to contribute to the evaluation of specific modulatory frequencies for therapeutical use in a given pathological cause of the oral cavity.
This paper describes the Orthoscope, an equipment for acquisition, processing, and archiving of images of patients mouth or skin. The equipment can capture and process images of single tooth, group of teeth or the whole dental arc. A dentist can easily observe the situation in mouth, demonstrate intended plan of treatment to patient and document its results. A dermatologist can evaluate treatment progress. Unlike other methods, our device shows geometrically undistorted calibrated image.The presented equipment is intended for daily practice. The image processing module is connected to an insurance office system and medical archives. This eliminates time consuming literal description of the patient dental/dermatological status. The images can be used later checking of the diagnosis and treatment.
To prepare the enamel, the energy used was mainly 345 mJ and repetition rate 2 Hz, for dentine the optimal energy of Er:YAG drilling machine was 200 mJ and repetition rate from 1 to 2 Hz, depending on cavity depth. Subject of treatment were caries of enamel and dentine and it was possible to remove the old insufficient fillings. The average number of pulses was 111.22, ranging from 16 to 489. During preparation, vibrations of microexplosions were felt by 8 patients, however, neither pain or unpleasant sensations were experienced. The filling materials used were composite resins and glassionomer cements. Their clinical evaluation 6 months post insertion was similar to that of the classical drilling system.
Clinical tests of the caries treatment with a Er:YAG laser system have been very promising. The problem of the Er:YAG laser drilling machine is the speed of preparation. It is not possible to increase the laser energy and repetition rate because this process is directly connected with temperature elevation. Therefore attention has been paid to define the differences between the classical and the laser drilling effect with a safe but effective laser energy and repetition rate. For the experiment, an Er:YAG laser drilling machine with an articulated arm was designed. Thirty samples of extracted human teeth were cut by both this system and classical drilling machine. The circumference, area and structure of surface sections were observed and analyzed. From the comparison of the measured time of preparation significant differences followed from the time of preparation. The time of preparation related to 1 mm2 of the cut surface was 5.42 sec for the Er:YAG laser machine and 0.66 sec for the classical method. From this comparison it follows that the laser system is 8 times slower than the classical preparation technique. In both cases the roughness of the surface analyzed by SCAN was found similar. Also, there were no differences between the distribution of the elements, especially calcium and phosphorus.
The aim was to study the reproducibility of deposition conditions and physical parameters of thin hydroxyapatite (HA) layers created on flat Ti substrates and the deposition of HA layers on real tooth prostheses. Films were created by KrF excimer laser ablation from sintered HA target in Ar- water atmosphere. The small fluctuations in deposition parameters exhibited the greatest impact on the color of HA films; influence on XRD spectra and film morphology was smaller.
This study compares the effects of acid treatment and Er:YAG laser radiation on the enamel. The permanent human molars were used. Oval cavities in the buccal surface were prepared and the edges of cavities were irradiated by Er:YAG radiation. The energy of laser was 105 mJ and repetition rate 1 Hz. The radiation was focused by CaF2 lens and the sample was placed in the focus. Ten samples were etched by 35 percent phosphoric acid during 60 s. Than cavities were filled with composite resin following manufacturers directions. By laser etching the structure enamel in section was rougher. The optimal connection between the enamel and composite resin was achieved in 75 percent by acid etching and in 79.2 percent by Er:YAG laser etching. Er:YAG laser etching could be alternative method for etching of enamel.
Thin films of hydroxyapatite were created on flat, polished Ti6Al4V substrates by pulsed laser deposition. Results of physical analysis and in-vitro analysis are presented and discussed.
Solid state lasers make possible rapid technological advances in medical applications by virtue of their wavelength
and temporal mode versatility, convenience, relative coinpacmess, and portability. The possibility of using solid state laser
radiation in ophthalmology, dentistry and dermatology is discussed and analyzed.
Thin films of biocompatible ceramic were fabricated by pulsed laser deposition on cylindrical implants. Diamond- like carbon films were deposited in vacuum on titanium alloy prostheses, heated to 90 degrees C. Coated prostheses were implanted into legs of rats and osseointegration higher than 60 percent was determined. Thin films of hydroxyapatite were created on real dental implants at 500 degrees C in Ar-water vapor atmosphere. Coated implants were implanted into mandibula of minipigs to study load free osseointegration. Results and experiences are presented and discussed.
The cavity surface and shape after Er:YAG laser ablation at different energies, number of pulses and at a different repetition rate were observed. Longitudinal sections of extracted human incisors and transverse sections of ivory tusk were cut and polished to flat and glazed surfaces. The samples thickness was from 3 to 5 mm. The Er:YAG laser was operating in a free-running (long pulse) mode. The laser radiation was focused onto the tooth surface by CaF2 lens (f equals 55 mm). During the experiment, the teeth were steady and the radiation was delivered by a special mechanical arm fixed in a special holder; fine water mist was also used (water-mJ/min, a pressure of two atm, air-pressure three atm). The shapes of the prepared cavities were studied either by using a varying laser energies (from 70 mJ to 500 mJ) for a constant number of pulses, or a varying number of pulses (from one to thirty) for constant laser energy. The repetition rate was changed from 1 to 2 Hz. For evaluating the surfaces, shapes, and profiles, scanning electron microscopy and photographs from a light microscope were used. The results were analyzed both quantitatively and qualitatively. It is seen that there is no linear relation between the radiation pulse energy and the size of the prepared holes. With increasing the incident energy the cavity depth growth is limited. There exists some saturation not only in the enamel and dentin but especially in the homogeneous ivory.
The aim of present study was to experimentally evaluate osteointegration of the KrF laser diamond-like carbon coated titanium alloy Ti6Al4V cylindrical implants in a preliminary study in vivo. The films were created on cylindrical titanium substrates. Substrates were heated to 70 degree(s)C or 100 degree(s)C by resistively heated holder positioned 17 mm from sample. Target substrate distance was 5 cm, energy density of KrF laser beam on the target was 15 Jcm-2. Deposition chamber was evacuated to 10-2 Pa. Film various thickness were created. Control group contained the two samples of Ti6Al4V and two samples from sapphire. Ten rats Wistar were used in this investigation. The cylindrical implants were placed horizontally into the host bone. The position of implant in femur was controlled with radiograph. The implants were retrieved for 6 weeks. 70-nm thick sections (from 2 to 4 sections from each implant) were cut. The section were viewed using a polarized light photomicroscope Nikon. The percentage of bone/implant contact were determined. The level of osteointegration of the host bone were observed. The bone-implant femur and control femur were measured. Total or partial osteointegration was seen and measured depending on deposition conditions.
Depth and profile cavity were studied after laser ablation with different energy of Er:YAG laser beam. Longitudinal sections of extracted human teeth were cut and polished to the flat surfaces. The thickness of layer of prepared teeth was from 3 to 5 mm. The check group contained glazed samples of ivory with the similar thickness. The Er:YAG laser drilling machine was operating in a free-running mode. For the preparation we used the energy up to 500 mJ. The repetition rate was 1 or 2 Hz. The laser radiation was focused on the tooth surface using CaF2 lens (f equals 55 mm). During the experiment, teeth were steady and the radiation was delivered by the mechanical arm which was fixed in a special holder. The fine water mist (water - 50 ml/min with the pressure to atm, air-pressure three atm) was used. Samples with the flat surfaces from the enamel, dentin and ivory were irradiated with five different energies from 100 to 500 mJ. Quantities of one, five, ten, twenty and thirty pulses were used. The depth of cavity and its profile were observed and measured. It was found that depth of cavity depends on the value of energy, type of hard dental tissue and number of pulses. With increasing energy or number of pulses the saturation effect in depth of holes in dentine or enamel were proved.
Thin films of hydroxylapatite were created on Ti and Ti6A14V flat substrates by excimer laser ablation. Wide scale of deposition conditions were varied as deposition atmosphere (vacuum, pure water vapors, mixture of Ar and water vapors), substrate temperature, target-substrate distance and energy density. Results of physical, mechanical and biological analysis are summarized. No clear correlation between physical and mechanical properties and results of biological tests (activity of T-lymphocytes) were found.
Thin films of biocompatible materials such as hydroxylapatite (HA) - Ca10 (PO4)6(OH)2 were deposited by laser ablation technique. The films of HA were created on Ti substrates by KrF laser. The layers were deposited in vacuum, in pure H2O vapors (pressure 2 X 10-3 mbar - 2 X 10-1 mbar), and in Ar/H2O vapor mixture. Influence of laser energy density ET (3 Jcm-2, 13 Jcm-2) and substrate temperature Tg (500 degree(s)C - 760 degree(s)C) on the film parameters was studied. Two different technological processes were used for HA target preparation. Films and targets were characterized by Rutherford backscattering analysis (RBS), particle induced x-ray emission (PIXE), x-ray diffraction (XRD), scanning electron microscopy (SEM) and by Knoop microhardness and scratch test. The best crystalline HA films were reached in the mixture of Ar/H2O. Higher Tg had to be used for such deposition. Higher Tg was also preferable from the point of film microhardness. Adhesion of films to the substrates in the range of tens of Newtons was measured. The preliminary results of in vitro experiments of films biotolerance and resorbability are also presented.
This study investigates the checks of cavity margin after enamel and dentin ablation. The Er:YAG laser enamel and dentin ablation can be directly connected with the danger of cracks originating in the enamel near the cavity. This study evaluates the quality of the enamel edges after Er:YAG laser preparation. The enamel and dentin of buccal surfaces were ablated by the Er:YAG laser radiation. An Erbium:YAG laser system with the energy of 200 mJ was used to generate 200 microsecond(s) long pulses of mid-infrared 2.94 micrometers light in multimode configuration. The laser was operating in a free running mode, the repetition rate being 0.5 Hz with average laser power of 100 mW. Laser radiation was focused on the tooth tissue. Water cooling was used during the procedure in order to prevent tooth tissue destruction. The time of laser preparation was 5 minutes. A cavity of class V was prepared. The teeth were immersed into 0.5% basic fuchsin and then centrifuged at 6000 rev/min for 20 minutes. The microphotographs of the margins stained with 0.5% basic fuchsin were made and then the longitudinal section of the teeth were evaluated. The micrographs of the longitudinal section were checked and measured afterwards. The effect of the investigated laser irradiation on the origin of cracks was analyzed in the scanning electron microscope. Micrographs of each tooth before and after the laser ablation were compared. Micrographs of the intact teeth after extraction present the cracks of the enamel. They depend on the pressure exerted during extraction. The influence of the laser ablation proper is it bears no signs of new cracks. The conclusions of this study demonstrate the non-invasive nature of the Er:YAG laser ablation of the hard dental tissues.
This paper summarizes three recent applications of computer vision techniques in dentistry developed at the Czech Technical University. The first one uses a special optical instrument to capture the image of the tooth arc directly in the patient's mouth. The captured images are used for visualization of teeth position changes during treatment. The second application allows the use of images for checking teeth occlusal contacts and their abrasion. The third application uses photometric measurements to study the resistance of the dental material against microbial growth.
We are presenting the results of the thermal changes of enamel, dentin and pulp temperature monitoring in extracted human teeth subjected to a pulsed Er:YAG laser radiation. We made a series of experiments irradiating the tooth using the pulsed Er:YAG laser and monitoring simultaneously the temperature of various parts of the tooth. The temperature was measured by the bead thermistor either in contact with the tooth surface or built in the pulp chamber. In the former experiments it was demonstrated, that the uncooled preparation can cause irreversible changes of the pulp. In the second part of the experiments the teeth have been cooled by flowing water. During the laser preparation of the enamel and the dentin the temperature did not increase more than 2 degree(s)C. In the moment of dentin perforation and hence laser irradiation of the pulp, the pulp temperature increased rapidly. The opening of the pulp coincides with the rapid temperature increase. These studies verified the feasibility of the pulsed Erbium:YAG laser use in stomatology.
The results of evaluation of Er:YAG radiation cavity preparation under transmitted and polarized light and by the electron microanalyzer are presented. We examined the longitudinal sections of intact teeth, teeth with early dental caries, teeth with laser preparation in enamel and teeth with Er:YAG laser preparation in enamel and dentine class I and V. We examined intact teeth and laser prepared teeth for the variation of mineralization. Phosphorus and calcium were regularly distributed. The margins of cavities had no necrosis zones. The defects of mineralization in caries depend on demineralization of hard tissues. In the structures was irregular loss of calcium and phosphorus. Thus, Er:YAG laser irradiation with water cooling has been found to be a non-invasive preparation technique.
Extracted molars were used in order to study the efficiency of Erbium YAG, Holmium YAG, and Neodymium YAG radiation on the removal of dental enamel, dentin. The hard tissues were penetrated with standard energy and pulse parameters with or without water cooling, laser beam or fiber and black paint. The specimens were analyzed with SEM. Differences between laser wavelengths were observed. Morphologic alterations and crater formation depend directly on the wavelength and energy of the laser beam.
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