In dental health care, the application of ultrashort laser pulses enables dental tissue ablation free from thermal side effects, such as melting and cracking. However, these laser types create undesired micro- and nanoparticles, which might cause a health risk for the patient or surgeon. The aim of this study was to investigate the driving mechanisms of micro- and nanoparticle formation during ultrashort pulse laser ablation of dental tissue. Time-resolved microscopy was chosen to observe the ablation dynamics of mammoth ivory after irradiation with 660 fs laser pulses. The results suggest that nanoparticles might arise in the excited region. The thermal expansion of the excited material induces high pressure in the surrounding bulk tissue, generating a pressure wave. The rarefaction wave behind this pressure wave causes spallation, leading to ejection of microparticles.
Clinical surveys show a continuous increase of antimicrobial resistance related to the frequency of the
administrated medication. The antimicrobial photodynamic therapy (aPDT) is an effective adjuvant to
reduce the need of antibiotics in dentistry, especially in periodontics. The antimicrobial effect of lightactivated
photosensitizers in periodontics is demonstrated in clinical studies and case reports.
Indocyanine green (ICG) as a new adjuvant shows the high potential of antiphlogistic and antimicrobial
effects in combination with laser-light activation. In trying to answer the question of just how far the
influence of temperature is acting on bacteria, this study was carried out.
The influences of ICG at different concentrations (0.01 up to 1 mg/ml) in combination with a culture
medium (brain-heart-infusion) and a bacteria culture (Streptococcus salivarius) at different optical
densities (OD600 0.5 and 0.1) were investigated under laser-light activation. Laser activation was carried
out with diode laser at 810 nm and two different power settings (100 mW/300 mW). The pulse repetition
rate was 2 kHz. Taking account of the fiber diameter, distance and spot size on the sample surface, the
applicated intensities were 6.2 and 18.7 W/cm2. Total irradiation time was 20 s for all meaurements.
Transmitted laser power and temperature increase in the culture medium as well as in the bacteria
culture were determined. Additionally the influence of ICG regarding bacterial growth and bactericidal
effect was investigated in the bacteria culture without laser irradiation.
Without laser, no bactericidal effect of ICG was observed. Only a bacteriostatic effect could be
proved. In dependence of the ICG concentration and the applied intensities a temperature increase of ΔT up to 80°C was measured.
Ultra-short pulsed laser (USPL) systems for dental application have overcome many of their initial disadvantages. However, a problem that has not yet been addressed and solved is the beam delivery into the oral cavity. The functional system that is introduced in this study includes an articulated mirror arm, a scanning system as well as a handpiece, allowing for freehand preparations with ultra-short laser pulses. As laser source an Nd:YVO4 laser is employed, emitting pulses with a duration of tp < 10 ps at a repetition rate of up to 500 kHz. The centre wavelength is at 1064 nm and the average output power can be tuned up to 9 W. The delivery system consists of an articulated mirror arm, to which a scanning system and a custom made handpiece are connected, including a 75 mm focussing lens. The whole functional system is compact in size and moveable. General characteristics like optical losses and ablation rate are determined and compared to results employing a fixed setup on an optical table. Furthermore classical treatment procedures like cavity preparation are being demonstrated on mammoth ivory. This study indicates that freehand preparation employing an USPL system is possible but challenging, and accompanied by a variety of side-effects. The ablation rate with fixed handpiece is about 10 mm3/min. Factors like defocussing and blinding affect treatment efficiency. Laser sources with higher average output powers might be needed in order to reach sufficient preparation speeds.
Due to the high intensities of USP laser radiation, the interaction with matter is always attended with a plasma formation. Therefore the surrounding tissue can be influenced by heat generation and additional light emission from the UV up to the near and mid infrared. In dentistry it is of importance that the treatment of bone and soft tissues, i.e. oral mucosa, with a USP laser should not cause any kind of morphological changes on the cell level leading to a delayed wound healing or cell mutation.
HaCaT keratinocyte cells were used for epidermal (soft tissue) and MG-63 osteoblast-like cells for hard tissue (bone) modelling. Cell growing was realized on glas cover slips. Irradiation was carried out with a USP Nd:YVO4 laser having a center wavelength at 1064 nm. Based on the pulse duration of 8 ps and a pulse repetition rate of 500 kHz the laser emits an average power of 9 W. For efficiency testing of cell removal on glas cover slips, 1, 5, 25, 50 and 75 repetitions of the scanning pattern (scan loops) were used. Heat distribution during laser irradiation was measured with an infrared camera system. Subsequently haematoxylin staining and SEM investigations were used to analyse the morphological changes.
Differences of cell removal efficiency were observed with repetitions ≤25. Irradiated areas with repetitions ≥50 were cell-free. Additionally, repetitions ≥25 showed side effects for both cell lines. Cell destruction in both cell lines could be verified using the haematoxylin staining and the SEM pictures.
The exposition of nanoparticles caused by laser application in dental health care is an open
discussion. Based on the fact that nanoparticles can penetrate through the mucosa, the knowledge
about particle characteristics after irradiation with an USPL is of high importance. Therefore, the aim of
this study was to investigate the particle characteristics, especially the size of the ablated debris after
USPL irradiation.
The irradiation was carried out with an USP Nd:YVO4 laser with a center wavelength of 1064 nm.
Based on the pulse duration of 8 ps and a pulse repetition rate of 500 kHz the laser emits an average
power of 9 W. The materials investigated were dental tissues and dental restorative materials
(composite and amalgam), ceramic and different metals (gold and aluminium). The samples were
irradiated with a power density in the order of 300 GW/cm2 at distances of 5, 10, 15, and 20 mm. The
debris was collected on an object plate. SEM pictures were used for analysis of the ablation debris.
Depending on the irradiated material, we observed different kinds of structures: vitreous, flocculent,
and pellet-like. The mean particle sizes were 10 x 10 up to 30 x 30 μm2. In addition, a cluster of ablated
matter (nanometer range) distributed over the whole irradiated area was found. With increasing
distances the cluster structure reduced from multi-layer to mono-layer clusters.
Particle sizes in the micrometer and nanometer range were found after irradiation with an USPL. The
nanoparticles create a cluster structure which is influenced by increasing distances.
During ablation of oral hard tissue with an USPL system a small amount of the incident laser power does not contribute
to the ablation process and is being transmitted. Partial transmission of ultra-short laser pulses could potentially affect the
dental pulp. The aim of this study was to assess the transmission during ablation and to deduce possible risks for the
patient. The study was performed with an Nd:YVO4 laser, emitting pulses with a duration of 8 ps at a wavelength of
1064 nm. A repetition rate of 500 kHz and an average power of 9 W were chosen to achieve high ablation efficiency. A
scanner system created square cavities with an edge length of 1 mm. Transmission during ablation of mammoth ivory
and dentin slices with a thickness of 2 mm and 5 mm was measured with a power meter, placed directly beyond the
samples. Effects on subjacent blood were observed by ablating specimens placed in contact to pork blood. In a separate
measurement the temperature increase during ablation was monitored using an infrared camera. The influence of
transmission was assessed by tuning down the laser to the corresponding power and then directly irradiating the blood.
Transmission during ablation of 2 mm specimens was about 7.7% (ivory) and 9.6% (dentin) of the incident laser power.
Ablation of specimens directly in contact to blood caused coagulation at longer irradiation times (t≈18s). Direct
irradiation of blood with the transmitted power provoked bubbling and smoke formation. Temperature measurements
identified heat generation as the main reason for the observed coagulation.
The theory of the ablation of dental hard tissue with erbium lasers is based on a process of thermomechanical interaction, which is explained by the absorption of the radiation in the water component of the tissue. The abrupt evaporation of the water is the cause of tissue fragments being blasted out of the tooth structure. The aim of this study is to examine the effect of the water contained in dental hard tissues on the efficiency of ablation. 192 specimens of both bovine dental enamel and bovine dentin are irradiated with an Er:YAG and an Er,Cr:YSGG laser. Half of the specimens are dehydrated beforehand. Irradiation is carried out in subgroups: without water spray and with water spray at flow rates of 0.8 and 3 ml/s. The ablated volume is determined following histological preparation. Only in dentin, and then only with irradiation with the Er:YAG laser, is the water contained in the tissue found to have a significant influence (p<0.0001) on the ablated volume. The water content has no effect on the efficiency of laser ablation in any of the other test groups. In contrast, the externally supplied water always has a significant influence on the effectiveness of the ablation process.
Due to the high absorption coefficient of water in biological tissues at 3 micrometer, the Er:YAG (2.94 micrometer) and the Er:YSGG laser (2.79 micrometer) are very effective tools for medical applications. A widespread use of these lasers is prevented by the lack of a lightguide which satisfies the demands of medical practice, e.g. flexibility, low bending radius and unbreakability. If teflon (FEP) tubes filled with carbontetrachloride (CCl4) are used for high laser energies, absorbing and scattering particles in the liquid core are responsible for the decreasing transmission and damaging of the lightguide. A system was developed therefore to purify the liquid continuously even during laser irradiation. Two concentric FEP tubes are used to realize a circulation system. Different inner diameters of cladding tubes (1.6 mm and 0.5 mm) were tested with an Er:YAG and a Ho:YAG laser. A theoretical model of the different intrinsic attenuation losses in those lightguides was developed, which is in good agreement with the experimental results. Distal energy densities of 88 J/cm2 (Er:YAG) up to 220 J/cm2 (Ho:YAG) could be achieved with the small cladding tubes. These values were only limited by the output power of our laser devices. This waveguide setup has a better flexibility than those with a solid core. Due to the high numerical aperture (NA equals 0.54) the bending losses are negligible down to a bending radius of 15 mm. The high flexibility and transmittable power of the presented circulation system is particularly attractive for medical laser treatments.
Fused silica capillaries proved to be a suitable cladding material for liquid core lightguides. They have small diameters, a good mechanical stability and a high flexibility. Due to these properties such lightguides can be used for applications in minimally invasive surgery for endoscopical treatments. Filled with carbontetrachloride (CCl4), the optical properties were investigated spectrometrically and with various lasers. The transmission measurements of straight and 180 degree bent fibers were performed with a free-running Er:YAG, Er:YSGG, Ho:YAG, and Nd:YAG laser. Due to an overlap of the refractive indices of CCl4 and fused silica between 500 nm and 1 micrometer, laser wavelengths in this spectral range, e.g., of the Nd:YAG and the HeNe laser, cannot be transmitted in this lightguide. If the core liquid is a mixture of CCl4 and tetrachloroethylene (C2Cl4) the lightguide is transparent from the near UV (380 nm) up to the NIR (3 micrometer) and consequently, it is suitable also for the Nd:YAG laser. With the CCl4-filled fused silica capillaries distal energy densities up to 30 J/cm2 were achieved and thus the ablation threshold of soft tissue is exceeded.
The purpose of this in vitro study was to investigate and compare effects of currently available laser systems at different wavelengths (XeCl excimer laser, Holmium:YAG laser, Erbium:YAG laser) on porcine articulating facets, capsule and meniscus of the temporomandibular joint via photomacroscopy, light and scanning electron microscopy. From a critical review of the relevant literature and the preliminary observations of this investigation, it appears that the Neodymium:YAG laser is inappropriate for TMJ arthroscopic surgery with regard to the huge thermal injury caused to the remaining tissue. The Holmium:YAG laser suffers from remarkable photomechanical and photothermal side effects, whereas the Erbium:YAG laser ablates temporomandibular joint tissue efficiently with minimal adjacent damage--similar to the XeCl excimer laser, without entailing the risk of potential mutagenity. To sum up, it can be concluded that there is a clinical need for laser- assisted arthroscopic surgery of the craniomandibular articulation. Nevertheless, at present none of the available laser systems meet the medical demands completely. Currently, the Erbium:YAG laser seems to be the most suitable for TMJ arthroscopic surgery.
With the development of infrared transmitting fibers, medical applications such as minimally invasive surgery are becoming feasible. In particular we investigate liquid core waveguides with an Er:YAG laser at 2.94 micrometer. Because of their advantages like variability in diameter, high flexibility, and mechanical stability, liquid core waveguides appear to be an alternative to conventional IR waveguides. In this work we present two types of liquid CCl4 filled lightguides that have been developed with plastic tube and quartz capillary as cladding. The former with an inner diameter of 1.6 mm showed an attenuation of 2.6 dB/m at 2.94 micrometer. For the quartz glass capillary with an inner diameter of 550 micrometers an attenuation of approximately 4.8 dB/m was determined in first experimental results. Due to the great flexibility and the high mechanical stability of both lightguides, bending radii below 10 mm are possible. Transmission losses depending on bending radii are discussed. A comparison between measurements with an IR-spectrometer and an Er:YAG laser shows that a minimum transmission loss of 2 dB/m can be achieved.
In order to introduce Er:YAG lasers at 2.94 micrometers into medical applications such as minimally invasive surgery, appropriate infrared transmitting fibers are necessary. Because of their cheapness, variability in diameter, high flexibility, mechanical stability and regenerability, liquid core fibers have been taken into consideration as one type of conceivable lightguides. In this work IR absorption effects of water in the core and permeation of atmospheric water and of the solvent through the cladding are studied. The absorption of 2.94 micrometers which is due to the unresolved rotational structure of the stretching vibrations of dissolved water at 3617 and 3708 cm-1 increases when the water content rises. According to preliminary permeation measurements, keeping a liquid-filled plastic fiber under normal atmospheric conditions leads to an increasing water concentration in the core and, simultaneously, to a loss of the solvent. On the other hand the water content could be reduced when the lightguide was stored in a desiccator. These problems could be solved by using a liquid lightguide with an appropriate jacket. Compared to unjacketed counterparts it has a better long time transmission at 2.94 micrometers . Meanwhile the transmission could be improved to up to 55% (pathlength: 1 m). As these first results are thought to be further improvable they are well promising towards the realization of a liquid lightguide for medical purposes.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.