Rene Franzen

Influence of the water content in dental enamel and dentin on ablation with erbium YAG and erbium YSGG lasers

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 mls. 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.

Influence of the pulse duration of an Er:YAG laser system on the ablation threshold of dental enamel

Abstract.The present study examines the dependence of the ablation threshold on the duration of the applied laser pulses in the dental enamel of human wisdom teeth. To this end, 600 treatments with the Er:YAG laser (λ=2940 nm) were carried out on a total of 50 extracted teeth. The laser light was coupled into a fluoride glass light guide for this purpose, in order to ensure almost gaussian distribution of the light in a radially symmetrical beam. The beam diameter on the specimen was 610 µm. The radiant exposure on the tooth surface was varied between 2 and 20 J/cm2, while the duration of the pulses applied was changed in four steps from 100 µs to 700 µs. The irradiated tooth surfaces were examined for visible signs of ablation under a reflected-light microscope. The experiments revealed that, when pulses of shorter duration are used, the limit at which ablation sets in is reduced by up to approx. 3 J/cm2. This expands the ablation threshold range of Er:YAG laser radiation to between 6 and 10 J/cm2. In this context, both the pulse duration and the radiant exposure have a statistically significant influence on the ablation threshold (logistic regression, p<0.0001). Although the ablation threshold of the dental enamel can be changed by varying the pulse duration of the Er:YAG laser, no clinical consequences can be expected, as the shift is only slight.

Influence of the spatial beam profile on hard tissue ablation Part I: Multimode emitting Er:YAG lasers

AbstractUniform dosimetry is a prerequisite for reproducible laser applications in research and practice. The light–tissue interaction is dependent on the absorbed energy (J) per unit of time (τ) in the case of pulsed lasers, and on the absorbed power (W) per unit of volume (e.g. mm3) in the case of continuous-wave (cw) lasers, and thus directly dependent on the energy distribution within the laser beam. Consequently, precise knowledge of the spatial beam profile, and of the pulse duration and treatment time, is indispensable. The objective of this paper was a theoretical study of the impact of different mode profiles on energy distribution in the beam. Also examined was the question of the influence of changes in the laser parameters on the mode structure. Three erbium:YAG lasers (λ=2.94 μm) were used for this purpose. The transversal mode structure of the lasers was observed by irradiating thermal paper and verified by means of calculations. The effect induced in the mode profile by changing the pulse energy and pulse repetition rate was investigated. The results of the tests show that changes in the laser parameters result in jumps in the transversal modes and associated energy distributions in the beam. The experiments confirm that simply changing the transversal modes has a substantial effect on the threshold energy required for the ablation of dental enamel (50 mJ with TEM00, 22.6 mJ with TEM31). In practice, inhomogeneity makes it impossible to determine the irradiated area in order to calculate the energy or power density. In addition, the energy distribution in the beam changes as a result of variation of the laser output energy and the pulse repetition rate. Consequently, simply measuring the beam diameter yields a totally incorrect result for the applied flux density when using a beam profile with a relatively high mode.

Influence of the spatial beam profile on hard tissue ablation, Part II: pulse energy and energy density distribution in simple beams

When calculating applied flux densities in practice, the beam profile of a laser is often erroneously assumed to be homogeneous. In addition, there is usually no consistency in the choice of a suitable measuring method for determining the beam diameter. This failure to observe the inhomogeneous intensity distribution within the beam cross-section, combined with the imprecise knowledge of the beam diameter, leads to flux densities being stated that represent mean values at best. The present paper gives definitions for the flux densities of simple, radially symmetrical beam cross-sections, taking the top-hat and Gaussian profiles as examples. In connection with the inhomogeneous energy distribution in the Gaussian beam, a concept of integral and local energy density is discussed, which differs from the customary definition of the energy density as a constant. Also presented are the consequences of the mathematical concepts in terms of measurement, giving particular consideration to the case where the energy density as the measured variable matches the integral energy density. The significance of the integral and local energy density for hard-tissue ablation is described, based on the practical example of the ablation of dental hard substance. The central result is that the integral flux density is directly accessible as a measured variable, while the effect on the tissue is determined by the local flux density. If the form of the beam is known, the integral flux density can be converted into the local flux density.

Laser Supported Reduction of Specific Microorganisms in the Periodontal Pocket with the Aid of an Er,Cr:YSGG Laser: A Pilot Study

Objective. The aim of this study was to evaluate the effectiveness of a radial firing tip of an Er,Cr:YSGG laser as an adjunct to a nonsurgical periodontal treatment. Methods. Twelve patients with chronic or aggressive periodontitis were treated by conventional periodontal treatment using ultrasonic devices and hand instruments and, additionally, in two quadrants with an Er,Cr:YSGG laser. A new radial firing tip (RFPT 14-5, Biolase) was used with 1.5 W, 30 Hz, 11% air, 20% water, and pulse duration 140 μs. Microbiological smears were taken before treatment, one day after lasing, and three and six months after lasing. Pocket depths of all periodontal sites were measured before and six months after treatment. Results. The total bacterial load of Prevotella intermedia, Tannerella forsythia, Treponema denticola, Fusobacterium nucleatum, Porphyromonas gingivalis, and Aggregatibacter actinomycetemcomitans inside the pocket was reduced significantly throughout the whole examination time. Greater pocket depth reductions were observed in all groups. There was a slight higher reduction of pocket depth in the lased group after six months. Conclusions. These results support the thesis that Er,Cr:YSGG laser supported periodontal treatment leads to a significant reduction of periopathogenes and thereby helps the maintenance of periodontal health.

The Bactericidal Effect of 2780 and 940 nm Laser Irradiation on Enterococcus faecalis in Bovine Root Dentin Slices of Different Thicknesses

OBJECTIVE The aim of this in vitro study was to investigate the antibacterial effect of the dual wavelength (2780 nm Er,Cr:YSGG and 940 nm diode) laser in elimination of Enterococcus faecalis in comparison with a 2780 nm Er,Cr:YSGG laser alone. BACKGROUND DATA Various laser wavelengths have been introduced as an adjunct in root canal treatment because of lasers bactericidal effect. MATERIALS AND METHODS Seventy- five slices of dentin with thicknesses of 300, 500, and 1000 μm (n = 25 each) obtained from caries-free bovine teeth were inoculated with 1 μL of E. faecalis suspension [1.67 × 10(7) colony-forming units (CFU)] and divided randomly into three groups: (A) samples indirectly irradiated with power settings of 1.06 W, 50 Hz, and 50 μs for Er,Cr:YSGG laser; (B) samples indirectly irradiated with Er,Cr:YSGG laser with the same power settings as group A and simultaneously with a 940 nm diode laser of 0.51 W in pulsed mode; and five samples from each thickness that were chosen as an unirradiated control group (Co). After irradiation, the CFU of E. faecalis were counted and the bacterial reduction was analyzed using Kruskal-Wallis nonparametric and post-hoc Dunnett tests. RESULTS There were statistical differences between groups A and B compared with the control group over all the three dentin slice thicknesses (p < 0.001). However, there was no statistical difference between groups A and B in killing of E. faecalis on 500 μm dentin slices. There were significantly more viable bacteria in group A than in group B in 300 and 1000 μm dentin slices (p < 0.01). CONCLUSIONS The results of this in vitro study showed that the dual wavelength laser system obtained a significantly higher bactericidal effect on E. faecalis than Er,Cr:YSGG laser, reaching a depth of 1000 μm of dentin.

Multireflection pumping concept for miniaturized diode-pumped solid-state lasers

An innovative pump concept for diode-pumped, solid-state lasers is introduced as an example for an Er:YSGG laser, permitting its miniaturization. Embedded in a multireflective pump cavity, the laser crystal is simultaneously side and end pumped. Specially calculated and shaped deflecting optics distribute the coaxially input pumping light homogeneously over the lateral surface of the crystal, therefore reducing the size of the laser head, including the optical resonator, to a length of 27.5 mm and an outside diameter of 12.5 mm. The differential efficiency achieved is between 8.7% and 24%. The laser emits energy of 15.7 mJ at an absolute efficiency of 9.1% and a repetition rate of 4 Hz.

Evaluation of Temperature Elevation During Root Canal Treatment with Dual Wavelength Laser: 2780 nm Er,Cr:YSGG and 940 nm Diode

OBJECTIVE The purpose of this study was to evaluate the effects of dual wavelength (2780 nm Er,Cr:YSGG and 940 nm diode) laser with radial firing tip (RFT) on the external root surface and sub-surfaces, in terms of temperature changes during laser-assisted root canal treatment. BACKGROUND DATA A significant factor that may limit the use of lasers in endodontics is the possible thermal injury to tooth supporting structures. MATERIALS AND METHODS A total of 50 sound single-rooted extracted teeth were divided randomly into two groups (n = 25). Group A, irradiated with Er,Cr:YSGG laser at 1.06 W, 50 Hz, and 50 μs was a control group, and group B was irradiated with dual wavelength of Er,Cr:YSGG laser with the same settings as group A and a diode laser of 0.51 W at 4 ms and 10 ms pulse duration. K-type thermocouples were used to record temperature changes at the cervical, middle, and apical root thirds, on root surfaces and sub-surfaces, arising from delivery of laser energy through RFT. RESULTS Temperature elevation in group B was significantly higher in the middle and apical thirds of the prepared samples than in group A (p < 0.0001). Group B presented a mean temperature elevation of 5.07°C on the apical surface region corresponding to a 1.48 mm dentin thickness, whereas a mean temperature increase of 7.72°C was recorded corresponding to dentin thickness of 0.95 mm. CONCLUSIONS Within the studied parameters, the dual wavelength laser did not result in adverse thermal changes on the external root surface in vitro.

Ablation of articular cartilage with an erbium:YAG laser: An ex vivo study using porcine models under real conditions—ablation measurement and histological examination

The use of an erbium:YAG laser in arthroscopic surgery has the advantage of a precise treatment of soft tissue. Due to the high absorption in water, the laser energy is perfectly matched to smoothing the hydrous, fibrillated articular cartilage surface. In minimal invasive surgery, the workspace is filled with aqueous liquids for enlargement. This appears contrary to the absorption characteristics of erbium:YAG laser radiation in water. The purpose of this study was to evaluate the ablated volume per pulse of cartilage lesions and the potential side effects including thermal damage and tissue necrosis.

Intrapulpal temperature changes during root surface irradiation with dual-wavelength laser (2780 and 940 nm): in vitro study

Abstract. The present study evaluated the intrapulpal thermal changes that occurred during the treatment of the root surfaces with a laser system emitting Er,Cr:YSGG 2780- and 940-nm diode laser irradiation in an alternating sequence. Thirty single-rooted human teeth were collected. The teeth were divided into three groups (n=10 each) and irradiated with Er,Cr:YSGG alone or combined with a 940-nm diode laser. To investigate the intrapulpal temperature changes, specimens were embedded in a resin block with a set of thermocouples introduced at different positions within the root canals. The first group was irradiated with only Er,Cr:YSGG (25 mJ, 50 Hz, 50  μs pulse duration, water and air spray); the second group was irradiated with Er,Cr:YSGG (same setting) and a 940-nm diode (2 W, chopped mode with 20% duty cycle); the third group was irradiated with Er,Cr:YSGG (same setting) and a diode (2 W, chopped mode with 50% duty cycle). During all irradiations, thermal changes were recorded in real time with thermocouples. While group 3 showed thermal rises on average of 1.68±0.98°C in the pulp chamber, groups 1 and 2 showed average temperature rises of <0.5°C. The combined laser emission of 2780 and 940 nm is a promising way for root surface debridement without inducing intrapulpal thermal damage when using an appropriate water/air spray. All measured temperatures were considerably below the critical value of 5.6°C.