Steven R. Visuri

Shear Strength of Composite Bonded to Er:YAG Laser-prepared Dentin

An Er:YAG laser coupled with a cooling stream of water effectively removes dental hard tissues. However, before such a system can be deemed clinically viable, some safety and efficacy issues must be addressed. We compared the bonding of composite to dentin following the preparation of the dentinal surface with either an Er:YAG laser (A = 2.94 pm) or a standard dental bur and with and without a subsequent acid-etching treatment. The crowns of extracted human molars were removed, revealing the underlying dentin. We removed an additional thickness of material with either a dental handpiece or an Er:YAG laser (350 mj/pulse at 6 Hz) by raster-scanning the samples under a fixed handpiece or laser. Comparable surface roughnesses were obtained. Several samples from each group received an acid-conditioning treatment. A cylinder of composite was bonded onto the prepared surfaces. The dentin-composite bond was then shear-stressed to failure on a universal testing apparatus. The results indicate that laser-irradiated samples had improved bond strengths compared with acid-etched and handpiece controls. SEM photographs of the surfaces show exposed tubules following the laser treatment; tubules could also be exposed with acid etching. We conclude that Er:YAG laser preparation of dentin leaves a suitable surface for strong bonding of an applied composite material.

Erbium laser ablation of dental hard tissue : Effect of water cooling

Several lasers have been explored for hard dental tissue applications; used alone they have resulted in potentially harmful temperature increases in the pulp chamber.

Caries inhibition potential of Er:YAG and Er:YSGG laser radiation

Dental hard tissues can be ablated efficiency by (lambda) equals 3 micrometers laser irradiation with minimal subsurface thermal damage. However, the potential of lasers operating in the region of the infrared for caries preventive treatments has not been investigated. In this study, the caries inhibition potential of Er:YAG ((lambda) equals 2.94 micrometers ) and Er:YSGG ((lambda) equals 2.79 micrometers ) laser radiation on dental enamel was evaluated at various irradiation intensities. Pulsed IR radiometry and scanning electron microscopy (SEM) were used to measure the time-resolved surface temperatures during laser irradiation and to detect changes in the surface morphology. The magnitude and temporal evolution of the surface temperature during multiple pulse irradiation of the tissue was dependent on the wavelength, irradiation intensity, and the number of laser pulses. Radiometry and SEM micrographs indicated that ablation was initiated at temperatures of approximately 300 degree(s)C for Er:YAG and 800 degree(s)C for Er:YSGG laser irradiation, well below the melting and vaporization temperatures of the carbonated hydroxyapatite mineral component (m.p. equals 1200 degree(s)C). Nevertheless, there was marked caries inhibition for irradiation intensities below those temperature thresholds, notably 60% and 40% inhibition was achieved after Er:YSGG and Er:YAG laser irradiation, respectively. These results indicate that the Er:YSGG laser can be used effectively for both preventive dental treatments and for hard tissue removal.

Laser ablation of dental hard tissue: from explosive ablation to plasma-mediated ablation

We review the basic laser ablation processes of dental hard tissue for wavelengths ranging from the IR to the UV. The underlying tissue removal mechanisms extend from water- mediated explosive, to thermomechanical, to plasma-mediated processes. This discussion is based on a literature review of the current state of hard tissue removal under various irradiation conditions combined with some new data using surface temperature measurements. The most effective tissue removal mechanism is the water-mediated explosive process in the IR at wavelengths between 3 and 10 micrometers . Highly controlled tissue removal at low ablation rates can be obtained in the near IR (around 1 micrometers ) using plasma-mediated ablation, provided the irradiation parameters are chosen appropriately. Similarly small ablation rates combined with good tissue specificity characterize the ablation in the UV region of the spectrum. The ablation mechanism in the UV is largely dominated by photothermal processes, although photochemical and thermomechanical processes may contribute.

Infrared radiometry of dental enamel during Er: YAG and Er:YSGG laser irradiation

Time-resolved infrared (IR) radiometry was used to measure surface temperatures during pulsed Er:YSGG (l=2.79 mm) and Er:YAG (l=2.94 mm) laser irradiation of dental enamel. Scanning electron microscopy (SEM) was used to determine the melting and vaporization thresholds and to characterize other changes in the surface morphology. The magnitude and temporal evolution of the surface temperature during multiplepulse irradiation of the tissue was dependent on the wavelength, fluence, and pre-exposure to laser pulses. Radiometry and SEM micrographs indicate that ablation is initiated at temperatures well below the melting and vaporization temperatures of the carbonated hydroxyapatite mineral component (1200 °C). Ablation occurred at lower surface temperatures and at lower fluences for Er:YAG than for Er:YSGG laser irradiation: 400 °C vs. 800 °C and above 7 J/cm2 vs. 18 J/cm2, respectively. However, the measured surface temperatures were higher at l=2.79 mm than at l=2.94 mm during low fluence irradiation (<7 J/cm2). Spatially dependent absorption in the enamel matrix is proposed to explain this apparent contradiction.

Effect of water on dental material ablation of the Er:YAG laser

It is understood that if a laser is to replace the dental high speed handpiece it must be able to ablate dental materials which are present in teeth being treated with the laser. It is the intent of this paper to evaluate the effects of the Er:YAG laser on dental composite restorative material concentrating on the etch rate with and without waterspray. Composite dental material is used to form plugs of known thickness and the etch rate of the Er:YAG laser on this material is determined. The results are compared with those obtained from studies of the Er:YAG on dentin and enamel. In these studies the water reduced the efficiency of the Er:YAG laser 15 - 20% on these tissues.

Shear test of composite bonded to dentin: Er:YAG laser versus dental handpiece preparations

The erbium:YAG laser coupled with a cooling stream of water appears to be an effective means of removing dental hard tissues. However, before the procedure is deemed clinically viable, there are several important issues of safety and efficacy that need to be explored. In this study we investigated the surface that remains following laser ablation of dentin and compared the results to the use of a dental handpiece. Specifically, we studied the effect the laser radiation had on the bonding of composite to dentin. The crowns of extracted human molars were removed revealing the underlying dentin. An additional thickness of material was removed with either a dental handpiece or an Er:YAG laser by raster scanning the samples under a fixed handpiece or laser. Comparable surface roughnesses were achieved. A cylinder of composite was bonded onto the prepared surfaces following the manufacturers directions. The dentin-composite bond was then shear stressed to failure on a universal testing apparatus and the maximum load recorded. Preliminary results indicated that laser irradiated samples had improved bond strengths. SEM photographs of the surfaces were also taken to compare the two methods of tooth preparation.

Microfluidic tools for biological sample preparation

Researchers at Lawrence Livermore National Laboratory are developing means to collect and identify fluid-based biological pathogens in the forms of proteins, viruses, and bacteria. To support detection instruments, we are developing a flexible fluidic sample preparation unit. The overall goal of this Microfluidic Module is to input a fluid sample, containing background particulates and potentially target compounds, and deliver a processed sample for detection. We are developing techniques for sample purification, mixing, and filtration that would be useful to many applications including immunologic and nucleic acid assays. Sample preparation functions are accomplished with acoustic radiation pressure, dielectrophoresis, and solid phase extraction. We are integrating these technologies into packaged systems with pumps and valves to control fluid flow and investigating small-scale detection methods.

Microfluidic sample preparation for immunoassays

Researchers at Lawrence Livermore National Laboratory are developing means to collect and identify fluid-based biological pathogens in the forms of proteins, viruses, and bacteria. To support detection instruments, we are developing a flexible fluidic sample preparation unit. The overall goal of this Microfluidic Module is to input a fluid sample, containing background particulates and potentially target compounds, and deliver a processed sample for detection. We are developing techniques for sample purification, mixing, and filtration that would be useful to many applications including immunologic and nucleic acid assays. Many of these fluidic functions are accomplished with acoustic radiation pressure or dielectrophoresis. We are integrating these technologies into packaged systems with pumps and valves to control fluid flow through the fluidic circuit.

Thermal effect of Er:YAG laser radiation on dental hard tissues

The object of this paper is to evaluate the thermal effect of the Er:YAG laser on human teeth and discuss the preliminary studies of the effects of water on the ablation efficiency of the Er:YAG laser. Human extracted teeth were sectioned into varying thicknesses in a horizontal plane and placed in a holder and aligned in a position where the laser was in focus on the surface of the tooth. First the laser was set at a known energy and the number of pulses needed to ablate through the known thickness of tooth were counted and a proportion of energy vs. ablation depth (etch rate) was determined. After etch rate was determined a thermocouple was placed on the back surface of the tooth section in line with the laser. The laser was then used to cut into the tooth just above the thermocouple and the temperature determined with and without water.