Effect of the ArF excimer laser on human enamel

Physico-chemical changes of human enamel irradiated with ArF excimer laser

BACKGROUND AND OBJECTIVES

Irradiation of tooth enamel by lasers can alter its structure and chemical composition. The purpose of this work was to determine the compositional changes and to elucidate the mechanisms of laser-enamel interaction using ArF excimer laser.

STUDY DESIGN/MATERIALS AND METHODS

Human enamel irradiated with ArF excimer laser (wavelength, 193 nm) at different fluences, was examined using X-ray diffraction, infrared (IR) spectroscopy and microprobe analysis.

RESULTS

Ablation without significant compositional changes in irradiated enamel was evident when low fluences (approximately 200-380 mJ/cm2) were used. However, fluences between 640 and 2,300 mJ/cm2 resulted in an increased Ca/P ratio, decreased amount of carbonate and protein, and the formation of tricalcium phosphate and tetracalcium phosphate, suggesting the involvement of a photothermal mechanism.

CONCLUSIONS

The results show that ArF excimer laser can alter the chemical composition and morphology of the highly mineralized (96%) dental enamel, depending on the fluence used.

Dental laser research: selective ablation of caries, calculus, and microbial plaque: from the idea to the first in vivo investigation

One of the current dental laser research tracks is selective ablation, which is the removal of disease while not harming adjacent healthy structures. This article describes the scientific path from the first basic laboratory study of the absorption characteristics of caries to selective ablation of bacteria, microbial plaque, and calculus with a blue laser and the first in vivo safety studies in dogs. This article is an example of a typical research path for future studies of the uses of lasers in dentistry.

ArF-193 Excimer Laser and Emdogain® in the Treatment of Experimental Periodontitis: An Experimental Study in Rabbits

OBJECTIVE

We aimed to investigate how the progress made on laser technology during the last ten years could overcome this obstacle and allow the use of lasers in periodontology, together with the application of a number of products permitting the regeneration of periodontal tissues.

BACKGROUND DATA

The use of lasers in dentistry remains controversial, in spite of their increasing application in medical practice. The main reason for this discrepancy is the frequent report of damage to surrounding tissues and the dental pulp, due to the energy transfer, from the site of laser impact.

METHODS

Experimental periodontitis was initiated in fifteen rabbits. Animals were divided into five equal groups. In the control group, no therapy was applied. The remaining four groups were treated with curettage or ArF 193 excimer laser, under conditions of strict control of frequency, fluency, and application, without or with the application of a periodontal healing product (Emdogain). Laser was applied by the use of a new, articulated arm for beam delivery. Pocket depth and microscopic analysis were performed three weeks after treatment.

RESULTS

Our results show that all treatment groups decreased pocket depth significantly. ArF193 excimer laser does not produce any histological damage to the dental pulp, and facilitates periodontal regeneration. This result is highly facilitated by the application of Emdogain).

CONCLUSIONS

The use of UV lasers, under a tight control of its energy, may be a valuable tool for the treatment of periodontal diseases, especially combined with the use of healing products. Further study is need to confirm these results.

Combined UV and IR laser ablation of dentine

OBJECTIVE

The aim of this study was to increase the rate of removal of dentine tissue by a 213-nm laser through the introduction of an Er:YAG assisting laser.

BACKGROUND DATA

The rate of dentine removal is increased by using a CO2 laser to assist a XeCl excimer laser.

METHODS

Extracted human teeth were sliced parallel to the crown and exposed to 213-nm laser and Er:YAG laser beams that were spatially and temporally aligned. The 213-nm laser radiation was generated using a Q-switched Nd:YAG (5 nsec, 10 Hz) and three nonlinear crystals. The Er:YAG laser was free running with a pulse duration of 100 microsec and a pulse repetition rate of 10 Hz. A fluence range of 5-18.6 J/cm2 (213 nm) and 0.6-1.3 J/cm2 (Er:YAG) was used. Axial ablation rates were measured for different pulse energies and pulse overlaps.

RESULTS

The ablation rate of dentine increased in most cases by a factor of two. The highest ablation rate achieved was 18.3 microm/pulse +/- 2.51, which is more than twice the highest ablation rate previously published using a 213-nm laser. Changes in the pulse superpositions that were investigated did not present a significant change in the ablation rate.

CONCLUSIONS

The Er:YAG laser can be used to increase the removal rate of dentine by a short-pulse ultraviolet (UV) laser.

Safety of the ArF193 excimer laser for the removal of dental plaque and calculi: an in vitro histological study

OBJECTIVE

To assay the safety of the ArF excimer laser in the integrity of human pulp elements.

BACKGROUND DATA

The use of lasers in dentistry remains controversial, in spite of their increasing application in medical practice. The main reason for this discrepancy is the frequent report of damage to surrounding tissues and the dental pulp, due to the energy transfer, from the site of laser impact. The progress made on laser technology during the last 10 years, could overcome this obstacle and allow the use of lasers in dentistry.

METHODS AND RESULTS

The present study reports the use of the ArF 193 excimer laser, under conditions of strict control of frequency and fluency, for the ablation of dental carries, plaque, and calculi, by the use of a new, articulated arm. We have tested 10 teeth, extracted for prosthetic reasons, immediately after extraction. Our in vitro results show that the ArF193 excimer laser does not produce any harm to the dental pulp (at least at the photo- or electronic microscopy level), whereas in a matter of seconds, it can be effective in removing all dental deposits. In addition, the use of the flexible articulated arm, makes this treatment comfortable and easier for both the dentist and patient.

CONCLUSION

Under a strict control of laser technology, and the use of the new articulated arm presented, the use of the ArF excimer laser in dentistry is safe and comfortable.

Morphological effects of ArF excimer laser irradiation on enamel and dentin

BACKGROUND AND OBJECTIVE

The aim of this investigation to determine the range of morphological and ablative effects that can be achieved on dental enamel and dentin using ArF excimer laser irradiation at a wavelength of 193nm.

STUDY DESIGN/MATERIALS AND METHODS

Caries-free coronal enamel and dentin surfaces of 20 extracted human teeth were subjected to irradiation at 193nm using a Lamda-Physik model EMG 103 MSC and ArF fill. Morphology of cavity floors and walls were assessed by light microscopy and SEM.

RESULTS

Morphological surface effects and ablation could be controlled effectively and reliably by choice of parameter combination, allowing the operator to achieve either a smooth, flat, or increasingly rough surface with differing degrees of selective ablation. No signs of thermal damage were apparent.

CONCLUSION

Excimer laser irradiation at 193nm provided clinically useful cavity preparations and surface morphological effects.

Subsurface morphologic changes of ND:YAG laser-etched enamel

BACKGROUND AND OBJECTIVE

Etching the enamel surface with a Nd:YAG dental laser produces impact craters with cavities, micropores, and microfissures. This in vitro SEM study examined laser-etched enamel to determine the pattern and extent of subsurface changes.

STUDY DESIGN/MATERIALS AND METHODS

The facial surface of 10 maxillary central incisor teeth were coated with a black initiator and laser-etched with a pulsed Nd:YAG laser (1.06 lambda, 75 mJ, 15 Hz, 320 microns fiber, 94 J/cm2 fluence). The facial surface of five teeth were plastic-embedded under a low vacuum, then demineralized in 10% formic acid. The other teeth were split incisoapically. All samples were prepared for SEM.

RESULTS

Examination of the plastic impressions showed a delicate interlacing pattern of thin partitions and small knob-like expansions. Examination of the split teeth showed the penetration of microfissures into the enamel estimated at 10 microns.

CONCLUSION

These subsurface alterations may provide space for the infiltration and mechanical retention of dental resin.

Effect of XeCl-308nm excimer laser on the mineral content of human dentin

The effect of the XeCl-308nm excimer laser on the mineral content and surface morphology of cut dentin was examined in ten extracted human teeth. Each dentin specimen was lased for 4 s at a fluence of 1 J/cm2 and a frequency of 25 Hz. Non-lased area of the same specimen served as control. Scanning electron microscopy and energy dispersive spectrometry revealed a significant decrease in the phosphorus levels following laser treatment. A decrease in calcium levels also occurred but was not statistically significant. Nonsignificant changes in sulphur and potassium levels were also noted. Morphologically, the lased dentin showed an apparently melted surface with partial obstruction of the dentin tubules as well as cracks along the lased surface. Therefore, it appeared that laser treatment may alter the chemical structure as well as the surface morphology of the dentin.

Lasers in dentistry

Since the development of the ruby laser by Maiman in 1960, there has been great interest among dental practitioners, scientists, and patients to use this tool to make dental treatment more pleasant. Oral soft tissue uses are becoming more common in dental offices. The possible multiple uses of lasers in dentistry, beyond soft tissue surgery and dental composite curing, unfortunately, have not yet been realized clinically. These include replacement of the dental drill with a laser, laser dental decay prevention, and laser decay detection. The essential question is whether a laser can provide equal or improved treatment over conventional care. Safe use of lasers also must be the underlying goal of proposed or future laser therapy. With the availability and future development of different laser wavelengths and methods of pulsing, much interest is developing in this growing field. This article reviews the role of lasers in dentistry since the early 1960s, summarizes some research reports from the last few years, and proposes what the authors feel the future may hold for lasers in dentistry.

Dye-enhanced ablation of enamel by pulsed lasers

Laser removal of dental hard tissue has been proposed as a replacement for or augmented approach to the dental handpiece. The main limitation for widespread usage of lasers in dentistry has been inefficient ablation of dental hard tissue, accompanied by potential laser-induced damage to the surrounding tissue. The research focuses on a novel approach for enhancement of tissue ablation and confinement of laser interaction to a small tissue volume by controlled placement of an exogenous dye on the enamel surface. Studies were done with both pulsed alexandrite and pulsed Nd:YAG lasers, with indocyanine green and India ink, respectively, used as photo-absorbers. These dye-enhanced laser processes demonstrated the feasibility of this technique for cavity preparation. While control studies produced little or no appreciable crater, average preparation depth for the dye-enhanced ablation was from 1 to 1.5 mm, with a diameter of approximately 0.6 mm. Knoop hardness measurements show that, surrounding the crater, there is small annular region slightly softened by the laser action. SEM studies of the interior structure of the tooth did not show significant damage to the surrounding tissue. Temperature measurement studies indicated that the pulsed nature of the laser, combined with the photo-absorbing dye, effectively prevented significant temperature rise at the pulp. The remarkable effectiveness of this technique in creating cavity preparations and the absence of any notable collateral damage to the surrounding tissue suggest that dye-enhanced pulsed-laser ablation could be used as an alternative to the dental handpiece in selected procedures.