Femtosecond Laser Ablation of Human Enamel and Cementum – a Pilot Study

Abstract

Femtosecond lasers emit optical pulses with a pulse duration in the domain of femtoseconds typically ranging between a few femtoseconds to hundreds of femtoseconds. They focus the energy on a very short time scale within a single laser pulse. That leads to high peak powers that cannot be achieved by continuous wave lasers. The aim of this study is to investigate the effects produced by femtosecond laser light irradiation with different parameters on hard dental tissues.

A Pharos model Ph2-10-1000-02-H0-B femtosecond laser (LightConversion UAB, Lithuania), with bi/burst mode and automated harmonic generator, operating at three wavelengths – 1030 nm, 515 nm and 343 nm, with maximum average output powers of 10 W, 5.9 W and 2.8 W, respectively, was used for the irradiation of two freshly extracted healthy human teeth. All the studies presented in this paper were performed at average power of 2.8 W and pulse repetition rate of 100 kHz for all three wavelengths with pulse widths of 170 fs at 1030 nm, 130 fs at 515 nm, and 130 fs for 343 nm, respectively. A total of 24 experimental subgroups were formed so that each group corresponds to a unique combination of: wavelength, exposure duration, tissue type and age (group of the patient). The output powers of the laser radiation at all wavelengths with which the samples were treated was finally attenuated by internal power control, giving possibility to set the appropriate value in order to have equal power densities on the objects. The effects of the treatment were studied for 1 s and 10 s irradiation duration for young and old tooth enamel and cementum with the help of microscope ZEISS LSM 900 with Airyscan 2, resolution – lateral (XY) down to 120 nm, axial (Z) 350 nm. Digital scans in magnification were obtained. Profilometric images were used to obtain, access, and compare topographical data from the irradiated surfaces.

The observed changes of the irradiated enamel and cementum were described and compared. The amount of removed tissue for both is small. The results demonstrate that shorter wavelengths cause a more aggressive material ejection, whereas longer wavelengths contribute to increased thermal effects. Shorter wavelengths, particularly 343 nm, promote high ablation efficiency and controlled enamel removal, which is advantageous in minimally invasive procedures. However, excessive material ejection at this wavelength may lead to compromised structural integrity. Conversely, the 1030 nm wavelength results in increased thermal effects, including charring and cracking, highlighting the necessity of precise control over irradiation parameters. Carbonization is evident for cementum. The profilometric analysis shows roughness of the treated surfaces and demonstrates that femtosecond laser irradiation induces distinct modifications in enamel and cementum based on different laser parameters.

These findings provide critical insights into laser-tissue interaction mechanisms, with potential applications in precision dental treatments and conservative dentistry. Further investigations are needed to explore femtosecond laser treatments of healthy tooth structure, dental caries, and different dental materials.