Selective ablation of dental enamel and dentin using femtosecond laser pulses

Abstract

The study of the interaction of intense laser light with matter, as well as transient response of atoms and molecules is very appropriated because of the laser energy concentration in a femtosecond optical pulses. The fundamental problem to be solved is to find tools and techniques which allow us to observe and manipulate on a femtosecond time scale the photonics events on and into the matter. Six third human extracted molars were exposed to a femtosecond Ti:Sapphire Q-switched and mode locked laser (Libra-S, Coherent, Palo Alto, CA, USA), emitting pulses with 70 fs width, radiation wavelength of 801 nm, at a constant pulse repetition rate of 1 KHz. The laser was operated at different power levels (70 to 400 mW) with constant exposition time of 10 seconds, at focused and defocused mode. Enamel and dentin surfaces were evaluated concerned ablation rate and morphological aspects under scanning electron microscopic. The results in this present experiment suggest that at the focused mode and under higher average power, enamel tissues present microcavities with higher depth and very precise edges, but, while dentin shows a larger melt-flushing, lower depth and melting and solidification aspect. In conclusion, it is possible to choose hard or soft ablation, under lower and higher average power, respectively, revealing different aspects of dental enamel and dentin, depending on the average power, fluence and distance from the focal point of the ultra-short pulse laser on the tooth surface.

Laser Technology for Caries Removal

“…In this way, it is easier to adjust a laser fluence that can be bellow or above the ablation threshold of a specific material. Literature studies determined that the threshold fluence for ablating enamel with USPL is higher than the fluence for ablating dentin and, in the same way that using erbium lasers, it is easier and faster to ablate dentin than enamel, which suggests selectivity to the tissue removal (Lizarelli et al, 2008;Niemz et al, 2004;Strassl et al, 2008;Wieger et al, 2006;). In 2006, Wieger et al used a picosecond Nd:YVO 4 laser for ablation of sound dentin, and it was observed the production of a microretentive pattern with opened tubules and the absence of microcracks or melting.…”

“…Considering the advances in technology for the development of ultra short pulse lasers (USPLs) (Niemz, 1995;Strickland & Mourou, 1985), efforts have been implemented to understand their interaction with dental hard tissues and to determine safe and proper parameters to provide a future clinical application in dentistry (Altshuler et al, 1994;Freitas et al, 2010;Kruger et al, 1999;Lizarelli et al, 2008;Strassl et al, 2008). Due to the extremely short pulse length, these systems promote precise cutting and have a strong potential for obtaining well-defined cavities and controlled caries removal (Niemz, 2004;Serbin et al, 2002).…”

Femtosecond laser ablation on dental hard tissues—Analysis of ablated profile near an interface using local effective intensity

“…The use of lasers in the medical field, as an instru ment for contact free tissue removal of dental hard tis sues [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], osseous tissues [33][34][35] have been stud ied as a means for complementing conventional drill ing or cutting tools. In all applications, a balance between several phenomena must be taken into con sideration.…”

Time progression of ultrashort laser ablation in a transparent material

“…The use of ultrafast laser pulses is having an impact on materials and processing in biological tissues in a profound ways [1][2][3][4][5][6][7]. Laser precision engineering is being extensively applied in industries for device micro fabrication due to its unique advantages of being a dry and noncontact process, coupled with the availability of reliable light sources and affordable system cost [8,9].…”

“…When femtosecond laser pulses are tightly focused within a transparent bulk material, nonlinear absorption can be induced in the focal volume and 1 The article is published in the original. lead to highly localized energy deposition resulting in a range of possible changes in material properties [19].…”