Prediction of femtosecond laser ablation profile on human teeth

Antibacterial effect of femtosecond laser against Enterococcus faecalis and Fusobacterium nucleatum biofilms on dentin: an in vitro study

BACKGROUND

Removing infectious bacteria biofilms from the root canal system is crucial for a successful endodontic treatment. This study investigated the antibacterial effect of femtosecond laser (fs-laser) against Enterococcus faecalis (E. faecalis) and Fusobacterium nucleatum (F. nucleatum) biofilms on dentin.

METHODS

The chemical composition of dentin slices from extracted human teeth was analyzed using FTIR and Raman probes. The morphology of fs-laser ablated dentin grooves was evaluated by an optical profiler, and the fs-laser ablation fluence threshold was obtained by a mathematical model. A correlation between dentin chemical composition and ablation threshold was established. The antibacterial effect of different fs-laser irradiation dosages within the safe threshold on E. faecalis and F. nucleatum biofilms was firstly evaluated using the growth curve method. The biofilm removal efficacy on dentin and antimicrobial effect in dentinal tubules was further evaluated by CLSM and SEM analysis. The effect of fs-laser irradiation on the microhardness of dentin surface was also evaluated. The fs-laser irradiation process was observed using a spectrometer.

RESULTS

The peak intensity of phosphate group showed a positive correlation to the fs-laser dentin ablation fluence threshold in both FTIR and Raman spectroscopy. The safe fluence threshold of 1.8 J/cm2 was determined by a prediction model on 20 dentin samples. The antimicrobial effect of fs-laser increased along with the irradiation fluence or time. Both E. faecalis and F. nucleatum biofilms on dentin could be effectively removed by the fs-laser with 1.5 J/cm2 fluence for 20 s without compromising the microhardness of dentin surface. Meanwhile, fs-laser could also eliminate the bacteria in dentinal tubules. The generation of plasma occurred during the fs-laser irradiation process, and the plasma spectra exhibited distinguishable characteristics between the two kinds of biofilms.

CONCLUSIONS

Fs-laser could effectively remove both E. faecalis and F. nucleatum biofilms on dentin, along with a notable antibacterial effect in dentinal tubules.

Effects of femtosecond laser on hard dental tissues: A scoping review

Traditional tooth preparation can cause patient discomfort, thermal damage to tissues, and occupational health risks for clinicians. Laser-based techniques, particularly femtosecond lasers, offer an alternative due to precise, non-invasive treatment without the thermal and mechanical drawbacks. The objective of this study was to assess available evidence on the effects of femtosecond laser treatment on enamel and dentin. The study design included in vitro or in vivo studies on human teeth reporting on qualitative and quantitative parameters of laser-dental tissue interaction. The review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) statement. The review was registered in the Open Science Framework registry. A comprehensive literature search of PubMed, Scopus, EMBASE/Ovid, Cochrane Library, DARE, LILACS and Pro Quest databases was conducted by three reviewers until 10th January 2024 and then updated on 18th August 2024. Eligibility criteria included peer-reviewed articles published in English, focusing on human teeth, with available full text excluding reviews, conference proceedings and gray literature. The outcomes of interest were the quality of tooth preparation, surface characteristics, bond strength, thermal effects and damage to adjacent tissues with variables being laser parameters and tooth types. Methodological quality of studies was not conducted. The search yielded 48 articles after the removal of duplicates, irrelevant and non-retrievable articles. All were original in vitro studies investigating reporting on the outcomes of interest. Measurement methods included a range of microscopy, spectroscopy, optical coherence tomography, universal force testing and thermal imaging. Sapphire lasers were most commonly used with a wide range of parameters. Laser produced sharp-edged cavities with ablated surfaces free of melting (seen in approximately 10% of the craters), cracking, debris, with open dentinal tubules, increased wetting (Contact angle mean range 39.63 ̊(± 1.84 ̊) to 70.47 ̊(± 10.27 ̊) and roughness mean range 0.82 (± 0.05) to 4.20 (± 1.10)µm). Effects of femtosecond laser on bonding efficiency were inconsistent when compared to no treatment, conventional acid etching or Er:YAG laser. Femtosecond laser was shown to achieve precise tooth preparation with no or minimal thermal, mechanical and structural effects on adjacent tissue, however with variable bonding efficiency. Further research is needed to optimize laser parameters, investigate antibacterial effects, and establish long-term clinical outcomes and safety profiles.Date of registration: July 1st, 2024.Registration ID: OSF.IO/UQMNB.

High-Precision Implant Cavity Fabrication Using Femtosecond Lasers

Objective: This study aims to enhance the precision of implant cavity preparation, addressing a notable challenge in the current state of the field by utilizing femtosecond lasers. Background: The application of femtosecond lasers in implant cavity preparation heralds a noninvasive and efficient technique, characterized by diminished thermal damage and high biocompatibility. Despite these promising attributes, the realization of precise cavity preparation remains a significant challenge in the contemporary domain. Materials and Methods: Our research group devised a specialized femtosecond laser microsurgery robotic system tailored for sophisticated implant cavity preparation. This system facilitated the meticulous analysis of sheep shank bone samples, enabling precise three-dimensional cutting. The analysis included an extensive examination of ablation effects, using a laser scanning microscope and VK Analyzer software. This investigation spanned the phases of laser flux calibration and experimental validation, offering a critical evaluation of the automated preparation process. Results: The study delineated that at the focus position of our custom-made oral clinical femtosecond laser microsurgery robotic system, the laser spot diameter is 75.69 μm, and ascertained the ablation threshold for sheep shank cortical bone to be 1.47 J/cm2. Utilizing low laser flux with minimal ablation craters overlap compromised the sidewall precision of the implant cavity, whereas employing high laser flux with extensive ablation craters overlap resulted in an enlarged ablation angle. At a laser energy setting of 2.2362 J/cm2 and a 50% ablation crater overlap, an implant cavity was successfully crafted featuring a top diameter of 4.41 mm, a bottom diameter of 3.98 mm, and a depth of 3 mm, devoid of any adverse thermal effects such as cracking or carbonization. Conclusions: The oral clinical femtosecond laser microsurgery robotic system can achieve automated and precise implant cavity preparation. This advancement promotes the broader application of femtosecond lasers in the field of orthopedics.

In vivo biological safety investigation of Yb-CALGO femtosecond laser dental surgery

While lasers have found their successful applications in various clinical specialties, in clinical dental practice, traditional mechanical drills are still predominantly utilized. Although erbium-doped lasers have been demonstrated for dental therapy, their clinical performance is still not satisfactory due to the long pulse width, low peak power, and small repetition rate. To attain a smaller thermal diffusion thus better biological safety and surgical precision, as well as more rapid ablation, the advancement of femtosecond laser techniques has opened another route of dental surgery; however, no biological safety investigation has been reported. Here, we present a systematic study of dental ablation by a Yb:CaAlGdO4 regenerative amplifier with a central wavelength of 1040 nm and pulse width of 160 fs. The in vivo experiment of dental surgery investigating the inflammatory response has been reported, for the first time to the best of our knowledge. It is demonstrated that dental surgery by Yb:CaAlGdO4 femtosecond laser ablation has better biological safety compared to the turbine drilling, thanks to its non-contact and ultrafast heat dissipation nature.

Optical penetration models for practical prediction of femtosecond laser ablation of dental hard tissue

OBJECTIVES

To develop and practically test high-precision femtosecond laser ablation models for dental hard tissue that are useful for detailed planning of automated laser dental restorative treatment.

METHODS

Analytical models are proposed, derived, and demonstrated for practical calculation of ablation rates, ablation efficiency and ablated morphology of human dental enamel and dentin using femtosecond lasers. The models assume an effective optical attenuation coefficient for the irradiated material. To achieve ablation, it is necessary for the local energy density of the attenuated pulse in the hard tissue to surpass a predefined threshold that signifies the minimum energy density required for material ionization. A 1029 nm, 40 W carbide 275 fs laser was used to ablate sliced adult human teeth and generate the data necessary for testing the models. The volume of material removed, and the shape of the ablated channel were measured using optical profilometry.

RESULTS

The models fit with the measured ablation efficiency curve against laser fluence for both enamel and dentin, correctly capturing the fluence for optimum ablation and the volume of ablated material per pulse. The detailed shapes of a 400-micrometer wide channel and a single-pulse width channel are accurately predicted using the superposition of the analytical result for a single pulse.

CONCLUSIONS

The findings have value for planning automated dental restorative treatment using femtosecond lasers. The measurements and analysis give estimates of the optical properties of enamel and dentin irradiated with an infrared femtosecond laser at above-threshold fluence and the proposed models give insight into the physics of femtosecond laser processing of dental hard tissue.

In vitro effect of Er: YAG laser irradiation in caries cavity preparation on biobehaviors of adjacent human dental pulp cells in the pulp chamber

The erbium-doped yttrium aluminum garnet (Er: YAG) laser has been successfully applied in caries removal; however, little is known about proper parameters of Er: YAG laser on different conditions of caries removal, especially the influence of Er: YAG irradiation on human dental pulp cells (hDPCs). Here, we tested the effects of Er: YAG laser at different output energy levels (100, 200, 300, 400, and 500 mJ) on biobehaviors of hDPCs. To simulate clinical deep caries conditions, hDPCs were cultured on the pulpal side of 500-μm-thick dentin disks in an in vitro pulp chamber model. Temperature change, structural change, and ablation depth of dentin disk were also recorded. The findings suggested that the biological behaviors of hDPCs are strongly correlated with the energy output of the Er: YAG laser. Er: YAG laser irradiation at 100 mJ may be proper and safe for deep caries removal since it would not cause any adverse effect on hDPCs biobehaviors.

Sub-70 nm surface structures on femtosecond laser irradiated GaAs in distilled water and sensing application

This study reveals the possibility of distinct ablation mechanisms at different radial positions of the ablated track on GaAs when ablated with femtosecond pulses in distilled water. From the center to the edges of the ablated track, fascinating features such as micron-sized cones, nano-pores, and nano-ripple trenches (average size of 60-70 nm) were observed. The requirement for simulations incorporating the variations in a Gaussian beam fluence and dynamics of the melt flow/surrounding media is discussed. Deep-subwavelength structures, i.e., nano-ripple trenches with a ripple size of ∼λ/11 are achieved on the GaAs surface in this study. Further, these GaAs surface structures acted as excellent hybrid surface-enhanced Raman spectroscopy platforms upon gold coating.

Physiochemical characteristics: A robust tool to overcome teeth heterogeneity on predicting laser ablation profile

To avoid excessive tissue removal and collateral damage, the high-power density laser is apt for dental surgery also need to have high precision. For high-precision dental surgery with minimal tissue damage, the present work frames a method to predict laser ablation profile based on surface morphology and chemical composition of dentin. The surface morphology and chemical composition were studied on different dentin samples using scanning electron microscope (SEM) and Energy Dispersive X-ray Analysis (EDAX), respectively. The key laser ablation parameters (ω₀ , D_eff , and F_th ) were determined by laser irradiation study using 800 nm, Ti:Sapphire femtosecond laser at processing condition of 100 fs, 10 kHz and 10 mm/s. The dentin samples show a strong linear correlation between physiochemical characteristics and laser ablation parameters. The surface morphology exhibits a negative linear correlation with threshold fluence, whereas the converse is true for chemical composition. The laser ablation parameters of a random dentin sample are derived from the knowledge of linearity data. From the obtained laser ablation parameters, the complete theoretical ablation profile is constructed and validated with experimental ablation profile. Even though the surface morphology of dentin shows high linearity, the concentration of Ca and P can be used as the most feasible probe in clinical settings. Furthermore, the laser ablation rate and ablation efficiency are predicted by the method to optimize the laser processing condition for any specific teeth. The versatility of the method overcomes the problem of heterogeneity on various teeth and simplifies the method of finding optimal laser processing condition for immaculate laser surgery.

Shear bond strength of a self-adhesive resin cement to dentin surface treated with Nd:YAG and femtosecond lasers

This study aims to evaluate the effect of Nd:YAG and femtosecond lasers irradiation on the shear bond strength (SBS) of a self-adhesive resin cement to the human dentin surface. One hundred extracted third molar teeth were randomly divided into 10 experimental groups according to dentin surface treatments; with and without the bonding agent, Nd:YAG 302 J/cm² and 440 J/cm², femtosecond 4 J/cm² and 7 J/cm², and control groups were prepared. After surface treatments, a self-adhesive resin cement was luted by using a bonding jig (Ultradent Products Inc.). The specimens were then subjected to shear test at a crosshead speed of 0.5 mm/min, and failure loads were recorded as megapascal (MPa). Two-way analysis of variance and Tukey HSD tests were performed (p ˂ 0.05). Representative specimens from each experimental subgroup were examined by means of SEM. The highest SBS values were obtained in Group 302 J/cm² Nd:YAG with bonding agent, and there is no statistical difference between Group 440 J/cm² Nd:YAG with bonding and Group 7 J/cm² femtosecond with bonding (p > 0.05). The lowest SBS values were observed in Group control without bonding agent. Nd:YAG and femtosecond laser treatments improved the adhesion between the dentin surface and the self-adhesive resin cement.