Evaluation of bone healing following Er:YAG laser ablation in rat calvaria compared with bur drilling

Multimodal feedback systems for smart laser osteotomy: Depth control and tissue differentiation

OBJECTIVES

The study aimed to improve the safety and accuracy of laser osteotomy (bone surgery) by integrating optical feedback systems with an Er:YAG laser. Optical feedback consists of a real-time visual feedback system that monitors and controls the depth of laser-induced cuts and a tissue sensor differentiating tissue types based on their chemical composition. The developed multimodal feedback systems demonstrated the potential to enhance the safety and accuracy of laser surgery.

MATERIALS AND METHODS

The proposed method utilizes a laser-induced breakdown spectroscopy (LIBS) system and long-range Bessel-like beam optical coherence tomography (OCT) for tissue-specific laser surgery. The LIBS system detects tissue types by analyzing the plasma generated on the tissue by a nanosecond Nd:YAG laser, while OCT provides real-time monitoring and control of the laser-induced cut depth. The OCT system operates at a wavelength of 1288 ± 30 nm and has an A-scan rate of 104.17 kHz, enabling accurate depth control. Optical shutters are used to facilitate the integration of these multimodal feedback systems.

RESULTS

The proposed system was tested on five specimens of pig femur bone to evaluate its functionality. Tissue differentiation and visual depth feedback were used to achieve high precision both on the surface and in-depth. The results showed successful real-time tissue differentiation and visualization without any visible thermal damage or carbonization. The accuracy of the tissue differentiation was evaluated, with a mean absolute error of 330.4 μm and a standard deviation of ±248.9 μm, indicating that bone ablation was typically stopped before reaching the bone marrow. The depth control of the laser cut had a mean accuracy of 65.9 μm with a standard deviation of ±45 μm, demonstrating the system's ability to achieve the pre-planned cutting depth.

CONCLUSION

The integrated approach of combining an ablative laser, visual feedback (OCT), and tissue sensor (LIBS) has significant potential for enhancing minimally invasive surgery and warrants further investigation and development.

Er:YAG laser-assisted comprehensive periodontal pocket therapy for residual periodontal pocket treatment: A randomized controlled clinical trial

BACKGROUND

This study evaluated the effectiveness of a novel pocket therapy (Er:YAG laser-assisted comprehensive periodontal pocket therapy [Er-LCPT]) for residual pocket treatment, compared with conventional mechanical treatment alone, in a randomized controlled clinical trial.

METHODS

Two sites in 18 patients having residual periodontal pockets of ≥5 mm depth, extant following initial active therapy, or during supportive therapy, were randomized into two groups in a split mouth design: the control group received scaling and root planing (SRP) by curette, and the test group received Er-LCPT using curette and laser. With Er-LCPT, after root debridement, inflamed connective tissue on the inner gingival surface and on the bone surface/within extant bone defects was thoroughly debrided. Furthermore, removal of proximate oral epithelium and coagulation of the blood clot in the pocket entrance were performed with laser. Clinical parameters were evaluated, before and after treatment, through 12 months.

RESULTS

Both groups showed significant improvements in clinical parameters. With Er-LCPT, pocket debridement was thoroughly and safely performed, without any adverse side effects and complications, and favorable healing was observed in most of the cases. At 12 months, Er-LCPT demonstrated significantly higher probing pocket depth reduction (2.78 mm vs. 1.89 mm on average; p = 0.012, Wilcoxon signed-rank test), clinical attachment gain (1.67 mm vs. 1.06 mm; p = 0.004) as primary outcomes, and reduced BOP value (0.89 vs. 0.56; p = 0.031), compared with SRP alone.

CONCLUSION

The results of this study indicate that Er-LCPT is more effective for residual pocket treatment, compared with SRP alone.

Towards phase-sensitive optical coherence tomography in smart laser osteotomy: temperature feedback

Thermal effects during bone surgery pose a common challenge, whether using mechanical tools or lasers. An irrigation system is a standard solution to cool the tissue and reduce collateral thermal damage. In bone surgery using Er:YAG laser, insufficient irrigation raises the risk of thermal damage, while excessive water lowers ablation efficiency. This study investigated the potential of optical coherence tomography to provide feedback by relating the temperature rise with the photo-thermal expansion of the tissue. A phase-sensitive optical coherence tomography system (central wavelength of λ=1.288 μm, a bandwidth of 60.9 nm and a sweep rate of 104.17 kHz) was integrated with an Er:YAG laser using a custom-made dichromatic mirror. Phase calibration was performed by monitoring the temperature changes (thermal camera) and corresponding cumulative phase changes using the phase-sensitive optical coherence tomography system during laser ablation. In this experiment, we used an Er:YAG laser with 230 mJ per pulse at 10 Hz for ablation. Calibration coefficients were determined by fitting the temperature values to phase later and used to predict the temperature rise for subsequent laser ablations. Following the phase calibration step, we used the acquired values to predict the temperature rise of three different laser-induced cuts with the same parameters of the ablative laser. The average root-mean-square error for the three experiments was measured to be around 4 °C. In addition to single-point prediction, we evaluated this method's performance to predict the tissue's two-dimensional temperature rise during laser osteotomy. The findings suggest that the proposed principle could be used in the future to provide temperature feedback for minimally invasive laser osteotomy.

Real-time closed-loop tissue-specific laser osteotomy using deep-learning-assisted optical coherence tomography

This article presents a real-time noninvasive method for detecting bone and bone marrow in laser osteotomy. This is the first optical coherence tomography (OCT) implementation as an online feedback system for laser osteotomy. A deep-learning model has been trained to identify tissue types during laser ablation with a test accuracy of 96.28 %. For the hole ablation experiments, the average maximum depth of perforation and volume loss was 0.216 mm and 0.077 mm³, respectively. The contactless nature of OCT with the reported performance shows that it is becoming more feasible to utilize it as a real-time feedback system for laser osteotomy.

Influence of Er:YAG laser irradiation on the outcomes of alveolar ridge preservation at the infected molar sites: a randomized controlled trial

BACKGROUND

The purpose of this study was to investigate the socket healing outcome after alveolar ridge preservation at infected molar sites using an erbium-doped yttrium aluminium garnet (Er:YAG) laser.

METHODS

Eighteen patients who needed molar extraction and exhibited signs of infection were included and allocated into either the laser group or the control group. Er:YAG laser irradiation for degranulation and disinfection was performed with alveolar ridge preservation (ARP) in the laser group. Traditional debridement with a curette was performed in the control group. Two months after ARP, bone tissue samples were harvested at the time of implant placement for histological analysis. Assessment of dimension changes in alveolar bone was conducted by superimposing two cone-beam computed tomography (CBCT) scans taken at baseline and two months after extraction.

RESULTS

Histologically, after two months of healing, Er:YAG laser treatment resulted in more newly formed bone (laser: 17.75 ± 8.75, control: 12.52 ± 4.99, p = 0.232). Moreover, greater osteocalcin (OCN) positive expression and lower runt-related transcription factor 2 (RUNX-2) positive expression were detected in the laser group. However, no statistically significant difference was observed between the two groups. The difference in the vertical resorption of the buccal bone plate was statistically significant between groups (laser: -0.31 ± 0.26 mm, control: -0.97 ± 0.32 mm, p < 0.05). Major changes in ridge width were observed at 1 mm below the bone crest. However, the differences between groups were not significant (laser: -0.36 ± 0.31 mm, control: -1.14 ± 1.24 mm, p = 0.171).

CONCLUSIONS

ARP with Er:YAG laser irradiation seemed to improve bone healing by regulating osteogenesis-related factor expression in the early stage at infected sites.

TRIAL REGISTRATION

The trial was registered on the Chinese Clinical Trial Registry Platform ( https://www.chictr.org.cn/ ) (registration number: ChiCTR2300068671; registration date: 27/02/2023).

Bone Laser Patterning to Decipher Cell Organization

The laser patterning of implant materials for bone tissue engineering purposes has proven to be a promising technique for controlling cell properties such as adhesion or differentiation, resulting in enhanced osteointegration. However, the possibility of patterning the bone tissue side interface to generate microstructure effects has never been investigated. In the present study, three different laser-generated patterns were machined on the bone surface with the aim of identifying the best surface morphology compatible with osteogenic-related cell recolonization. The laser-patterned bone tissue was characterized by scanning electron microscopy and confocal microscopy in order to obtain a comprehensive picture of the bone surface morphology. The cortical bone patterning impact on cell compatibility and cytoskeleton rearrangement on the patterned surfaces was assessed using Stromal Cells from the Apical Papilla (SCAPs). The results indicated that laser machining had no detrimental effect on consecutively seeded cell metabolism. Orientation assays revealed that patterns with larger hatch distances were correlated with higher cell cytoskeletal conformation to the laser-machined patterns. To the best of our knowledge, this study is the first to consider and evaluate bone as a biological interface that can be engineered for improvement. Further investigations should focus on the in vivo implications of this direct patterning.

High-frequency pulsed diode laser irradiation inhibits bone resorption in mice with ligature-induced periodontitis

AIM

The purpose of this study was to elucidate the suppressive effect of high-frequency pulsed diode laser irradiation on bone resorption and its biological effects for gene expression and microbiome composition on the gingival tissue in ligature-induced periodontitis in mice.

MATERIALS AND METHODS

Ligating ligature around the teeth and/or laser irradiation was performed on the gingival tissue in mice as follows: Co (no ligature and no laser irradiation), Li (ligation without laser irradiation), La (no ligature but with laser irradiation), and LiLa (ligation with laser irradiation). Bone resorption was evaluated using micro-computed tomography. RNA-seq analysis was performed on gingival tissues of all four groups at 3 days post ligation. The differences in microbial composition between Li and LiLa were evaluated based on the number of 16S rRNA gene sequences.

RESULTS

Bone resorption caused by ligation was significantly suppressed by laser irradiation. RNA-seq in Co and La gingival tissue revealed many differentially expressed genes, suggesting diode laser irradiation altered gene expression. Gene set enrichment analysis revealed mTORC1 signaling and E2F target gene sets were enriched in gingival tissues both in La and LiLa compared to that in Co and Li, respectively. The amount of extracted DNA from ligatures was reduced by laser irradiation, and bacterial network structure was altered between the Li and LiLa.

CONCLUSIONS

High-frequency pulsed diode laser irradiation showed biological effects and suppressed bone resorption in ligature-induced periodontitis. This article is protected by copyright. All rights reserved.

High Precision Bone Cutting by Er: YAG Lasers Might Minimize the Invasiveness of Navigated Brain Biopsies

Biopsies of brain tissue are sampled and examined to establish a diagnosis and to plan further treatment, e.g. for brain tumors. The neurosurgical procedure of sampling brain tissue for histologic examination is still a relatively invasive procedure that carries several disadvantages. The “proof of concept”-objective of this study is to answer the question if laser technology might be a potential tool to make brain biopsies less invasive, faster and safer. Laser technology might carry the opportunity to miniaturize the necessary burr hole and also to angulate the burr hole much more tangential in relation to the bone surface in order to take biopsies from brain regions that are usually only difficult and hazardous to access. We examined if it is possible to miniaturize the hole in the skull bone to such a high extent that potentially the laser-created canal itself may guide the biopsy needle with sufficient accuracy. The 2-dimensional, i.e. radial tolerance of the tip of biopsy needles inserted in these canals was measured under defined lateral loads which mimic mechanical forces applied by a surgeon. The canals through the skull bones were planned in angles of 90° (perpendicular) and 45° relative to the bone surface. We created a total of 33 holes with an Er : YAG laser in human skull bones. We could demonstrate that the achievable radial tolerance concerning the guidance of a biopsy needle by a laser created bone canal is within the range of the actual accuracy of a usual navigated device if the canal is at least 4 mm in length. Lateral mechanical loads applied to the biopsy needle had only minor impact on the measurable radial tolerance. Furthermore, in contrast to mechanical drilling systems, laser technology enables the creation of bone canals in pointed angles to the skull bone surface. The latter opens the perspective to sample biopsies in brain areas that are usually not or only hazardous to access.

Hydroxyapatite Film Coating by Er:YAG Pulsed Laser Deposition Method for the Repair of Enamel Defects

There are treatments available for enamel demineralization or acid erosion, but they have limitations. We aimed to manufacture a device that could directly form a hydroxyapatite (HAp) film coating on the enamel with a chairside erbium-doped yttrium aluminum garnet (Er:YAG) laser using the pulsed laser deposition (PLD) method for repairing enamel defects. We used decalcified bovine enamel specimens and compacted α-tricalcium phosphate (α-TCP) as targets of Er:YAG-PLD. With irradiation, an α-TCP coating layer was immediately deposited on the specimen surface. The morphological, mechanical, and chemical characteristics of the coatings were evaluated using scanning electron microscopy (SEM), scanning probe microscopy (SPM), X-ray diffractometry (XRD), and a micro-Vickers hardness tester. Wear resistance, cell attachment of the HAp coatings, and temperature changes during the Er:YAG-PLD procedure were also observed. SEM demonstrated that the α-TCP powder turned into microparticles by irradiation. XRD peaks revealed that the coatings were almost hydrolyzed into HAp within 2 days. Micro-Vickers hardness indicated that the hardness lost by decalcification was almost recovered by the coatings. The results suggest that the Er:YAG-PLD technique is useful for repairing enamel defects and has great potential for future clinical applications.

Novel flapless esthetic procedure for the elimination of extended gingival metal tattoos adjacent to prosthetic teeth: Er:YAG laser micro-keyhole surgery

PURPOSE

This article describes a novel, minimally invasive procedure called Er:YAG laser micro-keyhole surgery (EL-MIKS) that removes metal or amalgam tattoos in the gingiva adjacent to prosthetic teeth without gingival deformity and recession. We aimed to evaluate the clinical efficacy of EL-MIKS for removing metal tattoos and present its long-term treatment outcomes.

METHODS

The EL-MIKS procedure consists of several steps that are all performed under a microscope. First, a micro-keyhole (1-2 mm diameter) was prepared using an Er:YAG laser in the center of the metal pigmentation. The connective tissue was evaporated in the deep layer, where metal debris was deposited. Second, within the accessible range, the irradiation angle was changed in various directions to ablate the metal pieces and discolored connective tissue without enlarging the keyhole. Finally, after blood filled the space created by the tissue evaporation, the surface of the blood clot at the entrance of the micro-keyhole was thermally coagulated with defocus laser irradiation. Pigmentation that could not be successfully removed from a single micro-keyhole was treated by forming new micro-keyholes at a distance of 3 mm or more from each previously created hole. Depigmentation over an extended area was completed over a few sessions every 4 weeks without gingival recession after surgery.

CONCLUSIONS

EL-MIKS, a novel depigmentation technique, was able to successfully remove an extended area of metal tattoos in the gingiva using a simpler, easier, and less invasive procedure than conventional periodontal plastic surgery. Esthetic restoration was successfully achieved without postoperative alteration of the gingival contour.

Low-Level Erbium-Doped Yttrium Aluminum Garnet Laser Irradiation Induced Alteration of Gene Expression in Osteogenic Cells from Rat Calvariae

Objective: The aim of this study was to investigate the effect of low-level erbium-doped yttrium aluminum garnet (Er:YAG) laser irradiation on gene expression in osteogenic cells from rat calvariae. Background: Previous studies showed beneficial effects of laser irradiation on bone-related cells. However, few studies have examined the gene expression alteration by laser irradiation on osteogenic cells in a calcified condition. Materials and methods: Osteogenic cells were prepared by culturing rat calvarial osteoblast-like cells in osteoinductive medium for 21 days. The cells at the bottom of the culture dish were irradiated with Er:YAG laser (wavelength: 2.94 μm, energy density: 3.1 and 8.2 J/cm²) positioned at distance of 25 cm. Lactate dehydrogenase (LDH) assay of the irradiated cells was performed. After screening for genes related to bone formation, mechanotransduction, and thermal effect by quantitative polymerase chain reaction (qPCR), gene expression at 3 h after 3.1 J/cm² irradiation was comprehensively analyzed using microarray. Results: No dramatical increase in surface temperature and LDH activities after laser irradiation were observed. Sost expression was significantly reduced at 3 h after 3.1 J/cm² irradiation. Bcar1 and Hspa1a expression was significantly increased following 8.2 J/cm² irradiation. Microarray analysis identified 116 differentially expressed genes. Gene set enrichment analysis showed enrichment of histone H3-K9 methylation and modification gene sets. Conclusions: Er:YAG laser irradiation, especially at 3.1 J/cm², showed positive effect on the expression of genes related to bone formation in osteogenic cells, without inducing significant cell damage. These findings may represent critical mechanisms of early bone formation after Er:YAG laser irradiation.

Residual periodontal pocket treatment with Er:YAG laser-assisted comprehensive periodontal pocket therapy: a retrospective study

OBJECTIVES

Recently, the application of erbium-doped yttrium aluminum garnet (Er:YAG) laser has been increasing in periodontal therapy. In this retrospective study, we evaluated the safety and effectiveness of a novel pocket therapy using Er:YAG laser in combination with conventional mechanical scaling and root planing treatment (Er:YAG laser-assisted comprehensive periodontal pocket therapy).

METHODS

Forty sites in 29 elderly patients having residual periodontal pockets of ≥ 5 mm depth were treated by curette and Er:YAG laser from 2006 to 2009. After root debridement by curette, laser irradiation was performed on the root surfaces. Then, inflamed connective tissue on the inner gingival surface and on the bone surface/within extant bone defects was thoroughly debrided by curette and laser. Furthermore, in most cases, removal of the outer epithelium and coagulation of the blood clot in the pocket entrance were additionally performed with laser. Clinical parameters were evaluated before and 3, 6, and 12 months after treatment.

RESULTS

With Er:YAG laser-assisted pocket therapy, debridement of pockets was thoroughly and safely performed, and favorable clinical improvements were observed in most cases, without any adverse side effects and complications. After 1 year, probing pocket depth significantly decreased from 6.4 ± 1.4 to 3.5 ± 1.3 mm (p < 0.001, 3.0 mm reduction), and clinical attachment level significantly decreased from 7.5 ± 1.6 to 5.2 ± 1.9 mm (p < 0.001, 2.3 mm gain).

CONCLUSION

The results of this study indicate that Er:YAG laser-assisted therapy is useful for the treatment of residual pockets as a minimally invasive flapless surgery.

CLINICAL RELEVANCE

Er:YAG laser-assisted comprehensive pocket therapy reduces the necessity of more conventional surgical therapies.

Chronological Gene Expression of Human Gingival Fibroblasts with Low Reactive Level Laser (LLL) Irradiation

Though previously studies have reported that Low reactive Level Laser Therapy (LLLT) promotes wound healing, molecular level evidence was uncleared. The purpose of this study is to examine the temporal molecular processes of human immortalized gingival fibroblasts (HGF) by LLLT by the comprehensive analysis of gene expression. HGF was seeded, cultured for 24 h, and then irradiated with a Nd: YAG laser at 0.5 W for 30 s. After that, gene differential expression analysis and functional analysis were performed with DNA microarray at 1, 3, 6 and 12 h after the irradiation. The number of genes with up- and downregulated differentially expression genes (DEGs) compared to the nonirradiated group was large at 6 and 12 h after the irradiation. From the functional analysis results of DEGs, Biological Process (BP) based Gene Ontology (GO), BP ‘the defense response’ is considered to be an important process with DAVID. Additionally, the results of PPI analysis of DEGs involved in the defense response with STRING, we found that the upregulated DEGs such as CXCL8 and NFKB1, and the downregulated DEGs such as NFKBIA and STAT1 were correlated with multiple genes. We estimate that these genes are key genes on the defense response after LLLT.

Effects of Low-Level Er:YAG Laser Irradiation on Proliferation and Calcification of Primary Osteoblast-Like Cells Isolated From Rat Calvaria

Several reports have shown that the photo-bio-modulation of cells by various lasers has favorable biological effects. However, the effects of low-level Er:YAG laser irradiation on osteoblasts remain unclear. The purpose of this study was to evaluate the effects of low-level Er:YAG laser irradiation on proliferation and osteogenic differentiation of primary osteoblast-like cells isolated from the calvariae of 3-5-day-old Wistar rats. Cells were irradiated by Er:YAG laser at energy fluences of 2.2, 3.3, and 4.3 J/cm2, respectively. After irradiation, cell surface temperatures were measured and cell proliferation was evaluated by flow cytometry and CCK-8. Calcification was evaluated by measuring areas of Alizarin red S staining after 7, 14, and 21 days culture in osteoinductive medium. Gene expression in non-irradiated and laser-irradiated cells was evaluated by qPCR at 3, 6, and 12 h, as well as 1, 3, 7, and 14 days after irradiation. Microarray analysis was performed to comprehensively evaluate the gene expression of non-irradiated and irradiated cells at 3.3 J/cm2 at 6 h after irradiation. No pronounced increase of cell surface temperature was induced by irradiation. Irradiation did not affect osteoblast-like cell proliferation. Osteoblast-like cell calcification was significantly increased 7 days after Er:YAG laser irradiation at 3.3 J/cm2. Bglap expression was significantly increased in cells irradiated at 3.3 J/cm2 6 h post-irradiation. Microarray analysis showed that irradiation at 3.3 J/cm2 caused an upregulation of inflammation-related genes and downregulation of Wisp2. Gene set enrichment analysis also clarified enrichment of inflammation-related and Notch signaling gene sets. In conclusion, low-level Er:YAG laser irradiation at 3.3 J/cm2 enhanced calcification of primary osteoblast-like cells via enhanced Bglap expression and enriched Notch signaling.

Combined Nd:YAG and Er:YAG lasers for real-time closed-loop tissue-specific laser osteotomy

A novel real-time and non-destructive method for differentiating soft from hard tissue in laser osteotomy has been introduced and tested in a closed-loop fashion. Two laser beams were combined: a low energy frequency-doubled nanosecond Nd:YAG for detecting the type of tissue, and a high energy microsecond Er:YAG for ablating bone. The working principle is based on adjusting the energy of the Nd:YAG laser until it is low enough to create a microplasma in the hard tissue only (different energies are required to create plasma in different tissue types). Analyzing the light emitted from the generated microplasma enables real-time feedback to a shutter that prevents the Er:YAG laser from ablating the soft tissue.

Thermal Assessment of Ex Vivo Laser Ablation of Cortical Bone

As a potential osteotomy tool, laser ablation is expected to provide rapid machining of bone, while generating minimal thermal damage (carbonization) and physical attributes within the machined region conducive to healing. As these characteristics vary with laser parameters and modes of laser operation, the clinical trials and in vivo studies render it difficult to explore these aspects for optimization of the laser machining parameters. In light of this, the current work explores various thermal and microstructural aspects of laser-ablated cortical bone in ex vivo study to understand the fundamentals of laser-bone interaction using computational modeling. The study employs the Yb-fiber Nd:YAG laser (λ = 1064 nm) in the continuous wave mode to machine the femur section of bovine bone by a three-dimensional machining approach. The examination involved thermal analysis using differential scanning calorimetry and thermogravimetry, phase analysis using X-ray diffractometry, qualitative analysis using X-ray photoelectron spectroscopy, and microstructural and semiquantitative analysis using scanning electron microscopy equipped with energy-dispersive spectrometry. The mechanism of efficient bone ablation using the Nd:YAG laser was evaluated using the computational thermokinetics outcome. The use of high laser fluence (10.61 J/mm²) was observed to be efficient to reduce the residual amorphous carbon in the heat-affected zone while achieving removal of the desired volume of the bone material at a rapid rate. Minimal thermal effects were predicted through computational simulation and were validated with the experimental outcome. In addition, this work reveals the in situ formation of a scaffold-like structure in the laser-machined region which can be conducive during healing.

Evolution of surface morphology of Er:YAG laser-machined human bone

The extensive research on the laser machining of the bone has been, so far, restricted to drilling and cutting that is one- and two-dimensional machining, respectively. In addition, the surface morphology of the laser machined region has rarely been explored in detail. In view of this, the current work employed three-dimensional laser machining of human bone and reports the distinct surface morphology produced within a laser machined region of human bone. Three-dimensional laser machining was carried out using multiple partially overlapped pulses and laser tracks with a separation of 0.3 mm between the centers of consecutive laser tracks to remove a bulk volume of the bone. In this study, a diode-pumped pulse Er:YAG laser (λ = 2940 nm) was employed with continuously sprayed chilled water at the irradiation site. The resulting surface morphology evolved within the laser-machined region of the bone was evaluated using scanning electron microscopy, energy dispersive spectroscopy, and X-ray micro-computed tomography. The distinct surface morphology involved cellular/channeled scaffold structure characterized by interconnected pores surrounded by solid ridges, produced within a laser machined region of human structural bone. Underlying physical phenomena responsible for evolution of such morphology have been proposed and explained with the help of a thermokinetic model.