Mid-infrared erbium:YAG laser ablation of bone: the effect of laser osteotomy on bone healing

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.

Bone Healing Evaluation Following Different Osteotomic Techniques in Animal Models: A Suitable Method for Clinical Insights

Osteotomy is a common step in oncological, reconstructive, and trauma surgery. Drilling and elevated temperature during osteotomy produce thermal osteonecrosis. Heat and associated mechanical damage during osteotomy can impair bone healing, with consequent failure of fracture fixation or dental implants. Several ex vivo studies on animal bone were recently focused on heating production during osteotomy with conventional drill and piezoelectric devices, particularly in endosseous dental implant sites. The current literature on bone drilling and osteotomic surface analysis is here reviewed and the dynamics of bone healing after osteotomy with traditional and piezoelectric devices are discussed. Moreover, the methodologies involved in the experimental osteotomy and clinical studies are compared, focusing on ex vivo and in vivo findings.

Comparing the Bone Healing After Cold Ablation Robot-Guided Er:YAG Laser Osteotomy and Piezoelectric Osteotomy-A Pilot Study in a Minipig Mandible

BACKGROUND AND OBJECTIVE

To take major advantage of erbium-doped yttrium aluminium garnet (Er:YAG) lasers in osteotomy-like freedom of cutting geometries and high accuracy-the integration and miniaturization of the robot, laser, and navigation technology was tried and applied to minipigs. The investigators hypothesized laser osteotomy would render acceptable bone healing based on the intraoperative findings and postoperative cut surface analysis.

STUDY DESIGN/MATERIALS AND METHODS

We designed and implemented a comparative bone-cutting surgery in the minipig mandible with a cold ablation robot-guided Er:YAG laser osteotome (CARLO) and a piezoelectric (PZE) osteotome. The sample was composed of different patterns of defects in the mandibles of six grown-up female Goettingen minipigs. The predictor variable was Er:YAG osteotomy and PZE osteotomy. The outcome variable was the cut surface characteristics and bone healing at 4 and 8 weeks postoperatively. Descriptive and qualitative comparison was executed.

RESULTS

The sample was composed of four kinds of bone defects on both sides of the mandibles of six minipigs. We observed more bleeding during the operation, open-cut surfaces, and a faster healing pattern with the laser osteotomy. There was a possible association between the intraoperative findings, postoperative cut surface analysis, and the bone healing pattern.

CONCLUSIONS

The results of this study suggest that characteristic open-cut surfaces could explain favorable bone healing after laser osteotomy. Future studies will focus on the quantification of the early healing characteristics after laser osteotomy, its diverse application, and the safety feature. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Laser surgery in management of medication-related osteonecrosis of the jaws: a meta-analysis

PURPOSE

The aim of this study was to perform a systematic review and meta-analysis to evaluate the efficacy of laser therapy on medication-related osteonecrosis of the jaw (MRONJ) treatment.

METHODS

This study followed PRISMA standards, and an electronic search was performed on the PubMed/MEDLINE, Scopus, and Cochrane databases. Eighty-nine articles were found. After reading the manuscripts, 15 articles remained for the review. Three of them were selected for meta-analysis.

RESULTS

Female gender was predominant (72.5%), and mean age was 66.5 years. Follow-up varied between 3 and 80 months, and the most used bisphosphonate was zoledronic acid (71.6%). Stage II of MRONJ was the most prevalent (68.9%), and the mandible was the most affected site (64.5%). Qualitative data showed that treatment with laser surgery (Er:YAG) was most effective regarding complete healing of the lesion (90%) compared with other treatments. Meta-analysis data showed that low-level laser therapy (LLLT) was more effective than medical treatment (P = 0.006), and surgical treatment was more effective than LLLT (P = 0.008).

CONCLUSION

Laser surgery was significantly superior to LLLT (p < 0.00001). Therefore, laser surgical therapy seems to be a great management strategy for MRONJ treatment from stage II. LLLT was shown to improve conservative management in earlier MRONJ stages.

Optimization of laser osteotomy at 1064 nm using a graphite topical absorber and a nitrogen assist gas jet

Laser ablation of bone for the purposes of osteotomy is not as well understood as ablation of homogeneous, non-biological materials such as metals and plastics. Ignition times and etch rate can vary during ablation of cortical bone. In this study, we propose the use of two techniques to optimize bone ablation at 1064nm using a coaxial nitrogen jet as an assist gas and topical application of graphite as a highly absorbing chromophore. We show a two order of magnitude reduction in mean time to ignition and variance by using the graphite topical chromophore. We also show that an increase in volumetric flow rate of the assist gas jet does show an initial increase in etch rate, but increased pressure beyond a certain point shows decreased return. This study also demonstrates a 2 ^nd order relationship between exposure time, volumetric flow rate of nitrogen, and etch rate of cortical bone. The results of this study can be used to optimize the performance of laser ablation systems for osteotomy. This is a companion study to an earlier one carried out by Wong et al. [Biomedical Opt. Express6, 1 (2015)].

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

The Er:YAG laser is currently used for bone ablation. However, the effect of Er:YAG laser irradiation on bone healing remains unclear. The aim of this study was to investigate bone healing following ablation by laser irradiation as compared with bur drilling. Rat calvarial bone was ablated using Er:YAG laser or bur with water coolant. Er:YAG laser effectively ablated bone without major thermal changes. In vivo micro-computed tomography analysis revealed that laser irradiation showed significantly higher bone repair ratios than bur drilling. Scanning electron microscope analysis showed more fibrin deposition on laser-ablated bone surfaces. Microarray analysis followed by gene set enrichment analysis revealed that IL6/JAK/STAT3 signaling and inflammatory response gene sets were enriched in bur-drilled bone at 6 hours, whereas the E2F targets gene set was enriched in laser-irradiated bone. Additionally, Hspa1a and Dmp1 expressions were increased and Sost expression was decreased in laser-irradiated bone compared with bur-drilled bone. In granulation tissue formed after laser ablation, Alpl and Gblap expressions increased compared to bur-drilled site. Immunohistochemistry showed that osteocalcin-positive area was increased in the laser-ablated site. These results suggest that Er:YAG laser might accelerate early new bone formation with advantageous surface changes and cellular responses for wound healing, compared with bur-drilling.

Effectiveness of platelet-rich fibrin matrix treated with silver nanoparticles in fracture healing in rabbit model

Aim:

The current study was conducted to evaluate the effect of platelet-rich fibrin matrix (PRFM) treated with silver nanoparticles (AgNPs) on enhancing the healing of the experimentally induced bone gap in a rabbit model.

Materials and Methods:

Twenty healthy male local rabbits aged between 6 and 8 months, their weights between 1.5 and 2 kg were used in this study and divided randomly into four equal groups, under general anesthesia (1 cm), bone gap was induced in the tibia bone to create a critical bone defect and leave it without any treatment in the first group (control group). While in the second group the bone gap was filled with PRFM; in the third group, the gap was filled with 0.3 ml AgNPs; and in the fourth group, the gap was filled with PRFM treated with AgNPs.

Results:

There was no infection at the operation site in all experimental animals, and the radiograph images showed periosteal and endosteal reaction; the gaps were bridged faster in the fourth group as compared with the other groups. The histological examination showed lamellar bone with haversian canal completely filled the fracture gap and contact with old bone in the fourth group as compared to other groups.

Conclusion:

Using a combination of PRFM and single nucleotide polymorphisms together gave better acceleration in the bone healing process than using each one of them separately.

Periodontal and peri-implant wound healing following laser therapy

Laser irradiation has numerous favorable characteristics, such as ablation or vaporization, hemostasis, biostimulation (photobiomodulation) and microbial inhibition and destruction, which induce various beneficial therapeutic effects and biological responses. Therefore, the use of lasers is considered effective and suitable for treating a variety of inflammatory and infectious oral conditions. The CO2 , neodymium-doped yttrium-aluminium-garnet (Nd:YAG) and diode lasers have mainly been used for periodontal soft-tissue management. With development of the erbium-doped yttrium-aluminium-garnet (Er:YAG) and erbium, chromium-doped yttrium-scandium-gallium-garnet (Er,Cr:YSGG) lasers, which can be applied not only on soft tissues but also on dental hard tissues, the application of lasers dramatically expanded from periodontal soft-tissue management to hard-tissue treatment. Currently, various periodontal tissues (such as gingiva, tooth roots and bone tissue), as well as titanium implant surfaces, can be treated with lasers, and a variety of dental laser systems are being employed for the management of periodontal and peri-implant diseases. In periodontics, mechanical therapy has conventionally been the mainstream of treatment; however, complete bacterial eradication and/or optimal wound healing may not be necessarily achieved with conventional mechanical therapy alone. Consequently, in addition to chemotherapy consisting of antibiotics and anti-inflammatory agents, phototherapy using lasers and light-emitting diodes has been gradually integrated with mechanical therapy to enhance subsequent wound healing by achieving thorough debridement, decontamination and tissue stimulation. With increasing evidence of benefits, therapies with low- and high-level lasers play an important role in wound healing/tissue regeneration in the treatment of periodontal and peri-implant diseases. This article discusses the outcomes of laser therapy in soft-tissue management, periodontal nonsurgical and surgical treatment, osseous surgery and peri-implant treatment, focusing on postoperative wound healing of periodontal and peri-implant tissues, based on scientific evidence from currently available basic and clinical studies, as well as on case reports.

Regulating Mid-infrared to Visible Fluorescence in Monodispersed Er3+-doped La2O2S (La2O2SO4) Nanocrystals by Phase Modulation

Rare earth doped mid-infrared (MIR) fluorescent sources have been widely investigated due to their various potential applications in the fields of communication, chemical detecting, medical surgery and so forth. However, with emission wavelength extended to MIR, multiphonon relaxation process that strongly quenched the MIR emission is one of the greatest challenges for such practical applications. In our design, we have described a controllable gas-aided annealing strategy to modulate the phase, crystal size, morphology and fluorescent performance of a material simultaneously. Uniform and monodispersed Er³⁺-doped La₂O₂S and La₂O₂SO₄ nanocrystals with a similar lattice structure, crystallinity, diameter and morphology have been introduced to investigate the impact of multiphonon relaxation on luminescence performance. Detailed spectroscopic evolutions in the region of MIR, near-infrared (NIR), visible upconversion (UC) and their corresponding decay times provide insight investigation into the fluorescent mechanism caused by multiphonon relaxation. A possible energy transfer model has also been established. Our results present direct observation and mechanistic investigation of fluorescent evolution in multiphonon relaxation process, which is conductive to design MIR fluorescent materials in the future. To the best of our knowledge, it is the first investigation on MIR fluorescent performance of La₂O₂S nanocrystals, which may find various applications in many photoelectronic fields.

Technology of Lasers and Their Applications in Oral Surgery: Literature Review

The word “Laser” is an acronym for “Light Amplification by Stimulated Emission of Radiation”. Recent advances in laser technology have brought a kind of revolution in dentistry. The purpose of this article is to provide an overview of clinical application of lasers in oral medicine and especially in oral surgery, including their advantages, disadvantages and safety.

Morphological and ultrastructural comparative analysis of bone tissue after Er:YAG laser and surgical drill osteotomy

OBJECTIVE

The purpose of this study was to analyze morphological, chemical, and crystallographic changes of bone tissue after osteotomy performed with an erbium:yttrium-aluminium-garnet (Er:YAG) laser and a low speed pilot drill.

MATERIALS AND METHODS

Bone blocks were prepared from porcine ribs, and on each block, two tunnel preparations were performed using the Er:YAG laser (pulse energy: 1000 mJ, pulse duration: 300 μs, pulse repetition rate: 20 Hz) or the low-speed surgical pilot drill. The morphological changes of the cortical and the spongious surface of the tunnel preparations were analyzed under the field emission scanning electron microscopy (FE-SEM) at low and high resolution. The distribution and the level of chemical elements in the treated surfaces were evaluated by qualitative and semiquantitative energy dispersive x-ray analysis (SEM-EDX). Diffraction x-ray analysis was used to detect any differences and thermally induced modifications of hydroxyapatite crystals.

RESULTS

FE-SEM revealed sharp edges of the Er:YAG preparations, with empty intertrabecular spaces and no signs of carbonization. In the drill group, the surface of the preparations was smooth, completely covered with smear layer and microcracks, and with hairy-like irregularities on the edges. SEM-EDX analysis did not reveal any differences in the number of specific chemical elements between the laser and the drill group. There were no thermally induced modifications of hydroxyapatite crystal structure in the bone tissue in either group.

CONCLUSIONS

The Er:YAG laser ablation did not cause any chemical or crystallographic changes of the bone tissue. Compared with the drill, Er:YAG laser created well-defined edges of the preparations, and cortical bone had no smear layer.

Femtosecond laser bone ablation with a high repetition rate fiber laser source

Femtosecond laser pulses can be used to perform very precise cutting of material, including biological samples from subcellular organelles to large areas of bone, through plasma-mediated ablation. The use of a kilohertz regenerative amplifier is usually needed to obtain the pulse energy required for ablation. This work investigates a 5 megahertz compact fiber laser for near-video rate imaging and ablation in bone. After optimization of ablation efficiency and reduction in autofluorescence, the system is demonstrated for the in vivo study of bone regeneration. Image-guided creation of a bone defect and longitudinal evaluation of cellular injury response in the defect provides insight into the bone regeneration process.

Bone ablation without thermal or acoustic mechanical injury via a novel picosecond infrared laser (PIRL)

BACKGROUND AND OBJECTIVE

A precise means to cut bone without significant thermal or mechanical injury has thus far remained elusive. A novel non-ionizing ultrafast pulsed picosecond infrared laser (PIRL) may provide the solution. Tissue ablation with the PIRL occurs via a photothermal process with thermal and stress confinement, resulting in efficient material ejection greatly enhanced through front surface spallation photomechanical effects. By comparison, the Er:YAG laser (EYL) ablates via photothermal and cavitation-induced photomechanical effects without thermal or acoustic confinement, leading to significant collateral tissue injury. This study compared PIRL and EYL bone ablation by infrared thermography (IRT), environmental scanning electron microscopy (ESEM), and histology.

STUDY DESIGN

Prospective, comparative, ex vivo animal model.

SETTING

Optics laboratory.

SUBJECTS AND METHODS

Ten circular area defects were ablated in ex vivo chicken humeral cortex using PIRL and EYL at similar average power (~70 mW) under IRT. Following fixation, ESEM and undecalcified light microscopy images were obtained and examined for signs of cellular injury.

RESULTS

Peak rise in surface temperature was negligible and lower for PIRL (1.56 °C; 95% CI, 0.762-2.366) compared to EYL ablation (12.99 °C; 95% CI, 12.189-13.792) (P < .001). ESEM and light microscopy demonstrated preserved cortical microstructure following PIRL ablation in contrast to diffuse thermal injury seen with EYL ablation. Microfractures were not observed.

CONCLUSION

Ablation of cortical bone using the PIRL generates negligible and significantly less heat than EYL ablation while preserving cortical microstructure. This novel laser has great potential in advancing surgical techniques where precision osseous manipulation is required.

The dawn of computer-assisted robotic osteotomy with ytterbium-doped fiber laser

Currently, laser radiation is used routinely in medical applications. For infrared lasers, bone ablation and the healing process have been reported, but no laser systems are established and applied in clinical bone surgery. Furthermore, industrial laser applications utilize computer and robot assistance; medical laser radiations are still mostly conducted manually nowadays. The purpose of this study was to compare the histological appearance of bone ablation and healing response in rabbit radial bone osteotomy created by surgical saw and ytterbium-doped fiber laser controlled by a computer with use of nitrogen surface cooling spray. An Ytterbium (Yb)-doped fiber laser at a wavelength of 1,070 nm was guided by a computer-aided robotic system, with a spot size of 100 μm at a distance of approximately 80 mm from the surface. The output power of the laser was 60 W at the scanning speed of 20 mm/s scan using continuous wave system with nitrogen spray level 0.5 MPa (energy density, 3.8 × 10(4) W/cm(2)). Rabbits radial bone osteotomy was performed by an Yb-doped fiber laser and a surgical saw. Additionally, histological analyses of the osteotomy site were performed on day 0 and day 21. Yb-doped fiber laser osteotomy revealed a remarkable cutting efficiency. There were little signs of tissue damage to the muscle. Lased specimens have shown no delayed healing compared with the saw osteotomies. Computer-assisted robotic osteotomy with Yb-doped fiber laser was able to perform. In rabbit model, laser-induced osteotomy defects, compared to those by surgical saw, exhibited no delayed healing response.

Comparison of Er:YAG laser and surgical drill for osteotomy in oral surgery: an experimental study

PURPOSE

High-energy lasers have been proposed as an alternative to the conventional surgical drill in oral and maxillofacial surgery. The aims of this study were to compare thermal changes of the bone surface, procedure time, and volume of the removed bone after drilling with an erbium (Er):yttrium-aluminum-garnet (YAG) laser versus a low-speed surgical drill. The bone sections were observed under light microscopy and examined histologically.

MATERIAL AND METHODS

Thirty bone blocks were prepared from porcine ribs. On each block 2 holes (tunnel preparations) were performed using a low-speed, 1.0-mm-wide, surgical pilot drill and an Er:YAG laser (pulse energy, 1,000 mJ; pulse duration, 300 μs; frequency, 20 Hz). The temperature induced by the preparation techniques was measured using an infrared camera. The removed bone volume was calculated by a modified mathematical algorithm. The time required for the preparation was measured with a digital stopwatch and a time-measurement instrument integrated within the computer program. The cortical and spongiose surfaces of the specimens were examined microscopically and histologically under a light microscope with a high-resolution camera.

RESULTS

The Er:YAG laser removed significantly more bone tissue than the drill (P < .01) in a significantly shorter time (P < .01). The temperature was statistically lower during the laser preparation (P < .01). Cavities prepared with the laser were regular with clear sharp edges and knifelike cuts. In the drill group, the preparations exhibited irregular edges full of bone fragments and fiberlike debris. Histologic examination of the laser sides showed a 30-μm-thick altered sublayer. The tissue in the drill group was covered with a smear layer without any alterations.

CONCLUSIONS

The Er:YAG laser produced preparations with regular and sharp edges, without bone fragments and debris, in a shorter time, and with less generated heat. Thermal alterations in the treated surface were minimal.

Femtosecond plasma mediated laser ablation has advantages over mechanical osteotomy of cranial bone

BACKGROUND

Although mechanical osteotomies are frequently made on the craniofacial skeleton, collateral thermal, and mechanical trauma to adjacent bone tissue causes cell death and may delay healing. The present study evaluated the use of plasma-mediated laser ablation using a femtosecond laser to circumvent thermal damage and improve bone regeneration.

METHODS

Critical-size circular calvarial defects were created with a trephine drill bit or with a Ti:Sapphire femtosecond pulsed laser. Healing was followed using micro-CT scans for 8 weeks. Calvaria were also harvested at various time points for histological analysis. Finally, scanning electron microscopy was used to analyze the microstructure of bone tissue treated with the Ti:Sapphire laser, and compared to that treated with the trephine bur.

RESULTS

Laser-created defects healed significantly faster than those created mechanically at 2, 4, and 6 weeks post-surgery. However, at 8 weeks post-surgery, there was no significant difference. In the drill osteotomy treatment group, empty osteocyte lacunae were seen to extend 699 ± 27 µm away from the edge of the defect. In marked contrast, empty osteocyte lacunae were seen to extend only 182 ± 22 µm away from the edge of the laser-created craters. Significantly less ossification and formation of irregular woven bone was noted on histological analysis for drill defects.

CONCLUSIONS

We demonstrate accelerated bone healing after femtosecond laser ablation in a calvarial defect model compared to traditional mechanical drilling techniques. Improved rates of early regeneration make plasma-mediated ablation of the craniofacial skeleton advantageous for applications to osteotomy.

Material attrition and bone micromorphology after conventional and ultrasonic implant site preparation

OBJECTIVES

Little is known about the recently introduced ultrasonic implant site preparation. The purpose of this study was to compare material attrition and micromorphological changes after ultrasonic and conventional implant site preparations.

MATERIAL AND METHODS

Implant site preparations were performed on fresh bovine ribs using one conventional (Straumann, Freiburg, Germany) and two ultrasonic (Piezosurgery; Mectron Medical Technology, Carasco, Italy and Variosurg; NSK, Tochigi, Japan) systems with sufficient saline irrigation. Sections were examined by environmental scanning electron microscopy (ESEM). Energy-dispersive X-ray spectroscopy (EDX) was performed to evaluate the metal attrition within the bone and the irrigation fluid.

RESULTS ESEM

After conventional osteotomy, partially destroyed trabecular structures of the cancellous bone that were loaded with debris were observed, whereas after ultrasonic implant site preparations, the anatomic structures were preserved. EDX: None of the implant site preparation methods resulted in metal deposits in the adjacent bone structures. However, within the irrigation liquid, there was significantly higher metal attrition with ultrasonic osteotomy (P < 0.0001 and P < 0.0001 for Mectron and NSK, respectively). Whereas for Straumann system used, 15.5% of the SEM/EDX findings were drill-origin metals, this percentage increased to 37.3% and 37.9% with the application of Mectron and NSK, respectively.

CONCLUSIONS

Ultrasonic implant site preparation is associated with the preservation of bone microarchitecture and with the increased attrition of metal particles. Therefore, copious irrigation seems to be even more essential for ultrasonic implant site preparation than for the conventional method.

Platelet Derived Growth Factor Secretion and Bone Healing After Er:YAG Laser Bone Irradiation

Er:YAG laser irradiation has been reported to enhance wound healing. However, no studies have evaluated the synthesis of growth factors after laser irradiation. The present study investigated the effects of laser irradiation on the amount of secretion of platelet derived growth factor (PDGF) in the wound, clarifying the effects of the Er:YAG laser on the bone healing. Osteotomies were prepared in the tibiae of 28 rats using an Er:YAG laser (test group). Maximum power of 8 watts, energy per pulse of 700 mJ, and frequency up to 50 Hz were used. The laser was used with external water irrigation, a spot size of 2 mm, energy per pulse of 500 to 1000 mJ/pulse, and energy density of 32 J/cm2. Twenty eight additional rats served as a control group and their osteotomies were prepared with a drill 1.3 mm in diameter at 1000 rpm, with simultaneous saline irrigation. Two rats from the tested group and 2 from the control group were sacrificed on each day following surgery (1–14 days), and the tissue specimens were prepared for histologic evaluation. Immunohistochemical staining with anti-PDGF was performed after histologic examination. The difference between the PDGF staining intensities of the 2 treatment groups was analyzed using a multivariate logistic regression test. A significant rise in PDGF staining occurred in both groups 2–3 days following surgery. However, while high PDGF counts remained for the 2-week experimental period in the laser group, PDGF levels in the control group returned to baseline levels 8 days post surgery. The 2 groups (laser and control) were found to be different throughout the experiment, and the rat type was found to be a significant predictor (P  =  .000011). The present study demonstrated that Er:YAG laser irradiation seems to stimulate the secretion of PDGF in osteotomy sites in a rat model. It is possible that the high levels of PDGF are part of the mechanism that Er:YAG irradiation enhances and improves the healing of osteotomy sites.

Bone healing after bur and Er:YAG laser ostectomies

PURPOSE

Ostectomies, performed by different methods, are often necessary in oral and maxillofacial surgery. Rotatory and reciprocating devices are most frequently used but have disadvantages, such as noise, vibration, and the potential for inducing thermal damage. Laser systems are interesting alternatives to these procedures. We analyzed bone healing in a rat model after mandibular ostectomy with a surgical bur or noncontact erbium:yttrium-aluminum-garnet laser using different energy levels.

MATERIALS AND METHODS

Four groups of 5 rats each underwent ostectomy of the bone cortical of the mandibular body, with irrigation, using a surgical bur or erbium:yttrium-aluminum-garnet laser with different energy parameters. A metal plate was used for morphologic standardization of the cavities. The samples collected after 7, 14, 45, 60, and 90 days were analyzed by optical microscopy.

RESULTS

The ostectomies performed with surgical burs resulted in bone healing from the cortical endosteum and remaining trabecular bone. The cortical endosteum was repaired after 45 days, followed by bone remodeling. After laser irradiation, healing involved bone neoformation from the external cortical surface and endosteum. Surface regions with thermal damage were observed after laser treatment in the 3 conditions used up to day 60, followed by bone remodeling.

CONCLUSIONS

Laser ostectomies resulted in a thin layer of thermal damage. Bone healing was faster when surgical burs were used, with similar results reached after 90 days.

Efeitos da aplicação do laser de baixa potência na regeneração do nervo isquiático de ratos

Os nervos periféricos sofrem constantes lesões de origem traumática, o que resulta em perdas funcionais. A terapia com laser de baixa potência vem sendo utilizada para minimizar os efeitos maléficos da inflamação e acelerar o processo de cicatrização dos tecidos lesados. Este estudo teve como objetivo verificar o efeito da irradiação do laser 830 nm no comportamento do nervo isquiático de ratos submetido a esmagamento. Foram utilizados 20 ratos, todos tendo tido o nervo isquiático esmagado, divididos em 4 grupos (n=5): P7 e P14, tratamento placebo por 7 e 14 dias; L7 e L14, tratamento por laser (dosagem de 4 J/cm²) por 7 e 14 dias. Os animais dos grupos P7 e P14 foram submetidos aos mesmos procedimentos, mas com o laser desligado. Os parâmetros analisados foram presença de infiltrado inflamatório e fibroblastos, destruição da bainha de mielina e degeneração axonal. Na análise estatística foi observada diferença estatística com relação a três parâmetros: os animais do grupo L14 apresentaram maior quantidade de fibroblastos (p=0,0001), menor degeneração da bainha de mielina (p=0,007) e menor quantidade de infiltrado inflamatório (p=0,001). A aplicação do laser de baixa potência contribuiu para a redução do processo inflamatório decorrente da lesão do nervo isquiático de ratos.

Long-term histologic analysis of bone tissue alteration and healing following Er:YAG laser irradiation compared to electrosurgery

BACKGROUND

The erbium-doped:yttrium, aluminum, and garnet (Er:YAG) laser is reportedly useful for periodontal therapy. However, the potential thermal damage that Er:YAG laser irradiation can produce on bone tissue has not been fully clarified. The purpose of this study was to histologically examine the effects of the Er:YAG laser on bone tissue and subsequent wound healing compared to electrosurgery in a long-term study.

METHODS

Calvarial bone from 30 rats was exposed to contact and non-contact Er:YAG laser irradiation (115 mJ/pulse, 10 Hz) without water coolant, or electrode contact. The treated surfaces were analyzed by scanning electron microscopy (SEM), and the healing process was histologically observed until 12 months post-surgery.

RESULTS

Contact irradiation resulted in substantial bone ablation, whereas non-contact irradiation produced slight tissue removal. Histologic and SEM analyses of the lased surface showed no severe thermal damage, except for the production of a superficially affected layer with a microstructured surface. The layer did not inhibit new bone formation, and the ablated defect was repaired uneventfully. Although the thickness of the layer gradually decreased, it generally remained in the cortical bone through the observation period. Electrosurgery produced a large area of thermal necrosis without ablation, and the damaged area was not replaced with new bone.

CONCLUSIONS

Unlike electrosurgery, Er:YAG laser irradiation without water coolant easily ablated bone tissue, and thermal alteration in the treated surface was minimal. The superficially affected layer did not interfere with the ensuing bone healing, resulting in favorable repair of the defect.

Osteonecrosis of the jaws caused by bisphosphonates: evaluation of a new therapeutic approach using the Er:YAG laser

A series of 49 patients diagnosed with osteonecrosis and all treated with latest-generation bisphosphonates was reviewed retrospectively to evaluate the use of erbium-doped: yttrium, aluminum, and garnet laser (Er:YAG) in terms of clinical outcome, and examine current trends from the clinical-therapeutic standpoint. Pathology reports on specimens submitted over the previous 7 years from either the mandible or the maxilla were reviewed; 49 patients were identified as having osteonecrosis of the jaws. For each of these cases, the medical history and profile were evaluated; 19 were treated with conservative therapy, 20 with radical surgery, and 10 with Er:YAG laser (2,940 nm). Of the 20 patients treated surgically (bone baquette, curettage, sequestrectomy of the necrotic bone), some required re-treatment, which resulted in bone fracturing. None of the patients were treated successfully. The 19 cases treated conservatively produced an improvement in symptoms, but not remission of the lesions. Of the ten patients treated with Er:YAG laser, six achieved total remission of signs and symptoms, four an improvement, and re-treatment was required in one case. Our present approach is to recommend intensive prophylactic care before the administration of bisphosphonates, and great caution is advised even in simple maneuvers like curettage, because this may exacerbate the avascular process. The use of Er:YAG laser appears to be promising (within the limits of our experience). It can be concluded that at 1 year of laser surgery, the treatment led to significant improvements in clinical parameters, and may represent a valid alternative, although studies on a larger scale are needed.

Promotion of regenerative processes in injured peripheral nerve induced by low-level laser therapy

OBJECTIVE

This study aimed to assess in vitro the influence of low-level laser therapy (LLLT) on the regenerative processes of a peripheral nerve after trauma.

BACKGROUND DATA

In peripheral nerve injury initiated after severing due to accident or by a surgeon during operation, photomodulation by light in the red to near-infrared range (530-1000 nm) using low-energy lasers has been shown to accelerate nerve regeneration.

METHOD

Twenty-four New Zealand adult male rabbits were randomly assigned to two equal groups (control and laser-treated). General anesthesia was administered intramuscularly, and exploration of the peroneal nerve was done in the lateral aspect of the left leg. Complete section of the nerve was performed, which was followed by suturing of the neural sheath (epineurium). Irradiation was carried out directly after the operation and for 10 consecutive days. The laser used was diode with wavelength of 901 nm (impulsive) and power of 10 mW; it was a square-shaped window type (16 cm(2)), and its energy was applied by direct contact of the instrument's window to the site of the operation. Three rabbits from each group were sacrificed at the end of weeks 2, 4, 6, and 8, and specimens were collected from the site of nerve suturing and sent for histopathological examination.

RESULTS

Two important factors were examined via histopathology: diameter of the nerve fibers and individual internodal length. Compared to the control group, significant variations in regeneration were observed, including thicker nerve fibers, more regular myelin layers, clearer nodes of Ranvier with absence of short nodes in the treated group. Variations between the two groups for diameter were significant for the 2(nd) week (p < 0.05), highly significant for the 4(th) and 6(th) weeks, respectively (p < 0.01), and very highly significant for the 8(th) week (p < 0.001). Variations between the two groups for internodal length were highly significant for the 2(nd) and 4(th) weeks (p < 0.01), and very highly significant for the 6(th) and 8(th) weeks (p < 0.001).

CONCLUSION

This experiment affirms the beneficial effect of LLLT on nerve regeneration, since LLLT produced a significant amount of structural and cellular change. The results of the present study suggest that laser therapy may be a viable approach for nerve regeneration, which may be of clinical relevance in scheduled surgery or microsurgery.

Accelerated bone repair after plasma laser corticotomies

OBJECTIVE

To reveal, on a cellular and molecular level, how skeletal regeneration of a corticotomy is enhanced when using laser-plasma mediated ablation compared with conventional mechanical tissue removal.

SUMMARY BACKGROUND DATA

Osteotomies are well-known for their most detrimental side effect: thermal damage. This thermal and mechanical trauma to adjacent bone tissue can result in the untoward consequences of cell death and eventually in a delay in healing.

METHODS

Murine tibial corticotomies were performed using a conventional saw and a Ti:Sapphire plasma-generated laser that removes tissue with minimal thermal damage. Our analyses began 24 hours after injury and proceeded to postsurgical day 6. We investigated aspects of wound repair ranging from vascularization, inflammation, cell proliferation, differentiation, and bone remodeling.

RESULTS

Histology of mouse corticotomy sites uncovered a significant difference in the onset of bone healing; whereas laser corticotomies showed abundant bone matrix deposition at postsurgical day 6, saw corticotomies only exhibited undifferentiated tissue. Our analyses uncovered that cutting bone with a saw caused denaturation of the collagen matrix due to thermal effects. This denatured collagen represented an unfavorable scaffold for subsequent osteoblast attachment, which in turn impeded deposition of a new bony matrix. The matrix degradation induced a prolonged inflammatory reaction at the cut edge to create a surface favorable for osteochondroprogenitor cell attachment. Laser corticotomies were absent of collagen denaturation, therefore osteochondroprogenitor cell attachment was enabled shortly after surgery.

CONCLUSION

In summary, these data demonstrate that corticotomies performed with Ti:Sapphire lasers are associated with a reduced initial inflammatory response at the injury site leading to accelerated osteochondroprogenitor cell migration, attachment, differentiation, and eventually matrix deposition.

Comparative histological analysis of bone healing of standardized bone defects performed with the Er:YAG laser and steel burs

This study compares the bone repair process after ostectomies performed either with the erbium:yttrium-aluminum-garnet (Er:YAG) laser or with the low-speed bur drilling. Eighteen rats were used for this study. In the control group, the ostectomy was performed with a low-speed bur drilling. In the experimental group, the ostectomy was made with an Er:YAG laser (500 mJ, 10 Hz). At 7 and 14 days after surgery, the experimental group presented earlier bone repair in comparison to the control group. The experimental group presented an altered layer of approximately 24-microm thickness, whereas the control group did not present any altered layer in the margins of the ostectomies. At 21 days, the histological features of the two groups were very similar, although the altered layer could still be seen. The Er:YAG laser successfully promoted the ablation of the bone tissue, but caused some thermal damage at the margins of the ostectomies.

Influence of implant bed preparation using an Er:YAG laser on the osseointegration of titanium implants: a histomorphometrical study in dogs

The aim of the present study was to evaluate the influence of implant bed preparation using an Er:YAG laser on the osseointegration of titanium implants. A total of 24 implant channels were prepared in the lower jaws of four beagle dogs using (i) an Er:YAG laser device (ERL), or (ii) conventional drills (CD) according to a split-mouth design (n=6 implant channels per animal). Three screw-type titanium implants of different manufacturers were randomly inserted in both groups to evaluate submerged healing at 2 and 12 weeks. Width of the peri-implant gap (WPG) and bone-to-implant contact (BIC) were assessed histomorphometrically. There were no identifiable signs of any thermal side effects in both groups. ERL osteotomy frequently resulted in wide peri-implant gaps particularly in the apical area of the implant supporting bone. The following mean scores were assessed (+/-s.d.): WPG (2 weeks): ERL: 0.89+/-0.48 mm; CD: 0.27+/-0.09 mm (P<0.001 respectively); BIC (2 weeks): ERL: 34.5+/-7.76%; CD: 48.5+/-11.08% (P<0.001 respectively); BIC (12 weeks): ERL: 64.1+/-8.97%; CD: 68.94+/-11.23% (P>0.05 respectively). Within the limits of the present study, it was concluded that ERL may represent a promising tool for implant bed preparation.

An Er:YAG laser bone cutting manipulator for precise rotational acetabular osteotomy

Rotational acetabular osteotomy (RAO) has an important advantage in that surgical bony defects are reconstructed with a patients' own tissue. We propose a surgical robot for the RAO using Er:YAG laser irradiating mounted on iliac bone to operate RAO precisely and to reduce recovery and trauma. A water-cooling Er:YAG laser (30 J/cm/sup 2/, l=2.94 mum, 20 Hz, 200 msec) that used optical fiber was operated 4-8 irradiation-overlapping ratio. We kept the distance between the laser and the bone at 0.25 mm using force sensor and spring to maintain effective ablation. Swine scapulae were ablated and performance was evaluated. The manipulator was operated mounting on iliac bone to get a filed position whereby resulting in precise bone cutting. The precision of the manipulator was within 0.3 mm and the efficiency of laser bone ablations per unit time optimized to 0.21 mm/sup 3//secW at the overlapping ratio of the irradiation area was 0.8, meaning a given ablated area was irradiated five times. The troughs showed m charring at this condition and the temperature of the surface was raised to 41.3 degrees C and it lasted only 5 seconds. We are sure that this research will be applied to orthopedics in the near future.

Microtomographic analysis of healing of femtosecond laser bone calvarial wounds compared to mechanical instruments in mice with and without application of BMP-7

BACKGROUND AND OBJECTIVE

This study investigated the healing of femtosecond laser created wounds in an animal model.

STUDY DESIGN

We have assessed the healing of critical size wounds in mice calvaria using three different wounding techniques: carbide bur, diamond end-cutting bur, and ultrafast femtosecond laser, and in the presence or absence of bone morphogenetic protein-7 (BMP). Wound closure was examined using microcomputerized tomography at 3, 6, 9, and 12 weeks.

RESULTS

Results have shown partial closure at up to 12 weeks with all techniques that did not involve the use of BMP, with the least closure noted in the laser groups as suggested by two-dimensional radiographic analysis. Bone volume measurements appeared slightly lower for the laser than for the mechanical groups, however statistically significant differences were seen only at week 6. No significant differences in closure were noted for the different methods in the BMP treated groups.

CONCLUSIONS

Femtosecond laser cutting demonstrated an unsurpassed precision when compared to mechanical instruments. The addition of BMP led to very rapid healing with complete closure seen as early as 3 weeks and overcomes any potential healing delays that may arise from laser tissue cutting.

A comparison of mass removal, thermal injury, and crater morphology of cortical bone ablation using wavelengths 2.79, 2.9, 6.1, and 6.45 µm

BACKGROUND AND OBJECTIVE

Previous investigations have reported evidence of wavelength dependence on cortical bone ablation. This study used mid-infrared laser wavelengths generated by a free electron laser (FEL) and mass removal measurements to further examine the ablation efficiency of a wavelength (2.79 microm) not previously reported and three wavelengths (2.9, 6.1, and 6.45 microm) previously demonstrated by crater morphology alone to be efficient for cortical bone removal.

STUDY DESIGN/MATERIALS AND METHODS

The wavelengths examined were provided by an FEL emitting 4 microseconds macropulses consisting of 1-2 picoseconds duration micropulses delivered at 350 picoseconds intervals. The mass removal measurements were conducted by a microbalance, and the collateral thermal injury and crater morphology of cortical bone were examined by light microscopy following standard histologic processing.

RESULTS

The study demonstrated that the highest mass removal was achieved at lambda = 6.1 microm followed by, in order, lambda = 2.9, 6.45, and 2.79 microm. The zones of thermal injury and crater morphology created in cortical bone at the selected wavelengths were examined at the radiant exposure of 28.3 J/cm2. Ablation using lambda = 6.1 microm provided the largest crater size and the least collateral thermal injury. The greatest amount of collateral thermal injury was produced by lambda = 2.79 microm at both the sides and base of the ablation crater.

CONCLUSIONS

The mass removal of cortical bone produced by FEL ablation at selected mid-IR wavelengths was measured as a function of incident radiant exposure. The ablation efficiency was found to be dependent upon wavelength. The lambda = 2.79 microm did not offer any improvement over the other wavelengths evaluated, suggesting that a potential shift in the dynamic optical properties of water during tissue irradiance with the FEL does not present an advantage to the cutting of cortical bone. The lambda = 6.1 microm provided the highest ablation efficiency with deepest crater and the least amount of collateral thermal injury.

Low-Level Laser Therapy Accelerates Collateral Circulation and Enhances Microcirculation

OBJECTIVE

To evaluate the efficacy of low-level laser therapy (LLLT) on collateral circulation and microcirculation if a blood vessel is occluded.

BACKGROUND DATA

Investigators have attempted prostaglandin and ultrasound therapy to promote improvements in the vascular bed of deprived tissue after an injury, which may lead to occlusion of the blood vessels.

MATERIALS AND METHODS

Thirty-four adult rabbits were used in this study, two of them considered 0-h reading group, while the rest were divided into two equal groups, with 16 rabbits each: control and those treated with LLLT. Each rabbit underwent two surgical operations; the medial aspect of each thigh was slit, the skin incised and the femoral artery exposed and ligated. The site of the operation in the treated group was irradiated directly following the operation and for 3 d after, one session daily for 10 min/session. The laser system used was a gallium-aluminum-arsenide (Ga-Al-As) diode laser with a wavelength of 904 nm and power of 10 mW. Blood samples collected from the femoral artery above the site of the ligation were sent for examination with high-performance liquid chromatography (HPLC) to determine the levels of adenosine, growth hormone (GH) and fibroblast growth factor (FGF). Tissue specimens collected from the site of the operation, consisting of the artery and its surrounding muscle fibers, were sent for histopathological examination to determine the fiber/capillary (F/C) ratio and capillary diameter. Blood samples and tissue specimens were collected at 4, 8, 12, 16, 20, 24, 48 and 72 h postoperatively from the animals of both groups, control and treated.

RESULTS

Rapid increases in the level of adenosine, GH, and FGF occurred. The F/C ratio and capillary diameter peaked at 12-16 h; their levels declined gradually, reaching normal values 72 h after irradiation in the treated group. Numerous collateral blood vessels proliferated the area, with marked increases in the diameters of the original blood vessels.

CONCLUSIONS

The results indicated that LLLT accelerated collateral circulation and enhanced microcirculation and seemed to be unique in the normalization of the functional features of the injured area, which could lead to occlusion of the regional blood vessels.

In vivo study of the healing processes that occur in the jaws of rabbits following perforation by an Er,Cr:YSGG laser

This study investigates the healing process that takes place in the bone and soft tissue of the maxilla and the mandible after perforation by an Er,Cr:YSGG laser device. The jaws of New Zealand white rabbits were irradiated with an Er,Cr:YSGG laser, forming wounds 0.4 mm in diameter. Irradiation parameters were as follows: repetition rate was 20 pulse/s, pulse duration was 140-200 micros, power was 2 W, exposure time was 10 s, energy density was 80 J/cm(2). After sacrifice at 0-56 days post-surgery, gross observations and histological examinations were performed. Effective hemostasis was achieved after Er,Cr:YSGG laser surgery. There was a minimal delay before the healing began. After 56 days all of the bone defects had been completely replaced by new bone. In conclusion, the Er,Cr:YSGG laser allows precise surgical ablation with minimal thermal damage to adjacent tissues in vivo. The overall subsequent healing was favorable. This laser may potentially be used in minor oral surgery.

In vivo animal trials with a scanning CO2 laser osteotome

BACKGROUND AND OBJECTIVES

We report first results of animal trials using an improved laser osteotomy technique. This technique allows effective bone cutting without the usual thermal tissue damage.

STUDY DESIGN/MATERIALS AND METHODS

A comparative in vivo study on mandibles of seven canines was done with a mechanical saw and a CO(2) laser based osteotome with a pulse duration of 80 microseconds. The laser incisions were performed in a multipass mode using a PC-controlled galvanic beam scanner and an assisting water spray.

RESULTS

A complete healing through a whole bony rearrangement of the osteotomy gap with newly build lamellar Haversian bone was observed 22 days after the laser operations under optimal irradiation conditions.

CONCLUSIONS

An effective CO(2) laser osteotomy without aggravating thermal side effects and healing delay is possible using the described irradiation technique. It allows an arbitrary cut geometry and may result in new advantageous bone surgery procedures.

Histological and TEM Examination of Early Stages of Bone Healing after Er:YAG Laser Irradiation

OBJECTIVE

The aim of this study was to analyze the early healing process of bone tissue irradiated by Er:YAG laser and compare it with that treated by mechanical drilling and CO(2) laser.

BACKGROUND DATA

Er:YAG laser has a great potential for cutting hard tissues as it is capable of ablation with less thermal damage.

METHODS

Twenty-four male Wistar rats were used for this study. The calvarial bone of rats was exposed and straight grooves were prepared by Er:YAG laser, mechanical bur and continuous wave CO(2) laser. Four rats each were sacrificed at six time points: 10 min, 6 and 24 h and 3, 7, and 14 days post-surgery. Sections were prepared for light and transmission electron microscopic (TEM) observations.

RESULTS

Compared to mechanical bur and CO(2) groups, the inflammatory cell infiltration adjacent to the irradiated bone surface, fibroblastic reaction, and revascularization were more pronounced in the Er:YAG laser-irradiated tissues. A cell-rich granulation tissue with fibroblasts and osteoblasts was predominant in 7-day specimens of Er:YAG laser group. Histopathological analysis of 14-day specimens in the Er:YAG group also revealed significantly greater new bone formation, compared with the mechanical bur and CO(2) laser groups.

CONCLUSIONS

Initial bone healing following Er:YAG laser irradiation occurred faster than that after mechanical bur and CO(2) laser. Er:YAG laser treatment may be advantageous for wound healing of bone tissue, presumably by providing a favorable surface for cell attachment.

Ultrastructural analysis of bone tissue irradiated by Er:YAG Laser

BACKGROUND AND OBJECTIVES

The use of erbium:yttrium aluminum garnet (Er:YAG) laser has been suggested for bone ablation, however, little is known about the nature of the tissue after irradiation. This study was aimed to analyze the ultrastructure of bone tissue treated with Er:YAG laser, as compared to those treated with CO(2) laser and bur drilling.

STUDY DESIGN/MATERIALS AND METHODS

Parietal bones of Wistar rats were treated and analyzed by light microscopy, transmission electron microscopy (TEM), electron diffraction analysis and energy dispersive X-ray spectroscopy (SEM-EDX).

RESULTS

This study demonstrated that Er:YAG laser irradiation resulted in a very thin changed layer of approximately 30 microm thickness, which consisted of two distinct sub-layers: a superficial, greatly altered layer and a deep, less affected layer.

CONCLUSIONS

The major changes found on bone surface after Er:YAG laser irradiation consisted of micro-cracking, disorganization, and slight recrystallization of the original apatites and reduction of surrounding organic matrix.

Scanning electron microscopy and Fourier transformed infrared spectroscopy analysis of bone removal using Er:YAG and CO2 lasers

BACKGROUND

A thorough analysis of laser-ablated bone tissue is required before applying the technique to osseous surgery. In this study, we examine the morphological features and chemical composition of the bone surface after Er:YAG and CO2 lasers ablation.

METHODS

Six Wistar rats were used. An Er:YAG laser was used for ablation at an output energy of 100 mJ/pulse and a pulse rate of 10 Hz (1 W). Continuous CO2 laser irradiation was performed at an output energy of 1 W. Sites drilled using a conventional micromotor were used as controls. Analysis using scanning electron microscopy (SEM) and Fourier transformed infrared (FTIR) spectroscopy was performed.

RESULTS

Er:YAG laser ablation produced a groove with similar dimensions to that produced by bur drilling, whereas the CO2 laser produced only a charred line with minimal tissue removal. SEM observations revealed that the groove produced by the Er:YAG laser had well-defined edges and a smear layer-free surface with a characteristically rough appearance and with entrapped fibrin-like tissue. The melting and carbonization produced by the CO2 laser were not observed on sites irradiated by the Er:YAG laser. FTIR spectroscopy revealed that the chemical composition of the bone surface after Er:YAG laser ablation was much the same as that following bur drilling. The production of toxic substances that occurred after CO2 laser irradiation was not observed following Er:YAG laser irradiation or bur drilling.

CONCLUSION

These results suggest that the use of Er:YAG laser ablation may become an alternative method for oral and periodontal osseous surgery.

Cortical bone healing following laser osteotomy using 6.1 microm wavelength

BACKGROUND AND OBJECTIVE

Use of laser wavelengths in the 6.1 microm (amide I) to 6.45 microm (amide II) regions and a macropulse width of 4.0 microseconds delivered by a computer-controlled delivery system have produced clean, deep cortical bone ablations with minimal collateral thermal injury and no char formation. The purpose of this study was to evaluate the healing of cortical bone following 6.1 microm wavelength laser osteotomy using a 4.0 microsecond pulse, and compare that response to the response of similar osteotomies made with a standard pneumatic surgical bone saw.

STUDY DESIGN/MATERIALS AND METHODS

Sixteen mature rabbits were divided equally into 2, 4, 6 and 8-week post-surgical survival groups. A nitrogen driven sagittal bone saw and an FEL generating 6.1 microm wavelength in 4.0 microsecond macropulses of 22.5 +/- 2.5 mJ/pulse directed into a 200 microm diameter spot were used to make 6.6 mm linear cuts into rabbit tibial cortex, and the healing response over time was monitored. Bone saw cuts were made halfway through the thickness of the cortex. Laser cuts were directed by a computer-controlled delivery system, and were either partial or full thickness cortical cuts. Location of the cortical bone cuts (saw or laser, partial or full thickness cut, proximal or distal, medial right or medial left tibia) were randomly assigned. At each predetermined post-surgical time point, rabbits of the appropriate group were euthanized, and the tibias of each subject collected, processed for histologic evaluation, and analyzed by light microscopy.

RESULTS

At 2 weeks post-surgery, bone saw cuts showed no evidence of a healing response, while both the partial and full laser cut sites were filled with trabecular bone and primitive bone marrow. By 4 weeks post-surgery, the bone saw cuts showed filling of the defect with trabecular bone and primitive marrow, and an intense osteonal remodeling of the original cortex adjacent to the cuts was evident. All laser cut defects were filled, reactive periosteal bone was being converted to osteons and consolidating, and secondary osteons were appearing in the original cortex. At 6 weeks following surgery, the bone saw defects were filed with a mixture of woven and lamellar bone. All laser defects were filled with lamellar osteons and woven bone, the osteons were remodeling from primary to secondary osteons. By 8 weeks following the surgery, all bone saw and laser cut specimens revealed complete healing.

CONCLUSIONS

Histologic evaluation of osteotomy sites made in skeletally mature rabbit tibia using the 6.1 microm wavelength, 4.0 microsecond macropulse FEL, delivered at 6 Hz at the osteotomy site, reveals a healing response which is at least as good as the healing of bone saw osteotomies, and appears to proceed at a faster rate during the first 2-4 weeks following surgery.