Cortical bone healing following laser osteotomy using 6.1 microm wavelength

Laser-Assisted Osteotomy for Implant Site Preparation: A Literature Review

PURPOSE

The aim of this study was to review the scientific evidence about the laser osteotomy in implant bed preparation.

METHODS

An electronic search was performed on relevant English articles up to April 2016 in the PubMed, Scopus, and Google Scholar databases.

RESULTS

Twenty-two articles (1 clinical, 13 animal, and 8 ex vivo studies) were included. Implant sites prepared by erbium family lasers and drill showed comparable results regarding the percentage of bone-to-implant contact, values of biomechanical tests, and healing process. Selection of proper laser wavelength and parameters was of paramount importance to minimize the risk of thermal bone damage. Lack of depth control and long time needed for implant site osteotomy with laser were the most challenging concerns for its clinical applicability. Computer-guided laser osteotomy showed promise for future use of laser osteotomy in clinical settings.

CONCLUSION

Evidence from animal studies shows promising results regarding laser osteotomy in implant site preparation. However, because of the lack of clinical studies, it is not possible to make a conclusive result whether there is superiority of laser osteotomy in clinical practice.

Miniature forward-imaging B-scan optical coherence tomography probe to guide real-time laser ablation

BACKGROUND AND OBJECTIVE

Investigations have shown that pulsed lasers tuned to 6.1 µm in wavelength are capable of ablating ocular and neural tissue with minimal collateral damage. This study investigated whether a miniature B-scan forward-imaging optical coherence tomography (OCT) probe can be combined with the laser to provide real-time visual feedback during laser incisions.

STUDY DESIGN/METHODS AND MATERIALS

A miniature 25-gauge B-scan forward-imaging OCT probe was developed and combined with a 250 µm hollow-glass waveguide to permit delivery of 6.1 µm laser energy. A gelatin mixture and both porcine corneal and retinal tissues were simultaneously imaged and lased (6.1 µm, 10 Hz, 0.4-0.7 mJ) through air. The ablation studies were observed and recorded in real time. The crater dimensions were measured using OCT imaging software (Bioptigen, Durham, NC). Histological analysis was performed on the ocular tissues.

RESULTS

The combined miniature forward-imaging OCT and mid-infrared laser-delivery probe successfully imaged real-time tissue ablation in gelatin, corneal tissue, and retinal tissue. Application of a constant number of 60 pulses at 0.5 mJ/pulse to the gelatin resulted in a mean crater depth of 123 ± 15 µm. For the corneal tissue, there was a significant correlation between the number of pulses used and depth of the lased hole (Pearson correlation coefficient = 0.82; P = 0.0002). Histological analysis of the cornea and retina tissues showed discrete holes with minimal thermal damage.

CONCLUSIONS

A combined miniature OCT and laser-delivery probe can monitor real-time tissue laser ablation. With additional testing and improvements, this novel instrument has the future possibility of effectively guiding surgeries by simultaneously imaging and ablating tissue.

Accelerated photo-induced hydrophilicity promotes osseointegration: an animal study

BACKGROUND

In the previous in vitro study, fluoride-modified, anodized porous titanium was proven to have enhanced its photo-induced hydrophilicity, which induced the hyperactivation of initial cell response.

PURPOSE

The purpose of the present study was to investigate in vivo bone apposition during the early stages of osseointegration in rabbit tibiae.

MATERIALS AND METHODS

Anodized porous titanium implants (TiU, TiUnite®, Nobel Biocare AB, Göteborg, Sweden) were modified with 0.175 wt% ammonium hydrogen fluoride solution (NH(4) F-HF(2) ). Twenty-four hours prior to the experiments, the surface-modified implants were ultraviolet-irradiated (modTiU). Blinded and unpackaged TiU implants were used as controls. Thereafter, the implants were placed in the rabbit tibial metaphyses and histomorphometrically analyzed at 2 and 6 weeks after insertion.

RESULTS

ModTiU demonstrated a significantly greater degree of bone-to-metal contact than TiU after 2 and 6 weeks of healing.

CONCLUSION

The results proved that the enhanced photo-induced hydrophilicity of the NH(4) F-HF(2) -modified anodized implants promoted bone apposition during the early stages of osseointegration.

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.

Effects of femtosecond laser irradiation on osseous tissues

BACKGROUND AND OBJECTIVE

Few studies have investigated femtosecond (fs) lasers for cutting bone tissue.

STUDY DESIGN/MATERIALS AND METHODS

A 775 nm, 1 kHz, 200 femtosecond, up to 400 microJ laser system was used to irradiate in vitro calcified cortical bone samples and bone tissue culture samples.

RESULTS

The ablation threshold in cortical bone was 0.69+/-0.08 J/cm(2) at 775 nm and 0.19+/-0.05 J/cm(2) at 387 nm. Plasma shielding experiments determined that the ablation plume and the plasma significantly affect material removal at high repetition rates and appear to generate thermal transients in calcified tissue. Confocal analysis revealed intact enzymatic activity on the surface of cells immediately adjacent to cells removed by fs laser irradiation.

CONCLUSIONS

These experiments demonstrate that fs lasers used for bone tissue cutting do not appear to generate significant temperature transients to inactivate proteins and that cellular membrane integrity is disrupted for only a few cell layers.

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.

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.

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.

Migration inhibitory factor-related protein (MRP)8 and MRP14 are differentially expressed in free-electron laser and scalpel incisions

Incisions made in mouse skin by scalpel or the free-electron laser heal at different rates. To identify genes that are differentially expressed in free-electron laser or scalpel wounds, we isolated total RNA from free-electron laser- or scalpel-produced incisions and normal skin at day 7 postwounding. cDNA microarray analysis identified 89 of 15,000 genes in a mouse microarray as having significantly different expression levels. Migration inhibitory factor-related protein (MRP) 14 was almost 30 times more highly expressed in scalpel wounds than in free-electron laser wounds. This result was confirmed by Northern blot analysis, which also showed that scalpel wounds expressed higher levels of MRP8, a related S100 protein that can heterodimerize with MRP14, at days 2, 7, and 14 postwounding. Free-electron laser wounds also showed elevated expression of MRP8 and MRP14 relative to normal skin. In situ hybridization showed that the patterns of MRP14 and MRP8 expression in free-electron laser and scalpel wound tissues were similar. MRP14 and MRP8 were expressed in the dermal wound margin, while a very low level of MRP14 and MRP8 expression was seen in the migrating epidermis. Dual immunofluorescence staining for MRP14 or MRP8 and macrophage (F4/80) showed that most of the wound macrophages simultaneously expressed MRP14 and MRP8. Some expression was also found in neutrophils, while neither antigen accumulated to a significant degree in the epidermis. Relatively lower MRP8 and 14 expression in free-electron laser wounds was correlated with a higher level of matrix metalloproteinase-13 expression and a reduced rate of wound healing. While the regulation of MRP8 expression in mouse may be different from human skin, we suggest that elevated expression of MRP8 and MRP14 may have a relevant therapeutic effect against inflammation in wound healing.

Comparison of Mouse Matrix Metalloproteinase 13 Expression in Free-Electron Laser and Scalpel Incisions During Wound Healing

Collagenase-3 (matrix metalloproteinase 13, MMP-13) was employed as a surrogate marker to compare the characteristics of incisional wound repair after surgery with the free-electron laser at 6.1 microm and the scalpel. Using a transgenic mouse strain with the MMP-13 or the COL1A2 promoter driving luciferase expression, we observed MMP-13 and COL1A2 expression, tensile strength, macrophage infiltration, and wound histology for up to 62 d. The scalpel incisions showed higher tensile strength than free-electron laser wounds from days 10 to 22 postwounding, despite minimal collateral thermal damage. After 45 d healing was similar. Trichrome staining confirmed that the scalpel incisions had more dense collagen deposition than free-electron laser incisions up to 36 d postinjury, but at day 45 they became similar. MMP-13 expression was biphasic, with peak activities at days 15 and 37 after injury, whereas free-electron laser wounds showed greater luciferase activity than scalpel wounds. Peak COL1A2 activity preceded the MMP-13 maximum. MMP-13 expression localized predominantly to dermal fibroblasts near the epidermis at day 15, and in the region of the deep dermis, muscle, and fascia at day 37 postwounding. Migrating muscle cells, but not all skeletal muscle cells, also expressed MMP-13. Free-electron laser incisions contained more macrophages than scalpel wounds at days 2 and 7 postinjury, suggesting that free-electron laser irradiation exacerbated the inflammatory response and thereby stimulated MMP-13 expression. These results revealed that MMP-13 was involved in a series of coordinated events during wound healing, not only the long-term remodeling of wound connective tissue, but also skeletal muscle repair. MMP-13 activity in vivo may correlate with the extent of tissue damage.