Optical characteristics of cartilage at a wavelength of 1560 nm and their dynamic behavior under laser heating conditions.

A double-integrating-sphere system was used to measure the diffuse transmittance, diffuse reflectance, and collimated transmittance of cartilage and polyacrylamide hydrogel samples as a function of temperature under 1560-nm laser heating conditions. The dynamic behavior of the absorption and scattering coefficients and scattering anisotropy of the biomaterials was calculated by the inverse Monte Carlo method. The absorption coefficient of the cartilage and hydrogel samples proved to be linear in temperature. Raising the temperature of the cartilage samples to 80°C caused their absorption coefficient to decrease by some 25%. The temperature-induced change of the absorption spectrum of the interstitial water was found to be responsible for the clarification of the cartilage tissue observed to occur under 1560-nm laser heating conditions. The temperature field produced in the tissue by the laser energy deposited therein was calculated using a bioheat transfer equation with temperature-dependent parameters. The calculation results demonstrated that the temperature-induced changes of the optical parameters of biological tissues should be taken into account to make their 1560-nm laser treatment effective and safe.

Infrared laser therapy after surgically assisted rapid palatal expansion to diminish pain and accelerate bone healing.

The aim of this study was to illustrate how gallium arsenite aluminum diode laser (824 nm) irradiation can reduce postsurgical edema and discomfort and accelerate sutural osseous regeneration after surgically assisted rapid palatal expansion (SARPE). An adult patient with an 8-mm transverse maxillary discrepancy was treated with SARPE. Infrared laser therapy was started on the 7th postoperative day, with a total of eight sessions at intervals of 48 hours. The laser probe spot had a size of 0.2827 cm2 and was positioned in contact with the following (bilateral) points: infraorbital foramen, nasal alar, nasopalatine foramen, median palatal suture at the height of the molars, and transverse palatine suture distal to the second molars. The laser was run in continuous mode with a power of 100 mW and a fluency of 1.5 J/cm2 for 20 seconds at each point. Subsequently, an absence of edema and pain was observed. Further, fast bone regeneration in the median palatal suture could be demonstrated by occlusal radiographs. These findings suggest that laser therapy can accelerate bone regeneration of the median palatal suture in patients who have undergone SARPE.

The effects of laser irradiation of cartilage on chondrocyte gene expression and the collagen matrix.

OBJECTIVES: Laser reshaping of cartilage is an emerging technology aimed at replacing conventional techniques for aesthetic and reconstructive surgery. Little is known about the mechanisms of wound healing following the photothermal heating during laser reshaping and, ultimately, how collagen remodels in the irradiated tissue. Healthy hyaline and elastic cartilage as found in the ear, nose, larynx, and trachea does not express collagen type I which is characteristic of fibro-cartilage and scar tissue. The aim of the study was to determine if collagen I and II gene expression occurs within laser irradiated rabbit septal cartilage. METHODS: Nasal septum harvested from freshly euthanized New Zealand White rabbits were irradiated with an Nd:YAG laser. After 2 weeks in culture, the laser spot and surrounding non-irradiated regions were imaged using immunofluorescence staining and evaluated using reverse transcription polymerase chain reaction (RT-PCR) to determine the presence of collagen I and II, and ascertain collagen I and II gene expression, respectively. RESULTS: All laser irradiated specimens showed a cessation in collagen II gene expression within the center of the laser spot. Collagen II was expressed in the surrounding region encircling the laser spot and within the non-irradiated periphery in all specimens. Immunohistochemistry identified only type II collagen. Neither collagen I gene expression nor immunoreactivity were identified in any specimens regardless or irradiation parameters. CONCLUSIONS: Laser irradiation of rabbit septal cartilage using dosimetry parameters similar to those used in laser reshaping does not result in the detection of either collagen I gene expression or immunoreactivity. Only collagen type II was noted after laser exposure in vitro following cell culture, which suggests that the cellular response to laser irradiation is distinct from that observed in conventional wound healing. Laser irradiation of cartilage can leave an intact collagen matrix which likely allows chondrocyte recovery on an intact scaffold.

Viability of human septal cartilage after 1.45 microm diode laser irradiation.

BACKGROUND AND OBJECTIVES: Chondrocyte viability following laser irradiation and reshaping has not been established for human nasal septal cartilage. Knowledge of the relationship between thermal injury and laser dosimetry is needed in order to optimize septal laser cartilage reshaping. The objective of this study was to determine the depth and width of thermal injury in human septal cartilage following laser irradiation. STUDY DESIGN/MATERIALS AND METHODS: Excess fresh nasal septal cartilage sections from rhinoplasty or septoplasty operations were irradiated using a 1.45 microm diode laser 1.25-3.6 W (2.8 mm spot diameter) with 1 second fixed exposure time, and then at exposure times of 1-4 seconds for a fixed power of 1.25 W. An infrared camera recorded surface temperature profiles during irradiation, and the temperature data were incorporated into a rate process model to numerically estimate thermal damage. Calcein AM and ethidium homodimer-1 fluorescent dyes combined with confocal laser microscopy (CLM) were used to measure thermal damage. RESULTS: CLM demonstrated clear demarcation between dead and living cells following irradiation. The extent of non-viable chondrocyte distributions increased with power and exposure time. The maximum depths of injury were 1,012 and 1,372 microm after 3.6 W 1 second and 1.25 W 4 seconds irradiation respectively. The damage predictions made by the rate process model underestimated thermal injury when compared with CLM measurements. CONCLUSIONS: The assay system identified regions of non-viable chondrocytes in human septal cartilage and defined how thermal injury varies with dosimetry when using a 1.45 microm diode laser.