Clinical uses of lasers in dermatology

Photoinactivation and Photoablation of Porphyromonas gingivalis

Several types of phototherapy target human pathogens and Porphyromonas gingivitis (Pg) in particular. The various approaches can be organized into five different treatment modes sorted by different power densities, interaction times, effective wavelengths and mechanisms of action. Mode 1: antimicrobial ultraviolet (aUV); mode 2: antimicrobial blue light (aBL); mode 3: antimicrobial selective photothermolysis (aSP); mode 4: antimicrobial vaporization; mode 5: antimicrobial photodynamic therapy (aPDT). This report reviews the literature to identify for each mode (a) the putative molecular mechanism of action; (b) the effective wavelength range and penetration depth; (c) selectivity; (d) in vitro outcomes; and (e) clinical trial/study outcomes as these elements apply to Porphyromonas gingivalis (Pg). The characteristics of each mode influence how each is translated into the clinic.

How efficient is laser therapy for telangiectasias, spider veins, and cherry angiomas?-A study using dynamic optical coherence tomography

OBJECTIVES

A clinical study to investigate the effectiveness of pulsed dye laser (PDL) versus Nd:YAG laser in the treatment of telangiectasias, spider veins and cherry angiomas. Dynamic optical coherence tomography (D-OCT) was introduced as an innovative follow-up tool for evaluation of blood flow within superficial vessels and to allow visualization of morphological changes of the vasculature in vivo. The final aim of this study was to demonstrate a possible treatment benefit comparing both laser types.

MATERIALS AND METHODS

Vessel structures of 102 skin lesions were documented photographically and dermoscopically. Subsequently, lesions were imaged using optical coherence tomography before laser therapy (a), directly after the treatment (p) and after a follow-up 4-6 weeks after laser treatment. All lesions were treated using either a 595 nm PDL or a 1064 nm Nd:YAG laser. Two main vessel parameters, namely density and diameter, and their possible changes during follow-up were observed in 150/300/500 µm penetration depth using D-OCT and were subsequently compared between both treatment groups. Other analyzed vessel parameters were depth of the plexus, mean diameter, mean density, top edge of the vessel, columns, and spikes.

RESULTS

Both laser types are suitable options for the treatment of vascular skin lesions, with the most significant effect on cherry angiomas. PDL shows better results treating smaller vessels in upper skin regions, in comparison to Nd:YAG laser, achieving better results on deeper vessels, like spider veins. Using the applied laser settings, there was no statistically significant effect on telangiectasias.

CONCLUSION

D-OCT represents a new, noninvasive imaging method to evaluate blood flow and vessel morphology in the follow-up of telangiectasias, spider veins, and cherry angiomas, which underwent laser therapy.

Passively mode-locked red Pr:LiYF4 laser based on a two-dimensional palladium diselenide saturable absorber

We report a passively mode-locked Pr:LiYF₄ (Pr:YLF) visible laser using a palladium diselenide (PdSe₂) as a saturable absorber (SA) for the first time, to the best of our knowledge. The nonlinear optical properties of two-dimensional (2D) PdSe₂ nanosheets in the visible band were studied by the open-aperture Z-scan technique. The results indicate the significant saturable absorption properties of PdSe₂ nanosheets in the visible region. Furthermore, the continuous wave mode-locked (CWML) visible laser based on PdSe₂ SA was successfully realized. Ultrashort pulses as short as 35 ps were obtained at 639.5 nm with a repetition rate of 80.3 MHz and a maximum output power of 116 mW. The corresponding pulse energy was 1.44 nJ and peak power was 41.3 W. These results indicate that 2D PdSe₂ SA is a promising high stability passively mode-locked device for ultrafast solid-state visible lasers.

Laser Resurfacing Monotherapy for the Treatment of Actinic Keratosis

Treating actinic keratosis (AK) and photodamaged skin is critical to reduce the risk of progression to skin cancer. Laser resurfacing for AK treatment is available as either lesion-directed or field therapy. Laser resurfacing removes the superficial epidermis and dermis containing actinic damage, promoting re-epithelialization of healthy skin. Although laser resurfacing has been explored as a modality for AK treatment in the literature, studies summarizing its efficacy in the treatment of AK are lacking. This review summarizes existing research on laser resurfacing as a monotherapy for AK treatment, highlighting the various laser resurfacing modalities available for AK treatment as well as their complications and efficacy in comparison to other therapies. Despite longer healing time, fully ablative laser resurfacing, including carbon dioxide and erbium-doped yttrium aluminum garnet were found to be more effective for AK treatment than fractional ablative techniques. Although some studies suggest laser resurfacing monotherapy as less efficacious than photodynamic therapy, and equally effective to 5-fluorouracil and 30% trichloroacetic acid, clinical trials of larger sample size are required to establish stronger evidence-based conclusions. Moreover, laser resurfacing used as lesion-directed therapy, as opposed to the usual field-therapy, requires further investigation.

The Impact of Proteomic Investigations on the Development and Improvement of Skin Laser Therapy: A Review Article

Introduction: Different molecular approaches have contributed to finding various responses of skin to external and internal tensions such as laser irradiation and many important mediators of skin disease have been identified through these approaches. However, different essential signals of skin biomarker pathways and proteins are partially detected or completely unknown. In the present study, the impact of proteomics on the evaluation of laser therapy for the treatment of skin diseases is investigated. Methods: The keywords of "Proteomics", "Laser therapy", "Skin", and "Skin disease" were searched in Google Scholar, Scopus and PubMed search engines. After screening, 53 documents were included in the study. Results: The global assessments revealed that different proteins in different signaling pathways of skin metabolism in terms of health or illness after laser therapy are expressed differentially. The results indicated that the application of proteomics is a useful method for promoting the results of laser interventions. Conclusion: This kind of research dealt with the practical proteomics of skin diseases and skin laser therapy.

Kerr-lens mode-locked Pr3+:LuLiF4 laser

We demonstrate the Kerr-lens mode-locked Pr³⁺:LuLiF₄ (Pr:LLF) laser pumped by a blue laser diode (LD). By theoretical calculation of the group velocity dispersion in the laser gain, the compensation was employed for the realization of the continuous-wave mode-locked laser at the wavelength of 604 nm with the pulse width of 1.1 ps which, to the best of our knowledge, is the shortest pulse width in the Pr³⁺ ion doped crystal lasers pumped with LDs. It can be believed that the present Pr:LLF laser should provide some inspiration for the development of the blue LD pumped visible lasers, especially in the mode-locking laser operation.

Retrospective Study on Laser Treatment of Oral Vascular Lesions Using the "Leopard Technique": The Multiple Spot Irradiation Technique with a Single-Pulsed Wave

OBJECTIVE

This study aimed to retrospectively evaluate the efficacy and safety of laser treatment of oral vascular lesions using the multiple spot irradiation technique with a single-pulsed wave.

BACKGROUND DATA

In laser therapy for vascular lesions, heat accumulation induced by excessive irradiation can cause adverse events postoperatively, including ulcer formation, resultant scarring, and severe pain. To prevent heat accumulation and side effects, we have applied a multiple pulsed spot irradiation technique, the so-called "leopard technique" (LT) to oral vascular lesions. This approach was originally proposed for laser treatment of nevi. It can avoid thermal concentration at the same spot and spare the epithelium, which promotes smooth healing. The goal of the study was to evaluate this procedure and treatment outcomes.

PATIENTS AND METHODS

The subjects were 46 patients with 47 oral vascular lesions treated with the LT using a Nd:YAG laser (1064 nm), including 24 thick lesions treated using a combination of the LT and intralesional photocoagulation.

RESULTS

All treatment outcomes were satisfactory without serious complications such as deep ulcer formation, scarring, bleeding, or severe swelling.

CONCLUSIONS

Laser therapy with the LT is a promising less-invasive treatment for oral vascular lesions.

Broadband atomic-layer MoS2 optical modulators for ultrafast pulse generations in the visible range

Visible lasers are a fascinating regime, and their significance is illustrated by the 2014 Noble prizes in physics and chemistry. With the development of blue laser diodes (LDs), the LD-pumped solid-state visible lasers become a burgeoning direction today. Constrained by the scarce visible optical modulators, the solid-state ultrafast visible lasers are rarely realized. Based on the bandgap structure and optoelectronic properties of atomic-layer MoS₂, it can be proposed that MoS₂ has the potential as a visible optical modulator. Here, by originally revealing layer-dependent nonlinear absorption of the atomic-layer MoS₂ in the visible range, broadband atomic-layer MoS₂ optical modulators for the visible ultrafast pulse generation are developed and selected based on the proposed design criteria for novel two-dimensional (2D) optical modulators. By applying the selected MoS₂ optical modulators in the solid-state praseodymium lasers, broadband mode-locked ultrafast lasers from 522 to 639 nm are originally realized. We believe that this Letter should promote the development of visible ultrafast photonics and further applications of 2D optoelectronic materials.

Intralesional laser therapy for vascular malformations

Intralesional laser therapy for the treatment of vascular malformations (VMs) has been previously reported for select patient populations. Larger studies, over a wider variety of indications, are needed to better define the potential role of this technology. In the current study, a 12-year, retrospective review of 44 patients who underwent 73 intralesional Nd:YAG or diode laser treatments of VMs was performed. The most commonly encountered lesions were venous malformations (66%) and the most commonly involved anatomic locations were the head and neck regions (41%) and lower extremity (39%). Primary indications for treatment were enlargement (73%) and pain (52%). Lesion size was reduced in 94% of cases after treatment and pain was improved in 91% of cases. Minor postoperative complications occurred in 16 (36%) patients. There was no difference in treatment response among various VM subtypes or anatomic locations (P=0.497, P=0.866) or in the incidence of complications (P=0.531, P=0.348). Age was the only factor associated with an increased risk of complications (odds ratio, 1.034; P=0.038). When used in accordance with the suggested guidelines, intralesional laser therapy is a safe and effective treatment modality for VMs of varying compositions and locations.

Laser-tissue interaction in tattoo removal by q-switched lasers

Q-switched (QS) lasers are widely considered the gold standard for tattoo removal, with excellent clinical results, impressive predictability, and a good safety profile. The generation of giant pulses by the method of Q-switching is responsible for the unique laser-tissue interaction that is seen in tattoo removal by QS lasers. The QS lasers work by impaction and dissolution of the tattoo pigments. Mechanical fragmentation of the tattoo pigments encased in intracellular lamellated organelles followed by their phagocytosis by macrophages is thought to be the major event in the clearance of pigments by QS lasers. A few novel techniques have been tried in recent times to hasten the clearance of tattoo pigments.

Effect of carbon dioxide laser ablation followed by intralesional steroids on keloids

Keloid is a difficult-to-treat condition and an ideal treatment modality is not available. Carbon dioxide (CO(2)) laser is one of the modalities to treat keloids.

AIM

To evaluate the effect of CO(2) laser ablation followed by intralesional steroids on keloids.

SETTINGS AND DESIGN

This was a prospective, single-center, uncontrolled, open study.

MATERIALS AND METHODS

Twenty-eight patients having 35 keloids were included in the study. Keloids were ablated or excised with CO(2) laser followed by intralesional steroid 3-4 weeks apart for 6 months. Results were evaluated after 6 months of stopping of intralesional steroids.

STATISTICAL ANALYSIS

Fisher's exact test was applied for obtaining difference in recurrence rate of regular and irregular patients.

RESULTS

Thirteen patients followed up regularly for intralesional steroids. During 6 months of follow-up after stoppage of steroids, only two patients showed recurrence. Ten patients were irregular for intralesional steroids and seven of them showed recurrence. Difference in recurrence rate of regular and irregular patients was significant.

CONCLUSION

Only CO(2) laser ablation is not sufficient for halting the pathogenesis of keloid formation.We therefore conclude that CO(2) laser followed by intralesional steroid is a useful therapeutic approach for the treatment of keloids; however, patients need to be observed for recurrence over the next 1 year.

Mitochondrial signaling for histamine releases in laser-irradiated RBL-2H3 mast cells

BACKGROUND

The low power laser irradiation (LPLI) can promote the wound healing, but the mechanism is still not fully understood. We have found in our previous work that the LPLI induces mast cells to release the histamine and thus suggested that the increased histamine release is probably one of the causes for promoting the wound healing since mast cells have been found to play positive roles in the process of wound healing. This study aims to explore the mechanism of histamine release in RBL-2H3 mast cells under laser irradiations.

MATERIALS AND METHODS

The wavelength effect of laser irradiations, the permeability function of mitochondrial membrane, the Bcl-2 effect, the cytosolic alkalinization and the increment of intracellular Ca(2+) ([Ca(2+)](i)), on histamine release in RBL-2H3 cells were studied, respectively, with the corresponding fluorescence probes.

RESULTS

The action bands of laser irradiations were consistent with the absorption bands of cytochrome c oxidase, suggesting that cytochrome c oxidase is the photoacceptor. After laser irradiation, (1) the cytochrome c releases from mitochondrial to cytosol reflecting an increased permeability of mitochondrial membrane, (2) the cytosolic alkalinization appears, (3) [Ca(2+)](i) increases, and (4) finally the enhancement of histamine release occurs. When Bcl-2 was used to inhibit the permeability of mitochondrial membrane these cellular signaling from (1) to (4) were all suppressed obviously.

CONCLUSION

As a photoacceptor, cytochrome c oxidase absorbs incident photons and initiates the mitochondrial signaling. When the signals are transferred from the mitochondrial to the cytosol, the cytosolic alkalinization appears leading to the opening of a Ca(2+) channel on the membrane, the transient receptor potential vanilloid (TRPV), and an increment of [Ca(2+)](i). The increased [Ca(2+)](i) consequently mediates an enhanced histamine release. Such a responding chain is a suggested mechanism to understand the histamine release in RBL-2H3 cells under laser irradiations.

Laser transport through thin scattering layers

Many modern applications of lasers involve understanding the transport of radiation through thin layers. The interactions of continuous wave and pulsed lasers with skin in dermatological use related to surgery and cosmetic procedures are examples of such. These highly scattering thin layers in skin are best modeled by the Monte Carlo method. However, most traditional Monte Carlo models may inaccurately account for the presence of thin layers. As an example, the very thin epidermis, with its highly absorbing melanin, is known to influence the laser penetration significantly. If the Monte Carlo model is implemented without special features, then the results of the simulation will show incorrect effects of thin layers because the path length of most photons would be significantly larger than the layer thickness. As a result, the computed photon travel path length would simply not feel the presence of the layer. In this paper, we present numerical and algorithmic features for computation of radiation transport through thin layers. It is noted that, while Monte Carlo without special features smears the radiative effect of the layers, the refined technique indicates that layers have a great impact on the absorption of energy, especially if the layer properties are distinctly different from those of the adjacent layers. The results have significant implications in the study of diagnostic and therapeutic applications of lasers in biomedicine and surgery.

Cosmetic tattoo refractive to Q-switched alexandrite laser

BACKGROUND

Lip tattooing is a common cosmetic technique not exempt from certain risks and which may lead an unsatisfied customer to seek tattoo elimination.

OBJECTIVE

To assess the clinical outcome of a patient with a brownish-colored cosmetic lip tattoo after treatment with the Q-switched alexandrite laser (QSAL).

METHODS

Two sites were tested using the pigment lesion dye laser (PLDL) and QSAL. The patient received 10 monthly sessions with QSAL, with an average fluence of 6.925 J/cm2. The double and triple shot technique was applied.

RESULTS

The brownish pigmentation turned black after the PLDL and QSAL tests. Epidermal splattering and bleeding made a fluence increase with QSAL inadvisable. Treatment was unsuccessful.

CONCLUSIONS

PLDL and QSAL may induce a photochemical alteration in brownish pigment. Factors that may contribute to the poor response of a cosmetic lip tattoo to QSAL treatment are related to pigment characteristics and laser parameters.

Intralesional laser treatment of voluminous vascular lesions in the oral cavity

OBJECTIVE

In laser treatment of voluminous vascular lesions, there are many cases in which submucosally located angioma remnants cannot be reached by noncontact superficial laser application. To diminish these remnants we used intralesional photocoagulation (ILP) in treatment of oral vascular lesions, because this approach is effective in treatment of voluminous vascular lesions of the skin.

STUDY DESIGN

Four cases of voluminous vascular malformation in the oral cavity were treated by ILP using a potassium-titanyl-phosphate (KTP) laser. In 1 case, treatment was carried out under ultrasound and manual control.

RESULTS

All lesions showed more than 70% regression after the first ILP session, and the treatment outcome was satisfactory. There were no serious complications, such as bleeding or invasive infection. Ultrasonography was useful for guiding laser treatment in the oral cavity.

CONCLUSION

Intralesional photocoagulation treatment with a KTP laser is effective and safe for treatment of a vascular lesion in the oral cavity.

Real time control of the spatial selectivity during laser treatment of a biological surface

We propose a new irradiation technique to improve the spatial selectivity and the dose control during a laser treatment of a biological surface. The technique is based on the use of a spatial light modulator to project a rectangular laser image of 8 mm x 5 mm. The spatial distribution of the irradiation is controlled in real time by image analysis applied to the acquired image of the surface to be treated. The aim is to discriminate between the target areas to be irradiated and the surrounding parts to be preserved. The resolution is about 12 microm and is limited by the resolution of the camera and the spatial light modulator. For treatments of a large surface we use an intensity correlator to measure the displacement and to avoid an unwanted second irradiation on a target.

Neodymium: yttrium-aluminum-garnet long impulse laser for the elimination of superfluous hair: experiences and considerations from 3 years of activity

This study examined the results obtained with a modern apparatus for laser hair removal (neodymium: yttrium-aluminum-garnet [Nd:YAG] laser at long impulses with a wave-length of 1,064 nm; Q-switched laser) over a follow-up period of 3 years. A large heterogeneous group of 480 patients was taken into consideration. These patients were treated according to a standard protocol with monthly checkups and a personalized protocol at deferred appointments. The results, discovered by means of the most objective procedure possible, were retrieved and put into a graph showing two different curves for the repopulation of hair. In their clinical travels, the authors observed an average variable regrowth of 40% to 65%, allowing them to affirm that laser hair removal using Nd:YAG at long impulses is decisively efficient in obtaining long-term results. The use of a protocol (denominated "prolonged monthly checkup") with laser sessions at ever-decreasing periods permits, among other things, more outstanding and advantageous results for the patient. Thanks to more efficiently synchronized phases of the biologic hair cycle, this shortens and moves the telegenic phases closer and also renders the anagenic phases (those in which the selective photoermolysis on the pilipheric follicle proves to be efficient) more efficient. Personalization of the treatment relative to the monthly health checkup sessions is of fundamental importance to the scope of obtaining the best results in terms of cost-benefit rate, provided submassimal fluxes are (i.e., those well-tolerated by the patient) used. All this allows hair removal that is not definitive, but which becomes progressively permanent (i.e., characterized by ever-growing periods of lack of hair sustained by sporadic maintenance laser sessions based on the individual's necessity).

Laser surgery: an approach to the pediatric patient

Revolutionary advances in laser research and technology have led to expanded dermatologic laser applications. With the wide range of lasers now available, a large spectrum of skin conditions in the pediatric population can be successfully treated or, in some cases, completely eradicated. Laser treatment of the pediatric population poses a unique challenge for the clinician on a variety of levels. Physically, the composition of many vascular and pigmented lesions changes as children age making them more resistant to laser therapy. Thus, in many cases, treating lesions at an early age has resulted in clearing in fewer sessions and with decreased complications. Mechanically, lasers and laser settings used for the treatment of adult lesions may have to be adjusted for the smaller vessels and the unpredictable nature of scarring with children's skin. For vascular lesions, the pulsed dye laser is considered the laser of choice for its efficacy and low-risk profile, whereas the Q-switched, pigment-specific lasers are ideal for most childhood pigmented lesions, allowing for single pigment cell destruction. Other conditions such as acne and acne scars, psoriasis, keloids, warts and hypertrichosis that traditionally have been treated with a variety of modalities are now being managed safely with laser surgery. Other issues specific to the pediatric population include the determination of suitable anesthesia, the provision of size-appropriate safety equipment, and the assessment and management of patient and parent anxiety. The use of lasers specifically designed for structural differences in pediatric lesions and the recognition of emotional issues surrounding a young patient during laser surgery are critical components of successful treatment.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be familiar with the mechanism of laser technology, current trends in the use of lasers for skin lesions in the pediatric population, and the issues specific to treating a patient with laser surgery.

In vitro and in vivo study of dye diffusion into the human skin and hair follicles

We present experimental results on the in vitro and in vivo study of dye diffusion into human skin and hair follicles. We have studied some commercially available dyes for potential using in the laser selective thermolysis. The degree and the depth of hair follicle dyeing inside the skin were determined. For hairs in different stages the sebaceous gland was stated as a reservoir for a dye administration. It was found that the penetration depth of dyes is about 1.2 mm from the skin surface. We have developed the biocompatible Indocyanine Green lotions and the method for in vivo dyeing and dye in depth monitoring. Shift on 16-21 nm of absorption peak of Indocyanine Green to the longer wavelengths due to Indocyanine Green binding with cell proteins in the human skin was found.

Propagation of focused and multibeam laser energy in biological tissue

The results of a Monte Carlo simulation of laser beam propagation in turbid media are presented. The study was performed to determine whether using a focused beam or multiple beams instead of a single collimated beam could improve subsurface laser energy delivery in biological tissue. A parametric study was carried out to determine both the laser fluence at a target depth and the ratio of fluence at the target over surface fluence as a function of tissue properties and the mode of energy delivery. It was found that the reduced scattering coefficient was the primary determinant as to whether multibeam or focused beam delivery could be effective. A focused beam was found to be extremely effective in increasing fluence at the target if the dimensionless reduced scattering coefficient was less than 2. The delivered fluence, however, was found to be extremely sensitive to tissue properties. A five-beam laser system was found to be less effective at increasing fluence at the target than a focused beam; but the fluence delivered by a five-beam system was far less sensitive to tissue properties, thereby making accurate dosimetry more feasible.

Selective photothermolysis in skin by using subcutaneous optical fibers

BACKGROUND AND OBJECTIVE

Vascular selective photothermolysis has been shown to be effective in treating hypertrophic scars. Performing selective photothermolysis on the vasculature deep within thick scars requires new methods for delivering laser energy. It is the objective of this study to model the use of subcutaneous fiber optics to perform selective photothermolysis in skin as a possible aid in the treatment of thick scars.

STUDY DESIGN/MATERIALS AND METHODS

A Monte Carlo simulation was performed to study the expected region of vascular necrosis in a two layer skin model when 585-nm radiation is delivered into the dermis by means of subcutaneous optical fibers.

RESULTS

The extent of vascular necrosis is independent of fiber diameter for a fixed total energy. A fiber penetrating barely below the epidermis decreases the maximum epidermal fluence by more than an order of magnitude relative to a superficial beam. Using four fibers simultaneously can significantly increase the depth of vascular necrosis.

CONCLUSIONS

Small diameter fibers are optimum if the maximum fluence tolerable in the dermis is not a limiting factor. Shallowly inserted fibers can significantly decrease epidermal damage to dark-skinned patients undergoing laser therapy.

Use of Er:YAG laser for benign skin disorders

BACKGROUND AND OBJECTIVE

The Er:YAG laser is of special interest in dermatology and cosmetic surgery since it ablates and cuts tissue with surgical precision with minimal collateral thermal damage due to the wavelength of the Er:YAG radiation (2,940 nm), which is strongly absorbed by liquid water in tissue. The study was designed to establish optimal laser parameters for treating various skin disorders.

STUDY DESIGN/MATERIALS AND METHODS

Sixty-four patients were treated for benign skin disorders: seborrhoic warts, plane warts, milia, xanthelasma palpebrarum, hidradenoma, chloasma, senile lentigo, epidermal naevi, actinic keratosis, fibroepithelial papillomata, scars. The lesions were irradiated with single pulse laser energies 100-1,000 mJ, repetition rates 2-10 Hz, and spot diameters 2-8 mm.

RESULTS

Epidermis was effectively removed on a layer-by-layer basis. For the ablation, energy densities higher than 2.5 J/cm2 were required. If bleeding appeared, the hemostatic effect was achieved by irradiating the bleeding surface with few Er:YAG laser pulses of lower power density (0.5-1.5 J/cm2). Healing was excellent and without apparent scarring.

CONCLUSION

It was established that Er:YAG laser with properly selected parameters offers a tool for tissue ablation and/or coagulation. The Er:YAG laser was found to be a perfect option for effective treatment of benign skin disorders.

A laser-powered hydrokinetic system for caries removal and cavity preparation

BACKGROUND

Laser systems have been developed for the cutting of dental hard tissues. The erbium, chromium:yttrium-scandium-gallium-garnet, or Er,Cr:YSGG, laser system used in conjunction with an air-water spray has been shown to be efficacious in vitro for cavity preparation.

METHODS

The authors randomly selected subjects for cavity preparation with conventional air turbine/bur dental surgery or an Er,Cr:YSGG laser-powered system using a split-mouth design. They prepared Class I, III and V cavities, placed resin restorations and evaluated subjects on the day of the procedure and 30 days and six months postoperatively for pulp vitality, recurrent caries, pain and discomfort, and restoration retention. Sixty-seven subjects completed the study.

RESULTS

There were no statistical differences between the two treatment groups for the parameters measured with one exception; there was a statistically significant decrease in discomfort levels for the laser system at the time of cavity preparation for subjects who declined to receive local anesthetic.

CONCLUSIONS

The Er,Cr:YSGG laser system is effective for preparation of Class I, III and V cavities and resin restorations are retained by lased tooth surfaces.

CLINICAL IMPLICATIONS

Hard-tissue cutting lasers are being introduced for use in operative dentistry. In this study, an Er,Cr:YSGG laser has been shown to be effective for cavity preparation and restoration replacement.

Hair removal using a long-pulsed alexandrite laser

The use of lasers for hair depilation has become a common modality for physicians in the recent past. As new lasers are developed, the complex mechanisms affecting this form of treatment are now under close investigation. The long-pulsed alexandrite laser functioning at a wavelength of 755 nm has recently been added to the armamentarium of health care providers to assist patients with unwanted body hair. A review of the embryology and anatomy of the hair follicle are discussed, as well as the findings of recent studies using this form of laser therapy. Using the suggested treatment protocols offered laser assisted depilation may be effectively achieved. The degree and duration of reduction vary with anatomic site and improve with multiple treatments.

Ultrasound-guided interstitial Nd: YAG laser treatment of voluminous hemangiomas and vascular malformations in 92 patients

In many cases voluminous vascular anomalies of the head and neck region are still treated with conventional surgery, although neodymium:yttrium-aluminum-garnet (Nd:YAG) laser therapy offers a valuable treatment alternative. Ninety-two patients with voluminous hemangiomas and vascular malformations were treated with interstitial Nd:YAG laser therapy (power density, 1300 to 3300 W/cm2), partly complemented by a noncontact-mode Nd:YAG laser light application (energy density, 1000 to 2500 J/cm2). The vascular tumors had a diameter of more than 3 cm in at least two dimensions. Treatment was carried out under ultrasound and manual control. Nearly 60% of the patients (n = 55) showed a complete clinical regression. Thirty-three patients (35.8%) had a partial regression and were satisfied with the treatment outcome. Four patients were treated unsuccessfully with the laser, and three of them subsequently underwent conventional surgery. Only nine of the 92 patients (9.8%) showed cosmetic or functional impairments. The results of this first consecutive series study with a retrospective clinical evaluation of the interstitial Nd:YAG laser therapy of voluminous hemangiomas and vascular malformations in a large patient group demonstrate a high effectiveness of this novel therapy modality.

Pulpal response to cavity preparation by an erbium, chromium:YSGG laser-powered hydrokinetic system

The near red-pulsed erbium, chromium:yttrium-scandium-gallium-garnet laser hydrokinetic system, or Er,Cr:YSGG laser HKS, is effective in cutting dental hard tissues. In this longitudinal study, the authors studied the continuously erupting open-apex incisors of New Zealand albino rabbits and the constricted apex teeth of beagles to determine the effects of HKS-produced lesions at various energy levels and of preparations produced by a tapered fissure bur on dental pulp. No pulpal inflammatory responses could be identified either immediately or 30 days after surgery in HKS preparations that removed enamel and dentin without pulp exposure.

Laser-assisted hair removal

The use of lasers in the treatment of a number of different skin disorders and diseases has become commonplace. This tremendous acceptance by both physicians and patients is a direct reflection of the high degree of precision and selectivity provided by lasers, which helps to minimize the risk of side effects and complications while simultaneously maximizing the opportunity for obtaining a satisfactory outcome. In an attempt to remove unwanted or excess hair, the principles of selective photothermolysis have been employed with several different laser and light devices that permit the effective treatment of large areas of hair-bearing skin with minimal discomfort and with low risk of scarring or other complications. It is possible using current laser technology to permanently remove some hair and induce a prolonged delay in the regrowth of many hairs. With additional experience and an improved understanding of how light can influence the rate and quality of hair growth, it is anticipated that permanent hair removal will be achieved in the near future.

Laser light delivery systems for medical applications

For medical applications, the choice of a delivery system will be governed by the characteristics of the laser system on the one hand and the tissue application on the other. The most important parts are the beam guide and the target optics. Most lasers have wavelengths in the visible and near-infrared and can be transported by silica fibres. For the mid- and far-IR other fibre materials or hollow waveguides are used. At the end of the waveguide or fibre, an optically active component is present to direct the beam and to control the power density on the target tissue. The laser beam can be delivered either by focusing handpieces and scanning devices to treat superficial areas or through microscopes, endoscopes and flexible fibres to treat areas almost anywhere inside the human body. The characteristics of the delivery systems can be determined looking at beam properties, transmission and thermal properties. The delivery of continuous wave or pulsed laser energy, contact or non-contact, will determine the contribution of optical, thermal and mechanical effects to the tissue. The practical use of laser delivery systems is illustrated by various clinical applications.

Mathematical modelling of dynamic cooling and pre-heating, used to increase the depth of selective damage to blood vessels in laser treatment of port wine stains

Based on the assumption that the maximum irradiance allowed during laser treatment of port wine stains is limited by the temperature rise at the dermoepidermal junction, we theoretically investigated how much the irradiance could be increased by dynamically cooling the skin surface. The heat condution equation was solved numerically in cylindrical coordinates using a skin model composed of four layers. The laser-light absorption was calculated using Monte Carlo simulations. The transient thermal behaviour of the skin was modelled when cooling with water at a temperature of 0 degrees C and with liquid nitrogen at a temperature of -196 degrees C. With cooling, an increase in the maximum irradiance by a factor of 2.3-3.6 was theoretically permitted depending on the irradiation time, wavelength and mode of cooling. The corresponding increase in vessel selective damage depth was predicted to be 0.4-0.5 mm. A new concept for increasing the depth of vessel selective damage is introduced where the initial temperature profile of the skin is reshaped by using not only surface cooling but also laser irradiation. By pre-irradiating the skin with near-infrared light without selective absorption by the tissue chromophores in conjunction with surface cooling, a maximum temperature at a depth of 1 mm from the dermoepidermal junction was theoretically achieved. A subsequent 0.1 s pulse from a frequency doubled Nd:YAG laser is theoretically shown to selectively destroy vessels up to a depth of 0.8 mm from the dermoepidermal junction. By pre-heating at 1064 nm and treating at 532 nm in conjunction with surface cooling, the theoretical results indicate that the Nd:YAG laser can compete in effectiveness with the flashlamp-pumped dye laser in the treatment of port wine stains.

In vitro changes in non-facial human skin following CO2 laser resurfacing: a comparison study

BACKGROUND AND OBJECTIVE

We evaluated the physical changes in human skin following CO2 laser cutaneous resurfacing with either the Sharplan SilkTouch handpiece or the Coherent UltraPulse laser.

STUDY DESIGN/MATERIALS AND METHODS

Three-hundred five human tissue samples and matched controls were used. Up to five laser passes were performed per specimen. Parameters evaluated included: lateral skin shrinkage, transient temperature change, isometric tension development, elasticity change, and histologic change.

RESULTS

Skin shrinkage increased in direct proportion to laser pass number. Isometric tension exponentially increased and elasticity exponentially decreased with successive laser passes. The zone of thermal denaturation for the SilkTouch handpiece was 115 +/- 15 microns, and was independent of laser pass number. The zone of thermal denaturation was patchy for the UltraPulse laser treatments, regardless of pass number. A greater temperature increase was also measured for SilkTouch irradiation than with the UltraPulse laser.

CONCLUSION

The observed alterations in tissue length, tension development, and elasticity obtained with SilkTouch or UltraPulse treatment may contribute to the changes in clinical appearance associated with laser cutaneous resurfacing. Our findings support a role for extracellular matrix contraction in the mechanism of action for CO2 lasers in cutaneous resurfacing.

Pulsed Erbium:YAG laser ablation in cutaneous surgery

BACKGROUND AND OBJECTIVE

Among the various pulsed midinfrared-lasers studied in skin surgery the 2.94 microns Erbium:YAG laser has been shown to combine most efficacious ablation with least thermal damage due to its unique absorption characteristics in tissue water. A newly developed high-power Erbium:YAG laboratory laser providing output energies (up to 1.5 J/pulse) and repetition rates (up to 15 Hz) appropriate for clinical use enabled us to investigate its potential indications in dermatological surgery.

STUDY DESIGN/MATERIALS AND METHODS

Erbium:YAG laser ablation was performed in vitro on pig skin and in vivo on a total of 30 patients presenting with different skin disorders.

RESULTS

In vitro ablation efficiency linearly increased with radiant exposure and was inversely correlated with pulse frequency. Ablation rate at 10 Jcm-2 (used clinically) measured from approximately 10 microns (at 10 Hz) to 40 microns (at 1 Hz). Also for high repetition rates thermal necrosis did not exceed 50 microns, corresponding clinically to capillary bleeding after exposure of the dermis. Superficial lesions, such as epidermal nevi, were easily ablated and re-epithelization was unimpaired owing to the absence of tissue necrosis. In tattoos, exposed pigment particles were precisely removed. However, in deeper lesions the casual onset of bleeding impeded the procedure and scar formation was observed after reepithelization.

CONCLUSION

Pulsed 2.94 microns Erbium:YAG laser surgery allows an extremely precise etching of delicate superficial skin lesions and also should have a potential for skin resurfacing.