A review of laser applications in orthodontics

FEATURE This article has been peer reviewed. A Review of Laser Applications in Orthodontics By Yunlong Kang, BDS,MSOrth, AdvDipOrth; A.B.M. Rabie BDS, PhD, MSc, Cert Ortho, FHKAM, FCDSHK, Hon FDSRCS; R.W.K. Wong BDS, MOrth, PhD, FRACDS, MOrthRCS, FHKAM, FCDSHK Abstract: Laser technique now is widely applied in orthodontic treatment and proved to have many benefits. Soft tissue lasers can be used to perform gingivectomy, frenectomy and surgical exposure of tooth with less bleeding and swelling, improved precision, reduced pain and less wound contraction. Other laser applications include enamel etching and bonding and bracket debonding. Lower level lasers have the potential effects of pain control and accelerating tooth movement. Clinicians must be aware of the safety issues and risks associated with laser and receive proper training before the laser treatment is started. Keywords: Laser; Orthodontics; gingivectomy; frenectomy; low-level laser; etching bonding; bone regeneration. ntroduction The name “LASER” stands for Light Amplification by Stimulated Emission of Radiation. A laser is a device that can produce light by transforming electrical energy into optical energy. To generate laser light, atoms must be excited to a higher energy level and release their energy in phase. It is a nearly parallel, monochromatic, and coherent beam of light, which is opposite to ordinary lights.1 History of Laser In 1917, Einstein published an article on the quantum theory of radiation which is considered to be the basic concept of laser technology.2 In early 1954, Townes, an American physicist, first amplified microwaves by stimulated emission. An acronym “MASER” which stands for Microwave Amplification by Stimulated Emission of Radiation was used to describe the device they invented.3 Four years later, Schawlow and Townes extended maser techniques into the optical and infrared region thus invented laser.4 In 1960, Maiman built the first working laser with ruby as the active medium material.5 Soon after Maiman’s ruby laser was constructed, Goldman6 introduced laser technique into the medical field. Since then, Goldman and other scholars published articles about different kinds of lasers and their range of applications in medicine, including dentistry. In 1964, he reported the impact of ruby laser on dental caries.The results showed crater formation and dentine fusion along with disappearance of dental caries.7 One year later, he wrote another report about the effect of ruby laser beams on teeth. This was the first report on laser applied to vital teeth.8 Stern and Sognnaes9 also reported similar tooth enamel changes subjected to ruby laser energy. In 1964, Bell Laboratories developed the neodymiumdoped yttrium aluminum garnet (Nd:YAG) laser and carbon dioxide (CO2) laser, researchers were able to extend laser technique to both hard and soft tissues in the oral cavity. Ruby laser was rarely used due to its large energy requirement and collateral damage to other adjacent dental tissues. In 1980, Nd:YAG laser was first reported to be used in dental caries IJO „ VOL. 25 „ NO. 1 „ SPRING 2014 prevention by Yamamoto and Sato. During the 1970s to 1980s, several papers were published regarding the application of CO2 laser in the treatment of hard and soft tissue lesions, periodontal diseases and in oral surgery.10-13 Before 1990, the use of laser in dentistry was limited being confined to a small group of clinicians, until the development of a pulsed Nd:YAG laser by Myers and Myers15 which allowed this technique to be widely used in general dentistry. Later, numerous types of lasers were developed (Holmium: YAG, Erbium:YAG, Argon, Erbium yttrium scandium gallium garnet) and applied to a range of dental areas including oral surgery, preventive dentistry, orthodontics, pedodontics, periodontology, oral pathology and oral medicine (Table 1). Laser Technology Basic Theory of Laser According to the quantum theory of physics first described by Niels Bohr,16 a photon which is the smallest unit of energy, is released after an atom has absorbed another photon and is excited. This phenomenon is called spontaneous emission. Einstein2 further developed this theory. He added that an excited atom may absorb a quantum of energy and then release two photons. Two identical photons travel as a coherent wave. More atoms will be excited by these photons which cause further emission of additional identical photons resulting in an amplification of light energy. Eventually, a laser beam will be produced.17 Properties of Laser Three unique properties of laser distinguish it from ordinary light. Monochromaticity: The wavelength of light emitted by laser is very narrow compared to conventional light sources which emit light of a broad wavelength. Therefore, instead of containing multiple colors, laser light has a single specific color. Collimation: The beam of a laser has a constant direction, size and shape while conventional lights diverge in all directions. Coherency: All the light waves are identical in laser light. 47 Basic Components of Laser A laser device basically contains three major parts: an optical resonant which consists of more than two mirrors, an active medium (gas, dye, solid-state electronic device or semiconductor) and an external energy source (pump source). The external energy sources usually involve a flash-lamp or electricity to excite the active particles in the active medium in order to produce stimulated emission. Photons are then released from the active medium and amplified by mirrors in the optical resonant and eventually emerge as laser light. Laser Delivery System and Emission Mode A laser beam must be delivered to the target tissue in a precise and ergonomic manner. There are two main delivery systems available for dental laser. A hollow tube-like wave guide with interior mirror. The laser beam is reflected by the mirrors along the wave guide and exits through a handpiece. The beam works on the tissue in a noncontact fashion (not direct physical contact with the tissue). CO2 laser is delivered with this system. Glass fiber-optic cable. Glass fiber cable with different diameters (200u to 1000u) can be used to deliver a laser beam. It is encased in a sheath, very fragile and can not be bent into a sharp angle. This system can be used in both contact (touch the tissue directly) and non-contact fashion, but it is mostly used in contact fashion in oral surgery. Nd:YAG, diode and erbium lasers are delivered with this system. A laser device emits light energy by three modes. In continuous wave, the laser beam is emitted at a constant power level (argon, diode and CO2). Another mode involves the periodic alteration of the laser energy being on and off in a short amount of time (diode, CO2), this is called gate-pulsed mode. The last mode is named free-running pulsed mode, where a large quantity of energy is released for a short period of time followed by a relatively longer time during which the laser is off (Nd:YAG, erbium and Ho:YAG). Laser biological effects When laser light hits the target tissue, four types of interactions occur: reflection, transmission and scattering and absorption. Reflection occurs when the beam redirects itself away from the tissue surface which results in no effect on the target. When the laser energy passes through the tissue and has no effect on the target tissue, transmission occurs. Scattering tends to transfer heat produced by laser beam to the adjacent site which weakens the laser energy. The absorption of laser energy by the target tissue is the primary and desirable effect of laser. The amount of energy absorbed by 48 the target tissue depends on the laser wavelength, emission mode and tissue characteristics.18,168 There are several photobiological effects of dental lasers: Photothermal effect of laser is the transformation of light into heat. Surgical incision, excision and ablation with precision and hemostasis are results of the photothermal effect. Laser chemical reactions such as curing composite resin and breaking the chemical bonds can be stimulated by laser which is the result of photochemical effects. The photoacoustic effect of laser can produce a shock wave, which can explode the tissue, create an abraded crater. This is beneficial for dental hard tissue procedures. Laser has a biostimulating effect which causes rapid wound healing and pain relief, an increase in collagen growth and the generation of an anti-inflammatory effect.59,169,170 Types of Dental Lasers Lasers applied in dentistry are named after the chemical elements, molecules or compounds that compose the active medium which is stimulated. There are six basic types of lasers now are used in dentistry. Their name, Table 1. History of Laser Development Year Name Development of Laser 1917 Einstein2 1954 1958 1960 1963 1964 1964 Townes3 Schawlow and Townes4 Maiman5 Goldman6 Goldman7 Bell Laboratories Invention of MASER Invention of LASER Built the first working laser Introduced laser into medical field Reported impact of laser beam to dental caries Nd:YAG laser and CO2 laser were developed. Extended the application of laser into soft tissue 1980 Yamamoto and Sato14 Nd:YAG laser was first reported to be used in dental caries prevention 1989 Myers and Myers15 Development of a pulsed Nd:YAG laser, made application of laser in general dentistry possible 1990- On the Quantum Mechanics of Radiation Ho:YAG, Er:YAG, Argon, Er:YSGG and other types of laser were invented. Laser has been widely applied in dentistry Table 2. Summary of Dental Lasers Name Active medium Wavelength CO2 Laser18-19 Gas-active, CO2 10600nm Nd:YAG Laser20 Solid active, crystal of yttrium-aluminumgarnet doped with neodymium 1064nm Diode Laser18,22 Solid active, solidstate semiconductor: aluminum, gallium and arsenide 800-980nm Argon Laser21 Gas active, argon 488nm; 514nm Er,Cr:YSGG and Er:YAG Laser18,21 Er,Cr:YSGG : solid active, crystal of yttrium-scandiumgallium-garnet doped with erbium and chromium Er:YAG: solid active, crystal of yttriumgallium-garnet doped with erbium Solid active, crystal of yttriumaluminum-garnet doped with holmium Er,Cr:YSGG 2790nm Er:YAG 2940nm Ho:YAG Laser18           2120nm Character Application Well absorbed by water; Highest absorption in hydroxyapatite; Non-contact mode Absorbed by water and pigment tissue(hemoglobin); Good hemostatic abliliy; Slightly absorbed by dental hard tissue Contact mode Well absorbed by pigment tissue and water; Poorly absorbed by dental hard tissue; Contact mode with small size instrument 488nm active camphoroquinone; 514nm absorbed by red pigment tissue; Poorly absorbed by dental hard tissue Highest absorption in water; high affinity for hydroxyapatite Soft tissue surgery; Enamel surface modification Absorption by water; Poorly absorbed by pigment tissue and dental hard tissue Soft tissue surgery Soft tissue surgery; sulcular debridement and remove surface carious lesion Soft tissue surgery; sulcular debridement Light curing dental materials; Sulcular debridement and highly vascularized lesions Caries detection Caries removal and tooth preparation; Soft tissue surgery IJO „ VOL. 25 „ NO. 1 „ SPRING 2014 wavelength, characters and functions are listed in Table 2. According to the energy output and focus, lasers can also be classified into three groups: high, medium and low power. Laser Application in Orthodontics Laser was invented and has been used in oral and oral maxillofacial surgery for more than three decades.23 It is a relatively new technique that has been introduced into orthodontics within the last twenty years.24-25 It soon gained its place in solving a variety of problems relating to orthodontic treatment ranging from ceramic bracket debonding26 and enamel surface etching27 to mucogingival surgery.28 Lasers with different wavelengths can manage both hard and soft tissue problems. Moreover, low level lasers were reported to be beneficial in pain control induced by orthodontic arch wire placement.29 Summary in Table 3. Soft Tissue Management Soft tissue abnormalities often occur before, during and after orthodontic treatment. The three main clinical situations associated with orthodontic therapy include gingival overgrowth,30-33 abnormal frenum34-35 and impacted teeth.36 Therefore surgical procedures such as gingivectomy, gingivoplasty, frenectomy and surgical exposure of impacted teeth are most commonly required to solve the above problems. According to previous studies, soft tissue lasers can replace the conventional scalpel to perform these operations with enhanced precision, better hemostatic ability, faster wound healing and less pain. Various soft tissue lasers that were used for intraoral soft tissue procedures were reported by case reports and uncontrolled clinical studies, among which the diode, CO2 and Nd:YAG, are the most dominant ones. Recently, Er:YAG and Er,Cr:YAG gained more attention in their application in soft tissue surgery.13,37-40 Gingival enlargement can affect orthodontic therapy from the beginning of bonding brackets to the final finishing stage. The etiology of gingival overgrowth can be divided into two categories; drug induced41 (phenytoin, ciclosporin and calcium channel blockers), and plaque accumulation with mechanical stimulation.4 Enlarged or irregularly contoured gingival margins tend to change the crown height and shape which in turn change the tooth proportion.43 Therefore, many clinicians find it difficult to accurately place the bracket on the clinical crown center. Sometimes it may not be possible to bond the brackets. During orthodontic treatment, teeth IJO „ VOL. 25 „ NO. 1 „ SPRING 2014 Table 3. Laser applications in orthodontics Category Application Type of Laser Advantage 51-52 Gingivectomy, gingivoplasty Soft tissue management Frenectomy Impacted tooth exposure Hard tissue management Enamel etching, bracket bonding *Nd:YAG, diode ; 43,46,48 ; CO2 Er:YAG, Er,Cr:YAGG53-56 *CO252,62-63, Er:YAG56,67-68; 56,64-66 Nd:YAG, diode *Er:YAG, Er,Cr:YAGG 56,73; CO272, Nd:YAG, diode40 Er:YAG, Er,Cr:YAGG 104-107 Less bleeding good hemostasis+; reduce 66,68,85 pain and swelling ; Precise incision#; less wound contraction and scar formation87; reduce healing period88-90 More acid resistant111; less microleakage112 CO2121-125, Nd:YAG126-127, Er:YAG128-129, Tm:YAG130 Avoid enamel fracture Low-level lasers141-144: GaAlAs, GaAlAs diode(twin laser) Reduce pain during tooth movement135-139 Tooth movement Low-level laser156-158 Increase the rate of tooth movement Bone healing after expansion Low-level laser181-185 Bracket debonding Pain control Miscellaneous PS. *most popular; + 39,43,47-48, 53,63,76-79; # Accelerate midpalatal suture opening and improve bone regeneration 182 40,43,74,80-81    disproportionality caused by gingival overgrowth makes it hard for clinicians  to correctly evaluate and judge the axial inclination of the teeth, leading to an  unsatisfactory finishing and compromised esthetic result.  Gingivectomy and gingivoplasty are required for the correction of problems  brought by gingival enlargement. CO2 laser has long been considered a favorite tool for oral surgery because its wavelength is well absorbed by soft tissue, since  it is mostly composed of water. In the 1980s, CO2 laser started to be used by  periodontists to perform gingivectomy on patients with drug-induced gingival  13,44-45 hyperplasia. Later, CO2 laser was widely used by dentists to remove excessive   gingival tissue for both functional and esthetic reasons.43,46,48,51-52 CO2 laser was  reported to have many benefits when used in orthodontic treatment. Advantages  include less bleeding and pain, less wound contraction and scarring, minimal  post-operative discomfort, reduced treatment time and fixed appliance could be fixed immediately after the surgical procedure.46-48 However, because CO2 laser energy is also well absorbed by hydroxyapatite (tooth enamel); there is a risk that temperature changes caused by laser energy delivery may compromise the dental pulp49 or result in etching or pitting of the enamel.50 Nd:YAG and diode lasers are more popular among clinicians in orthodontics and esthetic dentistry. They have the advantages that are similar to what CO2 laser has. They are more suitable for gingivoplasty because they are used in a direct contact mode which provides optimum control for esthetic surgery.51 It is also reported that they have improved hemostatic ability.52 Wavelengths of them are not well absorbed by dental hard tissues, therefore these lasers are safe to apply adjacent to teeth. Tony NF.,173 in a randomized trial, compared a group of patients receiving diode laser gingivectomy adjunct with non surgical periodontal treatment to a control group receiving only non surgical periodontal treatment after orthodontic treatment. The result of this research shows that laser gingivectomy using diode laser can quickly resolve gingival overgrowth and control gingival inflammation more effectively. Er:YAG and Er,Cr:YAGG lasers can work both on soft and hard tissues because both of their wavelengths are absorbed by water and hydroxyapatite. However, they are mostly used for caries removal and tooth preparation instead of soft tissue surgery due to their high affinity to enamel and relatively poor coagulation ability. Few reports have been published regarding the application 49 Figure 1A: A 12-year-old orthodontic patient with gingival hyperplasia. Figure 1B: Gingivectomy performed with erbium laser under local anesthesia. Figure 1C: One month after the treatment. Courtesy Dr. Fred S. Margolis. Figure 2: A - The upper labial frenum is extended to the palatal inter-incisal area causing upper diastema. )LJXUH% &7KHÀEHURSWLFRIGLRGHODVHUDSSOLHGRQ the labial area without local anesthesia under pai- free parameters. Figure 2D: Ten days post-treatment would healing assessed. Courtesy Dr Panagiotis Kafas. of Er:YAG and Er,Cr:YSGG lasers in intraoral soft tissue surgery.53-56 More interest has been directed to the Er,Cr:YSGG laser because it is an energy system specific to dentistry.57 In a recent study by Thongdee et al171 which assessed the effect of laser on the treatment of orthodontic-associated gingival overgrowth yielded promising results. Gingivectomy was carried out with the Er,Cr:YSGG laser. 22 patients were involved in this study, 168 tooth areas of gingival overgrowth were measured with minimum probing depth of 3mm. Immediately after surgery, the average probing depth was reduced to an average of 1mm. Post-operative follow up had been conducted with intervals at 2 weeks and 1, 2, 3, 6 and 12 months. After one year, the probing depth averaged 1.4mm. Hypertrophic labial frenum which remains inserted in the free gingival margin or on the palatine papillae causes a midline diastema.58 This type of low frenum can impede the insertion of temporary anchorage devices which are used for the intrusion of upper incisors in the case of gummy smile. A short lingual frenum may cause ankyloglossis, and lead to problems such as atypical swallow, disproportional lower jaw growth and a lower midline diastema.60-61 Frenectomy with lasers of different wavelengths has been reported by previous authors. CO2 laser is an ideal tool for intraoral surgery involving large amounts of soft tissue or dense fibrous tissues. It is a popular choice for frenectomy because of its high absorption by oral mucosal tissues, which contain 90% water. This laser works well in both soft and hard tissues.52 Comparing to the conventional scalpels, it causes less pain and swelling and has fewer postsurgical complications. It reduces postoperative bleeding and also promotes better healing.62-63 50 Nd:YAG and diode lasers are also used in frenectomy by many clinicians with cases reporting similar benefits as CO2 laser.56,64-66 Nevertheless, the application of Nd:YAG and diode lasers on labial frenectomy is limited.39,52 Their wavelengths are not well absorbed by dental hard tissues. They operate in a continuous or interruptedcontinuous wave mode which promotes high thermal side effects. Therefore, Nd:YAG and diode lasers cannot be used in direct contact with bone where one end of the labial frenum fibers are attached. But in lingual frenectomy, diode laser was reported to be useful due to its small size and low cost.28 Er:YAG laser is well absorbed by hard tissue and water and operates in a pulsed wave mode, promoting efficient ablation of hard tissue with minimal thermal effects. Since the Er:YAG laser has these characteristics, it should be used in conjunction with the Nd:YAG or diode laser for labial frenectomy. Er:YAG laser was also reported to induce an analgesic effect56 and require less or no local anesthesia.67-68 Impacted teeth can be aligned into position by orthodontic force following surgical exposure.69 Surgical exposure of impacted teeth is not uncommon in everyday orthodontic treatment.70 Laser techniques are especially beneficial when applied to perform surgical exposure of teeth which are either impacted at a mucogingival or bone level. Surgical exposure performed by laser is quick, clean and painless. A dry field without contamination of blood results after laser surgery, making it easier to directly bond a bracket on the exposed tooth.71 However, a incidence of subcutaneous emphysema following tooth exposure with laser was reported recently.172 Various laser wavelengths including erbium, diode, Nd:YAG and CO2 lasers were used to perform this procedure by previous studies.40,56,72 Erbium gained more interest from clinicians because it is able to cut both soft and hard tissues, thereby being able to expose teeth at bone level.73 It also has the effect of enamel etching which facilitates the bonding of orthodontic accessories immediately after surgery.56 The enamel etching effect of laser will be discussed in the next part of this article. Advantages and Disadvantages of Soft Tissue Lasers Main advantages of using lasers in soft tissue procedures had been summarized by previous articles:40,74-75 x Less bleeding during surgery and excellent postoperative hemostasis. This is confirmed by the majority of the previous papers, which are mainly case reports with some uncontrolled studies. It is considered to be one of the major advantages of lasers. A clear dry operation field can be achieved due to less bleeding.39,43,47-48,53,63,76-79 x Precise incision control because of less bleeding and a clear dry field during surgery. In contrast, bleeding usually compromises the accuracy of incisor when scalpel is used.40,43,74,80-81 x Reduced pain and swelling during and after laser surgery. Pain reduction is another major advantage. Several animal and randomized controlled clinical studies63,65,82-84 have compared the level of pain produced by laser and scalpel surgery. Most of the results indicated a dramatic reduction in post-operative pain with laser surgery. There were even reports of diode and erbium IJO „ VOL. 25 „ NO. 1 „ SPRING 2014 laser surgeries performed without local anesthesia.66,68,85 However Strauss et al86 revealed no statistically significant difference in the frequency and intensity of pain or the temporal distribution of pain after CO2 laser and scalpel biopsies. x Less wound contraction, scar formation and reduced healing period. The wound produced by laser surgery was reported to have little contraction, less collagen formation and fewer myofibroblasts.87 Other studies demonstrated shorter healing time and less scar formation with laser.88-90 Controversy arose after some researchers reported that wound repair was equivalent between laser and scalpel or electrosurgery in the later stages.91-93 Some studies showed that laser created more tissue damage than scalpel, with delayed wound healing.94-96 These studies included inconsistent parameters such as wavelength, frequency, time of exposure and power, which affect the response of tissues and duration of healing. Although there are a number of uses for soft tissue laser in orthodontics, it is not as well accepted as conventional techniques. One of the possible reasons may be lack of solid evidence to support the reported benefits of laser in soft tissue procedures. Is laser superior to the conventional scalpel? Can laser achieve same results? What are the long term effects of laser surgery? Answers to these questions are conflicting. The existing studies were mostly case reports, uncontrolled studies and animal histological studies. It is difficult to make a clear conclusion based on this data. Only a limited number of randomized controlled clinical studies were conducted on patients’ perception of laser compared to conventional techniques, and observing the short and long term results of laser surgery. In the future, more RCTs are indicated to provide solid support for laser. Enamel Etching and Bracket Bonding The bonding of brackets on the surface of a tooth requires the penetration of bonding material into the etched enamel. Enamel etched with 37% phosphoric acid achieves a high level of bonding strength.97 However, demineralization caused by acid etching leaves the enamel surface susceptible to acid attack in the oral environment, leaving the tooth prone to caries. In addition, the procedures required for acid etching are complicated and time consuming.98 Laser etching has become a Figure 3: Canine exposure performed with diode laser, Courtesy Dr Antonio Gracco. IJO „ VOL. 25 „ NO. 1 „ SPRING 2014 possible alternative to acid etching in the recent years. Etching with laser can produce microirregularities that are suitable for resin penetration.99 The shear bond strength of lased tooth is similar to those treated by acid etching.174 There are fewer steps in the etching procedure making it easier to handle. The acid resistant effect of laser is superior to conventional acid etching.100 Laser etching was introduced into orthodontic bonding in the 1990s. Initially, Nd:YAG laser was used to etch the enamel surface. The results of laser etching showed compromised bonding strength, longer bonding time and more discomfort than conventional acid etching. Nd:YAG laser was considered an ineffective pretreatment of bonding bracket to enamel.101-103 As the previous studies indicated, Nd:YAG laser is more suitable for soft tissue procedures. Application of Nd:YAG laser on dental hard tissue is ineffective and also has thermal side effect which can cause discomfort to the patient and is harmful to dental pulp.39,52 Er:YAG and Er,Cr:YAG lasers can be used for both soft and hard tissue procedures without creating a thermal side effect. After the introduction of Er:YAG and Er,Cr:YAG lasers, etching by laser has become more effective. The shear bond strength of tooth surface etched by Er,Cr:YAG laser is comparable to those prepared by acid and reaches an adequate level.104-107 However, some researchers disagree with the above findings.108,109 The conflicting findings are probably due to different power output and experimental design among different studies. Acid resistant effect of laser etching is superior to phosphoric acid. Aside from the bond strength, laser etching is useful when applied in immediate bonding on surgical exposed teeth without acid etching.56 The calcium-phosphate ratio of the enamel can be modified after laser irradiation leading to the formation of more stable and acid-proof compounds. It is similar to the effect of fluoride on enamel.100,110 Some studies have proven that enamel prepared by laser irradiation is more acid resistant than acid-etching. Kim, et al111 reported an in vitro study, where enamel was treated by Er:YAG laser and found to be more resistant to acid, than that treated by conventional acid etching. Hamamci, et al.,112 found less microleakage of brackets bonded by etching with Er:YAG and Er, Cr:YAG lasers than acid etching. Noel, et al.,113 studied the acid resistant effect induced by Argon laser. Even though laser etching has many advantages over conventional methods, it is not yet a routine procedure adopted in orthodontic bonding. Compared to acid etching, the unpredictable bonding results of laser are probably one of the reasons that has slowed the acceptance of laser etching in orthodontics. Bracket Debonding A major concern of brackets debonding in orthodontics is the risk of enamel damage.114-117 The occurrence of enamel fracture is relatively higher with ceramic brackets because of the high bond strength.118-119 In order to reduce the risk of enamel fracture, a debonding technique that requires less force is needed. Laser irradiation can soften the composite resin by heating the brackets, help reducing the force required for debonding. The mechanism of laser debonding includes: thermal softening, thermal ablation or photoablation. Thermal softening occurs 51 when laser with low power density irradiates the brackets until the resin softens. The brackets will slide off the tooth surface with gravity. Thermal ablation and photoablation vaporize the resin when its temperature is raised quickly by high power dentity lasers. The resulting bracket can be blown off the tooth surface.120,131 Different types of lasers (CO2,121-125 Nd:YAG,126-127 Er:YAG,128-129 Tm:YAG,130) brackets (monocrystalline and polycrystalline) and adhesive materials (Methyl Methacrylate MMA and Bisphenol A-Glycidyl Methacrylate Bis-GMA) were used to study the effect of laser in debonding brackets debonding. Most of the studies showed the benefits of laser debonding; more time efficient, significantly reduced debonding force and enamel damage. However, potential safety concerns have also been reported. The increase of pulp temperature and potential hazard to tooth vitality resulting from laser heating is the main concern of clinicians. According to Zach and Cohen,132, the pulp can only tolerate an increase of 5.5oC in intrapulpal temperature. Overheating will harm the pulpal tissue. Most of the previous studies had been carried out to evaluate the thermal effect of laser on pulp temperature and determine factors that cause temperature rise. Key factors include types of lasers and brackets, duration of heating, energy level and methods.122, 126, 129 It was also reported that different resins have varied reactions against certain types of lasers.133 The conclusions of these studies indicate that the temperature change will remain within the safety threshold if the appropriate laser can be chosen and the application duration and method can be precisely controlled. Pain Control Tooth movement is often associated with pain, especially within the first 7 days after force applied.134 Low-level laser therapy (LLLT) has been shown to have analgesic effect in a variety of therapeutic procedures.135-139 LLLT is a new technique and is defined as the laser treatment in which the energy output is low enough that the temperature of the applied area will not rise above body temperature.138 The mechanism of pain relief by LLLT is not yet well established. The analgesic effect is believed to be attributed to its anti-inflammatory and neuronal effect.140 Table 4. Laser Safety Hazard - Causes and Symptoms Protection Eye Damage - Cornea, retinal GDPDJHDTXHRXVÁDUH cataract formation 164-165 Choose proper eye wear for the correct wavelength of laser. Skin hazard - Dry skin blistering and burning164 Fully covered, no skin exposure167 Laser Plume - Emissions of High volume evacuation and masks noxious plume containing toxic FDQÀOWHUXSWRX164 checmicals and debris. Cause coughing, nasal congestion nausea and vomiting.166 Fire hazard - Heat generated by laser irritation contact with combustible material will cause ÀUH 52 No combustible or explosive material in the nominal hazardous zone; avoiding alcohol-based anesthetics and gauze; XVHZHWRUÀUHUHWDUGDQWPDWHULDO122 and O2 can only be used in a close circuit delivery sytem; perform the operation near a water source.164-165 Pain relief produced by LLLT in orthodontic treatment has been investigated by few researchers. Studies were carried out to evaluate and compare the pain perception of patients with or without laser irradiation at different times. Most of the studies showed positive results and concluded that LLLT helped reduce pain in orthodontic treatment within the first 5 or 7 days, especially within the first 2 to 3 days.141-145,176 Only few studies found insignificant differences of pain perception between patients with and without laser irradiation.146 In the previous studies, different treatment protocols and lasers were used which might lead to differing results. Some investigated pain relief with CO2 laser after the first wire was placed,141 while others studied pain relief after separators placement with gallium-aluminumarsenium and CO2 lasers.142,145-146,175 Further investigations are needed to study the analgesic effect of LLLT. Tooth Movement The “biostimulating effect” of LLLT has been studied since 1971. LLLT was reported to be able to stimulate fibroblast and chondrocyte proliferation, collagen synthesis, nerve regeneration, wound healing, and bone regeneration.147-153 It was suggested LLLT can accelerate bone remodeling and cause changes in alveolar bone during induced tooth movement. Changes were found in the number and proliferation of osteoblasts and osteoclasts and collagen deposition in both pressure and tension sites.154-155 Based on the previous basic science studies, LLLT has been demonstrated to increase the rate of tooth movement during orthodontic therapy. Animal and clinical studies were conducted to investigate this effect. Tooth movement with LLLT was found to be faster in some studies.156-158,177 Cruz et al156 showed an increase of 34% of canine retraction within 60 days with fixed appliance. The group irradiated by laser moved 4.39mm comparing to the control group which moved 3.30mm. Kawasaki157 showed a 1.3 fold more movement of rat teeth irradiated by laser after 12 days. However some studies found insignificant differences159-160 or even diminished tooth movement.161 According to some authors, if a laser dose is too low it will not cause a biostimulating effect, whilst a higher dose can inhibit tooth movement.162 Bone Regeneration after Expansion Rapid maxillary expansion is commonly used in orthodontic therapy.177-179 The separation of mid-palatal suture with an increased bone mass in the center can change the maxillary arch shape dramatically. Usually following expansion a retention period of 3 to 4 months is needed for bone regeneration and remodeling.180 Low-level lasers can accelerate the opening of the mid-palatal suture and improve bone regeneration during and after rapid maxillary expansion according to several studies.181-185 It can be helpful in reducing the retention time and preventing relapse. However, further study is required to closely investigate this effect. Dental Laser Safety Safety issues are a major concerns of laser applications in dentistry. Laser injuries are reported every year around the world. Laser hazards vary, depending on the type and use of laser. According to guidelines provided by American National Standards Institute Z136.1-2007, there are four classifications IJO „ VOL. 25 „ NO. 1 „ SPRING 2014 (ranging from 1 to 4) of lasers based on the potential of causing biological damage to the eyes or skin by the primary or reflected beam. Lasers used in dentistry mainly fall into classes 3B and 4. Class 3B represents a maximum output of 0.5W which can cause eye damage. Class 4 includes all high-powered lasers that are used in dentistry and oral maxillofacial surgery. There is no upper output limit, so lasers in this class will cause different injuries.163 All staff in clinics where lasers are used must receive appropriate safety training. Summary in Table 4. Eye Damage The cornea mainly consists of water, and absorbs the wavelength of CO2, erbium and holmium lasers. Thus these lasers can burn the cornea. They can also affect aqueous, vitreous humor and lens of the eye, resulting in aqueous flare and cataract formation. Lasers such as Nd:YAG, diode and argon are highly absorbed by pigment, and have greater penetration into tissue. Retinal damage caused by these lasers can lead to blindness.164-165 Eye protection is crucial for both the clinical staff and the patient. There is specific eye wear for different wavelengths available in the market. No goggle can provide protection against all wavelengths ranging from 400nm to 10600nm. When choosing eye goggles, be aware of the optical density and wavelengths printed on the goggles. It is important that eye wear is chosen for the correct wavelength of laser.165 1993, “a LSO is defined as a person who is trained and certified to take responsibility and have authority to monitor and enforce the control of laser hazards and to effect the knowledgeable evaluation and control of laser hazards.” A LSO must be present when using class 3B and class 4 lasers.165 Conclusion Laser therapy has influenced the orthodontic treatment in many aspects. The advantages of laser over conventional instruments were reported, which include improved hemostasis, reduced swelling and pain, faster wound healing and precise incision control. Other functions of laser have potential benefits for orthodontic treatment such as enamel etching, bracket debonding, pain control and accelerating tooth movement. Today, laser begins to attract the attention of more clinicians. However, an evidence-based approach of using laser in orthodontic treatment must be developed. More solid evidence must be provided to support the advantages of laser. Also, the potential hazards of laser should be taken into consideration and strict safety procedures must be carried out during the application of laser therapy. References 1. 2. 3. Skin Hazard Skin can be penetrated at wavelengths from 300nm to 3000nm. Laser-induced skin damaged includes excessively dry skin, blistering and burning.164 Clinical staff and patient should be fully covered during the laser therapy.167 4. 5. 6. Laser Plume The emission of noxious plume by the laser vaporization of tissue can obscure the surgical field and contains toxic chemicals and debris including bacterial spores, cancer cells and viruses (Human Papillomavirus HPV, Human Immunodeficiency Virus HIV and herpes). Inhalation of the plume can cause symptoms such as coughing, nasal congestion, nausea and vomiting. Apart from the regular dental protective equipment, high volume evacuation and masks that can filter up to 0.1u should be added as extra protection during laser therapy.164,166 9. 7. 8. 10. 11. 12. 13. 14. 15. Fire Hazard Heat generated by the laser beam may cause a fire if in contact with combustible materials or gas. Some precautions must be taken during laser therapy. Any combustible or explosive materials should not be placed in the nominal hazardous zone. Avoiding using any alcohol-based anesthetics and gauze. Use wet or fire retardant material only. Gas such as nitrogen dioxide and oxygen can only be used by dentist in a close circuit delivery system with high-speed evacuation system (ANSI Z136.3, 2005). Perform the operation near a water source.164-165 Laser Safety Officer A laser safety officer, LSO, is needed by every dental practice with laser. According to the ANSI Z136.1 standard, IJO „ VOL. 25 „ NO. 1 „ SPRING 2014 16. 17. 18. 19. 20. 21. 22. 23. 24. Gould RG. 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Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;109:38-46. 184. Santiago VC, Piram A, Fuziy A.Effect of soft laser in bone repair after expansion of the midpalatal suture in dogs. Am J Orthod Dentofacial Orthop. 2012 Nov;142(5):615-24. 185. Cepera F, Torres FC, Scanavini MA, Paranhos LR, Capelozza Filho L, Cardoso MA, Siqueira DC, Siqueira DF.Effect of a low-level laser on bone regeneration after rapid maxillary expansion. Am J Orthod Dentofacial Orthop. 2012 Apr;141(4):444-50. Dr. Yunlong Kang is a lecturer in Orthodontics Discipline of Orthodontics, School of Dentistry, James Cook University, Cairns, Queensland, Australia. He obtained his Advanced Diploma in Orthodontics from the University of Hong Kong and his Master of Stomatology in Orthodontics from the West China College of Stomatology, China. Dr. Bakr Rabie is a Professor of Orthodontics in the Faculty of Dentistry at The University of Hong Kong. He obtained his Certificate of Proficiency in Orthodontics, Master of Science, and PhD from Northwestern University, USA. Dr. Ricky Wong is a honorary associate professor in Orthodontics at the University of Hong Kong. He obtained his Master of Orthodontics and PhD from the University of Hong Kong. IJO „ VOL. 25 „ NO. 1 „ SPRING 2014