10 SCIENTIFIC REVIEW Journal of | 2014 Vol. 22, No. 1 store andtransfer energy to thelasergas. discharge process,electrical coolthe lasergas, and and ,usedto increase pressure, stabilize the addition ofothergasesto thelasertube was ableto achieve several Watts ofpower withthe delivered milliwattsofpower, butsoonthereafter he dioxide10.6-µm carbon gaslaser. Kumar N.Patel developed ofBellLaboratories thefirst developed theworld’s firstlaser(aruby laser),C. 1964,fourIn years after Theodore H.Maiman CO wavelength, 9.3 tissuesurgicalsoft . The difference isthenew that many considered to bethegoldstandard of heretoforenot experienced usingCO toenamelanddentincutting speed andefficiency to thisspecific wavelength. The 9.3-µmlaserbrings than 27years ofscientificdental research devoted laser canbeviewed astheculminationofmore provided. compared. Finally, withandpatientresponse ofclinicianexperience to laserinstrumentis thisnew areport clinical environment ispresented. lasersare clinicalcapabilitiesofboththe9.3-µmanderbium then Selected wavelength implementationofthisnew considerationsthatledtoof laserdevice thefirstpractical for the hard tissueswhileitretains theexcellent tissuesurgical soft abilitiesofconventional CO wavelength withuniquehydroxyapatite for characteristics optimumenergy absorption transfer into . how dioxide useofisotopic describes carbon gasasthelaser’s the9.3-µm mediumfurnishes It active to thedevelopment ofthislatest innovation whilereferencing itsroots inthe10.6-µm soft-tissue-only 2014; J Laser Dent Private Practice, Albany, New York, USA Kotlow,Larry DDS Private Practice, Haven, USA Connecticut, North Fantarella,David DMD Experiences Clinical Early and Development 9.3- The Fantarella andKotlow BACKGROUND SUMMARY 2 While new toWhile new clinicaldentistry, the9.3-µmCO summarizes someofthefindingsscientific researchThis article involving the9.3-µmlaserthatled is known for. isknown 22(1):10-27 µm µ vs. thetraditional10.6 m CO m 2 2 His initialsystem His Dental Laser: Technical Laser: Dental 2 ,

a medium 3 – 4 µm 1

that 2

well orbetter thanscalpelcontrols were fashioned.” dioxide incisionswhichhealas laser…clean skin dry year, Yahr andStrullystated: “Using anitrogen carbon- recognized itspotential surgical utility.” York, surgical withaCO experiments started senior surgical resident atMontefiore Hospitalin New developed. As Polanyi noted, in1966, “Early Yahr, a possible surgical dioxide applications ofthecarbon surgery. and dentistry, ophthalmology, and cardiovascular urology, oralsurgery generalsurgery, orthopedics, dermatology, plasticsurgery, gastroenterology, medicine, neurosurgery,pulmonary aestheticsurgery, applications are found ingynecology, otolaryngology, heat treating, anddrilling. cladding, marking, include cuttingofmetalsandnonmetals, welding, most biologic tissues. byin medicine, absorption withitsnear-complete the mostwidelyusedlasersinindustry robustness, themsomeof andreliability andmake µm wavelength for are theirversatility, known Today, dioxide carbon lasersattheirnative 10.6- DIOXIDE LASER DIOXIDE CARBON THE IN INTEREST BIOMEDICAL Not long after Patel’sNot longafter achievement, interest inthe 7 6 Typical applications industrial 2 at

10.6 µm. 8 5 That same That andalso A summary Asummary 2 5 laserand Surgical 9 SCIENTIFIC REVIEW

Then in 1970, Polanyi and colleagues wrote: they are in a gaseous state. The energies related to A renewed interest in has taken molecular vibrations and rotations are quantized just

place since the introduction of the CO2 laser to the like the electronic energy also in atomic-based lasers. medical field. The major characteristics of this laser Transitions between vibrational energy levels emit that make it interesting for surgical applications with wavelengths in the region, and are that it is a high power continuously operating transitions between rotational energy levels emit laser and that its wavelength of operation is in the photons in the microwave region. infra-red at 10.6 µm, a wavelength that is almost 10 completely absorbed by most biological tissues. The CO2 laser is based on the vibrational and

rotational transitions of the CO2 molecule used to Strong and Jako reported the first clinical use of a lase. This molecule consists of two oxygen atoms laser in otolaryngology in 1972.11 covalently bonded to a central carbon atom. In

From there, numerous accounts of the intraoral use diatomic molecules such as O2, N2, or CO, the of the 10.6-µm laser were published in the medical individual atoms are bound by a molecular binding literature.12-24 force, and when excited, the two nuclei will vibrate much like two masses connected by a spring. Although carbon dioxide is a triatomic molecule, CHARACTERISTICS OF THE 9.3-µm it behaves similarly to a simple diatomic molecule CO2 LASER because its structure is linear. Such a linear triatomic molecule has three normal modes of vibration, Most reports of the surgical use of the carbon depicted as the asymmetric stretch mode, the dioxide laser focused on the 10.6-µm wavelength. bending mode, and the symmetric stretch mode 25 Migliore points out that while CO2 lasers can (Figure 1). produce power at any wavelength between 9 and 11 µm, most units operate at 10.6 µm because that transition has the greatest gain (or degree of amplification). He continues: “There are several ways to force a CO2 laser to operate at other than 10.6 µm: Some manufacturers use a Littrow grating [a type of or reflective surface with fine lines used to produce optical spectra by diffraction], which allows complete tunability through the CO2 wavelength range, while others replace the normal 12 16 12 18 5 C O2 molecule with isotopic C O2…”

12 18 The use of isotopic C O2 as a laser gas to produce the 9.3 µm wavelength is fundamentally more efficient and less disruptive to the laser manufacturing process than the use of a Littrow grating. CO2 lasers are molecular lasers, as the lasing

medium is carbon dioxide, a molecule. Molecular 2014 Vol. 22, No. 1 | lasers function differently from atomic lasers, like Figure 1: Vibrational states of the carbon dioxide neodymium or erbium, because they have vibrational molecule. Adapted from Kverno and Nolen25 and rotational energies as well as electronic energy. These molecular vibrations occur because the relative Each of these normal modes of vibration for the orientations and positions of the atomic nuclei CO2 molecule is associated with a characteristic are not absolutely fixed within the molecule. The frequency of vibration (w) as well as a ladder of molecular rotations occur because the individual allowed energy levels. To manufacture a 9.3-µm CO2 Journal of Laser Dentistry molecules are free to rotate and spin in space since laser versus a 10.6-µm CO2 laser, the gas inside the Fantarella and Kotlow 11 12 SCIENTIFIC REVIEW Journal of Laser Dentistry | 2014 Vol. 22, No. 1 molecule, Ca laser, thathassignificance acharacteristic for operative dentistry. ofhydroxyapatite,characteristics “HA” mineralcomponentofhard (theprincipal tissue), thanthe10.6- The 9.3-µmCO platform leadsto highervolume, more reliability, andincreased repeatability. anda construction, “special” customized laserisnotrequired. ononebase Standardization inmanufacturing 9.3- changing thecompositionofCO produces the9.3- mode, stretch andthesymmetric mode, are from distinct thevibrationalmodesof and therefore stretch astheasymmetric itsthree modesofvibration,described mode, normal thebending energy levelisreferredtoasisotopicCO andstable.both are naturallyoccurring and becausethe most abundantstableisotope ofoxygen (99.762%naturalabundance)itisnotusuallyreferred atasanisotope, laser ischangedfrom with amixture Fantarella andKotlow Figure 2: µm wavelength,allother hydroxyapatite by thegreen line. Adapted from Featherstone andFried Absorption curves ofvarious Absorptioncurves tissuecomponents. Absorptionofwater isdepictedby theblueline, and 10 (PO 2 laser wavelength is of particular interest laserwavelength becauseitbetter matches isofparticular theabsorption 18 µm 4 ) O atom islessabundant,itcommonlyreferred to asanoxygen isotope, even though 6 (OH) wavelength ofenergy whilethe 2 , itsvibrationalenergy isinthefarinfrared andisnarrow band(Figure 2). aspects ofthelasercanremainaspects identicalto thestandard productionCO 2 12 lasergasinsidetheresonator isallthatrequired to produce the C 26 16 2 Consequently gas. neutrons Having extra two O 2 moleculesto with amixture 16 O produces the10.6- 12 C 18 O 2 gasusedinCO 27-29 BecauseHAisaratherlarge andcomplex 12 18 30 C O hasadifferent weight than andVogel andVenugopalan 18 µm wavelengt O 2 2 lasersto produce the9.3- molecules. Because 16 O. Hencetheheavier h. Consequently, 16 2 µm O isthe laser 31 16 µm

18 O, O, O

SCIENTIFIC REVIEW

The absorption of HA is shown with the green curve HARD TISSUE ABLATION with its peak absorption at 9.6 µm and drops off In 1993 Forrer et al. investigated the mechanism of rapidly between 9.2 µm to 10 µm.30 Determining bone ablation using 9.3, 9.6, 10.3, and 10.6 micron CO2 the wavelength where peak energy is transmitted lasers with different pulse parameters on samples of into the enamel is not strictly a function of HA’s pig rib bone. Among other findings, they determined absorption; reflection (scattering) and transmittance that the ablation threshold at 9.3 and 9.6 µm is lower also have to be considered. For peak absorption into than at 10.3 and 10.6 µm, possibly due to the higher the enamel, the light energy has to couple into the absorption of the mineral component in the bone by (not reflect or scatter at the surface), and then the 9.3 and 9.6 µm wavelengths.32 be absorbed and not transmitted. HA’s absorption peak is at 9.6 µm but HA’s reflection also peaks at Fried and colleagues noted in 1994 that the more 9.6 µm. While the absorption of HA is lower at 9.3 efficient absorption of the 9.3 and 9.6 µm laser µm, the reflection is lower, too. Transmittance at 9.3 wavelengths (vs. 10.3 and 10.6 µm) in human and to 9.6 µm is negligible. When one considers both bovine enamel samples “may be more advantageous reflection and absorption, the total energy transferred for fusing enamel surfaces while minimizing the into HA is the greatest at 9.3 µm where the reflection thermal loading of the pulp chamber.”33 coefficient is low and the absorption coefficient is still fairly high. The importance of maximum absorption In 1995 Wigdor and associates examined the use of is understood when trying to achieve the peak the CO2 laser for intraoral soft tissue surgery, reviewed energy transfer from the incident laser light into the the optical properties of hard dental tissues, and HA. Maximum energy transfer means the greatest surveyed the interaction of different lasers (including possible opportunity for the rapid ablation and 34 the CO2 laser) with hard tissue. vaporization of enamel and dentin. Also in 1995 a group of researchers from the Eastman Dental Center in Rochester, New York, the University SCIENTIFIC INVESTIGATION OF of Rochester, and the University of California – San THE 9.3-µm LASER Francisco (UCSF) reported results of their scanning WAVELENGTH IN DENTISTRY microscopic study of the effects of a tunable CO2 laser on extracted bovine and human enamel. More than 90 published reports have appeared in Specimens were irradiated at various fluences (laser the dental literature since 1986 that describe the basic energies per unit area) without water spray. At 10.6- science, tissue interactions, mechanisms of action, µm, no observable surface melting at low fluences was noted, but “distinct surface cracks associated with and operational parameters of the 9.3-µm CO2 laser wavelength on oral hard and soft tissue. The following the thermal stress created by the heat of the laser summarizes some of the key findings that support the beam” were evident; higher fluences were required safe and effective use of this laser. While this paper to melt the enamel and fuse the crystals. In contrast, concentrates on the tissue interactions with the 9.3- the 9.3-µm produced uniform surface melting at low fluences; enamel crystals were fused to varying µm wavelength, selected investigations of other CO2 wavelengths (including 9.5, 9.6, 10.3, and 10.6 µm) of degrees and droplets of recondensed enamel mineral historical interest are briefly examined to underscore surrounded the area of irradiation. The authors 2014 Vol. 22, No. 1 the differences in their tissue interactions and to conclude that the commonly available 10.6-µm | wavelength “behaves quite differently from the more provide a sense of the scope of research evident in 35 the literature. efficiently absorbed” 9.3-µm wavelength. Dentin surface and subsurface effects were the focus of a joint research investigation conducted by Showa University School of Dentistry in Tokyo and the University of California, Irvine, California and reported in 2000. Extracted human teeth were Journal of Laser Dentistry Fantarella and Kotlow 13 14 SCIENTIFIC REVIEW Journal of Laser Dentistry | 2014 Vol. 22, No. 1 that laserneedsto dimensions bescannedintwo “the the laserbeamisscannedalong oneaxis. They report ratiowhen depthandaspect crater reaches acertain Their studyshowed thattheablationstallsas to increased damage. heat accumulation andthermal water present; leads stalling may occurwhichinturn crater morphology, geometry, andtheamount of by theincidentlaserfluence, depthofcut,enamel bya9.3-µmand efficiency CO andFried that enamelablationrate Darling observed of water thatisneededto offset heataccumulation.” ashigh,whichincreasessystems istwice thevolume residual energy remaining inthetooth for thoselaser and Er:YAG laserpulses;hence, andEr:YSGG “the for conventionalof 50%to 60%observed 10.6-µm and dentin,respectively. This contrastswiththelevels 20% oftheenergy remains inthetooth for enamel intensities forirradiation efficientablation:34%and tooth eachablative after pulseattheoptimal also measured theresidual heatremaining inthe 30 to 40µm perpulsefor dentin. The investigators fromvaried 9to 20µmperpulsefor enamelandfrom water spray isused. The singlepulseablationrate damageifalow-volumerate with minimal thermal hard clinical dentaltissuesefficientlyand atapractical with apulsedurationof15to 20µswasableto ablate found thatthelaseroperatingathighrepetition rates scanning stage, withandwithoutwater spray. They molars andpremolars usingacomputer-controlled unerupted human produced ofextracted, insections ablation ofenamelanddentin.Lateral incisionswere at highrepetition rate (from for 10to the 400Hz) 2006,Fan,In Bell, andFried useda9.3-µmCO byconducted thegroup. inaprevious study laser-irradiated dentinsurfaces to theapproximate 60-µmdepthseenin10.6-µm (lessthanapproximately 20µm),comparedsurface energyirradiated seemedto beconcentrated atthe photographs, thatmostofthe theauthorsobserved layer usingCLSM.Judging fromthe subsurface CLSM Smallcrackswere orcracking. no cratering seenin some molten but andresolidified dentinparticles, scanning microscopy (CLSM). SEMimagesrevealed electron microscopy (SEM)andconfocal laser by changeswere scanning Morphological observed set atdifferent parameters, withoutwater spray. withonepulseofa9.3-µmCOirradiated Fantarella andKotlow 36 2 lasercanbeaffected 2 laser 2 laser 37 be sufficient to have thedesired butno effect, more handpiece (9of15samples). (2of15samples)thanby thehigh-speed irradiation each treatment. Fewer crackswere produced by laser humanmolarsandincisors, 15samplesforextracted prepared theeffect onsections fromobserve high-speed handpiece. Water spray wasusedto a mechanicallyscanned9.3-µmlaseranddental with mechanical damageto drilling enamelafter 2010Maung, Lee,In andFried compared the injury.” accumulation thatmay causepulpaloverheating and efficient ablation,but toalso avoid excessive heat if highrepetition rates are used, notonlyto ensure precise tissueablation. depth atatime, to achieve thefinestandmost rate pulsingto rapidlyremove tissueoneabsorption relaxationthermal times andwithahighrepetition ablation level, withpulsewidthsapproaching the Therefore pulseenergies shouldbeabove the 1). depth (Table coefficient,thesmallerabsorption the absorption relaxationwith thetissuethermal time. The higher wavelength lasershouldbematched approximately prevention thepulsedurationofappropriate without stalling. For optimumablationorcaries be delivered oftimeto ablate inanoptimumperiod pulsedurationsothatsufficientenergycorrect can to beabove theablationthreshold, butalsothe scattering, energyto thecorrect avoid unnecessary wavelength theright deposition nearthesurface, ishighenoughto containtheenergyabsorption one mustchoosetheproper wavelength, sothe Therefore, for theablationofenamelordentin stress, orpulpaldamageanddeathto thetissue. by surroundingabsorbed tissuecausingthermal energy canbe becauseextraneous than necessary FLUENCE DEPTH ABSORPTION AND The amountofenergy delivered to atissuemust 38 30 39 SCIENTIFIC REVIEW

Table 1: Comparison of CO2 and Erbium Enamel Properties (Derived from Featherstone and Fried30)

Absorption Absorption Depth Thermal Scattering Coefficient, (1/e*), µm Relaxation Coefficient, -1 -1 Wavelength µα, cm Time, µs µs, cm Near-Infrared 2.78 µm Er:YSGG 480 25 220 ~0 2.94 µm Er:YAG 800 12 90 ~0 Mid-Infrared

9.3 µm CO2 5,500 2 2 ~0

9.6 µm CO2 8,000 1 1 ~0

10.3 µm CO2 1,125 9 40 ~0

10.6 µm CO2 825 12 90 ~0

* Absorption depth is where the intensity of the surface light has been reduced 1/e (base of the natural log) = 63% reduction

CARIES REMOVAL In 1998 Takahashi, Kimura, and Matsumoto from the Showa University School of Dentistry in Tokyo examined the effects of a 9.3-µm CO2 laser on extracted human teeth. Their scanning electron microscopic examination of tooth surfaces showed that sound and carious hard tissues, smear layer, and debris could be removed by laser irradiation. Moreover, the effects were dependent on the level of laser energy: “Both sound and carious dentin were shown to be more sensitive to laser irradiation than enamel and the carious enamel and dentin reacted with more sensitivity … than did sound enamel and dentin.”40

The characteristic that the 9.3-µm wavelength is more efficiently absorbed by dental hard tissue than the conventional 10.6-µm CO2 wavelength was exploited in a study of successful caries removal from extracted human molars with artificially created caries-like lesions. The researchers, from Okayama University in Japan (Konishi) and UCSF (Fried, Staninec, and Featherstone), used a computer-controlled motion control system to scan the laser beam over the target tooth surface.41

The notion of preferential removal of carious lesions was examined by another group of UCSF investigators who used advanced imaging technologies (two-dimension near-infrared imaging and polarization-sensitive optical coherence tomography) to guide 9.3-µm CO2 . Their pilot system selectively removed artificial demineralized lesions on extracted bovine incisors, while sound enamel was conserved with minimal damage to sound tissue. They noted that the caries removal rate varied with the severity of demineralization; their findings “indicate the challenges involved in the selective removal of natural caries including overcoming the highly variable topography of the occlusal pits and fissures, the highly variable organic/mineral ratio in 2014 Vol. 22, No. 1 natural lesions, and the more complicated lesion structure.”42 | Journal of Laser Dentistry Fantarella and Kotlow 15 16 SCIENTIFIC REVIEW Journal of Laser Dentistry | 2014 Vol. 22, No. 1 that etching following ablationisbeneficial. They higher thanthenegative control, whichindicates groups irradiated and water-cooled were significantly bond strengths ofdentinto composite for theetched conditions. The researchers noted thatrespective irradiation for bothenamelanddentinundercertain revealed meanbondstrengths approaching 30MPa dentin and18.1N(s.d. =2.7)for control. Sheartests mechanical strengths of18.2N(s.d. =4.6)for ablated preparations. Four-point bendtests yieldedmean wet sandpaperto simulate320-grit conventional test andcompared to control samplesprepared with viathefour-point wasdetermined bend surfaces The mechanicalstrength oflaser-ablated dentin were by neitherirradiated thelasernoracid-etched. acid.with 35%phosphoric Negative control groups control groups were by notirradiated laserbutetched Positive Minn.). Minneapolis, composite (3M-ESPE, test. The bondingresin wasSingleBondwithZ-250 shear ablation acidetching usingthesingle-plane laser scanningparameters withandwithoutpost- forlaser-treated various enamelanddentinsurfaces measured theadhesionstrength of9.3-µmCO asubsequentstudy,In Nguyen etching following ablationisabenefit. than thenegative control whichindicates that groupscooled irradiated were significantly higher of dentinto composite for theetched andwater- researchers. Moreover, therespective bond strengths a clinicallyusefulbondstrength, asnoted by the ablation;thisfigure after acid-etched represents exceeded 20MPa for thatwere laser-treated surfaces laser-treated blockswasnotetched. Bondstrengths acid,with 35%phosphoric andtheothergroup of acid. Onegroup oflaser-treated blockswasetched control group wasonlyetched with35%phosphoric noretched.was neitherirradiated The positive Minn.). (3M, Minneapolis, The negative control group was SingleBondalongwiththeZ-250 composite the bondingagentto dentin. The bondingmaterial test wasusedto theadhesive determine strength of humanmolars. noncarious extracted The shearbond blockswere Dentin prepareddentin surfaces. from post-ablation acidetching to conventionally prepared treatment witha9.3-µmCO the shearbondstrength ofdentinto composite after Fantarella andKotlow BOND STRENGTH In 2009agroupIn ofUCSFresearchers compared 2 laser, withandwithout et al. from UCSF 43 2

absorbed laserlight(e.g.,absorbed 9.3µm)tends to localize revealed, amongother things, thattheuseofhighly without waterirradiated spray. Their human andbovine enamelandhumandentinwere tissues to different CO responseexamination ofthethermal ofhard dental Center inRochester, New York collaborated onan ofRochester,University andtheEastmanDental materials. major reduction ofadhesive strength to restorative reduction inthetissue’s mechanicalstrength ora high pulserepetition rates thatproduce nosignificant ablated withamechanicallyscannedCO concluded thatdentalhard tissuescanberapidly complex whenusedasahard-tissue tool…” drilling “induced onlyminimalresponse ofthedentine-pulp results in2005suggested thatthe laser reported pulsed 9.6-µmCO human third usinga molarsscheduledfor extraction asimilarstudyon Nair andassociates performed Walsh similarfindingsinbeagledogs. reported the dentalhandpiece. effect onthedentalpulpaltissuewhencompared to The researchers found thatthelaserhadanequal limited effect ontheodontoblasts andpulpaltissue. thelaserhadvery then examinedhistologically; immediately and14days after treatment after and reasons.or periodontal Teeth were extracted forhuman teeth scheduledfor orthodontic extraction with aconventional dentalhandpieceonthepulpsof of aprototype pulsedCO 2000 In Walsh andcolleaguescompared theeffect that endangersthepulp.” µm CO treatment” and more commonlyemployed 10.6- “The to therequired temperaturesurface for asuccessful damage, sincelessenergy isrequired to heatthe thermal significantly decreasesrisk ofsubsurface the They report: depth oftheabsorption “Minimizing the heatingto athinlayer atthesamplesurface. COLLATERAL DAMAGE COLLATERAL OF LACK PULPAL SAFETY, TEMPERATURE, In 1996agroupIn ofinvestigators from UCSF, the 2 laserwavelength leadsto cumulative heating 44 2 laser. histological Their preliminary 46 2 laserwavelengths. of Sections Two years later, Wigdor and 45 2 laseremittingat9.6µm in vitro 2 laserat results 47 48 SCIENTIFIC REVIEW

In 2006 another group of UCSF investigators used to visualize thermal damage) to look for changes in a 9.3-µm CO2 laser with and without water spray birefringence of the collagen. No thermal changes in on sections of dentin from human unerupted third the dentin samples were seen in the polarized light molars to determine extent of thermal damage after micrograph, indicating the zone of thermal damage irradiation at various laser fluences and repetition is less than 10 µm. The investigators conclude: “These rates. They found that high repetition rates were results suggest that dental hard tissues can be rapidly feasible with very little thermal damage in both ablated with a mechanically scanned CO2 laser at wet and dry conditions: “Polarized Light Microscopy high pulse repetition rates without excessive heat showed thermal damage zones of less than 22-μm for accumulation in the tooth or peripheral thermal dry dentin and less than 16-μm for wet dentin for all damage.”44 repetition rates less than 400-Hz. These experiments were performed with a fluence of 80-J/cm2 and the Another team of UCSF investigators conducted a results were compared to 40-J/cm2 and 20-J/cm2. The clinical study involving 29 patients requiring removal 2 2 thermal damage zones at 40-J/cm and 20-J/cm were of third molars. A pulsed 9.3-µm CO2 laser was used both smaller than those found at 80-J/cm2 at 400-Hz.” to irradiate the occlusal surfaces of the teeth prior to The authors indicate there was negligible charring of extraction for 1 minute at 50 Hz and 2 minutes at 25 dentin for laser pulses of less than 10-µs duration, and Hz with a fluence of 20 J/cm2 and 12-15 mJ/pulse, no mechanical damage was observed for any of the with water spray, for a total number of 3,000 pulses laser irradiation parameters.49 per tooth. Seventeen teeth treated at 50 Hz were extracted within 72 hours, and 11 were extracted In 2008, Assa, Meyer, and Fried reported their use after 3 months. At 25 Hz, 7 teeth were extracted at of a pulsed 9.3-µm with an 72 hours and 10 teeth after 3 months. These time integrated/programmable optical scanner to scan periods were selected to detect reversible pulpal the laser beam over the targeted area of human and changes such as inflammation (after 72 hours) and bovine samples to remove enamel and dentin tissue permanent changes to the pulp (after 3 months). No “without excessive peripheral thermal damage or significant adverse events occurred; no analgesic was heat accumulation.”50 used and 2 patients reported discomfort which was attributed to cold sensitivity from the air-water spray In the temperature portion of their 2011 study of the (the laser was turned off to confirm that the water effects of a pulsed 9.3-µm CO2 laser on noncarious spray alone caused the discomfort). Histologically, all extracted teeth, a team of UCSF researchers teeth showed a lack of pulpal response, regardless used computer-controlled XY galvanometers of treatment category and time extracted post- to scan the laser beam over sample surfaces. treatment. Limitations of the study included laser Microthermocouples placed within the pulp treatment of enamel only (no dentin ablation was chamber measured the temperature rise during a involved) and restricted repetition rate (25 and 50 Hz).

2-minute irradiation period with the laser set at a The authors state that the 9.3-µm CO2 laser should be pulse repetition rate of 300 Hz and two laser fluences electronically scanned to expose a new area for each (20 J/cm2 and 30 J/cm2). The scanner permitted the pulse for most effective tissue ablation.51 ablation of a 5.0-mm diameter cylindrical pattern over the occlusal surface of the tooth, under water spray.

Heat accumulation measurements indicated that 2014 Vol. 22, No. 1 the mean temperature change at 20 J/cm2 was 2.0 | ± 0.6°C, and at 30 J/cm2 was 3.2 ± 0.8°C. The authors note that a temperature rise of 5.5°C is indicative of excessive heat accumulation and can lead to pulpal necrosis. For the peripheral thermal damage investigation portion of the study, they used polarized light microscopy (considered the most effective way Journal of Laser Dentistry Fantarella and Kotlow 17 18 SCIENTIFIC REVIEW Journal of Laser Dentistry | 2014 Vol. 22, No. 1 “better matches the absorption characteristics of characteristics matches“better theabsorption ofthe9.3-µmwavelength which multifunctionality hard tissue andthereby recognized thepossible effect ofvarious CO the and colleaguesconcerning by McCormack Wilder-Smith effects ofa9.3-µm CO ontheincisionalandcollateral While reporting by directlytargeting collagen.” to ofthetissuemechanicalstrength theweakening They speculated that differences“these may bedue thanat10.6µm. with asmallerzone injury ofthermal removedlaser irradiation tissuemore efficientlyand (9.5µm). absorption They noted thatpulsed9.5-µm and where water andcollagenhave comparable (10.6µm) absorber where tissuewater istheprimary onporcine atwavelengths experiments dermis injury massremovalprocesses andthermal by performing 1998PayneIn andassociates examinedtheablation parameter configurationselected.” tissue,and predictably insoft dependingon the of clinicaleffects canbeachieved consistently findings indicated thatwiththislaser “a widerange pulsedmodes.operating invarious Their histologic tissueusinga9.3-µm incision effects insoft CO used pigmandiblesto therangeofclinical determine Two years later, Wilder-Smith, Dang, andKurosaki ratherthanwavelength.beam characteristics effects were related to theparameters usedand systems. andhistologicThey concludedthatthermal and 10.6-µmlasersequippedwithcoherent delivery examination showed littledifference the9.3- between structures are by impacted thelaserbeam.Histologic at eitherwavelength isminimalunlesstheadjacent tissues laserincisionofsoft adjacent structures during revealed damageto thatthedangerofthermal the oralmucosaofpigmandibles. analysis Thermal CO ofcontinuous-wavea comparison 9.3-and10.6-µm on reported from ofCalifornia theUniversity –Irvine 1995, In Wilder-Smithcounterpart. andcolleagues capabilities afforded by its9.3-µmwavelength were interested ininvestigating thesoft-tissue an effective device tissuesurgery,for soft researchers Fantarella andKotlow INTRAORAL SOFT TISSUE SURGERY SOFT INTRAORAL 2 Because the10.6-µmlaseriswell recognized as lasers used to make standardized lasersusedto make incisionsin et al. acknowledged the 1995 report the1995report acknowledged 2 laserwavelengths ondental 2 laser on soft tissue in1997, laseronsoft 54 53 52 2 laser applications” isaschallenging asthelaserphysics flexibility required to accommodate “multiple useful for clinicians.” ofequipmentisto become realisticallyif thistype costly devices, multiple applications are desirable over 15years agothat lasersare“because relatively 9.3- clinicians.” ofequipmentisto becomerealisticallytype usefulfor devices, multipleapplicationsare desirableifthis pulpal structures. Becauselasersare relatively costly damageto adjacentand tissues withoutthermal for modificationorefficientablationof hard dental hydroxyapatite than10.6µm,providing thepossibility design feature to achieve theclinicalbenefit: related clinicalbenefit,andtheassociated device oftherelevant researchimportance discoveries, the challenges. listed below explainsthe The overview research into platform alaserdevice creates multiple discoveries andbenefits found inthe27 years of explained above. therelevant technical Melding CONFIGURATION 2. 1. As noted above, Wilder-Smith µ For finedetailcuttingofenamelthe fluence For therapidablationofenamel, dentin, 10,000 Hz. focused spotsizes ofroughly 0.25mmat100to energies from 500µJto above 10mJwith should have to operate theflexibility withpulse less than0.3mm. should beabout20J/cm types. water and maximize theablationofalltissue inhydroxyapatite,the absorption collagen,and operate at a9.3- and water. inhydroxyapatite,high absorption collagen, should operate withawavelength thathas tissuewithhemostasis,and soft m 27 CO 2 55 LASER DEVICE DEVICE LASER The clinicallasersystem should 27 The inherent design device µm 7 4 4 37, wavelength to maximize The clinicallasersystem 2 withaspotsize of et al. recognized 51 the device thedevice SCIENTIFIC REVIEW

3. To ensure pulpal safety, the pulse widths of the in order to achieve char-free cutting of soft and laser must approach the relaxation time of both hard tissue, the clinical laser system should have hard and soft tissue.30, 56 The clinical laser system integral fine misting that avoids the laser beam should have the flexibility to operate with pulse path as much as physically possible. widths for hard tissue at 30 µs or less and pulse widths for soft tissue at 500 µs or less. CLINICAL DEVELOPMENTS 4. For interproximal cutting the device must have AND USES a long working distance while maintaining an ablation fluence level above 10 J/cm2.45 At this time there is only one 9.3-µm CO With a focused spot size of roughly 0.25 mm, 2 laser system cleared by the U.S. Food and Drug the clinical laser system should operate with Administration (FDA) for use in dentistry. The system fluence above the hard tissue ablation level at (Solea, Convergent Dental, Natick, Mass., USA) was 10 mm either side of the focused spot position. introduced for live patient use in August of 2013 5. To finely remove or “shave” enamel the device (Figure 3). This device received FDA clearance for must operate with a very shallow absorption ablation of hard tissue for caries removal and cavity depth.57 With very tightly focused spot sizes of preparation, and for incision, excision, vaporization, 0.25 mm or less, the clinical laser system must coagulation, and hemostasis of soft tissue in the oral operate with variable energy levels of 250 µJ to cavity. 20 mJ with repetition rates of 100 to 10,000 Hz. 6. For a fine surface finish on enamel the 9.3-to- 9.6-µm wavelength has to be used with a very shallow absorption depth. Pulse energies of 5 mJ to 25 mJ/pulse with repetition rates over 300 Hertz are used.51 For clean margins and flat bottom surfaces, the clinical laser system should integrate computer-controlled patterns that link the beam movement to the computer’s laser pulse repetition rate generation. 7. Caries tissue is composed primarily of destructed hydroxyapatite and water. To remove carious hard tissue, the clinical laser system must be highly absorbed by both hydroxyapatite and water.58 The clinical laser system must operate with tightly focused spots at 9.3 to 9.6 µm with long pulse widths out to 500 µs. 8. To ensure proper X and Y movement with a highly focused laser spot, computer control of the focused spot position is required.44 The clinical laser system requires a closed-loop 2014 Vol. 22, No. 1 feedback system, like galvanometers, that | control the laser beam position on the focus optic to the central laser system control box and customer graphical user interface. 9. To ensure rapid ablation without pulpal heating an integral water spray system is Figure 3: Solea 9.3-µm CO2 Laser System required.44, 59 Because the required laser

wavelength is required to be absorbed in water Journal of Laser Dentistry Fantarella and Kotlow 19 20 SCIENTIFIC REVIEW Journal of Laser Dentistry | 2014 Vol. 22, No. 1 repetition rate mentionedabove. the foot pedalfrom singledigit upto themaximum utilizingthefullrangeon mouth, dentistsreport frequencies the of50pulsespersecondorless. In use laserstypically per second. contrast,erbium By the maximumaverage repetition rate is2,200pulses from isfactored in, to onepointinapattern thenext pulses persecond. When thetimerequired to jump speed thelaserwillfire inburstsofup to 10,000 isexecuted. pattern which theselected At maximum foot pedal, thecomputer increases thespeedwith . As theuserincreases pressure onthe tosimilar inform thatofthetraditional andfunction foot pedal’sdepending onthevariable-speed input, additionally controls thesystem’s laserpatterns precise tissue. incisionsinsoft This laser’s computer margins andbottoms inhard tissueandmore resulting inthepattern, point to in smoother the next more timeto coolasthebeamismoved from one possible withthehumanhand. This allows the tissue a large area withmore thanis speedanduniformity theenergyuser andsituation,distributing over role inproviding achoiceofspotsizes to suitthe sizes.various galvosThe computer-driven play akey aiming andcuttingbeamsinto circular of patterns up to 10,000 timesinasecond, manipulatingthe to eachother.perpendicular The galvos canoscillate in theopticalchainare mounted onthegalvos The lasttwo outsidethepatient’s mouth or galvos, smallmotors located inthehandpiece. mouth. The computer isusedto drivegalvanometers, inthe for theuserandoptimizingperformance itmore manageable ofthebeam,making delivery extensive computer technology to managethe otherclinicaldentallasers, uses Unlike thisdevice chain utilizes atotal of12mirrors and4lenses. andhandpiece. arm articulated The complete optical mounted above thelasersanddelivered viaan The beamsare two combinedonanopticalplate beam since9.3µmisoutsideofthevisiblespectrum. intoincorporated thesystem to provide anaiming gas asdiscussedabove. Asecondlaserat532nmis produce the9.3-µmwavelength by usinganisotopic desired 9.3-µmwavelength. The laserismodified to Coherent, ofSantaClara,California Inc. to produce the This laserusesamodified CO Fantarella andKotlow 2 lasersuppliedby lasers more user-friendly andefficientwhen treating using dissipates. make Allthesecharacteristics or tongue before thenumbnessfrom theanesthesia associated withthechildbitinghisorherlip for injury is amajorbenefitbecauseiteliminates thepotential without theneedfor children this localanesthesia.In pain-free inachieving are factors treatment critical having to stop andadjustsettingsonthelaser. These orexcision/incision tissuewithout and caries ofsoft to increasing thespeedofablationenamel, dentin, a level oflaser-induced analgesiafor thepatientprior proceduresto atlower start power levels, facilitating settings orpower (J/cm speed foot change pedalto effectively andquickly repetition rate from withthevariable- 1to 10,000Hz easily adjustpulsedurationsfrom 1to 500µsand are changing theway lasersare used. The dentistcan foot pedal, andadjustablespotsizesvariable-speed The combinationofeasilycontrolled pulsedurations, patients (Figures 4-7) Figure 4:Case #1:Occlusal Caries Removal Figure 4b: Mid-preparation view Figure 4a:Preoperative view 2 ). theoperatorThis permits SCIENTIFIC REVIEW

Figure 5: Case #2: Distal Caries Removal

Figure 5a: Preoperative view

Figure 4c: Mid-preparation view, continued, prior to caries disclosure

Figure 5b: Mid-preparation view

Figure 4d: Completed restoration

In case #1 (Figure 4), a 26-year-old female presented with occlusal caries in tooth #3, confirmed with a tactile explorer stick and a reading of 28 from a caries detection device (DIAGNOdent, KaVo Dental, Charlotte, N.C., USA). Neither injected nor topical anesthesia was administered. The 9.3-µm CO2 laser- only (Solea, Convergent Dental, Natick, Mass., USA) Figure 5c: Interproximal matrix preparation of the tooth proceeded with a dentin band placed prior to restoration setting, 0.5-1.0 mm spot size, 5-10 mm tip-to-tissue distance, 30-100 µs pulse duration, 100% water, variable foot pedal speed of 30-90%. The tooth was then restored with a dual-curing self-etch bonding agent (Futurabond® DC, VOCO, Cuxhaven, Germany) 2014 Vol. 22, No. 1 and a bulk fill composite restorative material (SonicFill, | Kerr, Orange, Calif.). The complete procedure, from seating of the patient to dismissal, took approximately 10 minutes. The patient reported no sensitivity to the extent that she was unsure whether the procedure was being performed on a maxillary or mandibular Figure 5d: Completed restoration tooth. Journal of Laser Dentistry Fantarella and Kotlow 21 22 SCIENTIFIC REVIEW Journal of Laser Dentistry | 2014 Vol. 22, No. 1 restorations. patient requested thatthislaserbeusedfor future lower pulseduration (80µs).After theprocedure, the butthenwasableto tolerateinitial sensitivity a approximately 10minutes. The patientreported (SonicFill).material The complete procedure lasted (Futurabond bondingagent restored self-etch withadual-curing Milford, Del., USA)wasplacedandthetooth wasthen interproximal band(Palodent, matrix DENTSPLY Caulk, 100% water, foot variable pedalspeedof30-90%.An distance, 30-100µspulse duration, mm tip-to-tissue with adentinsetting, 0.25-1.0mmspotsize, 5-10 preparation ofthetoothlaser-only wasperformed ortopical) was administered.anesthesia (injection The presented intooth #20.No withdistalcaries Fantarella andKotlow In case#2(FigureIn 5),a23-year-old malepatient Figure 6:Case #3:Lingual Frenectomy Figure 6b:Immediatepostoperative view, ® DC) andabulkfillcomposite restorative DC) Figure 6a:Preoperative view nobleedingevident

and prilocaine 2.5%)wasapplied,and prilocaine followed by oflocalanesthetics)creammixture (lidocaine2.5% was administered; instead, topical EMLA(eutectic speechdifficulties.help correct Nolocalanesthesia referred by aphysician for alingualfrenectomy to was reported during the healinginterval. during was reported child were pleasedwiththeresults. Nodiscomfort revealed uneventful healing, andtheparents and days. postoperativeThe one-week examination promote healing, andto foods avoid for spicy several daily,lip twice applyvitaminEto thesurgical site to as needed. The parents were to instructed elevate the and couldimmediately proceed withspeechtherapy greater andimproved tongue mobility articulation, procedure. thepatientdemonstrated Afterward, the orafter eitherduring nodiscomfort reported procedure wasapproximately 25seconds. The patient 1-40%. The durationoflaserexposure for thesurgical duration, nowater, foot variable pedalspeedof distance,size, 77µspulse 25-40mmtip-to-tissue tissuesetting, withasoft 0.25mmspot performed cream. surgicalThe laser-only procedure wasthen aiming beamto enhancetheanalgesic effect ofthe 1-minute exposure to thelaser’s low-level 532-nm In case#3(FigureIn 6),a4-1/2-year-old childwas Figure postoperative 6c:One-week view showing uneventful healing

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Figure 7: Case #4: Maxillary and In case #4 (Figure 7), a 1-month-old infant was Lingual Frenectomy referred because of breastfeeding difficulties. Clinical examination indicated that both the lingual and maxillary lip attachments were interfering with the ability of the baby to achieve a good latch. Both mother and infant were experiencing difficulties with breastfeeding. No anesthesia (injection or topical) was administered. The laser-only surgical procedure was performed with a soft tissue setting, 0.25 mm spot size, 25-40 mm tip-to-tissue distance, 77 µs pulse duration, no water, variable foot pedal speed of Figure 7a: Preoperative view of lip frenum 1-40%. The duration of laser exposure for the surgical procedure was approximately 25 seconds for each site. No bleeding was evident upon completion. The parent was instructed to elevate the tongue and lip twice daily. At one-week follow-up, uneventful healing was underway, and the mother reported that the infant was able to breastfeed immediately after surgery without difficulties, and all presurgery problems were resolved. CONCLUSION Practitioner and patient experience with

Figure 7b: Preoperative view of lingual frenum the 9.3-µm CO2 laser confirms the ability of this unique wavelength to safely, effectively, quickly, and comfortably perform caries removal, cavity preparation, and intraoral soft tissue surgery with reduced need for conventional drills to complete

the procedures. Compared to other CO2 laser wavelengths, the isotopic 9.3-µm wavelength combines high absorption and low reflectance coefficients and shallow absorption depth in hydroxyapatite to make it the ideal wavelength for efficient ablation of hard dental tissue. Effective soft tissue incisions and excellent hemostasis are enabled by this wavelength’s high absorption into water and Figure 7c: Immediate postoperative maxillary view, collagen. no bleeding The current implementation of this new laser is based upon the findings of nearly three decades of scientific research. The pulse durations of this 9.3-µm dental 2014 Vol. 22, No. 1 laser are specifically designed to correlate with the | thermal relaxation time of hard and soft tissue to help ensure pulpal safety while the simultaneous water misting cools the targeted hard tissue. The pulse energies and repetition rates along with variable spot sizes enable fine detail cutting of enamel. The computer-controlled, galvanometer-guided laser beam and variable-speed foot pedal provide the Figure 7d: Immediate postoperative lingual view, clinician with unprecedented levels of precision and Journal of Laser Dentistry no bleeding control. Fantarella and Kotlow 23 24 SCIENTIFIC REVIEW Journal of Laser Dentistry | 2014 Vol. 22, No. 1 consultation services ontheXLASE™ and theLightWalker consultation services Board.Convergent ontheirClinicalAdvisory Hehasprovided andserves Dental Technology with 4Medicine Dr. isaconsultantto Kotlow Convergent CO onthedevelopment oftheSolea Dental andisaformer Schein, trainerfortechnology for Biolase. Henry He isaninvestor Board. inConvergent ontheirClinicalAdvisory Healsodemonstrates andserves Dental Disclosures: Fantarella andKotlow AUTHOR BIOGRAPHIES [email protected] Dr. Fantarella at may by becontacted e-mail for outstandingachievement inperiodontics. Academicand theAmerican award Practitioners award inLaw andEthicsinDentistry, ofDental Surgery,Maxillofacial theNationalSociety Association award for excellence inOraland degree from UConn, hewasawarded theAmerican Medicine Upon receiving ofDental hisDoctor Center. attheUConnto Medical dohisresidency andwasinvited Medicine (UConn) ofDental School graduate ofConnecticut studiesattheUniversity Excellence inScience. Dr. Fantarella completed his Goldwater AwardHe wasawarded for theBarry inphysics. College whilemajoring from Dartmouth Dr. Fantarella isaconsultantto Convergent CO onthe development oftheSolea Dental Bachelor of Science degreeBachelor ofScience dentistry. Hereceived his implant, cosmetic, andlaser He specializes ingeneral, Haven, Connecticut. and North the past15years inHamden generaldentistforpracticing Dr. David Fantarella hasbeena . dentistry and has contributed chapters andhascontributed inthree dentistry more than30papersonusinglasers andpediatric in theAcademy Hehaswritten ofLaserDentistry. Dr.Dentistry. hasachieved status Mastership Kotlow and diodefamilyoflasersfrom theAcademy ofLaser intheuseofNd:YAG certification proficiency intheuseofEr:YAGcertification lasersandstandard Children’s Hospital. Hehasadvanced proficiency [email protected] Dr.Dentistry. at may by Kotlow becontacted e-mail Leon Award Goldman for ClinicalExcellence inLaser Pediatric oftheALD’s Heistheco-recipient Dentistry. Academy (ALD) andtheAmerican of Laser Dentistry and Canada aswell asinmeetingsoftheAcademy of inAustralia,worldwide Israel, Taiwan, France, Italy, has beenusinglaserssince2000.Helectured dentistry. He onusinglasersinpediatric textbooks ® lasers. . training attheCincinnati,Ohio and received hispediatric School Dental Buffalo (SUNY) State ofNew University York York. Heisagraduate ofthe inAlbany,practicing New Dentist certified Pediatric Dr. isaBoard- Kotlow Larry 2 laser. Heisaninvestor in 2 laser.

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