ICurrent Concepts

Current Concepts provides ttie opportunity for ini/ited individ-uals to express their opinions or selected current topics ofinterest in the field of dentistry. The comments expressedherein represent personal opinion and not ttie positions ofQuintessence International.

What is the future of lasers in dentistry?

JOHN FEATHERSTDNE, iVlSc, PHD

Lasers iii dentistiy are about tocome of age. There are many den-tists already ¡n the United Stateswho useaUiserof one sort or anoth-er to do soft tissue protechires.These are first generation laserstliat have been on the market forsome years and are approved forsoft tissue applications onl\. Otherswill soon follow. Some will be ver\'different. At the time of this writ-ing, the Federal Drug Administra-tion (FDA) had not approved lasersfor hard tissue procedures in dentalapphcations, Hovvever, studies havealready been done demonstratingflinical efficacy and safety for theremoval of enamel uaries, and thesecond and third générations ofdental lasers are currently beingdeveloped and tested for severalapplications. What am I talltingabout? What is in the future? Asyou read on, open your mind andbe prepared to accept unconven-tional procedures as realities, notjust dreams for the future.

Dentists are trained that "thedrill" is the tool that is used toremove caries, and then to go onand remove sound surrounding tis-sue to make a safe cavity prepara-tion. What if you were just toremove carious enamel or dentinand leave sound tissue selectively,just by tuning your special laseraccordingly? That will be somethinga dentist can do with a speciallydesigned laser. What if you couldthen alter the settings and treat thewalls of your new cavity preparationto make the mineral resistant tosecondary' decay and prepare it forbonding at the same time, all in afew seconds? That will be possible,but it will require a iaser that isspecifically designed to do thosevery precise procedures. It willrequire carefully defined conditionsof wavelength, energy, fluence(energy per surface area), beamdiameter, number of pulses, andpulse duration, Researeh is airead)'well-advanced toward bringing

these concepts to clinical reality.You caunot use your existing laserfor these tasks. The second andthird generation lasers are on theway. It vvill also be necessary toretrain dentists with a differentmindset from that of the traditionalrestorative approach, "Mininiiiminten'ention for pre\entiori" will herequired, along with a very differentunderstanding ofthe laser approachrather than t!ie tracîitional "drill andfill" approach.

Let us go one step further now,A hig step! Imagine you have aclient with a continuing caries prob-lem. Based on their history, youassume the patient is at high risk ofcaries, so you deal with the bucterialchallenge by a short course ofantibacterial therapy. As a furtberpreventive strategy, you treat eachof the patient's occiusal surfaces bylaser, not for restorative reasons,but to inhibit caries progression!Just like a sealant only you alter thestructure ofthe mineral aud make it

286 Quintessenoe International Volume 27, Number 4/1995

highly resistant to furtlier deiitu!deca\. This is all done in a few sec-onds per tooth.

Anotlier patient fomes in with aroot curies priiblem. You selectivelyremo\'e tlie carious ti.ssiie by lasei;prepare the underlying surface bylaser for a glass-ionomer (or special-ly designed composite) restoration,and then treat the other e\po.sedroot surlLice.s by laser as a caries-pre\-ention measure. You "ill needdifferent settings for the laser and adifferent handpiece for each pur-pose, but the procedures are pre-cise, timely, vibration free, andlargely pain free. Is this fantasy?Not at all; the research is welladvanced. Howe\er, it will be someyears before all of tlie steps havebeen taken to prove chnical safetyand efficacy, and to obtain FDAapprovals for tbe new lasers. Den-tists will also need to be specidlytrained to u.se these procedures.

Lasers must only be u.'ied asapproved and recommended, sodentists must understand the newtools, some diat use invisible hght!Just why is it possible to ii.se laserlight to do the above hard ti.s.sueprocedures? The principle of laser-tissue interaction is b;isicall)' simplein concept, but complex in detail.Laser light can be delivered at asingle, chosen wai'elengtb, in sbortpulses, at defined energy levels, and

to a precise po.sition. The basicrequirement is tbat the tissue¡Livolved miLSt strongly absorb tbelight, preferably in a selective fash-ion. The stronger tbe absorption,tbe bigbei- tbe ti ansient temperaturerises and tbe more pronounced the

9.3- and 9,6-pm wavelengths arebest suited lor these two purposes.Delivery systems that enable thesewavelengtbs to be delivered clinical-ly have recently become available.On the contra™, lasers with visibleor near-infrared wavelengths will be

These unconventional procedures arerealities, not just dreams for the future.

effect. Water in hard dental tissuesabsorbs strongly in tbe mid-infnired,especially around 3 pm, and hencetbe Er:YAG laser can be used foreffective ablation of enamel anddentin. Carbon dioxide lasers areconventionally available with awa\'elength of 10.6 pm, but ean alsobe con.striicted to dehver at 9.3, 9.6,or 10.3 pm. The pbosphate in themineral of enamel, dentin, andcarious tissue absorbs very stronglyfrom 9 to 11 }im (as well as someabsorption by water here), andbence tbe carbon d!O.>âde laser eanhe used for ablation or for treatingthe mÍTieral to inhibit caries progres-sion. The very strongly absorbed

mueb less efficient because absorp-tion at these wavelengtbs is very low.

We can expect many excitingdevelopments in the use of lasersfor hard tissue dental applicationsto be available very soon, and toperhaps see a revolution in dentistryas a result.

Dr Featherstone is Proiessor of Restora-tii/e Dentistry at University oí CaliforniaSan Francisco. Ha leads an activeresearch program tiiat studies theettects of iasers on hard tissues, as wallas other aspects of caries prevention. HeIS former chairman of the Department o¡Oral Sciances at tiie Eastrran DentaiCenter in Rochester, NY,

R. J.BLftNKENAU, DDS

Lasers (Light Amphfication byStimulated Emission of Radiation)include a wide variety of very differ-ent instruments. Tbese instrumentsdiffer in how and wbere tbey can beused. The ligbt produced is colli-mated, coberent, and monochro-maüc for all laser types. Tbe specif-ic wavelength for each laser ty;i3ehas various tissue responses depen-dent on absorption, transmissions,reflection, and scattering of thelaser beam.' Tbe optical propertiesof tbe target tissue and tbe specificwavelength of the laser, combined

witb power output, spot size, totalligbt dose, and mode of delivery al!are factors tbat help us use laserenergy in dentistry.' It is importantto understand tbe differencesbetween tbe various laser types tounderstand bow and wbere tbey canbe used in dentistry.

Before we can look at the futureof laser technology, we need toreview tbe present uses and tberesearcb being conducted. Al-thougb lasers were first developedby Tbeodore H, Maiman' in 1960tbe original theory was developed

by Einstein^ in 1916. However, itwas not until the early 1980s thiitapplication of lasers for dentistrywas proposed. The first laser usedfor soft tissne was tbe CO^ laser.Teams of researchers from theUnited Kingdom, Franee, and theUnited States were the early users.From tbat group of researchersinterest grew, and a varietj' of otberwavelengths have been studied.Today, over 5,000 papers bave beenpublished worldwide, and the mim-ber of people researching lasersCiintinnes to grow rapidly. Tbe early

ence International Voiume 27, Number 4/1996 287

researchers íound that lasersoffered bloodless surgery and mini-mal postoperative discomfort, anddepending on power .settings andtnode of deliveiy, soft tissue couldbe cut, coagulated, or vaporized. Inaddition, one laser, the Argon laser,has been found to be useful in pho-topolymerization uf light-sensitiverestorative rnaterials, producingproducts with superior physicalproperties in considerably less time.The wavelengths that have beenaccepted by the FDA for use in theUnited States are the CO^, Nd:YAG. Argon, Er:YAG, Ho:YAG, andDiode. The e\cimer soft lasers andthe frequency-doubled alexandritelasers are currently under review.All can be used for a wide variety ofsoft tissue applications, such as gin-givectomies, biopsy, hemotoma,frenectomy, crown lengthetiing, andother excisional aud incisional pro-cedures, hi addition to the soft tis-sue application, the Argon wave-length can also be used for pho-topolyinerization of all light-activat-ed Tnaterials.

Gitrrent research is being con-ducted on caries prevention, diag-nosis, hard tissue cutting, calculusremoval, caries removal, vvoundhealing, pulp vitality testing, tem-poromandihular joint surgery, den-tal material testing, and endodonticprocedures, such as root canals, api-coectomies, and puip capping, toname a few of the many areas ofresearch interest.

A review of the current researchhas provided me with the informa-tion used in my assessment of thefuture dental applications of lasertechnology. IIow soon we canexpect to sec this technology inevery office is a bit more difficult topredict. Cost associated with laserimplementation will probably re-main high until demand increasesto allow savings through volumeproduction.

What can be predicted with astrong degree of probability is thatmultiple wavelengths will be part ofthis technology: Because each wave-length can offer optimum advan-tages for specific tasks, there will be

a need for more than one wave-length. This will be accomphshedby one machine that will include avariety of lasers designed to allowthe operator to select the requiredwavelength for the task at hand.Examples would include a laser fordiagnosis of dental caries, withoutthe need of radiographs, by fluo-rescing the tooth with a laser andrecording the information with anintraoral camera, thereby reducingradiation exposure. When needed,cutting of hard or soft tissue will bedone by the laser designed for thespecific task. Selective removal ofcalculus without damage to anydental tissue has already beendemonstrated. In the area of hardtissue cutting, we will be able toselectively remove carious enameland dentition with minima! removalof healthy tissue, and hecause thereis no drill, the lack of vibration willrequire a minimal need for anes-thetics. Small ca\it)" preparation willbe restored with a resin compositethat is polymerized with a laser thatnot only initiates the polymerizationbut also changes the tcoth to makeit more resistant to acid attack andfuture caries.

Teeth with fractures will be"melted" to fuse the enamel andrepair the broken tooth. It shouldbe possible to replace a fracturedcusp by welding the tooth fragmentwithout using luting agents. Laserswill also be used to expedite woundhealing as well as offer bloodlesssurgery and selective removal ofpathology without causing damageto healthy tissues.

Endodontics will be accom-plished by removal of soft tissueand sterilization of the canal with alaser dehvered hy glass fibers assmall as the size of a No. 10 endo-dontic fue. The apex may be sealedby root fusion and the tooth re-stored with a resin that chemicallybonds to the tooth and is polymer-ized by a laser. This would minimizethe Ioss of tooth and provide maxi-mum strength. Combined withintraoral microscopes, it should bepossible to treat even (he most diffi-cult cases. Pulp capping will be very

effective by using a laser to controlhemorrhaging and a resin base toprevent mechanical damage to thepulp. Continued \4tality ofthe toothwill be monitored by using theDoppler effect to measure pulpalblood flow.

With the knowledge of today'slaser advantages, {ie, high patientacceptance, improved physicalproperties of resin restorative mate-rial accomplished in a significantlyreduced time period, reduction ofthe demineralization of laser-treat-ed hard tissues, bloodless soft tissuesurgery, and minimal postsurgicaldiscomfort, to name a few), coupledwith a growing number of world-wide researchers working withlasers, it is apparent as to how thesechanges will occur in the nearfuture. The current number onereason why only some 6,000 den-tists worldwide are currently usinglasers is the cost of the equipment.In the past 5 years the costs havedramatically lowered and will even-tually be reduced even more. Thequestion each dentist will need toanswer is, "When will 1 be ready tobegin to offer my patients the bestavailable treatment?" Many of themhave already begun, and more v\dllsoon join with them. Laser dentistr)is on the edge of a truly exciting erain dentistry with a future as brightas the sun.

References

1. Dederidi DN. Laser-tissue interaction.Alpha Omega 1991;84:33-36.

2. Maiman TH. Stimulated Optical Radia-tion in Ruby. Nature 1960; 187:493-498.

3. Einstein A. Zur Quantum Theorie DerStraJung. Vork Dnihcli Pliys Ces 1916;IS 318"

Dr Blankenau has bGen Professor atCreighton University in Omaha, Nebras-ka, since 1985 and served as AssociateDean ûf Academe Affairs for 2 years. HeIS a niGmber of several professional• rganizations, inciiiding the Society forPhoto-Optical Instrumentation Engineersand ISLD International Congress, Lasersin Dentistry.

Quintessence International Volume 27. Number 4/1996

KENNETH L. ZAKARIASEW. DDS. MS PHDJOSEPH R, BARRON, BSC

Tlie detection of dental caries hastraditionally been accotnplishedtlirongh wsuid and tactile examina-tion and dental radiography. Mostoften, by the time such methodsdetect caries, the process hasreached a stage where removal ofcaries and replacement v̂ qth a den-tal restorati\'e material is necessary.Oftentimes, these methods candetect caries at a relati\'e!y earlystage, and the ca\it\' prepai ation andrestoration can be kept minimal.However, regardless of whethersuch restorations can be kept at aminimal size, tlie fact remains thatwe are most often still resorting tohard tissue remoyal ;ind replace-ment. The ideal situation would hefor the clinician to ha\e the capabili-ty' of detecting carious lesions at avery early, incipient stage whenreversal of the lesion through re-mineralization is still possible.

The traditional concept of cariespre\'ention i.s to put into place thosestrategies, such as fluoride treat-ments and oral hygiene practices,that will prevent the caries processfrom heginning, Howcyer, once ithas begun, we normally surgicallyintenene. The concept of ver\' earlydetection of deniineralization andsuhsequent remineralization wouldactual!} expand the breadth of pre-vention in many cases by eliminat-ing surgical intervention throughdisease reversal, thus bringing thehard tissue back to litll health.

Laser fluorescence detection ofincipient caries is based on the prin-ciple that the optical properties ofdemincralized enamel are differentfrorn the optical properties ofhealthy enamel. When enamel isirradiated with low levels of theappropriate wavelength energy, theenamel fluoresces. The fluores-cence of normal enamel has adifferent wavelength intensity thandemineralized enamel, and thesedifferences can be used as a basisfor differentiation of healthy andcarious enamel.

The appropriate combination ofnarrow band-pass filters, optics.

electronics, and computerizationcan be used to provide a yisualiza-tion or graphic image of toothstructure that clearly shows whereincipient demineralization is occur-ring. The data developed throughthese systems can qualitatiyely rep-resent normiil and demineralizedareas for eas)- identification, andcan also be utilized in a very analy-tic fashion, through optical micro-probes, to arrive at verj' specific flu-orescence measurements, whichcan serye for quantitative cotnpad-son. This makes possible the use of

definitely not one of these areas.Our research group at MarquetteUniversity and the very distin-guished group headed hy Dr J. J,Ten Bosch in The Netherlands haveworked in this area of developmentand science for a number of years.While this area of research is mov-ing forward very quickly, as it isintroduced for wide use in dentalpractice, it will have an outstandingfoundation of science to validate itsusefulness and effectiveness.

While we now live in a worldwhere a great number of our young

Early detection of demineralization andsubsequent remineralization would expand

the breadth of prevention.

laser fluorescence diagnosis ofincipient carious lesions as an easilyapplied clinical modality and a veryprecise analytic too! for cariologyresearch. We believe that we arejust scratching the surface inresearch today relative to the clini-cal and re.search imphcations of thisnew science. It is our predictionthat what is being developed in thisarea for dental caries diagnosis willbe eventually much more widelyapplied in other areas of dentistry,Fluorescerice-bascd systems arealso currently used in medicine forsophisticated diagnostic detection.

Dentistry today is facing a virtualexplosion of technological develop-ment. Unfortunately, much of thenew technology is foisted upon thepracticing dental community longbefore the dental science is suffi-cient to justify- its application. Thearea of laser dentistry certainly is aprime example of this phenomenon.However, the use of laser fluores-cence diagnosis of caries is most

people do not experience the devel-opment of carious lesions, we alsoliye in a world where people are liv-ing longer, where they are keepingtheir teeth longer, where they stilldo experience dental disease, andwhere they need dental care. Ourgoal should be to keep these indi-viduals healthy whenever possible,rather than to pursue a progressive"drill and fill" course of action. Theuse of laser fluorescence diagnosisfor early detection of caries will ulti-mately go a long way toward makingthis a reality.

Dr Zakariasen is Dean and Professor alMarquette llniversjtv School of Dentistry¡n Milwaukee, Wisconsin, and ExecutiveDirector Designate for the CaliforniaDentai Associatian,

Mr Barran is Research Associate atMarquette University School of Dentistryin Milwaukee, Wisconsin.

Quintessence International Volume 27, Number 4/1996289

DouGUSN. DEDERICH, BS, DDS, MSc, PHD

Our times are marked b>' rapidtechnological change and the con-comitant changes in the way we liveiind work, ln the field of dentistiy,the last 10 years have introducedsignificant technological change,inclticling CAD/CAM fabrication ofrestorations, computerization ofoffice and marketing tasks, intraoralcameras, air/powder abrasive diills,advances in implant systems,site-specific deliver)' tjf antimicro-bials in periodontics, sharing ofinformation over the Internet, andlasers. Of these technologies, thisarticle focuses on the futnre oflasers in dentistr\'.

occur: (I) the issue ol polential col-laterid damage must be resolvedwith respect to each specific appli-cation and laser wavelength andwaveform; and (2) multiple applica-tions that offer increased quality ofresult, greater ease of deliveringtreatment, und/or the ability to pi'o-vide needed treatment heretotoreimpossible must be developed.From an economic perspectivealone, the latter is of paramountconcern if a general practitioner isto justify purchasing lasers at cur-rent prices. From a scientific per-spective, 1 believe these new hardtissue applications will not be de\'el-

Several laser wavelengths have theability to increase the resistanceof enamel and dentin to caries.

To best appreciate where Ihelieve lasers are going, it is best tofirst understand where they arenow. Very briefly, since the adventof lasers in the early 1960s, soft tis-sue applieation for purposes of tis-sue incision and ablation hasbecome accepted, first within inedi-cine and more recently in dentistr\'.To date, however, the FDA hasappro\'ed or eleared only the CO ,̂Nd:YAG, Argon, Ho:YAG, Er:YAG,and Diode lasers for soft tissueapplications, with the exception ofthe Argon laser when used to eurecomposites. Numerous attempts toapprove lasers lor use on hard tis-sue have failed, in my opinion, dueto concerns regarding the potentialfor unacceptable eollateral tissuedamage, especially \vith the pene-trating wavelengths such asNdiYAG laser energy.

For laser use to become wide-spread, I believe two things tnust

oped without a multidisciplinarycollaboration between scientists,clinicians, and the industry.

The good news is that, tor all theeinhellished early claims and result-ing confusion within our practicingcoinmunit)', the haze is beginning toclear In response to early concerns,research in the basic science oflight-tissue interaction has chal-lenged early assertions regardingtissue effects of various laser wave-lengths and waveforms. For exam-ple, we now know that air-vt'atercooling of pulsed Nd:YAG lasersdoes not appear to minimize pene-tration of the energy, as originallyclaimed. Rather, it seems to slow orprevent vaporizing of surface tissue,leaving the energ)' that would havesupplied the latent heat of transfor-mation (ie, vaporization) availableto penetrate and actually increasethe risk of collateral damage atdepth. This is only one example of

why 1 helieve the future lies inwell-absorbed wavelength,s whereabsorption occurs on the surface,leaving few to no wavelengths topenetrate beyond lOO |jm.

Specifically, for soft tissueremoval, I believe the best ftiturelies with the CO^ laser, whichremoves tissue far more quickly andeffieiently than do other la,sers avail-able in dentistrj' and with tnuch lessrisk of damage at depth. I believethe best future in hard tissue appli-cations will be with well-ab s orbed,pulsed wavelengths, for example,certain excimer lasers, the alexan-drite laser, Er:YAG, or the 9,32- or9,6-pm-puised CO, lasers as investi-gated by Featherstone and Tulipamong others. These lasers pro\idea way to thertnally treat a very shal-low surface layer of enamel anddentin. If properly developed, Ibelieve the,se lasers will offer usclinical hard tisstie applications thatwill allow us to (J) increase thecaries resistance of enamel, dentin,and root surfaces without alteringthe appearance of the structure; (2)nonthermally and efficiently remo\etooth structure without damagingthe pulp; (3) sterilize root surfacesand root canals; and (4) seal rootcanals by fusing plugs either in theapical or eoronal portion of thecanals. I also believe that the pulsedNd:YAG laser, due to its efficientabsoiption in metal, will find a placeas an intraoral welding device tosimplify fabrication of both tradi-tional and implant prostheses.

Low-level la,ser therapy, sueh asHelium-Neon and Gallium-Arse-nide lasers, will continue to fasci-nate us with their inconsistent abili-ty to enhance wound healing andproduction of growth hormones, butI do not believe we ̂ '̂ill soon see theFDA approve applications in thisregard until basic scientific researchdetermines more pieces of this pviz-zle and both safet)' and efficacy canhe more clearly demonstrated.

One exciting area utilizinglow-level laser irradiation, which Ibelieve has great potential, is laserfluoreseenee. This teehnique has

290 Quintessence International Volume 27, Number 4/1995

already been shown to possess theability to detect incipient caries atstages so early that no radiographieimage of the disease is yet seen andit is still possible to reniineralizerather than excavate and restore.Although it is now a research toolunder de\elopmeiit, it is not hard tobelieve clinically marketable de-vices will appear, probabl)' iuconjunction \núi intraoral video andimage-processing systems.

Another application that Ibehe\e will continue to draw greatinterest is tbe ability of se\ eral laserwavelengths to increase the resis-tance of enamel and dentin tocaries. Research into the mecha-nisms by which this occurs ispre\'alent and continues today. Theimportance of such an effect is

ob\nous when one thinks not onlj- ofthe problems of caries in enamel,but also of the rising problem of"root caries in oiir aging population,I belie\e the Argon laser will con-tinue, in one form or another, topro\ade an alternative way of curingpol) uiers and vaporizing soft tissue,

1 do not see lasers of any typenegating the relevance of traditionalperiodontal concepts, such as theneed for proper root debridementin cases cf periodontitis. However,the ability of some lasers to sterilizeand facilitate the production ofgrowth hormones will prowde fer-tile ground for applications reseaichin the area of regeneration and aug-mentation surgery.

To conclude. I beheve stronglythat lasers ha\ e a bright future in

dentistiy, but the rate at which newapplications are promoted willdecrease in response to both thehigher level of knowledge of lasersamong the practicing communityand the time required to properlydevelop and test new hard tissueapplications.

Dr Dederich currently serves as AdjunctAssociate Professor at the Uniwersity ofiowa Coliege of Dentistry in iowa City,iowa, while maintaining a fjii-time per-iodohtics practice in Cedar Rapids, Iowa,He IS a member of several professionaiassociations, is wideiy published, andiectures nationaiiy and internationaiiy onthe topic of iasers in dentistry.

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Qjintessence International Volume 27, Number 4/1996291