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  476BRITISH DENTAL JOURNAL VOLUME 188. NO.9 MAY 132000 PRACTICE conservative dentistry  T he techniques used in carious dentineremoval have developed since GVBlack, in 1893, initially proposed the princi-ple of ‘extension for prevention’ in the oper-ative treatment of carious lesions. Heproposed that the removal of sound toothstructure and anatomical form at sites thatmight otherwise encourage plaque stagna-tion (eg occlusal fissures, approximal con-tact points) would help minimise cariesonset and progression. These principles of cavity preparation were based on the clinicalpresentation of caries and constrained by the knowledge of the disease process and therestorative materials available at that time.However, in more recent years, with theadvent of adhesive restorative materials andthe subsequent developments in minimalcavity design, this widely accepted principlehas been challenged and is now consideredtoo destructive a method for cariesremoval. 1 Latest theories regarding therationale of carious dentine removal are alsobeginning to question the amounts of tissuethat need to be excavated in order to suc-cessfully treat a carious lesion. 2,3 When removing demineralised dentine itis not always easy to know at what point tostop excavation because there is an apparentlack of objective clinical markers. Figure 1shows a longitudinal cross-section througha typical occlusal and approximal dentinelesion with the colour gradations clearly evident. What these colour changes mean interms of the demineralisation process andthe level of infectivity is not entirely clear.The clinician tends to rely on the consis-tency of the tissue while the researcher may now use the autofluorescence of cariousdentine as a reproducible, objective, histo-logical, in vitro marker allowing clinically relevant comparisons between excavationtechniques to be made. 3–6 Tissue removal techniques There are a number of techniques availablefor cutting tooth tissue (see Table 1). Someclaim to remove demineralised dentineselectively whereas others are not able tomake this distinction and indeed, may noteven be able to remove softened tissue effec-tively. For this reason it is important that thepractitioner knows what might be expectedfrom these various techniques and thisreview intends to provide the reader withsuch information. The ideal cutting instrument should fulfilcertain factors to satisfy both operator andpatient. These factors might include: 1*  Clinical Lecturer, Conservative Dentistry,  2 Reader in Microscopy and Biomaterials in Dentistry, 3 Professor of Cariology, Division of ConservativeDentistry, Guy’s, King’s and St. Thomas’ Dental Institute, KCL, London Correspondence to: Dr A Banerjee, Division of Conservative Dentistry, Floor 26, Guy’s Tower, GKT Dental Institute, London Bridge, London SE1 9RT email: avijit.banerjee@kcl.ac.uk R  EFEREED P APER  Received09.09.99; ACCEPTED 27.01.00© British Dental Journal  2000; 188 : 476–482   Dentine caries excavation: a review of current clinical techniques  A. Banerjee, 1 T. F. Watson, 2 and E. A. M. Kidd, 3 Since the invention and application of rotary instruments, theoperative treatment of carious lesions has often resulted inconsiderable removal of tooth structure. More recently, newertechniques for removal of carious dentine have been developedin an attempt to minimise this excessive tissue loss. Thefollowing article reviews and discusses some of the techniquesavailable to excavate demineralised dentine clinically. Thesemethods can be classified as mechanical and non-mechanical,rotary and non-rotary and include: dental handpieces/burs,manual excavators, air-abrasion, air-polishing, ultrasonication,sono-abrasion, chemo-mechanical methods, lasers andenzymes. The advantages and disadvantages of each techniqueare discussed. Fig. 1 Reflected lightphotomicrograph of alongitudinally-sectioned, approximaland occlusal lesionshowing colourgradations from theheart of the lesion(subjacent to the EDJ) tothe advancing lesionfront (TD – translucentdentine). Scale bar = 1 mm  BRITISH DENTAL JOURNAL VOLUME 188. NO.9 MAY 132000477 PRACTICE conservative dentistry  ·Comfort and ease of use in the clinicalenvironment·The ability to discriminate and removediseased tissue only ·Being painless, silent, requiring only min-imal pressure for optimal use ·Not generating vibration or heat duringperiods of operation, and·Being affordable and easy to maintain.No mechanical method at present bene-fits from all these attributes. Indeed, clinicalprogress in this field seems, relatively speak-ing, to be lagging behind that in restorativematerial science and even the theory andrationale of caries treatment. Excavators, handpieces and burs The history and development of theseinstruments have been reviewed compre-hensively in papers by Stephens, Crawfordand Siegel and Fraunhofer and thereforewill not be discussed further in thispaper. 7–9 Even though the rotary bur is in universaluse, there are still problems that need to beovercome. Five factors are potentially responsible for the discomfort and pain thatis associated with cavity preparation: 10,11 ·The sensitivity of vital dentine·Pressure on the tooth (ie mechanicalstimulation),·Bone-conducted noise and vibration·The high-pitched noise of the air-turbinehandpiece, and ·Development of high temperatures at thecutting surface (ie thermal stimulation).Several studies have showed that temper-atures at the cutting surface of burs andstones could easily rise above the painthreshold and, even with water spray lubri-cation, some damage to the underlying pulpmight still occur. 12–15 The rotating bur eas-ily cuts through carious dentine to eventu-ally open up healthy tubules deeper in thetissue and in conjunction with water stimu-lation of odontoblast processes, this willresult in the pain associated with cavity preparation using this technique. Even if theoperator maintains continuous bur move-ment over a large surface area and keeps thebur speed and pressure constant through-out use, the type and size of bur used (forexample, a large diameter round bur) can allhelp to reduce these detrimental factors tosome degree; however, they are not com-pletely eradicated and thus still pose a sig-nificant problem. In current practice,having gained access to the carious dentineusing the high-speed air turbine handpieceand bur, the slow-speed bur or hand excava-tor can be used for carious dentine excava-tion. As the hand excavator will removesoftened tissue with more sensitive tactilefeedback than a bur, this method is the moreself-limiting of the two.  Air-abrasion Air-abrasion was srcinally developed by RB Black in 1945 who instigated prelimi-nary investigations into an alternativepseudo-mechanical method for dental tis-sue removal which involved bombardingthe tooth surface with high-velocity parti-cles (conventionally aluminium oxide(Al 2 O 3 )) carried in a stream of air. 16 Depending on the nature of the abrasiveused, this technique has the ability of abrad-ing efficiently both sound dentine andenamel. There are several parameters thatcan be altered in order to adjust the cuttingcharacteristics of the instrument: the typeand size of abrasive particle will affect thecoarseness of the abraded surface —thelarger the size and harder the particles, thegreater is the transferred kinetic energy tothe surface and thus the rougher the finalfinish. The speed of the particles altered by varying the air pressure, the distancebetween the nozzle and tooth surface andthe length of cutting time will also play animportant part in adjusting the effectivenessof the instrument —reduced velocity willreduce the transferred kinetic energy to thetooth surface thus reducing the overall abra-siveness of the system. 10,17,18 The first unitsto be commercially manufactured were theAirdent machines. Early patient surveysindicated that this technique was greatly favoured by patients and dentists alike. 19–22 This method of cutting teeth seemed to dra-matically reduce the problems of heat gen-eration, 15 vibration and other mechanicalstimulation 10,17,22 resulting in relatively pain-free procedures when compared withthe dental drill. There have been reports toindicate that there were no significant dif-ferences in pulpal response between airabrasion and high-speed bur preparationusing copious water spray. 23 Air-abrasion has been used for severaldifferent applications within the field of restorative dentistry including removal of external stains and calculus, minimal cavity preparations, crown preparations and fis-sure sealant/preventive resin restorationplacement. 11,16,22,24–27 Note that to date,these applications using commercially avail-able alumina abrasive do not include theefficient removal of softened, carious den-tine. Disadvantages of the technique includethe total loss of tactile sensation whilstpreparing the cavity because the nozzle doesnot touch the surface of the tooth. This,coupled with the fact that the operator mustbe able to envisage the position of the cavity boundaries prior to cutting, leads to the sig-nificant risks of cavity over-preparation andinadequate carious dentine removal. 26–28 Itmust be emphasised that the aluminiumoxide abrasive particles will remove soundenamel and dentine very efficiently, whereas   Table 1 Classification of various tooth-cutting techniques   Category  Mechanical, rotaryMechanical, non-rotaryChemo-mechanicalPhoto-ablation Technique Handpieces + bursHand excavators, Air-abrasion, Air-polishing, Ultrasonics, Sono-abrasionCaridex™, Carisolv™, EnzymesLasers  478BRITISH DENTAL JOURNAL VOLUME 188. NO.9 MAY 132000 PRACTICE conservative dentistry  was found that the harder the tissue, theeasier it was to cut. Soft, carious dentineapparently could not be removed, but theharder, leathery, deeper layer was more sus-ceptible. 42,43 However, in light of currentknowledge regarding the structure of thecarious lesion in dentine, it is a debatablepoint as to whether this harder, leathery,deeper surface should actually be removedas it probably represents the dentine that hasbeen affected by the carious process but only minimally infected, with a collagen struc-ture permitting remineralisation. There aremany parameters that could potentially beadjusted to alter the cutting characteristicsand Nielsen attempted to analyse the resultsfrom altering the pressure applied, thelength of use of the instrument, the powder :water ratio in the slurry, the nature of thematerial cut and the type of abrasive used.However, due to the erratic and unpre-dictable performance of the instrument, hisresults were inconclusive. 43 Even thoughthis method was developed only to a prelim-inary stage, it was used on forty patients in aclinical trial where they found the techniqueto be favourable in terms of the reducedvibration and sound generated when com-pared with the dental drill. 44 ‘ Sono-abrasion ’   A recent development from the srcinalultrasonics mentioned above is the use of high-frequency, sonic, air-scalers withmodified abrasive tips – a technique knownas ‘sono-abrasion’. The Sonicsys micro unit,designed by Drs Hugo, Unterbrink andMösele in a venture between Ivoclar-Vivadent and KaVo (KaVo Dental Ltd,Amersham, Bucks, UK), is based upon theSonicflex 2000L and 2000N air-scaler hand-pieces that oscillate in the sonic region(<6.5 kHz —see Figure 2). The tipsdescribe an elliptical motion with a trans-clinically soft, carious dentine is notremoved due to the reduced hardness of thecarious substrate when compared with thealumina particles themselves. 3 There is alsothe potential of inhalational problems, withstudies from the 1950s showing evidence of chronic granulomatous reactions, patchy atelectasis and emphysematous changes inrabbits’ lungs after particle inhalation. 29,30 However, no reference was made to the sizeof the inhaled particles in either paper. In1952, Van Leeuwen and Rossano performedexperiments using particles of 40 µ m diam-eter. This size was well above the size consid-ered injurious from a respiratory standpoint. They concluded that on a basisof dust counts, particle size and composi-tion, the normal use of an air abrasive unitpresents little health hazard to patient anddentist. 31 The technique at present has fullUS FDA approval for clinical use of 27.5 µ malumina particles.Recent advances in microabrasion tech-nology allow a metered flow of alumina par-ticles, higher operating pressures andalmost instantaneous initiation and termi-nation of the abrasive stream. Further inves-tigation into the use of alternative abrasivemixtures has indicated that softer particles,eg polycarbonate resin or alumina-hydrox- yapatite mixtures might be more selective incarious dentine removal as they are only capable of removing tissue of equivalenthardness, leaving healthier, sound tissue vir-tually unscathed. 3,32,33 These factors, cou-pled with the use of protective rubber dam,barrier masks for the clinical team, moreefficient suction units to expel the unwanteddust and rapid progress in the developmentof adhesive restorative materials with conse-quent changes in cavity design, might allow the air-abrasive technique to make a come-back in the dental surgery of the future. 1,34  Air-polishing Air-polishing is the process by which water-soluble particles of sodium bicarbonate, towhich has been added tricalcium phosphate(0.08% by weight) to improve the flow char-acteristics, are applied onto a tooth surfaceusing air pressure, shrouded in a concentricwater jet. 35,36 This is the important differ-ence between this technique and that of air-abrasion. The fact that the abrasive is watersoluble means it does not escape too farfrom the operating field. 37 The bombard-ment of the hard tooth surfaces by theseparticles results in a continuous mechanicalabrasive action which removes surfacedeposits. 38 Razzoog and Koka noted thatincreasing the air pressure beyond 90 psiactually reduced the abrasiveness of theMicroprophy System (Danville EngineeringCo., Danville, CA). This was due to a phe-nomenon found in one-dimensional, two-phase fluid dynamics —‘choked flow’. Inthis scenario, as the air pressure exceeds thecritical pressure, the mass flow of particleswill reduce thus limiting the system’s abra-siveness. 39 The commercially recommendeduse of this technique is to remove surfaceenamel stains, plaque and calculus wellaway from the gingival margins of healthy teeth. 35 However, due to the non-selective,abrasive, detrimental surface attack of restorations and sound enamel and dentine,overzealous use could easily remove a con-siderable amount of healthy tooth structureespecially at the cervical margin. 40,41 It hasbeen suggested that air-polishing could beused for the removal of carious dentine atthe end of cavity preparation. 37 Ultrasonic instrumentation Investigation of this technique has beenconfined to work carried out in the 1950swhere studies by Nielsen et al. indicated thepossibility of using an ultrasonic instru-ment to cut tooth tissue. 42,43 He designed amagnetostrictiv instrument with a 25 kHzoscillating frequency. This, used in conjunc-tion with a thick aluminium oxide andwater slurry, created the cutting action, themechanism of which was the kinetic energy of water molecules being transferred to thetooth surface via the abrasive through thehigh speed oscillations of the cutting tip. It Fig. 2 KaVo Sonicflex 2000L air-scaler handpiece with diamond-coated tip  BRITISH DENTAL JOURNAL VOLUME 188. NO.9 MAY 132000479 PRACTICE conservative dentistry  verse distance of between 0.08 – 0.15 mmand a longitudinal movement of between0.055 – 0.135 mm. They are diamondcoated on one side using 40 µ m grit dia-mond (figure 3) and are cooled using waterirrigant at a flow rate of between 20–30 mL /min. The operational air pressure for cavity finishing should be around 3.5 bar (ie thenominal pressure at the coupling). Thereare currently three different instrumenttips: a lengthways halved torpedo shape (9.5mm long, 1.3 mm wide), a small hemi-sphere (1.5 mm diameter) and a large hemi-sphere (2.2 mm —Figure 3). The torqueapplied to the instrument tips should be inthe region of 2 N. If the applied pressure istoo great, the cutting efficiency is reduceddue to damping of the oscillations. Thistechnique was initially developed, using dif-ferent shaped tips, to help prepare pre-determined cavity outlines (Sonicsysapprox) but also works well in removinghard tissue when finishing cavity prepara-tion. Favourable results from laboratory studies using sono-abrasion to remove soft-ened, carious dentine have indicatedanother possible use for this technique inthe future. 3,33 Chemo-mechanical methods:Caridex and Carisolv  In the previous sections, various mechani-cal methods of tooth tissue removal havebeen discussed. There is, however, anotheralternative and in 1976, Goldman and Kro-nman reported on the possibility of remov-ing carious material chemically usingN-monochloroglycine (NMG, GK-101). 45 Subsequently, after modification, theCaridex system, containing N-monochloro-D,L-2-aminobutyrate (NMAB, GK-101E),was introduced. 46 This system was devel-oped as a chemico-mechanical method forcaries removal. Carious dentine, softenedfurther by NMAB (GK-101E), should havebeen readily removed by lightly abrading itssurface with the applicator tip. Several early studies found the technique to have advan-tages including increased patient compli-ance and a reduced need for localanaesthesia. 47,48 Brannström et al. showedit to be a successful way of removing softcarious dentine without any significantdamage to the underlying dentine, 49 butother studies showed no beneficial effect of the system in excavating carious dentinewhen compared with a control systemusing water alone, no reduction in operat-ing time and the need for copious volumesof solution. 50 Further studies also indi-cated that in permanent teeth, the ability of carious dentine removal using NMABwas no greater than that using a controlsolution of isotonic saline. In deciduousteeth, however, addition of urea to thesolution significantly improved cariousdentine excavation compared with thesame control solution without urea. 51,52 Following on from this a gel-based systemwas developed and recently Carisolv gel hasbeen introduced, to be used with specially designed non-cutting hand instruments toabrade the carious dentine surface. Carisolv consists of two carboxymethylcellulose-based gels: a red gel containing 0.1 M aminoacids (glutamic acid, leucine and lysine),NaCl, NaOH, erythrosine (added in orderto make the gel visible during use); and asecond containing sodium hypochlorite(NaOCl —0.5% w/v). The two are thor-oughly mixed in equal parts at room tem-perature before use and then applied, usingthe hand instrument, onto the exposed cari-ous dentine and left for 60 seconds prior togently but firmly abrading away the soft-ened dentine to leave a hard, caries-freecavity. The solution has a pH of around 11and it is postulated that the positively andnegatively charged groups on the aminoacids become chlorinated and further dis-rupt the collagen crosslinkage in the matrix of the carious dentine. The gel consistency will allow the active molecules access to thedentine for a longer period than the equiva-lent irrigating solution in the Caridex system.It is also highly probable that the gel has amechanical lubricating action for the handinstrument which will also aid in theremoval of the softened tissue. Early resultsfrom clinical trials indicated an increasedpatient compliance to this technique overthe use of the dental drill to excavate cariousdentine. 53 However, drawbacks may includethe prolonged operating time (when com-pared with rotary instrumentation) and thesimple fact that the more conventionalrotary methods are still necessary in order togain access to the carious dentine to allow the gel to function. Therefore, the techniquemay only be useful in certain lesions e.g.exposed carious buccal, cervical root lesionsor grossly cavitated, deep lesions in anattempt to minimise pulp exposures.Results from initial lab-based experimentstesting its efficiency and effectiveness haveshown this technique to have the potentialto be a more selective method of cariousdentine removal. 3,54,55 It also appears toproduce a cavity with an incomplete smearlayer with open tubules evident. 44 Thispoint may have clinical relevance to the den-tine bonding ability of adhesive materialsand requires further investigation. Lasers — for the future? Since the development of the first ruby laserby Maiman in 1960, researchers postulatedthat it could be applied to cutting both hardand soft tissues in the mouth. However,early studies found that the ruby laser pro-   Fig. 3 Sonicsys micro diamond-coatedhemispherical cutting tipsFig. 4 Diagram of the cutting tips of the hand instruments supplied withCarisolv gel
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