Review Article

Laser-Induced Fluorescence for Subgingival CalculusDetection: Scientific Rational and Clinical

Application in Periodontology

Zahi Badran, D.D.S.,1 Julien Demoersman, D.D.S.,1 Xavier Struillou, D.D.S.,1 Herve Boutigny, D.D.S., Ph.D.,2

Pierre Weiss, D.D.S., Ph.D., 3 and Assem Soueidan, D.D.S., Ph.D.1

Abstract

Objective: To review the data available on the laser-induced calculus fluorescence phenomenon and the calculusdetection devices as well as to determine the clinical relevance of using commercialized calculus detectiondevices in periodontal treatment. Methods: In vitro or in vivo English publications found on Medline. Results: Invitro and in vivo studies showed that the devices on the market had a satisfactory detection capacity. Very fewstudies demonstrated that the erbium:yttrium-aluminium-garnet (Er:YAG) laser debridement, when performedwith automatic calculus detection, could lead to improvements at the clinical level, and the outcome was similarto that obtained with conventional treatments. Conclusions: Although preliminary data were encouraging, therewas a lack of scientific data concerning the calculus detection devices. Therefore, future studies are crucial fordetermining the clinical relevance of such equipment.

Introduction

Periodontitis is an inflammatory disease of infectiousetiology.1,2 The periodontal pathogens present in the

bacterial biofilm3 initiate and maintain the inflammatory hostresponse. The latter is responsible for the periodontal break-down, attachment loss, and the formation of pockets. Themain treatment strategy for periodontitis consists of profes-sional scaling and root planing (RP), accompanied by theimplementation of rigorous oral hygiene.4 Therefore, con-trolling the supra- and subgingival biofilm is essential forperiodontal healing. All plaque-retaining factors, such as iat-rogenic restorations, caries, supragingival calculus, should beeliminated prior to the root debridement (RD). Calculus isformed when the bacterial biofilms calcify.5,6 The roughnessof the calculus makes it an ideal surface for bacterial adhesionand proliferation. Subgingival calculus (SGC) removal is themain purpose of root instrumentation,7 which requires me-chanical or photomechanical (laser) instrumentation. RD re-establishes the composition of the subgingival biofilm, whichis compatible with periodontal healing. Therefore, periodon-tal pockets (PP) could heal (reestablishing healthy sulci),mainly through the formation of a long junctional epithelium.Alternatively, the complete elimination of SGC was not foundto be realistic. Residual SGC varied from 12 to 30% after the

nonsurgical RP. A surgical access flap was made to obtain adirect visual detection of SGC, especially when treating thedeep pockets. However, microscopic calculus could not beseen. Therefore, the negative effects of surgery (e.g., patientdiscomfort, increased gingival recession) should not be ig-nored. So far, the endpoint of RD was based on a clinicalassessment by the practitioner, guided by the tactile sensationusing a dental probe. Research has been conducted to developa reliable tool for detecting SGC. New calculus detectiontechniques have been suggested in the literature, and subse-quently placed in the market. These techniques rely on ultra-sound or laser-induced fluorescence (LIF). The latter wasused to develop one of the SGC detection tools in the market(Kavo� Diagnodent�, Germany), which could be coupled toan erbium:yttrium-aluminium-garnet (Er:YAG) laser device(Kavo Laser Key 3�, Germany). The latter was used to performthe LIF-controlled laser debridement (LD). The present reviewfocuses on the scientific rationale behind LIF in SGC detectionand discusses the clinical relevance of using this device.

LIF of Dental Calculus

Fluorescence is a luminescence in which the absorptionof a photon triggers the emission of another photon witha longer wavelength. Several reports have described the

1Department of Periodontology, Faculty of Dental Surgery, Nantes, France.2Department of Periodontology, Faculty of Dental Surgery, Lille, France.3Osteo-articular and Dental Tissue Engineering Laboratory, Faculty of Dental Surgery, Nantes, France.

Photomedicine and Laser SurgeryVolume 29, Number 9, 2011ª Mary Ann Liebert, Inc.Pp. 593–596DOI: 10.1089/pho.2010.2951

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autofluorescence of hard dental tissues, which vary de-pending on the pathological changes.8, 9 Carious lesions havegreater fluorescence intensity (FI), followed by monochro-matic light excitation. The successful use of a red light(638 nm, 655 nm) to induce fluorescence has been used todifferentiate the sound and the carious tissue. The above-mentioned phenomenon facilitated the development of adental caries detection tool, which was commercialized in1998 (Diagnodent). It was suggested that this difference in FIwas caused by the demineralization and alteration of thecrystalline structure of the hard dental tissues.10 Therefore,Hibst et al. explored the origin of fluorescence in the dentalhard tissues.11 The dominant components of enamel anddentine are calcium phosphates, organized in hydroxyapatitecrystals and are essentially organic components. In anotherstudy, Hibst et al. compared induced fluorescence signals(FS) in enamel and various calcium phosphates to find outwhether inorganic components contributed to the signal.12 Itwas observed that calcium phosphates were not responsiblefor the baseline fluorescence of sound teeth. The cariousprocess started with a demineralization phenomenon, whichresulted in the dissolution of calcium. The impact of thisdemineralization was analyzed in the induced fluorescence.It was observed that demineralization increased the FS. Al-ternatively, red light excitation of the incubated bacterialstrains revealed the fluorescing metabolites. This fluores-cence was caused by the presence of bacterial fluorophores inthe carious lesions. These molecules belonged to the por-phyrins group. Protoporphyrin IX was found to be largelyresponsible for the induced fluorescence observed in thecarious lesions. Porphyrins are metabolites that occur as anintermediate bioproduct in the synthesis of heme. Severaltypes of oral periodontopathic bacteria, such as Porphyr-omonas gingivalis or Prevotella intermedia, synthesize the por-phyrins and the other fluorophores. Calculus, especially inthe subgingival area, contains large amounts of porphyrinsbecause of the involvement of P. gingivalis and P. intermediain the periodontal diseases. In fact, these period-ontopathogens are frequently present in the subgingivalpocket’s biofilm. Therefore, using bacterial autofluorescenceto detect SGC has been suggested for the periodontal diag-nosis as well as as therapy. The fluorescence spectroscopy ofthe dental calculus was studied by Buchalla et al. Theemission spectra was investigated from supra- and SGC at awide range of excitation wavelengths in the ultraviolet andvisible range (from 360 to 740 nm).13 The emission spectrafrom calculus differed significantly from the clean rootspectra. However, supra- and SGC had similar emissionsignals. Emission peaks at excitations of 570 and 740 nmwere observed from calculus, but not from the clean rootsurfaces.

Kurihara et al. found that the subgingival calculus had 700and 720 nm fluorescence peaks when excited at 635 and655 nm,14 respectively. Under these conditions, the fluores-cence measurements of blood and periodontopathogenicbacteria showed no fluorescence peaks. It was concludedthat the blood clot and the bacterial colonies masked thefluorescence peaks and prevented calculus detection.Therefore, a total elimination of the bacterial and blood de-posits on the root surface was recommended before at-tempting to detect the calculus autofluorescence. This couldbe achieved by a thorough irrigation of any PP.

Diagnodent is a caries detection tool that relies on thefluorescence of demineralized carious lesions, as was men-tioned previously. It has been suggested that Diagnodentcould also be used as a clinical diagnostic tool for detectingthe subgingival calculus. For the purpose of excitation, thedevice used a diode laser beam with a wavelength (InGaAsP,655 nm) in the appropriate range to induce the calculusfluorescence peaks. A laser light was beamed through acentral quartz fiber on to the root surface. Around this fiber,the additional secondary fibers collected the FS from thecalculus and the hard dental tissues. The FS was transmittedto an optical detection unit after filtering the ambient and thereflected light. A detector (photodiode) measured the FS, andexpressed it in relative units [U] (0–99 range). The relativeunit was displayed on a digital screen, which informed thepractitioner of the presence of calculus or a carious lesion.

Recently, this device has been coupled with an Er:YAGlaser (Kavo, Laser key 3) to detect calculus by means of laser-fluorescence. The Er:YAG laser was found to be effective inthe debridement of PP and based on experimental and clin-ical data the Er:YAG laser appears to possess characteristicsmost suitable for the nonsurgical treatment of chronic peri-odontitis 15 (for review see Schwarz et al.15). In the above-mentioned hybrid laser device, the Er:YAG beam is onlytriggered when SGC is detected on the root surface. There-fore, the FS of SGC is a feedback signal for the selectiveelimination of calculus.

Basic Studies

Krause et al. explored the efficacy of the Diagnodentsystem in detecting calculus.16 The FS were analyzed on theextracted teeth with a periodontal involvement. A histo-metric analysis was conducted for the same areas tested withthe Diagnodent. Toluidine blue staining was used to visu-alize the subgingival calculus in the histological sections. Acorrelation was found between the FI detected by the deviceand the presence of SGC. The addition of blood or salinesolution to the root did not disturb the FS. Folwaczny et al.evaluated 30 extracted teeth for the FI of the root surfaces.17

The samples were divided into three groups depending uponthe media in which the FI was measured: air, electrolytic saltsolution (ES) and bovine blood (BB). In air, the Diagnodentsystem detected a FI of 0.4 ( – 0.51) for cementum and 54.1( – 29.09) for calculus. The signal was weakened in thepresence of BB or the ES. The difference in FI between ce-mentum and calculus was nevertheless significant in eachgroup, which made it possible to distinctly detect the cal-culus FS. In the present study, the threshold value of FI fordetermining calculus was 5 [U], which made it possible todetect SGC with 100% specificity and sensitivity. Recently,the same group explored the effect in vitro of the thresholdvalue on the residual calculus.18 The residual calculus de-creased with a decrease in the threshold level. The meancementum thickness was 80 lm after LD and 90 lm on theuntreated control roots. The loss of cementum after the laserirradiation was considered to be clinically acceptable. It wasconcluded that a threshold of < 5 could be used in clinicalpractice to reduce the amount of the residual calculus.

Another study evaluated the amount of residual calculusafter the mechanical RP of 40 extracted teeth.19 The treatmentendpoint was determined using a probe (control specimens)

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or the Diagnodent device (FI < 5 [U]). On molars, the latterpermits the reduction of the amount of residual calculus afterRP, in comparison to the subjective probe appreciation. Thedetection superiority of Diagnodent was absent on single-rooted teeth.

Schwarz et al. compared the nonsurgical fluorescencecontrolled LD with ultrasonic debridement (UD). They usedan experimental periodontitis model in beagles.20 Both thetreatments reduced the periodontal inflammation and al-lowed for new cementum to be formed, thereby making theconnective attachment possible. Periodontal regenerationwas more pronounced in the group receiving the lasertreatment. LD was less time-consuming than UD.

In addition, when compared to UD, fluorescence-controlledEr:YAG LD performed in vitro appeared to have the sameefficacy in removing the root calculus. Furthermore, it per-mitted selective removal of calculus without any noticeablemodification of the root surface (i.e., dentinal exposure).21 Thepresent findings are in accordance with an in vivo/histologicstudy (i.e., periodontally compromised teeth, considered forextraction), where the control therapy was scaling and RP.22

Schwarz et al. compared the residual subgingival calculus(RSC) on the root surfaces after laser (Kavo Key Laser 3),ultrasonic (Vector� system) or manual debridement.23 Thetreated teeth were periodontally compromised and pro-grammed for extraction. Debridement was performed in vivobefore the extraction. In the laser group, the LIF detection toolwas used for all the specimens, and the absence of FI wasconsidered to be the endpoint of the treatment. There were nosignificant differences between the laser and the ultrasonicgroups in terms of the RSC values when the appropriatesettings (140 mJ, 10 Hz) were used. Both the treatments weremore effective in eliminating SGC than was the manual RP.Alternatively, the RSC in the laser-treated groups were pro-portional to the pocket depth, which suggested a lesser ef-fective calculus detection in the deep pockets. Regarding thelength of the procedure, LD was found to be less time con-suming than the ultrasonic RP. LD resulted in a homoge-neous root surface with rare alterations. Optimal cementumconservation was observed and the mean depth of the rootchanges was significantly lower than that found after UD.

Clinical Studies

To the best of our knowledge, no clinical research has beenperformed to determine the advantages of LIF over themanual detection tools, when performing the same therapy.In addition, few clinical studies have evaluated the treatmentoutcomes after LD by using an LIF-controlled Er:YAG device(Kavo Key Laser 3). These studies were not designed toevaluate the efficacy of the calculus detection device.

In the split-mouth study of Sculean et al. it was observedthat LIF-controlled LD (160 mJ, 10 Hz) led to clinical im-provements at 3 and 6 months, similar to UD.24 In anotherstudy, Tomasi et al. compared LD (160 mJ, 10 Hz) using LIFcalculus detection, to UD.25 For the first treatment modality,the endpoint was the absence of calculus detection, whereasfor the second it was based on subjective judgement by thepractitioner. The mean debridement duration per pocket was3.6 min ( – 1.3) for the LD group and 4.0 ( – 1.1) for the UDgroup. Both the procedures were effective in reducing thepocket depth and increasing the clinical attachment levels, at

4 months post-treatment. Based on the patients’ perceptions,it was observed that the laser treatment generated less dis-comfort than did UD.

Recently, a study evaluated the adjunctive effect of LIF-controlled LD to scaling and RP.26 The addition of LD(160 mJ, 10 Hz) to the mechanical therapy did not improve theclinical outcome at 1 and 2 months. However, LIF-controlledLD permitted a reduction of the Il-1b and TNF-a amounts inthe gingival crevicular fluid. Furthermore, it also permitted areduction of the microbial recolonization rate.

Conclusions

LIF of the subgingival calculus is a proven phenomenon.All the in vitro studies have demonstrated the differential FIbetween the calculus and cementum, regardless of the en-vironment (e.g., blood or water). However, the FS may beperturbed by the bacterial biofilms, cellular debris, and initialdeep pockets. Prior rinsing of PP could be useful for pre-venting a weakened FS that can undermine the reliability ofthe system. Grafting the detection system onto an Er:YAGlaser device represented a progress in the LD of PP. The dataavailable confirmed the efficacy of this hybrid system forselectively ablating SGC without undermining the cemen-tum layer. However, further research is required to deter-mine the optimal detection threshold that would make itpossible to increase the detection sensitivity with clinicallyacceptable root surface damage. In addition, the detectiondevice seems to reduce the time needed for LD. In a clinicalstudy, where the Er:YAG laser device was used in a con-tinuous mode, the mean working time for the laser treatmentin single-rooted teeth was 5 min, whereas it was 4 min for theultrasonic treatment. It was observed that in all the otherstudies, where LD was found to be less time consuming, theLIF detection was responsible for the saving of time.

Calculus detection could be a valuable aid for the less-experienced practitioners who wish to perform laser pocketdebridement, as it makes it possible to determine the end-point of the treatment in a simple manner.

Future clinical studies should make it possible to confirmthe data available on the advantages of LIF detection ofsubgingival calculus in the clinical periodontal practice.There is also a need to determine the relevance of using thestandard threshold indicated by the manufacturer.

Acknowledgments

The present work was supported by a grant from ERT2004 (Faculty of Dental Surgery, University of Nantes). Wethank Dr. Pierre Layrolle for his valuable contribution to thepresent work.

Author Disclosure Statement

No competing financial interests exist

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Address correspondence to:Assem Soueidan

Faculte de Chirurgie Dentaire 1 Place Alexis Ricordeau44042 Nantes

France

E-mail: assem.soueidan@univ-nantes.fr

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