a comparison between the occluding effects of the

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Introduction

Dentine hypersensitivity is a common painful den-tal problem. Exposure of cervical dentine andpatency of dentinal tubules may occur due tothe loss of covering enamel and/or gingival reces-sion with loss of cementum. Both processes havemultifactorial aetiology.1,2 The most acceptabletheory to explain the mechanism of dentine hyper-sensitivity is the hydrodynamic theory.3 Fluidsmove within dentinal tubules in response to var-

ious thermal, chemical and bacterial stimuli fromthe dentinal surface, and stimulate mechanore-ceptors in the pulp to cause pain. Pulp irritationassociated with permeation through dentinaltubules is often dictated by the permeability of dentine.4 Therefore, occlusion of the dentinaltubules reduces sensitivity by minimising the per-meability of dentine.

Various findings concerning the occluding effectof desensitising agents on open dentinal tubuleshave been reported, but the problem of permea-tion through dentinal tubules has not been solved.

Strontium combines with phosphate in dentinalfluid and by exchanging for calcium in the hydroxylapatite of the dentinal tubule walls, it may producestrontium phosphate crystals and dentinal tubuleocclusion.5 Other researchers have suggested thatstrontium ions alter neural transmission, whichmay account for the immediate improvement inrelieving sensitivity, and that strontium may sti-mulate the formation of irritation dentine to bindto the matrix of the tubule, thus reducing itsradius.6,7

After using laser in many dental applications, thefibre optic could made of hydroxyapatite by thedeposit to plug the tubules would be inorganic toothsubstance,8 and fused hydroxyapatite can be used toseal the root apex or repair a crack in the tooth.When laser is used at a level of 150—190 millijoules(mJ), the dentine is not only vaporised, but it alsomelts and closes off the dentinal tubules,9 a phe-nomenon noted was the melting and deposit of thesilicon fibre optic. The combined use of scanningelectron microscopy and ink permeability measure-ments revealed sealing of the dentinal wall bydeposition of glass-like material, and bridging of

the lateral canal leading to partial occlusion.10 Tothe authors’ knowledge, this is the first study tocompare the occluding effect of a desensitisingagent with the sealing effect of neodymium:yt-trium—aluminium-garnet (Nd:YAG) laser on thedentinal tubules.

Aims of the study

The purpose of this study was to compare theoccluding effect of Nd:YAG laser and sensodyne

(active ingredient strontium chloride) on exposeddentine by: (1) determining the ink permeationthrough exposed dentinal tubules at the cervicallevel of endodontically treated teeth; (2) using ascanning electron microscope (1500) to show thedentinal surface before and after using Nd:YAG laserand sensodyne.

Materials and methods

Sample selection

Forty freshly extracted human maxillary anteriorteeth were collected at random for use in this study.The age, sex, pulpal status or reasons for extractionwere not recorded.

Sample preparation

After extraction, all teeth were stored in normalsaline solution at room temperature. External softtissue and debris were removed using an ultrasonicscaler. The coronal portion of each tooth wasremoved to the level of the cervical line using adiamond disc with a straight handpiece. Thepatency of each canal was established by passinga no. 10 k-type file through the apical foramen,the pulpal tissue was removed by using barbedbroaches, and the working length was determinedby subtracting 1 mm from the length at whichthe tip of the no.10 file just appeared at theapical foramen. The canals were instrumentedusing a conventional hand instrumentation tech-nique with circumferential filing action to masterapical file no. 60 k-type files. Each canal was

536 L.M. Al-Azzawi, R.N. Dayem

showed partial deposition. Untreated specimens were free of deposition and thetubules remained patent.Conclusion: There is no significant difference in the occluding effect of Nd:YAG laserand sensodyne toothpaste. Both treatments have a promising effect on the reductionof permeation through exposed dentinal tubules. However, the occluding effect of Nd:YAG laser occurs within seconds whereas that of sensodyne takes at least 3 weeks.# 2006 Elsevier Ltd. All rights reserved.


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irrigated after each instrument size with 2.5%sodium hypochlorite solution throughout the canalpreparations, and the canals were dried withpaper points. Master gutta percha cones werefitted to within 1 mm of the working length in35 of 40 teeth; five teeth were not obturatedand were reserved as positive controls. The canals

were obturated completely using the lateral con-densation technique (using zinc oxide type sealer,‘DORIFILL’, Austria). Excess gutta percha wasremoved with a heated instrument to a level2 mm apical to the orifices of the canals, and thenthe coronal access preparations were closed withzinc phosphate cement.

All teeth were stored in 100% humidity at 37 8Cfor 48 h to allow time for the sealer to set. In35 of 40teeth, the dentine was exposed by removing thecementum. The remaining five teeth represented anegative control group in which the cementum wasreserved (dentine not exposed). A 3 mm wide ring of

root surface, 2 mm apical to the coronal rim of eachspecimen, was cut by a rotary instrument attachedto a special microlathe. Each root was clampedhorizontally in front of the microlathe, which wasset to cut 1 mmaround the root while it was rotatingto obtain a collar of 3 mm width and 1 mm deptharound the root in order to remove all the cemen-tum and expose the dentine in this area. The desen-sitising agent used was sensodyne, which containsstrontium chloride; this product was chosen basedon its popularity and its relative effectiveness. Thelaser used was Nd:YAG due to its availability and

affectivity.

Sample grouping

The specimens were divided randomly into fivegroups:

Group 1. Ten teeth were treated with an Nd:YAGlaser (focus mode at a wavelength of 1064 nm,100 mJ, 100 Hz repetition rate for 2 s with awater cooling system) on the exposed dentinalsurfaces which were coated with black Chineseink.

Group 2. Ten teeth were treated with sensodyneon the exposed dentine. A 10 g load was applied tothe toothbrush and the brushing frequency wastwo brushes/s.

Group 3. Ten teeth were not treated with eithersensodyne or Nd:YAG laser.

Group 4 (positive control group). Five teeth werenot obturated but the cementum was removedand the dentine was exposed.

Group 5 (negative control group). Five teeth wereobturated without exposing the cementum.

The procedure

Sticky wax coating

The external surfaces of each tooth were coatedwith two layers of sticky wax except for the ring thathad cementum removed. The external surfaces of

the teeth in Group 5 were entirely coated with twolayers of sticky wax.

Citric acid treatment

The teeth were treated for 30 s with 50% citric acidto remove the smear layer from the ring cut out of the tooth surfaces. They were subsequently washedwith distilled water for 5 min.

Storage in saliva

All specimens were stored in whole human salivacollected from the same person and changed dailyfor 21 days. During this period, teeth from Group 2were brushed twice daily (1 min each time) withsensodyne toothpaste using a medium brush, andwere rinsed with distilled water and re-immersed insaliva at the end of 21 days. The teeth of Group 1were subjected to the Nd:YAG laser (focus mode at awavelength of 1064 nm, 100 mJ, 100 Hz repetitionrate for 2 s with a water cooling system) on the ringcut out of the toothsurfaces which were coated withblack Chinese ink.

Storage in ink

After washing, teeth were immersed in pelikan inkfor 72 h. Subsequently, they were removed from theink, washed with water for 30 min, and the stickywax was removed with a sharp wax knife.

Clearing

Specimens were decalcified in 5% nitric acid for 5days, and the acid was renewed daily. Subsequently,teeth were washed for 4 h under running water,

dehydrated in ascending concentrations of ethylalcohol, and immersed in methyl salicylate for24 h to make them transparent.

Scanning electron microscopeexamination

Specimens were air-dried and mounted on alumi-nium stubs. After sputtering with a 40 nm layerof gold using Balzers SCD 050 apparatus, wallsurfaces of the treated samples were examined

A comparison between the occluding effects and the desensitising agent sensodyne 537


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using a Jeol 6100 scanning electron microscope(1500) operating at 10—15 kV. This showed thesurface topography of the dentine substratebefore and after treatment with Nd:YAG laser orsensodyne.

Data collection and statistical analysis

Linear ink penetration was measured using a ver-nier from the apical border of the ring cut from theroot to the maximum optical extension of the ink.Two readings were taken from each tooth on twooccasions by two trained evaluators who had noknowledge about the experimental groups (dou-ble-blind technique). The average of the two mea-surements from each tooth was considered forstatistical analysis. Collected data were analysedby descriptive and differential statistical analysis.Analysis of variance (ANOVA) and Student’s t-testwere performed.

Results

Individual ink penetration measurements for eachtooth from Groups 1—3 are shown in Table 1. All teethfrom Group 3 (not treated with Nd:YAG laser orsensodyne) showed much more ink penetration thanthe teeth treated with Nd:YAG laser or sensodyne.

Teeth treated by Nd:YAG laser showed the leastink penetration, followed by teeth treated by sen-sodyne (Fig. 1). The positive control group (Group 4)demonstrated complete ink penetration, while thenegative control group (Group 5) showed no inkpenetration.

Table 2 shows that there was a highly significantdifference in permeation between and withingroups (ANOVA). Table 3 shows that there was nosignificant difference (t-test, P < 0.05) in permea-tion between Group 1 (Nd:YAG laser) and Group 2(sensodyne).

The difference in permeation between Group 1(Nd:YAG laser) and Group 3 (no treatment) was


Table 2 Analysis of variance of the permeation means

Source of variance Sum of squares d.f. Mean square F Significance level

Between groups 11.802 2 5.901 93.379 P < 0.01 HSWithin groups 1.706 27 0.063

Total 13.508 29

d.f., degree of freedom; HS, highly significant; F , F value.

Table 1 Level of ink penetration (in mm)

1 2 3 4 5 6 7 8 9 10 Mean S.D.

Group 1, Nd:YAG laser 0.3 0.32 0.32 0.39 0.33 0.42 0.38 0.35 0.41 0.36 0.358 0.039Group 2, sensodyne 0.31 0.42 0.3 0.33 0.31 0.35 0.34 0.42 0.45 0.37 0.369 0.054Group 3, untreated teeth 1.52 1.83 1.9 2.02 2.18 1.91 0.98 0.95 1.62 2.03 1.694 0.408

S.D., standard deviation.

Figure 1 Microphotograph shows an area of dentine treated with Nd:YAG laser (original magnification 1500).


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highly significant, and the difference betweenGroup 2 (sensodyne) and Group 3 (no treatment)was significant.

Stereomicroscopic examination results

Stereomicrographs for specimens of Group 1(Nd:YAG laser) showed many deposits on the dent-inal surface in and around the orifices of the dentinaltubules (Fig. 1), and those for Group 2 (sensodyne)showed partial deposits on the dentinal surface and

some orifices of dentinal tubules that remainedpatent (Fig. 2). The micrographs for specimens of Group 3 showed that the dentinal surface was freeof deposits and the tubules remained patent(Fig. 3).

Discussion

Permeation is thought to occur after exposure of dentinal tubules to oral cavity fluids. Determining

A comparison between the occluding effects and the desensitising agent sensodyne 539

Table 3 Paired t-test of the permeation values for comparison between each pair of groups for each treatment

Groups Mean Maximum leakage Minimum leakage t values d.f. Statistical significance

1 and 2 0.358 0.42 0.3 0.522 10 P > 0.050.369 0.45 0.3 NS

1 and 3 0.358 0.42 0.3 2.847 10 P < 0.011.694 2.03 0.95 HS

2 and 3 0.369 0.45 0.3 2.720 10 P < 0.025

1.694 2.03 0.95 Sd.f., degree of freedom; NS, not significant; HS, highly significant; S, significant.

Figure 3 Microphotograph shows an area of dentine before treatment with Nd:YAG laser or sensodyne (originalmagnification 1500).

Figure 2 Microphotograph shows an area of dentine treated with sensodyne (original magnification 1500).


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factors are maintenance of patency of dentinaltubules, number of dentinal tubules exposed andexposure time. This study focused on radicular den-tine, the permeability of which has been observedto be much lower than that of coronal dentine. Inaddition, there is good correlation between tubulenumber/diameter and permeability.11 In addition to

permeation through exposed dentinal tubules, thepresent study investigated the potential tubule-occluding effect of Nd:YAG laser and strontiumchloride hexahydrate 10% (in sensodyne tooth-paste). Teeth from the positive control group (Group4) showed complete ink penetration throughout theroot canal length, while teeth from the negativecontrol group (Group 5) showed no ink penetration.This proved that ink permeation was occurringthrough the exposed dentine, which indicated goodexperimental design and a good coating process.

From data analysis of the experimental groups,Group 3 (untreated with Nd:YAG laser or sensodyne)

was found to have higher ink penetration than Group1 (Nd:YAG laser) and Group 2 (sensodyne), with ahighly significant difference between Group 1 andGroup 3 and a significant difference between Group2 and Group 3. However, there was no significancedifference in ink penetration between Group 1 and2, which means that Nd:YAG laser and strontiumchloride had an equal occluding effect on the dent-inal tubules.

This effect was confirmed by scanning electronmicroscopy, which depicted irregular deposits in andaround the orifices of dentinal tubules of specimens

after treatment with Nd:YAG laser and sensodyne.The results of this study are comparable toothers,2,12,13 but the studies differed in durationof exposure to saliva. In the present study, teethwere exposed to saliva for a fixed period of 21 days,while in Berutti’s study,2 teeth were exposed tosaliva for 20, 40 and 80 days and only sensodynewas used as a desensitising agent. This is in accor-dance with other studies.12,13

The results of the present study were not com-parable with the results of Ling et al.14 who used2 min of brushing, 6 h of rotation in saliva and 10 s of rinsing with distilled water. The differences in tech-nique and the amount of toothpaste applied overtime between the present study and Ling et al.’sstudy may explain this disagreement.14 Topbasiet al.15 reported that sensodyne did not have asignificant effect on the occlusion of dentinal

tubules in vitro but most tubules were occluded invivo. Topbasi et al.15 stored teeth in distilled water,while the teeth in the present study were stored innatural human saliva.

In conclusion, there is no significant differencein the occluding effect of Nd:YAG laser and sen-sodyne toothpaste. Both treatments have a pro-

mising effect on the reduction of permeationthrough exposed dentinal tubules. However, theoccluding effect of Nd:YAG laser occurs withinseconds whereas that of sensodyne takes at least3 weeks.

References

1. Addy EG, Addy M, Adams D. Dentinhypersensitivity, a study of the patency of dentinal tubules in sensitive and non-sensitivecervical dentin. J Clin Periodontol 1987;14:280—4.

2. Berutti E. Permeation of human saliva through dentinaltubules exposed at the cervical level in teeth treated endo-

dontically. J Endo 1996;22:11.3. Brannstorm M. Sensitivity of dentin. Oral Surg Oral Med Oral

Pathol 1966;21:517—26.4. Pashley DH, Pashley EL. Dentin permeability and restorative

dentistry. Am J Dent 1991;4:5—9.5. Kleinberg K. Dentinal hypersensitivity. Part II. Treatment of

sensitive dentin. Compond Cont Educ 1986;7:281.6. Goodman CH. Therapeutic modalities in the treatment of

dentinal hypersensitive.Proceedings on dentinalhypersensitivity. Block Drug Com 1987:18.

7. Jensen ME, Doering JV. A comparative study of two clinicaltechniques for treatment of root surface hypersensitivity.Gen Dent 1987;35:128.

8. Levy GA. Cleaning and shaping of the root canal using a fiberoptic Nd:YAG laser pulsed beam presentation. Am Assoc

Endod 1990.9. Ingle JI, Bakland LK. Endodontics. 5th ed. London: BCDecker;

2002.10. Miscerendino L, Pick R, Blankenau R. Laser safety in dental

practice. In: Miserendino L, Pick R, editors. Laser in dentis-try . Quintessence 1995;6:85—102.

11. Fogel HM, Marshall FJ, Pashley DH. Effects of distance fromthe pulp and thickness on the hydraulic conductance of human radicular dentin. J Dent Res 1988;67:1381.

12. Collins JF, Perkins L. Clinical evaluation of the effectivenessof three dentifrices in relieving dentin sensitivity. J Period-ontol 1984;12:720—5.

13. Gillam DG, Khan N, Mordan NJ, Barber PM. Surface charac-teristics of selected desensitising agents in the dentin discmodel. Scanning microscopy meeting, vol. 5. 1996:10—5.

14. Ling TYY, Gillam DG, Barber PM, Mordan NJ. An investigationof potential desensitising agent in the dentin disc model. JOral Rehabil 1997;24:191—203.

15. Topbasi B, Turkmen C, Gunday. An investigation of the effectof a desensitising dentifrice on dental tubules in vitro and invivo. Quintessence 1998;29:197—9.


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