Intemational Endodontic Journal il994:) 27. 318-324

Ultrasonic root-end preparation Part 1. SEM analysis]. L. GUTMANN*, W. P. SAUNDERS^ L. NGUYEN*, I. Y. GUO* &E. M. SAUNDERS**Bay lor College of Dentistry. Dallas, Texas 75246 USA, ^Glasgow Dental Hospital and School Glasgow G2 3JZand

fThe Dental School University of Dundee, Dundee DDl 4}iN. UK

Summary

Preparations of apical cavities in resected root endsusing rotary burs, with and without citric acid rinse, andultrasonic tips were compared based on the presence orabsence of superficial debris and smear layer. Threegroups of 20 extracted teeth each were prepared asfollows; I, a size 010 round bur was used to prepare anapical cavity 2-3 mm down the long axis ofthe root; II,treatment as per group I followed hy a 60-s rinse with asolution of 10:3 (10% citric acid, 3% Fe2a3); and III, anultrasonic retrotip was used to prepare a 2-3 mm deepapical cavity. Roots were grooved longitudinally, splitand prepared for SEM analysis at XlOO and X780magnification. Examiners were calibrated to a standard-ized grading system. Extensive statistical analysesindicated statistically significant diiferences within andamong the groups (P<0.05). Root-end preparation witha bur created a heavy smear layer at all levels of thepreparation. This layer was partially removed duringultrasonic preparation in the apical two-thirds. Agreater removal of the smear layer was achieved withthe citric acid rinse (P<0.05). Coronally, root-end prepa-rations were contaminated with moderate to heavyamounts of debris with all techniques.

Keywords: root end preparation, ultrasonics.

Introduction

Root-end preparation and filling are commonlyemployed procedures during periradicular surgery(Gutmann & Harrison 1991). Their specific goals are tocreate a mechanically designed cavity which can befilled, hence sealing the apical terminus ofthe root canalsystem. Multiple techniques and instruments have beenadvocated for root-end preparation (Gutmann &

Correspondence: Professor James L, Gutmann, D.D.S., Department ofRestorative Dentistry. Baylor College of Dentistrj'. 3302 GastonAvenue, DaUas. TX 75246 USA.

Harrison 1991), As early as 1939 Tangerud (1939)developed a miniature handpiece to facilitate access toand preparation ofthe apical opening ofthe canal. Thistechnique was the standard approach in clinical practiceuntil the recent development of ultrasonic retrotips andultrasonic preparation techniques (Excellence in Endo-dontics, San Diego. CA, USA) (Carr 1990. 1992.Pannkuk 1992). Advantages of this new approach havebeen cited as elimination of the need for bevelled rootends to gain access to the apical canal system, the abilityto create a preparation in the long axis of the root.greater depth of preparation, and the ability to debridethe root end effectively, especially of cements, pastes andforeign objects. An evaluation of this technique of root-end preparation by Wuchenich et al (1993) showedthat ultrasonically created cavities had more parallelwalls, deeper depths for retention, preparations whichfollowed the line of the root canal, and cleaner surfacesthen those created with burs.

Concomitant with the creation of any cavity prepara-tion is the development of a smear layer (Pashley 1984).It is tenacious, not easily removed by water, and gener-ally requires acid etchants (citric acid) (Register &Burdick 1975) or chelating agents (ethylene diaminete-traacetic acid, EDTA) for removal (Ciucchi et al 1989).Likewise, ultrasonic cleaning has been suggested as anadjunct for removal, especially in the root canal system(Cunningham & Martin 1982). The smear layer hasbeen identified as containing fine inorganic particles ofcalcified tissue, tissue debris, blood cells, and, poten-tially, microorganisms (McComb & Smith 1975,Goldman et al 1982) (Eig. 1). In the root-end prepara-tion, root canal obturating materials such as gutta-percha, sealers and pastes would be included.

The presence of the smear layer has been postulatedas an avenue for leakage and source for bacterial growthand ingress (Pashley 1984), particularly following root-end preparation and filling (Pitt Ford & Roberts 1990).Likewise, it may serve to support growth of bacteria leftin the dentinal tubules (Olgart et al 1974, Brannstrom

318

VUrasonic root-end preparation— SEM 319

> " • - • - -

V •-

Fig. 1. SEM appearance of a smear layer created in a root-end prepara-tion, Dentina! chips are intermingled with organic debris which areboth packed against the dentine wall and loosely arranged on thesurface. Original magnification X7S0,

1984). It would appear logical to attempt to remove theapical cavity smear layer, thereby enhancing root-endliliing material adaptation and potentially minimizing oreliminating apical leakage.

The purpose of this study was to determine the degreeof superficial debris and smear layer present on thedentinal walls of root-end cavity preparations, usingthree techniques: cavity preparation with a bur only.cavity preparation with a bur followed by a 10:3 citricacid: Ee3Cl3 rinse, and cavity preparation with an ultra-sonic retrotip. Part 2 of this study further assesses theseal obtained over short and long term time periods,with each apical cavity preparation technique.

Materials and methods

Sixty single-rooted, recently extracted premolars andcanines were endodontically accessed, and root canalswere cleaned and shaped using a modified double-fiaretechnique (Saunders & Saunders 1992), Subsequently,the canals were obturated with gutta-percha andSeaiapex (Kerr Manufacturing Co., Romulus, MI, USA)using the hybrid technique according to Tagger (1984).

Root ends were resected at a 45° angle using a high-speed diamond bur with water spray. Twenty teeth pergroup had apical cavities prepared as follows.

Group I. A size 010 round bur in a slow-speed hand-piece with water cooling was used to prepare a cavity2-3 mm down the long axis ofthe canal. All visible gutta-percha was removed from the cavity walls. Cavitieswere rinsed with water and dried with paper points.

Group II. Following cavity preparation as in group I, asolution of 10% citric acid and 3% ferric chloride (10:3)(pH = 1.62) was used to lightly fiush the apical cavityand resected root surface for 60 s. Subsequently, thecavity was rinsed with water and dried with paperpoints.Group III. A 2-3 mm deep apical cavity preparationwas cut using an ultrasonic retrotip on the ENAC ultra-sonic system (Osada Electric Co., Los Angeles. CA, USA)at a power setting of 10 under water spray. All cuttingoccurred in a period of 3-5 min. Cavities were dried withpaper points.

All roots were longitudinally grooved, buccal-lingually, with a small round bur without penetratinginto the cavity preparation. The teeth were split with achisel and the two halves were dried, mounted on asingle stud, and sputter coated with gold (Denton DV-502 Sputter Coater. Denton Vacuum, Cherry Hills, N],USA) for SEM evaluation (JBOL JSM-35CF, JEOL.Peabody. MA. USA). Specimens were coded for blindevaluation.

Specimen viewing and evaluation were done by twocalibrated examiners at magnifications of XlOO forassessment ofthe superficial debris iayer, and X780 forassessment of the remaining smear layer; These levels ofviewing were chosen because they showed best thedetail required to make an accurate evaluation, whilestill maintaining as large a field as possible. Criteria ofevaluation were modified from Baumgartner et al(1984) (Tables 1 and 2) after both examiners mutuallyreviewed, at random. 12 coded SEM photomicrographsat both levels of magnification. Prior to scoring the testspecimens, the examiners reviewed samples to ensurecalibration and to reach a mutual understanding as towhat amounts of superficial debris, smear layer, andpatent or blocked dentinai tubules constituted eachranking from 1 to 4. Four photomicrographs of thesuperficial debris (X100) and four of the smeared layer(X780) were taken to represent the four gradations of

Table 1. Superficiai debris

Score Criteria

1 Little or no superficial debris covering up lo 25% of thespecimen

2 LitUe to moderate debris covering between 2 5 and 5O''/i, ofthe specimen

3 Moderate to heavy debris covering between 50 and 75% ofthe specimen

4 Heavy amounts of aggregated or scattered debris coveringover 75% ofthe specimen

320 J.L. Gutmann etal

Table 2. Smear layer

Criteria

Little or no smear layer: covering less than 21:)% of thespecimen; tubules visible and patent

Little to moderate or patchy amounts of smear layer;covering between 25 and 50% of the specimen: many

tubules visible and patentModerate amounts of scattered or aggregated smear layer;

covering between 50 and 75% ofthe specimen; minimalto no tubule visibility or patency

Heavy smear layering covering over 75% of the specimen:no tubule ortfices visible or patent

the scoring system (Figs 2 and 3). These photomicro-graphs served as visual reference standards for theexaminers during the scoring of the test specimens. Bothhalves of each root were independently evaluated ateach magniflcation within each group, in the apical.

middle, and coronal portions of the preparation. As thespecimens were scanned, the examiners independentlyscored each area. Statistical analyses were carried outon the qualitative scores among the levels within thegroups (Friedman two-way test/Wilcoxon signed rankstest), and between the groups {Kruskal-WaUis test/Mann-Whitney U test) to determine whether there wereany significant differences in the degree of superficialdebris or smear layer with each technique at differentcavity levels.

Results

Superficial debris (X100)

A Friedman two-way test within the groups showedthat statistically significant differences (SSD) existed inthe degree of superficial debris (P<0.05). Application ofthe Wiicoxon signed ranks test showed there were

• • • ' • . • • • • • " • : • • " • : :

• : • : : • • ' \

Fig. 2. Standardized gradations of superficial debris used for specimen evaluation (XJOO)(see Table 1 for descriptions), (a) = Score 1: (b)= score 2: (c) =score 3; and (d) = score 4,

Ultrasonic root-end preparation — SEM 321

o:,..^";;:•:,!;'>!• Li«2i;! :

- - - ? • , - , ' ' . [ • ' •

•' - • V "

Fig. 3. Standardized gradations of smear layer used for specimen evaiuation (x780)(see Table 2 for descriptions), (a) = Score 1; (b) =Score 2; (c) = Score 3: and (d) = Score 4,

SSD among all levels in group II (cavity preparationrinsed with citric acid), with the apical level the cleanest(Table 3). Within group I (cavity preparation only) therewere SSD between the apical one-third and the middleone-third, and apical one-third and coronal one-thirdof the preparation, hut not between the middle andcoronal one-thirds. There were no SSD among all threelevels with the ultrasonic preparation, each demon-strating the same amounts of superficial debris. The leastamount of superficial debris was present in the apicalone-third of the cavity preparations rinsed with citricacid.

Among the groups, a Kruskal-Wallis test showed SSD(P<0.05). Further assessment with the Mann-WhitneyU test showed that differences occurred between groups Iand III, and groups II and III. In other words, greateramounts of superficial debris Were present with both burpreparation techniques compared with ultrasonic pre-

paration. However, there were no differences betweengroups I and II (Table 4).

Smear layer (X 780)

Here also, application of the Friedman two-way testindicated there were SSD among the levels evaluated.The Wilcoxon signed rank test showed the differences tobe among all levels in group n. with the apical levelbeing the most devoid of smear layer (Table 3). Mostspecimens demonstrated a clean dentinal surface withpatent tubules. Group I had no SSD among its levels,with all levels demonstrating a heavy smear layercovering over 75% (by definition in Table 2) of thespecimen with no tubule orifices visible (Fig. 4). .

Group III also showed no SSD among all three levels,with moderate amounts of scattered or aggregratesmear layer covering up to 50% (by definition in Table 2)

322 /. L. Gutmann et al.

Table 3. Within-group analyses (mean values)

Group

I

II

III

Debris (XlOU)Smear (X 780)

Debris (XlOO)Smear(x780)

Debris (XlOO)Smear{X780)

Apical1/3

1.9003.950b

1.3501.225

1.700c2.625d

(SD)

(0.82)(0.15)

(0.46)(0.44)

(0.85)(0.43)

Middle1/3

2.475a3.975b

2.1252.375

1.700c2.725d

(SD)

(0.99)(0.11)

(0.60)(1.05)

(0.82)(0.60)

Coronal1/3

2.625a4.000b

3.0003,200

1.700c2.875d

(SD)

(1.09)(0.00)

(0.86)(0.9S)

(0.68)(0.67)

P

0.0210"0.8936

< 0.0001*< 0.0001*

0.91620,1304

* indicates significance at a level = 0.05Values followed by the same letter show no significant differences.(SD) = standard deviation

Table 4. Between-gronps analyses (mean values)

Magniflcation

XlOOX780

I

2.33a3.98

(SD)

(0.85)a(0.08)

n

i 2 7

(SD)

(0.51)(0.71)

m

1.702.74

(SD)

(0.701(0.52)

P

0,0095*<0.0001*

* Indicates significance at a level = 0,05Values followed by the sam.e letter show no significant differences(SD) = standard deviation

of the tubules. Also evidenced was the cutting orgouging of the root canal walls with the ultrasonic tip,which created an. irregular, layered effect {Fig. 5).

Analyses among the groups using the Kruskal-Wallistest showed there were SSD (P<0.05). The Mann-Whitney U test showed the differences to be among allthree groups, with group 11 showing the least amount ofsmear layer and the greatest amount of clean dentineand patent tubules (Table 4}.

Discussion

The presence of debris in the apical cavities, bothsuperficial and smear, is consistent with findings inrestorative dentistry (Pashiey 1984): likewise is theremoval of this debris with cavity cleansers and acidetchants (Register & Bvirdick 1975. Baumgartner et al1984. Ciucchi et al 1989). While the removal of thisdebris subsequent to coronal cavity preparation and

I..

Fib , ._, „layer is forced into the tubnles as plugs. Original magniflcationX2400.

. ^

s

Fig. 5, Ultrasonic root-end preparation with irregular surface textureand variable amounts of smear layer. Original magnification K 780.

UUrasonic root-end preparation— SEM 323

restoration has been advocated in some clinical situa-tions (Brannstrom 1984), the removal of this debrisfrom apical cavity preparations has not been clinicallyaddressed. However, because these layers of debris canserve as either an avenue for leakage or impediment toseal, or as a bacterial substrate (Pitt Ford & Roberts1990), the removal of this debris prior to apical fillingmay be clinically appropriate. This is especially applic-able if root-end filling materials which can bond todentine are advocated, i.e. glass ionomer cements, or ifpenetration of the filling material into the dentinaltubules is considered as ideal.

All three techniques resulted in a significant accumu-lation of dentine debris and root canal filling materials inthe base (coronal one-third) of the apical cavity. Thisdeeply placed debris could serve as a reservoir of futurecontamination in the presence of either apical or coronalleakage. While the ultrasonic preparation was moreeffective in removing the superficial debris in this portionof the preparation, neither the ultrasonic nor the acidrinse was effective in removing of the smear layer.

While the use of ultrasonics would tend to favour theremoval of cavity debris, in this study ultrasonicretrotips provided little more removal than that noted inthe cleaning of root canal systems (Cunningham &Martin 1982, Goldman ft a/. 1982). Apparently, for anycurrent ultrasonic system to be effective in debrisremoval, specific irrigants. acids or chelates must beused in conjunction with the vibratory action.

Standard cavity preparation with a bur followed by anacid rinse provided a cleaner cavity preparation in thecoronal two-thirds than the use of ultrasonic prepara-tion only. In this respect the use of the 10% citric acid:3% ferric chloride (10:3) cavity cleaning solution mightnot only provide a cleaner apical cavity, bul it also mayenhance cemental deposition on the resected root end(Gutmann & Pitt Ford 1993). First, the use of citric acidalone has been shown to be highly effective in theremoval of the smear layer from the root canal system(Baumgartner et al, 1984). Second, the use of the citricacid:ferric chloride combination (10:3) as a surfacecleanser has been shown: (1) to enhance the adherenceof restorative materials which bond to both the organicand inorganic phases of dentin; (2) to provide a cleandentinal surface, free of smear layer and debris; (3) tostabilize the dentine collagen during the demineraliza-tion process (Wang & Nakabayashi 1991). In addition-ally, applications of higher concentrations of citric acidalone for longer periods have been shown to denaturethe collagen (Wang & Nakabayashi 1991). which mayaffect the quality of the collagen available for splicing

with newly formed collagen fibrils during precementalformation. This may be critical to the quality of thein.itial healing on the resected root end.

The cutting of the root-end preparations with theultrasonic retrotips required a greater amount of timethan did preparation with a bur. Also, the gutta-perchafilling material was difficult to remove without spendingadditional time with the retrotip or the adjunctive use ofhand instruments. This may have been a function of theultrasonic unit, retrotip, power setting or operator skill.The power setting of 10 on the EN AC ultrasonic unit waschosen based on a pilot study which determined themost efficacious technique for cavity preparation.Because this was the same setting commonly used forremoval of cemented or foreign objects in the root canal,it is possible that the level of vibration may have had adeleterious effect on the thin unsupported, resected rootends. Although no visible cracks or craze lines werepresent prior to dehydration and preparation for SEManalysis, a further assessment of this possibility iswarranted (see Part 2 of this study).

Statistical analyses of the qualitative data have shownthat SSD exist in the amount of remaining debris withthe different root-end cavity preparation techniques.While the use of an ordinal scale to rank observable,qualitative phenomena is acceptable, this approach toanalyses may not have revealed all pertinent differencesthat were present. However, it was obvious that none ofthe techniques was capable of eliminating the superficialdebris or smear layers which occurred as a result ofcavity preparation. The role and significance of thisremaining debris in the root-end preparation has notbeen addressed with regard to clinical success or failure,with a plethora of studies indicating leakage of all root-end filling materials to some degree (Gutmann &Harrison 1991). Yet there are many studies whichhave addressed the effective removal of all tissue debris,superficial debris and smear layer in the root canalduring non-surgical root canal treatment, using a multi-tude of irrigating agents coupled with ultrasonic devices.These studies have been based on the premise thatthorough debridement before sealing the root canalsystem is the key to long-term successful endodontictreatment. It would seem reasonable then, that tech-niques of root-end preparation should receive the sameemphasis on thorough cleaning prior to filling and theirsuccess would be based on the same premise.

Conclusions

1. There were significant differences (P<0.05) in the

324 /. L. Gutmann et al.

amount of superficial debris remaining in root-endpreparations in both the bur-prepared cavities andthe bur-prepared cavities rinsed with a solution of10% citric acid and 3% ferric chloride.

2. There were no significant differences at all levels inthe amount of smear layer produced with tbe burpreparation only. All levels showed a thick layeringof adherent debris.

3. There were significant differences (P<0.05) at alllevels in the amount of smear layer with the burpreparations which were rinsed with the solution of10% citric acid and 3% ferric chloride. The apicalone-third demonstrated the least amount of smearlayer of all techniques and areas evaluated.

4. There were no significant differences at all levelsof root-end preparations made with the ultra-sonic retrotip for either superficial debris or smearlayer.

5. There were significant diflerences (P<0.05) betweenthe three methods of cavity preparation with regardto both superficial debris and smear layer. The leastamount of superficial debris was observed in theultrasonic group; the least amount of smear layerwas observed in the bur preparation rinsed with asolution of 10% citric acid and 3% ferric chloride.

6. No technique effectively removed the smear layer inthe coronal one-third ofthe preparation.

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