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Violich & Chandler Smear layer in endodontics suggested that the smear layer consisted not only ofdentine as in the coronal smear layer, but also theremnants of odontoblastic processes, pulp tissue andbacteria. Lester & Boyde (1977) described the smearlayer as ‘organic matter trapped within translocatedinorganic dentine'. As it was not removed by sodiumhypochlorite irrigation, they concluded that it wasprimarily composed of inorganic dentine. Goldmanet al. (1981) estimated the smear thickness at 1 lmand agreed with previous investigators that it waslargely inorganic in composition. They noted its pres-ence along instrumented canal surfaces. Mader et al.
(1984) reported that the smear layer thickness wasgenerally 1–2 lm. Cameron (1983) and Mader et al.
(1984) discussed the smear material in two parts: first, Figure 2 Scanning electron micrograph of dentine surface superficial smear layer (Fig. 1) and second, the material showing smear plugs occluding tubules. The surface has been packed into the dentinal tubules. Packing of smear treated for 60 s with Tubulicid Blue Label (Dental Therapeu- debris was present in the tubules to a depth of 40 lm.
tics AB, Nacka, Sweden).
Bra¨nnstro¨m & Johnson (1974) and Mader et al. (1984)concluded that the tubular packing phenomenon wasdue to the action of burs and instruments. Components surface-active reagents in the canal during endodontic of the smear layer can be forced into the dentinal instrumentation. The thickness may also depend on the tubules to varying distances (Moodnik et al. 1976, type and sharpness of the cutting instruments and Bra¨nnstro¨m et al. 1980, Cengiz et al. 1990) to form whether the dentine is dry or wet when cut (Barnes smear plugs (Fig. 2). However, Cengiz et al. (1990) 1974, Gilboe et al. 1980, Cameron 1988). In the early proposed that the penetration of smear material into stages of instrumentation, the smear layer on the walls dentinal tubules could also be caused by capillary of canals can have a relatively high organic content action as a result of adhesive forces between the because of necrotic and/or viable pulp tissue in the root dentinal tubules and the material. This hypothesis of canal (Cameron 1988). Increased centrifugal forces capillary action may explain the packing phenomenon resulting from the movement and the proximity of the observed by Aktener et al. (1989), who showed that the instrument to the dentine wall formed a thicker layer penetration could increase up to 110 lm when using which was more resistant to removal with chelatingagents (Jodaikin & Austin 1981). The amount pro-duced during motorized preparation, as with Gates-Glidden or post drills, has been reported as greater involume than that produced by hand filing (Czonstkow-sky et al. 1990). However, McComb & Smith (1975)observed K-reamers, K-files and Giromatic reciprocating filescreated similar surfaces. Additional work has shownthat the smear layer contains organic and inorganicsubstances that include fragments of odontoblasticprocesses, microorganisms and necrotic materials(Pashley 1992). The generation of a smear layer isalmost inevitable during root canal instrumentation.
Whilst a noninstrumentation technique has beendescribed for canal preparation without smear forma-tion, efforts rather focus on methods for its removal, Figure 1 Scanning electron micrograph of smeared surface of such as chemical means and methods such as ultra- dentine. The crack shapes are processing artefacts overlying sound and hydrodynamic disinfection for its disruption.
dentinal tubules.
Root canal preparation without the creation of a smear ª 2010 International Endodontic Journal International Endodontic Journal, 43, 2–15, 2010

Smear layer in endodontics Violich & Chandler Vassiliadis et al. 1996, Taylor et al. 1997, Timpawat& Sripanaratanakul 1998, Economides et al. 1999,2004, von Fraunhofer et al. 2000, Froe´s et al. 2000,Goya et al. 2000, Timpawat et al. 2001, Clark-Holkeet al. 2003, Cobankara et al. 2004, Park et al. 2004).
Workers have reached different conclusions, with current knowledge of interactions between the smearlayer and factors such as filling technique and sealertype being limited. In addition, the methodology ofstudies, the type and site of leakage tests, and thesample size should be taken into account and consid-eration given to these variables before conclusions arereached (Shahravan et al. 2007).
Some authors suggest that maintaining the smear layer may block the dentinal tubules and limit bacterial Figure 3 Scanning electron micrograph of dentine surface or toxin penetration by altering dentinal permeability with typical amorphous smear layer with granular appear- (Michelich et al. 1980, Pashley et al. 1981, Safavi et al.
ance and moderate debris present (courtesy of Dr Artika 1990). Others believe that the smear layer, being a loosely adherent structure, should be completelyremoved from the surface of the root canal wallbecause it can harbour bacteria and provide an avenue layer may be possible. A noninstrumental hydrody- for leakage (Mader et al. 1984, Cameron 1987a, namic technique may have future potential (Lussi et al.
Meryon & Brook 1990). It may also limit the effective 1993), and sonically driven polymer instruments with disinfection of dentinal tubules by preventing sodium tips of variable diameter are reported to disrupt the hypochlorite, calcium hydroxide and other intracanal smear layer in a technique called hydrodynamic medicaments from penetrating the dentinal tubules.
disinfection (Ruddle 2007).
When viewed under the SEM, the smear layer often Should the smear layer be removed? has an amorphous irregular and granular appearance(Bra¨nnstro¨m et al. 1980, Yamada et al. 1983, Pashley The question of keeping or removing the smear layer et al. 1988) (Fig. 3). The appearance is thought to be remains controversial (Drake et al. 1994, Shahravan formed by translocating and burnishing the superficial et al. 2007). Some investigations have focussed on its components of the dentine walls during treatment removal (Garberoglio & Bra¨nnstro¨m 1976, Outhwaite (Baumgartner & Mader 1987).
et al. 1976, Pashley 1985), whilst others have consid-ered its effects on apical and coronal microleakage(Madison & Krell 1984, Goldberg et al. 1995, Cha- The significance of the smear layer ilertvanitkul et al. 1996), bacterial penetration of the Root canal treatment usually involves the chemome- tubules (Pashley 1984, Williams & Goldman 1985, chanical removal of bacteria and infected dentine from Meryon & Brook 1990) and the adaptation of root within the root canals. The process is often followed by canal materials (White et al. 1987, Genc¸og˘lu et al.
an intracanal dressing and a root filling. Amongst 1993a, Gutmann 1993). In support of its removal are: important factors affecting the prognosis of root canal It has an unpredictable thickness and volume, treatment is the seal created by the filling against the because a great portion of it consists of water (Cerg- walls of the canal. Considerable effort has been made to neux et al. 1987).
understand the effect of the smear layer on the apical 2. It contains bacteria, their by-products and necrotic and coronal seal (Madison & Krell 1984, Goldberg et al.
tissue (McComb & Smith 1975, Goldberg & Abramo- 1985, 1995, Evans & Simon 1986, Kennedy et al.
vich 1977, Wayman et al. 1979, Cunningham & 1986, Cergneux et al. 1987, Saunders & Saunders Martin 1982, Yamada et al. 1983). Bacteria may 1992, 1994, Genc¸og˘lu et al. 1993a, Karago¨z-Ku survive and multiply (Bra¨nnstro¨m & Nyborg 1973) & Bayirli 1994, Tidswell et al. 1994, Lloyd et al. 1995, and can proliferate into the dentinal tubules (Olgart Behrend et al. 1996, Chailertvanitkul et al. 1996, et al. 1974, Akpata & Blechman 1982, Williams & International Endodontic Journal, 43, 2–15, 2010 ª 2010 International Endodontic Journal Violich & Chandler Smear layer in endodontics Goldman 1985, Meryon et al. 1986, Meryon & Brook filling materials into dentinal tubules, whilst the basis 1990), which may serve as a reservoir of microbial of leakage studies remains questionable. Pashley et al.
irritants (Pashley 1984).
(1989) observed an extensive network of microchan- 3. It may act as a substrate for bacteria, allowing their nels around restorations that had been placed in deeper penetration in the dentinal tubules (George et al.
cavities with smear layer. The thickness of these channels was 1–10 lm. Smear layer may thus present 4. It may limit the optimum penetration of disinfecting a passage for substances to leak around or through its agents (McComb & Smith 1975, Outhwaite et al. 1976, particles at the interface between the filling material Goldberg & Abramovich 1977, Wayman et al. 1979, and the tooth structure. Pashley & Depew (1986) Yamada et al. 1983). Bacteria may be found deep reported that, when experimenting with class 1 cavi- within dentinal tubules (Bystro¨m & Sundqvist 1981, ties, microleakage decreased after the removal of smear 1983, 1985) and smear layer may block the effects of layer, but dentinal permeability increased. Saunders & disinfectants in them (Goldberg & Abramovich 1977, Saunders (1992) concluded that coronal leakage of Wayman et al. 1979, Yamada et al. 1983, Baumgart- root canal fillings was less in smear-free groups than ner & Mader 1987). Haapasalo & Ørstavik (1987) those with a smear layer.
found that in the absence of smear layer, liquid 6. It is a loosely adherent structure and a potential camphorated monochlorophenol disinfected the den- avenue for leakage and bacterial contaminant passage tinal tubules rapidly and completely, but calcium between the root canal filling and the dentinal walls hydroxide failed to eliminate Enterococcus faecalis even (Mader et al. 1984, Cameron 1987b, Meryon & Brook after 7 days of incubation. A subsequent study con- 1990). Its removal would facilitate canal filling cluded that the smear layer delayed but did not abolish (McComb & Smith 1975, Goldman et al. 1981, Cam- the action of the disinfectant (Ørstavik & Haapasalo 1990). Bra¨nnstro¨m (1984) had previously stated that Conversely, some investigators believe in retaining following the removal of the smear layer, bacteria in the smear layer during canal preparation, because it the dentinal tubules can easily be destroyed.
can block the dentinal tubules, preventing the ex- 5. It can act as a barrier between filling materials and change of bacteria and other irritants by altering the canal wall and therefore compromise the formation permeability (Michelich et al. 1980, Pashley et al.
of a satisfactory seal (Lester & Boyde 1977, White et al.
1981, Safavi et al. 1990, Drake et al. 1994, Galvan 1984, Cergneux et al. 1987, Czonstkowsky et al. 1990, et al. 1994). The smear layer serves as a barrier to Foster et al. 1993, Yang & Bae 2002). Lester & Boyde prevent bacterial migration into the dentinal tubules (1977) found that zinc oxide – eugenol based root (Drake et al. 1994, Galvan et al. 1994, Love et al.
canal sealers failed to enter dentinal tubules in the 1996, Perez et al. 1996). Pashley (1985) suggested presence of smear. In two consecutive studies, White that if the canals were inadequately disinfected, or if et al. observed that plastic filling materials and sealers bacterial contamination occurred after canal prepara- penetrated dentinal tubules after removal of smear tion, the presence of a smear layer might stop bacterial layer (White et al. 1984, 1987). Oks¸an et al. (1993) invasion of the dentinal tubules. Bacteria remaining also found that smear prevented the penetration of after canal preparation are sealed into the tubules by sealers into dentinal tubules, whilst no penetration of the smear layer and subsequent filling materials. Some sealer was observed in control groups. Penetration in studies provide evidence to support the hypothesis that their smear-free groups ranged from 40 to 60 lm. It the smear layer inhibits bacterial penetration (Pashley may be concluded that such tubular penetration et al. 1981, Safavi et al. 1989). A major limitation is increases the interface between the filling and the that the experiments were undertaken with dentine dentinal structures, which may improve the ability of a discs or root cross-sections, models with little relevance filling material to prevent leakage (White et al. 1984).
in terms of simulating the clinical conditions of root If the aim is maximum penetration into the dentinal canal treatment. Drake et al. (1994) developed a more tubules to prevent microleakage, root canal filling clinically relevant model to determine the effect of the materials should be applied to a surface free of smear presence or absence of the smear layer on bacterial and either a low surface activity or, alternatively, an colonization of root canals.
adequate surface-active reagent must be added to them Williams & Goldman (1985) reported that the smear (Aktener et al. 1989). However, there are no reports of layer was not a complete barrier and could only delay a correlation between microleakage and penetration of bacterial penetration. In their experiment, using the ª 2010 International Endodontic Journal International Endodontic Journal, 43, 2–15, 2010 Smear layer in endodontics Violich & Chandler motile, swarming bacterium Proteus vulgaris, the smear tubule penetration, increased sealer to dentine bond layer delayed the passage of the organisms through the strength and enhanced fluid-tight seal, a recent report tubules. Madison & Krell (1984) using ethylenedi- concluded that smear layer removal did not necessarily aminetetraacetic acid (EDTA) solution in a dye pene- equate to improved resistance to bacterial penetration tration study found that the smear layer made no along these and older types of sealers (Saleh et al.
difference to leakage. Goldberg et al. (1995) studied the sealing ability of Ketac Endo and Tubliseal in an Indiaink study with and without smear layer and found no Methods to remove the smear layer difference. Chailertvanitkul et al. (1996) found nodifference in leakage with or without smear layer, however the time period was short. When the smearlayer is not removed, the durability of the apical seal The quantity of smear layer removed by a material is should be evaluated over a long period. Since the smear related to its pH and the time of exposure (Morgan & layer is nonhomogenous and may potentially be Baumgartner 1997). A number of chemicals have dislodged from the underlying tubules (Mader et al.
been investigated as irrigants to remove the smear 1984), it may slowly disintegrate, dissolving around a layer. According to Kaufman & Greenberg (1986), a leaking filling material to leave a void between the working solution is the one which is used to clean the canal wall and sealer. Meryon & Brook (1990) found canal, and an irrigation solution the one which is the presence of smear layer had no effect on the ability essential to remove the debris and smear layer created of three oral bacteria to penetrate dentine discs. All by the instrumentation process. Chlorhexidine, whilst were able to digest the layer, possibly stimulated by the popular as an irrigant and having a long lasting nutrient-rich medium below the discs.
antibacterial effect through adherence to dentine, does The adaptation of root canal materials to canal walls not dissolve organic material or remove the smear has been studied. White et al. (1987) found that pHEMA, silicone and Roth 801 and AH26 sealersextended into tubules consistently when smear layer Sodium hypochlorite was removed. Genc¸og˘lu et al. (1993b) found removingthe smear layer enhanced the adaptation of gutta- The ability of NaOCl to dissolve organic tissues is well- percha in both cold laterally compacted and thermo- known (Rubin et al. 1979, Wayman et al. 1979, plastic root fillings without sealer. Gutmann (1993) Goldman et al. 1982) and increases with rising tem- also showed that after removing the smear layer, perature (Moorer & Wesselink 1982). However, its themoplastic gutta-percha adapted with or without capacity to remove smear layer from the instrumented root canal walls has been found to be lacking. The A systematic review and meta-analysis by Shahra- conclusion reached by many authors is that the use of van et al. (2007) set out to determine whether smear NaOCl during or after instrumentation produces super- layer removal reduced leakage of root filled teeth ex ficially clean canal walls with the smear layer present vivo. Using 26 eligible papers with 65 comparisons, (Baker et al. 1975, Goldman et al. 1981, Berg et al.
54% of the comparisons reported no significant differ- 1986, Baumgartner & Mader 1987).
ence, 41% reported in favour of removing the smearlayer and 5% reported a difference in favour of keeping it. They concluded that smear layer removal improvedthe fluid-tight seal of the root canal system, whereas Smear layer components include very small particles other factors such as filling technique or the type of with a large surface : mass ratio, which makes them sealer did not produce significant effects.
soluble in acids (Pashley 1992). The most common Urethane dimethacrylate (UDMA) based root canal chelating solutions are based on EDTA which reacts sealers have been introduced. Their aim is to provide a with the calcium ions in dentine and forms soluble better bond to allow less microleakage and increase the calcium chelates (Fig. 4). It has been reported that fracture resistance of root filled teeth through the EDTA decalcified dentine to a depth of 20–30 lm in creation of monoblocks, when a core material such as 5 min (von der Fehr & Nygaard-O ¨ stby 1963); however, Resilon replaces gutta-percha. Whilst some studies Fraser (1974) stated that the chelating effect was indicate that smear layer removal leads to higher almost negligible in the apical third of root canals.
International Endodontic Journal, 43, 2–15, 2010 ª 2010 International Endodontic Journal

Violich & Chandler Smear layer in endodontics of EDTAC (EDTA and cetavlon). The optimal workingtime of EDTAC was suggested to be 15 min in the rootcanal and no further chelating action could be expectedafter this (Goldberg & Spielberg 1982). This study alsoshowed that REDTA was the most efficient irrigatingsolution for removing smear layer. In a study using acombination of 0.2% EDTA and a surface-activeantibacterial solution, Bra¨nnstro¨m et al. (1980) ob-served that this mixture removed most of the smearlayer without opening many dentinal tubules orremoving peritubular dentine. Bis-dequalinium-acetate(BDA), a dequalinium compound and an oxine deriv-ative has been shown to remove the smear layerthroughout the canal, even in the apical third (Kauf-man et al. 1978, Kaufman 1981). BDA is well tolerated Figure 4 Scanning electron micrograph of dentine following 60 s exposure to 18% ethylenediaminetetraacetic acid solu- by periodontal tissues and has a low surface tension tion (Ultradent Products Inc., South Jordan, UT, USA).
allowing good penetration. It is considered less toxicthat NaOCl and can be used as a root canal dressing. Acommercial form of BDA called Solvidont (De Trey, Different formulations of EDTA have been used as A.G., Zurich, Switzerland) was available in the 1980s root canal irrigants. In a combination, urea peroxide is and its use as an alternative to NaOCl was supported added to encourage debris to float out of the root canal experimentally (Kaufman 1983a,b, Chandler & Lilley (Stewart et al. 1969). This product (RC-Prep, Premier 1987, Lilley et al. 1988, Mohd Sulong 1989). Salvizol Dental Products, Plymouth Meeting, PA, USA) also (Ravens Gmbh, Konstanz, Germany) is a commercial includes a wax that left a residue on the root canal brand of 0.5% BDA and possesses the combined actions walls despite further instrumentation and irrigation of chelation and organic debridement. Kaufman et al.
and which may compromise the ability to obtain a (1978) reported that Salvizol had better cleaning hermetic seal (Biesterfeld & Taintor 1980). Many properties than EDTAC. When comparing Salvizol with studies have shown that paste-type chelating agents, 5.25% NaOCl, both were found comparable in their whilst having a lubricating effect, do not remove the ability to remove organic debris, but only Salvizol smear layer effectively when compared to liquid EDTA.
opened dentinal tubules (Kaufman & Greenberg 1986).
A recent experiment examining the addition of two Berg et al. (1986) found that Salvizol was less effective surfactants to liquid EDTA did not result in better smear at opening dentinal tubules than REDTA.
layer removal (Lui et al. 2007).
¸ alt & Serper (2000) compared the effects of ethylene A quaternary ammonium bromide (cetrimide) has glycol-bis (ß-aminoethyl ether)-N,N,N¢, N¢-tetraacetic been added to EDTA solutions to reduce surface tension acid (EGTA) with EDTA. The smear layer was com- and increase penetrability of the solution (von der Fehr pletely removed by EDTA, but it caused erosion of the ¨ stby 1963). McComb & Smith (1975) peritubular and intertubular dentine, whilst EGTA was reported that when this combination (REDTA) was not as effective in the apical third of root canals. EGTA used during instrumentation, there was no smear layer is reported to bind calcium more specifically (Schmid & remaining except in the apical part of the canal. After Reilley 1957).
using REDTA in vivo, it was shown that the root canal Tetracylines (including tetracycline hydrochloride, surfaces were uniformly occupied by patent dentinal minocycline and doxycycline) are antibiotics effective tubules with very little superficial debris (McComb et al.
against a wide range of microorganisms. Tetracyclines 1976). When used during and after instrumentation, it have unique properties in addition to their antimicro- was possible to still see remnants of odontoblastic bial aspect. They have low pH in concentrated solution, processes within the tubules even though there was no and because of this can act as a calcium chelator and smear layer present (Goldman et al. 1981). Goldberg & cause enamel and root surface demineralization (Bjor- Abramovich (1977) observed that the circumpulpal vatn 1982). The surface demineralization of dentine is surface had a smooth structure and that the dentinal comparable with that of citric acid (Wikesjo¨ et al.
tubules had a regular circular appearance with the use 1986). Barkhordar et al. (1997) reported that doxycy- ª 2010 International Endodontic Journal International Endodontic Journal, 43, 2–15, 2010 Smear layer in endodontics Violich & Chandler cline hydrochloride (100 mg mL-1) was effective in (1989) introduced 25% tannic acid solution as a root removing the smear layer from the surface of instru- canal irrigant and cleanser. Canal walls irrigated with mented canals and root-end cavity preparations. They speculated that a reservoir of active antibacterial agents smoother than walls treated with a combination of might remain, because doxycycline readily attaches to hydrogen peroxide and NaOCl, and the smear layer was dentine and can be subsequently released (Baker et al.
removed. Sabbak & Hassanin (1998) refuted these 1983, Wikesjo¨ et al. 1986). Haznedaroglu & Ersev findings and explained that tannic acid increased the (2001) showed that 1% tetracycline hydrochloride or cross-linking of exposed collagen with the smear layer 50% citric acid can be used to remove the smear layer and within the matrix of the underlying dentine, from surfaces of root canals. Although they reported no therefore increasing organic cohesion to the tubules.
difference between the two groups, it appeared that the McComb & Smith (1975) compared the efficacy of tetracycline demineralized less peritubular dentine than 20% polyacrylic acid with REDTA and found that it the citric acid.
was no better than REDTA in removing or preventing In an effort to produce an irrigant capable of both the build up of smear layer, thought to be as a result of removing the smear layer and disinfecting the root its higher viscosity. McComb et al. (1976) also used 5% canal system, Torabinejad et al. (2003) developed a and 10% polyacrylic acid as an irrigant and observed new irrigating solution containing a mixture of a that it could remove smear layer in accessible regions.
tetracycline isomer, an acid, and a detergent (MTAD).
Polyacrylic acid (Durelon liquid and Fuji II liquid) at Their work concluded MTAD to be an effective solution 40% has been reported to be very effective, and because for the removal of the smear layer. It does not of its potency users should not exceed a 30 s applica- significantly change the structure of the dentinal tion (Berry et al. 1987).
tubules when the canals are irrigated with sodiumhypochlorite and followed with a final rinse of MTAD.
Sodium hypochlorite and EDTA This irrigant demineralizes dentine faster than 17%EDTA (De-Deus et al. 2007) and bacterial penetration When irrigating a root canal the purpose is twofold: to into filled canals is similar with both solutions (Ghod- remove the organic component, the debris originating dusi et al. 2007).
from pulp tissue and microorganisms, and the mostlyinorganic component, the smear layer. As there is nosingle solution which has the ability to dissolve organic tissues and to demineralize the smear layer, the The effectiveness of citric acid as a root canal irrigant sequential use of organic and inorganic solvents has has been demonstrated (Loel 1975, Tidmarsh 1978) been recommended (Koskinen et al. 1980, Yamada and confirmed to be more effective than NaOCl alone in et al. 1983, Baumgartner et al. 1984). Numerous removing the smear layer (Baumgartner et al. 1984).
authors have agreed that the removal of smear layer Citric acid removed smear layer better than polyacrylic as well as soft tissue and debris can be achieved by the acid, lactic acid and phosphoric acid but not EDTA alternate use of EDTA and NaOCl (Yamada et al. 1983, (Meryon et al. 1987). Wayman et al. (1979) showed White et al. 1984, Baumgartner & Mader 1987, Cengiz that canal walls treated with 10%, 25% and 50% citric et al. 1990). Goldman et al. (1982) examined the effect acid solution were generally free of the smeared of various combinations of EDTA and NaOCl, and the appearance, but they had the best results in removing most effective final rinse was 10 mL of 17% EDTA smear layer with sequential use of 10% citric acid followed by 10 mL of 5.25% NaOCl, a finding con- solution and 2.5% NaOCl solution, then again followed firmed by Yamada et al. (1983). Used in combination by a 10% solution of citric acid. However, Yamada with EDTA, NaOCl is inactivated with the EDTA et al. (1983) observed that the 25% citric acid–NaOCl remaining functional for several minutes.
group was not as effective as a 17% EDTA–NaOClcombination. To its detriment, citric acid left precipi- Ultrasonic smear removal tated crystals in the root canal which might bedisadvantageous to the root canal filling. With 50% Following the introduction of dental ultrasonic devices lactic acid, the canal walls were generally clean, but in the 1950s, ultrasound was investigated in end- with openings of dentinal tubules that did not appear to odontics (Martin et al. 1980, Cunningham & Martin be completely patent (Wayman et al. 1979). Bitter 1982, Cunningham et al. 1982). A continuous flow of International Endodontic Journal, 43, 2–15, 2010 ª 2010 International Endodontic Journal Violich & Chandler Smear layer in endodontics NaOCl activated by an ultrasonic delivery system was or 1% sodium hypochlorite to achieve the desired used for the preparation and irrigation of canals.
Smear-free canal surfaces were observed using thismethod (Cameron 1983, 1987a,b, Griffiths & Stock 1986, Alac¸am 1987). Whilst concentrations of 2–4%sodium hypochlorite in combination with ultrasonic Lasers can be used to vaporize tissues in the main energy were able to remove smear layer, lower canal, remove the smear layer and eliminate residual concentrations of the solutions were unsatisfactory tissue in the apical portion of root canals (Takeda et al.
(Cameron 1988). However, Ahmad et al. (1987a) 1998a,b, 1999). The effectiveness of lasers depends on claimed that their technique of modified ultrasonic many factors, including the power level, the duration of instrumentation using 1% NaOCl removed the debris exposure, the absorption of light in the tissues, the and smear layer more effectively than the technique geometry of the root canal and the tip-to-target recommended by Martin & Cunningham (1983). The distance (Dederich et al. 1984, O ¨ nal et al. 1993, Tewfik apical region of the canals showed less debris and et al. 1993, Moshonov et al. 1995).
smear layer than the coronal aspects, depending on Dederich et al. (1984) and Tewfik et al. (1993) used acoustic streaming, which was more intense in variants of the neodymium–yttrium-aluminium-gar- magnitude and velocity at the apical regions of the net (Ne:YAG) laser and reported a range of findings file. Cameron (1983) also compared the effect of from no change or disruption of the smear layer to different ultrasonic irrigation periods on removing actual melting and recrystallization of the dentine.
smear layer and found that a 3- and 5-min irrigation This pattern of dentine disruption was observed in produced smear-free canal walls, whilst an 1-min other studies with various lasers, including the carbon irrigation was ineffective. In contrast to these results, ¨ nal et al. 1993), the argon fluoride other investigators found ultrasonic preparation un- excimer laser (Stabholz et al. 1993), and the argon able to remove smear layer (Cymerman et al. 1983, laser (Moshonov et al. 1995, Harashima et al. 1998).
Baker et al. 1988, Goldberg et al. 1988).
Takeda et al. (1998a,b, 1999) using the erbium- Researchers who found the cleaning effects of ultrasonics beneficial used the technique only for the strated optimal removal of the smear layer without final irrigation of root canal after completion of hand melting, charring or recrystallization associated with instrumentation (Ahmad et al. 1987a, Alac¸am 1987, other laser types. Kimura et al. (2002) also demon- Cameron 1988). This is given the term passive ultra- strated the removal of the smear layer with an Er:YAG sonic irrigation and has been the subject of a recent laser. Although they showed removal of the smear review (van der Sluis et al. 2007). Ahmad et al.
layer, photomicrographs showed destruction of peri- (1987a,b) claimed that direct physical contact of the file with the canal walls throughout instrumentation removal of the smear layer is access to the small reduced acoustic streaming. Acoustic streaming is canal spaces with the relatively large probes that are maximized when the tips of the smaller instruments vibrate freely in a solution. Lumley et al. (1992)recommended that only size 15 files be used to maximize microstreaming for the removal of debris.
Prati et al. (1994) also achieved smear layer removal Contemporary methods of root canal instrumentation with ultrasonics. Walker & del Rio (1989, 1991) produce a layer of organic and inorganic material called showed no significant difference between tap water and the smear layer that may also contain bacteria and their sodium hypochlorite when used with ultrasonics, but by-products. This layer covers the instrumented walls they reported that neither solution was effective at any and may prevent the penetration of intracanal medica- level in the canal to remove the smear layer ultrason- ments into the dentinal tubules and interfere with the ically. Baumgartner & Cuenin (1992) also observed close adaptation of root filling materials to canal walls.
that ultrasonically energized NaOCl, even at full The data presented indicate removal of the smear layer strength, did not remove the smear layer from root for more thorough disinfection of the root canal system canal walls. Guerisoli et al. (2002) evaluated the use of and better adaptation of materials to the canal walls.
ultrasonics to remove the smear layer and found it There are, however, no clinical trials to demonstrate necessary to use 15% EDTAC with either distilled water this. Current methods of smear layer removal include ª 2010 International Endodontic Journal International Endodontic Journal, 43, 2–15, 2010 Smear layer in endodontics Violich & Chandler chemical, ultrasonic and laser techniques – none of Baumgartner JC, Mader CL (1987) A scanning electron which are totally effective throughout the length of all microscopic evaluation of four root canal irrigation regi- canals or are used universally. However, if the smear mens. Journal of Endodontics 13, 147–57.
layer is to be removed the method of choice seems to be Baumgartner JC, Brown CM, Mader CL, Peters DD, Shulman JD (1984) A scanning electron microscopic evaluation of the alternate use of EDTA and sodium hypochlorite root canal debridement using saline, sodium hypochlorite, solutions. Whilst much is known about individual and citric acid. Journal of Endodontics 10, 525–31.
irrigants, their use in combination and their interac- Behrend GD, Cutler CW, Gutmann JL (1996) An in-vitro tions (and in some cases precipitates) is less well study of smear layer removal and microbial leakage along understood. Conflicting reports exist regarding the root-canal fillings. International Endodontic Journal 29, 99– removal of the smear layer before filling root canals.
As several new sealer and core materials have recently Berg MS, Jacobsen EL, BeGole EA, Remeikis NA (1986) A been introduced, further investigations are required to comparison of five irrigating solutions: a scanning electron determine the role of the smear layer in the outcome of microscopic study. Journal of Endodontics 12, 192–7.
Berry EA III, von der Lehr WN, Herrin HK (1987) Dentin surface treatments for the removal of the smear layer: an SEM study. Journal of the American Dental Association 115, Biesterfeld RC, Taintor JF (1980) A comparison of periapical Ahmad M, Pitt Ford TR, Crum LA (1987a) Ultrasonic seals of root canals with RC-Prep or Salvizol. Oral Surgery, debridement of root canals: acoustic streaming and its Oral Medicine and Oral Pathology 49, 532–7.
possible role. Journal of Endodontics 13, 490–9.
Bitter NC (1989) A 25% tannic acid solution as a root canal Ahmad M, Pitt Ford TR, Crum LA (1987b) Ultrasonic irrigant cleanser: a scanning electron microscope study.
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ª 2010 International Endodontic Journal International Endodontic Journal, 43, 2–15, 2010

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