Solubility of Root-endFilling Materials: A ComparativeStudyClaudio Poggio, DMD,* Marco Lombardini, DDS, PhD,* Conti Alessandro, DDS,*and Rindi Simonetta

AbstractThis study tested solubility of 3 root-end filling mate-rials (IRM, Pro Root, and Superseal) and an endodonticsealer (Argoseal) used as positive control. The test wasperformed according to the International StandardsOrganization 6876 standard and the American DentalAssociation specification #30. Six specimens of eachmaterial were prepared and immersed in water. Solu-bility was determined after 24 hours and 2 months andanalyzed statistically with a one-way analysis of vari-ance test. All retrograde filling materials were of lowsolubility. Under the conditions of the present study,IRM, Superseal, and Pro Root are virtually insoluble;this is an adequate physical property for use as root-end filling materials. (J Endod 2007;33:10941097)

Key WordsEndodontic sealer, root-end filling materials, solubility

When nonsurgical root canal treatment has been unsuccessful or is inadvisable,surgical root canal treatment is often carried out to save teeth. This procedureroutinely consists of root-end exposure of the involved apex, resection of its apical end,a retrofilling preparation, and the placement of a root-end filling material to seal theroot canal system. A number of materials have been evaluated for use as root-endfillings. They include amalgam, gutta-percha, zinc oxideeugenol cements, compositeresins, glass ionomers, polycarboxylate cements, ethoxybenzoic acid (EBA) cement,and mineral trioxide aggregate (MTA) (1). Ideal materials for sealing root-end cavitiesshould prevent leakage (2). They should have dimensional stability, should adhere tothe walls of the cavity, should be resistant to resorption, and should be moisture-resistant; they should also be nontoxic and biocompatible to promote healing (3).Johnson (4) reviewed the different root-end filling materials, highlighting the indica-tions and contraindications of each one.

Originally amalgam was the material of choice for root-end fillings; however,several disadvantages are associated with amalgam, including initial marginal leakage,secondary corrosion, moisture sensitivity, and concerns over mercury toxicity.

Although some investigators have shown glass ionomer cements (5) and compos-ite resins (6) to provide a better seal than amalgam, the issue ofmoisture contaminationremains a valid concern with these materials. The seals of 2 glass ionomers wereadversely affected when the root-end cavities were contaminated with moisture at thetime of material placement (7). Intermediate restorative material (IRM) has addressedsome of the disadvantages concerning amalgam; this material also has potential disad-vantages including moisture sensitivity, irritation to vital tissues, solubility, and difficultyin handling.

Among the available root-end filling materials, super-EBA and MTA have beenshown to have superior sealing characteristics (8, 9), although both these materialshave specific drawbacks. Super-EBA is zinc oxideeugenol cement, modified with EBAto improve the setting time and increase the strength of the mixture. Super-EBA hasmuch better physical properties than zinc oxideeugenol. It shows high compressivestrength, high tensile strength, neutral pH, and low solubility. Even in moist conditions,super-EBA adheres to tooth structure. Super-EBA adheres well to itself and can beadded incrementally as necessary. Reports showed a good healing response to super-EBA with minimal chronic inflammation at the root apex (10). On the other hand,super-EBA is sensitive to moisture, radiolucent, and technique sensitive. The eugenolcontent can irritate periradicular tissues. Leakage studies on the use of EBA cement asa retrograde filling material show conflicting results (11).

MTA was developed by Torabinejad et al (12) to address shortcomings of com-monly used root-end filling materials. The main components in MTA cement are trical-cium silicate, tricalcium aluminate, tricalcium oxide, and silicate oxide (12). MTA is apowder consisting of hydrophilic particles that set in the presence of moisture. Hydra-tion of the powder results in a colloidal gel that solidifies to a hard structure. Severalstudies on MTA have demonstrated that this material possesses many ideal properties.The sealing ability of MTA in root-end fillings was found to be superior to that ofamalgam, IRM, and super-EBA with both dye and bacterial leakage methods (1316),but extended setting time and difficulties in handling MTA have resulted in limited usein many surgical situations.

Marginal adaptation and crack formation with super-EBA and MTA were analyzedafter subjecting them to occlusal loads equivalent to those generated by masticatory

From the *Department of Operative Dentistry and De-partment of Biochemistry, University of Pavia, Pavia, Italy.

Address requests for reprints to Claudio Poggio, DMD,Department of Operative Dentistry, Policlinico San Matteo,Piazzale Golgi 3, 27100 Pavia, Italy. E-mail address:c.poggio@unipv.it.0099-2399/$0 - see front matter

Copyright 2007 by the American Association ofEndodontists.doi:10.1016/j.joen.2007.05.021

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movements for 5 years (17). Both materials were found to offer excel-lent marginal adaptation, with somewhat superior performance whenusing MTA.

Insolubility of root-end fillings might have a great impact on thesuccess rate of the surgical procedure. Moreover, sealers should havelow solubility because components leaching from the root canal mighthave undesirable biologic effects on the surrounding tissues (18). Sur-prisingly, few studies have been carried out on the solubility of thesematerials (19).

The purpose of this study was to compare solubility at 24 hoursand at 2 months of different root-end filling materials: 2 zinc oxideeugenol cements (IRM and Argoseal), 1 EBA cement (Superseal), andMTA.

Materials and MethodsThree root-end filling materials, representing different chemical

classes of materials, and one endodontic sealer (used as positive con-trol) were included in the present study. Table 1 shows chemical com-position of the materials tested.

The solubility of IRM, ProRoot, Superseal, and Argoseal was de-termined in accordance with the International Standards Organization(ISO) 6876 method and with American Dental Association (ADA) spec-ification #30 (20, 21). This International Standard specifies require-ments for materials used for permanent obturation of the root canalwith or without the aid of obturating points. Stainless steel ring moldswith an internal diameter of 20! 0.1mm and a height of 1.5! 0.1mmwere used for sample preparation. All molds were cleaned with acetonein an ultrasound bath for 15 minutes. All molds were weighed 3 timesbefore use (accuracy, !0.0001 g) on a Mettler AE-163 (Mettler To-ledo) balance, which was used throughout the experiment. The moldswere placed on a glass plate and filled to slight excess with the mixedmaterials. All root-end fillings were mixed by the same operator inaccordance with manufacturers instructions (Table 2). After filling the

molds, another glass plate covered with a Mylar strip was placed on topof themolds, exerting a light pressure to remove any excessmaterial. Sixsets of specimens for each material were prepared in 1 operation. Allsamples were left to set for 24 hours on a grating in a cabinet at 37C and100% relative humidity. The samples in their molds were then exposedto air for 15 minutes and weighed 3 times, and the average reading wasrecorded to 3 decimal places. The specimens of each material wereindividually placed in tarred bottles containing 5 mL of distilled water.The bottles were then transferred to an oven at 37C in which theyremained for 24 hours. They were then removed from the oven andrinsed with distilled water, which was then collected in the same bottles.After that, the water was evaporated at a temperature slightly belowboiling point. Bottles and residues were dried in an oven at 105C,cooled down in the same desiccator, and weighed. The differencesfound between this weight and the original bottle weight were divided bythe initial dry weight of the specimens and multiplied by 100. The resultwas recorded as solubility (22, 23). The solubility test was performedagain at 2 months by using the same method. Results were analyzed byanalysis of variance test. Statistical difference was set at P".01.

ResultsThe results of solubility test (after 24 hours and after 2 months)

are listed in Table 2. All the materials fulfilled the requirements of theInternational Standard 6876, demonstrating a weight loss of less than3%. There was no statistical significance in solubility among the mate-rials tested after 24 hours (P" 0.01). The weight loss of the 4 root-endfillings after 2 months was not statistically significant; thus the materialswere virtually insoluble.

DiscussionThe purpose of inserting a root-end filling material is to provide an

apical seal that inhibits the leakage of irritants from the root canalsystem into the periradicular tissues (24). Sutimuntanakul et al (25)experimentally investigated the sealing properties of MTA in relation toother materials such as super-EBA, Ketacfill, and gutta-percha. Theyreported less leakage with MTA compared with amalgam. Pichardo et al(26) compared apical leakage of Geristore, MTA, and super-EBA root-end filling materials in human teeth previously stored in 10% formalin;they found less leakage in teeth restored with Geristore compared withMTA and super-EBA, regardless of storage medium.

Torabinejad et al (12) and Bonson et al (27) suggested that MTApromotes healthy apical tissue formation more often than other mate-rials, as confirmed by a lower incidence of inflammation. Shahi et al(28) studied biocompatibility of grey MTA, white MTA, and amalgam.They stated that after 3 and 7 days, amalgam produces a more severe

TABLE 1. Chemical Composition of Materials Tested

Type of RootendFillup Material Manufacture Chemical Composition

Zinc oxideeugenol IRM Dentsply, JohnsonCity, TN

Powder ZnO 80%; polymethyl methacylate 20%

Liquid Eugenol 99%MTA Pro Root Dentsply, Johnson

City, TNPowder Calcium phosphate, calcium oxide,

silica, bismuth oxideLiquid Sterile distilled water

EBA Superseal Ogna, Milano,Italy

Powder Zinc oxide 30%; aluminum oxide 38%;calcium tungstate and resin

Liquid Eugenol 37.5%; 2 EBA 66%Zinc oxideeugenol Argoseal Ogna, Milano,

ItalyPowder Silver 30%; zinc oxide 40%; natural

resin 15%; diiodothymol 15%Liquid Bidistilled eugenol 78%; purified

olcoresin 22%

TABLE 2. Solubility Percentage After 24 Hours and 2 Months and StandardDeviation of Weight Loss for Each Material and for Each Immersion Period

Material

Solubility After24 Hours

(in Percentage)and SD

Solubility After2 Months

(in Percentage)and SD

IRM 0.65% (0.19) 1.01% (0.22)Pro Root 0.70% (0.26) 0.91% (0.29)Superseal 0.23% (0.25) 0.40% (0.24)Argoseal 0.97% (0.33) 1.50% (0.35)

SD, standard deviation.

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inflammatory response than grey and white MTA. However, after 3weeks, the inflammatory response was the same for all 3 materials.

Endodontic surgery has now evolved into endodontic microsur-gery. Following their clinical experience and published research, Kim etal (29) affirmed that endodontic microsurgery with MTA is a reliableprocedure to save teeth. In a retrospective study, Tsesis et al (30)confirmed that modern surgical endodontic treatment with operativemicroscope and ultrasonic tips significantly improves the outcome ofthe therapy compared with the traditional technique; however, onlycases that used IRM as a retrograde filling material were included in thestudy.

The choice of root-end filling material is not the only factor thatcan influence the outcome of the surgical therapy; it also depends on theway the material is handled. Walker et al (31) stated that a moistenedcotton pellet should be placed onto the intracanal MTA surface undertemporary restoration; this procedure could significantly improve itsmechanical properties. The capacity of tooth-colored MTA to maintainan apical seal in the presence of bacteria, when contaminated withblood, saline, or saliva, was investigated (32). Tooth-colored MTA con-taminatedwith saliva leaked significantlymore than the uncontaminatedtooth-colored MTA.

Solubility is a very important factor in assessing the suitabilityof potential substances to be used as restorative materials in den-tistry. Lack of solubility has also been stated as an ideal character-istic for root-end filling materials (33). In the ISO 6876, the pro-cedure for determining the solubility of root canal sealers in wateris described. The solubility test performed in the present studyfollowed the procedures laid out in this International Standard. Atpresent, root-end fillings are not included in the scope of this stan-dard, and they are, as yet, not subjected to standardization. Thisprocedure was followed because root-end fillings get direct contactwith periapical tissues as endodontic sealers. The results might atleast be qualitatively transferable to a clinical situation. However, inany clinical situation, only part of the root-end fillings will be incontact with the aqueous environment (ie, the periapical tissues),whereas under the conditions of the present study, the osmoticeffect would be more important, because the whole specimen is incontact with a large amount of distilled water (22). The test wasrepeated after 2 months, because Schafer et al (19) stated that the24-hour period of the specification test is not sufficient.

This study indicated that IRM, Superseal, and MTA showed nosigns of solubility in water. As for MTA, our results are in accordancewith the studies of Torabinejad et al (12) and Danesh et al (8). On thecontrary, Fridland et al (23) demonstrated with the same method thatMTA might partially release its soluble fraction to an aqueous environ-ment during a long period of time with decreasing rate. The authors alsoconfirmed that this soluble fraction is mainly composed of calciumhydroxide, which yields high pH values.

IRM gave good results, but in clinical studies (34) the use of MTAas a root-end filling material resulted in a high success rate, better thanthat of IRM although not statistically significant.

Argoseal, a zinc oxideeugenol endodontic sealer, was used as acontrol. This material also provided a very low weight loss, lower thanthe one accepted by the ISO 6876 International Standard.

The root-end filling materials are normally in contact with perira-dicular tissue fluid until they are covered with fibrous connective tissueor cementum. Clinically, biocompatible root-end filling materials withgood sealing ability should generate little or no inflammatory responsein periradicular tissues and encourage formation of connective tissuecovering the entire root-end.

Within the limitation of this in vitro study, the root-end fillingsstudied showedminimal solubility, which is an important physical prop-erty of root-end filling materials.

AcknowledgmentsWe would like to thank Sheila McVeigh, language assistant at

the University of Pavia, for the revision of the text.

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Solubility of Root-endFilling Materials: A Comparative StudyMaterials and MethodsResultsDiscussionAcknowledgmentsReferences