JOURNAL OF ENDODONTICS Copyright © 2001 by The American Association of Endodontists
Printed in U.S.A. VOL. 27, NO. 6, JUNE 2001
Formaldehyde Release from Ground Root Canal Sealer In Vitro Martin J. Koch, MD, Erik Wu¨nstel, Dipl-lng (FH), and Gu¨nter Stein, PhD
• Amubarut (Wera Karl, Bietingen, Germany), batch no.: 9891 • N2 (Indrag Agsa, Bologna, Italy), batch no.: 1201297.
The formaldehyde release from three different ground root canal sealer materials was examined. Ten specimens each of AH26, Amubarut, and N2 were stored under dry conditions for 6 months. An amount of ⬃100 to 200 mg ground material was obtained from each sample by using a round bur and stored for 10 min in distilled water. The formaldehyde concentration of the immersion water was determined by high-performance liquid chromatography. The mean formaldehyde release per mg material was 6.6 (ⴞ2.5) g for AH26 and 8.3 (ⴞ1.0) g for Amubarut. A lower formaldehyde release was detectable by our method from the N2 samples (0.3 ⴞ 0.1 g/g; p < 0.0001). In conclusion formaldehyde release from ground root canal material is low, although a risk of an allergic reaction in susceptible patients cannot be excluded.
The materials were mixed using the manufacturers’ instructions. Specimens (diameter, 8 mm; thickness, 5 mm) were prepared by using polypropylene reaction vessels and stored for 6 months under dry conditions at room temperature. A round bur (HS 018, Komet, Lemgo, Germany) was used without water spray to obtain ground root canal sealer samples. The powder obtained was immersed into 10 ml distilled water at 37°C. The amount of powder (⬃100 to 200 mg) was recorded by weighing for each sample. After 10 min the suspension was centrifugated; 1 ml of the solution was mixed with 4 ml Dimedon-solution (40 mg/100 ml) and stored for 12 h at 37°C. This solution was mixed with 5 ml of ¨ thanol abs. zur Analyse, Merck, Darmstadt, Ger100% ethanol (A many) to dissolve processed crystals. It was analyzed by using an Hitachi LC-Organizer, a Merck-Hitachi L4200 UV-VIS detector ( ⫽ 260 nm), a Merck-Hitachi L 6200 pump, and a 25 cm column packed with LiChrosphere 100 RP-18 (5 m, Merck, Darmstadt, Germany). Standard solutions were prepared from a formaline stock solution (following iodometric titration). The analytic procedure was adopted from Ruyter (8). As eluant methanol with 25% (vol/vol) phosphate buffer (10 mM/L) was used with a flow of 1 ml/min. For statistical analysis a 2 test for contingency tables was performed.
Substance release from dental materials may occur before clinical use, during or immediately after treatment, during the period of use due to wear, corrosion, chemical degradation, etc., and finally during removal of the material. In the past there has been much attention focused on formaldehyde release from endodontic materials. Formaldehyde releasing root canal sealers have been in use for decades. Adverse local effects such as paresthesia of the mandibular nerve have been attributed to the release of formaldehyde from the sealer in overfilled root canals. Although the systemic effects of formaldehyde must not be overestimated, there are a few reports of allergic reaction against formaldehyde-releasing endodontic materials (1– 6). There is evidence that the formaldehyde release drops after setting of root canal sealers (7). However there is no information on formaldehyde release from set root canal sealers during removal of a root canal filling. During apicectomy detrimental material may contact periapical tissue easily.
RESULTS The mean release of formaldehyde from the different materials is given in Fig. 1. The mean formaldehyde release from AH26 specimens was 6.6 g (⫾2.6)/mg material. The mean formaldehyde release per mg ground sealer was 8.3 g (⫾1.0 g). N2 released 0.3 ⫾ 0.1 g/mg material. The difference between the materials was statistically significant (p ⬍ 0.0001). The difference between Amubarut and AH26 was not statistically significant by using a one-tailed t test (p ⫽ 0.08).
MATERIALS AND METHODS DISCUSSION
Three different materials were included: • AH26 (De Trey/Dentsply, Konstanz, Germany), batch no.: 941036
Substance release of dental materials has been under discussion for a long time. The release can be intentioned (such as fluoride 396
Vol. 27, No. 6, June 2001
FIG 1. Formaldehyde release of ground sealer (g/mg material in 10 min).
release from a restorative material), but much more attention has been focused on potentially undesirable effects due to substance release. Formaldehyde release has been demonstrated from different materials, such as composites (9), denture adhesives (10), and root canal sealers (7, 11). Potential systemic effects of formaldehyde have been discussed for restorative materials (12), even if the formaldehyde release seems to be low (compared with endodontic materials). The amounts of sealer used in this in vitro study exceed the mass of ground material, which can be expected from an apicetomy of a small root canal. Many apicetomies are performed on underfilled, narrow, and curved canals that do not contain much sealer. In those clinical situations where larger amounts of ground sealer may occur (e.g. root canal fillings in immature permanent teeth), the rapid removal of detrimental material should be routine. Careful removal of the sealer from the apicetomy site is required not only due to a potential formaldehyde release, but also to avoid irritation of the wound. The clinical systemic exposure probably is smaller than the release in our in vitro samples. It can be estimated that even under normal conditions the total systemic formaldehyde exposure does not exceed the exposure from smoking one cigarette. In vitro AH26 releases no detectable amounts of formaldehyde from intact specimens after setting (7). The epoxide-resin apparently seals the methenamine powder in the depth of the specimen, and it cannot process formaldehyde. However during removal of the material, unprocessed methenamine is exposed and hydrolyzed by water to ammonia and formaldehyde. It can be speculated that this might occur also with material which was stored much longer than 6 months. The setting reaction of Amubarut (also known as Riebler’s paste) is a polycondensation of formaldehyde and a phenolic compound (resorcin). Because this reaction is reversible a formaldehyde release from this material is easy to explain. The low formaldehyde release from the paraformaldehyde-containing N2 in this study is no surprise. This material shows a prolonged release after setting (7). It subsequently “runs out” of its available formaldehyde. However it cannot be excluded that another sampling method (e.g. sampling of formaldehyde by using heat) might reveal more formaldehyde from the ground N2. At least the low formaldehyde release under these experimental conditions must not be taken as a proof of biocompatibility. Other substances—such as unpolymerized monomers, metals (e.g. bismuth), allergenic resins, etc.—also have to be considered. The total amount of formaldehyde released during apicectomy depends not only on the root canal sealer, but also on the size of
In Vitro Formaldehyde Release
the canal and the use of gutta-percha. Apicetomy might be performed at sites where an apical root canal is not filled at all. The proportion between gutta-percha and sealer in the different regions of the root canal cannot be assessed. Formaldehyde allergy is a frequent and complex problem. Formaldehyde is a hapten, a partial allergen, which may react with another molecule to become a complete allergen. There are different types of allergies, depending on the type of reacting molecule (e.g. serum albumin) and on the exposure site (e.g. skin, inhalation etc.) (13). In individuals with formaldehyde allergy, formaldehyde-free root canal sealers should be chosen. Because apicectomies normally are performed several years after the initial root canal treatment there might be no awareness of any substance release from the sealer. In addition it can be difficult to find out which material has been used. Although this study shows only in vitro results some practical recommendations can be discussed. The removal of formaldehydereleasing root canal sealer (especially an apicectomy) in patients with formaldehyde allergy should be performed with caution. Patients with formaldehyde allergy or predisposition for allergy ideally should not receive formaldehyde-releasing endodontic materials. In conclusion there can be a substance release from root canal sealers during removal. The substance release from ground material can be higher compared with unground material. Dr. Koch is affiliated with Poliklinik fu¨r Zahnerhaltungskunde, Ruprecht-KarlsUniversity, Heidelberg, Germany. Dipl.-Ing. Wu¨nstel and Dr. Stein are affiliated with Fachhochschule Wiesbaden, Abteilung Ru¨sselsheim, Fachbereich Mathematik, Naturwissenschaften und Datenverarbeitung, Ru¨sselsheim, Germany. Address requests for reprints to Dr. Martin J. Koch, Poliklinik fu¨r Zahnerhaltungskunde, Ruprecht-Karls-University, Im Neuenheimer Feld 400, D-69120 Heidelberg, Germany.
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