Sheila Clemente MENDONÇA1
Jacy Ribeiro de CARVALHO Jr.1
Danilo M. Zanello GUERISOLI2
Jesus Djalma PÉCORA2
Manoel D. de SOUSA-NETO1
1Faculdade de Odontologia, Universidade de Ribeirão
Preto, Ribeirão Preto, SP, Brasil.
2Faculdade de Odontologia, Universidade de São Paulo, Ribeirão Preto, SP, Brasil.
Braz Dent J (2000) 11(2): 71-78 ISSN 0103-6440
Introduction | Material and Methods | Results | Discussion | Conclusions | Acknowledgments | Resumo | References
In the present study, the effect of aged eugenol (up to 180 days) on the flow, setting time and adhesion of Grossman root canal sealer was evaluated, following the American Dental Association specification number 57 for root canal sealers. An Instron Universal testing machine 4444 was used for testing adhesion. There were statistically significant differences between groups, with a higher flow, lower setting time and adhesion for aged eugenol. It can be concluded that time affects eugenol, with consequent effects on Grossman sealer.
Key Words: dental materials, root canal sealing materials, physicochemical analysis, Grossman root canal sealer.
Not only the technique, but also the quality of the material used is crucial for successful dental treatment. Much research has been carried out in the field of Endodontics in order to produce a material capable of hermetically sealing the root canal system.
In 1936, Grossman developed a root canal sealer with the following composition: powder: silver, hydrogenated resin and zinc oxide; liquid: eugenol and 4% zinc chloride solution. In 1958, observing that silver produced sulfides that darkened the teeth, Grossman eliminated it from the powder composition and also substituted zinc chloride with almond oil to retard the setting time, giving the dentist more time to work on the root canal. Still researching, Grossman (1962) added anhydrous sodium tetraborate to the powder to also retard the setting time and in 1974, he concluded that the addition of almond oil to eugenol was not necessary, because anhydrous sodium tetraborate provided a satisfactory working time.
According to the requisites that a sealing material must have, it is possible to establish research parameters for developing new products, as well as to evaluate those already available. Properties of root canal sealers can be divided into physicochemical, antimicrobial and biological. The investigation of these properties was standardized with the publication of the American Dental Association specification number 57 (American National Standards Institute, 1984). Thus, research and methods could be easily reproduced, making accurate comparisons between different materials and results possible.
Different commercial brands of Grossman cement contain hydrogenated resin or rosin, not having uniformity in the formula. The role of each component of the Grossman cement powder on its physicochemical properties has been studied, as well as the effect of the addition of different vegetable oils to eugenol (Sousa Neto, 1994). It is necessary, however, to study the effects of aged eugenol on these properties, since it suffers an oxidation process and the clinician may not discard this material.
Material and Methods
The cement powder was obtained from the formula proposed by Grossman (1974), as follows: zinc oxide (42%), rosin (27%), bismuth subcarbonate (15%), barium sulfate (15%) and anhydrous sodium tetraborate (1%).
Setting time and flow determination were performed according to the ADA specification number 57 for root canal sealers. Adhesion tests were performed using an Instron universal testing machine 4444 (Instron Corp., Canton, MA, USA). The ADA determines that all tests must be carried out at 23 ± 2ºC and 50 ± 5% relative humidity. Tested materials were submitted to experimental conditions at least 48 hours before the beginning of procedures.
For this study, eugenol was submitted to aging by leaving its flask exposed to environmental light, near a window, for 30, 60, 90, 120, 150 and 180 days, simulating a dental practice environment.
The powder/liquid ratios for the modified cements and spatulation times were obtained as described by Sousa Neto (1997) and are shown in Table 1. The Kruskall-Wallis test was used for statistical analysis.
To test flow, a 3.0 ml Luer glass syringe was prepared to receive 0.5 ml of cement in an ideal clinical consistency, allowing it to be placed in the center of a clean, smooth 10 x 10 cm glass surface. After 180 ± 5 s from the beginning of spatulation, a device composed by another glass surface and an additional load, for a total of 120 g, was placed over the cement. Ten minutes from the beginning of spatulation, the additional weight was removed and the largest and smallest diameters of the disc produced were measured.
Two conditions were necessary to validate the tests: the difference between the largest and the smallest diameters could not exceed 1.0 mm and the disc should be uniformly circular. If these conditions were not found, the test was repeated following the same experimental protocol. Five repetitions were carried out for each cement and the arithmetic mean was obtained, representing the flow of the tested material.
To measure setting time, stainless steel rings, with an internal diameter of 10 mm and a thickness of 2 mm, were fixed with wax on their external surface on a 1 x 25 x 75 mm glass plate. The cement was manipulated, according to the proportion cited in Table 1 and placed inside the metallic ring, until it was completely filled. After 120 ± 10 s from the beginning of spatulation, the apparatus was placed over a grate inside a hermetically sealed plastic container and kept at 37ºC and 95% relative humidity.
After 150 ± 10 s from the beginning of spatulation, a 100 g, 2 mm active point Gillmore needle was positioned vertically on the surface of the material. This test was repeated every 60 s until the needle did not mark the surface of the cement. The setting time was considered as the average of 5 measurements.
For the adhesion test, 105 human molars from laboratory stock were used. These teeth had their crowns intact and were kept in 0.1% aqueous thymol solution under refrigeration until use. Twenty-four hours before the experiment, they were washed with running water to eliminate all traces of thymol. The enamel of the occlusal surface of these teeth was removed with a number 1212 diamond bur (KG Sorensen, Barueri, SP, Brazil) in a high speed handpiece cooled with water. After obtaining a flat occlusal surface, teeth were fixed by their roots in an acrylic resin base to be adapted to the Universal testing machine. Aluminum cylinders (10 mm high x 6 mm internal diameter) with stainless steel handles were placed on the dentin surface and fixed laterally to the teeth with wax. The cements, after manipulation, were placed carefully inside the cylinders with the aid of a vibrator. The material was then placed in a 37ºC, 95% humidity environment for a period three times greater than the normal setting time of the cement.
The samples were placed in an Instron 4444 Universal testing machine with a grip that held the aluminum cylinder handle, by means of exerting vertical traction. An oscillating joint placed between the grip and the measuring cell prevented the appearance of other forces that could cause experimental errors (Sousa Neto, 1997). The machine was calibrated to run at a constant speed of 1 mm/min until the detachment of the aluminum device containing the cement. The traction force necessary to detach the device from the tooth, given in MegaPascal (MPa), was recorded. Five repetitions for each cylinder were performed.
The flow results are shown in Table 2. Statistical analysis showed significant differences (p<0.05) between control, 30, 60 and 90 day old eugenol when compared to 120, 150 and 180 day old eugenol.
Setting time and adhesion results are shown in Tables 3 and 4, respectively. For both properties, statistical analysis showed differences (p<0.05) between groups.
Powder/liquid ratio determination for each sealer was necessary due to the lower pH of eugenol, which decreases the speed of the chemical reaction between this liquid and zinc oxide, allowing incorporation of a greater amount of powder to the sealer (Sousa Neto, 1998). This test became frequently used after the results obtained by Batchelor and Wilson (1969), who concluded that the amount of powder incorporated to the liquid affects the rheological properties of cements. These authors also reported that humidity and temperature influence setting time. This procedure was also followed by Benatti et al. (1978), Hyde (1986), and Sousa Neto (1994, 1999).
For testing the flow, ADA specification number 57 recommends the formation by the sealer of a disc of at least 25 mm in diameter. As can be seen in Table 2, all sealers met this condition. Control as well as 30, 60 and 90 day old eugenol were statistically different from 120, 150 and 180 day old eugenol, which shows a directly proportional relationship between age of eugenol and flow, i.e., as eugenol ages, sealer flow increases. The flow of a root canal sealer is an important factor for clinical performance of the material, because it reflects its capacity to penetrate into small irregularities of dentin and also into lateral canals (Grossman, 1976). Sousa Neto (1994) reported that liquid viscosity influences the flow of a sealer. In the present study, it could be observed that the sealer obtained using 120-180 day old eugenol had greater flow, with a possible decrease of liquid viscosity due to oxidation.
Analysis of setting time results showed that after 30 days eugenol was altered causing a decrease in sealer setting time. The setting reaction of zinc and eugenol is basically an ionic reaction, where eugenol acts as a proton donator (H+) (Fragola et al., 1979). The setting mechanism of the zinc-oxide-eugenol-based cements is the result of equimolar mixtures of zinc oxide and eugenol, consisting of zinc oxide involved in a long crystal matrix of zinc eugenolate chelate. Any excess of eugenol is absorbed either by eugenolate and zinc oxide (Brauer, 1967). Based on the research of Fragola et al. (1979), Brauer (1967), and Grossman (1982), the influence of pH on the setting reaction can be explained as follows: zinc oxide (ZnO) reacts with water, producing zinc hydroxide (Zn(OH)2). By reacting with hydrogen (2H+), ionic zinc (Zn2+) and water (2H2O) are produced. Phenolic hydrogen from eugenol is substituted by zinc ions in order to form a zinc-oxide-eugenol chelate, the solidification of the cement then occurring. The pH indicates a higher hydrogen ionic (H+) concentration. This means that the higher the amount of H+, the higher will be the speed of reaction that produces zinc in ionic form (Zn2+). This greater amount of Zn2+ makes the reaction with eugenol faster, decreasing the setting time.
In this study, preliminary tests with a pH measuring tape (Merck, Germany) were performed, and it could be observed that as time passed, eugenol became more acid, which probably accelerated the reaction between this liquid and zinc oxide. Thus, it can be observed that Grossman root canal sealers obtained from aged eugenol are prone to a faster setting time.
Traction is a vectorial force constituted by intensity, direction and orientation. Traction tension is a scalar value constituted only by intensity.
Considering that the adhesion of a sealer is directly proportional to the traction tension, it can be said that adhesion will be as great as the force necessary to displace the sample containing the tested sealer. Adhesion of a root canal sealer means its capacity to attach to the dentinal walls of the root canal and provide bonding between it and gutta-percha points. Adhesion is among the properties that an ideal root canal sealer must have, according to Grossman (1958).
The American Dental Association did not standardize any method for studying the adhesion of root canal sealers due to a lack of consensus among researchers. In the present study, the method reported by Ørstavik (1983), employing the Universal testing machine to perform the adhesion tests of the root canal sealers, was used. This method was also used by Hyde (1986), Wennberg and Ørstavik (1990), and Sousa Neto (1999). The authors observed that the adhesion test gauged by the Universal testing machine promotes a better uniformity and greater reproducibility, providing more accurate results. Tension values in MegaPascal (MPa) favor the comparison between results, because it is an internationally accepted unit.
Sousa Neto (1997), studying the effect of different rosins and hydrogenated resins on the composition of Grossman root canal sealers, observed that rosins are responsible for the adhesion of this cement to the dentin. Different kinds of rosins release a greater amount of ions, which have a higher electrical affinity to dentin, constituted by large amounts of inorganic substances. Thus, the adhesion of Grossman type root canal sealers to the dentin is established by electrostatic bonding, weak in nature (Sousa Neto, 1997).
Analyzing Table 4, it can be observed that Grossman cement powder mixed with aged eugenol resulted in a sealer with less adhesion, probably because this eugenol interfered in the ionic bonding of the sealer.
1. Powder/liquid ratios were different for control, 30, 60, 90, 120, 150 and 180 day old eugenol. Thus, it is necessary to determine this proportion.
2. All Grossman sealers evaluated presented a flow compatible with ADA specification number 57. However, the flow was increased after 120 days of exposure of eugenol.
3.As eugenol ages, pH becomes more acid, which accelerates the reaction between this liquid and zinc oxide, decreasing its setting time.
4. Aging of eugenol decreases adhesion of Grossman root canal sealer.
This research was supported by FAPESP grant #98/12044-0.
Mendonça SC, Carvalho Jr JR, Guerisoli DMZ, Pécora JD, Sousa-Neto MD: Estudo in vitro da influência do eugenol envelhecido sobre o escoamento, o tempo de endurecimento e a adesividade do cimento obturador dos canais radiculares do tipo Grossman. Braz Dent J 11(2): 71-78, 2000.
No presente estudo foi analisado a ação do eugenol envelhecido sobre as seguintes propriedades físico-químicas do cimento de Grossman: escoamento, tempo de endurecimento e adesividade. Os experimentos foram realizados de acordo com a Especificação 57 para materiais obturadores da American Dental Association (ADA), à exceção dos testes de adesividade, que foram realizados utilizando uma Máquina Universal de Ensaios Instron 444.
Unitermos: materias dentários, cimento obturador de canal radicular, análise físico-química, cimento de Grossman.
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Correspondence: Manoel D. Sousa-Neto, R. Cav. Torquato Rizzi 1638, Apt. 43, 14020-300 Ribeirão Preto, SP, Brasil. tel: +55-16-623-6002, fax: +55-16-603-6783. e-mail: firstname.lastname@example.org
Accepted May 17, 2000
Eletronic publication october, 2000