Braz Dent J (1998) 9(1): 11-18 ISSN 0103-6440

| Introduction | Material and Methods | Results and Discussion | Conclusion | References |

In this study, the effect of different grades of rosin and hydrogenated resin on the setting time of Grossman cement was evaluated. The experiments were carried following the American Dental Association Specification number 57 for root canal sealers. For this analysis, different Grossman cement powders were prepared using different grades of rosin (X, WW and WG) and hydrogenated resins (Staybelite and Staybelite ester 10). The pH and electrical conductance of the different grades of rosin and hydrogenated resin were evaluated. The physicochemical properties of the Grossman cements obtained with the different grades of rosin and hydrogenated resins interfere in the powder-liquid ratio of the cements. The sealers obtained with the hydrogenated resin showed a higher powder-liquid ratio.

Key Words: Grossman cements, powder-liquid ratio.

Endodontic literature reports the need to seal the root canal in a hermetic way. Leonardo and Leal (1991) affirmed that to seal a root canal means to fill it in all its extension with an inert, antiseptic material, obtaining the most hermetic seal possible. This must not interfere and, if possible, should stimulate the process of apical and periodontal repair occurring after endodontic treatment.
Golberg (1982) classified root canal sealers as two types: those placed into the root canal in a solid state (silver and gutta-percha points), and those placed into the root canal in a plastic state (pastes and cements).
The root canal sealers proposed by Grossman (1936, 1958, 1962, 1974) are based on zinc oxide and eugenol and are placed into the interior of the root canals in a plastic state.
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 the silver produced sulfides that darkened the teeth, Grossman eliminated it from the powder composition. He also substituted the zinc chloride with almond oil. The addition of vegetable oil had the purpose of retarding the setting time, giving the dentist more time for root canal treatment. In 1962, Grossman included anhydrous sodium in order to retard the setting time. In 1974, he concluded that the addition of almond oil to eugenol was not necessary, since the anhydrous sodium tetraborate provided adequate working time.
The properties and qualities of root canal sealers can be described as physicochemical, antimicrobial and biological.
Ørstavik (1981, 1988) and Moorer and Genet (1982), among others, investigated the antimicrobial properties and qualities of these materials. The biological aspect was researched most notably by Holland et al. (1971, 1983). The physicochemical properties of the root canal sealers were studied by many researchers, most notably Hyde (1986), Wennberg and Ørstavik (1990), Fidel (1993), and Sousa Neto (1994).
The action of each component of the powder of Grossman cement on the physicochemical properties has been studied, as well as the effect of the addition of vegetable oils to eugenol. It is still necessary, however, to study the action of the different grades of rosin and hydrogenated resin on those properties. Grossman (1982) observed the effect of the vegetable resins in relation to the setting time and in this investigation we studied the powder-liquid ratio.

The root canal sealer proposed by Grossman is based on zinc-oxide and eugenol, as a powder and liquid stored in separated containers. This characteristic places it within ADA Specification number 57, which also states that every test must be carried out under the conditions of 23 ± 2ºC and 50 ± 5% relative humidity, which was observed in the experiments of this research. The materials tested were submitted to the environmental conditions 48 hours before the beginning of the tests.
Three gum rosins [Grade X (Eucatex, São Paulo, Brazil); Grade WG (Madeitex, São Paulo, Brazil); Grade WW (Coimbra, Porto, Portugal)] and two hydrogenated resins [Staybelite ester 10 (Hercules, Wilmington, USA); Staybelite resin (Hercules)] were added to Grossman cements.
All rosins and hydrogenated resins studied came in the gross form. To pulverize these materials, a porcelain mortar and pestle were used. The rosins, as well as the resins, were triturated and passed through 60 and 100 mesh sieves, in order to obtain the conditions proposed by Grossman (1958).
Firstly, the tests to determine the electric conductance and the pH of the rosins and hydrogenated resins were carried out. Twelve grams of each rosin and hydrogenated resin were weighed and placed in a beaker with 48 ml of distilled and deionized water. This mixture was constantly agitated in a magnetic agitator for 1 hour. The electric conductance and pH at 1, 2, 5, 10, 20, 30 and 60 minutes were then measured for each material with an ohmmeter (Digimed) and a potentiometer (Photovolt), respectively.
The powders were prepared according to Grossman’s (1974) specifications, only varying the grade of rosin or hydrogenated resin employed, according to the formula: 42% zinc oxide, 27% rosin or hydrogenated resin, 15% bismuth subcarbonate, 15% barium sulfate, 1% anhydrous sodium tetraborate.
All chemical components used in the powder preparation were obtained in particle sizes that passed easily through a 100 mesh sieve. All rosins and hydrogenated resins were pulverized and passed through 60 and 100 mesh sieves, as recommended by Grossman (1958).
After mixing the components, the powder obtained was placed in a rotary mixer for 30 min, until it was homogenous. The different powders were then packed in tightly closed plastic containers to avoid contact with air, identified and stored to be used in the physicochemical properties tests.
The first stage for the tests of physicochemical properties consisted of the determination of the powder-liquid relationship for each type of prepared cement. The objective was to establish an exact amount of powder that, manipulated with eugenol (SS White), could provide a sealer that presented the ideal clinical consistency proposed by Grossman (1974).
Initially, 3 grams of powder of the cement that was being studied was weighed and, with a graduated pipette, 0.20 ml of the liquid (eugenol) that would be mixed with the powder was placed on a flat glass plate (20 mm thick). The powder was incorporated slowly into the liquid, with a flexible metallic spatula (number 24) and submitted to vigorous mixing.
Once the ideal clinical consistency was obtained, the amount of remaining powder was weighed and using simple subtraction, the amount of powder that had been used was determined. The time spent mixing the cement was also recorded.
Thus, for each sealer, a powder-liquid relationship was obtained that took a certain number of seconds until the ideal clinical consistency was reached. This was repeated five times for each material. An arithmetic average of these values was calculated and the amount of powder necessary was determined so that, when mixed with 1 ml eugenol, manipulated during the certain time, the ideal clinical consistency was obtained.
According to Grossman (1974), the root canal sealer reaches the ideal clinical consistency when it fulfills the following conditions: a) after manipulation, it requires 10 to 15 seconds to drop when placed on a spatula and lifted off the glass plate; b) when the spatula is placed on the softened mass of the manipulated cement and lifted off the glass plate it forms a thread of approximately 2.5 cm, from the spatula to the mass that was on the plate without breaking up.

The preliminary tests of electric conductance and pH of the different types of rosins and hydrogenated resins used in this study were determined with the objective of verifying the relationship with the powder-liquid ratio of the root canal sealers.
Table 1 shows the results obtained for the pH and electric conductance.
The rosin or colophony, according to the Farmacopéia do Brasil (1959), is the solid residue of the coalition of distillation and filtration of the terebinth of several species of pine trees, mainly Pinus palustris miller, Pinus elliotti engelm and Pinus pinaster solander. This material is a resinous mass of yellow or brownish-yellow color, translucent, brilliant, friable, with a scent and terebinthine flavor. It is easily pulverized, resulting in a yellowish white color; when using a water-bath, it forms a clear yellow, limpid and viscous liquid. Its alcoholic solution is acid. Rosin is insoluble in water and completely soluble in alcohol, benzene, ethyl ether, chloroform, acetic acid and in diluted solutions of alkaline hydroxides. Its density varies from 1.07 to 1.09. The composition of rosin is 90% abietic acid (C20H30O2) and the other 10% is a mixture of dihydroabietic (C20H32O2) and dehydroabietic (C20H28O2) acids. The spatial formula of abietic is shown in Figure 1.
 

Figure 1 - The spatial formula of abietic.

Conductivity is a property that indicates the amount of ions present in a solution. The higher the value, the larger the amount of ions in the medium. When different grades of rosins were compared, we observed that Grade X presented low conductivity. This characteristic can be justified by the purification method that this rosin is submitted to during its manufacturing process. Grade X rosin has a uniform light yellow color, different from Grades WG and WW, which have a dark yellow color with differences in pigmentation, indicating the presence of impurities (inorganic ions). Grade WG rosin has high conductivity, indicating large quantities of inorganic ions in its composition.
Hydrogenated resins are obtained from the hydrogenation of rosin. This process consists of adding hydrogen to a molecule, by the reaction with gaseous hydrogen, with or without the presence of a catalyst, lowering the number of double links of an unsaturated chain. The low conductivity found in the hydrogenated resins is due to the hydrogenation process, which removes the impurities from the rosin and makes the chain saturated. These resins showed the least amount of inorganic ions among the studied rosins.
The values of pH reported in Table 1 show that the hydrogenated resins and Grade X rosin have pH values varying from 5.0 to 5.6, which indicates smaller hydrogen ionic concentration than rosin Grades WG and WW, that have pH values lower than 5. Grade WG rosin presents pH 3.6, indicative of high hydrogen ionic concentration.
Thus, the pH and electric conductance values obtained for different types of rosins and hydrogenated resins allows us to point out the following: a) the hydrogenated resins (Staybelite ester 10 and Staybelite) present pH values of 5.6 and 5.1, respectively and low electric conductance; b) the rosins have lower pH and higher electric conductance than the hydrogenated resins; c) Grade WG rosin presents pH 4.7 and the largest index of electric conductance.

Powder-liquid ratio

Table 2 shows the results of the relationships between the powder and the necessary liquid for each sealer tested in this study, as well as the time spent with mixing in order to obtain the desired clinical consistency.
The data presented in Table 3 were submitted to a series of statistical tests indicating that their distribution was not normal. Thus, the Kruskal-Wallis statistical analysis was performed. This test indicated an H0 probability of 0.02% (P<0.1). The differences of the averages were then compared, two by two and are reported in Table 3. The powder-liquid ratios of the cements obtained from the hydrogenated resin Staybelite ester 10 and hydrogenated resin Staybelite are statistically similar between them indicating that, given a certain amount of liquid, they can incorporate the same amount of powder.
Those results can also be observed when the Grade X rosin is compared with Grade WG rosin.
The powder-liquid ratio of the cements obtained from hydrogenated resins are statistically different from the sealer obtained from rosins (Grades X, WG, WW). The cements obtained from the hydrogenated resins needed a larger amount of powder to obtain the consistency recommended by Grossman (1974).
In the present study, different grades of rosins and hydrogenated resins influenced the powder-liquid ratio of the prepared root canal sealers.
The cements that contain hydrogenated resin present a higher powder-liquid ratio, which can be explained as follows: a) the hydrogenated resin presents lower inorganic character (electric conductance), which propitiates its fast dissolution in the eugenol allowing a larger powder incorporation; b) with a less acid pH the reaction between zinc oxide and eugenol proceeds more slowly, allowing a greater incorporation of the powder into the liquid.
Thus, as the several grades of rosins presented higher electric conductance and pH, they provided cements with smaller powder-liquid ratio. A directly proportional relationship between the pH of the rosins and the hydrogenated resins with the powder-liquid ratio was observed, i.e., the higher the pH, the higher the powder-liquid ratio necessary to obtain the ideal clinical consistency.
After verification by Batchelor and Wilson (1969), studies of the powder-liquid ratios of root canal sealers have shown that the amount of incorporated powder into the liquid affects the properties of the cements. Thus, the determination of the powder-liquid ratio became necessary for each cement submitted to the study of the physical properties which was followed by Benatti et al. (1978), Hyde (1986), Fidel (1993), Sousa Neto (1994), among others.
Cements obtained from different grades of rosins and hydrogenated resins reached the consistency proposed by Grossman (1974) in approximately 2-min spatulation time.

Based on the methodology employed and the results obtained it can be concluded that:
1.Grades X, WG, and WW rosin present lower pH than the hydrogenated resins Staybelite ester 10 and Staybelite.
2. The hydrogenated resins Staybelite ester 10 and Staybelite present lower conductance in relation to the 3 grades of rosins (X, WG, WW).
3. The cements obtained from the hydrogenated resins present a higher powder-liquid ratio than the cements obtained from the 3 grades of rosins (X, WG and WW).
4. The pH of the rosins and hydrogenated resins influenced the powder-liquid ratio. The higher the pH, the lower the powder-liquid ratio.

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Correspondence: Manoel D. Sousa Neto, Faculdade de Odontologia, Universidade de Ribeirão Preto, Ribeirão Preto, SP, Brasil.

Accepted December 14, 1997
Electronic publication: October, 1998