EFFECT OF PARTICLE SIZE OF GROSSMAN'S CEMENT POWDER ON SETTING TIME

EFEITO DO TAMANHO DAS PARTÍCULAS DO PÓ DO CIMENTO DE GROSSMAN SOBRE O TEMPO DE ENDURECIMENTO

 

Jesus Djalma PÉCORA ^*
Ricardo Gariba SILVA ^*
Ricardo Novak SAVIOLI ^*
Luis Pascoal VANSAN ^*

 

 

PÉCORA, J. D.; SILVA, R. G.; SAVIOLI, R. N.; VANSAN, L. P. Effect of particle size of Grossman's cement powder on setting time. Rev Odontol Univ São Paulo, v.12, n.1, p.1-4, jan./mar. 1998.

A study was conducted on the hardening time of three Grossman's cements with different powder particle sizes (60, 100 and 150 mesh) using Specification n. 57 of the AMERICAN DENTAL ASSOCIATION1 (1983). The cement obtained from mesh 150 particles showed the longest hardening time (22 minutes), which was different when compared to mesh 60 (17 minutes) and 100 (17 minutes) particles.

UNITERMS: Dental cements; Particle size; Setting time.

 

 

INTRODUCTION

The hardening time of a root canal cement was studied to determine whether the operator would have sufficient time to adjust the silver or gutta-percha cones inside the root canals, if necessary. This is particularly important when filling teeth with multiple roots (GROSSMAN⁶, 1976). The determination of the hardening time of filling materials has been studied by several investigators (MOLNAR; SKINNER⁸, 1942; NORMAN et al.⁹, 1964; BATCHELOR; WILSON², 1969; GROSSMAN ^5,6, 1974, 1976; FRAGOLA et al.⁴, 1979; HYDE⁷, 1986; SAVIOLI¹⁰, 1992; SILVA¹², 1992; SAVIOLI et al.¹¹, 1994; SILVA et al.¹³, 1994; FIDEL et al.³, 1995).

The objective of the present study was to determine the effect of the particle size of Grossman's cement powder on hardening time according to Specification n. 57 of the AMERICAN DENTAL ASSOCIATION¹ (1983).

 

MATERIALS AND METHOD

The cements tested were obtained from the formula proposed by GROSSMAN⁵ (1974), but sifted through meshes 60, 100 and 150, whose respective orifice sizes are 0.250, 0.149 and 0.105 mm.

The powder/liquid ratios were determined by the method of SILVA¹² (1992) and are listed in Table 1. The fluid used to manipulate the cements was eugenol, Metaldente brand.

 

Table 1 - Powder/fluid ratios and spatulation times of the cements tested.

 

The determination of cement hardening times was carried out strictly following Specification n. 57 of the AMERICAN DENTAL ASSOCIATION¹ (1983).

Each cement was manipulated according to the proportions listed in Table 1. After manipulation, the material was placed inside a circular mold, 10 mm I.D. and 2 mm thick, resting on a glass slide until the mold was filled to the upper level of its surface. Approximately 12,010 seconds after the beginning of the mixing procedure, the glass slide/cement-filled mold ensemble was placed on a 10 X 20 mm metal block which was stored inside a hermetically sealed plastic container that was maintained at a constant temperature of 37^oC inside an oven. An atmosphere with 97% relative air humidity was maintained inside this container using a HYGRO-HAAR-SYNTH apparatus of German origin installed there. Thus, the set consisting of the test body/glass slide/metal block was left inside the chamber until the end of the test. After 15,010 seconds from the beginning of the mixing procedure, a Gillmore-type needle was vertically lowered on the horizontal surface of the material.

This needle has a mass of 100 g and a flattened end 2.0 mm in diameter, becoming cylindric in the final 5 mm portion. The needle was placed on the material at 60 second intervals until it no longer indented the material that was being tested. The hardening time of a material was considered to be the time elapsed between the beginning of mixing and the moment when Gillmore needle indentations were no longer visible on the surface of the test material.

To obtain a final figure, three determinations differing by no more than 5% were performed and their arithmetic mean was calculated. The value obtained was considered to be the hardening time for the material in question. The minimum hardening time of a material determined by this method was supposed to be within 10% of the time indicated by the manufacturer according to the specifications followed in the present study.

 

RESULTS

The hardening times for the cements tested are given in Table 2.

 

Table 2 - Hardening times of the cements tested, in minutes.

 

The data were submitted to statistical analysis, which revealed the lack of normality of data distribution. Thus, the non-parametric Kruskal-Wallis test was used for comparison of the means. But this test did not differentiate the variables, since Hc=5.6092 against critical value c² 2 gl. 5 per cent = 5.99 and p=6.05 per cent. The Miller's comparisons obviously confirmed this rigorous result, as shown in Table 3.

 

Table 3 - Kruskal-Wallis teste and Miller’s comparisons.

 

The data showed that the hardening times for the materials obtained from 60 and 100 mesh particles did not differ significantly, whereas the hardening time for the material obtained from 150 mesh particles showed a high tendency for longer hardening time compared to the others.

 

DISCUSSION

HYDE⁷ (1986) stated that the determination of the hardening time of a filling material depends on some variables such as type of equipment used, thickness of the material to be tested, weight of the Gillmore needle, and the environmental conditions under which the tests are carried out, a fact that makes rigorous adherence to Specification n. 57 of the ADA¹ even more important.

BATCHELOR; WILSON² (1969) stated that the consistency and hardening time of any cement are related, both of them being measurements of force development, and both are affected by factors influencing the rate of the hardening reaction, such as humidity and temperature.

NORMAN et al.⁹ (1964) reported that particle size significantly affects hardening of the material, with cements composed of smaller particles hardening more rapidly than cements composed of larger particles. According to these investigators, resin retards the hardening reaction. With respect to the relationship between particle size and hardening time, the opposite was detected in the present study, i.e., the smaller the particle size (150 mesh), the longer the hardening time.

The data reported by FRAGOLA et al.⁴ (1979) agree with those reported by NORMAN et al.⁹ (1964) in terms of the particle size/hardening time relationship, whereas GROSSMAN⁶ (1976) contradicted these authors and denied such a relationship, in agreement with the data obtained here.

GROSSMAN⁵ (1974) stated that the quality of the resin affects the hardening time of the material. In a 1976 study, the same investigator stated that increased temperature and humidity reduced hardening time, in agreement with BATCHELOR; WILSON² (1969). GROSSMAN⁵ (1974) also stated that the fact that zinc oxide is of mineral or mixed origin also affects hardening time. The hardening of the material on the plate is not related to processes occurring in clinical practice, which suffer the interference of the temperature and humidity of the mouth. The amount of material used under clinical conditions differs from that used in laboratory experiments. To minimize the effects of humidity and temperature on the results, the ADA recommends the environmental conditions described in its Specification n. 57.

SAVIOLI¹⁰ (1992) and SAVIOLI et al.¹¹ (1994) clearly demonstrated the effect of natural resin on the hardening reaction of zinc oxide-eugenol, proving that GROSSMAN⁵ (1974) was correct. The addition of natural resin (tar) to the cement powder works as an accelerator, as also reported by MOLNAR; SKINNER⁸ (1942). The authors also stated that natural resin predominantly contains abietic acid which accelerates the hardening reaction of zinc oxide-eugenol. The hydration of sodium borate also affects the process.

Studies by SILVA¹² (1992) and SILVA et al.¹³ (1994) have reported marked differences in hardening time between the materials tested, except for FORP-USP and Grosscanal cements. This indicates that there may be differences in the composition of the materials, as qualitatively detected by the laser microanalysis spectrographic test.

Subjective considerations, which are difficult to analyze, should also be kept in mind. With respect to the particle size of the powder, although the smallest particles are easier to manipulate, the professional tends to use more energy during spatulation while manipulating the material containing greatest particles, a fact that will clearly cause trituration of the particles, thus reducing or eliminating the differences in their size.

 

CONCLUSIONS

On the basis of the methodology employed, we may conclude that:

1. The cement obtained from 150 mesh particles presented the longest hardening time (22 minutes) compared to 60 mesh and 100 mesh, which presented identical hardening times (17 minutes).

2. The cement with the smallest particle size presented the longest hardening time.

 

 

PÉCORA, J. D.; SILVA, R. G.; SAVIOLI, R. N.; VANSAN, L. P. Efeito do tamanho das partículas do pó do cimento de Grossman sobre o tempo de endurecimento. Rev Odontol Univ São Paulo, v.12, n.1, p.1-4, jan./mar. 1988.

Foi realizado um estudo sobre o tempo de endurecimento de três cimentos de Grossman com diferentes tamanhos de partículas do pó (malhas 60, 100 e 150), utilizando a Especificação nº57 da AMERICAN DENTAL ASSOCIATION1 (1983). O cimento cujas partículas foram obtidas a partir da malha 150 apresentou o mais longo tempo de endurecimento (22 minutos), que diferiu do daqueles cujas partículas foram obtidas a partir das malhas 60 (17 minutos) e 100 (17 minutos).

UNITERMOS: Cimentos dentários; Tamanho das partículas do pó; Tempo de endurecimento.

 

 

REFERENCES

1. AMERICAN DENTAL ASSOCIATION Specification n. 57 for endodontic filling materials. Washington: ADA, 1983. 1v.        [ Links ]

2. BATCHELOR, R. F.; WILSON, A. D. Zinc oxide-eugenol cements. I: the effect of atmospheric conditions on rheological properties. J Dent Res, v.48, n.5, p.883-887, Sept./Oct. 1969.        [ Links ]

3. FIDEL, R. A. S. et al. Tempo de endurecimento de alguns cimentos endodônticos que contêm hidróxido de cálcio. Rev Odontol Brasil Central, v.5, n.16, p.15-17, dez. 1995.        [ Links ]

4. FRAGOLA, A. et al. The effect of varying particle size of the components of Grossman's cement. J Endod, v.5, n.11, p.336-339, Nov. 1979.        [ Links ]

5. GROSSMAN, L. I. Endodontic practice. 8. ed. Philadelphia: Lea & Febiger, 1974. p.299-300.

6. GROSSMAN, L. I. Physical properties of root canal cements. J Endod, v.2, n.6, p.166-175, June 1976.        [ Links ]

7. HYDE, D. G. Physical properties of root canal sealers containing calcium hydroxide. Michigan, 1986. 80p. Thesis (Master) - University of Michigan.        [ Links ]

8. MOLNAR, E. J.; SKINNER, E. W. A study of zinc oxide-resin cements. I: some variables which affect the hardening time. J Am Dent Assoc, v.29, n.5, p.744-751, May 1942.        [ Links ]

9. NORMAN, R. D. et al. The effect of particle size on the physical properties of zinc oxide-eugenol mixtures. J Dent Res, v.43, n.2, p.252-262, Mar./Apr. 1964.        [ Links ]

10. SAVIOLI, R. N. Estudo da influência de cada componente químico do cimento de Grossman sobre as suas propriedades físicas. Ribeirão Preto, 1992. 123p. Dissertação (Mestrado) - Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo.        [ Links ]

11. SAVIOLI, R. N. et al. Influência de cada componente do cimento de Grossman sobre as propriedades físicas de escoamento, tempo de endurecimento e espessura do filme. Rev Paul Odontol, v.16, n.3, p.14-16, mai./jun. 1994.        [ Links ]

12. SILVA, R. G. Estudo de algumas propriedades físicas dos cimentos obturadores de canais radiculares. Ribeirão Preto, 1992. 190p. Tese (Doutorado) - Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo.        [ Links ]

13. SILVA, R. G. et al. Estudo do tempo de endurecimento e da espessura do filme de alguns cimentos obturadores dos canais radiculares do tipo Grossman. Rev Fac Odontol Lins, v.6, n.2, p.22-26, jan./dez. 1994.        [ Links ]

 

Recebido para publicação em 20/03/97
Aceito para publicação em 10/07/97

 

 

* Professor, Ribeirão Preto School of Dentistry, University of São Paulo.