Gutta-Percha: A Look at the Need for Sterilization

Many have argued that the prevention of contamination becomes a problem when gutta-percha cones are used to obturate the root canal space. This study evaluated the extent of contamination of commercially available gutta-percha cones taken directly from the manufacturer’s box. Results show that if gutta-percha is not intentionally contaminated, there is no need for chemical decontamination before obturation.

One of the key goals of successful endodontic therapy is complete obturation of the root canal system. This success is directly related to the thorough elimination of microorganisms during cleaning and shaping. Use of improperly sterilized endodontic instruments increases the potential for contamination. This is easily avoided through autoclaving of the endodontic instruments, having a clean set-up, and using a rubber dam to isolate the tooth from the oral microflora.

Many have argued that the prevention of contamination becomes a problem when gutta-percha cones are used to obturate the root canal space.¹ However, since gutta-percha does not readily lend itself to sterilization by heat, other methods have been studied. This argument triggered a series of studies testing various chemical agents in the decontamination of gutta-percha cones. Sodium hypochlorite^2-5 and gluteraldehyde⁶ were the two chemicals that gained the most support from researchers in the decontamination of gutta-percha cones. Other chemicals used to decontaminate gutta-percha were chlorhexidine,³ ethyl alchohol,³ isopropyl alchohol,³ hydrogen peroxide,⁴ Zephirin,⁷ Zephirin chloride,^8-10 untinted tincture of Metaphen,¹¹ thimerosal,¹² povidine-iodine,¹ formaldehyde gas,¹³ and paraformaldehyde.^3,14 In many of these studies, researchers intentionally contaminated the gutta-percha with various strains of bacteria prior to testing the efficacy of these chemical decontaminants.

It is interesting to note that there are only two studies published that focused on testing gutta-percha, taken directly from the manufacturer’s packaging, for contamination. In 1971, Montgomery published his findings in which gutta-percha was taken out of the factory packaging and placed directly into culture media. In this study, 8 percent of the commercially manufactured cones tested showed growth. He concluded that the organisms identified were pathogens, indicating the necessity of decontaminating gutta-percha cones prior to placing them in root canals. Doolittle and colleagues, in 1975, took 24 gutta-percha points directly from the manufacturer’s box and placed them in a culture broth. None of the gutta-percha cones tested were positive for bacterial growth. It was on the basis of Montgomery’s article alone that the subsequent studies were done using chemical agents to "rapidly decontaminate" gutta-percha cones.

In 1982, Moorer and Genet did a study testing the antibacterial property of gutta-percha cones and found zinc oxide, which is the major component of gutta-percha, to be responsible for some antibacterial properties of the cones. Martin, in 1999, published an article promoting a medicated gutta-percha cone. This formulation (containing iodoform) has been developed to act as an inhibitor of microbial growth within the root canal.

In addition to the gutta-percha cones, root canal sealers are routinely used to help provide a hermetic seal in the obturation process. To achieve this effective seal and subsequent healing of an endodontic lesion, a root canal sealer should possesses certain characteristics. Grossman¹⁸ has identified several characteristics considered to be ideal for a root canal sealer. One of these characteristics is that it must have bactericidal and/or bacteriostatic activity. Studies have been done evaluating the antimicrobial activity of various endodontic sealers. One study found that many sealers inhibited the growth of certain known dental pathogens.¹⁹ Al-Katib and colleagues, in 1990, tested the ability of sealers to inhibit the growth of Streptococcus mutans (a gram-positive microaerophile), Staphylococcus aureus (a gram-positive facultative anaerobe), and Bacteroides endodontalis (a gram-negative obligate anaerobe).²⁰ B. endodontalis, a known endodontic pathogen, has been found in necrotic pulps and radiolucent periapical lesions.^21,22 In the study done by Al-Katib and colleagues, of all the sealers tested, AH26 was most effective against B. endodontalis.

The purpose of this study was to:

* Evaluate the extent of contamination of commercially available gutta-percha cones taken directly from the manufacturer’s box.

* Assuming contamination was present on the gutta-percha cones, the antimicrobial effect of 5.25 percent sodium hypochlorite was evaluated.

* Assuming contamination was present on the gutta-percha cones, the antimicrobial effect of a root canal sealer was evaluated.

Materials and Methods

This experiment was conducted in a decontaminated clinical environment to duplicate as close as possible an actual clinical setting. All testing procedures were performed by a single operator in OSHA-approved clinical attire. A total of 64 ISO size #40 gutta-percha cones were used. The 64 cones were separated into two groups.

Group 1

The first group consisted of 32 gutta-percha cones taken directly from a sealed manufacturer’s box (Figure 1). This group was subdivided into four subgroups. Group 1a consisted of eight gutta-percha cones removed from the box and placed directly onto a blood agar plate (Figure 2). The cones were then carefully rolled across the agar surface. Group 1b contained eight gutta-percha cones taken directly from the box and immersed in undiluted 5.25 percent sodium hypochlorite for one minute. (This strength of sodium hypochlorite was used based on the findings of Senia and colleagues in 1975.) The cones were allowed to air dry for five minutes on a sterile surgical drape and placed on the agar plate as mentioned in group 1a. Group 1c consisted of eight gutta-percha cones evenly coated with AH-26 cement that was mixed on a sterile glass slab according to the manufacturer’s directions. The cones were placed on the blood agar immediately after being evenly coated with cement but were not rolled as in groups 1a and 1b (Figure 3). Group 1d also consisted of eight gutta-percha cones that were immersed in 5.25 percent undiluted sodium hypochlorite as in group 1b and were then coated with AH-26 cement and place on the blood agar as in group 1c.

Group 2

A common practice for many endodontists is to store their gutta-percha cones in a plastic organizer (Figure 4). As part of this research, the authors were interested in evaluating the contamination of gutta-percha stored in these organizers.

Group 2 consisted of 32 gutta-percha cones taken from one of these organizers. As in group 1, group 2 was divided into four subgroups (a, b, c, d); and the same testing procedures were performed.

A positive control group was also incorporated into this study. Four gutta-percha cones taken from the manufacturer’s box were intentionally contaminated by rolling in the operators degloved hand for one minute. These four cones were then placed on the agar plate and rolled as in groups 1a and 2a.

All agar plates were incubated at 37 degrees C and examined for bacterial growth at three, seven and 14 days.

Summary of Groups

Group 1 (32 gutta-percha cones)

* Group 1a -- eight cones from manufacturer’s box.

* Group 1b -- eight cones from manufacturer’s box with NaOCl.

* Group 1c -- eight cones from manufacturer’s box with AH-26 cement.

* Group 1d -- eight cones from manufacturer’s box with NaOCl and AH-26 cement.

Group 2 (32 gutta-percha cones)

* Group 2a -- eight cones from endodontist’s box.

* Group 2b -- eight cones from endodontist’s box with NaOCl.

* Group 2c -- eight cones from endodontist’s box with AH-26 cement.

* Group 2d -- eight cones from endodontist’s box with NaOCl and AH-26 cement.

Group 3 (four gutta-percha cones) positive control

Four intentionally contaminated cones.

Results

Tables 1, 2 and 3 show the results of bacterial growth of the same gutta-percha cones at three, seven, and 14 days.

The results of the cultures are listed in Tables 1, 2 and 3. The results in Table 1 show that after three days of incubation, two cones in Group 1a, showed the presence of bacteria. After one week of incubation, depicted in Table 2, two additional cones, this time in Group 2a, showed the presence of the same bacterial species. The 14-day group, shown in table 3, had no changes from Table 2. It was explained to the authors by the microbiologist performing the cultures that the bacteria were of the Bacillus species. This particular organism is a nonpathogenic, gram-negative rod.

Table 1. Three-Day Results
Group	Colony Counts	Bacteria	Comment
1a	Two cones-Hemolysis zone	Bacillus species	Gram-negative rod Nonpathogenic
1b	No growth
1c	No growth
1d	No growth
2a	No growth
2b	No growth
2c	No growth
2d	No growth
3	2, 13, 50, 44

The positive control group, Group 3, had colony counts that ranged from two to 50. Aside from the positive control group, no other bacteria were detected in the culturing of the agar plates.

Discussion

As mentioned earlier, several studies have been done on the chemical decontamination of gutta-percha.^2-14 Most of these studies used gutta-percha cones that were intentionally contaminated with various strains of bacteria prior to testing the efficacy of the chemical decontaminating agent. These studies were done based on the findings of Montgomery, in 1971, who found that 8 percent of the cones he tested directly from the manufacturer’s box were positive for bacterial growth.

The purpose of Group 1a was to test gutta-percha from the sealed manufacturer’s box, essentially duplicating that aspect of Montgomery’s study in 1971. The results showed that 25 percent, or two out of the eight cones tested in Group 1a were positive for the presence of bacteria. The zone of hemolysis on the blood agar surface indicated the presence of the Bacillus species of bacteria, which is a nonpathogenic, gram-negative rod.

In Group 1b no bacterial growth was present. In this group, the gutta-percha was submerged in sodium hypochlorite for one minute and allowed to air dry on a sterile surgical drape before being placed on the agar plate. Advocates of chemical disinfectants would support that the absence of bacteria in this group is due to the antibacterial effects of the sodium hypochlorite.

Group 1c also showed no bacterial growth. In this group, the gutta-percha was coated with the sealer AH-26 prior to being placed on the agar plate. As reported in the studies of Barkhordar, 1989, and Al-Khatib and colleagues, 1990, one could argue that this is due to the antimicrobial properties of AH-26.

Group 1d contained gutta-percha, which was submerged in sodium hypochlorite for one minute as in group 1b and coated with AH-26 as in group 1c. As one might expect from groups 1b and 1c, no bacterial growth was present.

In Group 2, gutta-percha was tested from the plastic organizing boxes. The results from Group 2 were identical to group 1. Given these results, these boxes may be a safe alternative for the storage of gutta-percha. In addition, these gutta-percha points may not require chemical decontamination with sodium hypochlorite if they are to be coated with AH-26 prior to placement in the canal.

Doolittle, in 1975, found no gutta-percha cones positive for contamination when taken directly from the manufacturer’s box. Montgomery, in 1971, found eight percent of the gutta-percha tested was contaminated. In addition, Al-Khatib and colleagues stated the antimicrobial effects of AH-26 in 1990. Given these results and the results from the current study, the chemical decontamination of gutta-percha points with sodium hypochlorite may not be a necessary if AH-26 root canal sealer is used.

Conclusion

It can be concluded from this study that:

* Of the gutta-percha tested, two out of eight cones were positive for the presence of bacteria.

* Gutta-percha taken directly from the manufacturer’s box and immersed in sodium hypochlorite for one minute showed no bacterial growth when placed on an agar plate.

* Gutta-percha taken directly from the manufacturer’s box and coated with AH-26 showed no bacterial growth when placed on an agar plate.

It was the authors’ purpose to address the issue of chemical decontamination of gutta- percha. According to the results, if gutta-percha is not intentionally contaminated, there is no need for chemical decontamination before obturation. Furthermore, if AH-26 root canal sealer is to be used, there is more assurance of the decontamination of the gutta-percha.

Authors

M. Sadegh Namazikhah DMD, MSEd, is a professor of clinical dentistry, acting chairman of the Endodontic Department, and director of the Advanced Endodontic Program at the University of Southern California School of Dentistry

David M. Sullivan, DMD, is a first-year resident in the Graduate Endodontic Department at the USC School of Dentistry.

Gregory L. Trnavsky, DDS, is a first-year resident in the Graduate Endodontic Department at USC.

References

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18. Grossman LI, Root Canal Therapy. Lea and Febiger, Philadelphia, 1978:293-4.

19. Barkhordar RA, Evaluation of antimicrobial activity in vitro of 10 root canal sealers on Streptococcus sanguis and Streptococcus mutans. Oral Surg Oral Med Oral Pathol 68: 770, 1989.

20. Al-Katib ZZ, Baum RH, et al, The antimicrobial effect of various endodontic sealers. Oral Surg Oral Med Oral Pathol 70:784, 1990.

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22. Tronstad L, Barnett F, et al, Extraradicular endodontic infections. Endod Dent Traumatology 3:86, 1987.

To request a printed copy of this article, please contact/ M. Sadegh Namazikhah, DMD, MSEd, USC School of Dentistry, 925 W. 34th St., Room 124C, Los Angeles, CA 90089-0641.