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J Am Dent Assoc, Vol 133, No 10, 1357-1367.
© 2002 American Dental Association
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RESEARCH

JADA Continuing Education

Cross-reactivity between gutta-percha and natural rubber latex

Assumptions vs. reality



CURT HAMANN, M.D., PAMELA A. RODGERS, Ph.D., HARRI ALENIUS, Ph.D., JOHN F. HALSEY, Ph.D. and KIM SULLIVAN


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 
Background. Immunological cross-reactivity between gutta-percha and natural rubber latex, or NRL, has not been demonstrated clearly despite recent concerns and several suspected cases reported in the literature.

Methods. The authors analyzed aqueous extracts of commercial gutta-percha points and raw gutta-percha samples for cross-reactivity to NRL by radioallergosorbent test, or RAST, inhibition; immunoblot inhibition; direct enzyme-linked immunosorbent assay, or ELISA; and ELISA inhibition using sera from NRL-allergic people as the source of anti-NRL immunoglobulin E, or IgE, antibodies. To confirm in vitro results, the authors conducted skin prick testing, or SPT, on a patient with type I NRL allergy using aqueous extracts from raw gutta-percha, ammoniated gutta-percha and gutta-percha points.

Results. Aqueous extracts from commercial gutta-percha points did not cross-react to NRL in RAST inhibition or immunoblot inhibition, ELISA or ELISA inhibition assays. However, three of 13 sera from subjects with type I NRL allergy exhibited IgE binding to raw gutta-percha extracts in direct ELISA. Moreover, in ELISA inhibition, the binding of IgE to raw gutta-percha extracts was inhibited in a dose-dependent manner by raw NRL and vice versa. SPT results from a subject with type I NRL allergy were positive for NRL and raw gutta-percha extracts but negative for gutta-percha point extracts.

Conclusions. The authors found no detectable cross-reactivity between NRL and commercial gutta-percha points. However, their ELISA and SPT results demonstrated that some allergenic cross-reactivity exists between raw gutta-percha and raw NRL.

Clinical Implications. Gutta-percha alone is not likely to induce symptoms in patients with type I NRL allergy. However, other materials used in obturating root canals may be irritating and potentially allergenic in patients with pre-existing allergies.

Introduced to dentistry in the mid-19th century, gutta-percha is a widely used endodontic material that generally is considered nontoxic and inert.1 This hard crystalline substance is a major constituent of endodontic points used in the obturation of root canals. Gutta-percha contains the rubber molecule trans 1,4-polyisoprene and is harvested from Palaquium gutta trees found in southeast Asia. The purity of the raw gutta-percha; the manufacturing process; and the addition of fillers, opacifiers, waxes, resins and plasticizers all influence the character of gutta-percha points. Gutta-percha point formulations vary by manufacturer, but reportedly contain 56 to 80 percent zinc oxide, 20 to 30 percent gutta-percha, 1 to 17 percent heavy metal sulfates, 1 to 4 percent waxes and resins and 0.1 to 0.3 percent color pigments (including erythosin).1–3 Additional variables in commercial gutta-percha point formulations include blends with gutta-balatta or synthetic trans-polyisoprene.4 Unfortunately, labels on commercial gutta-percha points provide limited information and do not identify source material, degree of purity or the presence of other plant-based fillers. As a result, the composition and allergenic character of gutta-percha points is difficult for clinicians to evaluate.

Gutta-percha alone is not likely to induce symptoms in patients with type I natural rubber latex allergy.

As awareness of allergy to natural rubber latex, or NRL, has increased, concerns have been raised about possible cross-reactivity of gutta-percha and NRL antigens. Two case reports in the medical literature attributed adverse reactions to gutta-percha observed in subjects with type I NRL allergy who underwent endodontic treatment.5,6 However, their conclusions most likely were based on assumptions that potential botanical relationships between gutta-percha and NRL implied cross-reactivity; that finished endodontic points contain significant amounts of bioavailable gutta-percha protein; and that other endodontic materials are not allergenic.

To date, no study has conclusively demonstrated that gutta-percha is a causative agent of adverse allergic reactions. Moreover, in other case reports, no adverse effects were observed when gutta-percha was used in people with type I NRL allergy.7,8 Consistent with these observations, a recent investigation by Costa and colleagues4 reported no evidence of immunological cross-reactivity in vitro between NRL and gutta-percha points using radioallergosorbent test, or RAST, inhibition analysis.4

Several patient groups are considered at risk of experiencing a type I NRL allergy, including health care workers; patients with myelodysplasia (for instance, spina bifida and myelomeningocele), urogenital congenital abnormalities or a history of multiple surgeries during early childhood; and people with a history of skin or whole-body allergic reactions to rubber, fruits, plants and pollens.9 The prevalence of type I NRL allergy is highest in patients with myelodysplasia or urogenital congenital abnormalities, in whom it ranges from 25 to 55 percent.10–12 The prevalence of type I NRL allergy in health care workers varies with each specialty, ranging from 4 percent to 17 percent in hospital personnel and laboratory workers and from 6 percent to 12 percent in dental professionals.13–17 Assuming an average prevalence of 10 percent, more than 800,000 health care workers in the United States may have a type I NRL allergy. However, a type IV allergy (that is, allergic contact dermatitis) to one or more of the chemicals found in dental and health care products—such as gloves and disinfectants—may be twice as common.18,19 Many symptoms of a type IV chemical allergy are similar to those of a type I NRL allergy, confounding appropriate diagnosis and treatment.

Of the 15 million endodontic therapy procedures performed annually in the United States, a portion involves these groups at high risk.20 As a result, it is important that dental professionals better understand the allergenic potential of endodontic materials. Therefore, we undertook an investigation of the immunological cross-reactivity between NRL and gutta-percha using both in vitro and in vivo methods. In this article, we report our results; we also review dental treatment strategies for patients with this allergy, including recognition of symptoms and potential allergens used during endodontic procedures.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 
Materials. Through collaboration with the Forest Research Institute of Malaysia in Kepong, we obtained raw gutta-percha samples by collecting either liquid or coagulated gutta-percha gel from tapped mature Palaquium gutta trees. We obtained ammoniated gutta-percha samples by rinsing off the partially coagulated gel. In addition, we purchased 22 lots of commercial gutta-percha points from different distributors to obtain a reasonable representation of the material available for sale in dentistry (Table 1Go, page 1358). Because information on foreign production sources is not readily available and manufacturers may obtain gutta-percha from multiple sources, we tried to sample multiple lots from each manufacturer. According to manufacturer labels or technical information, the principal ingredients were zinc oxide, gutta-percha, barium sulfate and a coloring agent. One package label noted that the gutta-percha points contained "dry natural rubber." We coded commercial gutta-percha point packages with identification numbers and removed the brand labels.


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  		TABLE 1 INGREDIENTS AND RAST* INHIBITION ANALYSIS OF COMMERCIALLY AVAILABLE GUTTA-PERCHA POINTS.

 
Gutta-percha extraction methods. We first pulverized (using a KSM2 grinder, Braun, Boston) or homogenized (using the Ultra-Turrax T8 homogenizer, IKA-Werke GMBH & Co., Staufen, Denmark) commercial gutta-percha points and raw gutta-percha samples in extraction buffer, which was either 20-millimolar ammonium bicarbonate (pH 8.5) or phosphate-buffered saline, or PBS (10 mmol phosphate, pH 7.4). We extracted 1-gram samples in at least 5 milliliters of extraction buffer for 24 hours at 23 C with constant shaking.

Any remaining particulate was removed by filtration and the clear supernatant used for subsequent analysis. We subjected gutta-percha samples to different analyses, as summarized in Table 2Go.


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  		TABLE 2 IMMUNOLOGICAL ANALYSES APPLIED TO DIFFERENT TYPES OF GUTTA-PERCHA SAMPLES.

 
Protein analysis. We conducted an initial analysis of the raw gutta-percha samples and all 22 lots of gutta-percha points (Table 1Go) for total protein content. We then selected four brands of gutta-percha points (identification nos. 3, 5, 13 and 18) from the same original lots for secondary protein analysis. We assayed protein level using a modified Lowry analysis based on acid precipitation (equal volumes 72 percent trichloroacetic acid and 72 percent phosphotungstic acid) of a 0.15 percent deoxycholate-solubulized sample.21 The limit of detection of this assay is 4 micrograms per mL. Excessive precipitation after the addition of acid to ammoniated gutta-percha samples precluded subsequent protein analysis.

RAST inhibition analysis. We analyzed aqueous extracts from raw gutta-percha and commercial gutta-percha points by RAST inhibition assay for their ability to competitively inhibit the binding of immunoglobulin E, or IgE, anti-NRL antibody to a solid-phase NRL allergen.22,23 We diluted NRL reference allergen (nonammoniated NRL, ProGene Corp., Lenexa, Kan.) or gutta-percha extracts in PBS containing 1 milligram/mL human serum albumin and incubated for one hour with a 50-microliter aliquot of pooled high-positive human sera. These sera were determined by technicians at IBT Reference Laboratory (Lenexa, Kan.) to contain a high titer of anti-NRL IgE levels by one of three routine latex-specific IgE immunoassays: radioimmunoassay, or RIA; Pharmacia CAP System (Pharmacia Diagnostics, Kalamazoo, Mich.); or AlaSTAT (Diagnostic Products Corp., Los Angeles). We transferred incubated extracts to nonammoniated NRL-coated microwells, incubated them for four hours and washed them with tris-buffered saline containing 0.5 percent polyethylene glycol sorbitan monolaurate (Tween-20, ICI Americas Inc., Bridgewater, N.J.). Microwells were incubated overnight with 50 µL of I125-labeled equine antihuman IgE (Kallestad-Sanofi, Chaska, Minn.), washed repetitively and counted for five minutes. We quantified cross-reacting NRL allergen levels by comparing them with the quantity of the NRL reference allergen required for 50 percent inhibition. If inhibition by undiluted samples was below 30 percent, we considered antigen content not detectable. The detection limit of the assay is approximately 1 µg/g.

Immunoblot inhibition analysis. We evaluated extracts from ammoniated gutta-percha by the immunoblot inhibition using reagents from the AlaBlot immunoblotting kit (Diagnostic Products Corp.). We incubated nonammoniated NRL nitrocellulose strips (AlaBlot) sequentially with 50 µL of either NRL reference allergen (1.96 mg/mL) or gutta-percha extract; a 50-µL aliquot of pooled high positive human sera; and 400 µL of diluent buffer. After a two-hour incubation at 20 C, we processed the strips and visualized the bands with the enzyme-labeled anti-IgE reagent system provided by the manufacturer.

Direct ELISA. We analyzed raw gutta-percha and four randomly selected commercial gutta-percha points (nos. 3, 5, 13 and 18) for their ability to directly bind IgE in sera from 13 subjects with type I NRL allergy known to have IgE antibodies to hevein (Hev b 6.02), a major NRL allergen.24 We prepared polystyrene microtiter plates as previously described but coated them with 100 µL of extracts (10 µg/mL protein) from either raw gutta-percha or gutta-percha points.22 We prepared reference plates with purified hevein (1 µg/mL protein) for comparison. After washing, we incubated plate wells with 100 µL of sera from NRL-allergic patients or non–NRL-allergic control subjects (1:10 dilution). After subsequent washes, we determined binding with biotinylated antihuman IgE and detected it with streptavidin-conjugated alkaline phosphatase (absorbance monitored at 405 nanometers).

ELISA inhibition. We examined cross-reactivity between dried raw gutta-percha and raw NRL by means of competitive inhibition of the binding of anti-NRL IgE to solid-phase gutta-percha by raw NRL. We coated polystyrene micrometer plates with 100 µL of extracts (10 µg/mL protein) from either raw gutta-percha or raw NRL as described above. Sera from three subjects with type I NRL allergy that exhibited binding of IgE to solid-phase gutta-percha in direct IgE ELISA were used. Sera (50 µL; 1:10 dilution) were incubated with an equal volume of inhibitor solution. Inhibitor solutions consisted of serial dilutions of raw NRL extract (500, 100, 10 and 5 µg/mL protein) or raw gutta-percha extract (100, 10, 0.1 µg/mL protein). We added the mixture to plate wells and incubated it for two hours, and we determined binding as described previously for direct IgE ELISA.

In vivo skin prick test. We prepared test reagents from dried raw gutta-percha, ammoniated raw gutta-percha and two commercial gutta-percha points (nos. 3 and 13). We pulverized dried raw gutta-percha and extracted it as described above (1 g/5 mL PBS). We vortexed the ammoniated raw gutta-percha and then diluted it 1:2.5 and 1:1.5 with PBS, rotating the mixture for 24 hours at 23 C. Commercial gutta-percha points were pulverized and extracted as described above, but at 1 g/2.5 mL PBS. All test reagents were stored at –20 C and used within 30 days.

The skin prick testing, or SPT, subject was a female orthodontic assistant with a documented (SPT-positive) type I allergy to NRL. The subject’s medical history included atopy with chronic hay fever, throat constriction when eating pineapple, and bronchospasms and hives when exposed to NRL. The subject’s dental history did not include endodontic work.

We obtained informed consent and performed testing by placing seven drops on the inside volar surface of the lower arm in the following sequence:

– histamine positive control (10 mg/mL);
– standardized NRL extract (Stallergenes SA, Fresnes, France);
– commercial gutta-percha point (no. 3) extract;
– raw gutta-percha extract;
– commercial gutta-percha point (no. 13) extract;
– diluted ammoniated gutta-percha;
– saline (150 mmol) negative control.

We pricked the epidermis lightly with a sterile lancet (Prick Lancetter, Hollister-Stier Laboratories LLC, Spokane, Wash.) and blotted any remaining solution with 4-inch gauze. We recorded wheal size (in millimeters) at each prick at 15 minutes. We considered reactions positive if the wheal size was greater than or equal to one-half the size of the histamine wheal (positive control) and observed no reaction to saline (negative control).


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSION
 REFERENCES
 
Protein extraction and analysis. On the basis of preliminary studies, a 24-hour extraction period was needed to solubilize sufficient protein for detection owing to gutta-percha’s low solubility in aqueous solutions. Total protein content extracted from raw gutta-percha varied from 500 µg/g to 2,400 µg/g. By comparison to raw gutta-percha, the protein content of commercial gutta-percha point extracts was much lower: 39 µg/g total protein from a single gutta-percha point and 76 µg/g from a subsequent analysis of four commercial gutta-percha points.

RAST inhibition. Neither the raw gutta-percha extracts nor the 22 lots of commercial gutta-percha point extracts competitively inhibited binding of IgE anti-NRL antibody to solid-phase NRL allergen. If these gutta-percha extracts contained any epitopes that cross-reacted with allergens from NRL, their concentrations were below the detection limit of the assay (1 µg/g).

Immunoblot inhibition. Ammoniated raw gutta-percha did not inhibit recognition and binding of nonammoniated NRL by pooled high-positive human sera (Figure 1Go, page 1361).



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  		Figure 1. Human immunoglobulin E binding to solid-phase nonammoniated natural rubber latex, or NRL, inhibited by NRL reference allergen (Lane 1, positive control), unaffected by diluent buffer (Lane 2, negative control) and unaffected by ammoniated gutta-percha extract (Lane 3).

 
Direct ELISA. Three of 13 (23 percent) sera from subjects with type I NRL allergy had IgE antibodies that bound solid-phase gutta-percha prepared from raw gutta-percha extracts (Figure 2AGo). In contrast, none of the sera had IgE antibodies that recognized solid-phase antigen prepared from commercial gutta-percha point extracts (Figure 2BGo). Simultaneous analysis of IgE binding to solid-phase hevein is shown for comparison (Figure 2Go, page 1362). Control serum from subjects without a type I NRL allergy did not bind either gutta-percha extracts or hevein (data not shown).



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  		Figure 2. Direct enzyme-linked immunosorbent assay results of (A) raw gutta-percha extracts and (B) extracts prepared from gutta-percha points nos. 3, 5, 13 and 18 (see Table 1Go for point identification) using immunoglobulin E, or IgE, in sera from patients with allergy to natural rubber latex. IgE binding to solid-phase hevein (Hev b 6.02) is shown for comparison. A 405: Absorbance at 405-nanometer wavelength.

 
ELISA inhibition. Using sera from the three subjects with type I NRL allergy that bound solid-phase gutta-percha by direct ELISA, we observed cross-reactivity between raw gutta-percha and NRL. Raw NRL inhibited the binding of IgE to solid-phase gutta-percha antigen (prepared from raw gutta-percha extracts) in a dose-dependent manner (Figure 3AGo, page 1363). In addition, extracts from raw gutta-percha inhibited the binding of IgE to solid-phase raw NRL antigen in a dose-dependent manner (Figure 3BGo, page 1363).



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  		Figure 3. A. Natural rubber latex, or NRL, inhibition of the binding of serum immunoglobulin E, or IgE, to solid-phase raw gutta-percha. Serum samples were obtained from select NRL-allergic patients and incubated with 50 microliters of raw NRL extract solutions of 5, 10, 100 and 500 micrograms per milliliter of protein. B. Gutta-percha inhibition of the binding of serum IgE to solid-phase raw NRL. Serum samples were obtained from select NRL-allergic patients and incubated with 50 µL of raw gutta-percha extract solutions of 0.1, 1.0, 10 and 100 µg/mL protein.

 
SPT. The type I NRL-allergic subject exhibited positive SPT reactions to histamine (7 mm), NRL standardized allergen (5 mm) and raw gutta-percha extract (5 mm) as shown in Figure 4Go. We observed a smaller reaction (approximately 2 mm) at the site associated with diluted ammoniated gutta-percha. We observed no reactions in response to saline (150 mmol) negative control or extracts of commercial gutta-percha points no. 3 or no. 13.



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  		Figure 4. Skin prick test results in a patient with type I allergy to natural rubber latex, or NRL: histamine (labeled "hist") positive control, 7-millimeter wheal; NRL (labeled "latex") standard, 5-mm wheal; extract from commercial gutta-percha point no. 3 (labeled "GP 1"), no wheal observed; extract from dried raw gutta-percha (labeled "GP 2"), 5-mm wheal. No wheal was observed with saline (150 millimolars) negative control (not shown).

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSION
 REFERENCES
 
Gutta-percha generally is viewed as a nontoxic obturating material. Although more than 100 years have passed since its introduction, gutta-percha still is considered the material of choice for filling root canals. In 1994, Boxer and colleagues5 reported diffuse urticaria, or hives, and swelling in a type I NRL-allergic dental hygienist during endodontic surgery.5 Symptoms persisted after surgery but apparently resolved when the gutta-percha was removed one month later. In the 1980s, Gazelius and colleagues6 recorded a similar case of a long-term reaction to gutta-percha in a nurse with a type IV allergy to rubber-compounding chemicals. By comparison, other clinicians have described successful root canal placement of gutta-percha in patients with type I NRL allergy.7,8 These divergent clinical outcomes could be caused by variations in patients’ immunological sensitivity, the allergenicity of gutta-percha, endodontic chemical allergens or procedural differences such as NRL-allergy management procedures.

We examined the potential cross-reactivity between different gutta-percha sources and NRL using the in vitro techniques of RAST inhibition, immunoblot inhibition, direct ELISA and ELISA inhibition (Table 2Go). Our results showed that no detectable cross-reactivity exists between NRL and the 22 lots of commercial gutta-percha points we tested according to RAST inhibition, direct ELISA and ELISA inhibition. These results are similar to the RAST inhibition findings recently reported by Costa and colleagues.4 In addition, our in vivo SPT results confirm that a patient with type I NRL allergy is unlikely to react to commercial gutta-percha points.

Our direct ELISA and ELISA inhibition results suggest that some allergenic cross-reactivity exists between raw gutta-percha and raw NRL. Our in vivo SPT results also confirmed this potential cross-reactivity. This is not unexpected; patients with type I NRL allergies have been shown to have allergic reactions and antibodies to related proteins such as the chitinases from ficus plants, avocados and bananas.25–27 However, the cross-reactivity between raw gutta-percha and raw NRL is not likely to have clinical relevance. Raw gutta-percha is processed through a combination of heat and petroleum-based–solvent extractions during the manufacture of endodontic points. As a result, any remaining proteins in the solvent-extracted, fully refined gutta-percha are probably highly denatured with minimal antigenic character.

RAST inhibition and immunoblot inhibition results differed from ELISA inhibition results, most likely caused by IgE differences in the serum pools used. For our ELISA inhibition testing, we selected sera obtained from three patients with a type I NRL allergy confirmed by both clinical history and positive in vivo skin prick test results. These serum samples also contained antihevein IgE antibodies and recognized and bound to raw gutta-percha. In contrast, our RAST and immunoblot inhibition methods used pooled human sera with high overall anti-NRL IgE levels determined by in vitro immunoassays. However, this sera was not selected for specific antibodies to gutta-percha or major NRL allergens such as hevein. Therefore, this pooled human sera probably did not contain sufficient quantities of specific anti-NRL antibodies that could recognize and bind the cross-reacting structures in raw gutta-percha.

While our results showed minimal potential for commercial gutta-percha points to elicit a response in people with type I NRL allergy, these patients can have an allergic reaction to other materials used in endodontic treatment. Patients with type I NRL allergies can have concomitant allergies to certain foods, plants, pollens, chemicals and fragrances.9 As shown in Table 3Go, endodontic chemicals that are potential allergens include eugenol (in fragrances and root canal sealers), disinfectants such as glutaraldehyde and chlorhexidine, methacrylates in bonding agents and epoxy resins, formaldehyde derivatives (in root canal sealers and resins) and the rubber-compounding chemicals thiurams, carbamates, thioureas and thiazoles that are used in synthetic and natural rubber products (such as gloves, carpule stoppers and dental dams).19,28–30 Routes of exposure could include direct contact with skin or oral mucosa, apical leakage or injection. In patients with a type IV allergy to one or more of these chemicals, the oral mucosa and facial skin may redden, burn, swell, itch, crack, scale or scab within a few hours of exposure. These symptoms can take weeks or months to subside. And acute allergic reactions such as hives and anaphylaxis, while uncommon, have been reported after exposure to eugenol, formaldehyde and chlorhexidine.31–33 If not allergenic, the remaining chemicals used in endontic treatment—including zinc oxide, disinfecting hypochlorite (bleach) solutions and softening solvents such as chloroform and halothane—often are strong irritants. 6,34,35


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  		TABLE 3 CHARACTERISTICS OF TYPE I AND TYPE IV ALLERGIES AND POTENTIAL DENTAL ALLERGENS THAT CAN EVOKE SYMPTOMS IN ALLERGIC PATIENTS.

 
Dental professionals must evaluate patients’ medical histories carefully for documented allergies. They also should be aware of critical signs of undocumented allergies such as unexplained rashes, breathing problems, hives or anaphylactic reactions.7 When treating patients with a documented or suspected type I NRL allergy, dentists should pay attention to potential reactions to dental chemicals and materials, including rubber dams, rubber anesthetic cartridge stoppers, epoxy resins, anesthetics and disinfectants.30,35 Dentists should address any concerns regarding the content of gutta-percha points or other dental materials with the manufacturers before proceeding to treat patients with the materials. Dental professionals also may need to confer with primary care providers for optimal patient management. In general, dental patient care should follow guidelines outlined by an NRL allergy management protocol established by the dental practitioner. Moreover, patients with type I NRL allergy should be educated with regard to the dental materials used and their allergenic or irritant potential. This strategy is essential in lowering anxiety, reducing symptoms that falsely mimic an allergic reaction and improving endodontic treatment outcomes in patients with an NRL allergy.36


   CONCLUSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
REFERENCES
 
Consistent with the results of a recent study by Costa and colleagues,4 we found that commercial gutta-percha points did not contain allergens that cross-reacted to NRL in immunological testing. Furthermore, when using sera selected for recognizing antigens in raw gutta-percha and purified NRL allergen, we still were unable to demonstrate cross-reactivity in finished commercial gutta-percha points. Therefore, gutta-percha points alone are unlikely to cause an allergic response in patients with an existing or suspected type I NRL allergy. However, these patients often have a strong and lengthy history of allergies and, as a result, may react to one or more of the dental chemicals used in root canal obturation. Therefore, these patients may require careful management before, during and after root canal obturation procedures.


   FOOTNOTES
 

Dr. Hamann is chief executive officer and medical director, Smart-Practice, 3400 E. McDowell Road, Phoenix, Ariz. 85008, e-mail "hamann{at}smarthealth.com". Address reprint requests to Dr. Hamann.


Dr. Rodgers is a clinical research scientist, Clinical Research Department, SmartPractice, Phoenix.


Dr. Alenius is the chief, Laboratory of Immunotoxicology, Department of Industrial Hygiene and Toxicology, Finnish Institute of Occupation Health, Helsinki, Finland.


Dr. Halsey is the laboratory director and president, IBT Laboratories, Lenexa, Kan.


Ms. Sullivan is director of clinical research, Clinical Research Department, SmartPractice, Phoenix.


   REFERENCES
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 

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