Various types of lasers have been studied in an attempt to develop improved treatment methods in health care. In 2002, the U.S. Food and Drug Administration (FDA) approved the erbium, chromium: yttrium, scandium, gallium, garnet (Er,Cr:YSGG) laser for use in conventional and endodontic therapy. The Er,Cr:YSGG crystal generates photons through a fiber-optic cable delivery system terminating in a handpiece with a sapphire crystal that is bathed in air-water spray.1 The Er,Cr:YSGG laser emits an invisible beam in the infrared range of 2.79 micrometers, coupled with a nonabsorbing light source that serves as a pointer for the working laser.2
The photon energy for this system interacts with the water spray; the maximum energy is delivered 1 to 2 millimeters from the sapphire tip. The laser ablates tissue in less than a 5-mm range.1
A review of the literature revealed that investigations of the use of the Er,Cr:YSGG laser in endodontics exist, but they are limited in number and scope. Some of these studies have addressed the response of pulpal and canal walls to irradiation temperature, the morphology of laser-instrumented root canal walls, and the presence or absence of the smear layer after laser treatment.3–5 Ishizaki and colleagues’6 study found that the Er,Cr:YSGG laser caused a rise of 8 C on the root surface and that it was efficient in removing the smear layer without carbonizing or melting the dentin.
Infection is the cause of pulpal and periradicular diseases.7 Bacteria and their byproducts are considered to be the primary etiologic agents of pulpal necrosis and periapical lesions. Therefore, the elimination of bacteria and their byproducts is one of the most important steps in endodontic treatment.8,9 A few studies have dealt with using lasers to disinfect root canals, but their methods and materials were not sufficient. For example, Schoop and colleagues10 concluded that all of the lasers that they investigated (Er,Cr:YSGG, neodymium-doped yttrium aluminum garnet and erbium substituted:yttrium aluminium garnet) are suitable for disinfection of even deep layers of dentin. However, the authors only allowed bacteria to infect the dentin for four hours before using the lasers.
Microbiological studies have shown that in failed endodontic therapy, the microbial flora often consists of a single species of predominantly gram-positive organisms. The most commonly recovered isolates were from the bacteria Enterococcus faecalis.11,12
In reference to microbiology, no studies have examined the ability of Er,Cr:YSGG laser to disinfect root canals during endodontic treatment. Therefore, we conducted this study to compare the ability of an Er,Cr:YSGG laser (WaterLase, Biolase Technology, San Clemente, Calif.) to disinfect the root canals of extracted human teeth infected with E. faecalis with the ability of the nickel titanium Profile 0.06 taper rotary file series (Dentsply Tulsa Dental Products, Tulsa, Okla.).
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MATERIALS AND METHODS
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We used 40 extracted, permanent, anterior, single-rooted teeth in our study. We decoronized and instrumented the teeth with International Organization for Standardization (ISO) nos. 10, 15 and 20 with hand files to the teeth’s working length. We determined working lengths by inserting a no. 10 hand file into the root canal until it was visible at the apical foramen and then subtracted 1 mm from that length. We stored the teeth in sterile saline (0.9 percent sodium chloride) for three days and then autoclaved for them 20 minutes at 121 C.
Infection and instrumentation.
We used facultative anaerobic bacteria (E. faecalis ATCC no. 27792 [American Type Culture Collection, Manassas, Va.]) in our experiment. We rehydrated a freeze-dried culture pellet with 0.5 milliliters of phosphate-buffered saline solution, streaked onto Brucella blood agar (Anaerobe Systems, Morgan Hill, Calif.) plates and incubated them at 37 C in anaerobic incubator boxes.
We saw colony growth after three days. We used an inoculating loop to take single colonies from the plates and used them to inoculate 7 mL of thioglycollate (THIO) medium broth (Anaerobe Systems) in sterile test tubes. We then randomly divided the autoclaved teeth into three experimental groups of 10 teeth each (Groups A–C), one positive control group of five teeth (Group D) and one negative control group of five teeth (Group E). We infected the dentin according to the method described by Haapasalo and Orstavik.13 We placed the teeth to be infected (those from Groups A–D) in separate test tubes containing THIO broth inoculated with E. faecalis. We then placed the test tubes in anaerobic incubator boxes and incubated them at 37 C for 21 days. Every third day, we replaced 3 mL of the inoculated THIO broth with 3 mL of fresh THIO broth. At the end of the incubation period, all the test tubes showed positive turbidity for bacterial growth. We removed the infected teeth from their test tubes, rinsed them with sterile saline and treated them as follows.
We laser instrumented the 10 infected teeth in Group A following the steps outlined in the manufacturer’s instructions. The firing range settings for the Z2, Z3 and Z4 laser tips were 1.50 watts, 34 percent air and 24 percent water. We irrigated the canal with 2.5 percent sodium hypochlorite (NaOCl) after instrumentation with the Z2 and Z3 laser tips. After instrumentation with Z4 laser tip, we irrigated the canal with 1 mL of 17 percent ethylene-diamine-tetra-acetate (EDTA) for one minute, followed by a rinse of 2.5 percent NaOCl. The total volume of 2.5 percent NaOCl we used to irrigate each tooth was 3 mL via a plastic syringe with a 23-gauge needle.
We laser instrumented the infected teeth in Group B in almost the same manner as we instrumented the infected teeth in Group A. The only difference was that we used sterile saline instead of 2.5 percent NaOCl to irrigate the canal. The firing range of settings for the Z2, Z3 and Z4 laser tips were 1.50 W, 34 percent air and 24 percent water. We irrigated the canal with sterile saline after instrumentation with the Z2 and Z3 laser tips. After instrumentation with the Z4 laser tip, we irrigated the canal with 1 mL of 17 percent EDTA for one minute, followed by a rinse with sterile saline. The total volume of sterile saline we used to irrigate each tooth was 3 mL via a plastic syringe with a 23-gauge needle.
We instrumented the infected teeth in Group C with the taper rotary file series in sizes ISO nos. 20, 25, 30, 35 and 40. We irrigated the canal with 2.5 percent NaOCl after instrumentation with each rotary file. After instrumentation with the no. 40 rotary file, we irrigated the canal with 1 mL of 17 percent EDTA for one minute, followed by a rinse with 2.5 percent NaOCl. The total volume of 2.5 percent NaOCl we used to irrigate each tooth was 3 mL via a plastic syringe with a 23-gauge needle.
After 21 days of incubation at 37 C, the infected teeth in the positive control group (Group D) were not instrumented. Instead, we collected dentin shavings from the teeth and incubated them for 21 days at 37 C in sterile test tubes containing 7 mL of THIO broth.
We did not inoculate teeth in the negative control group (Group E), but we did incubate them for 21 days at 37 C in sterile test tubes containing 7 mL of THIO broth.
We analyzed the differences between groups using the Fisher exact test.
Dentin shaving collection.
Immediately after laser or rotary instrumentation of teeth from Groups A to C, we rinsed the teeth from all five groups (A–E) with sterile saline. We collected dentin shavings, using the methods described by Gomes and colleagues.14 For each tooth, we obtained dentin shavings using sequential sterile Gates-Glidden (GG) burs nos. 2, 3 and 4 at low speeds. We used GG bur no. 2 until it went to working length and burs nos. 3 and 4 until we felt resistance. After instrumentation with the GG burs, we used an ISO no. 25 hand file until it went to the working length of each canal. We then suspended the dentin shavings with sterile saline within the canal. We introduced sterile paper points into the canals to collect the dentin shavings and transferred the shavings into separate test tubes containing fresh THIO broth. We placed the test tubes in anaerobic incubator boxes and incubated them at 37 C. After 72 hours, we examined the test tubes for microbial growth and checked for medium turbidity. To confirm the presence of E. faecalis, we plated all of the broths that resulted in turbidity on Brucella blood agar plates.
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RESULTS
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Of the 10 test tubes from Group A, two showed no turbidity, while eight were positive for bacterial growth (Figure
). All 10 of the test tubes from Group B were positive for bacterial growth. In Group C, four test tubes showed no turbidity, while six test tubes were positive for bacterial growth. All five of the test tubes from Group D were positive for bacterial growth. None of the five test tubes from Group E had bacterial growth. When we conducted statistical analyses using the Fisher exact test, we found that the differences between Groups A, B and C were not statistically significant.
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ABSTRACT
MATERIALS AND METHODS
