TAŤJANA DOSTÁLOVÁ Assoc. Prof., M.D., Ph.D.,¹ HELENA JELÍNKOVÁ, Prof. Dr.Sci.,² DĚVANA HOUŠOVÁ, MD., ¹  JAN ŠULC, M. Sc. ² MICHAL NĚMEC, M.Sc.,²JANA DUŠKOVÁ M.D., Ph.D.,¹ MARTIN KRÁTKÝ, M.Sc.,¹ MITSUNOBU MIYAGI, Prof.,³

 

 ¹ Institute of Dental Research, GFH, Prague, Czech Technical University,  ² FNSPE, Prague, Czech Republic,  ³Tohoku University, Graduate School of Engineering Department of Electrical Communications, Sendai, Japan

 

INTRODUCTION

Enlargement and shaping of a root canal is necessary to attain success in root canal treatment. Various methods have been employed to alter the architecture (morphology) of the root canal system dentin. These methods include the use of chemical (irrigants, chelating agents), physical (sonication, ultrasonics), and mechanical (hand, rotary instrumentation) means or their combinations. Treatment objectives of root canal system preparation include the removal of all canal contents, sterilization of the root canal space and alteration of the shape of the space to receive a root canal filling material. The procedures used in root canal system preparation result in the creation of a smear layer and smear plug composed of organic tissue remnants, dentin shavings, and microorganisms¹. The smear layer adheres to the prepared root canal walls while the smear plugs extend some short distance into the orifices of the dentin tubules. The tubules run from the inner dentin walls of the root canal space towards the outer root surface ². The primary irrigant used in root canal system preparation is sodium hypochlorite (NaOCI). It was used either alone or in combination with other chemical agents³.

Conventional endodontic treatment is not fully effective due to the rest microbial colonization of root canal walls dentin in premolars and molars. It was observed that before endodontic treatment only 80 % of frontal teeth are fully disinfected⁴. Microorganisms can reach the dental pulp by any of six routes: through the open cavity, through dentinal tubules, trough the gingival sulcus or periodontal ligament, through the bloodstream, through a broken occlusal sea or faulty restoration of a tooth previously treated by endodontic therapy, and through extension of a periapical infection from adjacent infected teeth.

In beginning (year 1979) Adrian demonstrated the potential of laser technology to sterilize dental instruments. From those days many authors have published the bacteria can effectively killed by various lasers. The interest in laser endodontics has concentrated on the possibility to extirpate the contents of the root canal, to sterilize and to "melt" the walls of the root canals. In the previous research CO_2, excimer, argon, Nd: YAG, Ho: YAG, and Er:YAG lasers were used^5-9. The continuous wave Nd:YAG laser had variable re­sults: from no effect to disruption of the smear layer, and to melting and resolidification of the dentin. The pulsed Nd: YAG laser was unable to glaze the dentin surface of the canal walls of split roots. Its radiation tended to vaporize the dentin, resulting in craters and perforations. The Nd: YAG laser removed the smear layer created with hand instruments and NaOCI irrigation, but did not al­ter the calcospherite appearance of the dentin walls. It was confirmed that the Nd: YAG laser has bactericidal effect in the root canal. The argon laser could remove the smear layer, too. The contin­uous wave CO₂ laser consistently created a melted dentin surface with minimal cracking. Subablative irradiation with the Er: YAG laser had a cumulative bactericidal effect, and even single pulses were effective. It can be concluded that the laser is able to clean the root canal; with its radiation it is possible to remove the smear layer and most of the radiation has some bactericidal effect.

The objective of this study is to examine the ability of Er: YAG laser radiation; using movable waveguide helps to achieve antibacterial effect not only in root canal walls but also in the surrounding tissues.

 

MATERIALS AND METHODS

Laser equipment and experiment preparation

Erbium YAG laser system

For the experiment, an Er:YAG laser system  was used¹⁰. The wavelength generated was 2.94 mm, maximum generated energy 0.6 J, duration of the generated pulses around 250 msec, and the maximum repetition rate was 6 Hz. The laser output radiation was delivered to the investigated tissue by a cyclic olefin polymer-coated silver hollow glass waveguide (COP/Ag) with an inner diameter of 700 mm and a length of 0.1 m.

Preparation of the teeth

The root canal systems of 44 premolars and molars were treated endodontically; it means that access cavities were prepared and the root canal systems were shaped using a step-back technique with K-type endodontic files (Maillefer, Swiss). This shape was prepared by using conventional files from 10 to 55 (30 minimum average), which were applied from the body to the apex. A gates bur was placed loosely in the middle third of the canal system and allowed to contact the canal walls to smooth and slightly flare the preparations. A 5.25% solution of sodium hypochloride (10 ml) (Clordent, C.S.C. Czech Rep) was used to irrigate all the root canal systems between the uses of each endodontic instrument. The last irrigant applied was 10 ml saline solution (infusio natrii chlorati isotonica) (Infusia, Czech Rep.). Diagnostic RTG –radiovisiography (Trophy, France) was made to check the quality of preparation (Fig 1, 2).

Additional treatment after mechanical and chemical preparation

a) Calcium hydroxide paste application

10 teeth were then treated with calcium hydroxide paste Ca (OH)₂  (Dentbalsam, C.S.C, Czech Rep.) The paste was inserted with paste carrier (diameter 25, length 21 – Medin, Czech Rep.) to canals for  1-3 months period, depending on X-ray control and the patients´ feelings. Through that period the teeth were covered with temporary filling material Cavit (Espe, Germany)

 b) Experimental arrangement for laser treatment

22 teeth were irradiated through movable waveguide to receive antibacterial effect not only in root canal walls but also in surrounding tissues. The waveguide was inserted into the root canal apex and during laser irradiation moved from the apex to the body and gate. A dose of 30 pulses with the energy ranging from 70 to 130 mJ and repetition rate 4 Hz was applied. The corresponding fluence was between 18 to 34 J/cm².

Therapy

The premolars and molars were filled with gutta-percha points and sealant AH 26 or Apexit (Dentsply DeTrey, Germany, or Vivadent, Liechtenstein). The method of lateral condensation and finger spreaders was used.

Experimental setup for the bactericidal effect measuring 

Before and after treatment (before canal filling) the colony-forming units were counted to determine 21 various microorganisms - Streptococcus sanguis, Streptococcus mutans, Streptococcus viridans, Staphylococcus aureus, Staphylococcus epidermidis, Corynebacteriurn sp., Micrococcus albus, Micrococcus luteus, filaments, Nocardia sp., Peptostreptococcus sp., Lactobacillus sp., Actinomyces sp., Bacterionema sp., Bacillus sp., Pseudomonas sp., Bacterioides gingivalis, Haemophillus aphrophillus, Haemophillus paraaphrophillus, Actinobacillus actinomycetemcomitans, and  “others”.

The content of the root canal was removed via irrigation with 0.2 ml sterile RTF transport medium, which was inserted to the 3 ml brain heart infusion. The samples were incubated for 24 hours at 37⁰C. The sterile brain heart infusion under the same conditions was inoculated as a control¹¹.

RESULTS

 Classical enlargement and shaping of the root canal, including chemical disinfections by premolars and molars, is effective in 60% - Graph 1. Rests microbial content was detected, and only Peptostreptococcus sp., and Haemophillus paraaphrophillus were fully removed from the root canal. The presence of the microorganisms were found: Streptococcus sanguis - 50 % teeth, Streptococcus mutans - 38 % teeth, Streptococcus viridans - 38 % teeth, Staphylococcus aureus - 16 % teeth, Staphylococcus epidermidis - 26 % teeth, Corynebacteriurn sp. - 62 % teeth, Micrococcus albus - 62 % teeth, Micrococcus luteus -16 % teeth, filaments - 62 % teeth, Nocardia sp. - 50 % teeth, Lactobacillus sp. - 16 % teeth, Actinomyces sp. - 16 % teeth, Bacterionema sp. - 16 % teeth, Bacillus sp. - 16 % teeth, Pseudomonas sp. - 16 % teeth, Bacterioides gingivalis- 38 % teeth, Haemophillus aphrophillus - 16 % teeth, and Actinobacillus actinomycetemcomitans - 62 % teeth.

Application of calcium hydroxide paste can prepare sterile root canal in 80 % - Graph 1. Streptococcus sanguis, Staphylococcus aureus, Micrococcus luteus, filaments, Nocardia sp., Actinomyces sp., Bacterionema sp., Bacillus sp., Pseudomonas sp., Bacterioides gingivalis, and Actinobacillus actinomycetemcomitans were destroyed during the treatment process. The microorganisms were detected:  Streptococcus mutans - 18 % teeth, Streptococcus viridans - 18 % teeth, Staphylococcus epidermidis - 18 % teeth, Corynebacteriurn sp. - 18 % teeth, Micrococcus albus - 32 % teeth, filaments - 32 % teeth, Peptostreptococcus sp. - 18 % teeth, Lactobacillus sp. - 18 % teeth, Haemophillus aphrophillus - 32 % teeth, Haemophillus paraaphrophillus - 18 % teeth,  and  “others” - 32 % teeth.

Application of Er:YAG laser radiation through a movable waveguide is effective for root canal residual disinfections. With the application of a 30 - pulse dose with a mean energy of 100 mJ (repetition rate 4 Hz) the 100% sterilization was reached. From the previous experiments this dose was found optimal. The movable, flexible waveguide helps to irradiate the whole root canal surface.

 

DISCUSSION

Endodontic treatment in dentistry is one of the most frequent types of effort in dental surgery. The treatment could be complicated with inflammation and periapical irritation, and for that reason patients must repeatedly visit the dental surgery.

            Dental pulp death is most often caused by microorganisms extending from the coronal surface of the tooth; thus results in the need of root canal treatment. The ultimate goal of that treatment is sterilization of the prepared root canal space prior to completion of the treatment by filling the prepared space.  A problem of contamination occurs because the preparation of the root canal space creates a smear layer, which is hypothesized to harbor and support microorganisms leading to root canal failure. Methods used in past to sterilize root canal systems were ineffective because they did not remove the smear layer totally¹¹. The culturing before filling is positive from 10 to 40 %⁴. Culturing can, therefore, guide the clinical therapy, but routine sampling is clinically impracticable³. The appropriate antibiotic therapy as an adjunct to clinical procedure may be invaluable¹³; nevertheless, 35 % American dentists use regularly antibiotics during therapy.

            Mechanical preparation could damage periapical tissues mechanically, chemically, or penetration of infection. The inflammation process can continue several days after treatment. This unfavorable reaction can have negative influence on the one-step endodontic treatment. In the ideal case we removed only 80 % of bacterial infection from the root canal⁴. In premolars and molars the same results have obtained in our study after a long-term therapy – a combination mechanical and chemical preparation and application calcium hydroxide paste.

            Much more effective, however, seems to be Er:YAG laser radiation in the form of special waveguide tip which would immediately and sufficiently sterilize not only  the prepared root canal space but also the smear layer and root canal ramifications. The energy of 100 mJ, 30 pulses, and  repetition rate 4 Hz was the optimal dose for residual disinfection effect (sterilization 100 %).

A flexible waveguide can irradiate canal walls without surface destroying¹⁴. Hibst¹⁵ found that single laser pulses lead to a short time (ms) temperature rise on the surface, but only little heat is transferred to the tooth. Surface sterilization can be achieved by the cumulative effect of multiple pulses, which, however, can be separated by time intervals long enough to prevent heat accumulation. We have demonstrated that the tissue not directly subject to laser radiation or deeper tissues cannot be affected by the subablative effect of Er:YAG laser¹⁰. Real bactericidal effect can be observed at Er:YAG irradiation in direct contact via flexible waveguide or movable optical fiber.

            Looking through specific endodontic literature we can see that in 1984 Derdrick ¹⁶give us an early look at the effect of Nd: YAG laser in various time of duration and power level. It was found that dentin was melted and re-crystallize to non-porous surface. For endodontic treatment also excimer laser, CO₂  laser and Er:YAG laser were used ^{10, 17-21}. The conclusions from results are that lasers are not effective for shaping the canal.  One-step disinfection of the root canal during endodontic treatment with the help therapeutic dose of laser irradiation can  achieve strong bacterial reduction after conventional cleaning and shaping methods, without periapical irritation and inflammation after treatment.

 

CONCLUSIONS

Application of Er: YAG laser radiation through flexible waveguide helps to attain antibacterial effect not only in the root canal walls but also in the surrounding tissues. Therapeutic dose of laser radiation guarantees one-step disinfection including anaerobic microorganisms. 

ACKNOWLEDGMENTS

This research has been supported by the Grant Agency of the Ministry of Health of the Czech Republic No.6823-3, Preciosa Foundation, and Monbusho International Scientific Research program: Joint Research No.09044122 of Japan.

Figure 1.: Tooth 37 before treatment.

Figure 2.: Shaping of the tooth 37.

Graph 1:  Presence the 21 various microorganisms after mechanical and chemical treatment (A) and mechanical, chemical treatment and Calcium hydroxide paste application (B).

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