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The composite curing lamp – an unknown phototherapeutic tool

By Jan Tunér

Every dentist is familiar with the composite curing lamp. Some may not use it in their clinical work, like oral surgeons, but everyone has seen and used one. Most curing lights these days are based upon light-emitting diodes - LEDs. This blue light has a center wavelength around 460 nanometres and the power density is around 1000 mW/cm2. The output power is typically 200 - 250 mW.

Light can do many things, so is it possible that the curing light can do more than curing composites and cements? Yes, it can! In 2008 Enwemeka and co-workers [1] published a study, showing that blue light of 405 nm could efficiently kill strains of methicillin-resistant Staphylococcus aureus (MRSA) in vitro. The 390-420 nm spectral width of the 405 nm LED source, though, may raise safety concerns in clinical practice, because of the trace of ultraviolet (UV) light within the spectrum. Therefore, in 2009 the same researchers published a similar experiment [2], but using a LED with a centre wavelength of 470 nm. It turned out to be just as effective. 55 J/cm2 killed over 90% of the MRSA. Now, 470 nm looks familiar – we all have it in our curing lamps!

In everyday dentistry we do not see too many cases of MRSA, but we should still be aware of the potent tool at our hands if so happens. But what we see daily is dental plaque. And it is full of bacteria, so could the curing light be used to reduce dental plaque? Soukos [3] investigated the effects of blue light at 455 nm on the bacterial composition of human dental plaque in vivo. Eleven subjects who refrained from brushing for 3 days before and during phototherapy participated in the study. Light with a power density of 70 mW/cm2 was applied to the buccal surfaces of premolar and molar teeth on one side of the mouth twice daily for 2 min over a period of 4 days. Dental plaque was harvested at baseline and again at the end of 4 days from eight posterior teeth on both the exposed side and unexposed sides of the mouth. Microbiological changes were monitored by checkerboard DNA probe analysis of 40 periodontal bacteria. The proportions of black-pigmented species Porphyromonas gingivalis and Prevotella intermedia were significantly reduced on the exposed side from their original proportions by 25 and 56 %, respectively, while no change was observed to the unexposed side. Five other species showed the greatest proportional reduction of the light-exposed side relative to the unexposed side. At the same time, the percentage of gingival areas scored as being red decreased on the side exposed to light from 48 to 42 %, whereas the percentage scored as red increased on the unexposed side from 53 to 56 %. To use the curing light to reduce dental plaque seems a bit impractical, but it is an idea for innovative products in the near future. An impression-tray shaped product with blue light could be quite practical. And why not in combination with red light, for tissue biostimulation?

Fontana [4] tested the hypothesis that photo-targeting eight key periodontopathogens in plaque-derived biofilms in vitro would control growth within the dental biofilm environment. Cultures of eight bacteria were exposed to blue light at 455 nm with a power density of 80 mW/cm2 and fluence of 4.8 J/cm2. Suspensions of human dental plaque bacteria were also exposed once to blue light at 455 nm with power density of 50 mW/cm2 and fluence of 12 J/cm2. Microbial biofilms developed from the same plaque were exposed to 455 nm blue light at 50 mW/cm2 once daily for 4 min (12 J/cm2) over a period of 3 days (4 exposures) in order to investigate the cumulative action of phototherapy on the eight photosensitive pathogens as well as on biofilm growth. The selective photo targeting of pathogens was studied using whole genomic probes in the checkerboard DNA-DNA format. In cultures, all eight species showed significant growth reduction. High-performance liquid chromatography demonstrated various porphyrin patterns and amounts of porphyrins in bacteria. Following phototherapy, the mean survival fractions were reduced by 28.5 and 48.2 % in plaque suspensions and biofilms, respectively. DNA probe analysis showed significant reduction in relative abundances of the eight bacteria as a group in plaque suspensions and biofilms. The cumulative blue light treatment suppressed biofilm growth in vitro.

What else could a curing light do? Ishikawa and co-workers [5] state that dental curing lamps can emit blue-violet wavelengths around 380-515 nm with two peaks (410 nm and 470 nm). These wavelengths can cover the maximum absorption spectra of hemoglobin (430 nm). So could it be used to improve the coagulation process after extractions? In ten cases the extraction socket was irradiated with 750 mW/cm2, 10 sec, 7.5 J/cm2, 1 mm from the socket. Bleeding was stopped by conventional roll pressure in another five cases as a control. Bleeding time for both procedures was measured. Irradiation with the LED yielded immediate hemostasis of the socket. Five cases showed coagulation within the first 10 seconds, and another five cases required an additional 10 seconds to fully control the bleeding. In contrast, the conventional method required 2-5 min (median 180 sec) to obtain hemostasis. A week later, the LED-irradiated sockets were healed uneventfully with epithelial covering. TEM showed the formation of a thin amorphous layer and an adjacent agglutination of platelets and other cellular elements under the layer at the interface of the irradiated blood.

Okamoto [6] from the same group of researchers then went on to use the LED light in patients on warfarin. Patients who took warfarin and required tooth extraction were divided randomly into three groups. The first group was irradiated with LED after tooth extraction. The second group was treated with a hemostatic gelatin sponge and LED irradiation. The third group was treated with only hemostatic gelatin sponges. Hemostasis was evaluated at 30 seconds after treatment. Less than 30% of the patients achieved hemostasis within 30 seconds in the hemostatic sponge group; approximately 50% of the patients in the simple LED irradiation group achieved hemostasis within 30 seconds; and 86.7% of the patients in the LED and hemostatic sponge combined group achieved hemostasis within 30 seconds, indicating that combined treatment with LED and hemostatic sponges provided a higher hemostasis than in the hemostatic sponge group.

The studies by Enwemeka and Ishikawa triggered my own curiosity and I have been using my curing light for several indications lately. A special case was the old gentleman who had suffered from a MRSA infection in his scalp for about ten years. “Everything” had been tried but in vain. A combination of irradiation with the curing light and ozone led to an almost complete healing. Later on we discovered that he had been using the same cap for many years and constantly re-infected himself. The first photo shows the situation at day one, the second photo shows the pus coming out at session two and the photo three the situation at the last session.

The power of the curing light is similar to that of a traditional low level laser (200-250 mW). The “power” in manuals is actually the power density, which is the output power in mW divided by the irradiated area. So if the tip of the probe is 0.25 cm2, the power density becomes: 250 mW divided by 4 = 1000 mW/cm2. There is a trend to increase the power of the curing light in order to shorten the time necessary to cure a filling. A rapid curing may or may not be optimal for the quality of the filling, but care should be taken not to let the high temperatures harm the pulp. There are now curing lights with output in the W range, and power densities around 5000 mW/cm2. Certainly fast curing, but what about the temperature rise? Runnacles [7] tested the temperature rise in human premolars, using different intensities from a standard curing light. All irradiations produced higher peak temperature than the baseline temperature, with some teeth exhibiting a temperature higher than 5.5°C, an increase thought to be associated with pulpal necrosis.

Enjoy your curing light, but be careful not to harm the pulp.

 

References:

  1. Enwemeka CS, Williams D, Hollosi S, Yens D, Enwemeka SK. Visible 405 nm SLD light photo-destroys methicillin-resistant Staphylococcus aureus (MRSA) in vitro. Lasers Surg Med. 2008;40(10):734-737.
  2. Enwemeka CS, Williams D, Enwemeka SK, Hollosi S, Yens D. Blue 470-nm light kills methicillin-resistant Staphylococcus aureus (MRSA) in vitro. Photomed Laser Surg. 2009;27(2):221-226.
  3. Soukos NS, Stultz J, Abernethy AD, Goodson JM. Phototargeting human periodontal pathogens in vivo. Lasers Med Sci. 201;30(3):943-952.
  4. Fontana CR, Song X, Polymeri A, Goodson JM, Wang X, Soukos NS. The effect of blue light on periodontal biofilm growth in vitro. Lasers Med Sci. 2015 Mar 11. [Epub ahead of print]
  5. Ishikawa I, Okamoto T, Morita S, Shiramizu F, Fuma Y, Ichinose S, Okano T, Ando T. Blue-violet light emitting diode (LED) irradiation immediately controls socket bleeding following tooth extraction: clinical and electron microscopic observations. Photomed Laser Surg. 2011;29(5):333-338.
  6. Okamoto T, Ishikawa I, Kumasaka A, Morita S, Katagiri S, Okano T, Ando T. Blue-violet light-emitting diode irradiation in combination with hemostatic gelatin sponge (Spongel) application ameliorates immediate socket bleeding in patients taking warfarin. Oral Surg Oral Med Oral Pathol Oral Radiol. 2014;117(2):170-177.
  7. Runnacles P, Arrais CA, Pochapski MT, Dos Santos FA, Coelho U, Gomes JC, De Goes MF, Gomes OM, Rueggeberg FA. In vivo temperature rise in anesthetized human pulp during exposure to a polywave LED light curing unit. Dent Mater. 2015 Feb 21. [Epub ahead of print]