Dental Laser Utility Expanding As Research Supports Innovation

A laser beam is created from a substance known as an active medium, which when stimulated by light or electricity produces photons of a specific wavelength. Erbium and carbon dioxide (CO₂) are examples of active media.

Dental lasers can emit the beam as either a continuous stream or discrete pulses of photons. Continuous-wave emission mode means the laser is on the entire time it is turned on. As for pulsed laser modes, there are two basic forms: gated wave and free-running pulsed. A gated wave pulse is usually created with a shutter that blocks the beam of a continuous wave diode or CO₂ laser from reaching the handpiece and target tissue at varying speeds. The laser is on constantly, but the shutter device blocks the light from transmitting. Free-running pulsed lasers are not on constantly, but they emit photons in powerful bursts of energy measured in millionths of seconds.

Erbium and Nd:YAG are examples of free-running pulsed lasers. These temporal emission modes have important characteristics when the laser energy interacts with tissues. Each pulse has a set amount of energy, usually the millijoules displayed on the unit. As shorter free-running pulses are used, this same energy is effectively squeezed into a smaller space, which increases the peak power of the pulse; yet the actual energy expended is identical. Hard-tissue erbium dental lasers can have peak powers in the thousands of watts, and these short bursts of extreme power allow for the efficient cutting of enamel, dentin, and bone.

Substances known as chromophores absorb the light energy when a laser beam is aimed at tissue. A chromophore is a specific substance that absorbs the laser energy and converts it into thermal or mechanical energy in order to function. Examples of chromophores include water (for CO₂ and erbium lasers) and hemoglobin (for diodes and Nd:YAG lasers). The transfer of energy from laser photons to chromophores creates usable energy to do the necessary work.

The thermal implications for the target tissue of the three pulse modes are profound. Thermal relaxation refers to the ability of the target tissue to absorb heat produced by laser interaction. In continuous mode, there is no thermal relaxation at all, and potentially damaging heat can build in the tissue quickly. In gated wave mode, the ability of the tissue to absorb the heat is limited. Thermal relaxation occurs the most when free-running pulsed lasers are used. Each pulse is temporally very short, anywhere from 50 to 1,000 millionths of a second. There is adequate time between each pulse to allow the tissue to absorb and dissipate the heat to minimize thermal damage. This lack of tissue heating results in the lowered postoperative discomfort and predictable healing seen after many laser procedures. Osseous thermal damage is minimized as well, which has positive implications when used in periodontics and oral surgery. Thermal relaxation also explains the ability to perform many operative dentistry procedures and even some soft-tissue ones without local anesthesia.

Laser-assisted operative dentistry has increased in efficiency in recent years due to improvements in hardware, software, and pulse technology. Sophisticated pulse manipulation is an innovation that is making erbium lasers more efficient and comfortable. Er:YAG quantum square pulse (QSP) is an example of this trend. A common problem when preparing teeth with erbium lasers is the interaction of the laser beam with the ablation cloud of debris that forms while preparing the tooth. This cloud blocks the beam, reducing cutting ability, and interacts with the laser energy, leaving debris on the cavosurface that can reduce bond strengths. QSP breaks each laser pulse into smaller pulselets that are timed to avoid the ablation cloud. This technology has been shown to cut tooth tissue 40% faster than standard laser pulses.¹ Additionally, clinicians report that patients need local anesthesia less often when QSP is used.

A laser-assisted irrigation process known as photon induced photoacoustic streaming (PIPS^®) has recently been developed for Er:YAG lasers. Specially engineered tips are used along with extremely short digitally controlled low-energy pulses (20 mJ at 50 millionths of a second) to create a powerful shockwave in the irrigant solution that is non-thermal. This energetic movement of solutions has been shown to more thoroughly clean the complex 3-dimensional root canal system than traditional instruments.² A recent in-vitro study showed just 1 minute of PIPS-induced irrigation with 5% sodium hypochlorite eliminated Enterococcus faecalis from infected teeth and inhibited bacterial regrowth whereas the bleach alone could not.³ Scanning electron microscopy of the pulpal walls from the same study exhibited no signs of thermal damage whatsoever. Another study showed PIPS irrigation was superior to needle irrigation and ultrasonics for removing biofilm.⁴ PIPS can be paired with any instrumentation and sealing technique, as it is simply a way to agitate irrigants more profoundly.

An interesting variation on the use of PIPS has been investigated regarding internal bleaching. The concept is that the PIPS effect should help hydrogen peroxide penetrate tooth structure better. A recent benchtop study using artificially stained human teeth showed that PIPS-assisted 35% hydrogen peroxide was superior to multiple traditional intracoronal techniques.⁵

Hard-tissue dental lasers of the erbium family have been shown to be minimally traumatic to bone when proper parameters are followed. Studies indicate that the bone remaining after laser-assisted surgeries exhibits less thermal damage, no smear layer, and fewer signs of mechanical trauma as compared to bur-cut bone.⁶ Erbium lasers’ ability to cut bone less traumatically than burs makes them an excellent instrument for procedures such as crown lengthening and surgical extractions.

Another less well-known effect of dental lasers on bone is the phenomenon called photobiomodulation, or low-level light therapy (LLLT). This is achieved with near-infrared lasers such as diodes or Nd:YAG. These wavelengths applied in low doses to tissue induce a cascade of positive cellular effects that result in increased gene expression, cellular stimulation, and healing. For example, LLLT with diode lasers has been shown to increase orthodontic tooth movement in various studies.⁷ Another recent study showed diode-laser LLLT induced more rapid dentin bridge formation of pulp exposures in rats via pulpal stem cell stimulation.⁸

Intriguing examples of both hard-tissue erbium surgical use and near-infrared photobiomodulation on bone can be seen in the treatment of bisphosphonate-related osteonecrosis of the jaw (BRONJ). European studies using erbium lasers to excise necrotic bone either alone or in combination with Nd:YAG photobiomodulation showed complete BRONJ remission in the majority of cases.^9-11 The combination of less traumatic cutting by the erbium laser and cellular stimulation by the Nd:YAG yield these promising results. For the laser-using dentist doing more traditional osseous procedures, these outcomes indicate the beneficial effects of lasers on bone.

Lasers can enable dentists to both expand the mix of procedures they provide and deliver them with predictably improved comfort for their patients. Having a solid understanding of basic laser physics and biological interactions is vital, and, as with any technology, proper training is paramount.

References

1. Primc NM, Lukac M. Quantum square pulse mode ablation measurements with a digitally controlled Er:YAG dental laser handpiece. Journal of the Laser and Health Academy. 2013;(1):1-5.

2. Peters OA, Bardsley S, Fong J, et al. Disinfection of root canals with photon-initiated photoacoustic streaming. J Endod. 2011;37(7):1008-1012.

3. Olivi G, DiVito E, Peters O, et al. Disinfection efficacy of photon-induced photoacoustic streaming on root canals infected with Enterococcus faecalis: an ex vivo study. J Am Dent Assoc.2014;145(8):843-848.

4. Ordinola-Zapata R, Bramante CM, Aprecio RM, et al. Biofilm removal by 6% sodium hypochlorite activated by different irrigation techniques. Int Endod J.2014;47(7):659-666.

5. Arslan H, Akcay M, Yasa B, et al. Bleaching effect of activation of hydrogen peroxide using photon-initiated photoacoustic streaming technique. Clin Oral Investig.2014 May 25 [Epub ahead of print].

6. Panduric DG, Juric IB, Music S, et al. Morphological and ultrastructural comparative analysis of bone tissue after Er:YAG laser and surgical drill osteotomy. Photomed Laser Surg.2014;32(7):401-408.

7. Camacho AD, Cujar SA. Dental movement acceleration: Literature review by an alternative scientific method. World J Methodol.2014;4(3):151-162.

8. Arany PR, Cho A, Hunt TD. Photoactivation of endogenous latent transforming growth factor-β1 directs dental stem cell differentiation for regeneration. Sci Transl Med.2014;6(238):238ra69. doi:10.1126/scitranslmed.3008234.

9. Stubinger S, Dissmann JP, Pinho NC, et al. A preliminary report about treatment of bisphosphonate related osteonecrosis of the jaw with Er:YAG laser ablation. Lasers Surg Med. 2009;41(1):26-30.

10. Vescovi P, Merigo E, Meleti M, et al. Conservative surgical management of stage I bisphosphonate-related osteonecrosis of the jaw. Int J Dent.2014;2014:107690. doi:10.1155/2014/107690.

11. Vescovi P, Merigo E, Meleti M, et al. Nd:YAG laser biostimulation of bisphosphonate-associated necrosis of the jawbone with and without surgical treatment. Br J Oral Maxillofac Surg. 2007;45(8):628-632.

Steven R. Pohlhaus, DDS

Master Laser Trainer, Academy of Clinical Technology, San Clemente, California; Fellow, Academy of General Dentistry; Private Practice, Baltimore Center for Laser Dentistry,
Linthicum, Maryland