News | June 10, 1999

The State of Hard Tissue Lasers


•How Lasers Work
•Coming to Market
•Another Type
•Looking Ahead

Hard tissue lasers have fought a long, hard battle before making significant strides in the sometimes conservative dental profession. Many companies have tried and failed to obtain clearance for their lasers. The major concerns were the safety of the technology and the possible damage lasers could cause to teeth.

For more than 20 years, lasers have been used to cut soft tissues. Only in the past few years has the Food and Drug Administration (FDA) approved them for cutting hard tissues. In this article, we'll discuss the two currently approved hard tissue lasers, how they work, and offer a look ahead.

How lasers work

Lasers use thermal radiation in wavelengths throughout the visible to infrared light spectrum to cut targeted structures. They can use different primary elements, such as Erbium or Neodymium, that produce different wavelengths, heat, and power.

When lasers were first applied to hard tissues (enamel, dentin, or cementum), they generated excessive heat, causing potential damage to the pulp chamber. Laser companies then used water to try to cool the tooth and protect the pulp from trauma. Researchers noted that lasers using the Erbium element in the laser rod created a wavelength that was highly absorbed by water. These lasers produced a 2,490-namometer (nm) wavelength and were 10 times more absorptive in water than CO2 lasers, which were always regarded as having the wavelength most absorptive in water. Absorption prevents the laser beam from generating heat that would damage vital tissue and structures.

When Erbium energy is pulsed into water at 100- to 200-microsecond durations, a microexplosion occurs, causing a shockwave into water. This shockwave occurs serendipitously into the pooled water (sitting on the surface of the target tissue) that was intended to cool the tissue. Researchers observed the destruction of hard tissue without heat generation. This is what led to today's only two current hard tissue lasers.


Coming to market

To market these devices in the United States, of course, the FDA has to grant marketing clearance. Clearance is typically granted in two different manners: a premarket approval (PFM) or a 510K approval.

Premarket approvals are usually designated for pharmaceuticals or healthcare devices substantially different than those previously cleared to market. Achieving a PMA typically requires seven to 12 years, numerous clinical studies, and a lot of financing. The 510K, however, is a much easier clearance process. This clearance is awarded when a product performs similarly to a product already cleared to market by the FDA or "grandfathered" in with respect to healthcare devices in common use prior to government requirements. This requires one to two years and minimal clinical studies compared to PMAs.

Recall that the FDA isn't an approving body; rather, it clears companies to market their products based on the claims they make in their clinical studies or trials. The FDA then only determines whether the product is safe and effective for each claim. It doesn't pass judgment on the products' reliability, efficiency, capability, or profitability.

The first hard structure laser cleared to market was Irvine, CA-based Premier Laser Systems' Centauri Erbium: Yttrium, Argon, Garnet (Er:YAG). Most individuals associated with the dental laser industry assumed the company would have to apply via the PMA route because the FDA had earlier ruled that way for a Neodymium: Yttrium, Argon, Garnet (Nd:YAG) laser, which was declined.

However, Premier's management convinced the FDA to clear the device using the 510K rule. They did this by educating members of the FDA on the different properties applicable to different laser wavelengths. For example, the Nd:YAG laser has no absorptive properties for water, while the Er:YAG is extremely absorptive. Company researchers then exhibited the laser's ability to create microexplosions and the resulting shockwaves in water, which is called an acoustical effect.

Mutually, Premier's researchers and the FDA decided the acoustical effect could also be referred to as a mechanical effect, which was a giant step to using the 510K rule. The mechanical effect was important because it meant the Er:YAG laser was similar enough to the high-speed handpiece, which also cuts with a mechanical effect. They were also able to show that the laser produces less heat and vibration than the Nd:YAG.

Following two years of clinical trials, the FDA granted marketing clearance to Premier for its Centauri in May 1997. The clearance initially included caries removal and preparation, roughening enamel, and related applications on adults. The laser has since been granted clearance for these procedures on children.

Unfortunately, Premier's laser was found to be cumbersome and limited in its application on the front 20 teeth, particularly for classes I and II. Also, the fiber tip that delivers the laser beam was fragile and expensive, especially because it needed to be sent back to the company several times a year and replaced at least twice a year. The tips cost $1,000 each, so dentists needed an expensive back-up while the other tip was getting polished. Currently, Premier's engineers have addressed most of the concerns and have continued their efforts to provide dentists with more reliable and practical units.


Another type

In October 1998, almost one and a half years following Premier's clearance, a different type of Erbium laser was cleared to market for hard tissue applications--Biolase Technology's Millennium Erbium, Chromium: Yttrium, Scandium, Gallium, Garnet (Er,Cr:YSGG) laser. Previously cleared to market for soft tissue applications, it's much different than the Centauri/Er:YAG.

The Millennium's wavelength is 2,780 nm, which provides significant advantages compared to Centauri's 2,940-nm wavelength. It is 200% more absorptive in water than CO2 and is 0.20% as absorptive than the Centauri/Er:YAG. This allows for a delivery system (fiber tip) that is much less brittle than the sapphire required in the Centauri. Also, Er,Cr:YSGG laser energy has coagulative properties the Er:YAG doesn't, permitting it to perform effective soft tissue surgeries. Therefore, a laser for soft and hard tissues is conveniently and economically housed in one system.

Biolase (San Clemente, CA) refers to its cutting of hard tissue as a hydrokinetic effect, which received FDA clearance in the same manner as Premier's Centauri. The hydrokinetic tissue-cutting system uses the laser's wavelength to supply energy to a patented coaxial air/water spray. The pulses of laser energy hit the water molecules and accelerate them to the target tissue.

The difference between this method and Centauri's is that the atomized water, not the laser, does the cutting, which is biocompatible to the target tissue. The Centauri has a water stream delivered adjacently (not coaxially) to the tip for cooling purposes and cuts using an acoustical effect in pooled water. The advantages of coaxial delivery are less heat, vibration, and possible pain; the disadvantage is that it doesn't have the same antibacterial effect as when a laser beam directly hits a surface as with the Centauri.

Centauri offers handpieces with 30° tips, and the Millennium offers handpieces with 60° and 90° tips, which help dentists achieve greater access in the oral cavity.


Looking ahead

Dental lasers enable clinicians to perform various hard tissue procedures faster and without the need for anesthesia in most cases. They also rid the operatory of the noise, vibration, and pain associated with traditional handpieces. And unlike dental drills, which can possibly remove more tooth structure than necessary, lasers can pinpoint and excise diseased hard tissue with greater precision and preserve the tooth's overall integrity. Of course, dental lasers may not fully take the place of handpieces; some cases require extensive cutting, and lasers aren't sophisticated enough to perform every related drill procedure.

Currently, the dental laser market is quite soft because dentists fear the technology hasn't fully developed. But industry experts believe this technology will survive and increasingly progress into dental offices as patients demand pain- and needle-free dentistry.