In recent years dentistry (following the trend of the whole medical field) took advantage from technological improvements aiming to make these treatments minimally invasive while granting the best possible results to the patient.

With this in mind, the use of the surgical laser provides the practitioner with an irreplaceable set of tools that allow a large number of procedures to be performed with precision and drastically reduce pain, bleeding, and risk of contamination of the treated part. With the laser, it is possible to perform some procedures without anesthesia; in all cases, it is possible to reduce the stress to which the patient is subjected and to accelerate healing.

Before choosing a dental laser and a specific treatment, it’s important to know how the light interacts with the tissues and some basic concepts about medical usage of radiant energy.

Each light source, from light bulbs to medical lasers, emit a certain quantity of luminous energy, lower than the energy it is supplied with. The ratio between luminous emitted power and input power is called efficiency. Laser diodes have different efficiency that mostly depends on wavelenght.

Laser power is expressed in Watt. In simple terms, about 70 Watts are needed increase the temperature of 1 liter of water of 1°C. Watts are units of power, or energy emitted on every second. So, a 1W laser source releases 1J (Joule) of energy per second. In order to emit a 1W laser beam, a diode with 50% efficiency would require 2W of electrical energy. The balance is wasted as heat. Thanks to technological evolution it is possible to build new laser types able to emit light with better efficiency.

Laser power is mostly defined by two parameters: continuous mode power and pulsed mode power. The former tells the power that the system is able to withstand when emitting a continuous light beam. The latter, much higher, is the maximum power that the device can emit in a very short pulse.

As already stated in previous article, each tissue can absorb, reflect or transmit received laser light in a different manner. The graph below shows an approximated logarithmic curve of the absorption of the light spectrum of oxyhemoglobin, melanin and water.

The white bands indicate the wavelengths of the main types of lasers used in dentistry. Each wavelength is suitable for a specific set of applications. Intuitively, it is observed that water (transparent to visible light) has very low absorption of wavelengths between 400 and 700nm. Conversely, melanin and hemoglobin have much higher absorption in the spectrum between 400 and 900nm.

A tissue that absorbs the emitted light heats to the point of vaporization, producing a clean, sterile cut at the site of the cut. Because the tissues are not incised, their structures are mostly preserved; consequently, bleeding is limited and nerve endings are minimally stressed.

Each tissue has specific properties, it is essential to choose five parameters correctly: time, light power, angle of incidence, distance to the source, and wavelength.

When choosing a dental laser, the first parameter to decide is the wavelength. Most lasers for dental surgery available today emit light with 808 or 980nm. As stated in previous section, emitted wavelength depends on laser diode construction (mostly, junction materials). Each semiconductor has specific construction implications, including laser diode structure, efficiency and cost.

For the same amount of energy consumed, a typical 980-nm laser emits about twice as much light as an 808-nm laser. This allows for smaller, cheaper devices that claim a high power rating. However, when the laser is used for surgical purposes, the light absorption of hemoglobin-containing tissues is about 5 times greater for 808nm than for 980nm. For this reason, when treating soft tissue, it is generally preferred to use a diode at 808nm, which provides better results with lower power.
Another wavelength that is particularly used in the dental field corresponds to the water absorption peak at 2940nm, emitted by Erbium (YAG) lasers. Short pulses of light heat water present (or deposited) on the surface to the point that it is transformed into vapor in a very short interval of time. The expansion of the water molecules causes the surface layer of the treated fabric to disintegrate without affecting the lower layers. The heating of the fabric is practically imperceptible and the action limited to the outermost layer. This property makes it an excellent tool for treating hard tissue (e.g., caries), minimizing the need for anesthesia and without the use of a drill (avoids microfractures).

The light from dental lasers is normally uncollimated. This means that a few millimeters from the emission source the beam opens at an angle around 30°. When used for surgery, it is important that the spot is as small as possible (contact application or minimal distance to the surface). In the case of aesthetic treatments, regeneration or whitening, the beam must be diffused over the surface to be treated, and special handpieces with lenses and optics are used for different applications.

Angle of incidence changes the amount of absorbed and reflected light. Maximum absorption is possible when light emission is perpendicular to the surface. By tilting the light source, instead, light power touching the surface is decreased.

Application time considers both pulse type and total treatment time. A very short pulse with high power and a long pulse with lower power could carry the same energy but give very different results (similar to the difference of emptying a water bucket in small drops or all at once).

Laser systems are designed to allow the user to choose both parameters. Manufacturer or clinical literature, together with the experience, allows the operator to set each parameter to obtain the best results for the treatment of choice.

When evaluating laser emitted radiation a reference parameter is the fluency. It is the emitted light energy divided by the unit of surface. It is automatically calculated by the laser device as the product between emitted light power and emission time, divided by the surface intercepted by the beam.

Handpiece and fiber type are essential choices too. Some examples in the images below:

TIP Handpiece. It is the usual handpiece for intraoral surgery and other surgical applications. Termination is composed by an interchangeable fiber tip with bendable head. Tips are designed also for decontamination purposes, when using spherical emission tips.

It is used for whitening, dermatology, and aestetics.

It maintains the spot diameter when the distance changes. It is used when the surface has to be treated in the same way on an area that is larger than the beam.