The Latest Laser Innovations in Dentistry

Lasers emit a highly collimated light beam, which ensures that laser light is nearly monochromatic and directional. These two characteristics mean that laser light is highly structured in space and correlated in time—it is referred to as coherent light. The common characteristic properties of laser radiation are monochromaticity, directionality, coherence, and high brightness. The most important characteristics of laser radiation are the wavelength, power or energy, time of action (continuous or pulsed regime), and from the point of interaction also energy and/or power density. The laser wavelength directly influences radiation absorption in tissue, which is the main requirement of any efficient laser radiation–tissue interaction. ¹

At present, it is possible to generate hundreds of laser radiation wavelengths—from X-ray up to far infrared (IR). The laser radiation wavelength is given by the chosen laser active media and open resonator arrangement. According to their particular wavelengths, lasers are classified as X-ray (wavelength 0.01–25 nm), ultraviolet (UV 25–400 nm), visible (400–760 nm), and IR (−0.75 to 1 mm) lasers. For applying laser radiation, it has to be taken into account that the short wavelength photons are more energetic than infrared wave photons and, therefore, the effect of UV and IR radiations is different.

Lasers in dentistry create an innovative type of dental treatment and at the dental clinician's disposal there are a number of lasers approved for specified uses. Laser radiation eliminates a discomfort in cavity preparation, simplifies filling material insertion, and reduces pain and tooth sensitivity. Laser light can remove tumors, overgrown tissue, reshape the gums, provide gum surgery, or whiten the teeth. Laser treatment is also an optimal option for children, who become easily anxious in the dental office. Dentists mainly use lasers with focused light beams, which are able to remove a small amount of the tissue. The goal of this contribution is to give a summary of advantages and disadvantages of particular laser systems in clinical practice.

Laser radiation from the visible region (wavelengths approximately from 500 to 1000 nm) is absorbed in pigmented tissue and blood elements, e.g., argon laser radiation (wavelengths 458 or 515 nm) have an affinity for hemoglobin, diode, and Nd:YAG laser radiation (wavelength 700–1064 nm) have an affinity for both melanin and hemoglobin, and of interest is their good hemostasis. These lasers have varied dental clinical soft-tissue applications.

The next important factor from the interaction point of view is the absorption peaks of UV radiation and radiation with the following wavelengths: 1440 nm (Nd:YAG second line), ∼2000 nm (Tm, Ho lasers), ∼3000 nm (Er lasers), and ∼10,000 nm (CO₂ lasers) in water. They are responsible for photoablation or thermal ablation of tissue containing water. The maximum radiation absorption in water is at ∼3000 nm. Another important absorber besides water is hydroxyapatite. In this, CO₂ laser radiation absorption peak is at its maximum. ²

In general, laser radiation treatment is effective, minimally invasive, it reduces bacteria during therapy, and the procedure is often fast.

In dentistry, lasers can be used in clinical practice in the following way ³ :

Hard tissue lasers that generate powerful radiation are responsible for caries lesion detection, and deal with tooth sensitivity; they are useful in prevention (laser-enhanced fluoride uptake), and, most importantly, in cavity ablation for dental fillings.

Soft tissue low-power lasers are able to cut soft tissue together with sealing of exposed blood vessels. The main clinical indications are in the periodontal area, namely for the curettage after mechanical scaling, removing of gum inflammation, benign oral tumors, gum reshaping, crowns lengthening, and removing of soft tissue folds.

The other laser systems, namely, the Ho:YAG, Ho:YSGG, Nd:YLF, super-pulsed CO₂, diode and excimer lasers, and some wavelengths of Nd:YAG lasers, were tested experimentally in vitro but they were not used in general practice.

The benefits of laser application in dental treatment are as follows: less of bleeding compared with scalpel therapy, less damage to the surrounding tissue, shortening of healing time, tissue sterilization during the process, and no need of anesthesia and suture. All these advantages have been clinically verified and confirmed.

The disadvantage of laser application—as against the standard dental drill or scalpel—is the higher cost of the laser system (between $39,000 and $45,000) and the requirement of new skilled dentists and nurses in compliance with the laser safety guidelines. However, with the laser it is not possible to prepare smooth and flat surfaces, and, therefore, the dental laser technique is seldom used in clinical prosthodontists—curettage and crowns lengthening being the only exceptions.

Another, and now newly used laser application, is seen in the restorative dentistry. It is based on the three-dimensional (3D) laser impression system—3D laser print and CAD/CAM technology. ⁴ All these techniques are based on 3D laser sintering, printing, or rapid prototyping. This technology prepares layers of the material according to a 3D design based on computer data. Laser radiation scans metal powders or thermoplastic powder and transforms the radiation power into a thin melted layer.

Based on 3D computer data, the model, fixed, or removable denture are automatically formed. The advantages of this technique are saving of the raw material, cost reduction, and the end sample precision, and the smaller marginal gaps with less gingival irritation can also be prepared. The results have a direct impact on longevity of the restoration, mainly for implants superstructure reconstruction.

The 3D laser print in dentistry uses also the method of selective laser sintering for producing units. The building material is thermoplastic powder then sintered by layers of laser radiation. The size of one layer of the model built is ∼0.1 mm. The models can be used immediately after they have been built and cleaned. No support structure is necessary. The main advantage is the speed of the requested model creation. The main disadvantage of this technique is the limited number of types of possible useful materials. Up to now, the printer can prepare only polyamide, metal, or metal alloys samples. The model from these materials has excellent mechanical properties.

The last method for dental clinical practice that can be taken into account is the dental optical coherence tomography (OCT). With OCT, the imaging of gingiva and periodontal and mucosa imaging are possible. With a longer wavelength, OCT is also applicable in bone-related disease imaging. Also, this method can recognize mineral changes at early demineralization stages, which is necessary for early diagnosis of caries. OCT is a low cost, noninvasive, nonradiative, and high-resolution method. By miniaturization, this system can be used in the future also in telemedicine. ⁵

From the point of view of clinical applications, it can be stated that laser radiation now influences all individual disciplines of dentistry. New applications could appear with miniaturization of laser devices and the discovery of generation of other specific wavelengths.