Lasers in pediatric dentistry: a review of clinical uses

Laser is defined as the “Light Amplification by Stimulated Emission of Radiation” (Parker, 2007). In dentistry, the lasers were introduced back in the 1960’s by Goldman et al. (1964) when he experimented the pink ruby laser on caries removal. Decades later, the first laser approved by the U.S. Food and Drug Administration was in the 1990, specifically the neodymium-yttrium-aluminum-garnet (Nd:YAG) laser (Coluzzi, 2005).

Since then, many advancements in different areas of dentistry have developed, and lasers are now utilized in restorative & pediatric dentistry, periodontics, endodontics, oral surgery, and pain management in temporomandibular joint (AAPD, 2017).

In this paper we will discuss the clinical approach to the use of lasers in different aspects of the pediatric dentistry.

To properly understand the different aspects and uses of different lasers, the clinician must first learn the mechanism by which the laser function and the reaction between the laser and different tissue structures.

Different tissue structures require specific wavelengths and affinities for absorbing laser energy. Thus, the laser used is dependent on the targeted tissue (Coluzzi, 2005). This suggests that the oral tissues carry independent optical aspect of target tissue, this refers to the pigmentation and water content of the tissue, hence, affects the reaction of certain lasers to its distinct characteristics (Caprioglio et al., 2017).

Radiation by lasers interact with the tissue in contrasting ways, this is either, transmission, reflection, and absorption. Transmission is when the energy of the laser goes through the tissue without affecting it, reflection is on the other hand, when the laser redirects itself from the surface of the tissue. Reflection is the property that allow the laser to be used for diagnostic purposes where it can measure the extent of caries and differentiate the soft carious tissue from the sound tooth structure (Sinha et al., 2020).

Finally, Absorption is the direct tissue reaction by the energy absorption of the laser, this can result in different applications depending on the target tissue “coefficient of absorption” which is also demonstrated in Figure 1 (Sinha et al., 2020). This energy is essentially a photothermal interaction, where the lasers can lead to an increase in the temperature of the target tissue water content that lays intracellularly and extracellularly, thus, set about the evaporation of the water content at the boiling temperature of about 100 degrees Celsius (Coluzzi, 2004).

Ablation is then defined as the lasers ability to vaporize water content in the tissue and sets about the excision of soft tissue. Conversely, oral hard tissue contains calcium and hydroxyapatite crystals whereby it doesn’t get vaporized, but rather due to the escape of the water content, it breaks the crystals into particles and leads to its disarrangement (Fasbinder, 2008).

Laser types used in pediatric dentistry

Due to different coefficient of absorption of tissues and distinct wavelengths for oral tissue type, lasers can be classified according to their level into high-level lasers and low-level application lasers. Low level lasers are used in inhibitory and stimulatory biological process and diagnostic processes. On the contrary, high-level lasers are used for soft tissue surgeries, hard tissue removal and caries removal (Mahavir et al., 2011).

Low level application lasers include, He-Ne laser and Diode lasers, high level include CO2 lasers (CO2 gas), Nd: YAG lasers and Argon lasers (Sinha et al., 2020).

Laser applications in Pediatric dentistry

In this section we are going to categorize the applications of laser according to its diagnostic applications, soft tissue applications, and hard tissue applications.

Diagnostic applications

Lasers at wavelength 655nm is effectively used in caries detection, lasers like Diagnodent, this laser machine works on the amount of reflection from fluorescence of demineralized surfaces to a targeted area (Lussi et al., 2001). The fluorescence arises from bacterial porphyrins red light excitation, which then distinguish organic and inorganic substance (Olivi et al., 2009). Therefore, the machine then indicates the presence or absence of dental caries. This technique is also considered safe and conservative since there will be reduction in x-ray exposure.

However, the results are not always accurate, since it was shown from a study done by Hibst et al. (2001) that toothpaste residue and resin fillings can produce false positive readings, thus, it is recommended to be used with conjunction with conventional diagnostic tools (Olivi et al., 2017).

Soft tissue applications

Most of the lasers operates on the water content of the soft tissue that leads to vaporization or ablation, therefore, Diode lasers, CO2 lasers, Erbium lasers and Nd:YAG has the ability to decontaminate, excise and produce hemostasis (AAPD, 2017).

In the pediatric dentistry the use of laser for soft tissue application is mainly in surgeries like frenectomy and ankyloglossia, frenectomy is indicated when the patient or child has an abnormally high attachment of the frenum that leads to trauma in brushing, maxillary teeth spacing and poor oral hygiene due to trapping of food particles (Ghadimi et al., 2012). Ankyloglossia or tongue tie is a condition found in newborns which represents with lingual frenum attachment which limits tongue movement, this is accompanied by difficulties in breastfeeding, speech, and nutrition (Kotlow, 1999).

Erbium laser is the ideal laser medium to be used in these surgeries which is used simultaneously with water spray at “frequencies between 30-45Hz and energy between 35-55mJ” (Ghadimi et al., 2012), this will provide adequate cooling to prevent carbonization of the tissue, provides good healing outcomes and doesn’t require the use of sutures. On the other hand, diode lasers can also be used in frenectomies at power of 1 Watt, however, it was shown that it can lead to damage of the surrounding tissue and patients’ discomfort was reported (Kotlow, 2007).

Hard tissue applications

In this section we will discuss the 1) Caries removal and cavity preparation, 2) Caries prevention, 3) Cavity etching and fissure sealants, 4) Applications in pulpotomy and pulpectomies and 5) Low level laser application.

Caries removal and cavity preparation

In the 1990’s the FDA approved the use of Erbium lasers in caries removal due to its selective caries removal characteristics, in this application the erbium family is considered a high-power laser because of its spectrum that is mid-infrared. Lasers with this wavelength have a high affinity towards the water absorption and hydroxyapatite crystals, making them the most suitable for hard tissue cutting (Caprioglio, 2017). Additionally, the Er: YAG laser was tested for its ability to prepare tooth structure even without water cooling, the prepared tooth structure had no cracks and dentin had minimal remaining smear layer, furthermore, the pulp temperature rise was only 4.3 degrees Celsius (Parker et al., 2007). This is clinically insignificant and is considered to be safe for the pulpal health of the tooth (Geraldo-Martins et al., 2005; Rechmann et al., 1998).

When evaluated clinically Tokonabe et al. (1999) found that the enamel will appear chalky white and in dentine the margins were rough and sharp, with open dentinal tubules and no smear layer. This is believed to enhance the bond and improve sealing to resin restorations (Groth et al., 2001). Moreover, due to selective properties of Nd:YAG lasers in caries removal it was found that lasers ablation is comparable to the use of air motors, and is considered to be minimally invasive (Husien, 2006). However, the floor of the preparation wasn’t as smooth as the surface prepared by conventional bur (Husien, 2006).

It should be noted that many variables can affect the cavity preparation, factors like the laser angulation, pulse length, focus mode, power density and amount of cooling. These factors contribute to the amount of hard tissue structure removal. Therefore, closer to the final preparation of the cavity, the power of the laser must be in lower wattage for the enamel and dentine structure, to induce conditioning and prepare the structure for resin bond (Olivi et al., 2011).

However, it has been shown that “adhesion to dental hard tissues after Er: YAG laser etching is inferior to that obtained after conventional acid etching”. (Martinez-Insua et al., 2000). Which in turn necessitates the use of acid etching in conjunction to laser conditioning.

Caries Prevention

Various studies have examined the caries prevention properties of laser irradiation (Apel et al., 2003). It is believed that more stable and less soluble compounds can form on the tooth surface after laser treatment, this is feasible by the laser modification of the calcium to phosphate ratio, and by reducing the carbonate to phosphorous ratio. The compound formed is shown to be less susceptible to acid attack by cariogenic bacteria (Watanabe et al., 2001). An in vitro study by Featherstone et al. (2000) compared the acid threshold for dissolution of the enamel after laser conditioning, he found that the pH has been lowered from 5.5 to 4.8 reportedly. These findings are of significance to patients with hypoplastic lesions or developmental anomalies because of their high susceptibility to dental caries (Mast et al., 2013). Another study found that the preventive capabilities of lasers is comparable to the daily use of fluoride containing dentifrice (Featherstone et al., 2000).

These findings are very promising for the future of preventive dentistry. Nevertheless, the actual mechanism of how laser help in prevention of dental caries is still not clear and more studies are needed to evaluate the risks and benefits of this treatment (AAPD, 2017).

Cavity etching and fissure sealants

Long term clinical retention has been found when fissure sealants are applied to the sound tooth structure without preparation. However, etching with phosphoric acid was recommended to enhance the retention of the fissure sealant even after the laser irradiation of the pits and fissures (Shahabi et al., 2012). The micro and macro roughness produced by the laser on the enamel structure can produce mechanical retention means for the restoration or sealant, for this application Erbium lasers were used at low energies of 40-70mJ. In addition, owing to the decontamination and bactericidal properties of lasers, with long-term follow up studies, it was shown that there is lower recurrent caries in teeth treated with laser than conventional means of preparation (Olivi et al., 2011). Nevertheless, laser pretreatment should only be utilized as a supplementary to conventional acid etching to enhance the bond strength enamel (Sasaki et al., 2008) and to reduce leakage at the interface between the restoration and the tooth (Khogli et al., 2013)

Applications in pulpotomy and pulpectomies

Lasers use in pulpotomy have shown an increase in popularity, as it can controls hemorrhage and sterilizes the canal orifice which facilitates better placement of calcium hydroxide paste or MTA at the amputated pulp canal (Sinha et al., 2020). Laser energy has an obtundent and sedative effect on inflamed pulpal tissue which also further supports its use in pulpotomies (Sinha et al., 2020). According to a recent systematic review article they found that, “In general, high clinical, radiographic, and histopathological success rates were reported in laser groups in comparison to other assessed methods at 36 months follow up”, However, due to limited number of high-quality clinical research, reaching a definite conclusion cannot be made and more randomized clinical trials are needed (Ansari et al., 2018).

There are few documented studies evaluating laser pulpectomy. But in one study the Er,Cr:YSGG laser was found to consume less time than the rotary and hand instruments. However it was as effective as the rotary and superior to the hand instruments in terms of cleaning and canal preparation efficiency (Soares et al., 2008). Diode lasers also reported efficiency in elimination of enterococcus faecalis when compared to sodium hypochlorite and triphala (Durmus & Tanboga, 2014)

Low level laser application

Laser application in biostimulation and pain control, according to Gutknecht et al. (2005), and to Tuner & Hode (2004), are indicated for certain reasons in paediatric dentistry. They include pain relief of tender lymph nodes during teething, as a topical anaesthetic before mucosal injection and relief of pulpal pain in carious or traumatically exposed pulp. In addition to swelling and pain reduction following soft tissue trauma and increasing the treatment outcomes by irradiating a tooth while pulp capping procedure. More clinical studies are required to determine the suitable irradiation conditions.

Advantages of lasers in pediatric dentistry

Patient behavioral management modifications and pain control are considered the pillars of the pediatric dentistry, lasers are considered to be less invasive where the reduction in noise during preparation is significant in comparison to air driven handpieces (AAPD, 2017), which in turn can reduce the anxiety of the patient, reduce discomfort and lead to more cooperation in the treatment (David & Gupta, 2015). In addition, when utilizing lasers, it was shown that there is no need to obtain a local anesthesia this is due to the selective caries removal and precision, it is also reported that non-contact lasers will reduce the vibrations which can cause dentine sensitivity and discomfort. A study by Wakabayashi et al. (1993) demonstrated that by means of “photothermal effects” produced by Nd:YAG lasers it was able to block the sodium-potassium channels and stop nerve conduction of pain. However, another study that compared the pulp response after laser preconditioning found that there is no statistically significant effect on the pulp testing (Al Bukhara et al., 2015). The mechanism of pain control is still not known, and more studies must be conducted to understand the potential risks and effects of laser induced analgesia.

Olivi et al. (2009) conducted a study to evaluate the operating time between lasers and conventional surgical instruments in soft tissue surgery, they found that utilizing lasers can significantly reduce the chair time. Another study compared the post-operative edema and healing, and the sample that was treated with lasers, produced statistically significant inflammation and faster healing (Convissar & Goldstein, 2003; Boj et al., 2011).

Reduced post-operative infection is owing to the bactericidal and sterilization effects of lasers at the treatment site (Olivi et al., 2009). Additionally, faster healing is due to hemostasis control in soft tissue laser surgery (Boj et al., 2011). Therefore, owing to the promising advancements and benefits of utilizing laser in dentistry, there is an increase in the use of laser in the pediatric practice (AAPD, 2017).

Disadvantages and Limitations of lasers in pediatric dentistry

Since there is more than one wavelength for different oral tissue type, there might be a need for multiple laser machines, This result in higher startup cost for the clinician (David & Gupta, 2015). Moreover, laser operation requires training by the dentist, for protocols, function, and safety purposes.

It is not recommended for the lasers to be used for removal of crowns or amalgam restorations, firstly, as a consequence of its photothermal feature, it can result in overheating of the tooth and lead to irreversible pulp damage. Secondly, aerosols produced by amalgam filling removal can result in mercury vapor which can be hazardous to the operator and patient, therefore, high volume suctions must be used in that case (Parker, 2007). Other concerns around aerosols are with patients with infectious diseases where surgical soft tissue excision might be a better option (Garden et al., 2002).

Laser therapy in hard tissue preparations produces a rough surface which will require eventually the use of handpieces for finishing & polishing, in case of a pediatric patient this can result in loss of cooperation due to the noise and discomfort (Sinha et al., 2020).

As any type of radiation, laser has a detrimental side effects when non-targeted tissues such as the skin and eyes are exposed to the direct beam or the scattered radiation (Sinha et al., 2020). Visible wavelengths may selectively damage the red and green cones of the eyes leading to colour blindness, but as the majority of dental lights are located in the invisible range they tend to affect both the cornea and the retina (AAPD, 2017). That is why for safety reasons, a specific wavelength protective spectacles should be worn by all the individuals in the operating room (AAPD, 2017).

Conclusion

Lasers in dentistry are now recognized as an efficient tool that is utilized as a substitute for conventional surgical instruments, or used in combination with handpieces (AAPD, 2017). Its minimal invasive properties, time efficiency and preventive properties makes it an optimal treatment for soft and hard tissue. In pediatric dentistry, its advancement with laser is very promising in the future due to its acceptability by children and reduction of noise and anxiety which is contributed to lack of noise and vibrations found with conventional drills. However, it is important for the clinician to obtain theoretical and clinical training in lasers to understand the different physical characteristics of types of lasers to apply their use optimally.