**2. Laser interaction with dental hard tissues**

Depending on laser wavelength and tissue characteristics, laser irradiation can be absorbed, scattered, reflected or transmitted into dental tissues (Ana et al., 2006; Featherstone, 2000; Niemz, 2004; Seka et al., 1996). These effects must be well known by professionals to help them choose the best equipment for a specific clinical application and to avoid thermal and mechanical damages to the target and surrounding tissues. Depending on the clinical situation, dentists need different laser wavelengths and irradiation parameters to obtain distinct effects on the same tissue.

Considering the applications in restorative dentistry, the conventional high-intensity infrared lasers can be well-suited for caries removal (Neves et al., 2010; Tachibana et al., 2008; White et al., 1993), cavity preparation (De Moor & Delme, 2010; Moldes et al., 2009; Obeidi et al., 2009;) and tissue conditioning (Botta et al., 2009; Dundar & Gunzel, 2011). For that, continuous emission lasers or pulsed laser longer than 1 picosecond should be well absorbed by the main components of teeth, i.e., water and hydroxyapatite; to promote the desired thermal and mechanical effects on these tissues, in a process called *thermal ablation*

are erbium and CO2 (λ = 9.6 µm) lasers. However, the CO2 (λ = 9.6 µm) systems are not

Considering the advances in technology for the development of ultra short pulse lasers (USPLs) (Niemz, 1995; Strickland & Mourou, 1985), efforts have been implemented to understand their interaction with dental hard tissues and to determine safe and proper parameters to provide a future clinical application in dentistry (Altshuler et al., 1994; Freitas et al., 2010; Kruger et al., 1999; Lizarelli et al., 2008; Strassl et al., 2008). Due to the extremely short pulse length, these systems promote precise cutting and have a strong potential for obtaining well-defined cavities and controlled caries removal (Niemz, 2004; Serbin et al., 2002). Also, due to the use of low energies per pulse, it is possible to adjust parameters bellow the ablation threshold for sound tissue which, at the same time, can ablate and remove the carious tissue (Niemz, 2004; Strassl et al., 2008). In this way, the selective removal of carious tissue could be seen as a minimal intervention that does not depend on the professional experience, but essentially relies on the tissue chemistry (Serbin et al., 2002). The operation of laser systems and interactions with dental hard tissues, the clinical diagnosis and the knowledge of the characteristics of the tissue to be irradiated are extremely important to assure a well-succeeded therapy. Professionals must evaluate the mineralization degree and chemical composition of the tissue to be removed, the extension and localization of caries, the activity degree of lesions and the interference of the irradiation

In this chapter, focus will be given on the last developments concerning the use of highintensity lasers in restorative dentistry, describing the different laser wavelengths, the mechanisms of interaction with dental hard tissue and the influence of pulse width on removing these tissues. Also, the effects of laser irradiation on carious tissues will be described, and the possibility of removing dental caries with laser irradiation will be discussed to help dentists to choose a suitable equipment and technique for improving their

Depending on laser wavelength and tissue characteristics, laser irradiation can be absorbed, scattered, reflected or transmitted into dental tissues (Ana et al., 2006; Featherstone, 2000; Niemz, 2004; Seka et al., 1996). These effects must be well known by professionals to help them choose the best equipment for a specific clinical application and to avoid thermal and mechanical damages to the target and surrounding tissues. Depending on the clinical situation, dentists need different laser wavelengths and irradiation parameters to obtain

Considering the applications in restorative dentistry, the conventional high-intensity infrared lasers can be well-suited for caries removal (Neves et al., 2010; Tachibana et al., 2008; White et al., 1993), cavity preparation (De Moor & Delme, 2010; Moldes et al., 2009; Obeidi et al., 2009;) and tissue conditioning (Botta et al., 2009; Dundar & Gunzel, 2011). For that, continuous emission lasers or pulsed laser longer than 1 picosecond should be well absorbed by the main components of teeth, i.e., water and hydroxyapatite; to promote the desired thermal and mechanical effects on these tissues, in a process called *thermal ablation*

commercially available for applications in dentistry.

**2. Laser interaction with dental hard tissues** 

on the restorative procedure.

distinct effects on the same tissue.

clinical practice.

due to a *thermomechanical* effect (Fried, 2000; Niemz, 1995; Seka et al., 1996). For shorter pulses, such as femtosecond laser pulses, the ablation occurs due to non-linear interactions with the tissue resulting in a plasma-mediated ablation.

The thermal ablation process that occurs in dental hard tissues is also known as explosive (water-mediated) tissue removal (Fried, 2000; Niemz, 1995; Seka et al., 1996). In a few words, this process can be explained as a result of the fast heating of the subsurface water confined by the hard tissue matrix, due to the higher interaction with infrared laser irradiation. The heating of these water molecules leads to an increase on molecular vibration and, consequently, an increase on subsurface pressures that can exceed the strength of the above tissue. Finally, it can be noted an "explosion" of tissue due to the material failure, resulting in the material removal. This process happens in temperatures below the melting point of dental hard tissues (around 1200oC) and varies according to the laser wavelength (e.g., Er:YAG reaches 300o C at the ablation threshold, while Er,Cr:YSGG reaches 800o C and CO2 9.6 µm reaches 1000o C) ((Seka et al., 1996; Fried et al., 1996). This process has been studied for the past 30 years, with the intention of choosing the best laser wavelength and parameter to effectively promote tissue removal or selective caries removal with minimal thermal consequences (Stern & Sognnaes, 1964; White et al., 1993; Neves et al., 2010; Ana et al., 2007; Seka et al., 1996; Tachibana et al., 2008; Moldes et al., 2009; Botta et al., 2009; Dundar & Gunzel, 2011).

For understanding how laser irradiation can provide a more conservative treatment of caries lesions, the chemical composition of target tissue must be known by the professional. Human enamel is composed by 95% hydroxyapatite (Ca10(PO4)6(OH2)), 4% water and 1% collagen fibers (Gwinnett, 1992); as well as human dentine contains 70% hydroxyapatite, 20% collagen fibers and 10% water (Ziip & Bosch, 1993). Considering the differences in composition and the higher resonance of Er:YAG (λ = 2.94 µm) by water (λ = 3 µm), we can infer that Er:YAG laser can ablate dentin faster than enamel. The same rule is valid when comparing carious tissue with sound ones, taking into account that decayed tissues have a significant higher amount of water. In this way, in a clinical application, professionals can observe easier caries removal when compared to the removal of sound surrounding tissues, and this fact can influence the laser irradiation parameters that should be used for different application.

Dental enamel and dentin have a weak absorption in the visible (400–700 nm) and nearinfrared (1064 nm) wavelength ranges; however, absorption bands of water and carbonated hydroxyapatite is found from 2.7 to 11 µm (Figure 1) (Ana et al., 2006; Fried 2000). The optical penetration of Nd:YAG on enamel is significantly high, indicating that the dentin irradiation with Nd:YAG laser can affect the pulp tissue in case of high energy densities, long exposure or in the absence of a photoabsorber (Boari et al., 2009). However, Nd:YAG laser can be indicated for removal of stained caries tissue, promoting a selective removal of caries lesion without pulpal damages due to the higher interaction of Nd:YAG by pigments (Seka et al., 1996), as it was demonstrated by a clinical trial performed by White *et al*. (1993).

Considering the use of Er,Cr:YSGG laser, literature evidences (Stock et al., 1997) that the 2.78 µm is strongly absorbed by the dental hard tissue since the optical absorption coefficient of enamel is about 7000 cm−1. In this way, the optical penetration is a few micrometers smaller than the obtained by Er:YAG laser.

Laser Technology for Caries Removal 295

operate in free running mode, with pulse duration of 150-400 µs. This pulse duration is shorter than the thermal relaxation time of dental hard tissues (< 1ms) (Niemz, 2004), which provide heat dissipation during ablation and avoid excessive heat transmission to the pulp, for instance. However, at higher energy per pulses, erbium lasers can induce thermal injuries to dental hard tissue, such as the presence of microcracks, melting or even carbonization. In this way, during the clinical application, it is essential to use the correct set up of laser parameters and the use of an adequate air-water spray to provide proper refrigeration and avoid these side effects. However, although the presence of a thin layer of water can increase the ablation process (Fried at al., 2002), an excessive water layer can decrease erbium interaction with dental hard tissues (Niemz, 2004); in this way, the use of

Fig. 2. Absorbance of water and hydroxyapatite and their relation with Er:YAG and

Er:YAG lasers became popular for using in dental hard tissues at the end of 1980s, when researchers tested the Er:YAG for ablation of enamel, dentin and caries lesions on extracted teeth (Hibst & Keller, 1989). Since then, several studies have been performed to determine parameters and conditions for a safe and efficient application in daily practice for soft and hard tissue applications (Altshuler et al., 1994; De Moor & Delme, 2010; Eberhard et al., 2005; Fried et al., 1996, 2002; Hibst & Keller, 1989; Moldes et al., 2009; Neves et al., 2010; Stock et al., 1997; White et al., 1994). On the other hand, the popularity of Er,Cr:YSGG laser started later, since the first studies tested the possibility of ablation of dental hard tissues on early 90's. I*n vitro* (Altshuler et al., 1994; Ana et al., 2007; Bachmann et al., 2009; Botta et al., 2011; Dundar & Guzel, 2011; Fried et al., 1996; Moldes et al., 2009; Obeidi et al., 2009; Stock et al., 1997; Tachibana et al., 2008) and *in vivo* (Yazici et al., 2010; Yilmaz et al., 2011) studies confirmed the feasibility of this wavelength for several applications on dental hard tissues,

saliva suction is recommended.

Er,Cr:YSGG lasers (Ana et al., 2006).

such as cavity preparation and caries removal.

Fig. 1. Absorption coefficients for the main chromophores of biological tissues (Ana et al., 2006).

Since the approval of erbium lasers for dental hard tissues use by FDA in 90's, Er:YAG and Er,Cr:YSGG have been extensively studied for caries therapy. The literature present a number of advantages over the high-speed drills for the removal of caries, such as reduction of pain, noise, vibration (Fried, 2000; Niemz, 2004; Seka et al., 1996; White et al., 1993), the possibility of selective removal (Eberhard et al., 2005; Neves et al., 2010) and the changes in chemical composition of remaining tissue (Ana et al., 2006; Bachmann et al., 2009; Botta et al., 2011), leading to a tissue that is resistant to demineralization. That is why erbium lasers can be considered a clinical reality in dental offices.

#### **3. The use of erbium lasers for caries therapy**

The erbium lasers are solid-state lasers produced with different types of matrix crystals. Some of them, such as Er:YAG (λ = 2.94 µm), Er,Cr:YSGG (λ = 2.78 µm), Er:YLF (λ = 2.81 µm), Er:YAG (λ = 2.73 µm) and CTE:YAG (λ = 2.69 µm), were already studied for ablation of dental hard tissues (Altshuler et al., 1994). From all of them, the most popular and with commercially available equipments for dentistry are Er:YAG and Er,Cr:YSGG.

Comparing the absorption of Er:YAG with Er,Cr:YSGG lasers by dental hard tissues, it is possible to observe that Er:YAG have a strong interaction with OH- from water molecules contained in the teeth, while Er,Cr:YSGG is better absorbed by water and OH- contents of hydroxyapatite (Figure 2)(Ana et al., 2006). Due to this fact, Er:YAG promotes surface temperatures up to 300o C at the ablation threshold, and Er,Cr:YSGG reaches 800o C during ablation of enamel (Fried et al., 1996).

Although it have been tested some erbium lasers operating in the Q-switched mode (with pulse duration in the range of ns) (Fried, 2000), the commercially available erbium lasers

Fig. 1. Absorption coefficients for the main chromophores of biological tissues (Ana et al.,

can be considered a clinical reality in dental offices.

ablation of enamel (Fried et al., 1996).

**3. The use of erbium lasers for caries therapy** 

Since the approval of erbium lasers for dental hard tissues use by FDA in 90's, Er:YAG and Er,Cr:YSGG have been extensively studied for caries therapy. The literature present a number of advantages over the high-speed drills for the removal of caries, such as reduction of pain, noise, vibration (Fried, 2000; Niemz, 2004; Seka et al., 1996; White et al., 1993), the possibility of selective removal (Eberhard et al., 2005; Neves et al., 2010) and the changes in chemical composition of remaining tissue (Ana et al., 2006; Bachmann et al., 2009; Botta et al., 2011), leading to a tissue that is resistant to demineralization. That is why erbium lasers

The erbium lasers are solid-state lasers produced with different types of matrix crystals. Some of them, such as Er:YAG (λ = 2.94 µm), Er,Cr:YSGG (λ = 2.78 µm), Er:YLF (λ = 2.81 µm), Er:YAG (λ = 2.73 µm) and CTE:YAG (λ = 2.69 µm), were already studied for ablation of dental hard tissues (Altshuler et al., 1994). From all of them, the most popular and with

Comparing the absorption of Er:YAG with Er,Cr:YSGG lasers by dental hard tissues, it is possible to observe that Er:YAG have a strong interaction with OH- from water molecules contained in the teeth, while Er,Cr:YSGG is better absorbed by water and OH- contents of hydroxyapatite (Figure 2)(Ana et al., 2006). Due to this fact, Er:YAG promotes surface temperatures up to 300o C at the ablation threshold, and Er,Cr:YSGG reaches 800o C during

Although it have been tested some erbium lasers operating in the Q-switched mode (with pulse duration in the range of ns) (Fried, 2000), the commercially available erbium lasers

commercially available equipments for dentistry are Er:YAG and Er,Cr:YSGG.

2006).

operate in free running mode, with pulse duration of 150-400 µs. This pulse duration is shorter than the thermal relaxation time of dental hard tissues (< 1ms) (Niemz, 2004), which provide heat dissipation during ablation and avoid excessive heat transmission to the pulp, for instance. However, at higher energy per pulses, erbium lasers can induce thermal injuries to dental hard tissue, such as the presence of microcracks, melting or even carbonization. In this way, during the clinical application, it is essential to use the correct set up of laser parameters and the use of an adequate air-water spray to provide proper refrigeration and avoid these side effects. However, although the presence of a thin layer of water can increase the ablation process (Fried at al., 2002), an excessive water layer can decrease erbium interaction with dental hard tissues (Niemz, 2004); in this way, the use of saliva suction is recommended.

Fig. 2. Absorbance of water and hydroxyapatite and their relation with Er:YAG and Er,Cr:YSGG lasers (Ana et al., 2006).

Er:YAG lasers became popular for using in dental hard tissues at the end of 1980s, when researchers tested the Er:YAG for ablation of enamel, dentin and caries lesions on extracted teeth (Hibst & Keller, 1989). Since then, several studies have been performed to determine parameters and conditions for a safe and efficient application in daily practice for soft and hard tissue applications (Altshuler et al., 1994; De Moor & Delme, 2010; Eberhard et al., 2005; Fried et al., 1996, 2002; Hibst & Keller, 1989; Moldes et al., 2009; Neves et al., 2010; Stock et al., 1997; White et al., 1994). On the other hand, the popularity of Er,Cr:YSGG laser started later, since the first studies tested the possibility of ablation of dental hard tissues on early 90's. I*n vitro* (Altshuler et al., 1994; Ana et al., 2007; Bachmann et al., 2009; Botta et al., 2011; Dundar & Guzel, 2011; Fried et al., 1996; Moldes et al., 2009; Obeidi et al., 2009; Stock et al., 1997; Tachibana et al., 2008) and *in vivo* (Yazici et al., 2010; Yilmaz et al., 2011) studies confirmed the feasibility of this wavelength for several applications on dental hard tissues, such as cavity preparation and caries removal.

Laser Technology for Caries Removal 297

tissue due to the variation in chemical composition, such as the presence of proteins, bacteria and other contents. In this equipment, the fluorescence is induced by red laser that emits at the wavelength of 655 nm, and the Er:YAG laser is turned off when significant changes on fluorescence are detected during caries removal, established by a cut-off value that indicates that all decayed tissue was removed. Some *in vitro* (Eberhard et al., 2008; Jepsen et al., 2008) and *in vivo* (Dommisch et al., 2008; Krause et al., 2008) studies showed the feasibility of this equipment; however, there is no consensus about the correct values of cutoff in different clinical conditions. Also, it must be emphasized that there are limitations of this technique mainly in dentin (Eberhard et al., 2008; Krause et al., 2008), when falsepositive can be reported due to the presence of pigments in affected or tertiary dentin, for instance, which should not be removed. In this way, the association of manual instruments

and is still necessary to assure a safe and correct clinical removal of dental caries.

limited (Navarro et al., 2010).

procedure.

**4. Influence of pulse width on tissue removal** 

Clinical trials have demonstrated that Er:YAG and Er,Cr:YSGG lasers can be considered a safe and efficient treatment for caries removal, since it is reported pulpal response and histological effects similar to those obtained by the use of conventional bur. Also, due to the lack of noise, pressure, discomfort and sometimes the necessity of local anesthesia, it is reported a good compliance of patients, mainly the pediatric ones. However, it must be emphasized that the time necessary to remove caries by laser irradiation is almost two or three times longer than the bur treatment, depending on the repetition rate and energy density (Navarro et al., 2010; Yamada et al., 2001). The increase of energy density and repetition rate can lead to discomfort and pain to patients, besides increasing the surface temperatures. For this reason the strategies used for improving the laser ablation speed are

Although the pulse duration of most commercial lasers (range of µs) is shorter than the thermal relaxation time of dental hard tissues, laser ablation promotes irregular cavities (depending on composition of target tissue), desiccation of the surface (due to the removal of underlying water) and the presence of few microcracks (related to the energy density), the amount of water coolant and the repetition rate must be adjusted during the clinical

The adjustment of repetition rate is important to assure that the inter-pulse period is longer than the thermal relaxation time of tissues; in this way, it is possible that the temperature of the irradiated tissues decrease between laser pulses (McDonald et al., 2001). Another strategy for cooling the tissue during laser irradiation is reducing the pulse duration (Seka et al., 1995). Depending on the pulse duration (<1 ps), the process of ablation is changed and the non-linear processes (or non-thermal ones) take place (Ana et al., 2006; Freitas et al.,

According to Niemz (1995), lasers with pulse durations in the range of ms (10-3 s), µs (10-6 s) or ns (10-9 s) generate considerable heat during ablation of dental hard tissues, in a mechanism mediated by *thermal interaction*. On the other hand, lasers with pulse durations of ps (10-12 s) and fs (10-15 s) ablate the tissues by forming an ionizing plasma. These lasers, commonly called as USPL (ultra short pulse lasers), operates at very high repetition rate (larger than 15 kHz) and energy per pulse typically of hundreds of µJ (Wieger et al., 2006).

2010; Kruger et al., 2008; McDonald et al., 2001; Niemz, 2004; Strassl et al., 2008).

During cavity preparation, the ablation of sound enamel by Er:YAG laser promotes cavities with rough enamel margins, with irregular and rugged walls, with depth that depends on the energy density and pulse width (Navarro et al., 2010). As well, it is reported the absence of smear layer, cracks, carbonization or melting if the adequate parameters and refrigeration were used (Botta et al., 2009). As Er:YAG, the enamel cavities produced by Er,Cr:YSGG laser irradiation present their floor with fissures and conical craters with sharp enamel projections and, in some areas, with the exposition of the enamel rods. The roughness of cavities is also dependent on the energy densities used (Ana et al., 2007; Olivi et al., 2010; Tachibana et al., 2008).

In sound dentin, due to the differences in composition and morphology, erbium lasers promote a higher removal of peritubular than the intertubular dentin. In this way, both Er:YAG and Er,Cr:YSGG promote the formation of rough surfaces with opened dentinal tubules, absence of smear layer, cracks or melting, with protrusion of peritubular dentin due to its less amount of water when compared to the intertubular dentin (Botta et al., 2009, 2011). The irregularities promoted by laser irradiation vary according to the energy density applied. Considering these facts, the differences in temperature rises at the ablation threshold promoted by Er:YAG and Er,Cr:YSGG seem to be unable to induce significant distinct morphological effects during cavity preparation.

In contrast, the use of high-speed drills for cavity preparation promotes enamel and dentin cavities flattened, with smooth internal walls and geometrically well-defined shapes, with closed dentinal tubules and presence of smear layer (Botta et al., 2009; Navarro et al., 2010). These characteristics, as well as the changes in chemical and crystalline structure in remaining tissue promoted by laser irradiation, must be taken into consideration in order to choose an appropriate adhesive system for composite restoration, since the adhesive systems interact in a different way with laser or bur treated tissues (Moretto et al., 2011).

Erbium lasers are also effective on removal of dental caries. *In vitro* studies revealed that Er:YAG and Er,Cr:YSGG can selectively remove dental caries due to the higher amount of water and organic content when compared to sound tissues (Eberhard et al., 2008; Tachibana et al., 2008); in this way, it is possible to obtain a conservative therapy, with no removal of sound tissue and lack of thermal damages. However, the adjustment of laser energy density in commercial equipments is sometimes difficult to promote the selective ablation of infected dentin and in order to preserve the affected dentin, and the clinical results still depend on the experience and knowledge of the professional, added to the use of manual instruments for correct diagnosis of remaining tissue. In fact, clinical trials report the well acceptance of patients (Dommisch et al., 2008; Krause et al., 2008), the maintenance of pulp vitality and marginal seal, the good quality of restorations and the absence of secondary caries even after two years (Yazici et al., 2010). Also, it is reported that these lasers can fulfill the requirements of Minimal Invasive Dentistry, due to the possibility of conservation of the sound tissue structure during caries removal and to the possibility of surface decontamination of affected dentin (Kornblit et al., 2008).

To determine an end point for caries removal, there are some equipments that associate Er:YAG laser irradiation to the diagnosis by laser fluorescence (Dommisch et al., 2008; Eberhard et al., 2008; Jepsen et al., 2008; Krause et al., 2008;). The essential principle of this application is that the fluorescence of sound tissue differs from the fluorescence of carious

During cavity preparation, the ablation of sound enamel by Er:YAG laser promotes cavities with rough enamel margins, with irregular and rugged walls, with depth that depends on the energy density and pulse width (Navarro et al., 2010). As well, it is reported the absence of smear layer, cracks, carbonization or melting if the adequate parameters and refrigeration were used (Botta et al., 2009). As Er:YAG, the enamel cavities produced by Er,Cr:YSGG laser irradiation present their floor with fissures and conical craters with sharp enamel projections and, in some areas, with the exposition of the enamel rods. The roughness of cavities is also dependent on the energy densities used (Ana et al., 2007; Olivi et al., 2010;

In sound dentin, due to the differences in composition and morphology, erbium lasers promote a higher removal of peritubular than the intertubular dentin. In this way, both Er:YAG and Er,Cr:YSGG promote the formation of rough surfaces with opened dentinal tubules, absence of smear layer, cracks or melting, with protrusion of peritubular dentin due to its less amount of water when compared to the intertubular dentin (Botta et al., 2009, 2011). The irregularities promoted by laser irradiation vary according to the energy density applied. Considering these facts, the differences in temperature rises at the ablation threshold promoted by Er:YAG and Er,Cr:YSGG seem to be unable to induce significant

In contrast, the use of high-speed drills for cavity preparation promotes enamel and dentin cavities flattened, with smooth internal walls and geometrically well-defined shapes, with closed dentinal tubules and presence of smear layer (Botta et al., 2009; Navarro et al., 2010). These characteristics, as well as the changes in chemical and crystalline structure in remaining tissue promoted by laser irradiation, must be taken into consideration in order to choose an appropriate adhesive system for composite restoration, since the adhesive systems interact in a different way with laser or bur treated tissues (Moretto et al., 2011).

Erbium lasers are also effective on removal of dental caries. *In vitro* studies revealed that Er:YAG and Er,Cr:YSGG can selectively remove dental caries due to the higher amount of water and organic content when compared to sound tissues (Eberhard et al., 2008; Tachibana et al., 2008); in this way, it is possible to obtain a conservative therapy, with no removal of sound tissue and lack of thermal damages. However, the adjustment of laser energy density in commercial equipments is sometimes difficult to promote the selective ablation of infected dentin and in order to preserve the affected dentin, and the clinical results still depend on the experience and knowledge of the professional, added to the use of manual instruments for correct diagnosis of remaining tissue. In fact, clinical trials report the well acceptance of patients (Dommisch et al., 2008; Krause et al., 2008), the maintenance of pulp vitality and marginal seal, the good quality of restorations and the absence of secondary caries even after two years (Yazici et al., 2010). Also, it is reported that these lasers can fulfill the requirements of Minimal Invasive Dentistry, due to the possibility of conservation of the sound tissue structure during caries removal and to the possibility of

To determine an end point for caries removal, there are some equipments that associate Er:YAG laser irradiation to the diagnosis by laser fluorescence (Dommisch et al., 2008; Eberhard et al., 2008; Jepsen et al., 2008; Krause et al., 2008;). The essential principle of this application is that the fluorescence of sound tissue differs from the fluorescence of carious

Tachibana et al., 2008).

distinct morphological effects during cavity preparation.

surface decontamination of affected dentin (Kornblit et al., 2008).

tissue due to the variation in chemical composition, such as the presence of proteins, bacteria and other contents. In this equipment, the fluorescence is induced by red laser that emits at the wavelength of 655 nm, and the Er:YAG laser is turned off when significant changes on fluorescence are detected during caries removal, established by a cut-off value that indicates that all decayed tissue was removed. Some *in vitro* (Eberhard et al., 2008; Jepsen et al., 2008) and *in vivo* (Dommisch et al., 2008; Krause et al., 2008) studies showed the feasibility of this equipment; however, there is no consensus about the correct values of cutoff in different clinical conditions. Also, it must be emphasized that there are limitations of this technique mainly in dentin (Eberhard et al., 2008; Krause et al., 2008), when falsepositive can be reported due to the presence of pigments in affected or tertiary dentin, for instance, which should not be removed. In this way, the association of manual instruments and is still necessary to assure a safe and correct clinical removal of dental caries.

Clinical trials have demonstrated that Er:YAG and Er,Cr:YSGG lasers can be considered a safe and efficient treatment for caries removal, since it is reported pulpal response and histological effects similar to those obtained by the use of conventional bur. Also, due to the lack of noise, pressure, discomfort and sometimes the necessity of local anesthesia, it is reported a good compliance of patients, mainly the pediatric ones. However, it must be emphasized that the time necessary to remove caries by laser irradiation is almost two or three times longer than the bur treatment, depending on the repetition rate and energy density (Navarro et al., 2010; Yamada et al., 2001). The increase of energy density and repetition rate can lead to discomfort and pain to patients, besides increasing the surface temperatures. For this reason the strategies used for improving the laser ablation speed are limited (Navarro et al., 2010).
