Endodontic State of Art (Dr Kolnick)

 - Review of Literature for Er,Cr:YSGG lasers in Endodontics

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Total elimination of bacteriafrom infected root-canal systems remains the most important

objective of endodontic therapy. However, in spite of a plethora of new products and

techniques, achieving this objective continues to elude our profession. Historically,

endodontic treatment focused on root canal disinfection with “entombment” of

remainingbacteria within dentinal tubules and inaccessible areas of the root-canal system.

Although many factors have been implicated in the etiology of endodontic failures, it has

become evident that these “entombed” bacteria play a pivotal role in the persistence of

endodontic disease (Siqueira et al, 2008). With the introduction of Cone Beam CT, it has

been reported that from 30% to 75% of radiographically successful endodontic-treated

teeth show signs of Apical Periodontitis when viewed with CBCT (Wu et al, 2009;

Estrela et al, 2008)In teeth where reduced size of the existing radiolucency was

diagnosed by radiographs and considered to represent periapical healing,

enlargement of the lesion was frequently confirmed with CBCT (Wu et al, 2009).

Although impressive results have been obtained in vitro, laser energy alone has not been

able to achieve total bacterial kill in extracted teeth. From a clinical perspective, it is

apparent that a combination of different treatment modalities will be required in order to

eventually be able to sterilize root canal systems. In addition, many clinical obstacles

exist that further complicate the clinician’s ability to achieve this goal. These include, but

are not limited to: restricted endodontic access, complex root-canal anatomy, limitations

of irrigation and instrumentation techniques, inability to entomb bacteria, and the

inability to reach and eliminate bacteria deep within the tooth structure.

The erbium, chromium-doped yttrium, scandium, gallium and garnet (Er,Cr:YSGG)

laser, operating at a wavelength of 2,780 nm, has been suggested as a valuable toolin

endodontics. Since this wavelength is very similar to the absorption maximum of water in

hydroxyapatite, photo-ablation occurs where water evaporates instantaneously, thereby

ablating the surrounding tissue. Gordon et al (2007)postulated that it was possible to

achieve expansion and collapse of intratubular water as deep as 1000μm or more into

dentin.This micropulse-induced absorption was capable of producing acoustic waves

sufficiently strong to remove smear layer, disrupt biofilm and kill intratubular

bacteria.These findings are significant, as bacteria have been identified in dentin at depths

of 1100μm, with E. faecalis at depths of 800μm (Kouchi et al, 1980; Haapasalo and

Orstavik, 1987). Irrigants such as sodium hypochlorite have a limited effect on these

bacteria with penetration depths of only 100μm into dentinal tubules (Berutti et al, 1997).

Smear Layer Removal:

Smear layer (SL) removal is considered to be an important requisite of successful

endodontic treatment. By increasing dentin permeability,SL removal enhances the

penetration of intracanal medicaments and laser energy into dentin. In addition, SL

removal facilitates penetration of sealers into the dentinal tubules. Yamada et al (1983)

have extolled the virtue of smear layer removal and how it promotes a better apical seal

due to sealer penetration into dentinal tubules.

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Studies have shown incomplete removal of SL from the root canal walls, particularly in

the apical third, when chemo-mechanical preparation was used (Takeda et al, 1999;

Aktener and Bilkay, 1993). Extensive research has been performed into the use of the

Er,Cr:YSGG laser for smear layer removal in root canal systems. As early as 2004,

Ishizaki et al reported that laser irradiation at 5W using a 400μmfiber was efficient for

removing smear layer and debris without melting or carbonization, while preserving the

apical stop. In order to obtain a better understanding of the working mechanism of the

Er,Cr:YSGG laser in endodontics, Blanken and Verdaasdonk (2007), using specialized

imaging techniques, suggested that the working mechanism can be attributed to cavitation

effects inducing high speed fluid motions into and out of the canal. Franzen et al (2009)

using a 200μm fiber at 0.25W at 20Hz showed absence of SL and open tubules, with

intertubular dentin more ablated than peritubular dentin.

The development of the radial-firing laser tip (Biolase Technology, Inc.), with a tip shape

that emits the laser energy as a broad cone, allowed better coverage of the root-canal

walls than end-firing tips. George et al (2008) studied side-firing, conical-ended optical

fibers when Er:YAG and Er,Cr:YSGG lasers were used in root canals in which thick

smear layers were created to provide a challenge for the laser system. Lasing improved

the action of EDTAC in removing SL. Conical fibers performed better than plain fibers

but there was no difference in performance between the 2 laser systems when matched

for all other parameters. These results provided a “proof of concept” for lateral emitting

fibers for endodontic procedures. In a later paper, George and Walsh (2010) determined

that laterally emitting, conical fiber tips could be used safely under defined conditions for

intracanal irradiation without harmful thermal effects on the periodontal apparatus. This

was in agreement with the thermal findings of Schoop et al in 2007. Schoop et al (2009),

using a 200μm radial-firing tip (RFT2) at 3W, found most dentinal tubules exposed with

no signs of cracking or melting. They concluded that the beam expansion by the conical

tip geometry favored homogeneous energy distribution along the root canal walls.

When comparing laser-activated irrigation (LAI) to passive ultrasonic irrigation (PUI)

and conventional irrigation (CI), De Moor et al (2009) found that LAI was statistically

significantly more effective in removing artificially placed dentin debris in a root canal

than PUI and CI.In a follow-up study in 2010 the same authors evaluated the efficacy of

ultrasonic versus laser-activated irrigation to remove artificially placed dentin debris

plugs. They found that LAI techniques using erbium lasers (Er:YAG or

Er,Cr:YSGG) for 20 seconds (4 X 5 seconds) at 75mJ and 20Hz to be statistically

better than PUI for 20 seconds and as efficient as PUI with the intermittent flush

technique for 60 seconds (3 X 20 seconds).Peeters et al (2011) found duration of laser

irradiation to be more important than the size of apical enlargement. Placing the 600μm

tip above the pulp chamber and activating at 1W and 35Hz, completely clean canals were

found after irradiation for 60 seconds. Irradiation for 30 seconds had similar results to

PUI.Juric et al (2014) compared the antimicrobial efficacy of Er,Cr:YSGG laser-activated

irrigation with PUI and RinsEndo against intracanal E. faecalis. They found no

difference among the three active irrigation techniques, which were all significantly more

effective than the conventional syringe irrigation. LAI did, however, generate more

negative bacterial samples.

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Peeters and De Moor (2015) measured pressure changes during laser-activated irrigation

by the Er,Cr:YSGG laser, during continuous irrigation in the pre-enlarged canal.The laser

power used and the distance between the tip and the apex affected the magnitude of the

apical fluid pressure. The shape of the emitting tip did not affect the pressure produced at

the apex. The overall mean magnitude of the pressure changes developed using LAI at

0.75 and 1.75 W was comparable with the lymphatic capillary pressure when the tip was

placed at the cervical margin. When looking at obturation of root canal systems in fifty

two canals, Varella and Pileggi (2007) evaluated the number of canals and isthmuses

obturated after Er,Cr:YSGG laser treatment for 40 seconds at 1.5W and 20Hz. They

found that the laser-treated canalshad a statistically significant greater number of

lateral canals/isthmuses obturated than canals flooded with 17% EDTA for 3

minutes.

Ozer and Basaran (2013) evaluated microleakage of root canal fillings irradiated with

different output powers of Er,Cr:YSGG laser. They found the 1W and 2W settings were

most effective for debris and SL removal, exposing dentinal tubules in middle and apical

canal thirds and preventing microleakage statistically better than 2.5W irradiation or 17%

EDTA. Mohammadi et al (2013) studied the effect of Er,Cr:YSGG pretreatment on bond

strength of fiber posts to root canal dentin using a self-adhesive resin cement and found

that laser pretreatment significantly increased post retention.

In a recent, ground-breaking paper published by Al-Karadaghi et al (2015), the authors

compared the effectiveness of a dual wavelength (2780 nm Er,Cr:YSGG, 940 nm diode)

laser in the elimination of SL, comparing it with Er,Cr:YSGG alone, in terms of radicular

dentin permeability and ultrastructural changes of root canal walls. Dye permeation in

the dual wavelength laser group was significantly higher over the whole root length:

cervical, middle, andapical compared to the Er,Cr:YSGG laser group and non-irradiated

samples (p < 0.001). This translates to a significant increase in dentin permeability

with the dual laser group.Scanning electron micrographs of dual wavelength irradiated

samples showed a total removal of smear layer with preservation of the annular structure

of dentinal tubules. There was no sign of melting and carbonization.Er,Cr:YSGG laser

root canal irradiation produced uneven removal of smear layer and inefficient cleanliness,

especially in the apical third. These findings were consistent with those of Silva et al

(2010) in which Er,Cr:YSGG laser with 0.75 W average power produced uneven removal

of smear layer. Some area of insufficient cleanliness and absence of melting and

carbonization was observed due to irregular irradiation. Dentin permeability for all root

thirds was statistically similar to control group (non-irradiated samples).

Root Canal Disinfection

While the erbium laser has been shown to be extremely effective in smear layer removal

in root canals, its ability to disinfect root canals has been questioned. Jha and colleagues

(2006)conducted a study examining the antimicrobial effects of the Er,Cr:YSGG laser.

They concluded that the “Er,Cr:YSGG laser instrumentation was [not] able to eliminate

an E. faecalis infection in root canals” and that “the laser was completely ineffective in

Page 4 of 9

disinfecting root canals when sterilesaline was used as an irrigation solution.”In the Jha

and colleaguesstudy, the researchers recovered residual viable bacteria after laser

treatment of infected root dentin by collecting dentin shavings from the root canal wall.

They then transferred dentin shavings to broth tubes and incubated them. The

development of turbidity was taken as evidence of bacteria survival of the lasing

treatment. However, this model is not quantitative in the sense that a single surviving

bacterial cell from the infected dentinwould give precisely the same result as would a

million surviving organisms: in both cases, the tube receiving the infected dentin

shavings turned turbid following incubation. Therefore, according to this model, it

would be impossible to determine whether any reduction (disinfection) of the

bacterial population had occurred.

When comparing the bactericidal effect of different lasers, Gutknecht et al,in a series of

studies (1997 – 2002), reporteda bacterial kill rate (at a depth of 1000μm into dentin)of

only 38.6% for the Er,Cr:YSGG laser compared with 84.8% for the Nd:YAG, 63.9% for

the diode (810nm) and 13.9% for the Er:YAG.

Studies with the 200μm radial firing tip (RFT2 tip) showed more promising bacterial kill

rates. Gordon et al (2007) reported a disinfection reduction of 99.71% for E. faecalis at a

dentin thickness of approximately 200μm. They found that bacterial recovery decreased

when laser duration or power increased and when operating in the dry mode. Schoop et

al (2009)reported very high bacterial kill rates for E. coli and E. faecalisbut the sample

size was small and the teeth were only incubated for 4 hours prior to laser irradiation

resulting in a lack of penetration of the test bacteria into the dentinal tubules. Franzen et

al (2009) studied the decontamination of deep dentin by means of Er,Cr:YSGG laser

irradiation. Despite low pulse energy of 3.13mJ, the laser irradiation resulted in

significant bacterial reduction up to a dentin thickness of 500μm (p < 0.05). Arnabat et al

(2010) compared the antimicrobial effect of Er,Cr:YSGG laser with that of sodium

hypochlorite at various concentrations in root canals experimentally colonized with E.

faecalis.The use of NaOCl 5% was the most effective procedure, with NaOCl 0.5% being

the least effective; however, laser treatment was as effective as NaOCl 5% when

applied at 2 W for 60 s.

For root canal irrigation to be effective, the irrigant solution needs to reach the end of the

root canal, create a current and continuously replenish itself and carry away un-dissolved

debris (Chow, 1983). In many cases however, air is trapped at the end of the root canal,

creating an apical vapor lock. This in turn, prevents the irrigant from reaching the critical

apical third of the root canal.Ultrasonics, hand files, rotary instrumentation or paper

points will not dislodge this vapor lock. Apical negative pressure irrigation as well as

laser-activated irrigation will eliminate this vapor lock. Peeters and De Moor (2014)

studied the mechanism by which laser-activated irrigation removed the vapor lock.

Laser-activated irrigation overcame the airlock effect by releasing air trapped in the air

column. The mechanism underlying the removal of trapped air from the apical region

using an Er,Cr:YSGG laser in a dry root canal is via the disruption of the surface tension

at the solution-air interface. This disruption, caused by bubble implosion(cavitation),

displaced air in the form of bubbles from the apical region toward the solution, which

allowed the solution to travel apically.

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When comparing bacterial reduction in straight and curved canals using Er,Cr:YSGG

laser treatment versus a traditional irrigation technique with sodium hypochlorite,

Dewsnup et al (2010) reported that the laser reached higher sterilization levels in straight

canals (all samples) than in curved canals but no statistical significance was found

between all groups. On a cellular level, Lopez-Jimenez et al (2014) used atomic force

microscopy visualization of injuries in E. faecalis cells caused by Er,Cr:YSGG and diode

lasers. They concluded that the Er,Cr:YSGG laser at 2W of power was the most effective

in the extent of injuries and damage to bacterial cell surfaces.

Dual Wavelength Laser

While the erbium lasers have a high affinity for water and are therefor extremely efficient

in removing smear layer, they are rapidly absorbed and have little penetration into dentin.

Diode lasers, however, are selectively absorbed by pigment (melanin and hemoglobin)

and are relatively unaffected by water. This affords the diode laser greater penetration

through dentin with little interaction with it, making it possible to act on microorganisms

deeper in the dentinal tubules.

Recent research has been conducted on the effectiveness of a dual wavelength laser (2780

nm Er,Cr:YSGG, 940 nm diode) in endodontic treatment. In 2013, Gutknecht and

Franzen reported a 99.9% bactericidal effect at a depth of 1000μm in dentin using dual

laser therapy. Al-Karadaghi et al used thermocouples to record temperature elevation

during root canal treatment with a dual wavelength laser and found the temperature

elevation on the external root surface along the apical, middle and coronal thirds to be

below the periodontium critical limit (7°C). Franzen et al (2015)evaluated the

intrapulpal thermal changes that occurred during the treatment of the root surfaces with a

laser system emitting Er,Cr:YSGG 2780- and 940-nm diode laser irradiation in an

alternating sequence.They found that the combined laser emission of 2780 and 940 nm

was a promising way for root surface debridement without inducing intrapulpal thermal

damage when using an appropriate water/air spray. All measured temperatures were

considerably below the critical value of 5.6°C.Al-Karadaghi et al (2015) compared the

effectiveness of a dual wavelength (2780 nm Er,Cr:YSGG, 940 nm diode) laser in the

elimination of smear layer, comparing it with Er,Cr:YSGG alone, in terms of radicular

dentin permeability and ultrastructural changes of root canal walls. They reported a

significant increase in dentin permeability with the dual laser group,with no sign of

melting and carbonization. These results reflect a major paradigm shift in laser-assisted

endodontic therapy and further studies will be needed to determine if dual lasers will

improve clinical outcomes.

Clinical Outcome Studies

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To date, very few endodontic laser outcome studies have been reported in the literature.

Martins et al (2014) published a blind, randomized and controlled clinical study that

compared a laser-assisted endodontic treatment using an erbium,chromium:yttrium- scandium-gallium-garnet (Er,Cr:YSGG) laser and radial firing tips (RFT) versus the

conventional use of 3% sodium hypochlorite and interim calcium hydroxide paste, in

teeth with chronic apical periodontitis. Their findings suggest that for single-rooted and

premolar teeth, this laser-assistedprotocol can achieve predictable endodontic outcomes,

comparable to conventional strategies, in 1 year of follow-up.

Conclusion

The introduction of CBCT has highlighted the fact that recurrent/persistent endodontic

disease is more prevalent than previously reported. In addition, it has illustrated that

many lesions of endodontic origin are larger than they appear on standard dental

radiographs and that their healing takes significantly longer when evaluated in 3-D.

While many different factors can influence healing, it is now evident that bacteria left

behind in root canal systems play a pivotal role in the recurrence of endodontic

disease as well as the incomplete healing of endodontic lesions. A large body of

evidence supports the positive role of the Er,Cr:YSGG laser in smear layer removal,

increased dentin permeability as well as root canal and dentin disinfection. The ongoing

research into dual wavelength, laser-assisted endodontic therapy is extremely promising

and may change significantly the way endodontic treatment is performed in the near

future.

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