Photodynamic Therapy in Endodontics: A Literature Review

Abstract

Recently, several in vitro and in vivo studies demonstrated promising results about the use of photodynamic therapy during root canal system disinfection. However, there is no consensus on a standard protocol for its incorporation during root canal treatment. The purpose of this study was to summarize the results of research on photodynamic therapy in endodontics published in peer-reviewed journals. A review of pertinent literature was conducted using the PubMed database, and data obtained were categorized into sections in terms of relevant topics. Studies conducted in recent years highlighted the antimicrobial potential of photodynamic therapy in endodontics. However, most of these studies were not able to confirm a significant improvement in root canal disinfection for photodynamic therapy as a substitute for current disinfection methods. Its indication as an excellent adjunct to conventional endodontic therapy is well documented, however. Data suggest the need for protocol adjustments or new photosensitizer formulations to enhance photodynamic therapy predictability in endodontics.

Introduction

Microorganisms and their byproducts play a key role in pulpal and periapical disease development, directly linking the success of endodontic therapy to their complete elimination from root canal system.^1
–3 Although cleaning and shaping,⁴ application of an inter-appointment antibacterial dressing, and sealing of the root canal⁵ are accepted procedures to achieve and maintain root canal disinfection, the complete elimination of microorganisms from the root canal system seems to be an impossible task.⁴

According to Siqueira,⁶ the microflora associated with primary root canal infections are typically mixed, with predominance of gram-negative (G−) anaerobic rods. Infections in endodontic failures (secondary infections) are usually composed of one or a few bacterial species, generally gram-positive (G+) bacteria, with no apparent predominance of facultatives or anaerobes. Enterococcus faecalis is frequently isolated from persistent root canal infections, usually as the single species of microorganism, although yeast-like microorganisms and Candida spp. can also been found.³ This suggests that they may be therapy resistant, and probably the most significant mechanism for this resistance is microbial arrangement in a biofilm. Because of these microflora characteristics and anatomical variations in the root canal system, especially in the apical region, given its complexity, conventional endodontic procedures may not suffice to ensure complete disinfection.^1
–3

Aiming for complete disinfection, high-power lasers were used, leading to 99% of bacterial elimination by temperature rising and protein denaturation.^7,8 However, damages to dental and surrounding tissues, such as ankylosis, cement and dentin melting or carbonization, root resorption, and periradicular necrosis, can be associated with high-power lasers.^9,10

Because of their very low increase in temperature, ∼0.5°C,¹¹ low-power lasers do not promote morphological changes in tooth structure,^9,10 and also do not promote disinfection when used alone. When associated with exogenous photosensitizers (PS), a cascade of photochemical events starts, resulting in the production of reactive oxygen species, which are toxic to tumor cells, bacteria, and fungi.¹¹ This is the mechanism of action of photodynamic therapy (PDT), also called photoactivated disinfection (PAD), light-activated disinfection (LAD), or photodynamic antimicrobial chemotherapy (PACT).¹² PDT has found a place in various fields of dentistry, including endodontics.¹¹

Many in vitro and in vivo studies in recent years showed the excellent antimicrobial potential of PDT in root canal system disinfection, especially against E. faecalis. The purpose of this study was to summarize the results of research on photodynamic therapy in endodontics published in peer-reviewed journals.

Methods

A review of pertinent literature was conducted in PubMed by inserting the following key words and Boolean operators: photodynamic therapy OR photoactivated disinfection OR photodynamic antimicrobial chemotherapy OR photodynamic inactivation OR light activated disinfection OR photo-activated disinfection AND endodontics. All articles retrieved from the search were considered, with no restriction as to time period applied; however, only articles in English were included. Forty-nine articles were retrieved and 33 were selected after applying exclusion criteria for reviews and cytotoxicity studies. Data obtained from this review will be presented in the following sections in terms of relevant topics, added by relevant articles on the basis of PDT.

Review

PDT

The action mechanism of PDT relies on the topical or systemic administration of a nontoxic PS, followed by low dose irradiation with visible light of a suitable wavelength. Absorption of the light triggers excitation of the PS which, in the presence of oxygen, leads to a cascade of photochemical effects, resulting in the production of high ROS, that are toxic to tumor cells, bacteria, and fungi. These reactions can occur by electron transfer to hydrogen, leading to the production of free radicals (type I reaction) or by energy transfer to oxygen (type II reaction), resulting in the production of singlet oxygen.¹¹

Light sources (LS)

PS activation has been accomplished by using various LSs, such as argon lasers, Nd:Yag, gold, or copper vapor lasers, all complex and expensive equipment.¹¹ Diode lasers have now become the most used because of their low cost and portability. Other LSs, such as light-emitting diodes (LED) or conventional halogen light, have also been used, with good results.^13

–16 The use of intracanal optical fibers (ICFs) has also been studied as a way to increase the effectiveness of PDT.^17

–21 Calibration of the the LS should be correct. The resonance between the LS wavelength and the selected PS should be monitored¹² as should the radiation and PS delivery.

PSs

The desired properties of an optimal PS include favorable photophysical, chemical, and biological characteristics such as low citotoxicity, short-time photosensitivity, absorption peaks in the low-loss transmission window of biological tissues, simplicity in formulation, reproducibility, high stability and high affinity, and penetration into bacterial cells rather than healthy tissues (selectivity).¹¹

Although the photochemical principle for cancer and antimicrobial PDT is the same, there are important differences in the structures of PSs and cellular targets. For cancer treatment, porphyrins, chlorins, phthalocyanines, and bacteriochlorins are the indicated PSs, for their tumor location and low toxicity in the absence of light in mammalian cells. To eradicate microorganisms, the most studied PSs belong to the groups halogenated xanthenes, phenothiazines, acridines, and conjugated chlorins.¹²

Hamblin and Hasan²² have mentioned that PSs for antimicrobial purposes can be divided into three groups: those that strongly bind and penetrate the microorganisms (e.g., chlorin e6), those that bind weakly [i.e., toluidine blue (TB) and methylene blue (MB)], and those that do not demonstrate binding (i.e., rose bengal). This is because in bacterial cells, outer membrane damage plays a important role, differently from mammalian cells, where the main targets for PDT are lysosomes, mitochondria, and plasma membranes.²²

In endodontics, PSs derived from phenothiazines have been widely used.^{17

–21, 23

–48} Phenothiazines show intense absorption at 600–660 nm wavelength (red light), a useful spectrum in PDT, known as the therapeutic window required for efficient light penetration in biological tissues.¹² Both tumor cells and bacterial strains resistant to multiple antibiotics are sensitive to MB and ortho-TB.²²

According to Bouillaguet et al.,^13,14 blue LSs (380–520 nm), routinely used in dental offices for resin-based material photocuring, are attractive options for PDT in dentistry. However, despite this potential advantage, the use of blue light for PDT may be limited by a lack of appropriate PSs. They point to riboflavin, chlorin e6, and pheophorbide a polylysine as suitable PSs for blue LSs, but suggest further additional tests before their clinical indication.

Pre-irradiation time (PIT) and irradiation dose

PIT corresponds to the time elapsed between the PS application and its activation by light. This time is necessary to allow PS uptake by the target before irradiation, as it is expected to bind or even translocate cell membrane.

According to Wainwright,¹² a PS that is slowly uptaken by the microorganism may cause only cell wall photodamage at first, whereas nucleic acid strand breakage, for example, will be apparent after longer incubation times.

The total energy applied by the LS to the PS may also interfere with the chemical reactions and ROS release, changing the outcome of PDT. To be able to understand and control the irradiation, it is necessary to know some physical parameters. Energy (E) may be defined as the light amount deposited on the target, and it is defined by the relation between the LS power (P) and the application time (t) (E=P x t) and is expressed in Joules (J).

Fluence is a parameter that causes more confusion, because some authors suggest that its calculation should take the LS cross-sectional area,²⁸ whereas others prefer an estimated area of 1 cm² where light would be acting. In both cases, it is the rate at which energy is deposited in a determined area, and is expressed in J/cm².

Bactericidal effects of PDT

There is a fundamental difference in susceptibility to antimicrobial PDT between G+ and G− bacteria. In general, G+ bacteria are more susceptible than G− bacteria; therefore, the structural characteristics of different bacterial types must be observed.^12,49

High susceptibility of G+ species can be explained by their physiology. Cytoplasmic membrane is surrounded by a relatively porous layer of peptidoglycan and lipoteichoic acid, which allows the PS to cross. G− bacteria have an inner cytoplasmic membrane and an outer membrane, separated by a peptidoglycan-containing periplasm that forms a physical and functional barrier between the cell and its environment. Several different proteins are present in the outer membrane, some of which function as pores to allow the passage of nutrients, whereas others have enzymatic function or are involved in maintaining the structural integrity of the outer membrane.²² Neutral or anionic PS molecules are effective in binding and inactivating G+ bacteria. In G− bacteria, these molecules bind only with the outer membrane, to a greater or lesser extent, not being able to completely inactivate them after illumination.²² To inactivate a bacterial cell, the PS must be absorbed by the cell membrane and/or be translocated to the cytoplasm, leading to inhibition of further DNA, RNA, and protein synthesis.⁴⁹

According to Wainwright,¹² phenothiazines are more effective against G+ than G− species. Because of its hydrophilic nature, low molecular weight, and positive charge that allows passage through the porin-protein channels in the outer membrane of G− bacteria, MB interacts predominantly with lipopolysaccharide (LPS) anionic macromolecules. In an in vitro study by Usacheva et al.^,49 TB interacted with G− LPS significantly more than MB, which can be one of the main determining factors in the photo-oxidative effect against G− bacteria.

In vitro/ex vivo studies

Data referring to study type, microrganisms involved, and bacterial reduction, when available, are summarized in Table 1. Parameters used for PDT in each study can be found in Table 2. This section is meant to discuss some relevant topics regarding different methodologies and results.

Table 1.

Study Type, Microorganisms Studied, and Bacterial Reduction After Photodynamic Therapy in Root Canals

Reference	Study type	Microorganisms	Bact. ↓(% or log)
Seal et al. 2002	Ex vivo	S. intermedius	5log10
Bonsor et al. 2006²⁴	In vivo	Polymicrobial/naturally infected teeth	96.7
Bonsor et al. 2006²⁵	In vivo	Polymicrobial/naturally infected teeth	91
Williams et al. 2006	In vitro/ex vivo	Fusobacterium nucleatum, Peptostreptococcus micros, Prevotella intermedia, and S. intermedius	99
Silva Garcez et al. 2006	Ex vivo	Enterococcus faecalis	99.2
Soukos et al. 2006	In vitro/ex vivo	Porphyromonas gingivalis, P. intermedia, F. nucleatum, P. micros, Porphyromonas endodontalis, E. faecalis	97
George and Kishen 2007	In vitro/ex vivo	E. faecalis, Aggregatibacter actinomycetemcomitans,	100/99.77
Garcez et al. 2007	Ex vivo	Proteus mirabilis, Pseudomonas aeruginosa	98
Foschi et al. 2007	Ex vivo	E. faecalis	77.5
Fimple et al. 2008	Ex vivo	Actinomyces israelii, F. nucleatum, P. gingivalis, P. intermedia	>80
Garcez et al. 2008	In vivo	Polymicrobial/naturally infected teeth	99.9
Bergmans et al. 2008	Ex vivo	Streptococcus anginosus, E. faecalis, F. nucleatum	93.8/88.4/98.5
George and Kishen 2008	In vitro/ex vivo	E. faecalis	100
Fonseca et al. 2008	Ex vivo	E. faecalis	99.9
Lim et al. 2009	Ex vivo	E. faecalis	99.99
Pagonis et al. 2010	In vitro/ex vivo	E. faecalis	84.8
Souza et al. 2010	Ex vivo	E. faecalis	>99.48
Upadya and Kishen 2010	In vitro	E. faecalis, P. aeruginosa	100/99
Kishen et al. 2010	In vitro	E. faecalis	✪
Garcez et al. 2010	In vitro	Polymicrobial/naturally infected teeth	100
Schlafer et al. 2010	In vitro/ex vivo	Escherichia coli, Candida albicans, E. faecalis, F. nucleatum, S. intermedius	99.75
Rios et al. 2011	Ex vivo	E. faecalis	99.9
Ng et al. 2011	Ex vivo	Polymicrobial/naturally infected teeth	70
Nunes et al. 2011	Ex vivo	E. faecalis	>99.41
Garcez et al. 2013	Ex vivo	E. faecalis	99.99
Cheng et al. 2012	Ex vivo	E. faecalis	96.96
Shrestha et al. 2012	In vitro	E. faecalis	100
Shrestha and Kishen 2012	In vitro/ex vivo	E. faecalis	27–98
Silva et al. 2012	In vivo	Polymicrobial/naturally infected teeth	✪
Eldeniz et al. 2013	Ex vivo	C. albicans	✪
Stojicic et al. 2013	In vitro	E. faecalis, mixed plaque	0–100
Bago et al. 2013	Ex vivo	E. faecalis	99.99
Komine and Tsujimoto 2013	In vitro	E. faecalis	>99.0

✪ Uninformed.

Table 2.

Photodynamic Therapy Parameters Adopted per Study

Reference	PS	PS Concentration	PIT (sec)	LS	λ (nm)	ICF	RD (J or J/cm²)
Seal et al. 2002	TB	12.5, 25, 50, 100 μgmL–1	30	Laser	632.8	No	2.1–21 J
Bonsor et al. 2006²⁴	TB	✪	60	Laser	633±2	Yes	12 J
Bonsor et al. 2006²⁵	TB	✪	60	Laser	633±2	Yes	12 J
Williams et al. 2006	TB	10.0, 20.0 mg L-1	0/30/60	Laser	633±2	Yes	9.6–15.8 J
Silva Garcez et al. 2006	Azulen-based paste	✪	300	Laser	685	Yes	9 J
Soukos et al. 2006	MB	25 μg/mL	300	Laser	665	Yes	70 J
Gerge and Kishen 2007	MIX	✪	1800	Laser	664	No	36 J
Garcez et al. 2007	PEI+CE6	✪	600	Laser	660	Yes	9.6 J
Foschi et al. 2007	MB	6.25 μg/mL	300	Laser	665±2	Yes	18.96 J
Fimple et al. 2008	MB	25 μg/mL	600	Laser	665	Yes	30 J/cm²
Garcez et al. 2008	PEI+CE6	✪	120	Laser	660	Yes	9.6 J
Bergmans et al. 2008	PEI+CE6	12.7 mg mL-1	60	Laser	635	Yes	15 J
George and Kishen 2008	PF4	✪	600	Laser	664	No	31.84 J/cm²
Fonseca et al. 2008	TB	0.0125%	300	Laser	660	Yes	6.4 J
Lim et al. 2009	MIX	✪	0/1200	Laser	660	No	36 J
Pagonis et al. 2010	MB+PGLA	6.25 μg/mL	900	Laser	665	Yes	30 J/cm²
Souza et al. 2010	MB/TB	15 μg/mL	120	Laser	660	Yes	9.6 J
Upadya and Kishen 2010	MIX/PF4	✪	900	Noncoherent	660	No	2–40 J
Kishen et al. 2010	RB/MB/MB+EPI	100 μM EPI 0.49 mg mL-1	900	Noncoherent	540±15 for RB/660±15 for MB	No	2–30 J/cm²
Garcez et al. 2010	PEI+CE6	✪	120	Laser	660	Yes	9.6 J
Schlafer et al. 2010	TB	100 μg/mL	60	LED	600–660 (628 peak)	Yes	30 J
Rios et al. 2011	TB	✪	30	LED	600–660 (628 peak)	Yes	30 J
Ng et al. 2011	MB	50 μg/mL	300	Laser	665	Yes	30 J/cm²
Nunes et al. 2011	MB	0.01%	300	Laser	660	Yes	8.1–16.2 J
Garcez et al. 2013	MB	60 μM	600	Laser	660	Yes	9.6 J
Cheng et al. 2012	MB	0.01 mg/mL	0	Laser	660	Yes	12 J
Shrestha et al. 2012	CSRB	✪	900	✪	540	✪	5–60 J/cm²
Shrestha and Kishen 2012	CSnps/RB/MB	✪	900	✪	✪	✪	5 and 10 J/cm²
Silva et al. 2012	Phenothiazine chloride	10 mg/mL	60	Laser	660	Yes	3.3 J/cm²
Eldeniz et al. 2013	TB	0.1 mg/mL	60	LED	620–640 (630 peak)	Yes	30 J
Stojicic et al. 2013	MB+	15 μM/L-1	0/300	Laser	660	No	1.2/2.4/7.2 J
Bago et al. 2013	TB/phenothiazine chloride	155μg mL-1/ 10 mg mL-1	60/120	Laser	660	Yes	6 J
Komine and Tsujimoto 2013	MB	0.01%	0	Laser	660	No	53/106/159 J/cm²

PS, photosensitizer; PIT, pre-irradiation time; LS, light source; λ, wavelenght; ICF, intracal fiber; RD, radiation dose;

TB, toluidine blue; MB, methilene blue; MIX, MB in glycerol:ethanol:water (30:20:50); PEI+CE6, polyethylenimine and chlorin-e6 conjugate;

PF4, MB+perfluoro (decahydronaphthalene):H2O2:triton-X100; MB+PGLA, MB-loaded nanoparticles; RB, rose bengal;

MB+EPI, associated with efflux pump inhibitor (EPI), verapamil hydrochloride; CSRB, rose bengal-conjugated chitosan; CSnps, chitosan nanoparticles;

MB+, different associations.

✪ Uninformed.

It seems to be well established that neither the PS nor LS only are able to produce significant bacterial reduction. It is the combination of both that can activate the PDT mechanism and lead to bacterial death.^{15

–18,23,26,27,32}

LSs other than lasers (LEDs or noncoherent lights) do not affect PDT outcome. Bacterial reduction can be achieved regardless of the LS, because its wavelength is compatible with the PSs' absorption range.^{15,16,38,39,41,45} Various PS concentrations were evaluated, and phenothiazines (TB or MB) at 0.0125/0.01% seem to have more evidence available regarding their efficacy^15,23,26,48 with no statistical differences between them.³⁷

All bacterial strains tested seemed to be sensitive to PDT, at some level,^{15

–21,23

–44,46
–48} with exception of Candida albicans.⁴⁵ The substrates or tissue inhibitors appear to have an important effect on the PDT process.^15,26,27,43 Mature biofilms seem to be more challenging, and various methodologies have been investigated to improve their disrupting and inactivation.^25,35

The studies evaluating PDT alone usually found greater bacterial reduction^{14,17,18,26,28,32,34} than those comparing PDT with sodium hypochlorite (NaOCl) (3–6%), or conventional chemomechanical preparation (CMP).^16,23,35,41 Both NaOCl and CMP alone were reported to have better results.^16,23,35,41 Lower NaOCl concentrations (i.e., 0.5 and 2.5%) were less effective than PDTalone.^27,47 The combination of PDT and NaOCl or CMP, even with 2.5% NaOCl, seem to achieve the best results in bacterial reduction.^{16,19,30,35,37}

In vivo studies

Because in vivo studies are known to produce better clinical evidence, they are discussed more extensively. Four in vivo studies were performed in patients with irreversible pulpitis or apical periodontitis, for whom endodontic treatment was indicated. Microbiological samples were obtained after each step for colony-forming unit (CFU) counting.

Two studies combined PDT with conventional CMP,^24,31 and found reduction ranges from 87.7 to 91% for CMP alone, and from 96.7 to 98.5% when PDT was performed after CMP. Garcez el al.³¹ went further and performed a second session of therapies, after 1 week with calcium hydroxide (Ca[OH]₂) as an inter-appointment intracanal medication. The total first plus second reduction (99.9%) was significantly different from the first combination (p=0.00006). Results of these clinical trials suggest that PDT added to endodontic treatment may lead to an enhanced decrease of bacterial load and be an appropriate approach for the treatment of endodontic infections.

The antimicrobial effect of PDT in patients with antibiotic-resistant microflora was reported.⁴⁰ Initial samples showed that all patients had at least one microorganism resistant to antibiotics. CMP alone produced a significant reduction in numbers of microbial species, but only three teeth were bacteria free, whereas the combination of CMP with PDT eliminated all drug-resistant species.

Bonsor et al.²⁵ also compared two protocols, in which PDT was performed after coronal preparation with a chelating agent, previously to CMP with NaOCl, and after complete CMP. The authors found a greater proportion of bacteria-free teeth when PDT was performed after coronal preparation than after complete CMP. Results indicate that the use of a chelating agent acting as a cleaner and disrupter of the biofilm, associated with PDT, is an effective alternative to the use of hypochlorite as a root canal cleaning system.

A histopathological study, in which apical periodontitis was induced in dogs, was performed by Silva el al.⁴⁴ PDT-treated groups showed a moderately/severely enlarged periapical region with no inflammatory cells, moderate neoangiogenesis and fibrogenesis, and the smallest periapical lesions. Although apical closure by mineralized tissue deposition was not achieved, these findings suggest that PDT can be a promising adjunct therapy to cleaning and shaping procedures in teeth with apical periodontitis undergoing one-session endodontic treatment.

Optimizing PDT efficacy

To increase the antimicrobial activity of PDT, different PS formulations and associations and/or PDT protocols have been suggested.

The amount of singlet oxygen (¹O₂) generated from different MB concentrations was examined by Komine and Tsujimoto.⁴⁸ The largest amount of ¹O₂ was generated from 0.01% MB and was increased by laser irradiation in a dose-dependent manner. Associations of MB with 0.5% hydrogen peroxide (H₂O₂) and 0.05% chlorhexidine (CHX), 0.5% H₂O₂ and 0.05% EDTA or 0.05% EDTA and 0.05% CHX were tested by Stojicic at al.⁴⁶ With this modified PDT protocol, up to 100% of suspended E. faecalis and mixed plaque bacteria were killed. Up to 20 times more biofilm bacteria were killed by modified PDT than by conventional PDT with MB alone (p<0.001).

Formulations of MB, dissolved in a mixture of glycerol:ethanol:water (MIX)^29,35,38 and in an emulsion of perfluoro(decahydronaphthalene):H₂O₂:triton-X100 (PF4) were proposed.^33,38 According to the authors, these modified PS formulations effectively enhanced photo-oxidation and singlet oxygen generation and facilitated comprehensive inactivation of biofilm bacteria. An improved dual-staged PDT technique, utilizing MIX-based MB and/or PF4 as PS and the oxygen carrier perfluoro (decahydronaphthalene) (PF) as irradiation medium, was suggested.^29,33,35,38 This dual-staged protocol consists in removing PS excess after PIT and filling the root canal with PF, previously to irradiation, in order to achieve more thorough disinfection.

A broadly recognized component of microbial resistance to many classes of antibiotics, efflux pumps are found in both G+ and G− bacteria. Kishen et al.³⁹ investigated the role of a specific microbial efflux pump inhibitor (EPI), verapamil hydrochloride, in the MB-mediated PDT of E. faecalis biofilms. The ability to inactivate biofilm bacteria was enhanced when the EPI was associated with MB (p<0.001).

It has been pointed that the combination of PS with bioactive natural polymers such as chitosan, with inherent ability to permeate bacterial cell membrane and interact with bacterial cell biofilm structure, could further improve the anti-biofilm efficacy of PDT. A rose bengal-conjugated chitosan (CSRB) such as PS, activated by green light, was evaluated.⁴² The CSRB particles may be a synergistic multifunctional treatment approach with lower cytotoxicity and effective anti-biofilm activity as well as the ability to reinforce the dentin collagen to enhance resistance to degradation and improve mechanical properties. This may be a targeted treatment strategy to deal with infected dentin in a clinical scenario in which both disinfection and structural integrity need to be addressed concomitantly.

Recently, nanoparticles based on metals or polymers are being assessed for augmenting the endodontic disinfection methods.^36,43 The antibacterial activity of chitosan nanoparticles (CSnps) and PDT with RB and MB as PS were tested on the presence of various tissue inhibitors, such as dentin, dentin matrix, pulp tissue, bacterial LPSs, and bovine serum albumin (BSA).⁴³ The tissue inhibitors existing within the root canal affected the antibacterial activity of CSnps and PDT at varying degrees, suggesting further research to enhance their antimicrobial efficacy in an endodontic environment.

The uptake and distribution of poly(lactic-co-glycolic acid) (PLGA) nanoparticles loaded with MB by E. faecalis in suspension was investigated.³⁶ Transmission electron microscopy (TEM) showed nanoparticles concentrated mainly on the cell walls of microorganisms. To evaluate its effect in infected root canals after PDT, contents were sampled by flushing the root canals with a coronal application of 1 mL of brain–heart infusion (BHI) broth, for CFU counting. Survival fractions were 15.2%, and the authors suggest that the PDT effects were probably affected by the presence of serum proteins in BHI broth.

Although the great majority of studies retrieved for this review mention the use of an ICF (Table 2), its necessity was a specific subject of two studies.^20,21 Both studies used extracted single-rooted teeth contaminated with E. faecalis, MB, as PS and similar radiation doses. In the study performed by Nunes et al.,²⁰ all teeth had the crown removed and they achieved bacterial reduction from 99.41 to 99.65% without or with ICF respectively, suggesting that PDT was effective regardless of the use of an ICF. Garcez et al.²¹ used teeth with and without the crown. All teeth with crowns previously removed showed a reduction of two logs (99%). Teeth whose crowns were kept, showed a reduction of one log (85% and 97%, depending upon the size of the laser tip) and four logs (99.99%) when an ICF was used. These results suggest that, in clinical conditions, when teeth have crowns, the use of the ICF is better than when the laser light is placed on the pulp chamber.

Ng et al.¹⁹ suggested future studies exploring the use of ultrasonic waves for enhancement of the transdentinal movement and penetration of MB in canal biofilms. It has been already pointed that high-intensity focused ultrasound produces collapsing cavitation bubbles that can deliver antibacterial nanoparticles into the dentinal tubules, improving root canal disinfection.⁵⁰ This may be a good way to enhance PDT effects, and should be investigated in future experiments.

Conclusions

Studies conducted in recent years highlighted the antibacterial potential of PDT, although most of these studies were not able to confirm significantly improved disinfection when compared with conventional chemomechanical preparation with NaOCl. Planktonic bacteria are considerably more sensitive to PDT than bacteria in biofilms. Different PSs, different irradiation doses, and light sources with different wavelengths and power were used. Hence, it is almost impossible to reach a consensus about a protocol to be clinically recommended. Considering the literature reviewed, most recommended PIT is 1–5 min, and phenothiazines and their associations/modifications are the most tested PSs. Low-level lasers emitting red light (600–660 nm) appear as the most used light source, but LEDs or noncoherent lights can also be used. Irradiation dose can vary from 1.2 to 159 J, and the use of an intracanal fiber may increase uniformity of light distribution along the root canal, improving PDT efficiency. Further studies for adjustments in PDT protocol or PS formulation, in order to optimize PDT outcome, as well as more in vivo studies, are suggested.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

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