Clinico-microbiological Efficacy of Indocyanine Green as a Novel Photosensitizer for Photodynamic Therapy among Patients with Chronic Periodontitis: A Split-mouth Randomized Controlled Clinical Trial.

OBJECTIVE: Conventional nonsurgical periodontal therapy, i.e., scaling and root planing (SRP), is not sufficient to completely eradicate the microorganisms present in dental plaque biofilm due to the incapability of instruments to reach the inaccessible areas of a tooth with anatomical variations. Hence, to increase the effectiveness of SRP, many adjunctive treatment strategies are proposed, including photodynamic therapy (PDT). Therefore, the purpose of this study was to determine the clinical and microbiological efficacy of PDT using Indocyanine green (ICG) as a novel photosensitizer for the treatment of chronic periodontitis.
MATERIALS AND METHODS: Twenty individuals who fulfilled the eligibility criteria were enrolled for this randomized controlled clinical trial using split-mouth design. Treatment sites from each individual were randomly allocated into two groups: SRP was done for the sites of the control group and an additional session of PDT using ICG was performed for the sites of the test group. Subgingival plaque samples were collected from both the sites and sent for quantitative analysis of Treponema denticola, Porphyromonas gingivalis, and Tannerella forsythia using real-time polymerase chain reaction (RT-PCR) technique. Probing pocket depth (PD), clinical attachment loss (CAL), and count of all the three microorganisms were assessed at baseline and after 3 months.
RESULTS: After 3 months, PD and CAL showed statistically significant improvement in the test sites (P < 0.001) compared to the control sites. However, the differences in the microbiological parameters were statistically nonsignificant between the groups.
CONCLUSION: ICG as a photosensitizer may enhance the outcomes of SRP and can be used for PDT for the nonsurgical management of periodontal diseases. Copyright:

INTRODUCTION

Chronic periodontitis (CP) is a highly prevalent inflammatory disease of the tooth-supporting tissues. Dysbiotic microbial complex is the primary etiological factor for it. The cardinal signs of chronic periodontitis is the presence of periodontal pocket and clinical attachment loss.[1] Treponema denticola, Porphyromonas gingivalis, and Tannerella forsythia, the three anaerobic bacteria combinedly called 'red complex', are considered to be the primary etiological factor for CP.[2] The conventional nonsurgical treatment of periodontal diseases consists of reducing pathogenic microbiota through scaling and root planing (SRP). SRP performed with hand instruments, and even with the use of ultrasonic devices, can produce substantial clinical improvements in majority of the cases.[3] Although SRP is considered as the gold standard, the factors such as presence of deep periodontal pockets, the involvement of furcation areas, presence of anatomical variations, and tissue-invading ability of some bacteria decrease the effectiveness of nonsurgical periodontal therapy. Thus, the complete removal of bacterial deposits is hardly performed, and the bacterial reservoirs can survive in those inaccessible areas, cause the microbial activity to continue, and lead to the progression of the disease activity.[4] Several adjunctive modes such as the local or systemic use of antimicrobial agents, in conjunction with mechanical debridement, are well-established approaches to decrease the bacterial loads and improve the outcomes of periodontal therapy. However, severe drawbacks such as the development of antibiotic resistance and incapability of a particular antimicrobial agent against the polymicrobial nature of the oral biofilm motivate us to seek for a novel therapy, with lesser adverse effects.[5]

Photodynamic therapy (PDT) is a noninvasive method for infection control. The phenomenon of PDT requires three constituents, i.e., a photosensitizer, a light source, and oxygen. The photosensitizer molecule binds to the target cells and gets activated by light of an appropriate wavelength, following which singlet oxygen molecules and other reactive agents are produced that effectively kill the bacterial cells.[6] Although the technique of PDT was started as a treatment modality for cancer, its application in the field of periodontics is gaining much attention, recently. Effective removal of potent periodontopathogens was reported in several randomized controlled trials.[6] Toluidine blue, methylene blue, phthalocyanine, and hematoporphyrin are commonly used well-established photosensitizers for PDT.[6] Indocyanine green (ICG) is a novel photosensitizer. ICG, a tricarbocyanine by chemical nature, approved by the United States Food and Drug Administration (USFDA), is widely used in medicine, especially for cardiovascular use. Low toxicity, rapid systemic elimination, and the peak of absorption in the wavelength of the near-infrared spectrum which is close to the emission of commonly used diode laser are a few of the properties which make it a safe and good photosensitizer.[7] A recent review concluded that ICG possesses bactericidal properties against periodontopathogens and can be used for nonsurgical periodontal therapy.[8] Few recent clinical studies too had successfully proved its beneficial effects when periodontal treatment was considered.[91011] The bactericidal ability of ICG against antibiotic-resistant bacterial strains was also shown in a study.[12] However, currently, there is limited literature available to determine the clinical and microbiological benefits of ICG as a photosensitizer for PDT in patients with CP. Therefore, this study was designed to evaluate the clinico-microbiological efficacy of ICG-mediated PDT as an adjunct to nonsurgical periodontal therapy. Moreover, our study was also a first of its kind to determine the microbiological improvements by the real-time polymerase chain reaction (RT-PCR) technique which assessed a real-time viable count of the periodontopathogens.

MATERIALS AND METHODS

Study design and subject selection

Twenty individuals were selected from the Department of Periodontology, College of Dental Sciences, Davangere, India. The protocol for this split-mouth, randomized controlled clinical trial was reviewed and approved by Rajiv Gandhi University of Health Sciences, Bangalore, as well as the Institutional Ethical Committee (IEC No. ACA/DCD/SYN/CODS-DVG/14–15). The study period was from January 2015 to January 2017. After obtaining written informed consent, individuals who fulfilled the eligibility criteria were enrolled for the study.

Study participants were diagnosed with chronic generalized periodontitis, as defined by the American Association of Periodontology.[13] Individuals aged between 35 and 55 years, having a minimum of 20 teeth present in the oral cavity, and with more than 50% of teeth involved with the pocket formation and radiographic alveolar bone loss were considered. At least two or more sites with the probing pocket depth (PD) of ≥6 mm and clinical attachment loss (CAL) of ≥4 mm in two contralateral quadrants of the mouth were included in the study. The exclusion criteria were patients with a history of systemic antibiotic usage in the previous 6 months, any systemic disorder, extensive prosthetic involvement, history of anti inflammatory medications for long term, history of allergy to any kind of medication, smoking, and pregnancy. Besides, teeth having extensive caries or gingival morphological alterations or where cementoenamel junction was difficult to determine were excluded too, as they could impair the outcome of the study. For the eligible individuals, sites were randomly allocated for the treatment, as shown in Figure 1.

Figure 1

CONSORT flow diagram

Treatment protocol

All clinical examinations were done by the same examiner. For the clinical and microbiological evaluations, in each individual, two sites presenting PD ≥6 mm and CAL ≥4 mm in two contralateral quadrants were selected. The selected sites from each individual were then randomly subjected to the treatment. First, the individuals received full-mouth supragingival scaling (EMS Piezon ultrasonic system, EMS Electro Medical Systems, Switzerland) and proper home-care instructions. One week later, on the baseline day, individuals were recalled to undergo the treatment proposed for the study. Clinical measurements were recorded, and subgingival plaque samples were collected. Each individual was then treated with two treatment protocols: the test sites were treated with SRP + ICG-PDT and contralateral control sites were subjected to SRP only. The SRP was performed using both hand instruments and ultrasonic devices.

Preparation and application of photosensitizer dye

ICG tablet (PERIOGREEN tablet, Elexxion AG, Germany) suspended in distilled water at a concentration of 1 mg/ml was prepared to be used as a photosensitizer dye.[7] Immediately, after SRP, in the test sites, the freshly prepared photosensitizer dye was applied with a blunt side-release cannula. It was placed drop by drop in the bottom of the periodontal pockets until it overflows and leftover for 2 min for proper tissue exposure.[7] Then, the excess agent was removed by flushing with sterile water.

Application of laser

The soft-tissue diode laser unit (Picasso Diode laser, AMD Lasers, Indianapolis, United States) having a power setting of 300 mW and a wavelength of 810 nm was used subgingivally. Each site was irradiated for 30 seconds using an optical fiber tip of 400μ in diameter in a noncontact mode and a continuous manner.[7] Within the next 3 days, the subgingival scaling of the entire oral cavity was completed. Individuals received professional oral hygiene instructions following the treatment. They were again evaluated after 3 months.

Clinical monitoring

All the clinical parameters were recorded at the baseline and 3 months after the treatment. With the help of a calibrated periodontal probe (UNC-15 graduated periodontal probe, Hu-Friedy, Chicago, United States), PD and CAL were measured.

Microbiological monitoring

In each individual, from both the test and control sites, the subgingival plaque samples were collected at baseline and after 3 months of the treatment. The supragingival plaque was removed with a scaler. Then, subgingival plaque samples were collected with a sterile curette (Gracey curette #5/6, Hu-Friedy, Chicago, USA)[14] and immediately transferred to a sterile vial containing thioglycolate broth as a transport media. Counting of all three key periodontopathogens, i.e., T. denticola, P. gingivalis, and T. forsythia, was performed in each sample using the RT-PCR technique.[15]

Outcome variables

The primary outcome variables of the study were the changes in the mean PD and CAL at 3 months post-treatment, and the quantitative analyses of the three periodontopathogens were the secondary outcome variables.

Statistical analysis

R software version 3.4.2 was used to analyze the data. Both descriptive and inferential statistics were used in the present study. Microbiological data were presented as median counts in the logarithmic value of individual bacterium present, as determined by the RT-PCR technique. Independent Student's t-test and Mann–Whitney U-test were used to analyze the clinical and microbiological parameters, respectively. P < 0.05 was considered as statistically significant.

RESULTS

All individuals completed the study period. Demographic data revealed the number of females and males to be 14 and 6, respectively, and the mean age of the individuals was 38.2 ± 9.8 years (mean ± standard deviation). Uneventful postoperative healing was observed in all the individuals, and any kind of adverse effect to the photosensitizer or the laser irradiation was not reported by any of the individuals.

Baseline data from all the clinical parameters were comparable in both the groups. Sites additionally treated with ICG-mediated PDT presented a statistically significant reduction in PD and CAL when compared to sites treated with only SRP after 3 months of treatment [Table 1]. Microbial profile was profoundly affected by both the treatment protocols, and more reduction in the bacterial count was observed in the sites received an additional session of ICG-PDT. However, this difference failed to meet the level to be statistically significant [Table 2].

Table 1

Clinical outcomes of scaling and root planing and scaling and root planing + indocyanine green-mediated photodynamic therapy

Clinical parameters	Control site (SRP)		Test site (SRP+ICG-PDT)		P
	n	Mean±SD	n	Mean±SD
PD (millimeter)
Baseline	20	6.4±0.75	20	6.5±0.61	0.647
3 months	20	4.8±0.77	20	3.7±0.86	<0.001
CAL (millimeter)
Baseline	20	4.5±0.76	20	4.6±0.67	0.661
3 months	20	2.9±0.79	20	1.8±0.88	<0.001

SRP: Scaling and root planning, ICG: Indocyanine green, PDT: Photodynamic therapy, PD: Probing pocket depth, CAL: Clinical attachment loss, SD: Standard deviation

Table 2

Microbiological outcomes of scaling and root planning and scaling and root planning + indocyanine green-mediated photodynamic therapy

Microbiological outcome (log value)	Group								P
	Control site (SRP)				Test site (SRP+ICG-PDT)
	n	Minimum	Maximum	Median	n	Minimum	Maximum	Median
Treponema denticola
Baseline	20	0.0	6.76	4.52	20	0.0	6.76	4.31	0.859
3 months	20	0.0	4.71	0.00	20	0.0	4.58	0.00	0.183
Porphyromonas gingivalis
Baseline	20	4.6	6.81	6.43	20	0.0	6.78	5.79	0.310
3 months	20	0.0	4.71	4.53	20	0.0	4.72	3.72	0.096
Tannerella forsythia
Baseline	20	0.0	4.53	0.00	20	0.0	5.41	3.4	0.094
3 months	20	0.0	3.49	0.00	20	0.0	4.46	0.00	0.671

SRP: Scaling and root planning, ICG: Indocyanine green, PDT: Photodynamic therapy

DISCUSSION

This randomized controlled clinical trial using the split-mouth design was conducted to evaluate, both clinically and microbiologically, the efficacy of PDT, using ICG as a photosensitizer, when delivered as an adjunct to SRP, in patients diagnosed with CP.

SRP is considered as gold standard for the nonsurgical management of periodontal diseases, and additional benefits can be achieved by various adjunctive treatment procedures.[16] However, the limited access of the instruments to all the areas of plaque accumulation and the development of antibiotic resistance while using antimicrobials create a need to search for alternative approaches to improve the efficacy of mechanical debridement.[17] In PDT, singlet oxygen molecules are produced. These molecules directly act on the bacterial cells. The polysaccharides present in the extracellular matrix of dental plaque biofilm are also susceptible to photodamage. Such dual activity is shown by PDT, thus making it more advantageous over other adjunctive treatments.[17] Moreover, PDT is found to be equally effective against both antibiotic-resistant and antibiotic-susceptible microorganisms, and the production of antibiotic-resistant strains was also not seen even after repeated photosensitization.[1218]

In this study, we used a split-mouth design. The power of the study gets increased in this type of study design. Furthermore, the interindividual variabilities are virtually eliminated when the patient serves as his/her own control.[19] Besides, the possibility of crossover effect usually associated with the split-mouth design was eliminated here since the photosensitizer alone could not produce any antimicrobial effect, and only the test sites were exposed to laser irradiation.[16] Here, we used a novel photosensitizer, ICG, which is USFDA approved for use in cardiovascular diseases. Its excitation peak coincides with the wavelength of 810 nm which is commonly used for soft-tissue procedures.[7] Studies have suggested that the wavelength spectrum of 800–810 nm has around 6 mm of penetrating capability to the tissue, which is much more than the capacity of the rest of the spectrum.[7] ICG also has low toxicity, rapid systemic elimination, and can be considered as a good photosensitizer.[7] ICG appears to be a promising agent, and since it has not been characterized before for its efficacy against periodontopathogens by their real-time count, our exclusive study aimed to determine that.

In our study, significant improvement in probing PD and clinical attachment loss was observed from baseline to the final examination in sites of both the treatment groups. A reduction in PD and a gain in attachment level signify the resolution of inflammation, thereby arresting progressive periodontal breakdown. However, the greater clinical improvement was seen for the sites treated with SRP + ICG-PDT, and this difference was statistically significant. The result of our study is in accordance with recent studies where the efficacy of adjunctive photodisinfection was evaluated.[3202122]

Microbiological analysis showed a reduction in all the microorganisms tested, i.e., T. denticola, P. gingivalis, and T. forsythia, in sites of both the treatment groups at 3 months post-treatment, and a higher reduction was observed in the patients additionally treated with a single session of ICG-PDT along with SRP. Yet, this difference could not meet the level of statistical significance. Translocation of the periodontopathogens might have played a major role to produce such microbiological outcomes seen here.[23] However, this microbial reduction, in turn, contributed to the clinical improvements observed in our study, thereby ultimately achieved the goal of any periodontal therapy. However, contradictory results are also reported in a few studies.[2425] There is currently limited literature available to confirm the efficacy of adjunctive use of PDT to SRP since the results are not consistent. Most of the studies had significant heterogeneity in treatment protocols. The type and concentration of photosensitizer used, type of laser, their wavelengths, maximum power used, irradiation time and frequency of application, and even the follow-up duration had variations among the studies causing the results to be inconsistent.[26] This is justified by the lack of a protocol considered as ideal for the use of PDT in periodontal practice.[26] Among all the variables in the treatment protocol, the type of photosensitizer used in PDT may contribute to a great extent to the inconsistent result found in our study. Methylene blue, toluidine blue, and phenothiazines are some of the well-known photosensitizers and have been already demonstrated to have antibacterial property against periodontopathogens. ICG is a novel photosensitizer. Although a few in vitro studies successfully showed the efficacy of ICG on planktonic bacteria, there is no clinico microbiological study evaluating the real time bacterial count using PCR technique has been conducted. In that case, our study was an exclusive one and it showed significant benefits. Nevertheless, the facts such as patients' clinical benefits, lesser adverse effects compared to the other drugs, cost-effectiveness, patients' acceptability and satisfaction, ease of application, time needed for the therapy, improved patients' quality of life factors such as retention and function of teeth, and reduction of the related symptoms made our study clinically relevant and meaningful.[27]

CONCLUSION

Based on the findings reported in our study, it can be concluded that adjunctive PDT using ICG as a photosensitizer can be advocated as a treatment option in patients diagnosed with CP.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.