**5. Discussion**

One of the main reasons of implant failure is peri-implantitis. The prevalence rates of peri-implantitis differs among different studies and this is due to the different reporting methods and characteristics [62–64]. Van Velzen et al. [65] in their 10 years prospective cohort study reported a prevalence of 7%. Meijer et al. [66] reported that after 10 years 29.7% of patients were affected by peri-implantitis. Fardal et al. [67] report a rate of 53.5% at the patient level and 31.1% at the implant level, which is much higher than the data from other studies.

The treatment of peri-implantitis is complex and it often includes combination of conventional therapy with the addition of antimicrobials. However, use of antimicrobials does not have a long term effects and it can lead to antimicrobial resistance and development of superinfections [68]. Therefore, alternative antimicrobial approaches for achieving implant disinfection have been sought.

Photodynamic therapy is a promising alternative when treating periodontal diseases and peri- implant diseases. Up to date there have been many *in vitro* [69–71] and clinical studies [60, 61] evaluating the effect of photodynamic therapy in treating peri-implantitis.

Regarding the *in vitro* evaluation, the present study aimed to evaluate the efficacy of photodynamic therapy on dental implants contaminated under *in vitro* conditions. The implants were contaminated in order to try to recreate the adhesion stage of biofilm formation on the implant surface. Many *in vitro* studies have used similar methodology to achieve titanium implant contamination [62, 63, 71].

The main focus of our study was to evaluate if photodynamic therapy is efficient in eradicating the bacteria from the implant surface when compared to the negative control group (NC) and to the conventional treatment with chlorhexidine solution (PC). Furthermore, the focus was to evaluate different types of devices and with different parameters and photosensitizers and the reaction of different bacteria to aPDT.

The results from our study showed that PDT1 and PDT2 groups were more eliminated 98.3% and 97.8% of the total number of bacteria when compared to NC group. These groups were the most effective among the study groups. Both PDT1 and PDT2 groups were a combination of a diode laser with a wavelength of 660 nm and a photosensitizer.

The results of this study are similar to other *in vitro*, *in vivo* and clinical studies [64, 71, 72]. Marotti et al. [71] in their study demonstrated that aPDT is effective against the

**167**

*Evaluation of the Antimicrobial Efficacy of Different Types of Photodynamic Therapy…*

effective against this bacteria when compared to the other groups.

surfaces has not been evaluated in other studies up to date.

the adhesion of bacteria after coating the surfaces with saliva pellicle.

PDT1, PDT2 and PDT3 in addition to the significant difference compared to NC, they also had significant difference from the TB group. The results of the

bacteria present in peri-implantitis. The irradiation time did not influence the results. Similar results were obtained from both the groups (3 minute and 5 minutes irradiation time) and there was no significant difference between them. The effect of aPDT did not differ significantly from the disinfection with 0.12% chlorhexidine solution. Our results were similar to this study and even though we used a higher concentration of chlorhexidine (0.2%), both PDT1 and PDT2 had no significant difference when compared to PC. In a study done by Haas et al. [64] it was demonstrated that 60 seconds of light exposure in combination with photosensitizer can effectively eradicate *A. actinomycetemcomitans, P. gingivalis* and *P. intermedia*. One of the goals of the present study was to evaluate aPDT against each bacteria separately. The results obtained for *A. actinomycetemcomitans* and *P. gingivalis* were similar to the results obtained for the total bacterial count. Both PDT1 and PDT2 had significant difference when compared to the NC. However, the results of *P. intermedia* showed that PDT2 was more

The least effective treatment group was PDT3 without statistically significant difference compared to NC or PC groups regarding the total bacterial count. It must be noted that for the PDT3 group we used a modified dental LED light and not a diode laser. This was done to evaluate and compare the LED light against diode

The efficacy of LED lights as a light source in photodynamic therapy has been tested in many studies however, only a few studies have tested its efficacy on titanium implant surfaces. The results from these studies are conflicting since the study design and light source parameters differ greatly. In a study conducted by Cho et al. [73] the efficacy of a green LED light was tested. The LED light was combined with erythrosine dye and was evaluated against *A. actinomycetemcomitans*. Their results showed that this combination is effective and reduces the bacteria attached titanium surfaces up to 92.4%. The irradiation time in this study was 60 seconds and the treatment was done on only one surface of titanium discs. This provides uniform distribution of the light source. In contrast, in the present study we applied the light source in a rotating motion in order to emulate clinical application of aPDT around a contaminated implant. This might be the reason why our results showed differ with the aforementioned study [73]. In contrast to the *in vitro* study by Cho et al. [73], in a clinical study done by De Angelis et al. [74] the use of LED light showed no significant difference after 4 months of follow up when compared to mechanical debridement and scaling. In our study we evaluated the efficacy of aPDT on two types of implants: titanium and zirconia dental implants. The efficacy of aPDT on zirconia implant

The results obtained from our study showed that each test group was very effective in eliminating the bacteria from the zirconia surface and all had significantly lower bacterial count when compared to NC. However, in between the groups there was no significant difference. The higher efficacy of aPDT against zirconia surfaces when compared to titanium surfaces might be due to the surface properties of zirconia which might lead to a lower affinity of the bacteria to be attached to zirconia surfaces. Zirconia surfaces are smoother, have a lower surface roughness and lower surface free energy [75, 76]. In a study done by Scarano et al. [75] titanium and zirconia oxide discs were placed in the mouths of patients in order to evaluate in which surface the bacteria adhere less. After 24 h it was shown that there were significantly less bacteria on the zirconium oxide surfaces. Al-Radha et al. [76] showed similar results. In their study titanium blasted with zirconia and the zirconia material showed better results when compared to the titanium surface regarding

*DOI: http://dx.doi.org/10.5772/intechopen.94268*

lasers as a light source.

#### *Evaluation of the Antimicrobial Efficacy of Different Types of Photodynamic Therapy… DOI: http://dx.doi.org/10.5772/intechopen.94268*

bacteria present in peri-implantitis. The irradiation time did not influence the results. Similar results were obtained from both the groups (3 minute and 5 minutes irradiation time) and there was no significant difference between them. The effect of aPDT did not differ significantly from the disinfection with 0.12% chlorhexidine solution. Our results were similar to this study and even though we used a higher concentration of chlorhexidine (0.2%), both PDT1 and PDT2 had no significant difference when compared to PC.

In a study done by Haas et al. [64] it was demonstrated that 60 seconds of light exposure in combination with photosensitizer can effectively eradicate *A. actinomycetemcomitans, P. gingivalis* and *P. intermedia*. One of the goals of the present study was to evaluate aPDT against each bacteria separately. The results obtained for *A. actinomycetemcomitans* and *P. gingivalis* were similar to the results obtained for the total bacterial count. Both PDT1 and PDT2 had significant difference when compared to the NC. However, the results of *P. intermedia* showed that PDT2 was more effective against this bacteria when compared to the other groups.

The least effective treatment group was PDT3 without statistically significant difference compared to NC or PC groups regarding the total bacterial count. It must be noted that for the PDT3 group we used a modified dental LED light and not a diode laser. This was done to evaluate and compare the LED light against diode lasers as a light source.

The efficacy of LED lights as a light source in photodynamic therapy has been tested in many studies however, only a few studies have tested its efficacy on titanium implant surfaces. The results from these studies are conflicting since the study design and light source parameters differ greatly. In a study conducted by Cho et al. [73] the efficacy of a green LED light was tested. The LED light was combined with erythrosine dye and was evaluated against *A. actinomycetemcomitans*. Their results showed that this combination is effective and reduces the bacteria attached titanium surfaces up to 92.4%. The irradiation time in this study was 60 seconds and the treatment was done on only one surface of titanium discs. This provides uniform distribution of the light source. In contrast, in the present study we applied the light source in a rotating motion in order to emulate clinical application of aPDT around a contaminated implant. This might be the reason why our results showed differ with the aforementioned study [73].

In contrast to the *in vitro* study by Cho et al. [73], in a clinical study done by De Angelis et al. [74] the use of LED light showed no significant difference after 4 months of follow up when compared to mechanical debridement and scaling.

In our study we evaluated the efficacy of aPDT on two types of implants: titanium and zirconia dental implants. The efficacy of aPDT on zirconia implant surfaces has not been evaluated in other studies up to date.

The results obtained from our study showed that each test group was very effective in eliminating the bacteria from the zirconia surface and all had significantly lower bacterial count when compared to NC. However, in between the groups there was no significant difference. The higher efficacy of aPDT against zirconia surfaces when compared to titanium surfaces might be due to the surface properties of zirconia which might lead to a lower affinity of the bacteria to be attached to zirconia surfaces. Zirconia surfaces are smoother, have a lower surface roughness and lower surface free energy [75, 76]. In a study done by Scarano et al. [75] titanium and zirconia oxide discs were placed in the mouths of patients in order to evaluate in which surface the bacteria adhere less. After 24 h it was shown that there were significantly less bacteria on the zirconium oxide surfaces. Al-Radha et al. [76] showed similar results. In their study titanium blasted with zirconia and the zirconia material showed better results when compared to the titanium surface regarding the adhesion of bacteria after coating the surfaces with saliva pellicle.

PDT1, PDT2 and PDT3 in addition to the significant difference compared to NC, they also had significant difference from the TB group. The results of the

*Photodynamic Therapy - From Basic Science to Clinical Research*

One of the main reasons of implant failure is peri-implantitis. The prevalence

The treatment of peri-implantitis is complex and it often includes combination of conventional therapy with the addition of antimicrobials. However, use of antimicrobials does not have a long term effects and it can lead to antimicrobial resistance and development of superinfections [68]. Therefore, alternative antimi-

Photodynamic therapy is a promising alternative when treating periodontal diseases and peri- implant diseases. Up to date there have been many *in vitro* [69–71] and clinical studies [60, 61] evaluating the effect of photodynamic therapy

Regarding the *in vitro* evaluation, the present study aimed to evaluate the efficacy of photodynamic therapy on dental implants contaminated under *in vitro* conditions. The implants were contaminated in order to try to recreate the adhesion stage of biofilm formation on the implant surface. Many *in vitro* studies have used similar methodology to achieve titanium implant contamination [62, 63, 71].

The main focus of our study was to evaluate if photodynamic therapy is efficient in eradicating the bacteria from the implant surface when compared to the negative control group (NC) and to the conventional treatment with chlorhexidine solution (PC). Furthermore, the focus was to evaluate different types of devices and with different parameters and photosensitizers and the reaction of different bacteria to aPDT. The results from our study showed that PDT1 and PDT2 groups were more eliminated 98.3% and 97.8% of the total number of bacteria when compared to NC group. These groups were the most effective among the study groups. Both PDT1 and PDT2 groups were a combination of a diode laser with a wavelength of 660 nm

The results of this study are similar to other *in vitro*, *in vivo* and clinical studies [64, 71, 72]. Marotti et al. [71] in their study demonstrated that aPDT is effective against the

crobial approaches for achieving implant disinfection have been sought.

rates of peri-implantitis differs among different studies and this is due to the different reporting methods and characteristics [62–64]. Van Velzen et al. [65] in their 10 years prospective cohort study reported a prevalence of 7%. Meijer et al. [66] reported that after 10 years 29.7% of patients were affected by peri-implantitis. Fardal et al. [67] report a rate of 53.5% at the patient level and 31.1% at the implant

level, which is much higher than the data from other studies.

**166**

**5. Discussion**

*Application of the light source.*

**Figure 17.**

in treating peri-implantitis.

and a photosensitizer.

PDT3 group for the zirconia dental implants were comparable to PDT1 and PDT2. This can suggest that LED light with additional improvements in light distribution and parameters can have an antimicrobial effect. As mentioned before there are conflicting results regarding the antimicrobial effect of using LED. Several studies reported beneficial results following use of LED lights, as a light source [77, 78]. On the other hand, several studies reported insignificant improvement in the treatment outcomes using LED light for PDT [74]. However, it is difficult to compare the results of present study with the previous ones, mainly due to the differences in the study protocols and lack of studies conducted on zirconia implant surfaces.

The use of diode lasers in many studies has been shown to be safe in regard to the implant surface, compared to Nd:YAG, Er:YAG, CO2 and Ho:YAG lasers, which can damage the implant surfaces [57]. Castro et al. [79] concluded that 980 nm diode laser irradiation does not damage titanium implant surfaces and seems to be safe irrespective of power output used.

In the present research, no structural changes on the implant surfaces following therapy was observed. PDT1, PDT2 and PDT3, did not cause visible damage on titanium or zirconia implant surface at a magnification of 1:250.

Regarding the clinical use of PDT, several studies reported conflicting results. Many studies demonstrated improvement in clinical outcomes of patients with peri-implantitis when aPDT was combined with mechanical debridement [60, 80, 81]. Romeo et al. [82] suggested that PDT is a useful adjunct therapy but it could not replace the mechanical and surgical treatment of peri-implantitis. Similarly other studies suggest that the PDT improves the outcomes of peri-implantitis [60, 83, 84].

On the other hand, there are several studies that report no added benefit from using PDT when compared to conventional treatment modalities for peri-implantitis [85, 86].

The results of this *in vitro* study should be considered preliminary, since it cannot be generalized to *in vivo* and clinical conditions. The biggest concern related to future *in vivo* and clinical applications is stability of achieved *in vitro* results (short term beneficial effects in reducing the number of periopathogens). Also, the presence of plaque formation on implants, degree of salivation and host-immune response is very important.
