Adjunctive Antimicrobials in Nonsurgical Periodontitis Treatment: A Review of Recent Trials and Indications

Systemic Antibiotics in the Treatment of Periodontitis

The paradigm has shifted from attributing periodontitis to specific putative microbiological pathogens to an understanding that it is likely caused by a change from commensal flora to opportunistic pathogenic bacteria [42, 43]. Using antibiotics can reduce the bacterial load following NSPT and eliminate periodontal pathogens, which can stay hidden within the periodontal tissues [10, 44]. Teughels W, et al. [10] concluded after a systematic review on antibiotics and periodontitis treatment that the evidence supported a small but statistically significant improvements in PD (a weighted mean difference of 0.485 mm), CAL (a weighted mean difference of 0.285 mm), and BOP as well as a decreased number of residual pockets [10]. The use of amoxicillin and metronidazole was the most investigated systemic antibiotic treatment and presented the most adverse events. These results support the most recent clinical periodontitis treatment guidelines, which recommends considering systemic antibiotics only when treating severe periodontitis in young adults and recommends against their routine use [1]. This is important, especially since unnecessary antibiotics and their excessive use in both humans and animals are involved in the rise of antimicrobial resistance worldwide [12].

Cosgarea R, et al. [13] found that periodontal pathogens were still reduced in number at six months, and Porphyromonas gingivalis was still reduced a year after the administration of a 7-day regimen of amoxicillin and metronidazole [13]. Cosgarea R, et al. [14] also tested a 3-day course of an antibiotic combination for treating patients with at least Stage III Grade C periodontitis, a fast progressing and advanced disease [14]. The authors found that the 3-day course and the standard 7-day prescription were nearly identical in reducing residual pockets (6 mm or greater) after six months of follow-up. Both treatments led to improvements in clinical parameters, microbiological analysis and inflammatory markers measured in the gingival crevicular fluid (GCF). Five times as many adverse events were observed in the full 7-day course compared to the 3-day course of amoxicillin/metronidazole. Cruz D, et al. [15] recalled patients who had been treated five years prior with subgingival instrumentation and a combination of metronidazole and amoxicillin [15]. They found that without supportive therapy, clinical gains were mostly lost after five years for both the treatment and the control groups. Hagenfeld D, [17] used 16s rRNA sequencing to explore subgingival microbiota diversity and used the subgingival microbial dysbiosis index (SMDI) to evaluate the effects of adjunctive amoxicillin and metronidazole in severe periodontitis patients (periodontitis stage III-IV) [17]. Significant reductions in periodontal pathogens were seen up to 26 months after treatment. Faveri M, et al. [16] treated young patients with severe periodontitis and reported both clinical and microbiological data over one year of follow- up [16]. After 14 days of amoxicillin and metronidazole treatment, patients who had taken the antibiotics presented significantly greater decreases in red complex bacterial proportions, greater proportions of health-associated Actinomyces, and a greater chance of reaching endpoints of therapy. Red complex bacteria consist of Treponema denticola, Tannerella forsythia and P. gingivalis, which were increased in the subgingival samples of the patients affected by periodontitis [45, 46, 47, 48]. In addition, Aggregatibacter actinomycetemcomitans is a bacterial species specifically associated with juvenile periodontitis [49]. A specific serotype was identified as the exogenous pathogen causing periodontal breakdown. The authors then concluded that using antibiotics was justifiable in cases presenting a A. actinomycetemcomitans serotype b infection.

Araujo C, et al. [18] tested 500 mg of clarithromycin bid for seven days against the more widely used amoxicillin/ metronidazole combination [18]. Patients affected by rapidly progressing severe disease responded similarly to both antibiotic regimens. Azithromycin regimens were used for 3–5 days, with minimal-to-no clinical differences reported by the two publications included in this review [20, 21]. Morales et al. also included a probiotic treatment based on Lactobacillus rhamnosus SP1 consumption once daily for three months as an adjunct to subgingival debridement, which showed no difference compared to the control or adjunctive azithromycin group [21]. Although Cuk K, et al. [19] and colleagues found no difference in periodontal clinical parameters after using systemic azithromycin for 3 days as an adjunctive to subgingival instrumentation, they found that A. actinomycetemcomitans and Campylobacter rectus were more commonly absent in the test group [19]. The same publication reported greater decreases in A. actinomycetemcomitans, C. rectus and P. gingivalis in the adjunctive azithromycin group.

Local Delivery and Other Agents

Systemic antibiotic courses have been linked to more adverse events for patients, and their use is contributing to a community-wide rise in antibiotic resistance [1, 12]. Local delivery has the advantage of reducing adverse events, improving compliance and decreasing chances of bacteria developing resistance [50]. As an example of the low potential for increasing resistance, an investigation into locally delivered doxycycline showed a temporary increase in the proportion of resistant bacteria in the subgingival microflora, which was not present after three months or six months of follow-up [51]. Most importantly, the resistant bacteria had been identified at baseline. A recent systematic review and meta-analysis showed that, overall, local antimicrobial delivery resulted in a statistically significant decrease in mean PD of 0.365 mm and a mean CAL gain of 0.263 mm, while no increase in adverse events was found compared to the control [9]. The small difference seen, which may not be clinically meaningful, paired with the high heterogeneity between studies led to the recommendation that providers may use locally delivered antiseptics and antibiotics as adjuncts to subgingival instrumentation [1]. Most locally delivered antimicrobials studied were antibiotics, with the notable exception of chlorhexidine [9]. More specifically, previously investigated agents made commercially available included tetracycline, minocycline, doxycycline, chlorhexidine, metronidazole and piperacillin/ sodium tazobactam in combination. The articles published in the last five years included in this review investigated different locally delivered agents; these agents included antibiotics, ozonated water, tea tree oil and melatonin.

Teles FRF, et al. [25] treated residual pockets of patients with subgingival instrumentation and minocycline microspheres, finding that there was no clinical difference at six months between the use of adjunctive locally delivered antibiotics compared to subgingival instrumentation use alone [25]. There was a measurable increase in bacterial resistance to minocycline at one month after application, which was diminished but still present at 6 months of follow- up. This was the case for both plaque and saliva isolates. They also found that periodontal pathogens isolated during this study were rarely resistant to minocycline.

Four articles enrolled periodontitis patients who required initial subgingival instrumentation [22, 23, 24, 26]. Initial disease severity was variable. Taalab MR, et al. [24] enrolled Stage II periodontitis patients [24]. These patients were expected to respond well to non-surgical therapy [4]. The treatment group received adjunctive 5% tea tree oil gel, which was selected for its antimicrobial and immune- modulating potential. They found that the treatment resulted in significantly greater CAL at six months and there was also a significant reduction in the GCF levels of matrix metalloprotease 8 (MMP-8). MMP-8 is considered a host enzyme contributing to the tissue destruction seen in periodontitis. Gonde NP, et al. [26] used subgingival instrumentation and a 1% melatonin gel compared to subgingival instrumentation alone [26]. The enrolled patients had bilateral paired intrabony defects that were randomized to either the treatment or control according to a split-mouth experimental design. They found that the treatment group presented significantly better clinical and radiographic parameters, including PD reduction and bone fill calculated using cone beam computed topography. Melatonin was used for its potential as an immune modulator, improving osteoblastic differentiation.

Rapone B, et al. [23] investigated adjunctive ozonated water [23]. Through a powered unit, the treated water was used in a step-by-step oral disinfection protocol described, which included rinsing and irrigation paired with ultrasonic instruments. They found statistically significant improvements in PD, CAL and percentage BOP at six months. Ilyes I, et al. [22] used a protocol including piperacillin and tazobactam in a gel [22]. The trial also employed a treatment arm using a 14% doxycycline gel, and for the control, they used a placebo gel as the adjunctive to subgingival instrumentation. They found no differences between any of the treatment groups.

Photoactivated Antimicrobials

Photodynamic therapy is a treatment modality that has various uses in medicine and uses a photosensitizer to absorb the wavelength of a low-energy light source [11]. In turn, light absorption by the sensitizer leads to reactive oxygen species forming in the medium, effectively killing microorganisms. A systematic review from 2018 by Chambrone, et al. concluded that the evidence available at the time was insufficient to support a clinically significant difference in periodontal parameters following adjunctive photodynamic therapy for periodontitis and peri-implantitis treatment. The authors noted significant variation between studies. Wavelength of the lasers and agents used as photosensitizer are important in explaining the desired effect on bacteria and host tissues, but other determining parameters vary significantly between studies such as duration of exposure, power output and diameter of a diode tip used. These specifications should be reported by every trial protocol. The current review included 15 articles on this treatment modality.

Indocyanine green was used as a photosensitizer, and it is reported to cause cellular damage through increased intracellular temperature in free-floating bacteria and periodontal pathogens [28]. Hill G, et al. [30] used an 808 nm diode laser with ICG and found no difference compared to subgingival instrumentation alone in the residual pockets of patients in SPT [30]. Niazi FH, et al. [37] used ICG-based aPDT using an 810 nm laser as an adjunct to non-surgical periodontal therapy [37]. Patients in the treatment group presented significantly better PD reduction at six months in pockets that were 6 mm or greater in depth at baseline. In another treatment group, an adjunctive uncalibrated Salvadora persica gel was locally applied in periodontal pockets. The plant was selected for potential antimicrobial- and inflammatory-modulating properties and presented a greater reduction in BOP at six months compared to the control and aPDT groups. Sukumar K, et al. [33] also used ICG with an 810 nm diode laser for NSPT and found a significantly greater improvement in microbiological, but not clinical, parameters [33]. They found a significant reduction in periodontal pathogens at six months compared to subgingival instrumentation alone. Al-Momani MM, et al. [27] stratified patients in three groups prior to randomization: patients without diabetes, patients with diabetes presenting a glycated hemoglobin (HbA1C) percentage of less than 10% but greater than 6% and patients with more severely uncontrolled diabetes for whom HbA1C was greater than 10% [27]. Stratified groups based on glycemic control were then randomly assigned to the treatment and control subgroups. The adjunctive use of aPDT using ICG with an 810 nm diode laser led to a greater reduction in periodontal pathogens and improvement in clinical parameters in all groups, regardless of glycemic status. Annunziata M, et al. [40] used ICG aPDT with an 810 nm laser as an adjunct to subgingival instrumentation, providing three applications (day 1, 7, 28) and using ICG irrigation without laser activation as a placebo in the control subgingival instrumentation [40]. No statistical significance was found between the test and control groups at six months after treatment. Costa FO, et al. [28] investigated residual pockets in SPT patients. Patients with residual periodontal pockets were assigned to SRP with ICG aPDT (application at day 1 and day 15) or SRP with sham aPDT using saline irrigation [28]. The research group then found limited differences, with only BOP, periodontally inflamed surface area index and periodontal pathogen reductions being greater in the treatment group, while CAL and PD improvements were the same as those in the control.

Methylene blue was part of protocols developed by four authors. Katsikanis F, et al. [32] compared a higher- energy 940 nm diode laser to aPDT using a 670 nm diode laser and methylene blue [32]. They reported no significant difference six months after a single application, as both the 940 nm diode laser and the aPDT combination performed as well as subgingival instrumentation alone. Cláudio MM, et al. [35] compared adjunctive aPDT using a 660 nm diode laser with methylene blue to subgingival instrumentation alone [35]. They applied the aPDT protocol three times: once on the day of instrumentation, and they then retreated without performing further instrumentation on day 2 and day 4. The researchers found that, clinically, the mean PD and the number of residual pockets were significantly less in the test group. Andere NMRB, et al. [39] applied a similar methodology to treat residual pockets in periodontitis patients on maintenance [39]. They tested the same wavelength (660 nm) diode laser with methylene blue but applied the aPDT protocol once on the day of instrumentation, before repeating it on days 2, 7 and 14 for four exposures. Because initial subgingival instrumentation had been already performed six months prior to patients’ enrollment in the study, aPDT was compared to surgical debridement using a modified papilla preservation flap [39, 52]. This is the only study that made a comparison with open flap debridement (OFD) in the control group [39]. Andere NMRB, et al. [39] found that OFD performed better with significantly greater pocket depth reduction at initially deeper sites. In turn, OFD resulted in greater gingival recession and root sensitivity compared to the aPDT treatment of residual pockets. Inflammatory analysis of GCF found differences after two weeks in favor of aPDT in the cytokines measured, but these differences were not maintained after one year of follow- up. Only the surgical access in the control group led to a decrease in A. actinomycemtemcomitans. Cláudio MM, et al. [36] incorporated an oxygen-releasing gel into aPDT using a 660 nm diode laser and methylene blue [36]. There was also a control group using SRP alone and a group treated only with the adjunctive oxygen-releasing gel. Patients enrolled in the study had poorly controlled type 2 diabetes (HbA1C 7% or greater) and were already enrolled in SPT, presenting residual pockets requiring treatment. The results showed no difference between subgingival instrumentation alone and the repeated use of adjunctive aPDT in residual pockets.

Harmouche L, et al. [29] used another photosensitizer, toluidine blue, with a diode laser of 630 nm [29]. Patients enrolled in the study were systemically healthy patients receiving periodontal supportive therapy, presenting residual pockets requiring treatment. The aPDT test arm led to a greater reduction in the number of pockets with depths greater than 5 mm compared to subgingival instrumentation alone.

Al-Khureif AA, et al. [34] used a 670 nm diode laser with phenothiazine chloride as a photosensitizer in patients enrolled for initial subgingival instrumentation [34]. The application in the aPDT group was quadruple, starting on day 1 and continuing on days 3, 7 and 14. This is the only article using adjunctive systemic amoxicillin and metronidazole in the control group compared to aPDT. They also enrolled patients with Stage III Grade C or worse periodontitis, i.e., cases presenting with faster progression of CAL and a high level of pre-existing destruction. They found that the aPDT group improved significantly more for PD and CAL measured after six months of follow-up in sites with initially severe pocketing (7 mm or greater PD). The GCF analysis revealed that only the control group experienced improved cytokine profiles related to reduced IL-17 and increased IL-10 at six months Schär D, et al. [38]. used a 670 nm diode laser with phenothiazine chloride and compared it to subgingival instrumentation alone for the treatment of residual pockets in SPT patients [38]. The only statistical difference at six months was a greater reduction in BOP in the aPDT group; otherwise, both treatments presented similar improvements.

Ivanaga CA, et al. [31] treated residual pockets in patients with type 2 diabetes, using curcumin as a photosensitizer with a 475 nm diode laser [31]. There was another treatment group who only received pocket irrigation with curcumin, as well as a group who received pocket irradiation with the diode laser, and the control received saline pocket irrigation; all groups received subgingival instrumentation. Curcumin, an extract of Curcuma longa roots, was investigated to study its antimicrobial properties, as well as its anti-inflammatory potential. After three months, they found a statistically significant improvement in CAL gain using both the laser alone and the aPDT combination. These differences were not maintained at six months in these patients with type 2 diabetes (HbA1C percentage mean ± SD, 8.73% ± 1.82). Silva DNDA, et al. [41] investigated adjunctive chloro-aluminum phthalocyanine aPDT using a 660 nm laser for the initial subgingival instrumentation of periodontitis patients [41]. The control received subgingival instrumentation with saline irrigation, and both groups presented similar improvements after six months of follow-up.

Study Limitations

When comparing the results from the articles included in this review, care must be taken to understand the great variability in experimental protocols. Systemic agents were studied using randomized patients, while locally administered therapies like aPDT and medicated gels often were tested using split-mouth approaches. A split- mouth design allows the patient to act as their own control. When comparing results for the same patient, the authors could eliminate variability between subjects and identify a statistically significant difference with a smaller sample [9]. This was most significant in aPDT, where split-mouth randomization and the randomization of sites (periodontal pockets) were the most used experimental designs. One major consequence of split-mouth designs is the potential for a carry-across effect, where the treatment may affect more than just the target site.

Another limitation shared by many included studies in this review is the lack of a placebo/vehicle control. In particular, this was the case for most studies on local delivery [23, 24, 25, 26]. A similar trend was visible in the included studies on aPDT [27, 30, 32, 33, 34, 35, 36, 37, 39]. Specifically for aPDT, even for studies that included placebo in their control groups, there was heterogeneity in selection. Some protocols compared aPDT to active controls using systemic antibiotics and even surgical management of residual pockets [34, 39]. All the studies included in this review presented a small sample size, with only one study performing follow-up on more than 100 patients [17].

It is vital to present long-term data that justify the cost, risk of adverse events and additional treatment time incurred by using an adjunctive antimicrobial. Studies showing that statistically significant differences are maintained one year after treatment are rare, with only one aPDT trial and six out of nine adjunctive systemic antibiotic trials being identified. None of the locally administered agents were followed-up for 12 months or more. In total, 26 randomized controlled trials were also excluded from the initial 58 articles in the full-text review because of follow-up periods being less than 6 months long. Targeting patients with type 2 diabetes at a higher risk for disease progression was included in five trials. Various definitions were used to define patients with controlled and poorly controlled type 2 diabetes and guide inclusion in the studies. A threshold of seven percent HbA1C was used for uncontrolled diabetes used in the latest periodontitis staging and grading [4]. Al-Momani MM, et al. [27] considered diabetes controlled with a range from 6 to 10% [27]. Cruz D, et al. [15] and Cláudio MM, et al. [35] investigated patients with uncontrolled diabetes using a 7% glycated hemoglobin threshold [15, 35, 36]. Ivanaga CA, et al. [31] recruited diabetic patients reporting at least a 6.5% glycated hemoglobin [31]. Since poor glycemic control is associated with an increase in periodontal destruction and a decreased response to traditional treatment, the inclusion of patients with better controlled blood sugar levels in RCTs may not result in a response representative of the population most at risk of periodontitis progression, as would be found in patients with HbA1C levels greater than 7% [4, 53]. Future studies should include longer follow-up periods to help distinguish short-term benefit from lasting differences with any of the discussed agents on clinical, radiographical and microbiological outcomes. They should also use patients as a randomization unit, consider including all relevant treatment groups and controls, to identify the contribution of individual components of a combination treatment. This is especially important in the case of trials on aPDT. Complete disclosure of the selected diode laser parameters should be included. Finally, studies should also include patient- centered outcomes such as measures of discomfort during and after procedures.

Overall, the conclusions drawn from this review are limited because it did not follow the methodology of a systematic review. However, using the PubMed database, the review had a wide reach in capturing relevant published scientific articles in the past five years. The scope of the search was also limited to trials that included antimicrobials. This likely led to trials investigating agents for their immunological-modulating or bone-modulating properties such as statins being excluded in the search results [54].