Pharmacologic agents applied locally for the treatment of periodontitis are targeted to several areas. These include bacteria in the periodontal pockets, soft tissue walls of the pocket, and the exposed root cementum. Experimental evidence suggests that many forms of local delivery are not able to deliver medications to all these locations. For example, agents in mouthrinses and those used for irrigation do not predictably reach beyond 5 mm into the periodontal pocket. On the other hand, gaining access to the anatomical boundaries of the pocket does not mean penetration to the target bacteria, because bacterial aggregates (biofilm) impair diffusion or inactivate pharmacological agents. Also, rapid turnover of gingival crevicular fluid in the sulcus rapidly reduces concentration of the locally placed antimicrobial agent. It has been shown that the fluid present in a 5mm pocket is replaced about 40 times an hour! This high rate of clearance represents a major obstacle to maintaining effective concentrations of an antimicrobial agent within the pocket. Other anatomic limitations for effective local antimicrobial treatment in conjunction with scaling and root planning include root surface grooves, furcations, concavities, which all preclude predictable delivery of the agent to the target site.

Clinical evaluations of local drug delivery systems, approved by the FDA, showed limited benefits despite impressive statistical data. The difference between statistically significant and clinically significant outcome is enormous. For example, the most recent study that evaluated clinical effects of combining scaling and root planning with local minocycline delivery (Arestin) confirmed similar results achieved with scaling and root planning alone versus combination therapy with Arestin. Statistically, combination treatment was a lot better in reducing probing depths and gaining clinical attachment. However, clinical parameters were only marginally improved with combination therapy: probing depths on average were 0.41 mm better with combination therapy, and clinical attachment gain was less than 0.3 mm. Both of these figures cannot even be confirmed clinically because of crude periodontal measurements using a probe, which can only detect changes over 2mm, and potential operator's error during repeated periodontal recording, which is at least +/- 1 mm. Therefore, any clinician should interpret results of the study with caution, since statistical significance does not correlate with clinical improvement. And improvement of clinical measurements by less than 1mm is seldom the desired end result of any periodontal treatment. Also, there is no data to show that application of Arestin will stop the progression of periodontal destruction or achieve periodontal health.

Long-term clinical studies on local antimicrobial delivery systems are very scarce and are available for only a small number of agents. At present, there are 4 products that are commercially available in the United States: tetracycline fibers (Actisite), chlorhexidine chip (PerioChip), doxycycline hyclate (Atridox), and minocycline microspheres (Arestin). All of these products share one common characteristic, which is positive short-term (1-2 months) effects beyond scaling and root planning alone, resulting in decreased bleeding, some reduction in probing depth, and improved gingivitis index. These limited short-term benefits could not be confirmed after 9-12 months. Some of these products, particularly Arestin, have not even been evaluated enough in controlled clinical studies of over 9 months duration. To date, there is only one clinical study that evaluated the use of Arestin in conjunction with scaling and root planning.

Tetracycline fibers (Actisite) were evaluated most extensively due to their earlier introduction to the market in the 1990's. When the long-term therapeutic effect of Actisite used in conjunction with root planning was compared to root planning alone, there were no significant differences in probing depth reduction or gain in clinical attachment. Moreover, short-term (1-3 months) improvement in clinical parameters after using Actisite was non-existent after 12 months. The microbiological evaluation revealed that even high concentrations of tetracycline, maintained over at least 7 days (which was pretty rare), failed to completely eliminate periodontal pathogens from the treated sites.

Similarly, local application of chlorhexidine gluconate (PerioChip) did not achieve total pocket disinfection, which is probably due to inability of the agent to penetrate the depth of periodontal pocket and presence of biofilm in the subgingival environment. PerioChip is a bioabsorbable device comprised of 34% chlorhexidine gluconate in a gelatin matrix. Each chip is 5 mm long, 5 mm wide and 1 mm thick. This controlled device is pushed into the pocket, providing sustained release of the antiseptic agent for about a week. One of the limitations of PerioChip is inability to place it in narrow interproximal spaces as well as furcation areas. A small number of clinical studies showed that combining scaling and root planning with placement of PerioChip provides a defined, but limited clinical improvement versus results achieved with scaling and root planning alone.

Atridox is a biodegradable formulation containing 10% of Doxycycline hyclate by weight. Earlier studies showed that Atridox application resulted in significant improvement of probing depths and attachment levels versus placebo. However, 2 large randomized controlled clinical trials of 9 months duration, that compared the equivalency of Atridox alone to scaling and root planning, indicated there was no difference between the therapies in probing depth reduction or clinical attachment gain. At present time, the use of local drug delivery such as Atridox as a monotherapy is controversial. It seems prudent that use of antibiotics should be avoided if the same results can be achieved with conventional care (scaling and root planning). There is no data regarding the ability of Doxycycline polymer to enhance periodontal health when used in conjunction with root planning.

One interesting aspect of local antimicrobial therapy is its effect on potential periodontal surgical treatment. The results of one long-term study indicated that scaling and root planning with or without local antimicrobial therapy may result in a decrease in the perceived need for surgery, or at least minimize the area that still requires surgery. This is consistent with the notion that the need for surgery should be determined at periodontal re-evaluation, after sufficient time has elapsed for healing to occur. To this date, the hypothesis that systemic and/or local delivery of antimicrobials in combination with root planning might reduce the need for surgery is not proven, and any speculations on this matter have no scientific ground and should not be used in periodontal treatment planning.

1. Local delivery of antimicrobial agents requires the same caution as the systemic use of drugs:
   
   • it should not be used in subjects with known allergy to the active drug;
   • it does not preclude the possibility of emerging bacterial resistance in the pocket or overgrowth of intrinsically resistant organisms.
2. None of the drug agents are effective against all periodontal pathogens, and presence of even small number of bacteria may cause periodontal destruction.
   
3. Local drug delivery should not be substituted for meticulous oral hygiene and professional periodontal maintenance. It is also of questionable value in management of furcation lesions and other challenging anatomic areas, that allow only limited access for non-surgical therapy.
   
4. There are limited data with respect to the use of local delivery in the treatment of specific diseases, such as early-onset periodontitis, refractory periodontitis, or periodontitis associated with systemic disease.
   
5. Local antimicrobial therapy does not result in bone regeneration or repair.