Periodontal disease is among the most common inflammatory diseases and the major cause of tooth loss in adults. For years, the etiology of periodontal disease was thought to be bacterial plaque currently known as the microbial biofilm. Accordingly, therapy was restricted to efforts to remove as much bacteria from tooth surfaces as possible. The goal of periodontal therapy was to reduce or eliminate pockets. Even today, the success or failure of periodontal therapy is often determined by changes in pocket depth. However, recent studies by Payne et al1 based on a double-blind clinical trial indicate that pocket depth is a poor indicator of clinical attachment loss. This traditional view of periodontal disease is insufficient to address the effects of the oral environment on overall health. The role that inflammation plays in both oral and systemic diseases underscores the need to change the therapeutic approach to periodontal disease management.
On September 17, 1683, Anton Van Leeuwenhoek wrote to London’s newly formed Royal Society about his observations on the plaque between his own teeth. He noted, “an unbelievably great company of living animalcules, a-swimming more nimbly than any I had ever seen up to this time”.2 From that centuries old moment forward the emphasis on controlling periodontal disease was focused solely on bacterial control. Unfortunately, many dental professionals still make removal of bacteria from tooth surfaces the cornerstone of periodontal therapy. However, while periodontitis begins with microbial products irritating the adjacent gingival tissue, it has been long known that it is an induced, host-mediated generation of inflammatory mediators that cause clinically significant connective tissue and bone destruction which result in pocket formation.3
Research in the late 80’s began to delve into the aspect of a destructive host response as a causative etiologic factor in periodontal disease. A number of landmark studies began to draw the conclusion that periodontal disease was in fact an inflammatory disease.4 These papers, and literally hundreds of related papers, brought to the forefront the realization that it is the inflammatory response followed by the acquired immune response that drives the pathogenesis of periodontal tissue destruction.5
Research also confirms that inflammation plays a role in the development and progression of many chronic diseases of aging.6 The mouth can contribute to the body’s inflammatory burden when periodontal disease is inadequately treated.7 Thus, modulating the host-mediated inflammatory response, (in addition to controlling the bacterial etiology), in patients presenting with periodontal disease will likely improve overall as well as oral health.
During the 2012 landmark joint European Federation of Periodontology/American Academy of Periodontology workshop, participants summarized the emerging data suggesting that periodontal pathogens are more or less universally present in low numbers. In fact, current theory suggests that pathogens use inflammation to create an environment to foster their growth. In other words, in patients susceptible to periodontal disease, the pathologic biofilm emerges as a result of inflammation. Variations in inflammatory response are major determinants in periodontal disease susceptibility.8 The implication is that control of inflammation in addition to biofilm removal is essential to maximizing treatment outcomes.
Transition from infectious disease to inflammatory disease was redefined by the American Academy of Periodontology (AAP) in 2008. Today the AAP refers to periodontitis as an inflammatory disease with far reaching destructive effects on systemic health. “For a long time it was thought that bacteria was the factor that linked periodontal disease to other disease in the body; however, more recent research demonstrates that inflammation may be responsible for the association. Therefore, treating inflammation (and the resultant increase in host-derived, tissue-destructive enzymes, e.g., collagenase plus other MMPs [matrix metalloproteinase]) may not only help manage periodontal diseases but may also help with the management of other chronic inflammatory conditions.”9
Tissue Destruction Mediated by Inflammation
One of the most widely studied topics of medical research currently is the destruction caused by the inflammatory pathway when a transient infection becomes chronic. While an acute inflammatory response protects the host against transient pathogen insults, chronic persistence of the inflammatory response can literally turn the body against itself.10
Genetics, nutrition, environmental exposures, exercise and drug therapies can impact a patient’s inflammatory response. Differences in the intensity of the inflammatory response explain why certain patients have an elevated risk for developing periodontal disease.
The role of chronic inflammation and its association with today’s most prevalent diseases such as cardiovascular disease, Alzheimer’s, cancers, diabetes and autoimmune disorders is well documented.11 Coronary Artery Disease (CAD) remains the number one cause of death in the world. While traditional risk factors partially account for the development of CAD, chronic inflammation has been postulated to play a role in the development and propagation of this disease. A systematic review was carried out by Roifman et al and published in the Canadian Journal of Cardiology.12 The purpose of this systematic review was to determine if patients with chronic inflammatory diseases have higher rates of cardiovascular disease. The results indicated that patients with chronic inflammatory conditions are at elevated risk for the development of CAD. Chronic inflammation is now accepted as playing a potentially important role in the promotion of atherosclerosis, a main cause of CAD.13 In this regard, chronic periodontitis is a very common chronic inflammatory disease which is increasingly being recognized as having an association with, and a potential causal relationship to, coronary artery disease (CAD).14,15
A substantial body of evidence supports the conclusion that chronic inflammation can predispose an individual to certain types of cancers, as demonstrated by the association between chronic inflammatory bowel diseases and the increased risk of colon carcinoma. The longer the inflammation persists, the higher the risk of associated carcinogenesis.16 The chronic inflammatory states associated with infection and irritation may lead to environments that foster genomic lesions and tumor initiation.17 The links between chronic inflammation and numerous systemic diseases underscore the importance of addressing both the inflammatory and bacterial components of periodontal disease.
Treating Periodontal Disease as an Inflammatory Disease
The foundational characteristics of all inflammatory diseases are the up-regulation of cytokines, prostaglandins, MMPs (i.e., host-derived, tissue-destructive matrix metalloproteinases), reactive oxygen species, etc. The only apparent difference between an inflammatory response in these diseases such as rheumatoid arthritis, atherosclerosis, Crohn’s and periodontal disease is the anatomical location.
Periodontal disease is a chronic inflammatory disease resulting ultimately in alveolar bone loss. The release of excessive MMP-8 or collagenase (as well as other less prominent MMPs, e.g., MMP-13, MMP-12, plus other proteinases) is a key event in the pathogenesis of periodontal disease. Collagen forms 60 percent of the gingival tissues and the periodontal ligament. Moreover, 90 percent of the organic matrix (living part) of bone is collagen; calcium phosphate crystals are imbedded within this collagenous matrix to provide the mineral (calcified) part of this tissue. The destruction of collagen in all the periodontal tissues is largely mediated by elevated MMP
levels attacking the living organic matrix.
A major event in the link between local periodontitis and relevant systemic/medical conditions is the release, from the inflamed periodontal tissues, of inflammatory mediators into the bloodstream which subsequently travel to the liver. The following cascade of events illustrates how chronic inflammation plays a strong etiologic role in the exacerbation of a stroke or a myocardial infarction. Once inflammatory mediators are present in the blood (e.g., derived from the inflamed gingiva), the liver is stimulated to produce acute phase proteins, which are diagnostic markers and mediators of inflammatory disease, one being C-reactive protein (CRP) (Fig. 1). To add insult to injury, LDL (low density lipoprotein) cholesterol, when oxidized by the inflammatory response, then forms a chemical reaction with CRP. The end result is a complex of oxidized LDL combined with CRP which is taken up by macrophages in the atheroma. These macrophages differentiate into foam cells which is characteristic of this lipid-laden plaque in the arteries. They are an indication of plaque build-up in atherosclerosis, which is commonly associated with increased risk of heart attack and stroke. The foam cells, in turn, release MMP’s, such as MMP-8 also known as collagenase. Collagenase’s primary function is to breakdown collagen. The collagen rich protective cap, which encapsulates the atherosclerotic plaque, is now in great danger. The protective cap destroyed by collagenase results in rupture, thrombosis, followed by stroke or a myocardial infarction (heart attack).
FIGURE 1. Chronic Inflammatory Process. (Acknowledgment Dr. LM Golub).
A Call to Action
We can no longer afford to ignore the impact of the most common chronic inflammatory disease known to mankind, periodontitis. The consequence of relentless ongoing periodontal inflammation makes healing impossible and systemic disease more likely.
The human body is continually destroying old collagen followed by a renewal process of normal turnover. In chronic inflammatory disease, collagenases, particularly MMP-8, become excessive. The repair process is halted. Until the inflammatory response is resolved, we are at a standstill in our treatment progress resulting in further destruction and unpredictable outcomes.
What if we could now slow down the breakdown of collagen or somehow inhibit the production of collagenase to an acceptable level?
In research conducted at Stony Brook University (New York) on collagen-destruction mechanisms and periodontal disease, Golub and his colleagues made an unexpected discovery; namely, that tetracyclines, a class of drugs that had been recognized only as antibiotics, were unexpectedly found to block collagenase in mammals.4 This exciting discovery led to further research to develop a formulation of doxycycline that would inhibit collagenase (e.g., MMP-8) and other MMPs at a blood level so low that it would NOT perform as an antibiotic (Fig. 2). The sub-antimicrobial level would eliminate the typical antibiotic side effects (Table 1). The drug today is known as, and prescribed under the trade name of Periostat® (Fig. 3). To date, over 10 million prescriptions have been written in the U.S. alone and is the most widely prescribed drug for treating periodontal disease in the world.
FIGURE 2. Sub-antimicrobial Dose Doxycycline
TABLE 1. Incidence of Adverse Reactions
INCIDENCE (%) OF ADVERSE REACTIONS IN PERIOSTAT CLINICALS TRIALS
The American Dental Association (ADA) Council on Scientific Affairs have published the following statement; “Periostat® has been shown to help stop the progression of periodontitis when used as directed as an adjunct to scaling and root planing, in a conscientiously applied program of oral hygiene and regular professional care.”
[Note: scientifically, Periostat® is described as SDD or sub-antimicrobial-dose doxycycline.]
The science resulting from the following double-blind clinical studies on patients with periodontitis and published in leading journals is both extensive and compelling comparing SRP + SDD versus SRP + placebo;
• Significantly more effective than SRP + placebo with no antibiotic side-effects.18-21
• 75 percent fewer teeth lost than patients treated with SRP + placebo.22
• 80-90 percent reduction of “active” pockets;22-28 “active” pockets are defined as those which get deeper with time.
• No “rebound” effect.18, 29
• 50-60% reduction of biologic mediators of tissue breakdown and bone resorption (i.e., MMP-8/collagenase, MMP-9, IL-1β).18, 30
• In rapidly progressing periodontitis, adjunctive SDD (versus adjunctive placebo) produced a 73 percent reduction in “active” pockets; combined with two to three times greater mean attachment gain (e.g. 2.2 mm. vs. 0.8 mm); and significant reduction of BOP.19, 25
Who Would Benefit from SDD?
Despite the now well-established inflammatory component of periodontal disease, traditional means of identifying active disease still often rely solely upon the measurement of pocket depths or clinical attachment loss (even though attachment measurements indicate past disease and not necessarily current active disease). Clearly, the focus should be on inflammatory biomarkers in addition to probing data.
In the clinical setting, practitioners can use risk assessment to determine which patients can benefit from SDD. With the large baby-boomer cohort aging, our dental hygiene client population is experiencing a rapid increase in diabetes, cardiovascular disease and other prevalent diseases all with a common denominator, the inflammatory pathway. The success of low dose or subantimicrobial dose doxycycline (SDD), as the first-ever systemically administered collagenase inhibitor drug approved by the US FDA and by Health Canada for periodontal disease, has also made a resounding impact on other inflammatory mediated diseases. As expected this
has gained significant attention from the medical community.
Consider the diabetic patient; more than one in four Canadians lives with diabetes or pre-diabetes. This will rise to more than one in three by 2020.31 Chronic periodontitis is more prevalent and more severe in the diabetic patient. A six-month, multicenter, randomized clinical trial was conducted measuring the effect that non-surgical periodontal debridement had on participants who had type 2 diabetes. All were taking stable doses of medications, HbA1c levels between 7 percent and 9 percent (i.e., poorly controlled hyperglycemia) and untreated chronic periodontitis. The study concluded that nonsurgical periodontal therapy alone did not improve glycemic control in patients with type 2 diabetes and moderate to advanced chronic periodontitis.32
However, drastically different results were seen in a separate three-month, randomized placebo-controlled pilot clinical trial which included 45 patients with long-standing type 2 diabetes and untreated chronic periodontitis. These subjects received conventional nonsurgical periodontal therapy combined with either (a) a three-month regimen of sub-antimicrobial-dose doxycycline (SDD), or (b) a two-week regimen of antibiotic therapy, or (c) placebo. Note that all subjects were taking stable doses of oral hypoglycemic medications and/or insulin. Treatment response was assessed by measuring hemoglobin A1c (HbA1c), plasma glucose, and clinical periodontal disease measures. At one-month and three-month follow-up, clinical measures of periodontitis were decreased in all groups. At three months, mean HbA1c levels in the SDD group were reduced from 7.2 to 6.3 units (note that this value is reflective of good glycemic control in diabetics). In contrast, there was no significant improvement in HbA1c when debridement was supplemented with systemic antibiotic or placebo. Results suggest that comprehensive treatment of periodontitis (via debridement and modulation of the host response may decrease HbA1c in patients with type 2 diabetes taking normally prescribed hypoglycemic agents.33
The effect of subantimicrobial-dose-doxycycline (SDD) has been widely studied for its potential to reduce serum biomarkers of systemic inflammation. CRP (C-reactive protein, an acute-phase protein produced by the liver and an important biomarker in the circulation of systemic inflammation) along with several other serum biomarkers are widely studied risk factors for coronary artery disease (CAD), and these patients show elevated CRP in their blood samples indicating patients at elevated risk for future cardiac events such as heart attack. One of the groups who are particularly at risk for CAD are post-menopausal women.34,35 In a randomized, double-masked, placebo-controlled clinical trial 128 eligible postmenopausal women with chronic periodontitis were assigned to a twice-daily regimen of subantimicrobial-dose-doxycycline (SDD) or placebo tablets for two years as an adjunct to periodontal maintenance therapy. Following the two-year regimen, SDD significantly reduced the serum inflammatory biomarkers (CRP and MMP’s) and among women more than five years post-menopausal, increased the HDL (high density lipoprotein) “good” cholesterol which is correlated with reduced risk of atherosclerosis.36
As discussed earlier, chronic inflammation, whereby macrophages secrete excessive MMPs, eventually degrade the collagen rich, fibrous protective cap, which destabilizes the atherosclerotic plaques leading to plaque rupture, thrombosis, and heart attack (MI). It was hypothesized that if MMP activity could be inhibited or suppressed there may be less risk of rupture of the protective cap. A randomized, double blind, placebo-controlled pilot study of 6 months of SDD or placebo treatment to reduce inflammation and prevent rupture events was conducted. A total of 50 patients all diagnosed with severe CAD (i.e., acute coronary syndromes or ACS) were enrolled; 24 randomized to placebo and 26 to SDD (30 patients completed the 6-month study; 17 SDD and 13 placebo). In the SDD-treated patients, C-reactive protein (CRP) in the circulation was reduced by 46 percent, whereas CRP was not significantly reduced in placebo patients. Interleukin (IL)-6 was decreased in SDD-treated patients but did not decrease significantly in placebo-treated patients. MMP-9 (also known as type IV collagenase) was also reduced 50 percent by SDD therapy, whereas it was unchanged by placebo treatment. [It should be recognized that these reductions in CAD biomarkers in the patient’s blood samples are recognized as indicators of reduced risk for cardiac events including reduced risk for heart attack]. The study concluded that SDD appears to exert potentially beneficial effects on inflammation that could promote plaque stability preventing plaque rupture events.37
The medical condition of osteoporosis, a disease characterized by low bone mass and deterioration of bone tissue, leads to increased bone fragility and risk of fracture and, in many cases, fatality. Twenty-eight percent of women and 37 percent of men who suffer a hip fracture will die within the following year.38 A preliminary study by Payne et al had previously demonstrated that subantimicrobial-dose-doxycycline (SDD) treatment of post-menopausal women with periodontitis and either osteoporosis or osteopenia (the latter, reflects loss of bone mass of lesser severity than osteoporosis) reduced periodontal disease progression including decreased alveolar bone loss, and biomarkers of collagen destruction and bone resorption locally in periodontal pockets, in a double-blind placebo-controlled clinical trial.39
An earlier study by Golub et al (1999), using a rat model of post-menopausal osteoporosis, clearly demonstrated that oral administration of a NON-antimicrobial doxycycline not only reduced the severity of systemic bone loss in skeletal tissue (femur), but also reduced local bone loss in the periodontium, which was associated with reduced collagenase in adjacent gingival tissues.40
Subsequently a major National Institutes of Health (NIH)-funded-study screened 600 women of which 128 were selected. Participants had to be post-menopausal, have osteopenia, radiographic evidence of alveolar bone loss and not be taking bisphosphonates or other medications that would impact osteoporosis. The 128 post-menopausal women with chronic periodontitis and osteopenia randomly received SDD or placebo tablets daily for two years adjunctive to periodontal maintenance therapy every three to four months. Blood was collected at baseline and at one- and two-year appointments, and sera were analyzed for bone resorption and bone formation/turnover biomarkers. In conclusion, the two year regimen of SDD therapy not only reduced the clinical, radiologic and biochemical markers of periodontal disease in post-menopausal women but also reduced the risk of conversion of mild systemic bone loss (osteopenia) into a severe form of bone disease (osteoporosis).41
Rheumatoid Arthritis (RA)
A link between rheumatoid arthritis and periodontitis is well established. While historically this link was attributed to RA induced diminished manual dexterity (and its effect of daily biofilm removal), we now understand that the link exists through vascular transport into the circulation. The inflammatory mediators (cytokines, prostaglandin, MMPs) present with oral inflammation flow into the blood bi-directionally from the gingiva into the circulation resulting in systemic inflammation. The profiling of elevated inflammatory markers is similar for both periodontitis and rheumatoid arthritis.
In this regard, a clinical study was conducted to compare the efficacy of doxycycline plus methotrexate (MTX) versus MTX alone in the treatment of early seropositive rheumatoid arthritis (RA), and to attempt to differentiate the antibacterial and anti-metallopro
teinase (SDD) effects of doxycycline. Sixty-six patients with seropositive RA of <one year’s duration who had not been previously treated with disease-modifying anti-rheumatic drugs were randomized to receive 100 mg of doxycycline twice daily with MTX (high, antibiotic-dose doxycycline group), 20 mg (low, NON-antibiotic-dose, i.e., SDD) doxycycline twice daily with MTX (SDD), or placebo with MTX (placebo group), in a two-year double-blind study. The study concluded that in patients with early seropositive RA, initial therapy with MTX plus doxycycline was superior to treatment with MTX plus placebo. The therapeutic responses to low-dose and high-dose doxycycline were essentially the same, except that the high-dose doxycycline group exhibited greater side effects, while SDD was similar to the placebo group. This study demonstrated that the SDD effects on host response were responsible for the beneficial effects on RA rather than the antibacterial effect of the high-dose doxycycline.42
The recently published evidence-based clinical practice guideline on the nonsurgical treatment of chronic periodontitis by means of scaling and root planing with or without adjuncts in JADA, July 2015,43 identified ‘SRP with systemic subantimicrobial-dose doxycycline’ as the only local or systemic adjunctive therapy to SRP that the council was ‘in favor of’. The reader is encouraged to read the summary of clinical recommendations outlined in Table 4 of the recently published practice guidelines. A comprehensive review of relevant literature concluded that of all available adjunctive therapies, only SDD had adequate support and clinical significance to warrant its use and substantiate a recommendation.
Clearly, today’s management of the periodontal patient must be about more than just pocket reduction. It seems especially prudent to have a protocol in place to identify those patients in whom periodontal inflammation can have significant adverse effects on systemic health. While periodontal pocket reduction remains part of periodontal management, today’s dental professional should be primarily focused on helping patients achieve and maintain a functioning dentition that is relatively inflammation-free.OH
Timothy Donley, Private Practice Periodontics’, Adjunct Professor, Western Kentucky University, Bowling Green, KY, International Lecturer.
Jo-Anne Jones, President of RDH Connection Inc., International Lecturer.
Lorne M. Golub, SUNY Distinguished Professor, Department of Oral Biology and Pathology, Stony Brook School of Dental Medicine, S.U.N.Y.
Ying Gu, Associate Professor, Department of General Dentistry, Stony Brook School of Dental Medicine.
Maria Emanuel Ryan, Professor and Chair, Department of Oral Biology and Pathology, Stony Brook School of Dental Medicine.
Oral Health welcomes this original article.
1. Stoner JA, Golub LM, Payne JB. Probing depth: a poor predictor of clinical attachment level changes. J Dent Res 94 (Spec.Is.):Abstract 1670, 2015.
2. Gest H. The discovery of microorganisms by Robert Hooke and Antoni Van Leeuwenhoek, fellows of the Royal Society. Notes Rec. R. Soc. Lond, 2004;58:187 – 201.
3. Kornman KS, Page RC, Tonetti MS. The host response to the microbial challenge in periodontitis: Assembling the players. Periodontol 2000, 1997;14:33-53.
4. Golub LM, Lee HM, Ryan ME et al. Tetracyclines inhibit connective tissue breakdown by multiple non-antimicrobial mechanisms. Adv Dent Res 1998;12:12-26.
5. Van Dyke, TE. Periodontitis is characterized by an immune-inflammatory host-mediated destruction of bone and connective tissues that support the teeth. J Periodontol. April 2014.
6. Prasad S, Sung B, Aggarwal BB. Age-Associated Chronic Diseases Require Age-Old Medicine: Role of Chronic Inflammation. Preventive Medicine. 2012;54(Suppl):S29-S37.
7. Lockhart PB, Bolger AF, Papapanou PN, Osinbowale O, Trevisan M, Levison ME, Taubert KA, Newburger JW, Gornik HL, Gewitz MH, Wilson WR, Smith SC Jr, Baddour LM, on behalf of the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee of the Council on Cardiovascular Disease in the Young, Council on Epidemiology and Prevention, Council on Peripheral Vascular Disease, and Council on Clinical Cardiology. Periodontal disease and atherosclerotic vascular disease: does the evidence support an independent association?: a scientific statement from the American Heart Association. Circulation. 2012;125:2520 –2544.
8. Hasturk H, Kantarci A, Van Dyke TE. Paradigm shift in the pharmacological management of periodontal diseases. Front Oral Biol. 2012;15:160-76.
10. Hasturk H, Kantarci A. Activation and resolution of periodontal inflammation and its systemic impact. Periodontol 2000. 2015;69:255-73.
11. Willerson JT, Ridker PM. Inflammation as a Cardiovascular Risk Factor. Circ Journ 2004; 109: II-2-II
12. Roifman I, Beck PL, Anderson TJ et al. Chronic inflammatory diseases and cardiovascular risk: a systematic review. Can J Cardiol. 2011 Mar-Apr;27(2):174-82.
13. Wilson, PW. Evidence of systemic inflammation and estimation of coronary artery disease risk: a population perspective. Am J Med. 2008 Oct;121(10 Suppl 1):S15-20.
14. Craig RG, Yip JK, So MK, et al. Relationship of destructive periodontal disease to the acute-phase response. J Periodontol. 2003;74(7):1007–1016.
15. Friedewald VE, Kornman KS, Beck JD, et al. The American Journal of Cardiology and Journal of Periodontology Editors’ Consensus: periodontitis and atherosclerotic cardiovascular disease. Am J Cardiol. 2009;104(1):59–68.
16. Shacter E, Weitzman A. Chronic Inflammation and Cancer. Colorectal Cancer, Oncol Journ. January 31, 2002.
17. Rakoff-Nahoum S. Why Cancer and Inflammation? Yale J Biol Med. 2006 Dec; 79(3-4): 123–130.
18. Caton J, Ryan ME. Clinical studies on the management of periodontal diseases utilizing subantimicrobial dose doxycycline (SDD). Pharmacol Res. 2011 Feb;63(2):114-20.
19. Ashley RA. Clinical trials of a matrix metalloproteinase inhibitor in human periodontal disease. SDD Clinical Research Team. Ann N Y Acad Sci. 1999 Jun 30;878:335-46.
20. Preshaw PM. Host response modulation in periodontics. Periodontol 2000. 2008;48:92-110.
21. Gu Y, Walker C, Ryan ME, Payne JB, Golub LM. Non-antibacterial tetracycline formulations: clinical applications in dentistry and medicine. J Oral Microbiol. 2012;4: doi: 10.3402/jom.v4i0.19227.
22. Caton JG, Ciancio SG, Blieden TM, et al. Treatment with subantimicrobial dose doxycycline improves the efficacy of scaling and root planing in patients with adult periodontitis. J Periodontol 2000:71:521-32.
23. Lee JY, Lee YM, Shin SY, Seol YJ, Ku Y, Rhyu IC, Chung CP, Han SB. Effect of subantimicrobial dose doxycycline as an effective adjunct to scaling and root planing. J Periodontol. 2004 Nov;75(11):1500-8.
24. Preshaw PM, Hefti AF, Bradshaw MH. Adjunctive subantimicrobial dose doxycycline in smokers and non-smokers with chronic periodontitis. J
Clin Periodontol. 2005 Jun;32(6):610-6
25. Novak MJ, Johns LP, Miller RC, et al. Adjunctive benefits of subantimicrobial dose doxycycline in the management of severe, generalized, chronic periodontitis. J Periodontol 2002:72:762-9.
26. Mohammad AR, Preshaw PM, Bradshaw MH, Hefti AF, Powala CV, Romanowicz M.Adjunctive subantimicrobial dose doxycycline in the management of institutionalized geriatric patients with chronic periodontitis. Gerontology. 2005 Mar;22(1):37-43
27. Novak MJ, Dawson DR 3rd, Magnusson I, Karpinia K, Polson A, Polson A, Ryan ME, Ciancio S, Drisko CH, Kinane D, Powala C, Bradshaw M. Combining host modulation and topical antimicrobial therapy in the management of moderate to severe periodontitis: a randomized multicenter trial. J Periodontol. 2008 Jan;79(1):33-41
28. Preshaw PM, Hefti AF, Novak MJ, Michalowicz BS, Pihlstrom BL, Schoor R, Trummel CL, Dean J, Van Dyke TE, Walker CB, Bradshaw MH. Subantimicrobial dose doxycycline enhances the efficacy of scaling and root planing in chronic periodontitis: a multicenter trial. J Periodontol. 2004 Aug;75(8):1068-76.
29. Caton JG, Ciancio SG, Blieden TM, Bradshaw M, Crout RJ, Hefti AF, Massaro JM, Polson AM, Thomas J, Walker C. Subantimicrobial dose doxycycline as an adjunct to scaling and root planing: post-treatment effects. J Clin Periodontol. 2001 Aug;28(8):782-9.
30. Golub LM, Lee HM, Stoner JA, et al. Subantimicrobial dose doxycycline modulates gingival crevicular fluid biomarkers of periodontitis in postmenopausal osteopenic women. J Periodontol 2008:79:1409-18.
31. Diabetes: Canada at the Tipping Point. Canadian Diabetes Association. http://www.diabetes.ca/CDA/media/documents/publications-and-newsletters/advocacy-reports/canada-at-the-tipping-point-english.pdf
32. Engebretson SP, Hyman LG, Michalowicz BS, Schoenfeld ER, Gelato MC, Hou W, Seaquist ER, Reddy MS, Lewis CE, Oates TW, Tripathy D, Katancik JA, Orlander PR, Paquette DW, Hanson NQ, Tsai MY. The effect of nonsurgical periodontal therapy on hemoglobin A1c levels in persons with type 2 diabetes and chronic periodontitis: a randomized clinical trial. JAMA. 2013 Dec 18;310(23):2523-32.
33. Engebretson SP, Hey-Hadavi J. Sub-antimicrobial doxycycline for periodontitis reduces hemoglobin A1c in subjects with type 2 diabetes: a pilot study. Pharmacol Res. 2011 Dec;64(6):624-9.
34. Ridker PM, Hennekens CH, Buring JE, et al. C-reactive protein and other markers of inflammation in the prediction of cardiovascular disease in women. N Engl J Med. 2000;342(12):836–843.
35. Ridker PM, Rifai N, Rose L, et al. Comparison of C-reactive protein and low-density lipoprotein cholesterol levels in the prediction of first cardiovascular events. N Engl J Med. 2002;347(20):1557–1565.
36. Payne JB, Golub LM, Stoner JA, Lee HM, Reinhardt RA, Sorsa T, Slepian MJ. The effect of subantimicrobial-dose-doxycycline periodontal therapy on serum biomarkers of systemic inflammation: a randomized, double-masked, placebo-controlled clinical trial. J Am Dent Assoc. 2011 Mar;142(3):262-73.
37. Brown DL, Desai KK, Vakili BA, Nouneh C, Lee HM, Golub LM. Clinical and biochemical results of the metalloproteinase inhibition with subantimicrobial doses of doxycycline to prevent acute coronary syndromes (MIDAS) pilot trial. Arterioscler Thromb Vasc Biol. 2004 Apr;24(4):733-8.
39. Payne JB, Golub LM. Using tetracyclines to treat osteoporotic/osteopenic bone loss: From the basic science laboratory to the clinic. Pharmacological Res. 63 (2), pp 121-129, 2011.
40. Golub L.M., Ramamurthy N.S., Llavaneras A., Ryan M.E., Lee H.M., Liu Y., Bain S. and Sorsa T.: A chemically modified nonantimicrobial tetracycline (CMT-8) inhibits gingival matrix metalloproteinases, periodontal breakdown, and extra-oral bone loss in ovariectomized rats. Ann. N.Y. Acad. Sci., 878: 290-310, 1999.
41. Golub LM, Lee HM, Stoner JA, Reinhardt RA, Sorsa T, Goren AD, Payne JB. Doxycycline effects on serum bone biomarkers in post-menopausal women. J Dent Res. 2010 Jun;89(6):644-9.
42. O’Dell JR, Elliot JR, Mallek JA, Mikuls TR, Weaver CA, Glickstein S, et al. Treatment of early seropositive rheumatoid arthritis: doxycycline plus methotrexate alone. Arthritis Rheum. 2006;54:621-7.
43. Smiley CJ, Tracy SL, Abt E et al. Evidence-based clinical practice guideline on the nonsurgical treatment of chronic periodontitis by means of scaling and root planing with or without adjuncts.