Study design and overview
This will be a randomised, controlled trial, with predominantly blinded measurement of cardiovascular endpoints, and blinded statistical analysis. All participants will receive, or be offered, the periodontal intervention benefits. A schema outlining the study design is presented in Figure 2. The PerioCardio study has been registered with an international clinical trials registry (ANZCTR; ACTRN12610000817044), and will be reported as per the CONSORT statement. Recruitment for the study commenced in June 2010.
Setting & location
Participants will be recruited from urban centres within the Top End of the Northern Territory, Australia, facilitated through the following Aboriginal Medical Services or health facilities: Danila Dilba Health Services (Darwin and Palmerston), Bagot Community Health Centre (Darwin), Royal Darwin Hospital, Darwin Dental Centre (Northern Territory Oral Health Services, Department of Health), Northern Territory Correctional Services (Darwin), and Wurli Wurlinjang (Katherine).
Participants and recruitment
Participants will be Indigenous Australians aged ≥25 years that have lived in their current location for ≥2 years and who plan to live at their current location for the next 2 years. Those participants who have moderate or severe periodontal disease will be randomised to the intervention or control arm of the study. Those participants without periodontal disease, or only mild periodontal disease, will not be included in the trial. Baseline questionnaires will, however, be assessed in these participants in order to study the social, demographic, lifestyle and general health correlates of periodontal disease in Indigenous Australians.
Exclusion criteria include: a history of rheumatic heart disease, prior myocardial infarction, stroke or coronary revascularisation, other cardiac conditions requiring antibiotic prophylaxis for prevention of subacute bacterial endocarditis, obvious endodontic lesions, other sources of oral infection, treatment for periodontal disease within the previous six months.
Feedback to participants will be provided at the end of each examination. Participants with unexpected abnormal results will be referred to an appropriate health care provider. In addition, written results will be provided in a plain language and culturally appropriate manner to individual participants and to their nominated primary health care provider. Whenever possible, participants with abnormal results will be contacted by telephone or in person. The results packet will then be mailed or hand-delivered, as appropriate. A $50 gift voucher to a local store will be provided to participants at the end of the examination or with their results as a gift of appreciation for their participation in the study.
Funding was provided by the National Health and Medical Research Council of Australia (NHMRC, project grant #627100).
The study was approved by the joint Menzies School of Health Research - Northern Territory Department of Health Human Research Ethics Committee. The project was considered and approved by both the Aboriginal sub-committee, which has absolute right of veto, and by the main committee. The study was also approved by the Central Australian Human Research Ethics Committee, Northern Territory Correctional Services Research Committee, University of Adelaide Human Research Ethics Committee, and the Aboriginal Health Council of South Australia.
Three people are employed on contracts for the course of the study. Of these, two are Indigenous and one is non-Indigenous. Additional people are employed on a casual basis during visits to discrete locations or communities; these community members act as local facilitators. One post-graduate research student also participates in the study and is substantially involved in data collection, taking on the role of project manager. The majority of staff members have prior health qualifications and experience: one is an Aboriginal Health Worker, one has overseas dental qualifications and the post-graduate research student is an oral health therapist.
Potential participants are provided with written information about the study, face-to-face discussion with a staff member, and given an opportunity to ask questions. If required, an interpreter explains all information relating to the study. Those who indicate that they wish to participate are then asked to complete and sign a consent form. Consent is obtained using the NHMRC Guidelines for Ethical Conduct in Aboriginal and Torres Strait Islander Health Research. All participants are informed that their participation is voluntary and that they can refuse or withdraw from participating and need give no reason or justification for their decision and that it will not affect their medical or dental care. Participants are asked to provide separate consent for various elements of the study, including: vascular assessments, blood and urine samples, body measurements, blood pressure and questionnaires. They are also asked whether they want a report sent to their primary health care provider and whether their blood and urine samples can be stored at Menzies School of Health Research for 3 years.
Screening for periodontal disease
Following confirmation of contact details and eligibility, and after obtaining informed consent, a participant will be screened for periodontal disease, using the US Centers for Disease Control and Prevention and the American Academy of Periodontology definitions . Thus, a case of moderate periodontitis is considered as the presence of either two sites between adjacent teeth with ≥4 mm attachment loss or at least two such sites with ≥5 mm pockets, and severe periodontitis as having at least two sites between adjacent teeth with ≥6 mm attachment loss and at least one pocket ≥5 mm.
After screening for periodontal disease, those with moderate or severe periodontal disease are randomised on a 1:1 basis to either the treatment or control group. A computer generated permuted block randomisation sequence is used, stratified by recruitment site (Darwin/Palmerston, Katherine).
Individuals randomised into the 'treatment group' undergo a periodontal intervention based on the technique described previously . This involves intensive removal of subgingival and supragingival calculus and plaque biofilm by scaling and root-planing. Participants are offered local anaesthesia prior to the procedure. The procedures are carried out with the use of Hu Friedy hand scalers and a piezoelectric ultrasonic scaler with universal tips. Dental extraction of teeth that cannot be saved is not performed as part of the treatment protocol. The intervention is performed by two oral health practitioners who have received additional training with these techniques. The periodontal intervention occurs during a single untimed visit to the study clinic.
Oral hygiene instruction and an oral hygiene pack containing a toothbrush and tooth paste are provided to all participants at the baseline visit. Information concerning dental extractions during the course of the study is recorded.
Each participant randomised will attend the study clinic a total of 3 times (figure 2).
Periodontal treatment will be offered to those in the control group at 12 months post-randomisation, to ensure that all participants are able to receive the oral health benefits of the periodontal treatment. The periodontal treatment offered to participants in this study is beyond that which forms routine treatment within the government funded system. Participants are not restricted from seeking periodontal treatment during the study through the private health system.
Data collection techniques
including tooth presence, caries experience, periodontal destruction, gingivitis and calculus, plaque, oral mucosal lesions and trauma.
Clinical and anthropometric measures
Blood pressure is measured while seated using an automated device (Welch Allyn Medical Products, Skaneateles Falls, USA). Three measurements of systolic and diastolic pressure are made, with three minutes between readings. The mean values of the final two recordings will be used in statistical analysis.
Height is measured to the nearest 0.1 cm using a wall-mounted stadiometer.
Weight is measured to the nearest 0.1 kilogram, using a portable weight scale (Tanita HD-351, Arlington Heights, USA) with participants lightly clothed. Two separate measurements of weight are recorded and if they differ, then a third measurement of weight is taken.
Waist and hip circumference are measured to the nearest 0.1 centimetre using a 2-metre non-stretch flexible steel tape (Model W606PM Lufkin, USA), as previously described .
Common carotid intima-media thickness (IMT) and M-mode imaging
External ultrasound of the common carotid artery is performed with the patient lying in a supine position, neck slightly extended and the head tilted away from the side being scanned whilst connected to 3-lead ECG, to monitor cardiac cycle. Bilateral longitudinal images of the carotid bulb and common carotid artery, up to 15 mm proximal to the bulb, are obtained using a portable ultrasound (Sonosite MicroMaxx, Bothell, USA), with a 10-5 MHz linear array transducer. Loops are obtained of each artery, and stored in a digital format for batch analysis by an observer blinded to participant group, characteristics and study visit. Measurement of carotid IMT will be performed on the far wall of the common carotid artery at end diastole, within 10 mm proximal to the carotid bulb, on two consecutive cardiac cycles.
M-mode imaging of the arterial diameter during the cardiac cycle is used to assess regional stiffness of the common carotid artery. The area of interest for the stiffness measure is between 10 mm and 15 mm proximal to the bulb. Loops of each side are obtained, ensuring that both the near and far walls are clearly visible and the artery is perpendicular to the angle of insonation. Internal diameter of the artery during systole and end-diastole will be measured over three cardiac cycles to generate the following indices: pressure-strain elastic modulus, Young's modulus, cross-sectional compliance, distensibility coefficient.
Pulse wave velocity (PWV)
PWV is measured between the common carotid and dorsalis pedis arteries using applanation tonometry (SphygmoCor-PVMx device, AtCor Medical, Sydney, Australia), with participants in a supine position for at least 10 minutes prior to commencement of measures. The common carotid artery is located via lateral palpation along the thyroid cartilage while the dorsalis pedis artery is located between the first and second metatarsals on the dorsal surface of the foot. A pressure tonometer is placed transcutaneously above the corresponding artery to record the pulse pressure waveform while simultaneously recording the ECG signal, which provides an R-wave timing reference. The arteries are assessed consecutively. The resultant PWV score is calculated via computer algorithm as the mean time difference between the R-wave and the pressure wave per heart/pulse beat and the arterial path length between the two recording sites. To correct against measurement error, the distance from the common carotid location and the sternal notch will be subtracted from the distance between the sternal notch and the dorsalis pedis site. Data quality control for this measurement requires that standard deviation not exceed 10%. In the instances that this occurs, PWV will be remeasured. Measurement of PWV is undertaken automatically by the acquisition machine, and as such the observer will not be blinded to study participant characteristics.
Blood and urine derived measures of cardiovascular risk
non-fasting blood and urine samples will be collected to assess established measures of cardiovascular risk, inflammation and vascular health, including glycosylated haemoglobin (HbA1c), lipids and lipoproteins (total cholesterol, high-density lipoprotein cholesterol, apolipoprotein A-1 and apolipoprotein B), high sensitivity C-reactive protein (hs-CRP), interleukin-6 (IL-6), asymmetric dimethylarginine (ADMA), and urine albumin to creatinine ratio.
Collected blood samples are centrifuged for 10 min at 1300 g within 30 minutes of collection. If unable to be centrifuged immediately, blood is stored in a fridge or on ice packs in a cool-box until centrifugation a maximum of 2-hours after collection. Following centrifugation, samples are transported on ice to be processed by Westerns Pathology, Darwin for lipids and HbA1c. Total cholesterol is assayed by enzymatic methods, and high-density lipoprotein cholesterol measured directly, with an ADVIA chemistry system (Siemens, Tarrytown, USA). HbA1c is determined by turbidimetric inhibition immunoassay with a COBAS INTEGRA (Roche Diagnostics, Indianapolis, USA). Other samples are stored at -80 degree Celsius. For samples collected in remote locations, storage for transportation is either on dry ice or in liquid nitrogen ("Biological Shipper", CryoPak Series, Taylor-Wharton, USA). Samples are stored for analysis at a later date for hs-CRP, IL-6, ADMA, apolipoproteins and glucose.
Self-reported information pertaining to socio-demographic, oral health behaviours and general health factors is gathered at baseline, with the assistance of study personnel as required.
Socio-demographic details include age, sex, Aboriginal/Torres Strait Islander status, grandparental Indigenous status, education level, employment, English-as-first-language, house ownership, number of children, number of people who stayed in house the previous night and car ownership.
Oral health covariates include periodontal status and a self-report item pertaining to whether or not participants think they have gum disease.
General health covariates include behaviours such as smoking, current medication, current diagnoses (for diabetes etc), status of current diagnoses (controlled, uncontrolled etc) and stress (measured by the Kessler 10+ scale; a validated measure of distress that has been validated in a national health survey for Indigenous adults) .
Primary and secondary outcomes
The primary outcome measures for purposes of this investigation will be carotid IMT and PWV. Secondary outcome measures will include CRP, IL-6, ADMA, and HbA1c.
Based on recent studies of Indigenous adults residing in the Northern Territory, we estimate that a sample size of 144 will provide 0.80 power to detect a 10 percent difference between groups in carotid IMT progression over 12-months, and a 10 percent reduction in PWV in the intervention group compared to the control group, at P < 0.05. The literature indicates that it is reasonable to expect effects of this magnitude following the periodontal intervention [25, 26]. Allowing for an attrition rate of 45 percent over 12 months, 266 participants are required at baseline. In NSAOH, the proportion of Aboriginal adults with periodontal disease was estimated at 30 percent , however, it is likely that Aboriginal participants in NSAOH are not representative of the Aboriginal population in which we are interested. There are two main reasons: i) NSAOH participants were required to complete a telephone interview (ie to have an operating telephone and be registered in the electronic white pages); and ii) NSAOH participants were required to organise their own transport and to present for a scheduled dental examination at a local dental clinic. We posit that the NSAOH estimate is an under-estimation of periodontal disease prevalence in our target population, with anecdotal evidence suggesting that the prevalence is closer to 60 percent. We have estimated the prevalence of periodontal disease in our target population as 40 percent, meaning approximately 450 Indigenous adults will need to be screened in order to obtain 266 with moderate or severe periodontal disease.
Data handling and statistical methods
At the time of baseline assessment, data is collected on paper forms and then entered into a Microsoft Access database. Data is stored securely at Menzies School of Health Research. In brief, the plan for the analysis is:
Aim 1: descriptive statistics including mean and standard deviation for normally distributed variables, geometric mean and 95% confidence interval for non-normally distributed data, and percentages for categorical variables.
Aim 2: associations of the extent and severity of periodontal disease with measures of vascular health and inflammation from cross-sectional analysis at baseline, using correlation analysis, and multivariable regression modelling adjusted for cardiovascular risk factors.
Aim 3: intention to treat analysis comparing cardiovascular surrogate endpoints between the two randomised groups. Primary outcomes are carotid IMT at 12-months and PWV at both 3- and 12-months. Correlations between the changes from baseline to 3- and 12-months in carotid IMT, PWV and secondary outcomes will be determined.
Appropriate transformation of the data will be performed as required. Crude correlations will be detailed, followed by multivariable modelling. Statistical significance will be inferred at 2P ≤ 0.05.