This study followed the 2010 Consolidated Standards for Reporting Trials (CONSORT) statement. The trial protocol was approved by the Ethics Committee of the Faculty of Dentistry, Tokyo Medical and Dental University (TMDU; Registration No. D2016-028, date of final registration 25/1/2019), and is registered in the University Hospital Medical Information Network Center (UMIN-CTR Clinical Trial, Unique Trial No. UMIN000022753). All participants provided written informed consent before participation in the study. We recruited 112 patients who met the Japanese waist circumference criteria of MetS. This study was conducted in TMDU Dental Hospital. Participants consisted of TMDU staff and patients who visited TMDU Medical Hospital and/or Dental Hospital. Inclusion criteria were as follows: age ≥ 40 years, at the time when the consent form was signed; waist circumference criteria for MetS of ≥ 85 cm for men and ≥ 90 cm for women at the navel; missing tooth according to Eichner’s criteria A2, A3, B1, B2, B3, B4, C1, C2, C3, and/or patients with light–moderate periodontitis (4 mm ≤ PD < 6 mm); and signing of consent form after the explanation and understanding of the study objectives. In this study, we have modified the criteria of CPI, and defined PD ≥ 4 mm as mild to moderate periodontitis, where the patients would need professional dental care . We excluded PD > 6 mm, which is a status that needs periodontal surgery, since the long healing period after surgery might exceed the ethical time limit of study period. In the Eichner’s classification, patients would be divided into three main groups as Eichner’s index (A, B, and C), according to the occlusal status supported by remaining teeth . Occlusion is supported by four occlusal areas in the healthy dentition composed of the right and left premolars and molars, and areas that support occlusion are called occlusal support areas. Eichner classification groups A, B, and C were as follows: (A) Occlusal contacts are present in all four posterior support zones; (B) occlusal contacts are present in 1–3 zone(s); (C) occlusal contact is in the anterior region only and / or no occlusal contacts.
Patients were excluded from the study as per the following criteria: involvement in regular dietary and/or exercise guidance outside this study, barriers to attend and/or achieve dietary and exercise guidance and the study objectives, changes in medication prescription within the past 3 months, severe cardiovascular disease, and hyper/hypo function of the thyroid. Further, patients with severe disorders of the liver and/or kidneys, undergoing treatment for cancer, with pregnancy, or with possibility of pregnancy, and others who were judged as ineligible for this study by the principal investigator were excluded from the study. Participants were recruited using the following methods: all the TMDU employees who participated in regular medical examinations received recruiting brochures for this study, with a clear statement that their participation is optional and not compulsory or included as part of their business; posters and flyers were advertised in TMDU Medical and Dental Hospital; and participant selection was entrusted and contracted to competent companies.
A double-blinded parallel group RCT was initiated inside a single facility (TMDU Dental Hospital). Participants were allocated to ITG and CTG. All the patients who had gone through a baseline examination received dietary and exercise guidance, which consisted of the Total Fitness Analysis System (TFAS)  and a video-programmed dietary and exercise lecture. TFAS is a web application available on the Internet of TMDU, which was created as a life management tool by the TMDU Department of Health Science and Physical Education. This application has its concept based on “Health Promotion 2006: Physical Activity, Exercise, and Physical Fitness” , “Exercise Guide 2006” , and “Japanese Food Guide Spinning Top” . Participants typed in their recent dietary and exercise records, and they received their results and feedback from TFAS. Thereafter, they were instructed to watch 60 min of the video lecture about diet and exercise. This program was directed by a specialist in health science. There was no enforcement of specific diet or exercise since this guidance was intended to enhance motivation to improve health. The initial session of Specific Health Guidance  took a maximum of 80 min; therefore, the intensity of our trial seemed to be equivalent.
ITG underwent non-surgical periodontal treatment and/or prosthodontics, while CTG would receive their dental intervention after the study period. Three months was considered as the ethical limit to keep the controls away from undergoing needed dental treatment. Non-surgical periodontal treatment included tooth-brushing instruction (TBI) and supra/subgingival scaling and root planing (SRP). Prosthodontic treatment was performed for patients with missing tooth/teeth according to Eichner’s classification: A2, A3, B1, B2, B3, B4, C1, C2, and C3. Fixed partial dentures and removable partial dentures were used to fix the defects. For patients who needed both interventions, periodontal treatment was performed first, and then the prosthodontics was performed next. Six dentists with > 6 years of clinical experience had performed the dental intervention as operators. As a coordinator, a dentist who was not involved in dental intervention for participants, performed randomization and dietary and exercise guidance, outcome assessment, and statistical analysis.
The three following outcome measurements were obtained: first, before intervention (BL); second, 1 month after intervention (1M); and third, 3 months after intervention (3M). To avoid missing data, the investigator re-checked the questionnaires after participants had filled them. The primary outcome of this study was focused on waist circumference, which is the simplest method to assess visceral fat accumulation with accuracy . Waist circumference was measured horizontally around the navel in an upright standing posture. Along with the primary outcome, secondary outcomes, such as blood pressure, blood sample test, and anthropometric measurements using body composition analyzer, were assessed.
Blood pressure was measured to determine the presence of hypertension. The patient’s arm was stretched and positioned at the level of the heart in an upright sitting position. Thereafter, the cuff band was wrapped around their arm at the brachial artery. Subsequently, the blood pressure was measured using an electronic sphygmomanometer (OMRON digital automatic sphygmomanometer HEM-1000) . Blood samples were taken to determine hyperglycemia and dyslipidemia through the following indices: TG, HDL, low-density lipoprotein (LDL), FBS, and HbA1c levels. Further, 10 ml blood samples, taken from each patient at the cubital fossa, were then centrifuged and analyzed. Patients were asked to fast for at least 6 h before the tests.
TANITA MC-780A , a multi-frequency body composition analyzer, was used for the anthropometric measurements. Weight, BMI, body fat percentage, body fat mass, lean body mass, body muscle mass, estimated bone mass, body water mass, and body water percentage were scanned and assessed.
The number of teeth present was counted. Thereafter, the following dental measurements were performed to assess the periodontal statuses of patients: pocket depth (PD) and bleeding on probing (BOP), measured at six sites per tooth.
The sample size estimation was calculated from the change in waist circumference based on an RCT conducted by Munakata . A difference in waist circumference > 3.0 cm (standard deviation: 5.0 cm) within the two groups was regarded as statistically significant. Following the normal distribution of waist circumference, 80 participants were needed to obtain a significance level of 0.05 along with 95% confidence interval. Considering the dropout rate of 20%, 100 participants (50 in each group) were determined to be the goal of recruitment. For the randomization, sealed opaque envelope system was used to randomly allocate participants into ITG and CTG. For each patient, the coordinator had picked up sealed opaque envelope, and then the treatment allocation was generated. The allocation was written on a paper, which was folded with silver paper, and then was sealed into an opaque envelope. Coordinator had opened the envelope after writing the patient’s name onto the envelope. Also, the coordinator had done the preparation of envelopes and enrollment of participants and the assignment of participants. This trial was carried out as double-blinded parallel group RCT, since both the participants and the operator had been unaware of the allocation. Participants were blinded from the group allocation because they were not informed about the groups to which they belonged nor their study schedule. Operators were blinded because the coordinator scheduled the treatment, and they were unaware of the allocation. However, the blinding of the coordinator who performed both the allocation and assessment had been impossible.
Student-T test was applied for assessment between groups at baseline, and comparison between dropouts and those who retained. One-way analysis of covariance (ANCOVA) was applied to analyze the difference between the two groups in each assessment of the primary and the secondary outcomes. The difference between each assessment within groups was analyzed using repeated analysis of variance (Repeated ANOVA). Subgroup analysis for patients with missing teeth and those with periodontitis alone was performed to assess the deviation from treatment types using ANCOVA. Analyses were performed using SPSS Version17 software (IBM Japan) . Significance level of 0.05 has been used in each analysis.