Design and participants
The Institute of Tropical Medicine at Nagasaki University established the Health and Demographic Surveillance System (HDSS) in 2006 in Mbita Constituency, Homa Bay County in Kenya, which is located approximately 300 km west of Nairobi, Kenya. The HDSS program recruited 11,182 households and 55,929 inhabitants on July 1, 2011. From the list of names of recruited individuals in the HDSS, 150 individuals aged 65 years and over were randomly selected from four sub-locations in Mbita Constituency. The sampling rate of this study was 35% (150/434). The home visit study was conducted from 2014 to 2016 in the following sub-locations: Mbita center and south sub-location in 2014, east sub-location in 2015, and middle-south sub-location in 2016. Before commencing the home visit study, community health workers engaged in the HDSS program, visited the participants’ houses, and explained the purpose of the research, and made an appointment for the home visit. Informed consent was obtained at the time of the home visit by the authors after the purpose of the study was comprehensively explained to the participants.
A total of 131 participants provided informed consent, received a dental examination, and completed a questionnaire (collecting rate is 87.3%). One of the authors, a dentist (H.F.), examined the dental status of the participants by assessing the participants’ teeth using a disposable dental mirror and a portable light. The examination was performed outside the homes with the participants seated on an ordinary chair under direct sunlight. Dental status was assessed using the World Health Organization standards. The number of teeth present was counted, including the number of sound teeth, decayed teeth, and roots of the teeth. The present teeth ranged from 0 to 32. Functional tooth units (FTUs) are points derived from adding the number of pairs of molar and premolar. One pair of molars and one pair of premolars are equivalent to 2 points and 1 point, respectively, based on FTUs. FTUs range from 0 to 12 points per participant. If retained dental roots of the molars and/or premolars were observed, they were not counted as a pair.
Perceived general health was measured by answering “good,” “average,” and “bad” to the question “How is your general health?” Perceived general health was divided into the following two categories: “good/average” and “poor.” Data on subjective masticatory ability and periodontal symptoms “gum bleeding” and “tooth mobility” were also collected using self-recorded questionnaires.
Any participant having severe tooth pain and oral lesions were treated by prescribing medication and referring the participant to the nearest dental facilities by one of the authors, a Kenyan dentist (E.W.). None of the participants experienced severe tooth pain requiring medication or referral. A visual oral examination was performed without periodontal probing. Therefore, measuring the periodontal pocket depth was not possible. Traditional extraction of lower anterior incisor and canine teeth (33 to 43), which is common in the elderly population, was verbally confirmed by the participants.
Data analysis
A difference in percentages was tested using the chi-squared test and Fisher’s exact test. The mean number of teeth present was not a normal distribution. Therefore, the difference in the number of teeth present and FTU points based on the participants’ characteristics and perceived general health was verified using the Mann-Whitney U test and the Kruskal-Wallis test. The odds ratio of good general health based on the participants’ masticatory satisfaction was calculated by logistic analysis. All statistical analyses were performed using the IBM SPSS version 20.0. The level of significance was set at 5%.
Ethics approval
This study was conducted in full accordance with the World Medical Association Declaration of Helsinki. The study was approved by the ethics and research committee of the Kenyatta National Hospital/University of Nairobi (P328) on August 7, 2013.