The study was conducted in January–February 2016 and took place in Mara North Conservancy in Narok County of Kenya. Mara North Conservancy was established in January 2009 through a partnership among eleven member camps and over 800 Maasai landowners with long-term commitments to the environment, wildlife, and local communities.
The study population consisted of adolescents aged 14 to 18 years. They were recruited from the four primary and one mixed secondary schools present in Mara North Conservancy. Out of the total number of teenagers in this age group (n = 340), 284 (83.5%) teenagers [mean age: 15.0; SD 1.1; range 14–18 years] were recruited into the study. These were teenagers whose parents/guardians provided a written informed consent for their participation in the study. The teenagers, not included in the study, were those who failed to provide the consent, were absent, or sick on the day of the examination. The age of the participants was determined from the records kept by the schools, except for three of the teenagers, whose age records were missing in the school register. The distribution of the participants according to gender was 153 (55.6%) males and 122 (44.4%) females (information on gender had unintentionally been omitted in the record sheet for nine teenagers). Information on social and economic status of the teenagers and their families was not available to the researchers. The few schools (n = 5) in Mara North Conservancy, Narok County, are boarding schools, as the possibilities for transportation within the region is scarce and challenging. Thus, most often parents live far away from the schools. All schools were considered to be at a similar standard and with similar physical and educational possibilities.
The study consisted of two parts, one being a face-to-face interview with the teenagers using structured questionnaires to collect data on age, gender, medical history, IOM practice, and OHRQoL, while the second part included an examination of the participants` teeth present in the oral cavity, including oral photographing of the dentition.
Face-to face interview
Structured questionnaires were used to collect data on age, gender, medical history, IOM practice, and OHRQoL. In order to prevent copying of answers to the questionnaire amongst the participants from the same school class, a clear separation method was applied to prevent intermingling of the participants, until the interviews were finalized.
The OHRQoL part was assessed by the validated Child Perception Questionnaire (CPQ11–14), which is developed to measure the OHRQoL among teenagers [23, 24]. The CPQ includes 37 questions grouped into four domain subscales: oral symptoms, functional limitations, emotional well-being, and social well-being. The response format for all questions is a Likert-like scale. The response options and scores are: “never” (score 0), “once or twice” (score 1), “sometimes” (score 2), “often” (score 3) and “every day or almost every day” (score 4). The range of the additive total CPQ score is 0–148. The ranges of domain subscale scores are 0–24 (oral symptoms), 0–36 (functional limitations and emotional well-being), and 0–52 (social well-being). In addition, the CPQ includes two global questions: Q1) “How would you describe the healthiness of your teeth, mouth, lips or jaws?” (very good, good, okay, or bad) and Q2) “How much does the condition of your teeth, mouth, lips or jaws influence your life?” (not at all, very little, some, a lot, or very much).
The questionnaire for the collection of data on age, gender, medical history, and IOM practice was initially piloted and tested by the two Kenyan authors (AK and TM) concerning the understandability and relevance in a Kenyan context before being used. Further, the Kenyan authors were also the dentists who had the contact with the teenagers when they were interviewed, meaning that the teenagers had the possibility to ask probing questions in English or local languages. The original CPQ questionnaire is written in English [23, 24], and the spoken language in Kenya is English. The English CPQ questionnaire has been validated in other English-speaking communities [23, 24], but it has not been validated specifically in the Kenyan population. As a supplement, the CPQ questionnaire was also translated to the local tribe language of the Maasai population, in case a need arose of having the English version of some or all the questions in the local language for clarification. In addition, the participants did not fill out the questionnaire themselves, but the procedure was carried out by the interviewer and any assistance, if needed, was available from the Kenyan co-authors of the present paper. In practice, there was, however, no need for the translated questionnaire as only probing questions were asked by some participants and subsequently explained by the interviewers. The two interviewers were Kenyan dental researchers from University of Nairobi, Kenya, and they were trained in using the questionnaires, and in addition, they calibrated the interview procedure under field conditions after the finalization of the initial two interviews.
The oral examination was done under field conditions at the respective schools of the teenagers. This means that oral examinations were not performed in a dental office, but in a standard class room with natural lighting. No sophisticated dental equipment was available. The child was made to lie on the top of a table, facing a natural light source. As supplementary light source, a headlamp was used to augment the natural light during the examination of the oral cavity. With clean disposable mouth mirrors and tweezers, an oral examination was carried out to establish the status of the dentition and the dental occlusion. A record on the number of teeth present in the mandibular incisor and canine segments and signs of dental disruption was made on individual forms. Teeth were recorded as present when either partly or fully erupted. A tooth was recorded as having a dental disruption, if the tooth had an abnormal and irregular morphology with unusual hypoplastic defects consistent with previous germectomy in the affected area of the dental arch. Thus, dental disruption was defined as an extrinsic hypoplastic defect or interference with the normal developmental process of the tooth. Dental fluorosis was seen in the study population, but was not an aim to study in the present study. An IOM case was defined as an individual who was missing two or more permanent teeth in the mandibular incisor and/or canine tooth segments, as a result of IOM (also confirmed during interview). Intraoral photographs were taken as a part of the record, with the teeth in occlusion from right, left, and frontal perspective.
The dental occlusion was assessed according to definitions by Bjoerk, Krebs and Solow  and included measurement of the horizontal overjet (HO) and the vertical overbite (VO) with a caliper, classification of HO into mandibular overjet (HO ≤ 0 mm), neutral overjet (0 mm < HO ≤ 5 mm), maxillary overjet (5 mm < HO < 9 mm), or extreme maxillary overjet (HO ≥ 9 mm), and classification of VO into neutral overbite (0 mm ≤ VO ≤ 4 mm), deep bite (overbite ≥5 mm), or frontal open bite (VO < 0 mm). Furthermore, the molar occlusion on each side of the participants was assessed and classified as neutral (the mesiobuccal cusp of the maxillary permanent first molar occludes into the mesiofacial sulcus of the mandibular permanent first molar), distal (mandibular first molar deviates distally to neutral occlusion ½ cusp or more), or mesial (mandibular first molar deviates mesially to neutral occlusion ½ cusp or more). For each side, deviations from normal transverse occlusion was classified as cross bite (the buccal cusp of at least one maxillary canine, premolar, or molar occludes lingual to the buccal cusp of the mandibular teeth) or scissor bite (the lingual cusp of at least one maxillary canine, premolar or molar occludes buccal to the buccal cusps of the mandibular teeth).
Prior to the initiation of the study, training of the researchers, to standardize the methods to be applied, was carried out by studying pictures available in the published literature as well as clinical photos taken of the participants on the first day of the study period. Due to the limited working time at the research site, recall of patients for traditional intra-reliability evaluation was not an option. Only two dentists examined the children (HG, MLMN), while two other dentists (ML, DH) did the recording of the results and the oral photographing. Concerning the inter-rater reliability, the two clinical examiners did an examination twice of 12 participants randomly chosen among the 284 participants. The examinations done twice were executed with four students at the initiation of the study and with two participants another four times during the remaining part of the study. A maximum of (12 × 32 teeth) 384 teeth were included in the double examinations among which a total of 327 (85.1%) were actually found to be present in the oral cavity. Concerning the recording of the teeth present in the oral cavity and the teeth with dental disruption, the percentage agreement between the two examiners were 100%. The missing teeth recorded during the 12 examinations were 35 third molars, 4 s permanent molars, 15 mandibular permanent central incisors, two mandibular permanent canines, and one maxillary permanent canine.
All the children at the participating schools received free education on oral hygiene with a toothbrush and toothpaste provided to them for continued use in school/at home. The participants, who required emergency dental treatment, were referred to the nearest dental clinic or the Dental Hospital of the University of Nairobi.
The data collected were cleaned, coded, and entered into the computer, and analyzed with the use of SPSS 24 (Statistical Package for the Social Sciences, SPSS Inc., Chicago, IL) and STATA 14.0 (StataCorp LLC, Texas, USA). The number of maxillary teeth was compared to the number of mandibular teeth. The total number of missing maxillary incisors and canines was compared to the total number of missing mandibular incisors and canines. For studying the potential consequences of missing teeth due to IOM in the anterior segment of the mandible in relation to the dental occlusion, the IOM group was defined as participants with two or more missing mandibular incisors and/or canines. The group of participants, in whom all mandibular canines and incisors were present, was defined as the control group. Sixteen participants with the absence of only one mandibular permanent incisor or canine were excluded from the comparison between groups due to one missing tooth being below the defined cut-off level.
Overall CPQ11–14 score and domain scores for each participant were calculated by summing the response codes for the questions. If one or more of the questions in a domain were unanswered, the respective domain score as well as the overall CPQ11–14 score was recorded as missing for that participant. The mean additive score of each domain as well as the mean overall CPQ11–14 score were calculated and indicate the severity of impact on OHRQoL in the respective domains . For the CPQ11–14 scale as a whole and for each of the four domains, the number of answers, being reported as “often” or “every-day/almost every day”, were counted. The mean of these figures indicate the extent of severe impact on OHRQoL in the respective domains. The percentage of individuals answering “often” or “every-day/almost every day” was calculated and indicate the prevalence of severe impact on OHRQoL in the respective domains . In addition, the median additive scores in the respective domains as well as the median overall CPQ11–14 score were calculated due to the scores not being normally distributed.
Deviations on the dental occlusion and in the answers on IOM and CPQ were assessed according to the defined grouping of participants with or without IOM.
Statistical tests in terms of t-test, Wilcoxon rank sum test (Mann-Whitney), Fischer’s exact test, and Chi-square were carried out as appropriate.