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Year : 2019  |  Volume : 16  |  Issue : 1  |  Page : 24-31

A pilot study of the maximum interincisal distance among adult Northern and Southern Nigerians

1 Department of Oral Maxillofacial Surgery, Faculty of Dentistry, Obafemi Awolowo University, Ile-Ife, Nigeria
2 Department of Preventive Dentistry, Obafemi Awolowo University, Ile-Ife, Nigeria
3 Oral Diagnostic Sciences Department, Faculty of Dentistry, Bayero University, Nigeria; Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
4 Family Dentistry Department, Faculty of Dentistry, Bayero University Kano, Nigeria
5 Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan

Date of Web Publication5-Mar-2019

Correspondence Address:
Dr. Fadekemi Olufunmlayo Oginni
Deptartment of Oral Maxillofacial Surgery, Faculty of Dentistry, Obafemi Awolowo University, Ile-Ife, Osun State - 220005
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/njbcs.njbcs_44_17

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Objective: To study the average maximum interincisal distance (MID) and its association with individual physical parameters and dietary pattern in a representative convenient sample of healthy adult Nigerians from two ethnic groups. Materials and Methods: This was a pilot cross-sectional study of healthy adults, free of temporomandibular joint (TMJ) disorders, aged 18–58 years in Ile-Ife (Southwest Nigeria) and Kano (Northwest Nigeria). MID, body weight, and height were determined using a clean wooden spatula on a transparent plastic linear gauge, calibrated body weight electronic scale, and wall-mounted height scale, respectively. Dietary habits and history were assessed using a validated structured questionnaire. MID was compared in each group and related to subjects' age, sex, height, and weight. Results: Of 853 subjects screened, 794 (93.1%), aged 18–58 years, met the inclusion criteria. About 393 (49.5%) and 401 (50.5%) subjects were from the Northwest (Kano City) and Southwest (Ile-Ife), respectively. The mean age of the subjects from the Northwest and Southwest Nigeria was 35.4 years and 26.7 years, respectively, and M:F ratio was 1:1.02. Female subjects recorded higher body mass index (BMI) and were slightly older than the males. Mean MID (SD) values in millimeters were 45.68 (6.7), 47.60 (7.73), and 46.69 (7.29) in the Southwest, Northwest, and combined groups, respectively. MID was significantly higher in males than females, peaked at age 33 years in both the sexes and, thereafter, decreased with increasing age. Conclusion: The MID vary with ethnic origin, weight, height, age, and BMI. A peak MID in adult appears to exist at about 33 years.

Keywords: Adult, body mass index, interincisal distance, maximum, mouth opening, Nigerians

How to cite this article:
Oginni FO, Akinyemi JO, Bamgbose BO, Famurewa BA, Oginni OC, Kaura MA, Asaumi J. A pilot study of the maximum interincisal distance among adult Northern and Southern Nigerians. Niger J Basic Clin Sci 2019;16:24-31

How to cite this URL:
Oginni FO, Akinyemi JO, Bamgbose BO, Famurewa BA, Oginni OC, Kaura MA, Asaumi J. A pilot study of the maximum interincisal distance among adult Northern and Southern Nigerians. Niger J Basic Clin Sci [serial online] 2019 [cited 2020 Feb 28];16:24-31. Available from: http://www.njbcs.net/text.asp?2019/16/1/24/253411

  Introduction Top

The assessment of mouth opening is done routinely during patient examination and as a preoperative assessment for surgical and dental intraoral procedures. Maximum interincisal distance (MID) assessment is important in the management and follow-up of conditions such as maxillofacial fractures, orofacial infections, trismus secondary to scleroderma, oral submucous fibrosis, among others, and is useful in the design of dental prosthesis/instruments.[1],[2],[3] Limited mouth opening is associated with temporomandibular disorders, some neurogenic dysfunctions, advanced orofacial malignancies, coronoid process hyperplasia, possible sequelae of third molar disimpaction, and head and neck radiotherapy and it is a challenge during intraoral procedures.[4],[5],[6],[7],[8],[9] Limited mouth opening undermines efficient mastication and maintenance of oral hygiene.[10] MID, also referred to as maximum mouth opening (MMO), is a vital and objective clinical parameter for assessment of stomatognathic region and it represents the range of vertical mandibular range of movement.[11],[12],[13]

MID is defined as the distance between the mesioincisal edge of the maxillary central incisors and the mesioincisal edge of the mandibular central incisors with the mouth as widely open as possible.[1],[13] There is a wide variation in the values of MID with age, sex, and race.[2],[6],[8] There are reports that MID reduces with advancing age and is less in females compared to males of same age,[14],[15] while another study concluded that MID correlates less significantly with age and facial types than with stature.[3]

The normal range of mouth opening are relative to age, sex, and race, and these variables are important in the assessment and diagnosis of limited mouth opening.[2],[16],[17] To the best of our knowledge, there are two published Nigerian studies determining range of mouth opening among Nigerians. The study population for the studies was drawn from Nigerians in the southern part of the country.[17],[18] The results from these studies do not represent the age, sex, and ethnic differences among Nigerians.[8],[14],[19] The aim of our pilot study was to determine the range of MID in a representative adult Northern and Southern Nigerian population.

  Materials and Methods Top

This pilot cross-sectional and analytical study was conducted among a convenient sample of healthy adult Nigerians aged 18–58 years living in the Northwest and Southwest geopolitical zones of the country between April and July 2016. The Southwest geopolitical zone subjects were selected from Ile-Ife, representing the predominantly Yoruba Ethnic Nationalities, while the Northwest subjects were selected from Kano City, representing the predominantly Hausa Ethnic Nationalities. Potential subjects were randomly recruited from the Obafemi Awolowo Teaching Hospital and Aminu Kano Teaching Hospital. The details of the study, nature, and purpose of data collection were explained to the potential subjects in English language and it was also translated into Yoruba and Hausa languages for individuals who did not understand English language. Only potential subjects who gave verbal informed consent were recruited in the study. The consent was documented into the record files of the individuals. The inclusion criteria, apart from informed consent, included individuals with functional occlusion, no excursive interferences, and full complements of maxillary and mandibular anterior teeth. Individuals with missing or fractured central incisors, a history of temporomandibular joint (TMJ) dysfunction, dental or skeletal crossbite, and major dental treatment (orthodontics, orthognathic surgery, or extensive restorative therapy) within the last 3 years were excluded. Potential subjects who volunteered history of craniofacial trauma, oral facial infections or malignancies, bruxism, or those using dental prosthesis were excluded from the study.

A pre-tested and validated questionnaire [Appendix 1] was designed to determine socio-demographic characteristics, history of temporomandibular dysfunction, previous surgery, habits, weight, height, and body mass index (BMI) were administered to all subjects.

Subjects' weight and height were measured with a calibrated electronic body weighing scale and a wall-mounted plastic linear gauge, respectively. The linear gauge was positioned at the vertex of the subject's head to read off the height. The extraoral, intraoral, and TMJ examinations were conducted by two calibrated investigators at each center who wore examination gloves and face masks. During the TMJ examination, the presence or absence of joint clicks, crepitation, and pain were determined. The MID was determined as maximum distance between mesioincisal edges of maxillary and mandibular central incisors at the midline, upon full mouth opening. The MID was measured by placing a clean, single-use wooden spatula against the maxillary and mandibular incisors at MMO. Two points coinciding with the mesioincisal angles of the maxillary and mandibular incisors were marked off on the flat surface of the spatula. These markings were placed against a transparent plastic linear gauge to read off the mouth opening. The measurement was repeated three times at 2–3 min interval and the mean value of maximum incisal opening was recorded. The three measurements should be within 2 mm difference. Any reading differing by >2 mm was discarded and the measurement repeated.

The data were recorded on a spreadsheet and analysis was done using the statistical package for social sciences version 17.0 (SPSS) software. The MID was compared for age, sex, height, and weight. The quantitative data were presented descriptively and as mean ± SD along with the minimum and maximum values. Comparison of age and mouth opening was done in males and females using an independent sample test. Bivariate Pearson's correlation and scatter plot were done to determine the relationship between age, sex, BMI, (including normal/underweight and overweight/obese) location, diet type, and mouth opening. Statistical significance was inferred at P value ≤0.05.

  Results Top

A total of 853 potential subjects were recruited for the study and 794 (93.1%) met the inclusion criteria. About 393 (49.5%) and 401 (50.5%) subjects were from the Northwest (Kano City) and Southwest (Ile-Ife), respectively. The subjects were aged 18–58 years, with a mean of 31.0 (9.3) years. The overall sex distribution was nearly even, with a male to female ratio of 1:1.02. The educational attainment of the subjects is shown in [Figure 1]. Thirty seven percent (37.1%) had university education, while 47.2% had secondary education.
Figure 1: Educational attainment

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The mean (SD), median, mode, and range of subjects' age, weight, height, and BMI are shown in [Table 1] and [Table 2]. Male subjects were generally taller than females, but females were slightly older and had greater BMI than males. Although overall, males weighed more than females but females in the Northern sample weighed more than males.
Table 1: Distribution by the age group and sex

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Table 2: Distribution of physical characteristics by sex in both groups and the combined group

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The subjects' mean (SD) and range MID by their sex and age are shown in [Table 3]. A statistical significant difference exists in the MID values between males and females in the Southern Nigerian sample and in the combined (North and South) sample (P < 0.0001). The Northern group did not attain a significant level of difference. [Table 4] and [Table 5] show that MID values tend to increase with increasing weight and consistently higher in males than females. The difference between males and females in the southern and combined samples attained statistical significance (P < 0.001). Stratified by their heights, MID values increased with increasing heights in all groups, however, this pattern attained statistical significance in the Southern Nigeria and combined samples (P < 0.001) and not in the Northern sample. A positive correlation was found between MID and subjects' height, weight, sex, BMI, occupation, and ethnicity (P values < 0.05). However, we could not establish a correlation between MID and diet type, habits, age, and marital status (P > 0.05). The pattern of BMI differed significantly between male and female subjects in the Southern and combined samples (P = 0.0005 and 0.00037, respectively) but not in the Northern sample [Figure 2]. Obesity was significantly prevalent in females than males [Table 6]. The proportion of underweight and normal weight males exceeds the females. MID in our subjects increased with increasing BMI. Subsequently, a decline is observed until Class II obesity and a rise toward Class III obesity. Subjects weighing 77–87 kg reported the highest MID with mean 49.11 mm, while the lowest mean 42.79 mm was in respondents weighing 44–54 kg. Most subjects (60.0%) had normal BMI values ≤24.99 kg/m2 and only 8.6% were obese. The diet type among respondents was mostly a combination of tough fibrous and processed meals (58.0%). About 21.9% take mostly processed food and 20.0% eat mainly tough fibrous diets. MID differed significantly between these diet groups (P = 0.022). [Table 7] shows the summary of the Student's t-tests with subjects grouped by location, sex, and weight. Subjects' marital status, diet type, occupation, weight, MID, and BMI differ significantly by their ethnic group. Between male and female subjects, the marital status, height, BMI, and average MID differed significantly [Figure 3]. When grouped by weight, there was a significant difference in subjects' age, sex, marital status, height, BMI, and average MID.
Table 3: Distribution of the subject's mean and range MID by age group and sex

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Table 4: Distribution of mean and range MID by subject's weight and sex

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Table 5: Distribution of MID by subjects' height and sex

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Figure 2: Distribution of body mass index among subjects

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Table 7: Independent t-test analysis grouping subjects by location, sex, and weight

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Figure 3: A bar chart illustrating the mean maximum interincisal distance among males and females in the present study and previous studies

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  Discussion Top

Understanding the range of maximal, voluntary, physiologic, and painless mouth opening is necessary for the practice of dentistry, oral and maxillofacial surgery, and otorhinolaryngology. In our practice, we encounter limited mouth opening in patients with TMJ disorders, infections, malignant neoplasms, ankylosis, and trauma and the management of such cases require the restoration of normal mouth opening. It is, therefore, important to establish a range of normal mouth opening as a baseline for any population. From literature search, this is the third study conducted among Nigerians but the first to have samples stratified along ethnogeographic lines i.e., Northern Ethnic Group (Kano) and the Southern Ethnic Group (Ile-Ife). We measured mouth opening as the vertical distance between the mesioincisal angle of the maxillary and mandibular central incisor. This represents the range of functional jaw movement and the MMO or MID.[4],[7],[13],[20],[21] Some authors have suggested that the overbite should be added to the interincisal distance to get a more accurate measurement of the vertical mandibular movement.[4],[22] We do not consider this addition necessary because the overbite is opened up at a state of MMO. The common instruments used for measuring MID include, a pair of dividers, the Boley's gauge, and Vernier caliper.[14],[17],[18] Dosumu et al.[17] suggested the use of a more sophisticated instrument such as electronic goniometric device and pachymeter.[4],[13] The results from studies conducted with these devices did not differ from other studies that used less sophisticated instruments.[13],[14],[16],[17],[18] We used a clean wooden spatula and a transparent plastic linear gauge because of cost and the need to minimize cross-infection. There is no clear explanation for a preponderance of males in our study. This finding contrast the study among the Chinese and Irish.[14],[16]

Dosumu et al.[17] and Chima and Obiechina[18] reported greater average values of MID than we found in males and females in the present study. Our results, however, are in agreement with a few non-Nigerian studies.[2],[4],[5],[6],[8],[11],[14],[16] We attribute the differences partly to the variations in age group of subjects, sample size, multiethnic group and, possibly, an evolving dietary pattern. The age group of subjects in the present study is similar to other studies.[1],[4],[6],[13],[14],[17] However, some authors studied younger subjects and they reported lower mean MID which was found to increase up to a peak at age 14 years.[3],[5],[8],[11] In our study, MID increased to a peak at 26–33 years and decreased toward age 58 years. It is our opinion that a bimodal peak MID possibly exists at ages 14 and 26–33 years.

The dietary pattern appears to have an association with the MID. In the present study, most subjects admitted to taking a mixture of tough fibrous and processed diet. The traditional Nigerian diets are essentially fibrous. The pattern of MMO in males compared to females in our study is in agreement with finding in other studies.[2],[3],[5],[14],[16],[18] Men were taller than women in the present study and we found a positive correlation between height and MID. The MMO of individuals from the North appeared to be higher than individuals from the South. It is not clear if the dietary pattern in the North compared to the South or the preponderance of males in the study population in the North and variation in face type could be responsible for this observation. Fatima et al.[3] found an association between face types and MID in Kolkata children. Variation in face type and its association with MID has not been investigated in the African. We observed a positive correlation between MID and weight, similar to other studies.[3],[6],[17] However, there was no correlation between BMI and MID.

  Conclusion Top

The MMO of individuals from the North is higher than individuals from the South and is influenced by sex, height, and weight. There is a bimodal peak MID at ages 14 and 26–33 years. We identified a need to study the pattern of MID in younger Nigerian population and relate it to face types.


The authors acknowledge the cooperation of all subjects recruited for the study.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]


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