Introduction

Habits are formed when there is a tendency towards an act that has become a repeated performance, relatively fixed, consistent and easy to perform by an individual (Zwemer et al. 2008). Oral habits include sucking habits (digit and lip sucking), biting habits (lip, nail and object biting) tongue thrusting and bruxism.

Sucking is vital in the early development of an infant: it is essential for receiving nutrition, providing stability in distress and for exploring the environment (Harding et al. 2006). Some foetuses suck their digits in utero while the vast majority of infants do so during the first 6–24 months of life (Proffit et al. 2007). Infants grasp and put objects in their mouth during the first year of life to gain a sense of its size and shape, the sensori-motor stage of cognitive development (Berger 2008). During this stage, infants progressively construct knowledge and understanding of the world by coordinating experiences with physical interactions such as sucking on objects (Santrock 2008).

Sucking habits become detrimental to oral health when it persists beyond infancy. Sucking and other habits are associated with short and long term dental and orthodontic problems (Silva and Manton 2014b). They are determinants of malocclusion among pre-schoolers (Correa-Faria et al. 2014). They often have a negative impact on the developing occlusion (Lagana 2013a; Correa-Faria et al. 2014; Silva and Manton 2014b): the magnitude of which depends on the frequency, intensity and duration of practice.

Oral habits also have some benefits such as decreased caries incidence and a significant reduced risk of Sudden Infant Death Syndrome (Hauck et al. 2005;Yonezu and Yakushij 2008; American Academy of Paediatrics 2011). Bazysk (1990) also suggested that non-nutritive sucking for premature infants receiving tube feeds accelerates the transition from tube to oral feeding by allowing infants to practice using their oral motor musculature.

Prior studies had determined the prevalence and effects of oral habits on the oral health of children resident in urban areas of Nigeria (Onyeaso 2004; Quashie-Williams et al. 2010; Adegbite et al. 2012), they all highlighted deleterious effects of oral habits on the occlusion. None had however evaluated the cumulative effect of the frequency, intensity and duration of practice of oral habits on occlusion. The aim of this study was not only to determine the prevalence of oral habits in children aged 1–12 years resident in Ife Central Local Government Area of Osun State Nigeria—a sub-urban area; but also to determine the association between oral habits and malocclusion in children aged 6–12 years, identify the differences in the treatment needs of those with and without oral habits; and to determine the impact of the severity of digit sucking on occlusal profile.

Materials and methods

The methodology for this study had been earlier reported by Folayan et al. (2014) and Kolawole et al. (2016). This paper reports on some of the primary objectives of the study which was to determine the prevalence of oral habits and the association between oral habits and malocclusion in children aged 6–12 years in the study location. The data was collected through a household survey. Participants were recruited from Ife Central Local Government Area of Osun State. Ife Central Local Government Area is a semi-urban area; a different location profile from prior studies conducted on oral habits and malocclusion in Nigeria (prior studies were conducted in urban areas). It was chosen as the study location because it hosts the institutions of the authors thereby easing the logistics associated with the conduct of a household survey.

Study population

Participants were recruited if they were between the ages of 1–12 years, and their biological parents or legal guardians consented to participate in the study. Only children who were present in the home at the time of data collection were eligible to participate in the study.

Sample size determination

Sample size was calculated using Leslie Fischer’s formula (Araoye 2003) for study population > 10,000. Based on a prevalence of 34.1% for oral habits in Nigerian children (Quashie-Williams et al. 2010), it would be necessary to examine 1011 children to identify 345 children with oral habits, with a drop-out rate of about 10%.

Sampling technique

A multi-stage sampling procedure was adopted. Stage 1 involved the random selection of enumeration areas within the Local Government Area: eight out of the 25 enumeration areas within Ife Central Local Government Area designated by the National Populations Commission during the 2006 National census exercise was selected by balloting. Stage 2 involved identification of the household from which study participants will be recruited. At the enumeration site, every third household on each street was considered for study participant recruitment. Stage 3 involved identification of eligible individuals within households. Only one eligible child in each household was selected to participate in the study. Recruitment continued in the enumeration sites until the study sample per data collector was reached.

Data collection tool

Data collection was through face to face interviews using a structured questionnaire. Mothers were requested to respond to the questionnaires on behalf of children who were below 8 years old. They provided information about the socio-demographic profile of the child, medical and dental history, oral health practices and details about the presence or absence of oral habits in the children. Where the mother was unavailable, fathers completed the questionnaires.

Questions were asked about type of oral habit practiced by the child. The frequency of engaging in habit was explored with options ranging from ‘irregularly’, ‘once a week’, ‘2–3 times a week’, ‘once a day’ and ‘several times a day’. The duration of engaging in the habit per episode was also explored. Options ranged from ‘less than a minute’ to ‘1–5 min’, ‘5–10 min’, ‘10–20 min’, ‘20–30 min’, and ‘almost continuously’. The intensity of engaging in the oral habit was explored.

Intra-oral examination

All the children that participated in the study had an oral examination conducted in their homes on the day of study visits. The children were examined under natural light while sitting down on a chair, using sterile dental mirrors by trained dentists. Radiographs were not used in the study. Intra-oral examination was conducted to determine the presence of various malocclusion traits, assessment of malocclusion was performed using the Dental Aesthetic Index (DAI) (Cons et al. 1986) for children aged 6–12 years.

The DAI is an orthodontic index that links clinical and aesthetic components mathematically to produce a single score. It consists of 10 components namely number of missing visible teeth (incisors, canines, and premolars) in the maxillary and mandibular arches, crowding and spacing in the incisal segments, midline diastema, anterior irregularity in the maxillary and mandibular arches, anterior maxillary overjet and mandibular overjet (mandibular protrusion), vertical anterior open bite and the antero-posterior molar relationships. Scores for each of these morphologic characteristics are determined by direct measurement. Regression coefficients are used as the relative weights for each of these 10 morphologic characteristics. The multiplication of these scores by the weighting factor (regression coefficient), a summation of these products, and a constant produces the total DAI score. The World Health Organisation (WHO) has adopted the DAI as a simple and universally accepted index, which can be used in epidemiological surveys to assess unmet orthodontic treatment need, and a screening tool for determining priority for orthodontic care in public financed programmes (WHO 1997). The DAI scores were graded into four groups based on the pre-defined DAI categories (Cons et al. 1986; Otuyemi et al. 1998):

  • Scores of 13–25 represent Grade 1: ‘normal or minor’ malocclusions with slight or no treatment need;

  • Scores of 26–30 represent Grade 2: ‘definite’ malocclusions with treatment considered elective;

  • Scores of 31–35 represent Grade3: ‘severe’ malocclusions with treatment highly desirable;

  • Scores of 36 and higher represent Grade 4: ‘very severe or disabling’ malocclusions with treatment considered mandatory.

Extra-oral examination

Extra-oral examination of upper extremities were carried out to look for signs of digit sucking such as a clean digit, redness, wrinkling chapped or blistered finger, dishpan thumb, fibrous roughened wart like callus on superior aspect of digit, ulceration, corn formation, finger deformity, short upper lip. The details of the extra-oral findings were recorded for each child.

Severity of digit sucking habit

To arrive at a measure of the severity of the digit sucking habit, a composite score was developed as highlighted in Table 1. The following parameters were used to develop the composite score. Presence or absence of digit sucking habit, frequency of engaging in habit duration, intensity and presence or absence of clinical features of digit sucking on the upper extremities were combined to arrive at the score.

Table 1 Classification of severity of digit sucking
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A negative history of digit sucking was given a score of 0 while a positive history got a score of 1, Frequency of digit sucking was scored as follows “no history of sucking” got a score of 0, “less than once a day” was awarded a score of 1, “once a day” 2 and “several times a day” got a score of 3. For duration of digit sucking “no history” got a score of 0, “less than 10 min per day” was awarded a score of 1, “10–30 min per day” 2, “almost continually” was given 3; intensity was scored based on audible noise during sucking, where no sucking or popping sound was heard a score of 0 was awarded while an audible sucking or popping sound was given a score of 1. For presence or absence of clinical feature of digit sucking on the upper extremities, “No abnormality on digits was awarded a score of 0, “Clean digits due to digit sucking” 1, “Redness, wrinkled chapped or blistered finger” was awarded 2, while digit deformity ranging from dishpan nail to nail bed damage” was awarded a score of 3. Summation of all parameters gave a total score which was used to assign participants into categories as follows; a total score of 0 which was the minimum obtainable score meant there was no digit sucking habit, scores1–4 were regarded as mild digit sucking, scores ranging from 5 to 8 was moderate digit sucking, while scores of 9 and above indicated severe digit sucking.

Standardisation of examiners

The investigators undertook series of calibration exercises. All investigators were trained qualified dentists who were undergoing their postgraduate resident training. Investigators all work in the field of child dental health either as Paedodontists or Orthodontists. Intra- and inter- examiner variability for caries detection, gingivitis and malocclusion were determined, the intra-examiner variability ranged from 0.89 to 0.94, while inter-examiner variability ranged from 0.82 to 0.90.

Data analysis

Statistical analysis was conducted with SPSS version 20.0. Descriptive analysis was conducted to determine the prevalence of the different oral habits, and the prevalence of malocclusion traits present in the study population. Mean scores of malocclusion grades determined by the DAI were calculated for study participants aged 6–12 years with and without oral habits. Chi square tests were conducted to compare gender differences in the distribution of oral habits, Independent sample t-test was conducted to compare the DAI scores. Statistical significance was inferred at p < 0.05.

Ethical consideration

Ethical approval for the study was obtained from the Ethics and Research Committee of the Obafemi Awolowo University Teaching Hospital Complex Ile-Ife (ERC/2013/07/14). Approval for conduct of the study was obtained from the Local Government Authority prior to commencement of the study. The study was conducted in full compliance with the study protocol. Written informed consent was obtained from the parent of each study participant prior to enrollment after duly explaining the objectives of the study, risk and benefits, voluntary nature of study participation and freedom to withdraw from the study at any time. All children aged 8–12 years also provided written assent in addition to the written consent by parents.

Results

The data of 992 children (90.1% of the proposed 1011 study participants) recruited for the study were complete enough for analysis. This included 508 (51.2%) males and 484 females (48.8%) with a mean age of 5.8 ± 3.2 years. One hundred and thirty (13.1%) study participants had a total of 142 oral habits. One hundred and nineteen children (91.5%) engaged in a single habit, 10 (7.7%) engaged in two habits each, while one child (0.8%) had three habits.

Oral habits

Table 2 shows the age and gender profile of the study participants with and without oral habits. Seventy-five (52.8%) of the 142 oral habits occurred in the 1–5-year-old age group. The highest number of oral habits were identified in the 1-year age group (14.1%), the least occurrences were in the 9 year olds (2.8%). Although more males than females had oral habits, this difference was not significant (7.6% vs 6.6%; p = 0.61).

Table 2 Age and gender profile of participants with and without oral habits (N = 992)
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Table 3 shows the gender distribution of study participants with oral habits. The most common oral habit in the study population was digit sucking: 71 (50%) participants were digit suckers. No participant engaged in lip biting. There were no significant differences in the proportion of males and females that indulged in any of the oral habits.

Table 3 Gender profile of study participants 1–12 years with oral habits (n = 142)
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Fifty-five of the 71 digit suckers (77.5%) engaged in thumb sucking while 16 (22.5%) sucked other digits. Also 15 (21.1%) 44 (62.0%) and 12 (16.9%) digit suckers had mild, moderate and severe digit sucking habits. The most common sign of digit sucking on the upper extremities was clean digits observed in 23 (32.4%). Nine (12.7%) participants had redness of the digit. None had corn formation.

Malocclusion and oral habits

Table 4 shows the malocclusion traits profile of the study participants. The most common malocclusion traits were spacing, crowding and increased overjet observed in 297 (29.9%), 215 (21.7%), and 163 (16.4%) of study participants respectively. Only 36 (3.6%) and 21 (2.1%) of the study population had anterior open bite and buccal cross bite respectively. Also, 13 (18.3%), 25 (35.2%), 12 (16.9%) and 4 (5.6%) of digit suckers had crowding, spacing, increased and reverse overjet respectively.

Table 4 Malocclusion trait profile of children with and without oral habits (N = 992)
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The mean DAI score for study participants aged 6 to 12 years was 20.71 (SD = 4.56). The mean score for male participants was 20.86 (SD = 5.14) and that for female participants was 20.57 (SD = 3.94). There was no significant gender difference in the mean DAI scores (p = 0.48). Four hundred and fifty (90.9%) participants had no orthodontic treatment need. Treatment need was elective for 26 (5.3%) participants, highly desirable for 11 (2.2%) participants, and mandatory for 8 (1.6%) participants.

Table 5 highlights the outcome of the comparison of the DAI scores of study participants aged 6–12 years with and without oral habits. The mean DAI score was significantly higher in participants with tongue thrusting (p < 0.001) and bruxism (p = 0.01) when compared with participants who did not engage in the habits.

Table 5 Comparisons of mean Dental Aesthetic Index (DAI) scores of participants aged 6–12 years with and without oral habits (N = 495)
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Table 6 highlights the treatment needs of the 67 participants with oral habits, fifty-four (80.6%) participants had no need for treatment, 9 (13.4%) needed elective treatment, none of the participants was in the treatment highly desirable category and treatment was mandatory for 4 (6.0%) participants.

Table 6 Orthodontic treatment needs of participants aged 6–12 years with oral habits according to the Dental Aesthetic Index (DAI) (N = 67)
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Table 7 shows the relationship between the DAI scores and the severity of digit sucking; the most frequently practiced habits by study participants. The majority of digit suckers who were in the no need for treatment category practiced mild and moderate digit sucking; the only digit sucker in the mandatory treatment category practiced severe digit sucking.

Table 7 Digit sucking severity and orthodontic treatment need of participants aged 6–12 years according to the Dental Aesthetic Index (DAI) (N = 495)
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Discussion

The prevalence of oral habits was low in the study population, and there was no significant gender difference observed in the proportion of study participants who practiced each oral habit studied. The most commonly practiced oral habit was digit sucking. The most common malocclusion traits identified were spacing and crowding, with very few participants having buccal crossbite and anterior open bite. The majority of participants who engaged in oral habits had no need for treatment. The mean DAI scores of children who had tongue thrusting and bruxism habits were significantly higher than those who had no habits. No difference was observed in the severity of malocclusion between digit suckers and non-digit suckers.

This is the first most representative community based survey conducted to determine the prevalence of oral habits, and associated malocclusion traits in Nigeria. This household survey provides a true representation of the prevalence of oral habits and malocclusion in pre-school and school age children. However, the survey is not representative of Nigeria as the study population is a sub-urban population where the prevalence of oral habits is likely to be lower (Proffit et al. 2007). Exclusive breast feeding is also likely to be practiced in less cosmopolitan cities, thereby reducing the risk of acquiring non-nutritive sucking habits (Lopes-Freire et al. 2015). Ile-Ife is a community with a high prevalence of exclusive breast feeding (Ojofeitimi et al. 2000). This is reflected in the findings on the prevalence of oral habits in this study. The prevalence of oral habits in the study population was lower than the prevalence of 34.1% and 33% reported in cosmopolitan Lagos (Quashie-Williams et al. 2010; Adegbite et al. 2012); the prevalence of 45.2% reported in urban Ibadan (Orimadegun and Obokon 2015); and the prevalence of over 80% reported in children from Albania (Laganà et al. 2013a, b). Also, the proportion of children who engaged in a single habit was higher in this present study compared to the report in children from Albania where more than half of their study population engaged in more than one habit (Lagana et al. 2013a).

We found no significant gender difference in the prevalence of oral habits contrary to the reports by Laganà et al. (2013b) and Reyes et al. (2014) who found a higher occurrence of oral habits in females. A prior study in Nigeria also observed no gender difference in the prevalence of oral habits (Adegbite et al. 2012).

Digit sucking was the most common habit observed. This is similar to previous reports and probably a reflection of the continuation of the hand to mouth behaviour of childhood (Davidson 2008). The present study household survey permitted the inclusion of pre-school children; an age category that is excluded from school surveys; yet a highly important survey population for oral habits. Lagana et al. (2013a) found pacifier sucking as the most prevalent habit in Albania. We did not investigate the use of pacifiers in this study as this is a less common cultural practice in the Nigerian population (Orimadegun and Obokon 2015).

While Adegbite et al. (2012) found nail biting to be the most common habit among an older population of school children resident in cosmopolitan Lagos, we found this to be the second most common habit in the children resident in this sub-urban area. Nail biting is a thumb sucking transitional behaviour. The study however did not enquire about the possibility of these oral habit transition behaviours and so cannot validate the postulation by Tanaka et al. (2008).

Spacing and crowding were common malocclusion traits identified in children 6–12 year olds. Spacing is not an unusual finding for a population whose dentition is still developing like ours. The low prevalence of buccal crossbite and anterior open bite in a population with a high prevalence of digit suckers amongst those with oral habits, was a surprising finding. The effect of oral habits on the dentition depends on the frequency, duration and the intensity with which it is practiced. Oral habits result in abnormal changes in muscle forces causing malocclusions to develop (Loudon 2013). Only a few of our participants engaged in severe digit sucking, this may explain the study finding.

Though we observed that children with tongue thrusting and bruxism habits had higher mean DAI scores than children without this habit, the number of children who indulged in this habit in the study population are few. The finding however reflects our expectations: children can indulge in tongue thrusting and bruxism habits for long uninterrupted hours with profound effects on the occlusion often requiring multidisciplinary therapeutic approach to stop. (Saccomanno et al. 2012; Maspero et al. 2014). Future studies are required to determine how the severity of practice of these habits affects the DAI scores.

The mean DAI score and the need of children with oral habits for orthodontic treatments was low when compared with findings among Brazilian school children (Thomaz et al. 2013). This results reflects prior findings from studies conducted on orthodontic treatment needs of children in Nigeria: Nigerian children have lower orthodontic treatment need compared with their Caucasian and Oriental peers (Otuyemi et al. 1999).

A major limitation of this study was that respondents completed the questionnaires based on their ability to recall the details of past events. This predisposes the study to recall bias. Also, the small number of children with oral habits predisposes the data analysis to type 1 error for statistical analysis during subgroup analysis. Despite these limitations, the study was able to highlight relevant findings on oral habits and their association with malocclusion.

Conclusions

The prevalence of oral habits and orthodontic treatment needs of the study population was low compared to other similar studies within and outside Nigeria. Oral habits are more prevalent in the 1–5 year-old age group. There were no gender differences in oral habit practices. Digit sucking was the most frequently practiced oral habit in the study population. The most common malocclusion traits were spacing, crowding and increased overjet. Significant differences were identified with the malocclusion grades of children who had tongue thrusting and bruxism habits compared with their counterparts who did not have the habits.