ANALYSIS OF MAXIMUM MOUTH OPENING IN 3- TO 5-YEAR-OLD PRESCHOOL CHILDREN

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O R I G I N A L A R T I C L E

Analysis of maximum mouth opening and its related factors in 3- to 5-year-old Taiwanese children

Hong-Sen Chen^•Pei-Ling Yang^•Chen-Yi Lee ^• Ker-Kong Chen^•Kun-Tsung Lee

Received: 7 February 2013 / Accepted: 19 August 2013 ÓThe Society of The Nippon Dental University 2013

Abstract Maximum mouth opening (MMO) can reflect the function of the dentofacial musculature and joint system, and routine oral examinations should include its assessment. To diagnose abnormalities using MMO measurements, it is necessary to establish the normal range of MMO; however, few studies have investigated this subject in Taiwan. Therefore, the purposes of this study were to determine the normal MMO range in 3- to 5-year-old preschool children and to investigate the factors correlated with MMO. We examined the interincisal distance, defined as the distance between the edges of the upper and lower incisors, in 518 preschool children (age range 3–5 years;

271 boys and 247 girls) with a plastic sliding caliper. The MMO on both sides of the mouth and mouth width (MW) was measured 3 times. No differences in MMO were found between the genders. The interincisal distance was 37.47 (±4.11) mm for boys and 36.93 (±3.85) mm for girls,

whereas the mean MMO was 37.21 (±3.99) mm. The MMO increased with the increasing age of the children, and the mean value of MMO in children aged 3, 4, and 5 was 35.31 (±4.03), 36.61 (±3.79), and 38.31 (±3.88) mm, respectively. Furthermore, MMO was found to correlate with weight and MW. MMO increased by 0.19 mm per increased weight and 0.37 mm per increased MW. The mean value of MMO in 3- to 5-year-old preschool children was 37.21 (±3.99) mm. MMO in 3- to 5-year-old preschool children increased with age and was correlated with weight and MW

Keywords Maximal mouth openingInterincisal distancePreschool children Mouth width

Introduction

The masticatory system can be effectively and objectively evaluated by measuring the range of motion of the mandible [1]. Decreased range of motion of the mandible is considered abnormal. Therefore, the range of mouth opening should be measured during routine clinical examinations. In addition to monitoring abnormalities in masticatory muscle functions, examination of the maximum mouth opening (MMO) may help to identify other abnormalities to facilitate early treatment, provide simple and useful diagnoses, and evaluate treatment effectiveness [2]. Compared to adults, young children exhibit higher uncertainties in behavior. Thus far, most studies on MMO have focused on adults or participants belonging to a wide age group. In addition, most studies have focused on the MMO range in the background of temporomandibular joint (TMJ) disorders and limited mouth opening and trismus following wisdom tooth operations [3,4].

H.-S. ChenC.-Y. LeeK.-T. Lee

Department of Oral Hygiene, College of Dental Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan P.-L. Yang

Graduate Institute of Dental Sciences, College of Dental Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan K.-K. Chen

Departments of Conservative Dentistry, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan

K.-T. Lee (&)

Department of Family Dentistry, Kaohsiung Medical University Hospital, No. 100, Shih-Chuan 1st Road, Kaohsiung, Taiwan e-mail: [email protected]

K.-T. Lee

Graduate Institute of Dental Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan

DOI 10.1007/s10266-013-0136-z

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In 1960, Nevakari [5] was the first to study the MMO range in children: he examined the MMO of hundred 6- to 8-year-old children (50 boys and 50 girls) and reported an average MMO of 46 mm. Subsequently, Nowak and Ca- saamassimo [6] reported the necessity of understanding young children’s MMO because young children tend to suffer from facial trauma that causes damage to their mandibular function. Ideally, the MMO should be measured during a patient’s first medical examination so that it can be used as a reference during the evaluation of prognoses and treatment progress in the future. Therefore, in this study, we aimed to determine the normal MMO range in 3- to 5-year- old preschool children and to investigate the factors affect- ing MMO. Furthermore, an understanding of the MMO of normal children can be used as a reference by manufacturers to create toys of suitable sizes, based on the MMO ranges of different ages, thereby reducing choking incidents among children caused by swallowing overly small toys.

By surveying the MMO of preschool children (3- to 5-year old), this study aimed to construct a blueprint, which could be used to establish a MMO database for children belonging to different age groups in the future. In addition, the results of this study could serve as a reference for dentists when performing routine examinations and treat- ments for oral cavities in children (i.e., restoring caries and obtaining impressions).

Materials and methods

This study adopted a cross-sectional study design based on the population of kindergarten students. Using stratified random sampling with probability proportional to size, we randomly sampled 10 kindergarten students and recruited 754 preschool children aged 3–5 years. The subjects included children exhibiting all types of skeletal patterns (Class-I, Class-II, and Class-III). A total of 518 children who fulfilled the following criteria were included in this study: sound and immobile primary maxillary and mandibular central incisors, no caries, no history of facial and dental trauma, no anterior open-bite and no restorative materials that influenced the incisal edges, and no ortho- dontic appliances that could influence the position of the central incisors.

A trained dentist conducted face-to-face examinations of the children. Children were seated in an upright position, and the head was supported by the dentist’s hand to encourage the child to settle into a comfortable position.

This made it easier for children to relax their muscles and control mouth opening. Next, the dentist used a plastic sliding caliper to measure the MMO in a spontaneous and painless manner. In particular, the dentist measured the vertical distance between the edges of the primary upper-

right and lower-right central incisors, followed by the distance between edges of the primary upper-left and lower-left central incisors. Then, the dentist measured the distance between the angles of the mouth when in a closed resting position, which was defined as the mouth width (MW). Typically, a subject with a wider MW had a larger MMO. Therefore, it was interesting to investigate the relationship between MMO and MW. Both the measurements (MMO and MW) were repeated 3 times. The same dentist performed both the measurements to reduce bias.

The study participants were divided into 3 groups based on age: 3, 4, and 5 years. The overjet and overbite were not investigated in this study. This study was authorized by the education bureau of Kaohsiung city (southern city of Tai- wan) in 2008, and the study protocol was reviewed and approved by the human investigation review committee (KMUH-IRB-970239).

Data processing and statistical analysis

A paired t test was used to compare the average MMO between boys and girls. The analysis of variance (ANOVA) test was used to analyze the differences between the MMOs of boys and girls of various ages. We performed a Tukey–Kramer post hoc test to compare the average MMO between the 3 different age groups. Pearson’s correlation coefficient and simple linear regression were used to verify the correlation between MMO and factors such as height, weight, and MW. Subsequently, we used multiple linear regression analysis to examine the correlations between the various factors.

Results

The baseline characteristics of the 518 participants (271 boys, 247 girls) are shown in Table1. The majority of the participants were either 4- (n =229, 44.21 %) or 5-year old (n=229, 44.21 %). We measured the MMO 3 times and used the third measurement for our analysis which is relatively stable as the basis of data analysis regarding data distribution, such as the children’s height, weight, MMO, and MW. The results showed that boys were significant taller (108.96 vs. 107.34 cm) and heavier (18.84 vs.

17.73 kg) than the girls were. The average MMO values of the boys vs. girls at 3, 4, and 5 years of age were, respectively, 35.40 vs. 35.20, 36.95 vs. 36.27, and 38.54 vs.

38.05 mm (Table2). ANOVA revealed that the MMO was significantly different between the 3 age groups (F2,515=19.2776; p\.0001). Subsequently, we performed the Tukey–Kramer post hoc test and found that the average MMO of the 5-year-old children was larger than those of the 3- and 4-year-old children.

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The average MW of the boys vs. girls at 3, 4, and 5 years of age was, respectively, 35.10 vs. 34.10 mm, 36.05 vs. 35.99 mm, and 37.33 vs. 37.17 mm (Table2).

MMO and MW were not significantly different between the 2 groups (p[.05). ANOVA revealed that the average MW was statistically different among the 3 age

groups (F2,515 =23.1168; p\.0001). The Tukey–

Kramer post hoc test showed that the average MW of 5-year-old children was the largest, followed by that of 4- and 3-year-old children. Correlation analysis showed a slight correlation between height, weight, MMO, and MW.

Table 2 Data analysis in gender and age distribution

ANOVA test: ***p\0.001

Variables Total Boy Girl

Mean±SD Mean±SD Mean±SD

Height (cm)

3 years old 100.01±4.61 101.31±4.76 98.30±3.88

4 years old 106.30±4.72 107.26±4.97 105.33±4.27

5 years old 112.22±4.65 112.69±4.46 111.69±4.83

ANOVA test *** *** ***

Tukey’s pairwise comparison (age) 5[3, 4[3, 5[4 5[3, 4[3, 5[4 5[3, 4[3, 5[4 Weight (kg)

3 years old 16.23±2.32 16.69±2.44 15.62±2.06

4 years old 17.60±2.75 18.29±2.84 16.90±2.49

5 years old 19.57±3.28 19.96±3.60 19.12±2.83

Tukey’s pairwise comparison (age) 5[3, 4[3, 5[4 5[3, 4[3, 5[4 5[3, 4[3, 5[4 Maximum mouth opening (mm)

3 years old 35.31±4.03 35.40±4.17 35.20±3.92

4 years old 36.61±3.79 36.95±4.08 36.27±3.46

5 years old 38.31±3.88 38.54?3.82 38.05±3.94

Tukey’s pairwise comparison (age) 5[3, 5[4 5[3, 5[4 5[3, 5[4 Closed-mouth angle width (mm)

3 years old 34.67±2.95 35.10±3.08 34.10±2.72

4 years old 36.02±2.85 36.05±3.11 35.99±2.58

5 years old 37.25±2.86 37.33±2.90 37.17±2.81

Tukey’s pairwise comparison (age) 5[3, 4[3, 5[4 5[3, 5[4 5[3, 4[3, 5[4 Table 1 Basic data of Children in two samplettest

Variables Total Boy Girl Two samplettest

pvalue

N % N % N %

Gender 518 100 271 52.32 247 47.68

Age

3 years old 60 11.58 34 6.56 26 5.02

4 years old 229 44.21 115 22.20 114 22.01

5 years old 229 44.21 122 23.55 107 20.66

Height (Mean±SD, mm) 108.19±6.19 108.96±6.08 107.34±6.19 p=0.003**

Weight (Mean±SD, kg) 18.31±3.18 18.84±3.35 17.73±2.89 p\0.0001***

Maximum mouth opening

Mean±SD, mm 37.21±3.99 37.47±4.11 36.93±3.85 p=0.4339

Closed-mouth angle width

Mean±SD, mm 36.41±2.99 36.51±3.11 36.30±2.85 p=0.1206

**p\0.01; ***p\0.001

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In simple linear regression, factors that correlated with the average MMO were represented using Model-I, Model- II, and Model-III. Model-I (i.e., gender and age as correlation factors) analysis revealed that the correlation between age and average MMO was statistically significant. Model-II (i.e., gender, age, height, and weight as correlation factors) analysis indicated that the correlation between weight and MMO was statistically significant (p=.0032). Model-III (i.e., gender, age, height, weight, and average MW as correlation factors) analysis indicated that the correlations between MMO and weight and that between MMO and average MW factors were statistically significant (p=.0137 andp\.0001).

In simple linear regression, factors that correlated with the average MW were represented using Model-I, Model- II, and Model-III. Model-I (i.e., gender and age as correlation factors) analysis indicated that the correlation between age and average MW was statistically significant.

Model-II (i.e., gender, age, height, and weight as correlation factors) analysis indicated that the age of 5, height, and weight were significantly correlated with the average MW (p=.0327; p =.0268; p=.0403). Model-III (i.e., gender, age, height, weight, and MW as correlation factors) analysis indicated that the correlation between average MMO and average MW was statistically significant (p\.0001).

Discussion

In this study, we found that the average MMO of children at 3, 4, and 5 years of age was 35.31, 36.61, and 38.31 mm, respectively. The slope of the growth curve of MMO between 4 and 5 years was steep. We inferred that since children’s growth rates differ with age, the growth rate of MMO also varied with age. Within the same age group, the MMO of boys was slightly larger than that of girls; however, no statistically significant differences were noted (p=.4339).

Agerberg [7] performed correlation analysis and found that the MMO was significantly different between each measurement obtained in children. The average MMO increased with the number of measurements obtained. The most consistent results were obtained between the second and third measurements. In that study, the MMO was typically recorded during the third measurement, which is consistent with our study. We suggest that dentists should be repeatedly trained to obtain rapid and adroit measurements of children’s MMO to ensure measurement accu- racy. In addition, children must be encouraged to practice opening their mouth several times before opening their mouths to the maximum extent. Measurements obtained using this method may be the most accurate. Furthermore,

a single measurement is not sufficient for children aged 3–5 years. For this age group, we suggest that 3 or more measurements be obtained.

In this study, although the MMO increased with age for both the genders from all perspectives, the average MMO value was less than that obtained for 3- to 5-year-old children (MMO, 42.4 mm) in the study conducted by Sheppard and Sheppard[8] and that obtained for 5-year-old children (MMO, 45 mm) by Landtwing [9]. However, our results were similar to those of Nowak and Casamassimo [6], who measured the MMO of children at 3 years of age (35.7 mm). We attribute these differences in MMO values to the specific local and ethnic characteristics of popula- tions in different countries. Furthermore, these differences could be attributed to the following latent factors: between- participant differences, different measurement methods and instruments, and errors caused by human factors.

In this study, the average MMO was weakly correlated with height and weight (r=0.33, 0.32;p\.0001), which is similar to the results of a previous study conducted by Abou-Atme et al. [10], in which a weak correlation was found between MMO and height (r=0.27). Aberberg [7]

reported that MMO was not correlated with height and weight in children aged 1.5 years. However, in children aged 6 years, the average MMO was correlated with height, but not with weight. In this study, the average MW of 3-year-old children was 34.67 mm, which is narrower than their counterparts in the study by Nowak and Casa- massimo [6]. The average MW of children increased with age (MW of 5-year old[MW of 4-year old[MW of 3-year old): it was 36.02 and 37.25 mm for the 4- and 5-year old, respectively, and the differences were statistically significant between the 3 age groups. Little difference was observed between the MWs of boys and girls, which were, respectively, 36.51 and 36.30 mm, showing no statistically significant difference (p=.1206). The ANOVA results showed a weak correlation between average MMO and average MW (r=0.37,p\.0001).

Although MMO was weakly correlated with MW, we adjusted for gender, age, and height using a fit model because the study’s objective was to determine the factors that could be used to predict MMO. Comparing the MMO of Model-I and Model-II, we found that the correlation between age and MMO declined gradually. Therefore, age was classified as a confounding factor. With the inclusion of various correlation factors, the age factor in Model-III was not found to be significant. A similar result was obtained in the case of height. This indicated that the increase in children’s MMO was not solely correlated to their physiological development. Increased weight and MW were primarily correlated with increase in MMO.

Comparing Model-I and Model-II regarding average MW, we found that the correlation between MW among an age

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of 5, height, and weight declined gradually. Thus, MW, height, and weight were classified as confounding factors.

According to Model-III, age=5 years, height, and weight were not significantly correlated. This indicated that MW in children was not solely correlated with physiological development, but was chiefly affected by MMO. Therefore, these results showed that weight was correlated more significantly and positively with MMO than height. These results were identical to those reported by Nelson et al.

[11].

This study has the following limitation: factors such as overjet, overbite, open-bite, and skeletal pattern were not investigated. In general, children with increased overjet may have a higher MMO than those without overjet. A larger overbite or anterior open-bite may cause result in lower MMO. Moreover, different skeletal patterns and malocclusions may affect the MMO. Therefore, to over- come these limitations, future studies are warranted that consider the abovementioned factors in the measurement of MMO.

Conclusion

Our study revealed that the mean value of MMO in 3- to 5-year-old preschool children in Kaohsiung city was 37.21 (±3.99) mm. Within the same age group, the MMO values of preschool boys were greater than those of girls, but this difference was not statistically significant. After adjusting for gender, age, and height, average MW and weight were the chief factors correlated with MMO.

Conflict of interest The authors declare no conflict of interest.

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