INTRODUCTION

Research on facial growth and development is essential in orthodontics for a state-of-the-art diagnosis, prevention, interception, and correction of malocclusions. A knowledge of these events will improve treatment planning because most orthodontic treatments take place during growth.1 The growth and development events must be correlated with the maturational level of each individual to identify the residual growth and the subject's skeletal pattern and to decide on a proper treatment plan. The chronological age is not adequate to compare different subjects because most people show a discrepancy between chronological age and maturational events.2 Among several maturational indicators, skeletal development appears to be quite a simple and accurate one. Bone age is determined by radiographs, relating the appearance and development of certain bones with the maturational stages.3–6

This knowledge is useful to obtain a more specific diagnosis.7 Treatment modalities such as rapid palatal expansion, protraction mask, extraoral traction, and other orthopedic devices will obtain better results when applied in certain developmental phases.4 During adolescence the treatment cooperation usually is better and the skeletal changes are enhanced, leading to a shorter treatment time.8–10

Considerable attention is paid to the mandibular growth because it is reported that this bone enlarges the most during adolescence.1112 It is common sense that the lower jaw grows in a posterior-superior direction resulting in an anterior-inferior displacement.1314 Hunter15 in 1771, as well as Humphry16 in 1866, demonstrated that mandibular sagittal growth is due to posterior deposition and anterior resorption in the ramus. Although the mandibular growth sites and direction are well established, the presence of growth spurts is still controversial. Some authors agree that most individuals experience mandibular growth spurts,517–19 whereas others state that the growth spurts are common but not universal.2021 Moore et al22 believe that mandibular growth spurts may occur, but not in a uniform amount and duration.

The aim of this study is to determine mandibular growth velocity in white subjects during adolescence. Furthermore, it is intended to compare mandibular growth velocity among different stages of adolescence (accelerating, peak, or decelerating phase).

MATERIALS AND METHODS

The sample was composed of 85 white adolescent orthodontic patients, between 9 and 18 years of age (46 females and 39 males), residents of Porto Alegre, previously treated at Pontificia Universidade Catolica do Rio Grande do Sul (PUCRS), Brazil. The criteria for sample selection demanded ANB angle between 0° and 6°. In this manner, subjects with skeletal Class III and severe skeletal Class II were excluded. Furthermore, patients should not have any missing teeth or syndromes, cleft lip or palate, or any kind of pathology, and they should not use any type of medication that could affect growth.

The subjects had a Class I (49 individuals) or Class II (36 individuals) skeletal pattern. The patients had undergone minor orthodontic problems such as posterior crossbites, anterior open bite, and mild to medium crowding and were treated with removable expansion devices with or without a palatal grid, Nance lingual appliances, and, in 13 cases, fixed edgewise appliance.

Each patient was observed at two time points. The first evaluation (T1) included a lateral head film and a hand-wrist radiograph and the second evaluation (T2), a lateral head film. The interval between T1 and T2 ranged from 5 to 24 months. The lateral head films were manually traced by one examiner, and the cephalometric points were digitalized into the Dentofacial Planner Plus Software (DFP Plus 2.0) for cephalometric measurements.

This study used the following cephalometric landmarks: Nasion (N), point A (A), point B (B), Condylion (Co), Gonion (Go), and Gnathion (Gn). ANB angle was used for the determination of skeletal facial type. The three linear measurements for the determination of mandibular growth were mandibular body length (distance between Go and Gn), mandibular ramus height (distance between Co and Go), and mandibular length (distance between Co and Gn) (Figure 1).

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The hand-wrist films were evaluated by the same examiner and classified according to Fishman's method into 11 stages. This method was elected because it is very clear and easy to apply and it focuses on skeletal maturational index during adolescence.

The absolute growth amount was obtained by subtracting the T1 values from T2 values. Absolute growth amounts were divided by the number of months between the two evaluations and multiplied by 12 to establish an annual growth rate (mm/y).

The subjects were divided according to their bone maturation level into group I (accelerating phase or Fishman stage 1–3), group II (peak of growth velocity phase or Fishman stage 4–7), and group III (decelerating phase or Fishman stage 8–11). Table 1 shows the sample division according to sex, maturational stage, and skeletal pattern. The annual growth rate was compared between sexes, between individuals with skeletal Class I or II, and between the three groups.

Table 1.  Sample Distribution

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Intraexaminer study error was made with 12 lateral films that were randomly chosen and were retraced by the same examiner 45 days after the first cephalometric tracing. For the statistical analysis, the Student's t-test (95%), Mann-Whitney test, and Kruskall-Wallis test (SPSS 10.0) were used. This study protocol was approved by the Research and Ethics Department, Faculty of Dentistry, PUCRS, Brazil.

RESULTS

The results are shown in Tables 2 through 6. The intraexaminer error study (Table 2) did not show statistically significant differences between the first and the second measurements in the cephalograms (P < .05). None of the linear measurements had a difference greater than 1 mm.

Table 2.  Intraexaminer Error Study (n = 12)

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There was no difference in mandibular growth between Class I and II skeletal pattern individuals (Table 3) and there was no significant difference between the sexes (Table 4).

Table 3.  Means, Standard Deviation, and Mann-Whitney Test Comparing Mandibular Annual Growth Rates (mm/y) Between Skel etal Class I and II Individuals (n = 85)

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Table 4.  Means, Standard Deviation, and Mann-Whitney Test Comparing Mandibular Annual Growth Rates (mm/y) Between Sex es (n = 85)

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Table 5 shows the mean growth velocity among the three groups for each measurement. The mandibular annual growth rate in the adolescence phase was 2.16 mm for the mandibular body length, 3.16 mm for the ramus height, and 4.31 mm for the mandibular length. From Table 6, it is clear that the greatest mandibular growth velocity for two of the three measurements (mandibular body length and mandibular length) occurred in group II, although the amount was not statistically different from the other two groups. In the mandibular length, the annual growth difference between groups II and III was greater than 1 mm.

Table 5.  Whole Sample Means of Mandibular Annual Growth Rates (mm/y) (n = 85)

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Table 6.  Means, Standard Deviation, and Kruskall-Wallis Test Comparing Mandibular Annual Growth Rates (mm/y) Between the Three Groups (n = 85)

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DISCUSSION

Mandibular growth has been widely studied, especially because of the late-adolescent growth spurt.1112 From this study, it is clear that the mandibular growth amount is not significantly different in the various pubertal phases but that there is an accelerating tendency in group II, especially for mandibular length and mandibular body length. A possible explanation for the statistical results is the intense individual variation, which was noticed in this study once it was apparent that the standard deviation values were larger than the means. This individual variation has been reported by other authors.323–26 It should also be considered that 11 individuals of group 1 were studied for more than 18 months and they probably have changed their maturational stage.

The sample studied in this research comprised white residents of Porto Alegre, Brazil. Southern Brazilian population is mainly composed of Portuguese, German, and Italian descents and could be representative of a white population. Patients had undergone minor orthodontic treatment, and some of them were even treated with fixed appliances. Such therapies do not influence linear mandibular growth. Only mandibular position could be affected, but that was not studied here. Therefore, the results concerning mandibular body length (Go-Gn), mandibular ramus height (Co-Go), and mandibular length (co-Gn) are reliable.

Among the linear measurements, ramus height presented less variation in annual growth rates. It ranged from a lower value of 3.01 mm in group II to a higher value of 3.34 mm in group III. Lima27 found rates of 2.06 mm in males and 1.42 mm in females. However, subjects of that study were not classified according to maturational stages.

The mandibular length showed an annual rate of 3.92 mm for group III, which represented individuals in the decelerating phase according to Fishman7. For group I, which included subjects at the accelerating phase, annual rates were similar, reaching 4.02 mm. The greatest velocity of growth for mandibular length (5.01 mm) occurred in group II, where individuals were at the peak of growth velocity. No statistical differences between groups were found for annual growth rates, but group II did present greater growth (close to one mm) than groups I and III, and this should be considered in treatment planning.

Sato et al28 found that, in Japanese girls from 8 to 18 years of age, the mandibular length measured from condylion to gnathion increased 17.84 mm. If this amount was divided by 10 to obtain an annual rate, it would be 1.78 mm/y. It has to be considered that in this study rates were much higher because of the fact that the individuals in this study were at puberty, whereas in the Sato and coworkers report, the subjects were observed since childhood and it is expected that more growth will occur in our subjects since it was during puberty.

Mandibular body length showed lower annual rates of 1.81 and 2.05 mm for groups III and I, respectively. In group II (peak of growth), the annual rates reached 2.64 mm. The values found by Lima27 at a supposed puberty (12 to 16 years in males and 9 to 14 years in females) did not exceed 1.49 mm for females and 1.86 mm for males. Different results may be due to different samples because Lima studied Canadian individuals over a different time intervals between evaluations, ie, 2 years.

These results are really difficult to compare with the ones presented in the literature because there are several methodological differences among them. Most studies do not classify their samples by maturational indicators enhancing the growth differences regarding maturational levels. Probably, most differences among the results of the studies presented in the literature are because of different methodologies such as the cephalometric points used, cephalometric tracing technique, sample standardization, and the tendency to select samples by chronological age instead of maturational indicators.

The results of this study suggest that mandibular linear growth does not differ among skeletal Class I or II subjects, in agreement with other previous studies.29–34 It also suggests that there is no difference between sexes, enhancing the fact that classifying the individuals by their skeletal stage will diminish or even eliminate the sex differences. It is important to restate that although there was no statistical difference between the annual growth rates, the higher values found in the peak of velocity (group II) should be strongly considered in treatment planning. New studies should be carried out with a larger number of subjects, especially for individuals in the decelerating phase of growth (group III).

CONCLUSIONS

• The mandibular annual growth rate in the adolescence phase was 2.16 mm for the mandibular body length, 3.16 mm for the ramus height, and 4.31 mm for the mandibular length.

• There is great individual variation in mandibular linear growth.

• There are no differences in mandibular linear growth between sexes when individuals are considered as their maturational stages.

• The greatest rates occurred in the subjects in the peak of pubertal growth velocity, except for the ramus height, although there were no significant differences among the groups.