INTRODUCTION

It is generally held that anterior open bite tends to worsen throughout the juvenile and adolescent years, being mediated by characteristic changes in maxillo-mandibular relationships over this intensive growth period.^1,2 In addition, skeletal open bites may be linked to posterior growth rotations, although these are believed to be relatively rare.^3,4 This growth pattern and the associated occlusal effects may dictate a reticence to camouflage anterior open bite during the early to middle adolescent period, as orthodontic correction may be outstripped by latent growth.^1–4

The effect of vertical skeletal dimension on facial growth has been examined in previous longitudinal studies involving subjects ranging in age from 9 to 18 years by dividing the subjects into low-, average-, and high-angle groups according to mandibular plane to sella-nasion angle (MP-SN).^1,2 Similar levels of increase in SNA and SNB, and a reduction in ANB and MP-SN angles, were uniformly observed, suggesting that homogeneous growth changes were found in all groups regardless of the vertical dimension. Similarly, Karlsen reported that MP-SN decreased in both the high- and low-angle groups, concluding that a true posterior rotation may occur rarely and that the mandibular plane inclination may be constant.^3,4

In terms of the relationship between vertical skeletal growth and overbite, Adams and Kerr⁵ analyzed 10- to 15-year-old Class I and II subjects and observed a significant negative correlation between increase in facial height and overbite. However, in a longer-term analysis (from 9 to 18 years), dividing the subjects into low-, average-, and high-angle groups, overbite remained relatively stable over the observation period in both hyper- and hypodivergent subjects.^1,2

Detailed analysis of the nature of vertical changes in the juvenile and adolescent period is lacking and inconsistent.^1,5 As such, the evidence underpinning the timing of orthodontic camouflage in patients with increased vertical dimension is limited.⁶ The aim of this longitudinal study was therefore to evaluate the change in overbite in an untreated cohort from 9 to 18 years and to compare age-related changes in overbite depth among samples with increased and normal or reduced vertical skeletal proportions.

MATERIALS AND METHODS

In this retrospective cohort study, data held within the American Association of Orthodontists Foundation (AAOF) Craniofacial Growth Legacy Collection⁷ derived from the Case Western Bolton Brush Growth Study, the Denver Growth Study, and the Oregon Growth Study were included. No ethics approval was needed for this study as it used data from the AAOF Craniofacial Growth Legacy Collections Project. Participants were selected according to the following criteria: (1) presence of longitudinal data including high-quality lateral cephalograms available at the ages of 9–11 years, 13–15 years, and 17–19 years; (2) a diagnosis of skeletal Class I or II, determined from the baseline lateral cephalogram (ANB > 0°); and (3) no prior orthodontic treatment. Class III subjects were excluded in order to minimize the confounding effects of differential adolescent mandibular growth on the assessment of vertical change. All growth collections were screened, and all eligible subjects were included in the analysis.

Digital cephalometric analysis was undertaken using proprietary software (WebCeph, AssembleCircle Corp, Gyeonggi-do, Republic of Korea).⁸ The primary outcome was the overbite measured perpendicular to the occlusal plane based on the total crown height of the mandibular incisors overlapped by the maxillary incisors. The occlusal plane was defined as a line passing through the posterior occlusal point (Oclp) and anterior occlusal point (Ocla), perpendicular to the sagittal plane. Specifically, Oclp was the midpoint of overlap of the mesiobuccal cusps of the upper and lower first molars on the sagittal plane, and Ocla was the midpoint between the upper and lower incisal points in the sagittal plane. The following cephalometric parameters were also recorded: (1) mandibular plane to sella-nasion angle (MP-SN), SNA angle (sella, nasion, A point), (2) SNB angle (sella, nasion, B point), (3) ANB angle (A point, nasion, B point), (4) Wits index, (5) maxillary to mandibular plane angle (MMPA), (6) maxillary plane to sella-nasion angle (MxP-SN), (7) lower incisor to mandibular plane angle (IMPA), (8) upper incisor to maxillary plane angle (UIMx), (9) interincisal angle, and (10) overjet, measured parallel to the occlusal plane. All cephalometric outcome measures were assessed at three different time points at the ages of 9–11 years (T1), 13–15 years (T2), and 17–19 years (T3).

Descriptive statistics were obtained for demographic and clinical data including linear and angular cephalometric measurements at the study time points. Continuous variables were expressed as means and standard deviations, whereas categorical variables were expressed as absolute numbers and percentages. To evaluate intraexaminer reliability, 20 randomly chosen lateral cephalograms were retraced by the same examiner (Dr Ferrillo) 2 weeks after the initial tracing using Bland-Altman’s limits of agreement. Generalized estimating equation (GEE) regression models were fit to examine the effect of MP-SN on overbite adjusted for age and gender, with a P value of <.05 considered statistically significant. All statistical analyses were conducted with STATA version 17 software (Stata Corporation, College Station, Tex).

RESULTS

Of 303 subjects from the AAOF Craniofacial Growth Legacy Collections Project (Denver Growth Study, Bolton Brush Growth Study, and Oregon Growth Study), a total of 130 met the eligibility criteria and were included in the analysis. Fifty subjects (38.46%) were taken from the Denver Growth Study (27 males and 23 females; mean age: 10.11 ± 0.64 years), 41 (31.54%) from the Bolton Brush Growth Study (25 males and 16 females; mean age: 9.85 ± 0.76 years), and 39 (30%) from the Oregon Growth Study (14 males and 25 females; mean age: 10.02 ± 0.41 years). Overall, there were a similar number of males (n = 66, 50.77%) and females (n = 64, 49.23%). Good levels of reliability were confirmed for all measurements including overbite (95% confidence interval [CI]: −0.24, 0.15), MP-SN (95% CI: −0.42, 0.24), and MMPA (95% CI: −0.06, 0.76).

The mean values of the cephalometric measurements per time point (T1 to T3) are reported in Table 1. There was interindividual variability in the evolution of cephalometric measurements over time (Figures 1–2). Similar patterns were observed for each gender, although slight differences were noted for lower incisor to mandibular plane angle (IMPA) and the interincisal angle (Figure 1). Overbite reduced slightly in both genders, although a transient increase was noted in females at T2.

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Table 1. Mean (SD) Values of the Cephalometric Measurements per Time Point (T1 to T3)

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Generally, changes in overbite as well as incisor inclination changes were minor (Figure 2), reflected by limited flaring of both upper and lower incisors over the overall study period (T1–T3). On the corollary, overbite reduced overall (T1–T3) but increased from T1 to T2, reflecting transient proclination of the incisors.

Based on the GEE regression model adjusted for time and gender, a minor decrease in overbite arose as MP-SN increased (coefficient = −0.080; 95% CI −0.12, −0.04; P < .01). No significant change in overbite was observed between T1 and T2 (coefficient = 0.2; 95% CI −0.07, 0.48; P = .14) with a minor but statistically significant decrease from T3 to T1 (coefficient = −0.38; 95% CI −0.68, −0.09; P = .01). A weak tendency for an increase in overbite among males compared with females was noted (coefficient = 0.47, 95% CI −0.01, 0.96; P = .06). The linear predictions for the adjusted effect of MP-SN highlight a slight reduction in overbite with increasing MP-SN for both males and females (Figure 3).

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The adjusted effect of MP-SN on U1 to MxPlane and IMPA is also shown in Table 2. With increasing SN-MP, there was a significant decrease in IMPA (coefficient −0.51, 95% CI: −0.69, −0.34, P < .01).

Table 2. Population Average Generalized Estimating Equation (GEE) Model to Examine the Effect of Time Adjusted for MP-SN and Gender on the Outcome (Overbite, UIMx, and IMPA)

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DISCUSSION

The aim of this longitudinal study was to evaluate the change in overbite as a function of vertical skeletal proportions from 9 to 18 years of age in an untreated cohort. The age subsets of 9–11, 13–15, and 17–19 years were selected to evaluate the craniofacial changes in relation to the juvenile, pubertal, and postpubertal periods given that the pubertal growth spurt generally occurs from 10 and 12.1 years to 14.8 and 17.1 years in females and males, respectively.⁹

Based on the descriptive data, similar longitudinal changes in hyperdivergent subjects compared with hypo- and average-divergent subjects were observed from 9 to 18 years. The longitudinal sagittal changes in terms of intermaxillary relationship were also comparable. The results were in line with most longitudinal craniofacial growth analyses of untreated subjects spanning the mixed to adult dentition.^1,10–14 MMPA reduced by approximately 2.5° in hyperdivergent (MP-SN ≥ 36°) and 1.59° in normodivergent (MP-SN ≤ 35°) subjects over the 8-year observation period (Table 3). In terms of dental change, a slight reduction in interincisal angle and a significant increase in both IMPA and UIMx in hyperdivergent subjects were reported, mainly from T2 to T3. This was a contributor to the minor (0.99 mm) reduction in overbite in hyperdivergent subjects from T2 to T3. The timing of changes observed in the present study differed from a previous study reporting a 0.5-mm reduction in overbite and an increase in both total and lower facial height from 10 to 15 years, with a significant negative correlation between lower facial height and overbite changes.⁵ Conversely, the current results were in line with other studies that reported incisor proclination and a reduction of the interincisal angle in a hyperdivergent sample over a longer period (from 9 to 18 years), spanning the period of prepubertal and adolescent growth.^1,2

Table 3. Change in Cephalometric Scores From T1 to T3 Based on Vertical Dimension

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The mandibular incisor position is known to change during growth, being influenced by both the amount of incisor proclination and mandibular rotation.¹⁵ The results implied that the incisal proclination exceeded any mandibular forward rotation in the hyperdivergent subjects. On this basis, self-correction of reduced overbite was not universal. Similarly, as the magnitude of change was generally small, little deterioration in vertical relationships was generally observed. From a clinical perspective, the observed increase in IMPA (of 1.8°) and in UIMx (by 2.35°) in high-angle compared with average- and low-angle subjects was noteworthy. This may be of importance especially in dental open bites, particularly given the association between open bite closure and patient satisfaction.¹⁶ Notwithstanding, correction of open bite is known to be challenging and prone to instability, especially if achieved by extrusion of the anterior teeth.¹⁷ To date, there is little comparative research evaluating the relative impact of the mechanism of open bite closure on stability, although posterior intrusion may be augmented by occlusal forces during the posttreatment period.^18,19

In terms of limitations, this retrospective study was based on historical data available from the AAOF Craniofacial Growth Legacy Collections Project. This collection is an accessible research resource overcoming ethical challenges associated with serial cephalometry.²⁰ However, secular growth-related changes are known to occur and may affect facial skeletal growth, although there is little evidence that growth patterns have changed markedly over the past century.²¹ In addition, clinical and qualitative data, including patient concerns, were not obtained.²⁰

CONCLUSIONS

• Based on this longitudinal cephalometric analysis of facial growth over a period of up to 9 years, little change in overbite seems to occur irrespective of vertical facial type.

• In hyperdivergent subjects, a marginal decrease in overbite was observed from 9 to 18 years. This was punctuated by a transient increase from the period spanning 9–11 years old to 13–15 years but was offset by a decrease in overbite in later adolescence.

• On the basis of the present study, observation of vertical growth may not be required in most patients with a borderline increase in vertical facial proportions in the juvenile and pubertal phases.