# Studying the dynamics of mandibular growth spurts in individuals with Class I and Class II skeletal growth patterns using the Bayesian superimposition by translation and rotation (SITAR) model

## TL;DR

This study compares mandibular growth patterns in Class I and Class II children, finding that Class I individuals have larger mandibles and later growth spurts, but differences in timing and intensity are not clinically significant.

## Contribution

The study introduces the use of the Bayesian SITAR model to analyze mandibular growth spurt dynamics in Class I and Class II skeletal patterns.

## Key findings

- Class I children have a larger mandibular size than Class II children in both males and females.
- The growth spurt occurs later in Class I children compared to Class II children across both sexes.
- Differences in growth spurt timing and intensity are not clinically meaningful for either sex.

## Abstract

Comparing the mandibular growth patterns of Class I and Class II children offer valuable insights into adolescent growth dynamics that are crucial for planning growth modification procedures.

To test the null hypothesis of no class differences (Class I vs. Class II) in mandibular growth spurt parameters (size, timing, intensity) versus clinically relevant differences defined as ≥ 5 mm for size, ≥ 1 year for timing, and ≥ 1 mm/year for intensity

Data (Condyle–Pogonion distance) available from the American Association of Orthodontists Foundation Craniofacial Growth Legacy Collection is analyzed. The dataset includes 160 children, 40 each in Class I and Class II groups for both sexes. A three-level Bayesian SITAR model is fitted, incorporating individual- and study-level random effects for all three growth spurt parameters.

The average mandibular size is greater in Class I than in Class II for both males [5.0 mm, 95% CI (3.0, 7.0)] and females [4.4 mm, 95% CI (3.2, 5.7)]. The growth spurt occurs later for Class I than Class II across both sexes [males: 0.6 years, 95% CI (0.3, 0.9); females: 0.6 years, 95% CI (0.2, 0.9)], and the intensity of the growth spurt is slightly greater in Class I than in Class II [males: 0.2 mm/year, 95% CI (0.0, 0.4); females: 0.2 mm/year, 95% CI (0.0, 0.4)]. The results show individual-level variation in size, timing, and intensity parameters across both Class II and Class I.

No evidence found for clinically meaningful class differences in the timing or intensity of the adolescent growth spurt dynamics for either sex. The mandibular deficiency observed in Class II children is established early, during the pre-adolescent growth period. The cumulative deficiency in mandibular size for Class II children worsens with age, which leads to a more pronounced skeletal discrepancy in adulthood. The clinical implications for treatment planning are discussed.

Considering the retrospective nature of the historical data analyzed, caution is warranted when generalizing our findings to contemporary populations.