Geometric morphometric analysis of hard and soft tissue in class II division 1 malocclusion before and near-end treatment

Abstract

Geometric Morphometric Analysis (GMA) is a statistical toolset that can capture distinct shape variation and allows the shape of craniofacial hard and soft tissue to be analysed statistically. This study aims to determine the shape variation of hard and soft tissue of Class II division 1 malocclusion and its changes pre-treatment and near end treatment using GMA. 141 pre-treatment and near end treatment lateral cephalometric radiographs of Class II division 1 malocclusion patients aged 14-40 years old and with skeletal II pattern (ANB>4o) were included. Pre-treatment samples were also divided into different age, race, gender, maxillary and mandibular plane angle (MMPA) and gonion angle groups. 32 landmarks in x and y Cartesian coordinates were created and identified on the lateral cephalometric radiographs using TPSDig2 software, then exported into MorphoJ for shape and statistical analysis. The general shape of hard and soft tissue of showed the largest variation in vertical dimension (hypodivergent to hyperdivergent facial profile), followed by variation in antero-posterior dimension (mild to severe skeletal II pattern). Lip shape varies in length (long to short) and lip protuberance (everted to inverted), whereas nasolabial angle (NLA) varies from obtuse to acute. Significant hard and soft tissue size differences were found in different gender (p<0.0001) and age (p<0.05). Shape of the hard and soft tissue is significantly influenced by treatment (p<0.0001), gonion angle (p<0.0001), MMPA (p<0.0001), race (p<0.0001) and age (p<0.0001). Near end orthodontic treatment showed significant uprighting of upper incisors (17.5o) and lower incisor (3.7o), improved NLA (8o), increase in upper lip thickness (1.5mm) and reduce in lower lip thickness (0.7mm) (p<0.05). In conclusion, vertical as well as anteroposterior shape variation of hard and soft tissue was found. The shape and size of hard tissue is influenced by age, gender, race, MMPA, gonion angle, and orthodontic treatment. Hence, understanding the shape variation of hard and soft tissue as well as orthodontic treatment changes are crucial for diagnosis and treatment planning to ensure a successful treatment with excellent patient satisfaction.