Impact of Class II Elastics on Stress Distribution in Distinct Facial Growth Patterns.

Abstract

Aim: The objective of this research was to elucidate displacement of maxillomandibular complex and stress pattern formed on temporomandibular joint in horizontal and vertical growing facial forms in Class II elastic placement from lower first molar to upper canine; and from lower second molar to upper canine and compare stress pattern formed.

Methods: The model was determined from Cone-beam computed tomography of two individuals, one with a horizontal and one with a vertical facial profile. Four models, with brackets and archwires, were created with different elastic configurations. The models were subjected to finite element method validation with loading conditions for 200 g of orthodontic forces, and relevant material properties were assigned to obtain overall stress and deformation to the teeth model. The stress values were obtained on the condylar head and articular disc and were plotted.

Results: Displacement was more when elastic stretch was between maxillary canine and mandibular second molar in horizontal facial model (0.30 mm) and minimum in vertical facial model with elastic stretch from maxillary canine to mandibular first molar (0.24 mm). In vertical facial models, maximum principal stress was more on glenoid fossa of both the configurations (0.045 and 0.054 MPa); canines of both the configurations experienced more stress (0.039 and 0.027 MPa).

Conclusion: This FEM analysis demonstrated that vertical facial growth patterns experience higher stress concentrations in the TMJ under class II elastic traction compared to horizontal growth patterns. Similarly, special considerations are taken in cases where elastics are placed between upper canine and lower second molar, so as to not disturb the occlusal harmony and muscular balance in the oro-facial region. These findings highlighted the importance of biomechanical consideration when applying orthodontic elastics in different facial patterns. However, clinical symptoms such as pain or discomfort were not evaluated in this study and cannot be inferred from the simulation alone.