Influence of periodontal ligament heights on sequential and simultaneous maxillary molar distalization using clear aligners

This study investigates the influence of varying periodontal ligament (PDL) heights on maxillary molar distalization using clear aligners (CAs). The analysis emphasizes the biomechanical impacts of PDL height reduction on stress distribution, tooth displacement, and anchorage control across two distalization modes: sequential and simultaneous.

This study is a retrospective single-case finite element analysis conducted at the First Affiliated Hospital of Bengbu Medical College. Data was obtained from a 26 years old male patient with Angle Class II malocclusion who presented at the hospital on March 19, 2024. Data collection was completed on the same day, and finite element modeling and biomechanical analysis were performed from March 20, 2024 to December 29, 2024. A finite element (FE) model was developed to evaluate molar movement in both sequential mode (where the second molar moved 3.00 mm prior to the first molar's 0.25 mm movement) and simultaneous mode (where both molars moved 0.25 mm concurrently). Simulations were conducted under three PDL conditions: full height (1.0-control group), moderate reduction (0.67), and severe reduction (0.33). Key biomechanical responses, including stress distribution within the PDL and initial displacement of molars and anterior teeth along three axes (X, Y, Z), were analyzed.

Reduced PDL height significantly amplified stress concentration near the cervical margin of molars and anterior teeth, with uneven stress patterns becoming pronounced under severe PDL reduction (0.33). This led to increased molar tipping and heightened anterior anchorage loss in both modes. Although sequential distalization minimized these adverse effects due to more controlled stress distribution, reduced PDL height remained a critical factor driving greater inefficiency and mechanical instability.

PDL height variations fundamentally influence molar distalization mechanics and anchorage stability, overshadowing the effects of distalization modes. Reduced PDL height intensifies stress imbalances and risks periodontal damage, underscoring the importance of personalized force management strategies in patients with compromised periodontal conditions.