Vertical settling elastics for resolving posterior open bite during the fine-tuning staging for clear aligner therapy: A prospective clinical study.

BACKGROUND

Posterior open bite (POB) is a common and challenging complication during clear aligner therapy, primarily because of the biomechanical susceptibility of posterior teeth to intrusion, occlusal block effect, and excessive expansion. Although posterior vertical elastic traction has been proposed as a potential intervention, its clinical efficacy and the factors influencing treatment outcomes remain poorly understood. This prospective study aimed to evaluate the effectiveness of posterior settling elastics in correcting POB and identify key predictors of treatment success.

METHODS

Fifty-two patients treated with Invisalign (Align Technology, Santa Clara, Calif) who exhibited POB, defined as a vertical distance >0 mm for mesiobuccal (MB), distobuccal (DB), or palatal (PL) cusps of maxillary and mandibular molars in centric occlusion after the refinement of the aligner, were enrolled. A total of 172 molar sites were assessed, of which 95 received elastic traction (vertical or triangular), and 77 were treated with aligners alone. Digital models at pretreatment (T0), predicted (T1), and posttreatment (T2) stages were acquired via iTero Element scanning (Align Technology, San Jose, Calif) and registered to a standardized coordinate system using Geomagic Studio 2014 (3D Systems, Rock Hill, SC). Actual cusp extrusion distances relative to the reference xy-plane were measured, and occlusal contact areas were quantified using Boolean superposition. Univariate and mixed-effects multivariate linear regression analyses were conducted to identify predictors of cusp extrusion.

RESULTS

Multivariate analysis revealed that MB cusp extrusion was positively associated with elastic traction (P <0.001), baseline MB cusp distance (P <0.001), predicted extrusion (P <0.001), and female sex (P <0.001) and was negatively associated with pretreatment anterior overjet and overbite. Similar patterns were observed for the DB cusp extrusion. PL cusp extrusion was primarily predicted by its baseline distance (P <0.05) and predicted extrusion (P <0.05), and was negatively influenced by the pretreatment DB cusp distance.

CONCLUSIONS

Posterior vertical settling elastics are effective in correcting clear aligner-induced POB, particularly by improving maxillary buccal cusp occlusal contacts. Optimal correction requires substantial overcorrection in the planned posterior extrusion and careful evaluation of baseline POB severity, anterior overjet and overbite, and patient sex to maximize treatment predictability.