Comparative evaluation of lower incisor intrusion using conventional method and frog staging protocol in clear aligners: A three-dimensional finite element analysis.

Abstract

Objectives: Deep bite correction with aligners involves anterior intrusion and posterior extrusion. During lower incisor intrusion with clear aligners (CAs), root disengagement from the alveolar bone can cause complications. Frog staging protocol applies sequential forces, targeting lateral incisors first, then central incisors. This study compares conventional and Frog staging intrusion protocols using attachments for mandibular anterior teeth to optimize clinical practice.

Materials and methods: A 3D finite element (FE) model, including the clear aligner, periodontal ligament (PDL), and mandibular dentition, was established. Four groups were analyzed: Group 1 (Conventional intrusion with attachments), Group 2 (Conventional intrusion without attachments), Group 3 (Frog staging intrusion with attachments), and Group 4 (Frog staging intrusion without attachments). Rectangular molar attachments (4.0 × 2.0 × 0.75 mm) and vertical canine attachments (3.5 × 1.8 × 0.75 mm) provided anchorage. Incisor attachments (3.0 × 1.5 × 0.75 mm) facilitated precise force application. Stress distribution was evaluated using von Mises stress (overall stress), maximum principal stress (tensile), and minimum principal stress (compressive).

Results: Frog staging resulted in balanced stress distribution and reduced adverse effects compared to conventional intrusion. Attachments minimized stress and displacement, enhancing intrusion mechanics. Frog staging better controlled root displacement and stress concentration at the root apex.

Conclusions: Frog staging intrusion with attachments is biomechanically superior for lower incisor intrusion, reducing complications and providing a safer approach for deep bite correction with CAs.