A three-dimensional finite element analysis of molar distalization with a palatal plate, pendulum, and headgear according to molar eruption stage

Abstract

Objective: This study aimed to (1) evaluate the effects of maxillary second and third molar eruption status on the distalization of first molars with a modified palatal anchorage plate (MPAP), and (2) compare the results to the outcomes of the use of a pendulum and that of a headgear using three-dimensional finite element analysis.

Methods: Three eruption stages were established: an erupting second molar at the cervical one-third of the first molar root (Stage 1), a fully erupted second molar (Stage 2), and an erupting third molar at the cervical one-third of the second molar root (Stage 3). Retraction forces were applied via three anchorage appliance models: an MPAP with bracket and archwire, a bone-anchored pendulum appliance, and cervical-pull headgear.

Results: An MPAP showed greater root movement of the first molar than crown movement, and this was more noticeable in Stages 2 and 3. With the other devices, the first molar showed distal tipping. Transversely, the first molar had mesial-out rotation with headgear and mesial-in rotation with the other devices. Vertically, the first molar was intruded with an MPAP, and extruded with the other appliances.

Conclusions: The second molar eruption stage had an effect on molar distalization, but the third molar follicle had no effect. The application of an MPAP may be an effective treatment option for maxillary molar distalization.

Keywords: Class II; Distalizing; Headgear; Palatal plate.

Figure 1. The finite element model eruption stages. Stage 1, an erupting second molar at the cervical one-third of the first molar root; Stage 2, a fully erupted second molar without the third molar; and Stage 3, an erupting third molar at the cervical one-third of the second molar root.

Figure 2. Designs of the appliances. A, Modified palatal anchorage plate with brackets and orthodontic arch wire; B, bone-anchored pendulum appliance; and C, cervical-pull headgear.

Figure 3. Landmarks. 1, Distobuccal cusp of the first molar; 2, mesiolingual cusp of the first molar; 3, distobuccal cusp of the second molar; 4, mesiolingual cusp of the second molar; 5, palatal root apex of the first molar; 6, palatal root apex of the second molar; 7, midpoint of the incisal edge of the central incisor; and 8, root apex of the central incisor.

Figure 4. Contour images of tooth displacement from the modified palatal anchorage plate appliance. A, Buccal view; B, occlusal view. Positive values mean forward, left, and upward directions.

Figure 5. Contour images of tooth displacement from the bone-anchored pendulum appliance. A, Buccal view; B, occlusal view. Positive values mean forward, left, and upward directions.

Figure 6. Contour images of tooth displacement from the cervical-pull headgear. A, Buccal view; B, occlusal view. Positive values mean forward, left, and upward directions.

Figure 7. The von Mises stress distribution after the application of distalization forces using an modified palatal anchorage plate (MPAP), bone-anchored pendulum, and headgear appliances during Stage 2 eruption.