Does the trimline extension and attachment size affect maxillary arch expansion in clear aligner therapy ? A finite element study

Abstract

Abstract Objective Using finite element analysis (FEA), the aim of the present study was to evaluate the effects of different aligner trimline extensions and attachment sizes on maxillary first and second molars under expansive forces delivered by clear aligner therapy Methods The study utilised 3 mm and 4 mm horizontal rectangular attachments on the maxillary first and second molars. Two main models were created: a High and Flat Trimline Aligner (HTLA), and a Low and Flat Trimline Aligner (LTLA). Six distinct model variations were created for the analysis: (1) LTLA and no attachment (NA), (2) LTLA and 3 mm horizontal rectangular attachment (3HA), (3) LTLA and 4 mm horizontal rectangular attachment (4HA), (4) HTLA and NA, (5) HTLA and 3HA, (6) HTLA and 4HA. Results In all models, the crowns of the maxillary molars exhibited buccal displacement, whereas the root displayed palatal displacement. The LTLA-NA model had the greatest displacement of all models, whereas the HTLA-4HA model had the lowest displacement. The greatest PDL stress value was identified in the coronal third region of the palatal root of the molars. Conclusion Buccal tipping of the molars was observed during aligner expansion in all models. By increasing the attachment size and heightening the aligner trimline extension, the occurrence of buccal tipping was significantly reduced.