Scanning electron microscopy evaluation of aligner fit on teeth

OBJECTIVES: The fitting of aligners on anchorage teeth is a crucial factor in clear aligner orthodontics. The purpose of this experimental study was to evaluate the fitting of two aligner systems, Invisalign and CA-Clear Aligner, using scanning electron microscopy (SEM). MATERIALS AND METHODS: Passive aligners (Invisalign and CA-Clear Aligner) were adapted on resin casts obtained by stereolithography (STL) files of a patient, and then sectioned buccolingually. Upper and lower central incisors, upper and lower first premolars, and upper and lower first molars were the regions analyzed. Representative microphotographs of sections were taken with a scanning electron microscope (SEM); a total of 160 micrometric measurements were obtained and analyzed with ANOVA tests. RESULTS: Invisalign provided an overall better fit on lower incisors ( F = 11.48, P = .0095) and on lower molars ( F = 19.93, P = .0012). Considering the different regions, Invisalign provided better fit at the gingival edge of the buccal aspect on lower incisors ( F = 11.33, P = 0.0056) and at the gingival edge of the lingual aspect on upper premolars ( F =5.34, P = 0.0047). On the upper molars, Invisalign provided better fit at the gingival edge of the buccal aspect, while CA-Clear Aligner provided better fit at the buccal maximum convexity, on the buccal cusp, on the occlusal groove and at the palatal cusp. On lower molars, Invisalign showed a more accurate fit at the buccal aspect points. CONCLUSIONS: Invisalign and CA-Clear Aligner exhibited comparable fit on anchorage teeth. Invisalign provided better fit at the gingival edges of aligners, while the CA-Clear Aligner provided better fit on complex occlusal surfaces.