Smile outcome comparison of Invisalign and traditional fixed-appliance treatment: A case-control study

Introduction: The purpose of this study was to evaluate and compare smile treatment outcomes between patients treated with Invisalign clear aligners (Align Technology, Santa Clara, Calif) and those treated with traditional fixed appliances by integrating variables such as lip symmetry, smile index, smile cant, buccal corridors, and gingival display into smile outcome evaluation.

Methods: Records from 58 patients, 29 of whom received Invisalign treatment (mean age 19.03 years) and 29 of whom received traditional fixed-appliance treatment (mean age 13.83 years), were compared for their smile outcome. Pretreatment scores, posttreatment scores, and differences between within-group smile score before and after treatment were determined for each group. Fifteen variables comprised the smile outcome, and the data were analyzed with the Mann-Whitney U test and the Wilcoxon t test for 2 dependent samples.

Results: Six variables within the fixed-appliance group presented with better smile scores than those within the Invisalign group; buccal corridors (%) (mean difference = 8.42%), buccal corridors (mm) (5.35 mm), smile cant (0.42°), maxillary dental midline (0.21 mm), gingival display (0.56 mm), and smile index (1.09%) for P <0.05. Invisalign performed better on 2 variables that determined maxillary incisor position (1.26 mm) and inclination (2.09°). No significant difference (for P = 0.05) was shown between pretreatment and posttreatment scores for either of the 2 groups.

Conclusions: Using the 15 variables in this study, the results suggested that for patients with Class I nonextraction, treatment with traditional fixed appliances changes the patient's smile more than Invisalign treatment, and fixed appliances appear to be more effective in improving the variables that quantify posttreatment smile outcome.