Association between initial complexity, frequency of refinements, treatment duration, and outcome in Invisalign orthodontic treatment.

INTRODUCTION: This study explored possible associations between treatment duration, initial complexity, outcomes in Invisalign therapy, and the number of refinements. METHODS: Three-dimensional models (initial, final, and refinements) of 355 Invisalign patients (114 males and 241 females; 33.8 +/- 17.1 years) were analyzed using the Peer Assessment Rating (PAR) index questionnaire tool in the Ortho Analyzer software (version 2.0; 3Shape, Copenhagen, Denmark) to calculate the weighted total and individual PAR index scores for each component of the PAR index. Data related to demographics, treatment duration, and the number of refinements were collected. RESULTS: Treatment duration increased as the number of refinements increased. Percent of improvement was higher in PAR >/=22 group than PAR <22 with an increase in the number of refinements: 83.3% vs 73.8% for 2 refinements; 94.7% vs 91.2% for 3 refinements; and 100% vs 85.7% for >/=4 refinements. Those who achieved great improvement or improvement and those who did not were significantly different in treatment duration (P <0.001 and P = 0.027), number of refinements (>/=3 refinements; P <0.001), initial occlusal severity (PAR >/=22; P <0.01 and P = 0.031). Most subjects achieved improvement after the first refinement (64.5% for PAR <22 and 78.5% for PAR >/=22). Few had >/=4 refinements, and if they did, none achieved improvement with additional refinements. CONCLUSIONS: Initial complexity for an Invisalign case is associated with treatment duration, achieved outcomes, and the number of refinements. Treatment duration increased with an increased number of refinements. Great improvement or improvement for the first time dropped to 0 if additional refinements were carried out after 3. Therefore, performing additional refinements does not necessarily mean better occlusal outcomes.