Defense Date


Document Type


Degree Name

Master of Science in Dentistry



First Advisor

Steven Lindauer

Second Advisor

Bhavna Shroff

Third Advisor

Parthasarthy Madurantakam

Fourth Advisor

Caroline Carrico


Introduction: The aims of this randomized clinical trial were to compare the efficacy of extrusion of maxillary lateral incisors among “optimized”, rectangular “horizontal”, rectangular horizontal “incisally beveled”, rectangular horizontal “gingivally beveled” attachments, and to provide a clinically relevant recommendation for attachment planning for extrusion of maxillary lateral incisors during aligner treatment.

Methods: 30 16-to-58 year old Invisalign patients and 56 maxillary lateral incisors requiring extrusion were randomly allocated to one of four attachment groups (optimized, horizontal, incisally beveled, and gingivally beveled). Participants were recruited from two private practice offices and the Virginia Commonwealth University School of Dentistry. The outcome assessor was blinded. Each patient was given an initial series of 20 to 25 clear aligners and iTero scans were taken initially, and at the completion of the series. The predicted posttreatment model was derived from the Invisalign ClinCheck Pro software (Align Technologies). The initial model was superimposed with the predicted posttreatment model and actual posttreatment model using Geomagic Control X software (Rock Hill, SC, USA). Extrusion was measured using the predicted posttreatment and actual posttreatment superimpositions, and the amount of extrusion achieved was compared among attachment groups.

Results: The mean achieved extrusion was 71% of predicted extrusion and an average of 0.22 mm less than predicted extrusion. There was no significant difference among the extrusion of the four attachment groups. However, there was a significant increase of 17% in the absolute extrusion and 29%in the relative extrusion of the conventional attachment group compared to the optimized attachment group.

Conclusions: Conventional, 4 mm wide, horizontal attachments (horizontal, incisally beveled, or gingivally beveled) were significantly more reliable for achieving maxillary lateral incisor extrusion than optimized attachments. Achieved extrusion of maxillary lateral incisors was 76% of the amount predicted for conventional attachments and 59% for optimized attachments. More prospective studies are needed to explore other methods to improve the predictability of extrusion of maxillary lateral incisors with clear aligners.


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