The Effect of Attachment Flash on Clear Aligner Force Delivery

Abstract

Introduction: Composite attachments are a vital part of clear aligner therapy and crucial to accomplish the intended tooth movements throughout treatment. Due to the necessity and importance of attachments, accurate application is imperative. When attachments are bonded, placing them without excess composite flash going beyond the perimeter is nearly impossible. Recent research has studied certain attachment bonding protocols to investigate which bonding protocol produces the least amount of excess, but no research has been done to demonstrate clinical effects excess composite flash has on clear aligner treatment. Aim: To evaluate the effect attachment flash thickness and surface area has on the force delivered to a maxillary central incisors with a Zendura FLX clear aligner. Methods: The experiment was conducted in a lab setting using 3D printed models of the maxillary arch. Zendura FLX .030 mil clear aligners programmed for 0.25 mm of extrusion will be used on a maxillary central incisor. To evaluate the effect of flash thickness and surface area, a standard rectangular anterior extrusion attachment placed on the midfacial surface of the clinical crown was designed with no flash which served as the control. We tested three different surface areas (7mm2, 14mm2, 21mm2) at three different thicknesses (0.2 mm, 0.35 mm, 0.5 mm), making ten total designs. For each of the ten groups, five aligners were fabricated with margins 0.75 mm apical to the gingival zenith. Extrusive and lingual forces were measured using a force gauge. Means and standard deviations were calculated and presented by group. The one-way analysis of variance (ANOVA) was conducted to compare the means between the groups and Tukey’s method was used to adjust for multiple comparisons. P-values less than 0.05 were considered statistically significant. Results: The intended extrusive force decreases as flash surface area decreases and as flash thickness increases. The main finding to note when examining how the intended extrusive force was affected by flash was looking at the standard deviations for each group. The control group had the smallest standard deviation compared to all the groups with flash. When looking at the mean unintended lingual force, all groups including flash showed higher lingual force than the control group with seven out of the nine groups being statically significant. In general, as the thickness of the flash increases, the lingual force applied to the tooth by a clear aligner (CA) increases. Similarly, as the surface area of the flash increases, the lingual force applied to the tooth by a CA increases. Conclusions: This is the first study in which the effect of attachment flash on force applied by a clear aligner has been studied. In this benchtop study, a few conclusions can be made as to the effect attachment flash has on clear aligner therapy (CAT). CAs exert more lingual force when attachment flash is present compared to attachments without flash. As flash thickness increases and flash surface area increases the CAs exert more lingual force. As flash thickness increases and flash surface area decreases the intended extrusive force applied by CAs decreases. When flash is present, the intended extrusive force is less predictable compared to when no flash is present.