Related Experiment Video
Updated: Apr 28, 2026

Force System with Vertical V-Bends: A 3D In Vitro Assessment of Elastic and Rigid Rectangular Archwires
Published on: July 24, 2018
Retention Force Comparison between Hawley and Vacuum-Formed Retainers in Orthodontic Treatment of Maxillary Arch: A
Erfan Asadolahi1, Shabnam Saleh1,2, Yashar Rezaei3
1Department of Orthodontics, Tabriz University of Medical Sciences, Tabriz, Iran.
Background:
This study aimed to investigate the change in the retention force of Hawley and vacuum-formed retainers for the maxillary arch over a 6-month period.
Materials And Methods:
In this prospective, non-randomized cohort study, 50 patients who were prescribed Hawley or Vacuum-formed retainers for their maxillary arch were consecutively enrolled. Retainers were fabricated to the standardized design on casts and were exclusively checked for every patient. The retention force of retainers was evaluated based on the force (in Grams) required to remove them from the mouth. Retention force was assessed on delivery day, 3 and 6 months after treatment via force gauge. The changes in retention force from one timepoint to another were calculated as a ratio (retention change index) and were then compared between two retainers.
Results:
Forty-five patients (23 Hawley and 22 vacuum-formed) completed the study. The retention force of Hawley retainers throughout three-time points was 453-249-189 (g), while that of vacuum-formed retainers was 857-621-513 (g). The decrease in retention force was statistically significant for both retainers (P-value 0.001). The retention force decrease in Hawley retainers was significantly more than Vacuum-formed retainers throughout 6 months (P-value 0.05).
Conclusion:
Both retainers experienced a loss in retention force over the 6-month period. However, vacuum-formed retainers maintained a higher retention force compared to Hawley retainers, making them more effective in retaining the teeth in their corrected positions.
Related Concept Videos
Suctioning the Oropharyngeal Airway
After assembling the equipment, the nurse should practice hand hygiene and don appropriate PPE according to infection control guidelines to avoid the...
Three-Dimensional Force System
Force Classification
Contact and non-contact forces are two of the most widely used categories of forces. As the name suggests, contact forces require physical contact between two objects to act upon each other. Examples of contact forces include frictional,...
System of Forces and Couples
The principle of transmissibility plays a crucial role in this process. According to...
Simplification of a Force and Couple System: II

