Comparison of estimated and actual changes in gap widths of expansion screws in plate appliances with 7- and 14-day activation.

Objective: To determine how gap opening is affected by the activation intervals of expansion screws in removable orthodontic appliances and which gap widths are achievable during therapy.

Materials And Methods: In this retrospective study, the increases in gap widths for transverse and distalizing screws activated at 7- and 14-day intervals were calculated. These estimates were based on measurements taken with a caliper of the gap widths of 242 screws integrated in the plates of 137 patients examined during 4-5 follow-up visits over a 6- to 7-month therapy period.

Results: A comparison of the theoretical gap widths that we had estimated with those actually measured revealed for the first time that differences in activation intervals have a statistically significant effect on gap width. The 7- and 14-day activation intervals can lead to a linear or nonlinear increase in gap width that greatly depends on the type of expansion screw. Within the therapy period, transverse screws achieved gap widths as much as twice as wide as those achieved with the distalizing screw.

Conclusion: The gap widths are illustrated in graphs and summarized in tables. These values offer practical orientation for clinicians planning and controlling the therapy course, and they can help to prevent "overactivation" with removable expansion plates.