Comparison of Anchorage Pattern under Two Types of Orthodontic Mini-Implant Loading During Retraction in Type A Anchorage Cases

Abstract

Introduction: The orthodontic mini-screws are the mainstay of direct skeletal anchorage which requires minimal compliance and provides maximal anchorage control. However, the timing of initiation of orthodontic loading of these mini-screws is not clearly established in the available studies. Aim: The purpose of this study was to determine the reciprocal effects on mini-screw implant with immediate loading in comparison to that of delayed loading during retraction. Materials and Methods: The prospective clinical study included a sample of 25 orthodontic patients in the age range of 18-25 years. All the cases were of bi-maxillary proclination with Type-A anchorage demands. All the first premolars were indicated for extraction. A split mouth technique for each patient was utilized by loading mini-implant immediately after its placement on one side and the opposite side implant was loaded after a time lag of two weeks post-insertion. Retraction force of 150g was applied for three months on each side. The displacement of the head and tail of the implant, molar anterior tooth retraction was measured on Orthopantomograph (OPG) taken at T1 (initial) and T2 (after three months). A grid method with each 1mm magnified to 500 pixels was superimposed on OPG and the relative displacements were evaluated. Student’s unpaired ‘t’ test was used for comparison between left and right side and paired ‘t’ test for the parameters on the same side. The p-value equal to or less than 0.05 was taken as statistically significant. Results: The mean displacement of head of the implant on the immediate loading is 0.57mm where as the tail exhibited 0.75 mm. The head and tail of the implant on the delayed loading displaced by 0.35mm and 0.38mm respectively, on an average when data was analysed. Significant difference between the two types of loading was noted. Conclusion: Delayed loading is beneficial as compared to immediate loading during extraction space closure.

Keywords

• delayed
• grid method
• orthopantomograph
• split mouth
• tooth movement