Minimum required length of orthodontic microimplant: a numerical simulation and clinical validation

초록

Introduction: This study aimed to determine the minimum required length of microimplants (MIs) to prevent excessive micromotion during MI healing that can lead to MI failure. Methods: Hypothesizing that the implanta-tion depth of MI in cancellous bone (IDcancel) is the key to the control of micromotion during MI healing, we numer-ically investigated the minimum IDcancel required to maintain MI micromotion to below the threshold (30 mu m) that would threaten MI survival. Twenty MI and bone models were built using MIs of 4 lengths and bone specimens with 5 different cortical bone thicknesses to create IDcancel in the 0.5-5.5 mm. Then, applying a horizontal force of 1.5 N on the MI head, we calculated the micromotion (peak and average MI micromotions) and determined the minimum IDcancel. A clinical test was performed to verify the numerical result by placing 160 MIs in the posterior maxilla and mandible. Results: A strong correlation (r2 = 0.694) was found to exist between IDcancel and MI mi-cromotion. A minimum of 2.5 mm of IDcancel was needed to maintain the level of MI micromotion (peak micromotion) \30 mu m threshold. The 6-month survival rate of MI was strongly correlated with IDcancel (r2 = 0.744) and decreased sharply when IDcancel was #2 mm. Conclusions: The minimum lengths of MIs to provide the minimum IDcancel of 2.5 mm required to promote successful MI healing in the posterior maxilla and mandible are 5.2 and 6.5 mm, respectively. (Am J Orthod Dentofacial Orthop 2023;163:858-66)

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