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The influence of extraction on the stability of implanted titanium microscrews: a biomechanical and histomorphometric study.

PURPOSE
The purpose of this study was to explore the influence of extraction on the stability of implanted titanium microscrews.


MATERIALS AND METHODS
Six male beagle dogs received 96 microscrews between the mesial and distal roots of the second, third, and fourth premolars and the first molar in both maxillae and mandibles. The third and fourth premolars were extracted from each dog. Test implants were placed near the extraction sites, and control implants were placed at a distance from the extraction sites. The bone remodeling process at the interface was studied through biomechanical pull-out testing, histomorphologic observation, and histomorphometric assessment after different amounts of healing time (1, 3, or 8 weeks).


RESULTS
Two microscrews were loose in the test group at week 1. Near the extraction regions, both the peak pullout force at extraction (Fmax) and the bone-implant contact (BIC) of the microscrews were lower than that seen in the control group at week 1, but quickly surpassed the control groups at week 3. After 8 weeks of healing time, Fmax and BIC values between test and control groups exhibited no differences. The lowest BIC value was 10.12%, and the corresponding pull-out force was 100.23 N. At week 1, the inflammatory reaction at the bone-implant interface in the test groups was stronger than in the control groups. At week 3, many active osteoblasts gathered along the interface and a bone matrix excreted by osteoblasts around the microscrew were observed in the test group.


CONCLUSIONS
A BIC of at least 10% provided resistance to orthodontic forces. For microscrews placed near extraction regions, the risk of loosening was highest in the first week following implant placement. The most active bone remodeling at the implant-bone interface occurred 3 weeks after implantation, especially for screws near extraction regions.