Root contact during insertion of miniscrews for orthodontic anchorage increases the failure rate: an animal study

Miniscrews and miniplates are increasingly being used for absolute anchorage during orthodontic treatment. However, potential problems of damaging adjacent roots and their consequences during mini-implant placement in the alveolar process have not been clearly described.

Animal experiments were used to evaluate the stability of miniscrews placed with intentional root contact. The root repair was evaluated after screw removal. Seventy-two miniscrews were surgically placed in the mandibular alveolar bone of six adult mongrel dogs with metabolic bone labeling at 3-week intervals. Miniscrews of the experimental group were placed so that they contacted the root of the adjacent teeth, were retained for different time durations, and were then removed. The insertion torque, clinical measurements, removal torque, and histological findings were analyzed.

(1) miniscrews contacting the roots showed a significantly higher insertion torque than those without contact; (2) there was a significant difference in the removal torque measurements based on the mobility of miniscrews and the state of root contact; and (3) miniscrews contacting the root were at greater risk of failure.

During placement of miniscrews in the aveolar process, increased failure rates were noticed among those contacting adjacent roots. Failed miniscrews appeared to be surrounded with a greater volume of soft tissue. When more inflammation was present, the adjacent roots seemed to experience more resorption. Nevertheless, the created lesion was repaired with a narrow zone of mineralized tissue deposited on the root surface, which was likely cellular cementum, and was mainly filled with alveolar bone, with the periodontal ligament space being maintained.