A root contact during the installation of the orthodontic mini-implants may cause an iatrogenic trauma as well as instability of the mini-implants. In this study, intentional root contact while inserting mini-implants was performed on four Mini-pigs to test how the root contact influenced the insertion torques of the orthodontic mini-implants.
Orthodontic mini-implants were implanted into the interradicular alveolar bones of four Mini-pigs using a surgical engine. For each quadrant, 6 mini-implants were implanted, thus implanting 24 mini-implants in one pig, and implanting total of 96 orthodontic mini-implants for the entire experiment, while the insertion torques were recorded individually. Out of the 64 samples that had definite confirmation of whether there were root contact or not, 48 samples that had contacted the root were considered as the experimental group and 16 samples that had no contact with the root was considered as the control group. The maximum insertion torque values and the angular momentums were compared by using the time-torque graph, according to the jaws the mini-implants were inserted into, and the presence of root contact.
The results were as follows:
1. The maximum insertion torques and angular momentums were statistically higher (p < 0.01) in all the root-contacted mini-implants than in all the non root-contacted mini-implants.
2. At the point of root contact with the orthodontic mini-implants, insertion torque either reached a plateau region or decreased for a period of time, and then rapidly increased until it reached the maximum insertion torque.