Pre-drilling force and insertion torques during orthodontic mini-implant insertion in relation to root contact; [Vorbohr-Widerstand und Eindrehmomente bei der Insertion kieferorthopädischer Mini-Implantate in Abhängigkeit zu einem Zahnwurzel-Kontakt]

Background and Aim: The use of mi ni-implants for skeletal anchorage has greatly broadened the therapeutic spectrum in orthodontics over the last few years. The alveolar ridge is the most frequent insertion site, which however is associated with tooth injury, a risk not to be underestimated. The objective of this study was to examine the quantitative parameters of pre-drilling and implant insertion in association with the degree of a root contact. Material and Methods: Eleven lower jaw bones of adult pigs were prepared and embedded in resin. At 320 sites in the toothbearing alveolar ridge a 1.3 mm pre-drilling was carried out up to the complete implant length. The vertical force exerted against the pre-drilling upon penetration of the different bone layers and at a root contact was measured at a drift-speed of 0.5 mm/s. Dual Top™ screws (1.6 × 8 mm) were then inserted into the prepared implant sites, the insertion torques were measured, and recorded as a function of the rotation angle. After explantation, we prepared histological slides from the level of the implant's maximum diameter. The implant's contact with cortical and cancellous bone and to the roots was measured and correlated to vertical pre-drilling forces and insertion torques. Results: Vertical pre-drilling forces and insertion torques of orthodontic mini-implants varied in relation to the type of tissue penetrated and the degree of root contact. The insertion torques ranged from 32 to 345 Nmm and pre-drilling forces up to 6 N overall. Conclusion: Root contact can be recognized during pre-drilling by a distinct increase in resistance, and during mini-implant insertion by higher torques. © Urban & Vogel München 2008.