[Insertion of min-screws: with or without pre-drilling?].
The recent introduction of the new systems of intraosseous anchorages called mini-screw, allowing an immediate loading, has revolutioned the clinical and biomechanical approach of anchorage in orthodontics. Trans-gingival insertion by a manual screwdriver is done easily and most frequently without before-hole. The goal of this experimental study is to show that the realization of a before-hole limits the intraosseous constraints during screwing. This having short-term effects on the primary stability of the mini-screws and long-term effects on their maintenance.


METHODS
two self-drilling and self-tapping mini-screws Aarhus Medicon of 1.6 and 1.3 mm diameters are screwed with a manual screwdriver, without then with a before-hole, in a plate of cortical bone fixed on a sensor measuring the forces and the couple.


RESULTS
the realization of a before-hole in the cortical bone significantly decreases the maximum vertical force (FVM) at the beginning of screwing (p < 0.0001) and the maximum screwing couple (CVM) at the end of the screwing (p < 0.0001), this independently the diameter of the screw.


CONCLUSIONS
screwing without before-hole led to the alteration of the osseous surface layer caused by micro fractures which limit the possibilities of blocking of the mini-screws.
Massif
Laurent
L
Faculté d'odontologie, Département d'Orthodontie, Montpellier I, 545 avenue du Pr Jean-Louis Viala, 34193 Montpellier Cedex 5, France. lmassif@yahoo.fr
Frapier
Laure
L
Micallef
Jean-Paul
JP
D000818:Animals; D001863:Bone Screws; D002417:Cattle; D003758:Dental Implantation, Endosseous / Q000379:methods; D004548:Elasticity; D004867:Equipment Design; D008904:Miniaturization; D052280:Orthodontic Anchorage Procedures / Q000379:methods*; D013314:Stress, Mechanical; D013718:Tensile Strength; D019415:Torque