Histological Research Of The Microscrew Implant-bone Interface

ObjectiveAnchorage design and control is one of the most important factors in a successful orthodontic treatment. Extraoral or intraoral appliances, such as headgear and intermaxillary elastics, are used for anchorage control. Traditional anchorage methods have many problems such as the stability, comfort and convenience to the patients, and the greatest disadvantage of these systems is patient, s compliance. In recent years the microscrew implants anchorage were reported in some clinical and animal studies that could safely be loaded with 2 ~ 3N orthodontic force and remain stable in the loading period. Roberts et al reported that incomplete osseointegration represents a distinct advantage in orthodontic applications, allowing for effective anchorage with easy insertion and removal.To establish the animal experiment model of orthodontic microscrew implant , histologically observe implant - bone interface, evaluate the effect of different force on this interface with immediately loading and the stability of microscrew implant as orthodontic anchorage.MethodsSixteen titanium alloy microscrew implants ( d = 1. 6 mm, 1 = 8 mm) were inserted vertically into the maxilla of the experimental dogs under anaesthesia and loaded with horizontal force immediately. The force was added by using nickel - titanium coil spring and was adjusted every two weeks. All the subjects was divided into four groups according to the force level (Og, 200g, 400g,600g). Eight weeks after implantation, the dogs were euthanized.Implants and the surrounded bone tissues were fixed and underwent the following procedures: embedding with plastic, cutting with saw microtome ( Le-itzl6OO,Germany) , grinding into slices (30|jim -50|jun manually grinded bone - implant slices were obtained) and special staining by toluidine - blue and basic fuchsin. Toluidine - blue staining was used to analyze the different ages and the remodeling pattern of the bone. Basic fuchsin was used to distinguish the fibrous tissue and to have a better contrast.ResultsThere were no significant differences between the result of toluidine -blue and basic fuchsin staining under light microscope.The tissue around implants in Og group was mainly fibrous tissue . Osseoin-tegration were found at the cervix and apex part of implants in group 200g and 400g and the osteoid tissue increased with the force increasing. In group 600g, serious breakdown of bone trabecula can be seen at the neck part of the micro-screw, but tight integration could be found at the apex part.ConclusionThe junction of microscrew implant and bone is not totally mechanical gom-phosis. The osteoid tissue occurred on the microscrew implant - bone interface. Microscrew implant can be used as orthodontic anchorage. With the increasing of loading force, more fiber can be seen on the interface. Using force over 600g can cause serious breakdown of bone trabecula at the neck part of the microscrew implant, but there was no obviously effect on that of the apex part.