Implants of one type or another have been around for many years, however the introduction of mini screws for orthodontic anchorage was relatively unknown until a paper by Kanomi in 1997 reported the intrusion of mandibular anterior and buccal teeth using mini screw implants. Since that time their use has grown rapidly and today there are many varieties on the market.
Mini screws vary between 5 - 12 mm in length and 1.2 - 2 mm in diameter. Ideally they are placed in cortical bone in the attached gingival area, between the roots of the teeth. The self drilling variety can be screwed directly into the bone without the need for a pilot hole to be drilled first (the self tapping variety require a pilot hole). A small amount of local anaesthetic is infiltrated first - but only sufficient to give surface an-aesthesia. On entering the bone the patient will feel pressure, and pain only if the periodontal ligament or root surface is approached. This is the reason for light anaesthesia of the area, as it enables a warning system if the mini screw is going off course.
Their attachment to bone is mechanical with no intent to encourage osseointegration. Normally they are left in place for up to 6 months and then removed. Their removal is simply by unscrewing the mini screw and no local anaesthesia is required. A suitable mini screw implant kit is needed. Prior to placement a panoramic or periapical radiograph is taken to assess the inter-radicular space - normally a minimum of 2mm is needed. Radiographic markers in the form of a ligature wire may be placed as a guide to placement, prior to taking the radiograph.
