Gap Magazine Implant Dentistry Today No 17

Implant Dentistry Today 10 O nplants, Block & Hoffman (1995) promoted the use of an “onplant” palatal anchorage device, which requires an osseointegrated interface. It is 10 mm in diameter and 3 mm thick. Healing period is 10 weeks. Mini-plates, in 1999, Umemori et al discussed skeletal anchorage systems and titaniumminiplates for correction of open bite. Miniplates have two major components: the plate itself, which is contoured to fit on the surface of the bone where it is attached, and a connector that penetrates into the mouth. n Indirect anchorage is a tooth-tooth interaction where the reactive unit is attached rigidly to the skeletal anchorage device. I. CLINICAL APPLICATIONS Orthodontic applications The “mini-implants” have the advantage of being practically immovable when used for the purpose of exerting tooth moving forces. This ability of providing absolute anchorage helps in achieving difficult movements. The orthodontic load-bearing capacity is closely related to the size and biocompatibility (i.e., bonding strength at the implant-bone interface) of the micro- implant. According to a finite-element model (FEM) analysis study, a miniscrew- type TAD made of titanium alloy can withstand approximately 200 to 400 g of orthodontic force, depending on the bone Micro-Implants in Orthodontics Part 1 Dr Geoff Hall By Dr Geoffrey Hall Fig 1a Superficial surface of a titanium onplant Fig 1c Subperiosteal placement of the onplant in the central portio of the palate Fig 1b Textured/hydroxyapatite-coated under-surface of the onplant, which is placed directly on bone (under periosteum) Fig 2 Transpalatal wire secured to the onplant with a screw and connected to molars serves as anchorage The micro-screw implants are most often used because of their tiny size, immediate loading and low cost. The small size enables micro-implants to be placed easily and closer to the dental arch, facilitating the delivery of the desired mechanics. Bi-cortical titanium screws are most frequently used in orthodontics. Fig 3 Micro-screw implants Fig 4 Skeletal anchorage devices Selection of skeletal anchorage device is also based upon the type of anchorage system required. Classified as Direct and Indirect Anchorage. Both mini-implant and mini- plates can be used in direct or indirect applications to apply continuous or intermittent force. n Direct anchorage is the application of a force directly from the skeletal anchorage device to a tooth or group of teeth – a TAD – tooth interaction. In such a situation the line of action is invariably intrusive in action. Fig 5 Skeletal anchorage Fig 6 Direct anchorage Fig 7 Indirect anchorage