Australasian Dentist Issue 92

CATEGORY 48 AUSTRALASIAN DENTIST LINICAL 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 titanium miniplates 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. u 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 toothmoving 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 condition and diameter of the TAD. 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. u 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