Challenging orthodontic cases: the use of skeletal anchorage

A treatment objective of upper molar distalisation may often be indicated for the correction of a dentoalveolar Class II malocclusion with an associated increased overjet and/or anterior crowding. Due to aesthetic concerns and the duration of treatment, molar distalisation using headgear is unacceptable for many patients. This has resulted in a preference for purely intraoral distalisation appliances which require minimal patient cooperation. Unfortunately, most conventional devices for non-compliance maxillary molar distalisation produce unwanted side effects, such as anchorage loss. If the anchorage unit includes teeth, mesial migration and/or protrusion of the anterior dentition need to be considered as major disadvantages. To minimise or eliminate anchorage loss related to the anterior teeth, skeletal anchorage has been integrated into distalisation appliances. The anterior palate has proved to be an ideal site for miniscrew placement for the distalisation of upper teeth. The good bone quality, the attached mucosa, and the minimal risk of injury to nearby teeth have been suggested as major advantages of miniscrew placement in this region. Furthermore, the mini-implants are unlikely to be in the path of tooth movement. Skeletal anchorage mechanics can be divided in direct and indirect appliances. If the maxillary molars are to be distalised, direct anchorage is advantageous, since a major disadvantage of devices employing indirect anchorage is the need for a two-phase clinical procedure: (a) distalisation of the molars, and (b) stabilisation of the molars while retraction of the anterior dental segment occurs. To benefit from the advantages of direct anchorage mechanics and use the anterior palate as the most suitable mini-implant insertion site, the Beneslider and the Pendulum B mechanics may be employed.
 

Unilateral or bilateral missing upper teeth are diagnosed quite frequently: Congenitally missing lateral incisors / second bicuspids, extremely displaced canines or a severe trauma of a central incisor are potential findings that result in a reduced upper dentition. Especially the prevalence of missing maxillary lateral incisors is quite high (0.8 to 2%). The two major treatment approaches are space closure and space opening to allow prosthodontic replacements either with a fixed prosthesis or single-tooth implant. Both of these treatment approaches may potentially compromise aesthetics, periodontal health, and function. Single-tooth dental implants in the maxillary anterior region have the highest risk of esthetic complications from infra-positioning due to continuing growth and the continuing eruption of adjacent teeth. In many cases, space closure to the mesial seems to be the favourable treatment goal, since treatment already can be completed as soon as the dentition is complete. Thus, a second orthodontic treatment to upright tipped adjacent roots before insertion of a dental implant can be avoided. Canine substitutions can be accomplished with good aesthetic outcomes by tooth reshaping and positioning, bleaching and porcelain veneers. The more mesial the missing tooth is the higher will be the demands for anchorage, which can be realized by reverse headgear or class III elastics. However, both anchorage modalities require a high level of compliance and may cause some unwanted side effects such as TMJ problems or retrusion of lower teeth on case of class III elastics. With the goal to achieve a more reliable anchorage, the use of mini-implants has increased over the last couple of years. However, buccally inserted mini-implants are in the path of moving teeth. As a consequence, the palatal area seems advantageous, since all teeth can be moved without any interference with TADs. The Mesialslider enables clinicians to mesialize upper molars and thus close upper spaces unilaterally or bilaterally. In addition, even contralateral distalization is possible (Mesial-Distalslider).
 

Morphological features of skeletal class III malocclusion may comprise mandibular prognathism, maxillary retrognathism or a combination of both. Sagittal orthopaedic forces to protract the maxillary complex were commonly applied to the upper dental arch. This approach incurred well-known side effects such as proclination of the upper front teeth, bite opening, mesial movement of the lateral segments, and constriction of unerupted canines. New skeletal anchorage concepts involving surgical mini-plates or mini-implants have been developed to address these problems. Directing orthopaedic forces directly into the bony structures of the midface promised a significant reduction of dental side effects as well as an enhancement of skeletal response. To further increase orthopaedic treatment effects, some maxillary protraction protocols include rapid maxillary expansion (RME) in order to stimulate the midface sutures. RME can be carried out purely bone-borne or with a combination of dental and skeletal anchorage using mini-implants in the anterior palate (Hybrid-Hyrax).

The intrusion of overerupted upper molars is a difficult orthodontic treatment objective. When conventional appliances are used, the extrusion of adjacent teeth may occur. In recent years, temporary anchorage devices have been used to avoid these unwanted side effects. For this purpose, mini-implants have been primarily inserted in the alveolar process. However, due to many disadvantages of mini-implant placement between the roots of the upper molars, it is now preferred to insert mini-implants in the anterior palate ensuring a low risk of failure or mini-implant fracture. As a less bulky alternative to the “Mousetrap” appliance (with TPA) the “Mini-Mousetrap” (without TPA) was designed and comprised two mini-implants in the anterior palate and lever arms for molar intrusion. If a TPA is not used, molar movement must be monitored and the direction of the force adjusted to avoid unwanted molar tipping.

Unless a prosthetic replacement is inserted soon after extraction or loss of a first molar, the second molar may tip mesially into the edentulous space. Not only will the first-molar space contract mesiodistally, but eccentric occlusal loading will reduce the biomechanical loading capacity of the second molar. Such a situation requires preprosthetic uprighting of the second molar using appropriate mechanics. Simply tipping the molar distally will lead to extrusion and likely cause occlusal interference. Stable anchorage is critical, since simultaneous intrusion and uprighting forces create a high moment load on the anchorage unit. Otherwise, unwanted mesial tipping and extrusion of the anchorage teeth may occur. The use of an orthodontic mini-implant for direct anchorage can help avoid such dental side effects. This lecture describes a technique using mini-implants in an edentulous first-molar site as anchorage for uprighting mesially tipped molars.