A tipped mandibular molar is a frequent situation among orthodontic patients, which usually occurs after premature loss of adjacent teeth leading to the inclination of the molars [1, 2]. Inadequate mandibular arch length, excessive teeth size, loss of the adjacent first molar, premature eruption of the mandibular third molar, and unusually mesial eruption pathway of the second molar can also cause its partial or total impaction with a reported incidence of 0.03–0.3% of the general population and 2–3% of orthodontic patients [3,4,5].
Tilted molars can cause numerous problems in a patient’s mouth, especially if a prosthetic rehabilitation is planned. According to Zachrisson, periodontal status can be aggravated, with signs of inflammation, angular bone loss, and an apparent pocket at the mesial surface of a tipped mandibular molar [6]. In excessive inclination, overeruption of the antagonist molar, premature contacts, and occlusal interferences impede prosthetic restoration [7]. However, molar uprighting into its correct position leads to the normalization of the functional and periodontal condition [7]. Finally, an impacted mandibular second molar can lead to caries, periodontal disease, or external root resorption of the adjacent first molar [4].
Conventional methods for molar uprighting
Several orthodontic approaches are suggested for mandibular molar uprighting, such as Australian uprighting spring, cantilever spring, prefabricated Sander spring, helical uprighting spring, NiTi coil spring, push spring appliance, and traction from removable appliances are few of the currently available options [6, 8, 9]. Molar uprighting requires good anchorage control, and subsequently, a full-arch fixed appliance is necessary. Furthermore, ankylosed teeth, dental implants, and extraoral appliances could also be effective, enhancing anchorage, and protecting from undesirable tooth movements [8, 10].
Among others, the Uprighter Jet developed by Carano provides a complete control of molar uprighting, minimizing extrusion, requiring no brackets, and no special patient cooperation [1]. In another uprighting case of an impacted molar, in combination with rapid maxillary expansion (RME), vertical elastic forces were directed from a hook on the RME device to an orthodontic attachment bonded on the tooth to be uprighted. This method saves time, requires no additional anchorage preparation, and appears more physiologic as the force vector is in the direction of normal eruption path [9]. According to Pogrel [11], surgical uprighting of lower second molars is a quick procedure with minimal morbidity and long-term prognosis. Most of the uprighted teeth remained firm with excellent bone formation and periodontal status after 18 months of follow up [11].
However, conventional treatment methods for molar uprighting have some disadvantages, including extrusion of the target molar, unwanted reciprocal movement of the anchorage units, need for bulky appliances, and longer treatment time [1, 2, 12,13,14,15]. In order to minimize the first two side-effects, intra-arch stabilization is usually needed [2, 12, 13], which is undertaken through the use of osseointegrated implants. Yet, an osseointegrated dental implant is costly, needs sufficient bone space, limiting our choices, and is very difficult to be removed after the treatment. It also requires osseointegration before orthodontic force application, increasing the treatment time [5, 10, 12].
In addition, surgical uprighting should not be considered as a routine method due to the possible pulp necrosis, ankylosis, external root resorption, or even rupture during the procedure. After treatment, occlusal equilibration may be needed, and the post-surgical stability of the tooth may be questionable [4]. Further, the possibility of pulpal calcification and vitality loss is high [11].
Use of orthodontic miniscrew implants for molar uprighting
The development of orthodontic miniscrew implants (MIs) provided solutions to most of the aforementioned problems. MIs are fabricated from pure titanium or titanium alloy with a diameter of 1–2 mm and length of 8–20 mm [16]. They remain stable during orthodontic treatment with minimum anchorage loss and are more effective than conventional anchorage means [17,18,19]. Their success rate ranges from 59 to 100% with an average of 86.5% [18,19,20].
Their attachment to the bone is mechanical with no intent to establish any form of osseointegration [21, 22]. Therefore, after the treatment, when they are no longer needed, they can be removed through a simple procedure, with negligible risks for the patient [23].
This new type of skeletal anchorage is simpler, smaller, less-invasive, and more economical than conventional osseointegrated implants [16]. Moreover, MIs do not require a long interval between placement and force application since loading can occur immediately after placement [10, 16, 24].
Their main advantage though is their ability to move specific teeth or even the entire quadrants directly, without involving other teeth or using inter-arch mechanics. Thus, they eliminate the reaction forces usually applied on the anchor teeth, leading to unwanted tooth movement and anchorage loss [5, 14, 15]. Patients are also more satisfied with the more invisible treatment compared to conventional methods [10].
MI anchorage is preferable to conventional mechanics when a third molar is in direct contact with the second molar root [4]. In some cases, it is better from a biomechanical perspective not to extract the third molar bud, since its extraction can change the center of resistance of the second molar and uprighting can be realized with distal crown tipping. This is undesirable when the second molar is planned to be uprighted mostly with mesial root tipping [24].