Permanent teeth such as the maxillary and mandibular 3rd molars, the maxillary canines, the mandibular 2nd molars, and the mandibular 1st premolars are frequently impacted[1-3]. The prevalence of impaction of permanent molars, excluding the 3rd molar, has been reported to be 1.8% to 9.2%[4-6]. The main causes of impacted permanent molar are insufficient arch length, an ectopic position of the follicle, obstacles in the path of eruption, and failure of the eruption mechanism[7,8]. Eruption of the permanent molar is important because it provides harmony of facial growth and sufficient occlusal support for normal chewing. Failure of this tooth to erupt can cause many problems, such as a decrease in the vertical dimensions of the lower face, extrusion of opposing teeth, malocclusion, the formation of a follicular cyst, pericoronal inflammation, and root resorption in adjacent teeth[9,10].

Treatment options for impacted permanent molars include orthodontic traction, surgical repositioning, transplantation, and extraction of the impacted teeth. Orthodontic traction is recommended, because it is the most conservative method. Surgical repositioning or transplantation can be associated with unwanted side effects, such as ankylosis, replacement resorption, and loss of tooth vitality. In a recent study, transplantation of permanent molars showed a success rate of 11%. In contrast, orthodontic traction showed a success rate of 70%[11].

Anchorage is essential for successful orthodontic treatment. However, tooth anchorage is associated with limitations, such as mobility of the anchor teeth. In an effort to overcome these limitations, skeletal anchorage devices tailored for orthodontic use were developed. The development of skeletal anchorage devices has opened a new paradigm in orthodontic treatment, offering treatment options for many difficult conditions that were untreatable by conventional methods. Absolute anchorage can be achieved with skeletal anchorage devices because the anchorage device is fixed in bone, eliminating anchorage loss that causes dental shifting or tilting, side-effects commonly seen with conventional intraoral anchorage appliances[12]. Additionally, these skeletal anchorage devices are easily manipulated, able to target specific treatment goals, simplify treatment mechanics, and shorten total treatment times[13].

In this case report, 3 patients presenting with a chief complaint of unerupted permanent molars were treated orthodontically. The impacted teeth of these patients were surgically exposed, the orthodontic devices were attached, and traction of the impacted teeth was performed by utilizing skeletal anchorage devices.

Tooth impaction is defined as a tooth failing to erupt because of its functional position relative to the occlusal plane due to ectopic eruption, a physical barrier in the path of eruption, or an abnormal eruptive direction[14,15]. If the impaction is due to a physical barrier blocking the path of eruption, the recommended treatment is to provide adequate space in the arch and then remove obstacles, such as odontogenic tumors, cysts, or a supernumerary tooth. If the desired path of eruption is not along the long axis of the impaction, uncovering the tooth, bonding an attachment, and the application of orthodontic traction may be needed. Force level recommended for extrusion of impacted tooth range from 60 to 75 gm[16,17].

In this report, impaction of permanent molars due to physical obstruction was observed in all of the cases. In the past, it was presumed that impacted teeth could spontaneously erupt if the space was acquired and the obstacles were removed. Evidence-based studies, however, show that spontaneous eruption occurs in only 54 - 78% patients and can be delayed for 3 years. In a limited number of patients, spontaneous eruption followed by an acceptable alignment in the oral cavity is possible[18-20]. The possibility of spontaneous eruption varies according to the formation stage of the impacted tooth. The probability of spontaneous eruption failure is 2 times higher in teeth with completed root length growth than in teeth with about three quarters of their root length formed, and more than 3 times higher in teeth with a closed root apex[21]. In cases 1 and 2 of the present case report, the impacted permanent molars had complete growth of the root length but did not have a completely closed root apex at the time of the initial examination. In case 3, the impacted permanent molar had completed both root length growth and root apex closure at the time of the initial examination. Therefore, successful spontaneous eruption was unlikely to occur, and the patients as well as their parents requested orthodontic treatment and traction of the impacted teeth. Hence, immediate orthodontic force was applied to the impacted teeth without waiting for spontaneous eruption.

When a traction force is applied to a tooth, the force required varies depending on the type of tooth to be moved. The greater the root surface area, the greater the force required to move the tooth, and the greater the amount of anchorage required[22]. In this case report, as the impacted permanent molars were to be orthodontically extruded, increased force and anchorage were required compared to that for an anterior tooth or a premolar. When a tooth is used as an anchor, an impacted tooth may not react sufficiently to the traction force. Besides, the tooth used as an anchor, may itself move, leading to undesirable results. In particular, this phenomenon may occur when an impacted tooth is ankylosed. The diagnosis of tooth ankylosis has been considered challenging among clinicians because of the lack of a proper clinical diagnostic tool. A study has shown that the diagnosis of tooth ankylosis can be established by monitoring the response to the traction force. The diagnosis could be made only by therapeutic measures[23]. Hence, application of orthodontic force to tooth using skeletal anchorage is an effective and safe method for orthodontic traction of a heavily impacted tooth. Such procedures should be monitored using radiographs and periodic observation of the reaction. If orthodontic traction of impacted tooth is planned, treatment should be initiated only after providing patients and their parents with a complete information regarding the possibility of failures and alternative modes of treatment.

Absolute anchorage can be achieved with skeletal anchorage devices because the anchorage devices are fixed in bone, eliminating anchorage loss that can cause dental shifting or tilting, side-effects commonly seen with conventional intraoral anchorage appliances[12]. Such skeletal anchorage devices can be easily manipulated, are able to target specific treatment goals, can simplify treatment mechanics, and can shorten total treatment times[13]. However, the skeletal anchorage device may fail or cause complications. A study has reported that most cases of skeletal anchorage device failure occur during the initial 1 to 2 months, and more than 90% failures occur in the initial 4 months[24]. Thus, if the skeletal anchorage device can withstands the orthodontic force for 4 months or more, it can be regarded as stable. In adolescents, cortical bone is thin and has a poor bone quality, and oral hygiene control is often poor. Therefore, there is a high possibility of failure caused by soft tissue inflammation around the skeletal anchorage device[25]. Nevertheless, studies have reported that there is no significant relationship between failure of the skeletal anchorage device and age[26,27]. Consequently, if the skeletal anchorage device is appropriately placed according to guidelines and oral hygiene management is performed well, the possibility of failure can be reduced, even in adolescent patients[24]. In case 2 of the present case report, a miniscrew placed between the maxillary right 1st molar and the 2nd molar was removed after 3 months because of the redness of the surrounding soft tissue and mobility of the screw. After that, a miniscrew of 2.0 mm longer than the existing miniscrew was placed at the adjacent position and successfully maintained. In the case of a patient who requires a strong anchorage because of the need for traction for a severely impacted tooth, a skeletal anchorage device can be considered in patients aged 11 years or older. Both, the patients and their parents should be aware of the possibility of skeletal anchorage device failure and emphasize oral hygiene management.

In this case report, orthodontic traction of impacted permanent molars was performed using skeletal anchorage devices. The suspected obstacles, such as supernumerary tooth, the cyst, and the odontoma, were removed. The impacted teeth were surgically exposed and an orthodontic appliance was attached. A miniscrew or a miniplate was placed as an anchor at the site where the traction would be applied in the desired direction. As a result, all the impacted teeth responded to traction and successfully erupted to a functional chewing position on the occlusal plane.