Ⅰ. Introduction
An impacted tooth is defined pathologically as a tooth with a crown below the oral mucosa or the bone, although the period when it was supposed to have erupted has passed. It is also defined clinically as a tooth that is not expected to erupt normally, considering the morphology, location, and direction of the tooth. The most commonly affected teeth are the maxillomandibular third molars, and impaction of the mandibular first molar is rare [
1].
The treatment method of an impacted tooth in cases of potential eruption without abnormal findings is simply a periodic check-up. Treatment methods to induce eruption include surgical exposure, subluxation after surgical exposure, orthodontic traction and eruption guidance after surgical exposure, and surgical repositioning. If all of these treatments fail, surgical extraction can be an alternative [
2].
Considerations about determining treatment method regarding impacted teeth include the age of the patient, the development level of the root, and factors regarding eruption disturbance. The younger the patient and the more immature the tooth, the higher the possibility of spontaneous tooth eruption. Removing the physical disturbance associated with eruption may also increase the possibility of spontaneous eruption.
In this report, two patients with mandibular first molar impaction were taken. Satisfactory results with eruption guidance to normal occlusion using surgical exposure and orthodontic traction after surgical exposure were described.
Ⅲ. Discussion
The impacted tooth is far more common in permanent than primary teeth. The impacted mandibular first molar accounts for only < 0.01% of the population, so it is a rare occurrence [
3]. Proffit and Vig [
4] reported that the rate of impacted teeth was higher for posterior teeth than anterior teeth. Andreasen
et al. [
5] described that failure of eruption can be caused by displacement of the tooth germ, a physical disturbance interrupting normal eruption, and a failure of genesis.
In a study of eruption times of mandibular first molars, Kim
et al. [
6] and Shin [
7] reported that the mandibular first molar erupted through the alveolar bone in a half to a quarter of the time of root formation. This is consistent with the reports of Johnsen
et al. [
8] and Palmaetal
et al. [
3]. Moslemi
et al indicated that tooth eruption occurred in 97% of boys in 8 years and 3 months, and in 97% of girl in 7 years and 11 months; the average eruption time was 6 years and 10 months in boys, and 6 years and 6 months in girls. Thus, clinicians should suspect impaction in cases of unerupted teeth based on these eruption times according to gender, whether there is only unilateral impaction, and whether teeth are positioned under the alveolar bone despite formation of more than half of the root.
Unlike impacted anterior teeth that are readily identifiable by family members or the patient, the impaction of the mandibular first molar is not readily detectable. For this reason, it often took a long time to notice such impacted teeth, and their advanced stage required complex treatments and was associated with a poor prognosis. Indeed, impaction of the mandibular first molar is typically found in dental check-ups, so it is important for the dentist to check carefully [
2,
3].
Eruption failure due to impaction delays functional occlusion, and consequently leads to malocclusion [
3]. That can be caused not only by functional problems, but also by esthetic issues, such as loss of space due to the inclination of adjacent teeth, and pathological problems, such as cysts, infection, and referral pain [
1]. According to Wali [
10], referred pain accompanied by swelling can occur when the size of a dentigerous cyst associated with the impacted tooth is bigger than 2 cm. Especially for the first molar, this is very important because it plays a key role in mastication and the vertical occlusal relationship [
2,
11]. Frank [
12] described the complex decisions dividing the treatment of impaction, case by case, into four types: observation, intervention, relocation, and extraction. Surgical exposure is considered a high priority for the treatment of impaction; this was supported by Nielsen
et al. [
13], who reported that the first molar was more likely to erupt when treated at an early stage, following early detection. Nielsen
et al. [
13] stated that the tooth was more likely to erupt spontaneously when the crown was uncovered and tissues interfering with its eruption path were removed surgically in cases of eruption disorders of unilateral mandibular first molars with an open apex. There are even reports that surgical exposure can induce spontaneous eruption in cases which the tooth has almost completed root development, although it is difficult to expect spontaneous eruption where there is an ankylotic impacted tooth or an unusually shaped root [
14,
15].
In the first case in this study, the impeding material of the dentigerous cyst was likely the cause of the tooth eruption disorder. The patient was only 8 years old, so the root of the tooth stands a good chance of developing. Thus, we could induce eruption of the tooth by surgical exposure alone, in addition to marsupializing using an obturator. Spontaneous eruption using surgical exposure can be difficult; however, here the patient was so young that the root has the potential to develop, without the dentigerous cyst causing the eruption disorder.
Decompression using a Penrose drain was considered. The Penrose drain is inexpensive and causes little discomfort. Also, it can lead to the same effect as decompression method using an obturator. However, there are also problems in that the frequent changing of the drain can produce discomfort and the number of visits to the clinic is increased. In the first case, a young patient had difficulties in visiting our hospital frequently because of distance. Thus, use of a Penrose drain was excluded.
An alternative method can be considered if spontaneous eruption by surgical exposure fails. One method is orthodontic traction of the impacted tooth, which can be divided into two types. One is a closed technique in which the tooth is exposed surgically, and then covered again after attaching a hook on it. The other is an open technique, where the exposed tooth is pulled without recovering [
1]. While the prognosis of the impacted tooth is better using the closed technique, impaction right under the gingiva or mucosa is then subjected to the open technique.
In the second case in this study, orthodontic traction of the impacted molar was indicated when surgical exposure did not lead to spontaneous eruption, and no specific reason was observed. In this case, we used removable orthodontic appliances on pediatric patient’s upper and lower jaws. There was a possibility that this method could not lead to a desired result because the appliances cause the patient considerable discomfort and break her/his will to receive treatment. Therefore, this method has shortcomings such that compliance assessment is necessary before the treatment, since there is a high possibility of failure in many low-compliant patients. But, we had enough consultation before planning a treatment method and it was judged that her/his treatment compliance was good. So, we could carry out orthodontic traction therapy using removable appliances. Possible problems during orthodontic traction of impacted mandibular posterior teeth are that the elastic is not held in place with the removable maxillary appliance, and that most of the force is applied to the jawbone alone during functional movement. Thus, in this study, enough space for traction of the impacted tooth was available in the included bite plate of the removable appliance. Accordingly, it was possible to provide continuous force to it, and increase its stability.
A posterior bite plane not only made a traction space but also prevented the extrusion of the right maxillary first molar, which could have helped in resisting movement of the appliance during occlusion. However, it is difficult to use with mixed dentition and elimination, depending on the extrusion of a tooth, may be necessary.
In the second case treatment, after failure of surgical exposure carried out at a private dental clinic, orthodontic traction therapy was immediately carried out at this clinic. This case remains regrets such as spontaneous eruption could be possible though root apex formation finished and considering possibility of disturbed tooth eruption caused by unsatisfactorily removal of upper soft tissue or osseous tissue at a private dental clinic, attempting to carry out surgical exposure first could have been more conservative treatment method. Repeating the same treatment was severely unacceptable to protector and he wanted the teeth to erupt in a short time, so orthodontic traction therapy was immediately carried out.
An impacted tooth can erupt spontaneously if no specific cause disturbing the eruption is present, in cases of surgical exposure removing hard and soft tissue above the occlusal surface on the eruption path [
3,
15,
16]. However, it is certain that an impacted tooth is less likely to erupt when there is a physical problem, such as a supernumerary tooth, odontoma, or dental follicle.