Introduction
The eruption of permanent teeth in the dental arch is regulated by a significant genetic control [
1] and this guides the correct formation of tooth buds and their eruption in the dental arch in their right positions.
Certain anatomical conditions or previous traumas or affections of the corresponding deciduous tooth, may lead to eruption anomalies in terms of time or position, or in some cases can arrest completely the physiological eruption of the permanent tooth (dental inclusion).
The pediatrician is certainly the first physician to visit young patients and, as such, may be able to intercept all oral diseases. The pediatrician must provide general information to prevent the onset of caries, through proper nutrition and proper use of fluoride. The pediatrician may ask parents to make a dental visit and then implement all the measures of prevention as ambulatory care (for example, the sealing of the first permanent molars) [
2].
It is important that pediatricians know the importance of normal oral growth and development. Often the parents of a young patient ask their pediatrician to assess which is the right time to refer their child to a dental visit, or even orthodontics. This is the reason why it is better that the pediatrician is aware of complications that arise from the inclusion of permanent teeth, which can be prevented and cured when the patient is a child. In the most difficult clinical cases of impacted teeth it is very important to have an early diagnosis, which is essential to plan the treatment and achieve success. The pediatrician is in a strategic position to give an early diagnosis through a child’s medical history and by counting the child’s teeth.
A tooth is referred to as “retained” when it has not erupted in the dental arch within its physiological time but still shows radiographic evidence of eruptive capacity and has no anatomic obstruction on its eruptive path [
3,
4]. A tooth is referred to as “impacted” if it is completely or partially unerupted many years after normal eruption time or if it is positioned against another tooth, bone or soft tissue, so that its further eruption is unlikely [
3,
4]. The position of these teeth can often show a very marked ectopy [
3,
4].
Some studies demonstrated that the incidence of dental impactions ranges from 5.6% to 18.8% with a higher frequency among women [
5].
Teeth that most frequently face impactions are the lower and upper third molars (20 to 30%). Third molars, in order of frequency, are followed by upper canines (85% with palatal dislocation) which first face retention and then impaction. Upper canines are followed by lower second premolars (0.3%) that usually face the impaction because of the premature eruption of the first molar and the first premolar [
6,
7]. Upper central incisors (0.1%) represent the rarest case of impacted teeth [
7,
8].
To formulate a prognosis and a treatment plan it is necessary to consider the different aspects of impactions.
Depending on the grade of impaction there can be a distinction between complete or partial impaction. Partial impaction occurs when at least a portion of the crown is visible in the dental arch. Complete impaction occurs when the crown is not visible; it may be: endosteal, where the tooth is impacted completely within the bone; osteomucosal, where the tooth is completely covered by mucosa and partially by bone and mucosal, where the tooth is covered only by mucosa [
9].
Depending on the number of impacted teeth there is a distinction between single impaction and multiple impactions [
9].
Based on the duration the impaction of a tooth can be defined as temporarily impacted or permanently impacted [
10]. Temporary impaction relates to a retained tooth caused by an obstacle (odontoma, cyst or supernumerary) that, as the obstruction is removed, erupts spontaneously in the dental arch [
10]. By contrast, the impaction is permanent when surgical-orthodontic treatment is necessary to obtain eruption although the obstacle has been removed.
Finally, impaction can be primary or secondary depending on its cause [
11]. Primary impaction is due to dental intrinsic factors (such as anatomy, inclination), whereas secondary impaction is caused by external factors such as cystic pathologies, supernumerary or neoformations [
11].
The etiopathogenesis of impactions is very broad and causes are divided into general, local and structural.
-
General causes can be: hereditary, hypofunctional endocrine disorders (hypothyroidism, pituitary cretinism), hyperfunctional disorders (hyperthyroidism), dysmetabolic conditions (hypovitaminosis and rachitis) and infectious diseases (congenital syphilis, rubella, scarlet fever) [
12].
-
Local causes can be related to the deciduous tooth (persistence, ankylosis, premature loss, chronic periapical inflammation) or associated with the permanent tooth (radicular ankylosis, coronal or radicular morphological alterations, position anomalies, eruption pattern anomalies) [
13].
-
Structural causes are maxillary hypoplasia, severe hyperdivergence, skeletal open bite [
13,
14] and congenital disorders of the maxillofacial apparatus such as labiopalatoschisis, cleidocranial dysostosis, cranial stenosis and Down’s syndrome [
4,
15,
16].
The suspect of impaction or retention of one or more teeth can be derived from an accurate clinical examination, and family and personal medical history.
Inspection and palpation by a dentist may complete the clinical examination. The final diagnosis and prognosis can be done by an orthodontist with the support of an X-ray examination that shows the presence and the position of one or more unerupted teeth [
4,
17,
18].
Useful radiographs in the diagnosis of impaction are panoramic, occlusal or periapical X-ray, or for high accuracy or surgical planning conventional computed tomography (CT) scans or cone beam CT scans. The orthopanoramic radiograph provides diagnostic certainty of the impacted tooth, giving an idea of its position and inclination and its relations with adjacent anatomical structures but it lacks the third dimension in understanding the precise position of the impacted tooth. In adjunct to the panoramic examination, an occlusal projection allows a more accurate determination of the position of the impacted tooth. Currently, the most precise X-ray examinations to reveal the position of the impacted tooth and of the other nearby anatomical structures, are conventional CT scans and low-radiation cone beam CT scans [
19].
There are many different types of treatment options: classic orthodontic treatment; combined surgical-orthodontic treatment; preservative-surgical treatment; and radical surgical treatment [
13]. When the tooth is retained for a matter of space, only a classic orthodontic interceptive treatment is performed. When the tooth is impacted and shows abnormal inclination and position, or has a particular coronal-radicular morphology a combined surgical-orthodontic procedure is required. When tooth eruption is blocked by a pathological condition (such as cysts, odontomas, and so on), its eruption in the dental arch depends on the removal of the obstacle; this is the preservative-surgical procedure (removal of the obstacle). Only in extreme situations, and in the presence of severe anatomical or positional anomalies, a radical surgical treatment may be chosen (removal of the impacted tooth) with the agreement of the patient.
The interceptive retrieval of an impacted tooth gains in importance particularly during the developmental age to guarantee the trophism of adjacent tissues, to maintain space, for esthetic and functional reasons. Even in the case that the retrieved tooth does not guarantee a long-term result, the procedure is advisable within limits. In that case the retrieved tooth with no long-term prognosis will perform its function until the patient reaches the age for prosthetic substitution of the tooth.
To prevent impactions different types of dental extraction can be performed such as, serial extractions, extractions of unexfoliated or ankylosed deciduous teeth and extraction of supernumeraries.
Complications that might occur after dental impactions can be distinguished between mechanical (resorption of the adjacent tooth roots, decubitus), nervous, infective (lower third molar pericoronitis, periodontal diseases, root resorptions of the adjacent tooth) [
10,
20] and dysplastic (follicular cysts, keratocysts, ameloblastoma) [
4,
9,
11,
21].
Thus, the choice of the optimal treatment strategy depends on a correct diagnosis and the pedodontic-orthodontic approach.
As stated above, there are prevention methods against impactions that, however, are to be promptly carried out.
A radiographic screening at an early age is able to intercept dental retention allowing prompt treatment.
The more an impacted tooth is situated far from its correct position or with a seriously tilted axis the gentler and more time consuming will be the orthodontic movement to reposition it. Maximum care will be necessary to avoid damage to adjacent teeth. Connecting the traction device directly to the orthodontic arch will produce an excessive force on the teeth adjacent to the impacted one leading to unwilled traumas or movements [
4]. In these cases the use of auxiliary devices working with maximum anchorage to unload the teeth from traction counterforce is indicated [
4].
Assessing the position and path of eruption of an unerupted tooth from a true lateral skull, orthopantomograph or a standard occlusal radiograph is considered clinically important for developing a comprehensive treatment plan. Several studies have recommended many radiological parameters of practicability to bring about speedy treatment and its effective resolution. For the lower impacted canine, a problem exists with the transmigration of the impacted tooth. Howard observed that those unerupted canines that lie between 25° and 30° in the midsagittal plane do not migrate across the mandibular midline. Those canines that lie between 30° and 95° tend to cross the midline. An overlap appears to exist between 30° and 50°. When the angle exceeds 50°, crossing the midline becomes a rule [
22]. For the transmigrated canine, extraction or transplantation can be proposed.
It was stated that if the apex of the lower canine is seen to have migrated past the apex of the adjacent lateral incisor, it might be mechanically impossible to bring it into place [
23].
Among radiological parameters, it was also suggested that it may be impossible to bring the impacted lower canine to its correct position in the presence of an overly mesially angulated unerupted canine that has begun to migrate labially across the incisors [
24].
For the impacted first permanent molar, there is no clear standard solution for how to treat retained or impacted first molars, as treatment depends on several local factors such as the angulations/inclination of the impacted/retained tooth [
25].
Although these previous articles mentioned and discussed various principles for treating practicable impacted teeth, the treatment of impacted teeth out of recommended radiological parameters of practicability has rarely been reported.
In this report, two clinical cases are described in which impacted teeth out of recommended radiological parameters of practicability were treated orthodontically with new purposely conceived orthodontic devices, which achieved the desired treatment goals.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
ST organized the data, made the analysis of results, the discussion of results, the figures and drafted the manuscript; MTD organized the data, made the analysis of results, the discussion of results, the figures and drafted the manuscript; EM coordinated the recording of data and the review of the literature; GG reviewed the literature and helped in the treatment of the patients; SM helped in the review of the literature; ML organized the data, made the analysis of results, the discussion of results, the figures and drafted the manuscript; VC and GM treated the patients and coordinated the drafting of the manuscript. All the authors read and approved the final manuscript.