Key points
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The order of frequency of tooth impaction includes mandibular and maxillary third molars, maxillary canines, mandibular premolars, mandibular canines, maxillary premolars, maxillary central incisors, maxillary lateral incisors, and mandibular second molars.
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Treatment of supernumerary teeth or impacted teeth should be based on clinical symptoms, location of the teeth, and a comprehensive examination of the impact of these teeth on neighboring teeth.
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In most cases, a diagnosis of supernumerary or impacted teeth is based on clinical symptoms and radiographic examination; the most common diagnoses are made by panoramic, occlusal, and periapical radiographs.
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Most unusual impacted teeth may be reached by the direct surgical approaches used to remove the commonly impacted sites, often requiring extensions of flaps and the removal of more bone.
Ectopic dentition refers to a tooth or teeth located away from the normal position within the jaws or in the vicinity of odontogenic structures. In contrast, heterotopic dentition includes a tooth or teeth present distantly into a site of an organ or tissue it does not normally occupy, such as in the case of the ovaries, mediastinum, and so forth. Unusual impacted teeth may include a supernumerary tooth, a tooth that migrated, or one that failed to erupt. The incidence of supernumerary teeth generally affects 0.1% to 1% of the population.
Frequency and incidence of impacted teeth
The order of frequency of tooth impaction is mandibular and maxillary third molars, maxillary canines, mandibular premolars, mandibular canines, maxillary premolars, maxillary central incisors, maxillary lateral incisors, and mandibular second molars. Mandibular and maxillary first molars as well as maxillary second molars are very rarely impacted.
Frequency and incidence of impacted teeth
The order of frequency of tooth impaction is mandibular and maxillary third molars, maxillary canines, mandibular premolars, mandibular canines, maxillary premolars, maxillary central incisors, maxillary lateral incisors, and mandibular second molars. Mandibular and maxillary first molars as well as maxillary second molars are very rarely impacted.
Etiology of supernumerary teeth
The cause of supernumerary teeth is not completely understood. One theory suggests that the supernumerary tooth is created either from a thin tooth bud that arises from the dental lamina near the permanent tooth bud or from splitting of the permanent bud itself. Heredity may also play a role in the occurrence of this anomaly, because supernumeraries are more common in the relatives of affected children than in the general population. However, the anomaly does not follow a simple Mendelian pattern. Although the cause of ectopic growth is not well understood, it has been attributed to obstruction at tooth eruption secondary to crowded dentition, persistent deciduous teeth, or exceptionally dense bone. Multiple supernumerary teeth are often associated with cleidocranial dysostosis but rare in those with no other associated diseases or syndromes.
It is theoretically possible for any tooth to follow an abortive eruptive path and become impacted within the dentoalveolar process or in remote or heterotopic anatomic sites, such as the nasal or sinus cavities, the mandibular ramus, or the inferior border of the mandible. In addition, teeth may not erupt into the dental arch owing to direct or indirect effects of cysts and neoplasm or to abnormal hereditary patterns of phenotypic expression. Therefore, it is prudent to perform a thorough clinical examination and obtain adequate radiographs when teeth do not appear according to the usual eruption schedule.
In most cases, a diagnosis of supernumerary or impacted teeth is based on clinical symptoms and radiographic examination. The most common diagnoses are made by panoramic, occlusal, and periapical radiographs.
However, radiographic film has the following 2 inevitable disadvantages:
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Image overlap, which cannot reflect a 3-dimensional structure of the diseased region owing to a low-resolution ratio, and
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Different degrees of distortion or amplification. In contrast, 3-dimensional computed tomographic (CT) imaging can reflect supernumerary teeth’s shape, size, number, location, eruptive direction, and relative tissue conditions. Although there is still much debate as to when to order CT imaging from a medicolegal perspective, a CT’s or Cone-Beam Computed Tomography’s (CBCT) multidirectional and 3-dimensional display provides much information for treatment and surgical planning. One can assess the anatomic relationship between proximity of the inferior alveolar nerve (IAN) canal and the M3 roots and ascertain the location of the IAN canal relative to the roots.
Treatment of supernumerary teeth or impacted teeth should be based on clinical symptoms, location of the teeth, and a comprehensive examination of the impact of these teeth on neighboring teeth. Supernumerary teeth need to be extracted in cases of clinical pathologic changes, orthodontic treatment, or where the tooth will be replaced with implants. As in cases of supernumerary teeth that are not in the dental arch, those with no clinical symptoms, or those that involve vital anatomic structures, such as intracranial, extraction of the teeth is not necessary, but further observation and follow-up are expected.
Most unusual impacted teeth may be reached by the direct surgical approaches used to remove the commonly impacted sites, often requiring extensions of flaps and the removal of more bone. This article discusses indirect and alternative techniques that the practitioner could use when the direct techniques would increase the chance of morbidity to the patient.
Mandibular locations
The issue of IAN involvement during the removal of the lower third molars is a clinical and medicolegal problem. Any technique that can reduce the possibility of this involvement is worthy of exploration. Coronectomy was developed as a relatively new preventive method to decrease the prevalence of IAN injury compared with the conventional total removal of the lower third molar. A randomized controlled clinical trial published in 2009 has shown that coronectomy can significantly decrease the risk of an IAN deficit in high-risk cases. The procedure has also been shown to be safe in terms of pain, infection rate, and dry socket, at least for the short term.
The intention of coronectomy or deliberate root retention is that the part of the root intimately related to the IAN is undisturbed. However, enough of the root must be removed below the crest of the lingual and buccal plates of bone to enable bone to form over the retained roots as part of the normal healing process. It was also thought to be important not to mobilize the roots because they might damage the nerve. For this reason, complete transection of the crown and roots of the tooth was thought to be necessary.
The technique described by Pogrel and colleagues is as follows and is demonstrated in Fig. 1 :
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Following exposure of the crown, using a 701-type fissure bur, the crown of the tooth was transected at an angle of approximately 45°. The crown was totally transected so that it could be removed with tissue forceps alone and did not need to be fractured off the roots. This removal minimizes the possibility of mobilizing the roots. After removal of the crown of the tooth, the fissure bur is used to reduce the remaining root fragments so that the remaining roots are at least 3 mm below the crest of the lingual and buccal plates in all places, as can be seen in Fig. 2 . An alternative technique is to use a round bur from a superior aspect and remove the crown and superior part of the roots by drilling it away. In this case, only minimal lingual retraction may be required.
Fig. 2 Completeted coronectomy on lower right third molar. Note retained roots are 3 mm below the crest of bone and exposed pulp is untreated.( From Pogrel MA, Lee JS, Muff DF. Coronectomy: a technique to protect the inferior alveolar nerve. J Oral Maxillofac Surg 2004;62:1449; with permission.) - 2.
There is no attempt at root canal treatment or any other therapy to the exposed vital pulp of the tooth.
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After a periosteal release, a watertight primary closure of the socket is performed with 1 or more vertical mattress sutures.
The following conditions should be considered when evaluating whether to perform a coronectomy:
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Teeth with active infection around them, particularly infection involving the root portion, should be excluded from this technique.
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Teeth that are mobile should be excluded from this technique because it is thought that the roots may act as a mobile foreign body and become a nidus for infection or migration.
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Teeth that are horizontally impacted along the course of the IAN may be unsuitable for this technique because sectioning of the tooth itself could endanger the nerve. The technique is therefore better used for vertical, mesioangular, or distoangular impactions where the sectioning itself does not endanger the nerve.
Several studies comparing coronectomy with the total removal of the lower third molars have shown that an IAN deficit after coronectomy can be significantly decreased in high-risk cases. Root migration is a common finding in almost all studies on coronectomy of the lower third molars. As the root moves closer to the surface, it will be farther away from the nerve and carry a much smaller risk of nerve injury compared with removing the roots from their original situation. Sencimen and colleagues reported a higher failure rate when they performed root canal treatment after coronectomy, supporting the notion that the retained roots do not require any elective endodontics. Fig. 3 shows clinical examples of coronectomy with endodontic treatment and without endodontic treatment and the pulp left in place.
Marsupialization
Marsupialization may be advisable to allow eruption of an impacted or unerupted tooth associated with a cyst, if sufficient space exists. Two principal methods of treating a dentigerous cyst are removal and marsupialization. Excision is indicated when there is no likelihood of damaging anatomic structures, such as apices of vital teeth, maxillary sinus, or the IAN. Marsupialization can maintain the impacted tooth in its cavity and promote its eruption. Marsupialization is especially useful for dentigerous cysts with teeth displacement. The decompression can be performed by creating and protecting a surgical opening that unites the oral mucosa with the lining of the cyst. A biopsy is required to establish a reliable diagnosis of the lesion. Decompression of the cyst without tumor characteristics permits the displaced bone to regenerate and tooth to spontaneously erupt. New bone formation is stimulated because marsupialization decreases intracystic pressure. The major disadvantage of marsupialization is that pathologic tissue is left in situ, without a thorough histologic examination. In Fig. 4 , Ertas and Yavuz have shown a patient with a large cyst with displacement of 4 permanent teeth that was treated with marsupialization alone that resulted in eruption of all 4 displaced teeth. There is a close correlation between eruption and when the development of teeth roots had not been completed.
