Tooth impaction

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Jaspinder Kaur, MBBS[2]

Synonyms and keywords:

Overview

Impacted and embedded teeth are the two main types of unerupted teeth found in the mouth, and can sometimes be confused with each other. In both cases, the teeth remain below the surface of the gum, rather than erupting into an exposed position within the mouth, but the reason for the failure to erupt differs. Impacted teeth result from a situation in which an unerupted tooth is wedged against another tooth or teeth or otherwise located so that it cannot erupt normally. In contrast, an embedded tooth is an unerupted tooth that is covered, usually completely, with bone. That is to say, something that is physically blocking the pathway of eruption (such as another tooth) is the case for an impacted tooth, whereas the lack of eruptive force results in an embedded tooth.

Mandibular third molars are the most commonly found unerupted teeth, while maxillary third molars are second most common.

Tooth impactions are prevalent in clinical practice. 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. 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. Hence, diagnosis is based on clinical examination coupled with imaging, especially cone beam CT (CBCT) scans. Treatment of 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. Good Orthodontic mechanics, surgical planning, and patient education is essential to success. Surgical considerations include local anatomic concerns, anesthesia method, flap design, bone removal/coronal exposure, surgical instrumentation, bonding material characteristics, tooth ankylosis, and minimization of surgical complications.

Classification

• Traditionally, both the Winter’s and Pell & Gregory’s systems propose to classify the inclinations and positions of the third molars based on the relation among the dental longitudinal axis, occlusal plane and ascending mandibular ramus. Radiologically, individual anatomy, demographic aspects and operative factors are considered important variables to the determination of surgical difficulties and postoperative complication risks.
• Tooth impaction is classified based on various factors which are elaborated in following tables:

Table 1: Winter’s and Pell & Gregory’s criteria

Classification	Clinical description	Type
Pell and Gregory classification	Impaction depth: the relation of the cementoenamel junction (CEJ) of the third molar with the bone level is graded	Level A: The occlusal plane of the impacted tooth is the same level as the occlusal plane of the 2nd molar Level B: The occlusal plane of the impacted tooth is between the occlusal plane and the cervical line of the 2nd molar. Level C:The impacted tooth is below the cervical line of the 2nd molar.
Pell and Gregory classification	Ramus relationship: the position of the distal surface of the third molar crown in relation to the anterior border of the ascending ramus is categorized	Class I: There is sufficient space between the ramus and the distal part of the 2nd molar for the accommodation of the mesiodistal diameter of the 3th molar. Class II: The space between the 2nd molar and the ramus of the mandible is less than the mesiodistal diameter of the 3th molar. Class III: All or most of the 3th molar is in the ramus of the mandible.
Winter’s classification	Impaction angulation: the angle between the longitudinal axis of the second and third molars (which was measured by an orthodontic protractor) is categorized	Vertical: Long axis of the 3th molar parallel to the 2nd molar. Horizontal: Long axis of the 3th molar perpendicular to the 2nd molar. Mesioangular: Long axis of the 3th molar inclined in mesial direction to 2nd molar. Distoangular: Long axis of the 3th molar inclined in distal direction to 2nd molar. Inverted: Crown of the 3th molar directed to basilar of the mandible.
Nature of overlying tissue	This system is used by most dental insurance companies and one by which surgeon charges for his services.	Soft tissue impaction Partial bony impaction Fully bony impaction

Pathophysiology

• The normal development of the occlusion and craniofacial complex is largely dependent on the normal physiological eruption of teeth. Eruption is the process by which a tooth moves axially from its follicle position in the bone into its final functional position in the oral cavity. Following clinical and radiographic assessment, if a tooth is not expected to erupt, as a result of a positional deviation of its developing follicle or the presence of a physical barrier in its path, then the tooth is rendered impacted.
• Impacted teeth can be classified as entirely or partially unerupted teeth. The most common impacted teeth are the third molars since they are the last to erupt and usually remain impacted due to the lack of space in the dental arch. The mandibular third molar impaction is said to be due to the inadequate space between the distal of the second mandibular molar and the anterior border of the ascending ramus of the mandible. Partially erupted impacted third molars (ITM) have been associated with odontogenic infections, such as caries, periodontal diseases, and pericoronitis. Due to difficulties in reaching partially erupted teeth during oral hygiene, dental caries and endodontic illnesses are more frequently observed in comparison to entirely unerupted teeth. On the other hand, non-inflammatory conditions such as the dentigerous cysts (DC), odontogenic keratocysts (OKC), and ameloblastomas are mostly related to entirely unerupted ITM.
• This situation is pathological and can lead to various clinical conditions, including pericoronitis, adjacent root resorption, cystic lesions, or neoplasm.
• Process of tooth eruption involves complex interaction between osteoblasts, osteoclasts and dental follicular cell lines associated with the tooth germ which result in coordinated alveolar bone resorption and emergence of tooth within the oral cavity. Teeth may fail to erupt either as a result of mechanical obstruction, be it idiopathic or pathological in origin or because of disruption to the eruptive mechanism itself. The terms ‘impaction’ and ‘retention’ are often used synonymously for eruption failure but actually they are separate pathologies with different etiology and treatment approaches.
• An impacted tooth is one that is unable to fully erupt in its proper location because it is blocked by tissue, bone or another tooth. Sometimes an impacted tooth manages to erupt in the position of another tooth. A tooth that erupts in this manner is called, ectopic, meaning that it is displaced or incorrectly positioned. Ectopic eruption is a developmental disturbance in eruption pattern of permanent dentition. Often, an ectopic tooth is caused by trauma, larger width of permanent tooth, abnormal angulation of eruption of molar or delayed calcification of affected molars. The affected permanent molar may erupt at an angle to the normal eruption path, thereby ceasing the eruption and causing the resorption of the neighboring deciduous tooth.

Etiology

• The term impaction originates from a Latin word impactus. It is defined as a cessation of eruption of a tooth caused by a clinically or radiographically detectable physical barrier in the eruption path or by an ectopic position of the tooth. Common causes contributing to impaction are lack of space or crowding of dental arches, premature loss of the primary teeth with subsequent partial closure of the area, rotation of tooth buds, supernumerary teeth, odontoma or cyst in the path of eruption.
• According to the classification by Andreasen and Kurol the failure of eruption of the second molar can be classified into three events etiologically, clinically and radiographically:
  • Impaction: Caused by a physical obstacle, basically due to lack of space, and which could provoke a collision between the follicles of the second and third molar. Ectopic eruption of the tooth germ and obstacles in eruptive path (extra teeth, odontomas, tumors, cysts, giant cell fibromatosis, etc.) cause impaction.
  • Primary retention (unerupted and embedded teeth) is defined as a cessation of eruption before gingival emergence without a recognizable physical barrier in the eruption path or ectopic eruption. This kind of eruption failure is sometimes associated with syndromes where osteoclastic activity is compromised. Generally, all teeth distal to the affected tooth also fail to erupt.
  • Secondary retention (submerged, reimpaction, ankylosis) is termed as cessation of the eruption after emergence, without evidence of a physical barrier either in eruption path or as a result of an abnormal position. Clinically, secondary retention is suspected when tooth is in infraocclusion at an age when tooth would normally be in occlusion. Radiographically, a focal obliteration of periodontal space or resorption of root surface is found. Secondary retention is more common than primary retention and is caused by a small area of ankylosis especially in inter-radicular zone. The origin of ankylosis has been associated with genetic and systemic factors.

Differentiating Tooth Impaction from other Diseases

Table 2: Enlist the differential diagnosis for tooth impaction

System involved	Characteristic features
Cleidocranial dysostosis	Short tapered fingers and broad thumbs; flat feet; knock knees; short shoulder blades (scapulae); scoliosis; short skull (brachycephaly); a prominent forehead; wide-set eyes (hypertelorism); a flat nose; small upper jaw; impacted and crowded teeth.
Gardners syndrome	Multiple impacted and supernumerary teeth, multiple jaw osteomas, multiple odontomas, congenital hypertrophy of the retinal pigment epithelium (CHRPE), and multiple adenomatous colonic polyps.
Gorlin–Sedano syndrome	Short hands, short foot bones, short and straight collar bone, and multiple impacted teeth.
Yunis–Varon Syndrome	Agenesis or hypoplasia of clavicle, severe micrognathia, digital anomalies, hypodontia, spinal defects, and impacted teeth.
Osteogenesis Imperfecta	Blue sclera, abnormal and impacted teeth, hearing problems, osteoporosis, wormian bones, joint laxity, and short stature.

Epidemiology and Demographics

• It has been detected more often in the unilateral form than the bilateral and is more common in the mandible than in the maxilla.
• The impaction of permanent teeth (excluding third molars) is a frequent phenomenon, with a reported prevalence ranging from 2.9% to 13.7%. The most frequently impacted teeth are the canines and second premolars in both jaws with different incidence rates.
• The third molar impaction is occurring in about 73% of the young adults in Europe, these teeth generally erupt between the ages of 17 and 21 years. It has also been reported that the third molar eruption varies with races, such as in Nigeria mandibular third molars may erupt as early as 14 years and in Europe it may erupt up to the age of 26 years.

Risk Factors

• Microdontia: The presence of microdontia of the maxillary lateral incisor is significantly associated with more severe impaction, which emphasizes the importance of tooth size investigations in young patients and carrying out further analysis for those with small laterals.
• Age: With age, the angle of an impacted tooth might increase in severity; therefore, early diagnosis and treatment is mandatory, especially for the maxillary canines.
• Gender: Females suffer from more severe impaction of teeth in general, and of the maxillary canine in particular. Consequently, and because teeth erupt earlier in females, it is crucial to diagnose impaction earlier in females and carryout any necessary preventive or interceptive orthodontic procedures.
• Factors such as the nature of the diet that may lead to attrition, reduced mesiodistal crown diameter, degree of use of the masticatory apparatus and genetic inheritance also affect the timing of third molar eruption.
• A gradual evolutionary reduction in the size of the human mandible/maxilla has resulted in too small mandible/maxilla that may accommodate the corresponding molars.
• Modern diet does not offer a decided effort in mastication, resulting in loss of growth stimulation of jaws, and thus the modern man has impacted and unerupted teeth.
• Due to artificial feeding of babies, the habits developed during childhood, due to cross breeding, more consumption of sweet food by the children and youth which produces disproportion in the jaws and thus the teeth.

Natural history, Complications, and Prognosis

• In the United States, approximately 3 billion dollars are spent yearly on the extraction of third molars. Whether it be for prophylactic, orthodontic and prosthetic reasons or for the diagnosis of several associated pathologies, the surgical removal of these teeth is one the most performed dentoalveolar procedures in oral and maxillofacial surgery. Reasons for extracting ITM include the risk of developing dental caries, pericoronitis, periodontal defects, crowding, and occurrence of different odontogenic cysts and tumors. However, there is a lack of substantial evidence supporting the extraction of asymptomatic ITM, especially considering the morbidity and the costs of the procedure. Thus, further investigations on this topic are necessary to aid surgeons in the decision-making process. The presence of odontogenic cysts and tumors in the third molar region can cause severe consequences, such as pathological mandibular fracture and facial asymmetry. Nonetheless, surgical removal of ITM might present complications, which might occur in up to 15% of cases, such as nerve injuries, post-operative infections, and iatrogenic mandibular fractures. Therefore, the clinical conduct regarding asymptomatic ITM should weigh the risks of removal and benefits of tooth preservation.

Diagnosis

Staging | History & Symptoms | Physical Examination | Laboratory Tests | Chest X Ray | CT | MRI | Echocardiography or Ultrasound | Other Imaging Findings | Other Diagnostic Studies

• Impacted teeth may remain asymptomatic or may be associated with various pathologies such as caries, pericoronitis, cysts, tumors, and also root resorption of the adjacent tooth.
• Clinical signs and symptoms: Caries; Pain; Swelling; Paresthesia; Periodontal pocket; Pericoronitis
• Radiological changes:
  • Noninflammatory: Caries; Root resorption (internal or external); Interdental bone loss; Hyperplastic dental follicle
  • Mild inflammatory: Pericoronal radiolucent areas suggesting pericoronitis; Periapical radiolucent areas suggesting abcess
  • Severe inflammatory: Osteomyelitis
  • Radiological signs of cysts and benign tumors: Dentigerous cyst; Keratocystic odontogenic tumor; Odontomes; Ameloblastoma; Odontogenic fibroma
  • Radiological signs of malignant tumors: SCC; Fibrosarcoma; Mucoepidermoid carcinoma

Treatment

Medical Therapy | Surgery | Primary Prevention | Secondary Prevention | Cost-Effectiveness of Therapy | Future or Investigational Therapies

• Treatment can be instituted on the basis of etiology.
  • In case of impaction, early removal of physical barrier increases the chances of spontaneous eruption followed by orthodontic uprighting if required.
  • In case of primary retention, involved teeth tend to ankylose if orthodontic force is applied. Unerupted tooth can be surgically repositioned following segment alveolar osteotomy. Prosthetic replacement of missing (unerupted) tooth is the last resort.
  • In case of secondary retention, luxation of exposed tooth sometimes promotes eruption. If secondary retention develops prior to growth spurt, immediate removal of affected molar followed by orthodontic alignment of neighboring teeth can be done. Autotrasplantation of third molar into the space created by missing teeth can be done.

• The higher the rank of the position of the impacted tooth, the more difficult it is to align.
• the earlier the diagnosis and treatment of the impacted tooth, the less complicated and shorter the treatment duration will be, as suggested by the treatment difficulty index. It further suggest that a severely impacted tooth can migrate and cross the midline with time, which stresses the importance of an early diagnosis and treatment planning.