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.

Tooth impaction can be defined as the infraosseous position of the tooth after the expected time of eruption, whereas the anomalous infraosseous position of the canine before the expected time of eruption can be defined as a displacement. Most of the time, palatal displacement of the maxillary canine results in impaction.

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. Impacted wisdom teeth (third molars) occur because of a lack of space, obstruction, or abnormal position 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.
• Impacted canines: Shafer et al. suggested the following sequelae for canine impaction:
  • Labial or lingual malpositioning of the impacted tooth,
  • Migration of the neighboring teeth and loss of arch length,
  • Internal resorption,
  • Dentigerous cyst formation,
  • External root resorption of the impacted tooth, as well as the neighboring teeth,
  • Infection particularly with partial eruption, and
  • Referred pain and combinations of the above sequelae.

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.

• Impacted canines: The exact etiology of palatally displaced maxillary canines is unknown. The results of Jacoby’s study showed that 85% of palatally impacted canines had sufficient space for eruption, whereas only 17% of labially impacted canines had sufficient space. Therefore, arch length discrepancy is thought to be a primary etiologic factor for labially impacted canines. Two major theories associated with palatally displaced maxillary canines are the guidance theory and genetic theory. The guidance theory proposes that the canine erupts along the root of the lateral incisor, which serves as a guide, and if the root of the lateral incisor is absent or malformed, the canine will not erupt. The genetic theory points to genetic factors as a primary origin of palatally displaced maxillary canines and includes other possibly associated dental anomalies, such as missing or small lateral incisors. Baccetti reported that palatally impacted maxillary canines are genetically reciprocally associated with anomalies such as enamel hypoplasia, infraocclusion of primary molars, aplasia of second premolars, and small maxillary lateral incisors.

Table 1: Etiologic factors – associated with impacted canines

Localized	Tooth size–arch length discrepancies, Failure of the primary canine root to resorb, Prolonged retention or early loss of the primary canine, Ankylosis of the permanent canine, Cyst or neoplasm, Dilaceration of the root, Absence of the maxillary lateral incisor, Variation in root size of the lateral incisor (peg-shaped lateral incisor), Variation in timing of lateral incisor root formation, Iatrogenic factors, Idiopathic factors
Systemic	Endocrine deficiencies, Febrile diseases, Irradiation
Genetic	Heredity, Malposed tooth germ, Presence of an alveolar cleft

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. The incidence of impacted wisdom teeth is high, with some 72% of Swedish people aged 20 to 30 years having at least one impacted wisdom tooth.
• Wisdom tooth (third molar) impaction is common. Removal of impacted wisdom teeth (symptomatic and asymptomatic) is a commonly performed operation. The incidence of wisdom tooth removal is estimated to be 4 per 1000 person-years in England and Wales, making it one of the top 10 inpatient and day-case procedures. In a report from 1994, up to 90% of people on oral and maxillofacial surgery hospital waiting lists were awaiting removal of wisdom teeth. Fewer operations are done now, possibly because of guidance.
• Impacted canines: Maxillary canines are the most commonly impacted teeth, second only to third molars. Maxillary canine impaction occurs in approximately 2% of the population and is twice as common in females as it is in males. The incidence of canine impaction in the maxilla is more than twice that in the mandible. Of all patients who have impacted maxillary canines, 8% have bilateral impactions. Approximately one-third of impacted maxillary canines are located labially and two-thirds are located palatally.

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. Wisdom tooth impaction may be more common now than in the past, as modern diet tends to be softer.
• 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 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.

Complications

Pericoronitis

• The eruption process is also likely to cause minor gingivitis, where the symptoms may be similar to pericoronitis. It is the main problem faced by dentists when it comes to lower impacted third molars.

Dental caries

• According to Nordenram et al.; caries accounts for 15% of third molar extractions. Researchers in prospective studies of occlusal caries in patients with asymptomatic third molars reported an increased frequency of caries with an increase in age and erupted third molars. The impacted lower third molars are extracted more commonly also due to dental caries, involving either the impacted third molar itself or the distal surface of the second molar.

Associated cysts and tumors

• Odontogenic cysts and tumors may be observed in some patients with impacted third molars, although they are relatively rare. The incidence of large cysts and tumors occurring around impacted third molars differs greatly in various studies, showing a wide range from 0.001% when a biopsy was indicated to 11% when the diagnosis was clinically established. This wide variation indicates that the presence of a cyst is a weak indication for prophylactic extraction of impacted third molars. Cystic changes may be encountered in the histopathological examination of the associated soft tissue of the asymptomatic impacted third molars, commonly in patients older than 20 years. The incidence, multiple presentation, and recurrence of aggressive cysts of the jaws and the malignant transformation of cysts have been discussed by Stoelinga and Bronkhorst.

Periodontitis

• The incidence of periodontitis has been reported to vary from 1% to 5% on the distal surface of the second molar. The incidence and prevalence of periodontitis increases with age irrespective of the presence or absence of the third molars, and thus a higher incidence of periodontitis has been observed among the older patients in relation to the impacted wisdom teeth. There is a paucity of studies relating periodontitis associated with impacted third molars with oral hygiene, which may be a confounding factor.

Root resorption

• It has been shown in some studies that a third molar left in situ may cause resorption of the distal root of the adjacent second molar. Some studies have also reported an association between root resorption at the apex and increasing age.

Miscellaneous

• One of the most commonly reported pathologies is an association of pain directly related to the presence of a third molar. The prevalence of this condition varies greatly from 5% to 53%. The incidence of cellulitis and osteomyelitis has been reported to be around 5%. Few other conditions which are also believed to be associated with impacted third molars include functional disorders such as occlusal interference, cheek biting, mastication disorders, trismus and temporomandibular joint problems.

Diagnosis

• Impacted wisdom teeth may be diagnosed because of symptoms such as pressure, pain, or swelling; by physical examination with probing or direct visualisation; or incidentally by routine dental radiography.
• 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
• Physical exam: Inspection and palpation of the temporomandibular joint and movement of the mandible, determination of mobility characteristics of lips and cheeks, size and contours of the tongue and appearance of soft tissue overlying the impacted teeth.
• Radiographic evaluation: Assessment of root morphology, size of follicular sac, density of the surrounding bone, contact with the second molar, nature of overlying tissues, inferior alveolar nerve and vessels, relationship to body and ramus of mandible, relation with adjacent teeth and buccal to lingual position of the third molar.
• 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

• The treatment plans depend on the presenting complaint and the history of the patient, the physical evaluation, radiographic assessment, the diagnosis, and the prognosis.
• Treatment can be instituted on the basis of etiology.
  • Impaction: Early removal of physical barrier increases the chances of spontaneous eruption followed by orthodontic uprighting if required.
  • Primary retention: It 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.
  • 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.

Modes of treatment

• Observation:
  • If the impacted mandibular third molar is embedded in bone with no perceptible to the follicle, as may be seen in an older individual and has no history, signs of associated pathology, long‑term observation is appropriate.
  • Most impacted teeth retain an erupting potential, and annual/biannual evaluation would be recommended if no indications for direct surgical management arise.
• Exposure: This option is considered if there is probability that it may erupt into useful occlusion but is obstructed by follicle, sclerotic bone, hypertrophic soft tissue, odontoma, etc., If the second molar is absent, exposure of a blocked third molar may be considered.
• Transplantation of mandibular third molar: The variety of crown and root shape on the impacted third molar make them suitable for transplantation to other molar sites, bicuspid and even the cuspid locations depending on the anatomy of the coronal and radicular surface.
• Removal: The primary reasons to remove impacted teeth are to correct associated pathology and to intercept reasonably expected pathological process.

Indications for Mandibular Third Molar Extraction

• In 1979, the National Institutes of Health Consensus Development Conference agreed on a number of indications for removal of impacted third molars, which included infection, nonrestorable carious lesions, cysts, tumors, and destruction of adjacent teeth and bone.
• Development or progression of asymptomatic or symptomatic inflammatory dental disease (e.g., caries, acute and chronic periodontal disease, pain); incisor crowding; disruption to regular activities of daily living (e.g., chewing, speaking, and missing work or education); days of disability; oral health profile; damage to adjacent teeth or restorations; maxillofacial lesions (e.g., odontogenic cysts or tumours); facial cellulitis of odontogenic origin; need for future treatment (e.g., extraction) of initially asymptomatic wisdom teeth.

Post extraction risks and complications

• They depends upon local and general factors which include tooth position, age of the patient, health status, knowledge and experience of the dental surgeon, and surgical equipment used.
• Includes damage of the pain, sensory nerve leading to paresthesia, dry socket, infection, and hemorrhage. Bone loss, root resorption, and gingival recession around the treated teeth are some of the most common complications.
• Severe trismus, oro‑antral fistula, buccal fat herniations, iatrogenic damage to the adjacent second molar, and iatrogenic mandibular fracture may also occur, though very rarely. The rate of sensory nerve damage after third molar surgery ranges from 0.5% to 20%. The overall rate of dry socket varies from 0% to 35% among studies. The risk of dry socket increases with lack of surgical experience and tobacco use though this does not justify prophylactic removal. Many of these problems are not permanent; however, paresthesia may become permanent and lead to functional problems in some cases.
• Pain; swelling; prolonged or persistent trismus; persistent or excessive bleeding; surgical-site infection with or without cellulitis or osteomyelitis; disruption to regular activities of daily living (e.g., chewing, speaking, and missing work or education); wound dehiscence; alveolar osteitis; new or persistent periodontal defects on the adjacent teeth; damage to adjacent teeth or restorations; temporary, permanent, or prolonged symptoms related to inferior alveolar or lingual nerve injuries; maxillary tuberosity fracture; temporary or persistent oro-antral communication with or without sinusitis.