Overview and definition
An unerupted tooth is a normally formed tooth that has not emerged into functional occlusion at the expected time, remaining partly or wholly enclosed by bone and mucoperiosteum.[1] It is a developmental/positional finding, not a tumor or disease. The term is descriptive and overlaps with—but is broader than—"impacted," which is reserved for a tooth that cannot reach its normal position because of space deficiency, malposition, or a physical obstruction, conventionally applied once eruption is delayed beyond about a year past the recognized eruption age or 6 months after contralateral eruption with a mature root.[1][2][3] Delayed-but-still-developing teeth may yet erupt spontaneously; true impaction implies arrested potential.[3] Third molars are most frequently involved, followed by maxillary canines and premolars (maxillary incisors are a leading site in children); non–third-molar impaction prevalence is roughly 2.5–6% in hospital populations, and unerupted permanent incisors about 2% in children.[1][2][3][4]
Radiographic findings
Recognition. Panoramic radiography is the usual first-line modality for detecting and screening unerupted teeth given low dose and convenience, supplemented by periapical and occlusal views.[1][3]
Location and appearance. The finding is a tooth fully or partially enclosed in bone, short of the occlusal plane, often with an intact pericoronal (follicular) space and surrounding lamina dura/corticated crypt margin. For mandibular third molars, depth relative to the adjacent cementoenamel junction helps gauge eruption status—teeth at or below the neighboring second molar CEJ are clinically unerupted.[6] Angulation (mesioangular, distoangular, horizontal, vertical) and depth are captured by Winter's and Pell–Gregory systems for third molars.[2]
Localization. Buccolingual position is established with the parallax/tube-shift (Clark's) method, ideally a panoramic plus occlusal film, or two views at right angles; CBCT gives accurate 3D localization when 2D is ambiguous or intervention is planned.[3][7][8]
Normal variation vs mimics. A uniform, thin pericoronal radiolucency (generally a few millimeters) reflects a normal follicle. The principal mimic is a dentigerous cyst, suggested by an expanded, unilocular, corticated radiolucency enveloping the crown and attached at the CEJ, sometimes displacing the tooth.[9] Intracoronal radiolucency may represent pre-eruptive intramural resorption.[10]
Management and prognosis
Most unerupted teeth are asymptomatic incidental findings and may simply be documented and monitored.[2][11] Interpretation should correlate radiographic depth, angulation, and root maturity with clinical eruption stage, since horizontally inclined or deeper teeth are more likely truly unerupted.[6] Red flags warranting review or specialist referral include an enlarging or asymmetric pericoronal radiolucency, root resorption of adjacent teeth, cystic change, recurrent pericoronitis/infection, unexplained pain, or caries in the impacted or adjacent tooth.[2][3][11] In children with unerupted incisors, a retained primary tooth, midline shift, or a supernumerary/odontoma obstructing eruption merits early orthodontic/surgical assessment.[4][12] Definitive management (observation, surgical exposure with traction, removal, or transplantation) is individualized and beyond this descriptive entry.[10][12]