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Anomalies of Tooth Structure

Course Number: 651

Delayed Eruption

Eruption is considered to be delayed if the tooth has not surfaced 12 months after the normal eruption time or when the tooth root is ¾ complete.5 There are a number of reasons why teeth might be delayed in their eruption. The problem can be localized in which the eruption path is obstructed (Figure 12) or more widespread when a systemic disorder is implicated.5 Teeth continue to erupt after emergence to offset masticatory wear and jaw growth.5

Delayed Eruption - Figure 1

Figure 13.

Cropped panoramic radiograph depicting the obstructed eruption path of mandibular left premolar tooth #20.


Ankylosis is the cessation of eruption after tooth emergence.5 This is caused by fusion of the tooth dentin or cementum with the alveolar bone.7 The pathogenesis of this process is not known.5 While ankylosis can occur at any age, it is most common in children 8 to 9 years of age.7The teeth that are most frequently involved include the primary mandibular first molar, followed respectively by the primary mandibular second molar (Figure 14), the primary maxillary first molar, and the primary maxillary second molar.5 The involved ankylosed tooth usually has a submerged occlusal plane compared to the adjacent teeth and may, upon percussion, produce a sharp, solid sound.5 The periodontal ligament space may be absent radiographically.7 Permanent teeth rarely become ankylosed.5

Delayed Eruption - Figure 14

Figure 14.

Cropped panoramic radiograph depicting the obstructed eruption path of mandibular left premolar tooth #20.

Impacted Teeth

The term used to describe teeth that fail to erupt is impacted.8 Primary teeth impactions are uncommon but when they do happen, the primary second molar is usually involved.7 In the permanent dentition, the most commonly impacted teeth in order by frequency are the mandibular third molars, the maxillary third molars, and the maxillary canine teeth.7 See Figures 15‑17 for examples of impacted teeth. Impacted teeth are classified according to their position angulation relative to the rest of the erupted dentition such as: mesioangular, distoangular, horizontal, vertical, inverted or a combination thereof.7 They can be completely encased in the bone or partially erupted.

Delayed Eruption - Figure 15

Figure 15.

Cropped panoramic image showing a horizontal impaction of mandibular right third molar tooth #32 in a mesioangular orientation.

Delayed Eruption - Figure 16

Figure 16.

Cropped panoramic image of horizontal mesioangular impaction of maxillary left canine tooth #11 and buccolingual impaction of mandibular left third molar #17.

Delayed Eruption - Figure 6

Figure 17.

Panoramic radiograph of multiple impacted teeth with differing orientations. Note the kissing molars, mandibular left first molar tooth #19 in a horizontal distoangular position with the second molar tooth #18 trapped between the third molar tooth #17 in a horizontal mesioangular position.