D. Developmental anomalies
A number of structural dental anomalies have been described that can be attributed directly or indirectly to errors in the developmental process. Some of these will be reviewed in this section.
1. Enamel pearls
Enamel pearls are localized masses of enamel that develop
ectopically, typically over the root surface, in close proximity to the cemento-enamel
junction
Fig. 104 A: Extracted maxillary molar with large enamel pearl (EP) just apical to
the cemento-enamel junction (CEJ). Enamel pearls in this location can contribute to
the retention of bacterial biofilms that can, in turn, lead to severe periodontal lesions.
This tooth was lost because of such a periodontal problem. Unlike calculus,
which it resembles radiographically, the enamel pearl cannot be removed by scaling.
It has to be ground away to restore the normal contour of the tooth.
Fig.
104 B: Histologic section through a microscopic enamel pearl (E). The pearl is a
flat enamel patch located on dentin (D) and surrounded by otherwise normal cementum (C).
It is located just apical to the cemento-enamel junction. This anomaly
appears to be caused by the localized failure of Hertwig's epithelial root sheet to
separate from the dentin. Prolonged contact with the dentin presumably induces this
odontogenic epithelium to secrete enamel, albeit in limited quantity, while preventing the
normal deposition of cementum by adjacent cementoblasts. The enamel pearl is lined with
reduced enamel epithelium (REE). Epithelial cell rests ECR) can be seen close to the
normally formed adjacent cementum.
2. Enamel projections
Fig.
105 (Courtesy of Dr. James Deschner): If amelogenesis is not turned off after the
enamel of the crown has been laid down, the enamel organ may continue to produce enamel
over the root dentin. This additional enamel often takes the shape of enamel
spurs that project into the furcation of mutirooted teeth. These projections
may favor the onset of periodontal lesions in the affected furcations. Successful
treatment of periodontal pockets caused by this anomaly requires grinding away the enamel
projection. By restoring the normal contour of the tooth and exposing the underlying
dentin, it is more likely that new attachment procedures will succeed in eliminating the
lesion.
3. Hypercementosis
Fig. 106: Hypercementosis (HC) refers to abnormally large cellular cementum deposits on
the apical third of one or more teeth. Such deposits form bulbous enlargements on
the roots that may interfere with dental extractions, should these become necessary.
The cause of this anomaly is not known.
Fig. 107: Radiographic appearance of maxillary posterior teeth with evidence of
hypercementosis (HC).
4. Cementicles
Cementicles are small, spherical particles of cementum that may lie free in the
periodontal ligament adjacent to the cementum surface. These are classified as free
cementicles. They can also be attached to the cementum surface (attached
or sessile cementicles), or incorporated into the cementum layer (imbedded
cementicles).
Cementicles may be composed of fibrillar or afibrillar cementum, or
a mixture of the two. They are usually acellular. Their etiology is unknown.
Fig. 108: Histologic section through a free (FC) and a sessile (SC)
cementicle. It is likely that free cementicles close to the cementum surface become
incorporated into the cementum as sessile cementicles as the cementum layer grows by
apposition to its surface. Given enough time, a sessile cementicle may be
incorporated into the cementum layer as an imbedded cementicle.
Fig. 109 (From Schroeder, H.E.,1986): Scanning electron micrograph of root surface with numerous sessile
cementicles. The small cementicle outlined in the large micrograph is shown at higher
magnification in the round inset. Note the comparative size of the cementicle and
the Sharpey's fibers that surround it.
Fig. 110 (From Schroeder, H.E.,1986): Imbedded cementicle (CTC) within a thick layer of cementum.
Appositional lines reflect the cyclic nature of cementum deposition. Sessile
cementicles may mimic calculus, once they are exposed, and serve as promoters of
periodontal disease. Imbedded cementicles have no clinical relevance and are merely of
academic interest.
