1. Describe the different types of dentinogenesis imperfecta.
Dentinogenesis imperfecta (Dl) causes the teeth to be opalescent and
affects both the primary and permanent dentition.
Type I Dl with osteogenesis imperfecta
Type II DI without osteogenesis imperfecta
Type III Brandywine type, which also occurs in the absence of
osteogenesis imperfecta but is clustered within a racial isolate
in Maryland. In addition to classic findings of DI, radiographs
may exhibit multiple periapical radiolucencies, and large pulp
chambers may lead to multiple pulp exposures.
2. What is the difference between fusion and concrescence? Twinning
and gemination?
Fusion is a more complete process than concrescence and may involve
either (1) fusion of the entire length of two teeth (enamel, dentin, and cementum)
to form one large tooth, with one less tooth in the arch, or (2) fusion of the root
only (dentin and cementum) with the maintenance of two clinical crowns.
Concrescence involves fusion of cementum only.
Twinning is more complete than gemination and results in the formation of
two separate teeth from one tooth bud (one extra tooth in the arch). In
gemination, separation is attempted, but the two teeth share the same root canal.
3. What is a Turner’s tooth?
A Turner’s tooth is a solitary, usually permanent tooth with signs of enamel
hypoplasia or hypocalcification. This phenomenon is caused by trauma or infection
in the overlying deciduous tooth that damages the ameloblasts of the underlying
tooth bud and thus leads to localized enamel hypoplasia or hypocalcification.
4. What are “bull teeth”?
Bull teeth, also known as taurodonts, have long anatomic crowns, large pulp
chambers, and short roots, resembling teeth found in bulls. They are most
dramatic in permanent molars but may affect teeth in either dentition. They occur
more frequently in certain syndromes, such as Klinefelter syndrome.
Dental Secrets SE By Stephen T.Sonis, D.M.D., D.M.Sc. - 62 -
5. What is the difference between dens evaginatus and dens
invaginatus?
Dens evaginatus occurs primarily in persons of mongoloid descent and
affects the premolars. Evagination of the layers of the tooth germ results in the
formation of a tubercle that arises from the occlusal surface and consists of
enamel, dentin, and pulp tissue. This tubercle tends to break when it occludes
with the opposing dentition and may result in pulp exposure and subsequent pulp
necrosis. Dens invaginatus occurs mainly in maxillary lateral incisors and ranges in
severity from an accentuated lingual pit to a “dens in dente.” This phenomenon is
caused by invagination of the layers of the tooth germ. Food becomes trapped
in the pit, and caries begin early.
6. What are the causes of generalized intrinsic discoloration of teeth?
Amelogenesis imperfecta Fluorosis Porphyria
Dentinogenesis imperfecta Rh incompatibility Biliary atresia
Tetracycline staining
7. Why do teeth discolor from ingestion of tetracycline during
odontogenesis?
Tetracycline binds with the calcium component of bones and teeth and is
deposited at sites of active mineralization, causing a yellow-brown endogenous
pigmentation of the hard tissues. Because teeth do not turn over like some bone
tissues, this stain becomes a permanent “label” that fluoresces under ultraviolet
light.
8. Which teeth are most commonly missing congenitally?
Third molars, maxillary lateral incisors, and second premolars.
9. What conditions are associated with multiplesupernumerary teeth?
Gardner’s syndrome and cleidocranial dysplasia.
10. What are the most common sites for supernumerary teeth?
Midline of the maxilla (mesiodens), posterior maxilla (fourth molar or

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