23 Developmental Disturbances of Teeth and Bone










257
23
Developmental Disturbances
of Teeth and Bone
EDUCATIONAL OBJECTIVES
Upon completing this chapter, the student will be able to:
1. Dene the key terms listed at the beginning of the chapter.
2. Understand the formation and radiographic appearance of
developmental lesions of the teeth and surrounding bone,
as well as recognize developmental lesions of the teeth
and bone on dental images and know which radiographic
projections are necessary to formulate a diagnosis.
KEY TERMS
amelogenesis imperfecta
anodontia
cleft
concrescence
cyst
deciduous teeth
dens invaginatus (dens en dente)
dental papilla
dentinogenesis imperfecta
dentigerous cyst (follicular cyst)
dilaceration
distodens (distomolar, paramolar, or
fourth molar)
enamel pearls (enameloma)
ssural cysts
follicle (dental sac)
fusion
gemination
globulomaxillary cyst
hypercementosis
hypodontia
impaction
malposed
median palatine cyst
mesiodens
mixed dentition
nasopalatine cyst
oligodontia
overretention
primordial cyst
supernumerary teeth (hyperdontia)
taurodontia (taurodontism)
tooth eruption
transposed
tooth (Fig. 23.2). After the tooth erupts, the dental papilla
appears at the forming apices (Fig. 23.3).
Radiographic examination by either an intraoral series
or panoramic projections (extraoral projections) is essential
in determining the progress and pattern of tooth eruption
Introduction
e recognition of developmental conditions of the teeth
and surrounding bone is an important part of the dental
professional’s diagnostic responsibility. Most of the lesions
can be detected radiographically, and their early recogni-
tion can prevent further problems. e most common
conditions are discussed in this chapter. ere are many
developmental conditions that are linked to systemic
problems; an atlas or textbook discussing these lesions will
complement the material presented here.
Tooth Development (Odontogenesis)
e developing tooth can be seen at all stages on radiographs.
e tooth germ (Fig. 23.1) before calcication appears as
a round or oval radiolucency in the body of the maxilla or
mandible. As crown formation progresses, the radiolucent
follicle (dental sac) is seen surrounding the crown of the
Figure 23.1 Tooth germ of mandibular third molar.

258 CHAPTER 23 Developmental Disturbances of Teeth and Bone
Figure 23.2 Follicle of mandibular third molar.
Figure 23.3 Dental papilla. Figure 23.4 Mixed dentition in a child.
Figure 23.5 Mixed dentition on a panoramic image.
(Figs. 23.4 and 23.5). In this manner, conditions such as
premature loss of primary teeth, anodontia, hypodontia,
over-retained teeth, ankylosis, tumors, and supernumerary
teeth, which can aect the eruption pattern, can be identi-
ed (Figs. 23.6 and 23.7).
Eruption of Teeth
Periapical radiographs of patients, generally up to age 12
years, reveal some evidence of a mixed dentition (both
primary and secondary teeth are present). e permanent
teeth (secondary teeth) or tooth buds are seen apical to
the deciduous teeth (primary teeth) that they will replace
(Figs. 23.8 and 23.9). e rst, second, and third perma-
nent molars, which have no deciduous predecessors, also
can be seen in various stages of formation (Fig. 23.10). e
force of the erupting permanent tooth causes resorption of
the deciduous roots, with resulting loosening and loss
of the tooth (Fig. 23.11). If root formation is not complete,
a radiolucent area may appear around the root tip. is
radiolucency is the dental root sack and should not be
confused with periapical pathologic conditions (Fig. 23.12).
ere is a range of ±9 months in the normal development
and eruption time of the dentition. Systemic diseases,
such as hypopituitarism and hypothyroidism, can cause
delayed development. Other diseases, such as cleidocranial
dysostosis, can cause overretention of the primary teeth
and postponed permanent tooth eruption (Fig. 23.13).
Impacted Teeth
e radiograph is the prime diagnostic tool in locating
and dening the relative position of the impacted tooth,
because most impacted teeth are not visible on intraoral
examination. e maxillary and mandibular third molars
are the most common impactions. ese teeth must be

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25723 Developmental Disturbances of Teeth and BoneEDUCATIONAL OBJECTIVESUpon completing this chapter, the student will be able to:1. Dene the key terms listed at the beginning of the chapter.2. Understand the formation and radiographic appearance of developmental lesions of the teeth and surrounding bone, as well as recognize developmental lesions of the teeth and bone on dental images and know which radiographic projections are necessary to formulate a diagnosis.KEY TERMSamelogenesis imperfectaanodontiacleftconcrescencecystdeciduous teethdens invaginatus (dens en dente)dental papilladentinogenesis imperfectadentigerous cyst (follicular cyst)dilacerationdistodens (distomolar, paramolar, or fourth molar)enamel pearls (enameloma)ssural cystsfollicle (dental sac)fusiongeminationglobulomaxillary cysthypercementosishypodontiaimpactionmalposedmedian palatine cystmesiodensmixed dentitionnasopalatine cystoligodontiaoverretentionprimordial cystsupernumerary teeth (hyperdontia)taurodontia (taurodontism)tooth eruptiontransposedtooth (Fig. 23.2). After the tooth erupts, the dental papilla appears at the forming apices (Fig. 23.3).Radiographic examination by either an intraoral series or panoramic projections (extraoral projections) is essential in determining the progress and pattern of tooth eruption Introductione recognition of developmental conditions of the teeth and surrounding bone is an important part of the dental professional’s diagnostic responsibility. Most of the lesions can be detected radiographically, and their early recogni-tion can prevent further problems. e most common conditions are discussed in this chapter. ere are many developmental conditions that are linked to systemic problems; an atlas or textbook discussing these lesions will complement the material presented here.Tooth Development (Odontogenesis)e developing tooth can be seen at all stages on radiographs. e tooth germ (Fig. 23.1) before calcication appears as a round or oval radiolucency in the body of the maxilla or mandible. As crown formation progresses, the radiolucent follicle (dental sac) is seen surrounding the crown of the • Figure 23.1 Tooth germ of mandibular third molar. 258 CHAPTER 23 Developmental Disturbances of Teeth and Bone• Figure 23.2 Follicle of mandibular third molar. • Figure 23.3 Dental papilla. • Figure 23.4 Mixed dentition in a child. • Figure 23.5 Mixed dentition on a panoramic image. (Figs. 23.4 and 23.5). In this manner, conditions such as premature loss of primary teeth, anodontia, hypodontia, over-retained teeth, ankylosis, tumors, and supernumerary teeth, which can aect the eruption pattern, can be identi-ed (Figs. 23.6 and 23.7).Eruption of TeethPeriapical radiographs of patients, generally up to age 12 years, reveal some evidence of a mixed dentition (both primary and secondary teeth are present). e permanent teeth (secondary teeth) or tooth buds are seen apical to the deciduous teeth (primary teeth) that they will replace (Figs. 23.8 and 23.9). e rst, second, and third perma-nent molars, which have no deciduous predecessors, also can be seen in various stages of formation (Fig. 23.10). e force of the erupting permanent tooth causes resorption of the deciduous roots, with resulting loosening and loss of the tooth (Fig. 23.11). If root formation is not complete, a radiolucent area may appear around the root tip. is radiolucency is the dental root sack and should not be confused with periapical pathologic conditions (Fig. 23.12). ere is a range of ±9 months in the normal development and eruption time of the dentition. Systemic diseases, such as hypopituitarism and hypothyroidism, can cause delayed development. Other diseases, such as cleidocranial dysostosis, can cause overretention of the primary teeth and postponed permanent tooth eruption (Fig. 23.13).Impacted Teethe radiograph is the prime diagnostic tool in locating and dening the relative position of the impacted tooth, because most impacted teeth are not visible on intraoral examination. e maxillary and mandibular third molars are the most common impactions. ese teeth must be 259CHAPTER 23 Developmental Disturbances of Teeth and Bone• Figure 23.6 Supernumerary tooth blocking eruption of the rst premolar. • Figure 23.7 Odontoma blocking eruption of a permanent canine. • Figure 23.8 Maxillary central incisor area in a child. Permanent teeth are seen in bone. Note the root resorption of deciduous central incisor resulting from an eruptive force. • Figure 23.9 Mixed dentition in the mandibular molar area. • Figure 23.10 Mandibular mixed dentition. BA• Figure 23.11 Root resorption of deciduous second molar. A, Early. B, Late. 260 CHAPTER 23 Developmental Disturbances of Teeth and Bone• Figure 23.12 Root sack (arrow) on developing rst permanent molar. • Figure 23.13 Overretention of primary teeth as seen in an 18-year-old with cleidocranial dysostosis. • Figure 23.14 Bony impaction of the mandibular third molar. Note the relationship of the tooth to the mandibular canal and root resorption of the second molar. • Figure 23.15 Soft tissue impaction. Note the supernumerary tooth in the premolar area. localized not only in their mesiodistal position by periapi-cal, panoramic, or lateral oblique projections but also in the buccolingual relationship by right-angle (90-degree/cross-sectional) occlusal projections and/or computed tomographic or cone beam computed tomography (CBCT) scanning.Radiographically, bony impactions may be seen com-pletely or partially covered by bone (Fig. 23.14). A soft tissue impaction is not covered by bone. In some cases, the BA• Figure 23.16 A, Impacted mandibular third molar, not seen completely. B, Panoramic radiograph shows the extent of the dentigerous cyst. outline of the covering soft tissue appears on the radiograph (Fig. 23.15).Periapical radiographs of impacted teeth must show the entire tooth and at least 2 to 3 mm of surrounding bone. If periapical projections cannot accomplish this, a panoramic or another extraoral projection should be used. If the entire tooth is not seen, a lesion (such as, the dentigerous cyst (follicular cyst) seen in Fig. 23.16) might be missed, with negative consequences for the patient. 261CHAPTER 23 Developmental Disturbances of Teeth and Boneis positioned distal to the third molar, it is referred to as a distodens (distomolar, paramolar, or fourth molar).Supernumerary teeth may erupt into the mouth or remain impacted. ey may delay or prevent the eruption of the normal dentition. Supernumerary roots also can occur on teeth and may or may not be detected radiographically (Fig. 23.19).Congenitally Missing TeethHypodontia is the failure of teeth to develop. It can occur in either the primary or adult dentition. It can be a single missing tooth, many missing teeth (known as oligodontia), or a complete absence of teeth, known as anodontia). Missing teeth can be detected clinically. However, the diagnosis of hypodontia is made denitively only by radio-graphic examination of the underlying bone (Fig. 23.20).Supernumerary Teeth (Hyperdontia)Supernumerary teeth (hyperdontia), or extra teeth and their relative position to other teeth are easily detectable on the proper radiographs. As with impacted teeth, the buccolingual relationship can be established by the use of right-angle occlusal projections. e most common supernumerary teeth are mandibular premolars, maxillary incisors, and fourth molars (Fig. 23.17; see Fig. 23.15). If the supernumerary tooth occurs between the maxillary central incisors, it is called a mesiodens (Fig. 23.18). If it • Figure 23.18 Mesiodens. Supernumerary tooth between the central incisors. • Figure 23.19 Supernumerary roots. After extraction, two distal roots were found on the rst molar. Note how wide the distal root is (arrow). • Figure 23.20 Partial anodontia. Note the absence of the perma-nent lateral incisor and canine. NOTEThe generalized denition of a cyst is that they are abnormal, closed sac-like structures within a tissue that contain a liquid, gaseous, or semisolid substance. A dentigerous or follicular cyst usually forms around the crown of an unerupted or impacted tooth. The cyst encircles the crown from the cementoenamel junction (CEJ) of one side of the tooth to the other side of the same tooth and represents a retained intact tooth follicle that is usually shed when a tooth erupts into the oral cavity. The term dentigerous by denition actually means “containing or bearing teeth.”• Figure 23.17 Supernumerary premolar seen on the occlusal view. 262 CHAPTER 23 Developmental Disturbances of Teeth and Boneasymptomatic and are usually discovered through routine radiographic examination (Fig. 23.23).FusionFusion is a condition that occurs when two teeth join early in their development. e result is usually a single large crown with two root canals (Fig. 23.24).GeminationGemination occurs when a single tooth germ splits during its development. It usually appears as two crowns with a common root canal (Fig. 23.25).ConcrescenceConcrescence is the joining of two or more teeth by cemen-tum. Although seen radiographically, it may be very dicult to dierentiate concrescence from teeth in close contact or those superimposed on one another.Malposition of TeethTeeth that do not occupy their normal position in the mouth are said to be malposed. Tumors, cysts, supernumer-ary teeth, or lack of space may keep a tooth from achieving its proper position. If a tooth occupies the normal position of another tooth, it is said to be transposed (Fig. 23.21).HypercementosisHypercementosis is a condition characterized by the buildup of cementum on the root of the tooth. Normally, it is dicult to distinguish cementum from dentin because of its thin layers and similar densities. e buildup of cementum makes the root appear club-shaped instead of its usual conical appearance (Fig. 23.22). is condi-tion can be seen in patients who have Paget’s disease of bone.Enamel PearlsEnamel pearls (enameloma) are small, spherical-shaped pieces of enamel attached to the roots of teeth. Enamel pearls usually are seen at the trifurcation of maxillary molars or the bifurcation of mandibular molars. ey are • Figure 23.21 Tooth transposition. • Figure 23.22 Hypercementosis. Note the club-shaped root on the second premolar. • Figure 23.23 Enamel pearl. • Figure 23.24 Fusion. Note the single crown with two root canals. 263CHAPTER 23 Developmental Disturbances of Teeth and Bone• Figure 23.26 Dens invaginatus (arrow). • Figure 23.27 Dilaceration. Note the curved root on rst premolar. NOTEIt is important to distinguish between dilaceration and a distorted or bent image caused by overbending of the lm packet during lm placement. This occurs when lm packets, as opposed to digital sensors, are being used as the receptor. To differentiate between dilaceration and an image caused by overmanipulation of a lm packet, remember that only one part of the image of the tooth is distorted when the tooth is dilacerated and the rest of the structures are normal. When the manipulation of the lm packet is the cause, the whole image, or at least a majority of the image, is distorted.• Figure 23.28 Taurodontia. Note the longitudinal distortion and short roots. • Figure 23.25 Gemination. Note two crowns with a common root canal. Dens InvaginatusDens invaginatus, or dens in dente, is not a “tooth within a tooth,” as it is commonly referred to, but an invagination of the enamel organ within the body of the tooth. e point of invagination of the enamel is usually the cingulum of the tooth (Fig. 23.26).DilacerationDilaceration is a permanent distortion of the shape and relationship of either the crown or the root of the tooth. is abnormality would present a problem only if the tooth required root canal therapy or extraction. It is thought to be caused by trauma during development of the tooth (Fig. 23.27).Taurodontia (Taurodontism)In taurodontia (taurodontism), the body of the tooth is elongated with the extension of the pulp chamber into the elongation; the roots are short, but the size of the crown is normal (Fig. 23.28). It acquired its name because of a likeness to a bull’s head. e crown of the tooth is compared to the bull’s head, and the horns are represented by the roots of the tooth.Amelogenesis ImperfectaAmelogenesis imperfecta is a hereditary disturbance that aects both the primary and secondary dentition. e dentin and root formation are normal. e enamel on the teeth is thin and of poor quality and may fracture away completely. Radiographically, the absence of enamel or thin enamel is apparent (Fig. 23.29). 264 CHAPTER 23 Developmental Disturbances of Teeth and Bone• Figure 23.29 Amelogenesis imperfecta. • Figure 23.30 Dentinogenesis imperfecta. • Figure 23.31 Nasopalatine cyst. Dentinogenesis ImperfectaDentinogenesis imperfecta is also a hereditary disturbance that aects both the primary and secondary dentition. It is characterized by poor enamel that may wear thin or chip, early calcication of the pulp chambers and canals, and short roots, especially noticeable in the permanent teeth (Fig. 23.30).Fissural CystsFissural cysts are always found in predictable anatomic loca-tions, because they develop along embryonic suture lines. e nasopalatine cyst where the teeth are vital appears as a radiolucency in the midline near the apices of the maxillary central incisors and must be dierentiated from periapical pathologic processes. It was previously thought that the globulomaxillary cyst is a ssural cyst seen as a pear-shaped radiolucency between the maxillary lateral incisor and canine. However, this entity is now considered con-troversial as a result of more current research. e median palatine cyst is seen as an oval radiolucency in the midline of the palate. e nasopalatine and globulomaxillary cysts appear on periapical projections of their respective areas; the median palatine cyst is seen best on occlusal projections (Figs. 23.31 to 23.33).Cleft Palatee failure of embryonic processes to fuse in development causes clefts. ese clefts can occur in the hard palate, soft palate, or both. Clefts can disturb the dental lamina, result-ing in anodontia, malposition, or supernumerary teeth. Radiographically, the cleft appears as a radiolucent area in which one would normally expect to nd bone (Fig. 23.34).Dentigerous CystA dentigerous cyst, as previously discussed in this chapter, forms when the developing tooth bud undergoes cystic degeneration. e cyst may surround or be lateral to the developing tooth. It is most commonly seen in association with third molars. A cyst that forms from the dental lamina before the tooth bud forms is called a primordial cyst (Figs. 23.35 and 23.36). 265CHAPTER 23 Developmental Disturbances of Teeth and Bone• Figure 23.34 Cleft palate. Note the radiolucent defect between the lateral incisor and canine. • Figure 23.35 Dentigerous cyst (arrow) seen on a lateral oblique projection. • Figure 23.36 Dentigerous cyst (arrow) seen on a mandibular occlusal projection. • Figure 23.33 Median palatine cyst seen on an occlusal projection. • Figure 23.32 Globulomaxillary cyst. 266 CHAPTER 23 Developmental Disturbances of Teeth and BoneChapter Review QuestionsMatchingMatch the term in Column A with the appropriate radio-graphic appearance in Column B.Column A Column B1. Taurodontia2. Mixed dentition3. Concrescence4. Hypercementosis5. Mesiodens6. Dentigerous cyst7. Dens invaginatus8. Dilaceration9. Fusion10. Amelogenesis imperfecta11. Nasopalatine cyst12. Dentinogenesis imperfecta13. Distodens14. Enamel pearl15. Gemination a. Supernumerary tooth distal to the third molar b. Two teeth joined: single large crown and two root canals c. Club-shaped root d. Spherical-shaped piece of enamel on the tooth’s root e. Split tooth germ forming a tooth with two crowns/one canal f. Invagination of the enamel organ g. Permanent distortion of the crown or root h. Poor enamel, calcied pulp, and short roots i. Both primary and secondary teeth are present j. Joining of teeth at the cementum k. Extra tooth between the upper central incisors l. Cyst around an unerupted or impacted tooth m. Hereditary absent or thin enamel n. Fissural cyst at the apices of teeth #8 and #9 o. Tooth that looks like a bull’s headCritical Thinking Exercise1. An 18-year-old male patient presents to your dental facility with “missing teeth” as his chief complaint. What steps would appropriately be taken in establishing an explanation for his clinically apparent hypodontia? Please include the following in your discussion: a. e appropriate radiographic prescription b. A thorough medical history c. Classication of anodontia or oligodontiaBibliographyWhite SC, Pharoah MJ: Oral radiology: Principles and interpretation, ed 7, St Louis, MO, 2013, Mosby.Chapter Summary• A majority of the developmental disturbances of theteeth and surrounding bone are primarily recognized on a radiographic examination of the dental patient. It is important that dental professionals are able to radiographically identify these conditions and proceed with the patient’s diagnosis and treatment accordingly. It is also important to be able to request the appro-priate radiographs for proper identication of these disturbances.• e dental professional is responsible for knowing theradiographic appearance of normal tooth development and eruption patterns. is ability should include being able to recognize the absence of teeth, as well as the presence of supernumerary teeth.• Changes in the tooth anatomy can also be recognizedradiographically, including hypercementosis, fusion, gemination, concrescence, enamel pearls, dens invagina-tus, taurodontia, and dilaceration.• e recognition of various cysts—including ssuralcysts,dentigerouscysts, andprimordial cysts—arealsoa valuable skill when interpreting dental images.• Hereditary disturbances of tooth formation, such asamelogenesis imperfecta and dentinogenesis imperfecta, require both clinical and radiographic identication.

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