Developmental abnormalities

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Chapter 24

Developmental abnormalities

Introduction

There are many developmental abnormalities that can affect the teeth and facial skeleton. In most cases, clinicians need little more than to be able to recognize these abnormalities – this recognition being based on both the clinical and radiographic findings. Therefore, the bulk of this chapter is designed like an atlas to show examples of some of the more common and important abnormalities that have characteristic radiographic features. A broad classification of the main conditions is also included.

Two important developmental anomalies are often encountered: unerupted mandibular wisdom teeth and malpositioned maxillary canines. These two topics are described in more detail.

Classification of developmental abnormalities

Developmental anomalies of the maxillofacial region are usually classified into:

• Anomalies of the teeth

• Skeletal anomalies.

Anomalies of the teeth

These include abnormalities in:

Abnormalities in number

Missing teeth

• Localized anodontia or hypodontia – usually third molars, upper lateral incisors or second premolars

• Anodontia or hypodontia associated with systemic disease – e.g. Down’s syndrome, ectodermal dysplasia.

Additional teeth (hyperdontia)

• Localized hyperdontia

– Supernumerary teeth

– Supplemental teeth

• Hyperdontia associated with specific syndromes, e.g. cleidocranial dysplasia, Gardner’s syndrome.

Abnormalities in structure

Abnormalities in shape

Anomalies affecting whole teeth

• Fusion – two teeth joined together from the fusion of adjacent tooth germs

• Gemination – two teeth joined together but arising from a single tooth germ

• Concrescence – two teeth joined together by cementum

• Dens-in-dente (invaginated odontome) – infolding of the outer surface of a tooth into the interior usually in the cingulum pit region of maxillary lateral incisors.

Anomalies affecting the crowns

• Extra cusps

• Congenital syphilis

– Hutchinson’s incisors – crowns small, screwdriver or barrel-shaped, and often notched

– Moon’s/mulberry molars – dome-shaped or modular

• Tapering pointed incisors – ectodermal dysplasia.

Anomalies affecting roots and/or pulp canals

• Number – additional roots, e.g. two-rooted incisors, three-rooted premolars or four-rooted molars

• Morphology, including:

– Bifid roots

– Excessively curved roots

– Dilaceration – sharp bend in the root direction

– Taurodontism – short, stumpy roots and longitudinally enlarged pulp chambers

• Pulp stones – localized or associated with specific syndromes, e.g. Ehlers–Danlos (floppy joint syndrome)

• Cementoma (see odontogenic tumours in Ch. 27).

Odontomes

• Compound odontome – made up of one or more small tooth-like denticles (see Ch. 27)

• Complex odontome – complex mass of disorganized dental tissue (see Ch. 27)

• Enameloma/enamel pearl.

Abnormalities in position

Delayed eruption

• Local causes

– Loss of space

– Abnormal crypt position – especially and

– Overcrowding

– Additional teeth

– Retention of deciduous predecessor

– Dentigerous and eruption cysts

• Systemic causes

– Metabolic diseases, e.g. cretinism and rickets

– Developmental disturbances, e.g. cleidocranial dysplasia

– Hereditary conditions, e.g. gingival fibromatosis and cherubism.

Other positional anomalies

• Transposition, two teeth occupying exchanged positions

• Wandering teeth, movement of unerupted teeth for no apparent reason (distal drift)

• Infraocclusion, second deciduous molars apparently descend into the jaws. These teeth in fact remain in their original position while the adjacent alveolar bone grows normally. As these teeth appear to submerge the original term for this positional anomaly was submersion.

Skeletal anomalies

These include:

• Abnormalities of the mandible and/or maxilla

• Other rare developmental diseases and syndromes.

Abnormalities of the mandible or maxilla

Micrognathia

• True micrognathia – usually caused by bilateral hypoplasia of the jaw or agenesis of the condyles

• Acquired micrognathia – usually caused by unilateral early ankylosis of the temporomandibular joint.

Macrognathia (prognathism)

• Genetic

• Relative prognathism – mandibular/maxillary disparity

• Acquired, e.g. acromegaly owing to excessive growth hormone from a pituitary tumour.

Other mandibular anomalies

• Condylar hypoplasia

• Condylar hyperplasia

• Bifid condyle

• Coronoid hyperplasia.

Cleft lip and palate

• Cleft lip

– Unilateral, with or without alveolar ridge

– Bilateral, with or without alveolar ridge

• Cleft palate

– Bifid uvula

– Soft palate only

– Soft and hard palate

• Clefts of lip and palate (combined defects)

– Unilateral (left or right)

– Cleft palate with bilateral cleft lip.

Localized bone defects

• Exostoses (see Ch. 27)

– Torus palatinus

– Torus mandibularis

• Idiopathic bone cavities (see Ch. 26)

– Stafne’s bone cavity.

Other rare developmental diseases and syndromes

• Cleidocranial dysplasia (see Ch. 28)

• Gorlin’s syndrome (nevoid basal cell carcinoma syndrome) (see Ch. 26)

• Eagle syndrome

• Crouzon syndrome (craniofacial dysostosis)

• Apert syndrome

• Mandibular facial dysostosis (Treacher Collins syndrome).

Typical radiographic appearances of the more common and important developmental abnormalities

Fig. 24.1 Panoramic radiograph showing hypodontia in a patient with ectodermal dysplasia. Numerous teeth are missing.

Fig. 24.2 Periapical showing a supernumerary or mesiodens (arrowed) between .

Fig. 24.3 Oblique lateral showing two supplemental lower premolars (arrowed) and a developing .

Fig. 24.4 Right bitewing showing the enamel defects of amelogenesis imperfecta (arrowed) in both the deciduous and permanent dentitions.

Fig. 24.5 Periapical of maxillary premolars and molars showing the defects of dentinogenesis imperfecta. Note the near obliteration of the pulp chamber (black arrow) and loss of the overlying enamel (white arrows).

Fig. 24.6 Bitewing showing so-called *shell teeth* – a type of dentinogenesis imperfecta. The enamel is essentially normal but there is almost no dentine and the pulp chambers are very large (arrowed).

Fig. 24.7 Periapical showing a microdont (arrowed).

Fig. 24.8 Periapical of showing the typical gnarled enamel defects of a Turner tooth (arrowed), caused by previous infection of the deciduous predecessor.

Fig. 24.9 Periapical showing fusion of (arrowed).

Fig. 24.10 Part of a panoramic radiograph showing a macrodont (arrowed).

Fig. 24.11 A Periapical showing gemination of (arrowed). B Cross-sectional cone beam CT image showing gemination of (arrowed).

Fig. 24.12 Periapical suggesting concrescence of (arrowed). Note it is not possible to be certain simply from the radiograph that are joined together with cementum.

Fig. 24.13 Periapical showing a dens-in-dente or invaginated odontome involving (open arrows). There is an associated periapical area of infection (solid arrows) – a common occurrence with dens-in-dente.

Fig. 24.14 Congenital syphilis. A Periapical of maxillary incisors and canine showing Hutchinson’s teeth. Note the tapering screwdriver-shaped crowns (solid arrows) and the incisal edge notching (open arrow). B Bitewing showing Moon’s/mulberry molars. Note the dome-shaped, nodular appearance of the molars (arrowed).

Fig. 24.15 Periapical showing a bifid lower premolar root (arrowed).

Fig. 24.16 Periapical showing a three-rooted lower first molar (arrowed) (right).

Fig. 24.17 Periapical showing the typical tapering pointed incisor teeth (arrowed) of ectodermal dysplasia.

Fig. 24.18 A Periapical showing a dilacerated with a near right angle bend in the root (arrowed). B *Surface rendered* 3-D cone beam CT image showing a dilacerated . C Segmented *surface rendered* view showing only the teeth and the same dilacerated . (© Materialise Dental NV-SimPlant®.)

Fig. 24.19 Part of a panoramic radiograph showing a taurodont lower second molar with the typical large pulp chamber (arrowed).

Fig. 24.20 Bitewing showing pulpstones (arrowed) in the pulp chambers of .

Fig. 24.21 Periapical showing a compound odontome in the anterior maxilla – several small discrete denticles are evident (arrowed) (right).

Fig. 24.22 Cone beam CT image showing enamel pearls on the distal aspects of (arrowed).

Fig. 24.23 Periapical showing a complex odontome, a disorganized mass of dental tissues in region (arrowed).

Fig. 24.24 Upper oblique occlusal showing transposition of to give (arrowed).

Fig. 24.25 Right side of a panoramic radiograph showing distal drift of a wandering (arrowed).

Fig. 24.26 Periapical showing an *infra-occlusal* (arrowed). Note there is no underlying second premolar.

Fig. 24.27 True cephalometric lateral skull showing micrognathia (underdeveloped mandible) in skeletal Class II. The soft tissue profile has been drawn in.

Fig. 24.28 True cephalometric lateral skull showing macrognathia (overgrowth of the mandible) in skeletal Class III. The soft tissue profile has been drawn in.

Fig. 24.29 PA skull showing condylar hypoplasia on the left side (open arrow), with a marked deviation of the midline of the mandible to that side (closed arrow).

Fig. 24.30 Sagittal tomograph showing a bifid right condyle (arrowed).

Fig. 24.31 Periapical showing a unilateral cleft palate (arrowed). Note is absent.

Fig. 24.32 CBCT reconstructed panoramic type image showing a bilateral cleft palate (arrowed).

Fig. 24.33 Part of a panoramic radiograph showing a long calcified stylohyoid ligament (arrowed), a feature of Eagle’s syndrome.

Fig. 24.34 True cephalometric lateral skull showing the typical *copper beaten* appearance of the cranium resulting from craniosynostosis – premature fusion of the cranial sutures. This appearance is seen in both Crouzon’s and Apert’s syndromes. In this patient, there is also indentation of the anterior fontanelle (arrowed) and the maxilla is hypoplastic.

Fig. 24.35 Coronal CBCT image showing an irregular exostosis – palatal torus (arrowed).

Radiographic assessment of mandibular third molars

Clinical symptoms associated with lower wisdom teeth are common, the usual treatment being extraction. Many of the factors that influence that decision and determine the difficulty of the extraction are revealed by the preoperative radiographic assessment.

Radiographic views used

The usual radiographs used include:

• Periapicals

• Panoramic radiographs

• Oblique laterals or bimolars.

Periapicals need to be of good quality. In particular, the geometric relationship of the third molar to the surrounding structures must be accurate. To satisfy this requirement, modifications to conventional radiographic techniques are often necessary, as described in detail in Chapter 9. If available, cone beam CT, described in Chapter 16, can greatly facilitate this radiographic assessment by providing images in the coronal, axial and sagittal planes.

Radiographic interpretation

The specific features that need to be identified can be divided into those related to:

• The lower third molar itself

• The lower second molar

• The surrounding bone.

Lower third molar assessment

The main features to examine include:

• Angulation

• The crown

• The roots

• The relationship of the apices with the inferior dental (ID) canal

• The depth of the tooth in the alveolar bone

• The buccal or lingual obliquity.

Angulation (see Fig. 24.36)

The third molar could be:

Fig. 24.36 Diagrams illustrating the typical positions and angulations of unerupted lower third molars.

The crown

Note in particular:

• The size

• The shape

• The presence and extent of caries

• The presence and severity of resorption.

The roots

Note in particular:

• The number

• The shape

• Curvatures, whether they are favourable or unfavourable (see Fig. 24.37)

Fig. 24.37 Diagrams illustrating *favourable* and *unfavourable* root curvatures.

• The stage of development.

The relationship of the apices to the ID canal

The apices of the lower third molar often appear close to the ID canal. This apparent closeness is usually due to these structures being superimposed. However, an intimate relationship does sometimes exist. The root may be grooved by the canal, or rarely, included within the developing root, as illustrated in Figs 24.38 and 24.49.

Fig. 24.38 Diagrams illustrating the types of intimate relationships that can exist between the lower third molar root and the inferior dental canal.

The normal radiographic appearance of the ID canal (two thin, parallel radiopaque lines – the so-called tramlines) and the variations that indicate a possible intimate relationship are shown in Fig. 24.39. These variations include:

Fig. 24.39 Diagrams illustrating the radiographic appearances of a normal inferior dental canal, and those indicating an intimate relationship between the inferior dental canal and the tooth apex.

• Loss of the tramlines

• Narrowing of the tramlines

• A sudden change in direction of the tramlines or root

• A radiolucent band evident across the root if the tooth is grooved by or contains the ID bundle.

The depth of the tooth in the alveolar bone

Two main methods are used commonly to assess tooth depth:

• Winter’s lines

• Using the roots of the second molar as a guide.

Winter’s lines (see Fig. 24.40)

In this method, three imaginary lines (traditionally described by number or colour) are drawn on a geometrically accurate periapical radiograph, as follows:

Fig. 24.40 Diagrams illustrating Winter’s lines when applied to unerupted third molars in different positions.

• The first or white line is drawn along the occlusal surfaces of the erupted first and second molars.

• The second or amber line is drawn along the crest of the interdental bone between the first and second molars, extending distally along the internal oblique ridge, NOT the external oblique ridge. This line indicates the margin of the alveolar bone surrounding the tooth.

• The third or red line is a perpendicular dropped from the white line to the point of application for an elevator, but is measured from the amber line to this point of application. This line measures the depth of the third molar within the mandible. (As a general rule, if the red line is 5 mm or more in length, the extraction is considered sufficiently difficult for the tooth to be removed under general anaesthetic or using local anaesthetic and sedation.)

Using the roots of the second molar as a guide (see Fig. 24.41)

This method can be summarized as follows:

Fig. 24.41 Diagram illustrating the method relating the point of application of an elevator to the roots of the lower second molar to assess the depth of the third molar in the alveolar bone.

• The roots of the adjacent second molar are divided horizontally into thirds

• A horizontal line is then drawn from the point of application for an elevator to the second molar

• If the point of application lies opposite the coronal, middle or apical third, the extraction is assessed as being easy, moderate or difficult, respectively.

The buccal or lingual obliquity

• Buccal obliquity – the crown of the wisdom tooth is inclined towards the cheek

• Lingual obliquity – the crown of the wisdom tooth is inclined towards the tongue.

The lie of the tooth in the horizontal plane cannot be determined accurately from a periapical radiograph. The views of choice for this assessment include:

• Lower oblique occlusal

• Lower 90° occlusal, centred on the side of interest (see Ch. 11).

Lower second molar assessment

The second molar is assessed to decide the prognosis of the tooth and whether the second molar should be extracted instead of, or as well as, the third molar. The main features to examine include:

• The crown

• The roots.

The crown

Note in particular:

• The condition and extent of existing restorations

• The presence of caries

• The presence and severity of resorption.

The roots

Note in particular:

• The number

• The shape, and if it is conical

• The periodontal status

• The condition of the apical tissues.

Assessment of the surrounding bone

The main features to examine include:

• The anteroposterior position of the ascending ramus, to determine access to the tooth and the amount of overlying bone

• The texture and density of the bone

• Evidence of previous pericoronal infection.

All these points relating to the third molar, the second molar and the surrounding tissues are considered together, and a conclusion drawn as to the overall difficulty of the proposed extraction.

Examples of unerupted lower third molars, illustrating some of the more important radiographic features, are shown in Figs 24.42–24.49.

Fig. 24.42 Mesioangularly impacted . Note the unfavourable root curvatures (black arrow), the uninterrupted upper tramline of the inferior dental canal (open white arrow) and the conically shaped root of (solid white arrows).

Fig. 24.43 Slightly distoangularly impacted . Note the favourable conically shaped roots, the uninterrupted upper tramline of the inferior dental canal (open white arrows) and the radiolucent area distal to the crown (black arrows) caused by the residual follicle.

Fig. 24.44 Horizontally impacted . Note the pincer-shaped roots and their indentation of the upper margin of the inferior dental canal (open white arrows), radiolucency beneath the crown (solid black arrows) caused by the follicle. In addition, note the caries lesions in (open black arrows).

Fig. 24.45 Transversely positioned . The crown is viewed end-on. Note that the bucco/lingual obliquity of the tooth cannot be determined from this radiograph. B Vertically positioned with very unfavourable root curvatures.

Fig. 24.46 Two radiographs showing some of the radiographic features suggestive of an *intimate relationship* with the inferior dental canal. A A radiolucent band is evident across the root (arrowed) and there is a change in direction of the ID canal. B A radiolucent band evident across the root and the ID canal is narrowed (arrowed).

Fig. 24.47 A Slightly distoangularly impacted . Note the extensive area of bone resorption distal to the crown (black arrows) caused by previous pericoronal infection. There is a radiolucent band across the tooth apex which is also hazy in outline (open white arrows) caused by the inferior dental canal, implying an intimate relationship. B The extracted viewed as in the radiograph from the buccal aspect. C The extracted tooth viewed from the distal aspect showing clearly the notching of the tooth apex by the inferior dental canal. This explains the radiolucent band across the apex – there is simply less tooth tissue in this zone, because of the position of the inferior dental canal. (Specimen and radiograph kindly supplied by Dr A. Sidi.)

Fig. 24.48 Cone beam CT images showing the ID canal grooving the roots of the lower left third molar (arrowed).

Fig. 24.49 Small volume CBCT images of third molars (i-sagiftal, ii-coronal) showing A lingually positioned ID canal (arrowed), B buccally positioned ID canal (arrowed) and C ID canal included within the root of (arrowed). (Kindly provided by Dr J Brown and Mr J Rout.)

Radiographic assessment of unerupted maxillary canines

The upper canines are often misplaced and fail to erupt as a result of their long path of eruption, the timing of their eruption and the frequency of upper arch overcrowding. Again, many of the factors that influence the treatment of this anomaly can be obtained from the radiographic assessment, the purpose of which is two-fold:

• To determine the size and shape of the canine and any related disease, including possible resorption of the adjacent lateral incisor.

• To determine the position of the canine.

Assessment of the canine size and shape and the surrounding tissues

Radiographic views used (see Fig. 24.50)

The usual radiographs used include:

• Periapicals

• Upper standard occlusal

• Panoramic radiograph.

Radiographic interpretation

The specific features that need to be examined relate to:

• The crown

• The root

• Surrounding structures.

The crown

Note in particular:

• Crown size (in relation to the space available in the arch)

• Crown shape

• The presence and severity of resorption

• The presence of any related disease, such as a dentigerous cyst

• The effect on adjacent teeth, such as resorption.

The root

Note in particular:

• Root size

• Root shape

• Stage of development.

Surrounding structures

Note in particular:

• The deciduous canine

– Root length

– Degree of resorption

• The presence of an odontome or supernumerary

• The condition of the surrounding bone.

Assessment of the position of the canine – localization

There are several methods available for localization depending on available facilities. They can be used for canines and other unerupted teeth as well as odontomes and supernumeraries. Although emphasis in this section is on canines, examples of localization of other unerupted developmental anomalies are also shown.

Main localization methods

• Parallax in the horizontal plane

• Parallax in the vertical plane

• Stereoscopic views

• Cross-sectional tomography

• Cone beam CT.

The principle of parallax

Parallax is defined as the apparent displacement of an object because of different positions of the observer. In other words, if two objects, in two separate planes, are viewed from two different positions, the objects will appear to move in different directions in relation to one another, from one view to the next, as shown in Fig. 24.51.

Using the principle of parallax, if two views of an unerupted canine are taken with the X-ray tubehead in two different positions, the resultant radiographs will show a difference in the position of the unerupted canine relative to the incisors, as follows:

• If the canine is palatally positioned, it will appear to have moved in the same direction as the X-ray tubehead.

• If the canine is buccally positioned, it will appear to have moved in the opposite direction to the X-ray tubehead.

• If the unerupted canine is in the same plane as the incisors, i.e. in the line of the arch, it will appear not to have moved at all.

A useful acronym to remember the movements of parallax is SLOB, standing for:

Parallax in the horizontal plane

The movement of the X-ray tubehead is in the horizontal plane, for example:

• Two periapicals – one centred on the upper central incisor and the other centred on the canine region, as shown in Fig. 24.52.

Fig. 24.52 Diagram showing the two different tubehead positions required for parallax in the horizontal plane: **Position 1** centred on the upper central incisor. **Position 2** centred on the canine region.

• An upper standard occlusal, centred in the midline plus a periapical or an upper oblique occlusal, centred on the canine region.

Examples are shown in Figs 24.53–24.55.

Fig. 24.53 Two periapicals showing the relative positions of the unerupted to the incisors – M in the midline and R from the right. The X-ray tubehead (white arrow) and the canine (black arrow) appear to have moved in the *same* direction. The canine is thus palatally positioned.

Fig. 24.54 An upper standard occlusal (the mid-line view) and two periapicals centred on the unerupted canines on either side. The teeth can be localized as follows:

1. Examine the midline view radiograph (M), centred on the upper central incisors. The tip of the RIGHT canine appears opposite the root canal of ; the tip of the LEFT canine appears opposite the mesial aspect .

2.Examine radiograph (R), the periapical centred on the RIGHT canine region (i.e. the X-ray tubehead has been moved distally in the direction of the white arrow). The tip of the canine appears opposite the mesial aspect of . Therefore, it appears to have moved distally in the direction of the black arrow, i.e. in the same direction as the X-ray tubehead was moved.

3.Examine radiograph (L), the periapical centred on the LEFT canine region. The tip of the canine appears opposite the root canal of Again both the X-ray tubehead (white arrow) and the canine (black arrow) appear to have moved in the same direction.

Thus the crowns of both the right and left canines are palatally positioned in relation to the incisors.

Fig. 24.55 Two periapicals showing an unerupted mesiodens. It can be localized as follows:

1. Examine the mid-line radiograph (M). The tip of the mesiodens’ crown appears opposite the mesial aspect of while its apex appears opposite the root canal of .

2.Examine the periapical centred on the RIGHT canine region (R). The tip of the mesiodens crown appears opposite the root canal of , while its apex appears opposite the mesial aspect of .

3.The X-ray tubehead was moved distally in the direction of the large white solid arrow.

4.The crown of the mesiodens appears to have moved mesially (black open arrow), i.e. in the opposite direction to the tubehead. It is thus buccally placed.

5.The apex appears to have moved in the same direction (white open arrow) as the tubehead and is thus palatally placed.

The mesiodens thus lies across the arch, between the central incisors, with its crown buccally positioned and its apex palatally positioned.

Note: The advantage of the upper standard occlusal for the initial view is that it shows both sides of the arch and unerupted canines are often bilateral.

Parallax in the vertical plane

The movement of the X-ray tubehead is in the vertical plane, for example:

• A panoramic radiograph – the X-ray beam is aimed upwards at 8° to the horizontal

• An upper standard occlusal – the X-ray beam is aimed downwards at 65°–70° to the horizontal, as shown in Figs 24.56 and 24.57.

Fig. 24.56 Diagram showing the two different tubehead positions when taking a panoramic radiograph and an upper standard occlusal, allowing parallax in the vertical plane.

Fig. 24.57 Part of a panoramic radiograph and an upper standard occlusal showing an unerupted mesiodens. It can be localized as follows:

1. Examine the panoramic radiograph (P) taken with the tubehead aimed upwards at 8° to the horizontal. The tip of mesiodens’ crown appears opposite the neck of the lateral incisor, while its apex appears opposite the root of .

2.Examine the occlusal radiograph (O) taken with the tubehead aimed downwards at 65° to the horizontal. The tip of the mesiodens’ crown now appears beyond the apex of , while its apex appears opposite the crown of .

3.The X-ray tubehead has moved vertically upwards from view (P) to view (O) in the direction of the solid white arrow.

4.The crown of the mesiodens appears to have moved in the same direction (white open arrow) and is thus palatally placed.

5.The apex of the mesiodens appears to have moved in the opposite direction (black open arrow), and is thus buccally placed.

The mesiodens thus lies across the arch between the central incisors, with its crown palatally positioned and its apex buccally positioned.

Note: This combination of views is used frequently in orthodontics, when patients with unerupted canines are usually assessed. Use of these films to their full potential may obviate the need for further films merely to localize the unerupted canines.