20.3 Abnormalities of Teeth and Developmental Defects of the Oral Region
Key Takeaways
Excluding third molars, the most commonly missing permanent teeth are the mandibular second premolars and maxillary lateral incisors; multiple missing teeth with conical crowns and reduced sweating suggest hypohidrotic ectodermal dysplasia.
Gemination gives a normal tooth count when the bifid crown is counted as one tooth, whereas fusion usually reduces the count by one; concrescence joins teeth by cementum only.
Dentinogenesis imperfecta produces opalescent gray-brown teeth with bulbous crowns, short roots and obliterated pulps, and type I occurs with osteogenesis imperfecta.
Molar-incisor hypomineralization causes demarcated opacities and post-eruptive breakdown of first permanent molars and incisors, with hypersensitivity and difficult anesthesia.
Lingual thyroid is a mass at the foramen cecum on the posterior dorsum of the tongue, and it may be the patient's only functioning thyroid tissue, so thyroid imaging is needed before excision.
Questions on tooth anomalies give a clinical photograph description or radiograph and ask for the diagnosis or the associated syndrome. Classify each anomaly by number, size, shape or structure.
Anomalies of Number
| Anomaly | Key points |
|---|---|
| Hypodontia | One to five missing teeth (excluding third molars); most often mandibular second premolars and maxillary lateral incisors |
| Oligodontia | Six or more missing (excluding third molars) |
| Anodontia | All teeth missing; rare, usually with ectodermal dysplasia |
| Hypohidrotic ectodermal dysplasia | Usually X-linked; hypodontia, conical teeth, sparse hair, reduced sweating (heat intolerance); early prostheses, later implants |
| Supernumerary teeth | Most common is the mesiodens (between maxillary central incisors), which may prevent eruption of a central incisor or cause a diastema; multiple supernumeraries suggest cleidocranial dysplasia (RUNX2; hypoplastic clavicles, retained primary teeth, delayed eruption) or Gardner syndrome |
| Natal and neonatal teeth | Present at birth or in the first month; usually mandibular primary central incisors; tongue ulceration (Riga-Fede disease) |
Anomalies of Size and Shape
| Anomaly | Key points |
|---|---|
| Microdontia | Commonly the peg-shaped maxillary lateral incisor; generalized in pituitary dwarfism |
| Macrodontia | Generalized in pituitary gigantism; isolated cases |
| Gemination | One tooth germ tries to divide: a bifid crown with one root canal; normal count |
| Fusion | Two germs unite through dentin: usually one fewer tooth; separate or shared canals |
| Concrescence | Union by cementum only, after root formation (often maxillary molars); important during extraction |
| Dilaceration | Sharp root bend, often after trauma to the primary predecessor |
| Taurodontism | Elongated pulp chamber and apically displaced furcation; seen with Klinefelter syndrome and amelogenesis imperfecta |
| Dens invaginatus | Invagination of the enamel organ, usually maxillary lateral incisors; early pulp necrosis risk, so seal the pit prophylactically |
| Dens evaginatus | Occlusal tubercle on mandibular premolars, more common in people of East Asian descent; fracture exposes pulp, so protect or reduce gradually |
| Talon cusp | Accessory cusp on the cingulum of an incisor |
| Enamel pearl | Ectopic enamel at the furcation of maxillary molars; plaque retention and attachment loss |
| Hypercementosis | Bulbous roots; Paget disease, hyperfunction, idiopathic |
Anomalies of Structure
| Condition | Key points |
|---|---|
| Amelogenesis imperfecta | Inherited enamel defect affecting both dentitions: hypoplastic (thin enamel), hypomaturation (mottled, soft) or hypocalcified (soft, wears quickly); dentin and pulp normal on radiographs; open bite is common in some types |
| Dentinogenesis imperfecta | Opalescent gray-blue to amber teeth, bulbous crowns, cervical constriction, short roots, obliterated pulps; enamel chips off the abnormal dentin; type I with osteogenesis imperfecta (blue sclerae, fractures), type II isolated, type III "shell teeth" |
| Dentin dysplasia | Type I radicular: short or absent roots ("rootless teeth"), chevron-shaped pulp remnants, periapical radiolucencies; type II coronal: "thistle-tube" pulps in permanent teeth |
| Regional odontodysplasia | "Ghost teeth": thin enamel and dentin in one segment, often maxillary anterior |
| Molar-incisor hypomineralization (MIH) | Demarcated white-yellow-brown opacities on first permanent molars (often incisors too); post-eruptive breakdown, hypersensitivity, difficulty achieving anesthesia; management ranges from fluoride and sealants to GIC, stainless steel crowns or planned extraction |
| Dental fluorosis | Bilaterally symmetrical white flecks to brown mottling from excess fluoride during enamel formation |
| Tetracycline staining | Gray-brown bands; avoid tetracyclines in pregnancy and children under about 8 years |
| Turner tooth | Local enamel hypoplasia of a single permanent tooth (often a premolar or maxillary incisor) after infection or trauma of the primary predecessor |
| Chronological hypoplasia | Horizontal bands matching a period of systemic illness |
| Intrinsic color changes | Green teeth in neonatal hyperbilirubinemia; red-brown teeth in congenital erythropoietic porphyria |
| Congenital syphilis | Hutchinson incisors and mulberry molars (see infections) |
Developmental Conditions of the Oral Region
| Condition | Key points |
|---|---|
| Fordyce granules | Yellow papules of ectopic sebaceous glands on buccal mucosa and lips; normal variant |
| Leukoedema | Gray-white film on buccal mucosa that disappears when stretched |
| Geographic tongue (benign migratory glossitis) | Migrating red areas with white borders; occasionally sore with spicy foods; associated with fissured tongue and psoriasis |
| Fissured tongue | Deep grooves; Down syndrome; part of Melkersson-Rosenthal syndrome (with facial palsy and lip swelling) |
| Ankyloglossia | Short lingual frenum; frenotomy if it affects feeding or speech |
| Lingual thyroid | Mass at the foramen cecum; may be the only thyroid tissue, so scan before removal |
| Commissural and lip pits | Lower lip pits with cleft lip or palate in Van der Woude syndrome |
| Cleft lip and palate | See maxillofacial section |
Developmental cysts
- Nasopalatine duct cyst: the most common non-odontogenic jaw cyst; heart-shaped midline radiolucency between vital maxillary central incisors.
- Nasolabial cyst: soft-tissue swelling raising the ala of the nose.
- Epidermoid and dermoid cysts: midline floor of mouth.
- Thyroglossal duct cyst: midline neck mass that moves upward when the tongue protrudes.
- Branchial cleft cyst: lateral neck, along the anterior border of the sternocleidomastoid.
Exam Traps
- Dentinogenesis imperfecta affects dentin (short roots, obliterated pulps); amelogenesis imperfecta leaves dentin and pulps normal.
- A heart-shaped midline radiolucency with vital incisors is a nasopalatine duct cyst, not a periapical lesion.
- Check vitality before endodontic treatment of any midline radiolucency.
A 9-year-old has opalescent amber-brown teeth in both dentitions with marked attrition. Radiographs show bulbous crowns, short roots and almost complete pulp obliteration. He has had several long-bone fractures. What is the most likely diagnosis?
Dental fluorosis from drinking well water with high fluoride
Hypomaturation amelogenesis imperfecta with normal dentin and pulps
Molar-incisor hypomineralization of first molars and incisors
Dentinogenesis imperfecta associated with osteogenesis imperfecta
A radiograph shows a heart-shaped, well-defined midline radiolucency between the roots of teeth 11 and 21, both of which respond normally to cold and electric pulp testing. What is the most likely diagnosis?
Central giant cell granuloma crossing the midline
Nasopalatine duct cyst
Radicular cyst arising from a necrotic tooth 11
Periapical abscess of tooth 21 with a sinus tract
A 12-year-old has dark, sensitive first permanent molars with post-eruptive enamel breakdown and demarcated yellow-brown opacities on the maxillary central incisors. The other teeth are normal. What is the most likely diagnosis?
Amelogenesis imperfecta affecting the entire dentition
Tetracycline staining from antibiotics taken in infancy
Molar-incisor hypomineralization
Generalized dental fluorosis from excessive fluoride intake
Sections you finish are checked off in the contents.